bims-numges Biomed News
on Nucleotide metabolism and genome stability
Issue of 2020‒06‒14
forty-two papers selected by
Sean Rudd
Karolinska Institutet

  1. Mol Cell. 2020 Jun 02. pii: S1097-2765(20)30341-5. [Epub ahead of print]
    Álvarez-Quilón A, Wojtaszek JL, Mathieu MC, Patel T, Appel CD, Hustedt N, Rossi SE, Wallace BD, Setiaputra D, Adam S, Ohashi Y, Melo H, Cho T, Gervais C, Muñoz IM, Grazzini E, Young JTF, Rouse J, Zinda M, Williams RS, Durocher D.
      The APEX2 gene encodes APE2, a nuclease related to APE1, the apurinic/apyrimidinic endonuclease acting in base excision repair. Loss of APE2 is lethal in cells with mutated BRCA1 or BRCA2, making APE2 a prime target for homologous recombination-defective cancers. However, because the function of APE2 in DNA repair is poorly understood, it is unclear why BRCA-deficient cells require APE2 for viability. Here we present the genetic interaction profiles of APE2, APE1, and TDP1 deficiency coupled to biochemical and structural dissection of APE2. We conclude that the main role of APE2 is to reverse blocked 3' DNA ends, problematic lesions that preclude DNA synthesis. Our work also suggests that TOP1 processing of genomic ribonucleotides is the main source of 3'-blocking lesions relevant to APEX2-BRCA1/2 synthetic lethality. The exquisite sensitivity of BRCA-deficient cells to 3' blocks indicates that they represent a tractable vulnerability in homologous recombination-deficient tumor cells.
    Keywords:  APE2; APEX2; BRCA1; BRCA2; RNASEH2; TDP1; TOP1; ribonucleotide; synthetic lethality
  2. EMBO J. 2020 Jun 08. e102931
    Husain A, Xu J, Fujii H, Nakata M, Kobayashi M, Wang JY, Rehwinkel J, Honjo T, Begum NA.
      Sterile alpha motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1), a dNTP triphosphohydrolase, regulates the levels of cellular dNTPs through their hydrolysis. SAMHD1 protects cells from invading viruses that depend on dNTPs to replicate and is frequently mutated in cancers and Aicardi-Goutières syndrome, a hereditary autoimmune encephalopathy. We discovered that SAMHD1 localizes at the immunoglobulin (Ig) switch region, and serves as a novel DNA repair regulator of Ig class switch recombination (CSR). Depletion of SAMHD1 impaired not only CSR but also IgH/c-Myc translocation. Consistently, we could inhibit these two processes by elevating the cellular nucleotide pool. A high frequency of nucleotide insertion at the break-point junctions is a notable feature in SAMHD1 deficiency during activation-induced cytidine deaminase-mediated genomic instability. Interestingly, CSR induced by staggered but not blunt, double-stranded DNA breaks was impaired by SAMHD1 depletion, which was accompanied by enhanced nucleotide insertions at recombination junctions. We propose that SAMHD1-mediated dNTP balance regulates dNTP-sensitive DNA end-processing enzyme and promotes CSR and aberrant genomic rearrangements by suppressing the insertional DNA repair pathway.
    Keywords:   AICDA ; dNTP ; DNA repair; SAMHD1; genomic instability
  3. Sci Adv. 2020 May;6(22): eaaz4126
    Boeckemeier L, Kraehenbuehl R, Keszthelyi A, Gasasira MU, Vernon EG, Beardmore R, Vågbø CB, Chaplin D, Gollins S, Krokan HE, Lambert SAE, Paizs B, Hartsuiker E.
      The Mre11 nuclease is involved in early responses to DNA damage, often mediated by its role in DNA end processing. MRE11 mutations and aberrant expression are associated with carcinogenesis and cancer treatment outcomes. While, in recent years, progress has been made in understanding the role of Mre11 nuclease activities in DNA double-strand break repair, their role during replication has remained elusive. The nucleoside analog gemcitabine, widely used in cancer therapy, acts as a replication chain terminator; for a cell to survive treatment, gemcitabine needs to be removed from replicating DNA. Activities responsible for this removal have, so far, not been identified. We show that Mre11 3' to 5' exonuclease activity removes gemcitabine from nascent DNA during replication. This contributes to replication progression and gemcitabine resistance. We thus uncovered a replication-supporting role for Mre11 exonuclease activity, which is distinct from its previously reported detrimental role in uncontrolled resection in recombination-deficient cells.
  4. Proc Natl Acad Sci U S A. 2020 Jun 08. pii: 201916851. [Epub ahead of print]
    Wanrooij PH, Tran P, Thompson LJ, Carvalho G, Sharma S, Kreisel K, Navarrete C, Feldberg AL, Watt DL, Nilsson AK, Engqvist MKM, Clausen AR, Chabes A.
      Ribonucleotides (rNMPs) incorporated in the nuclear genome are a well-established threat to genome stability and can result in DNA strand breaks when not removed in a timely manner. However, the presence of a certain level of rNMPs is tolerated in mitochondrial DNA (mtDNA) although aberrant mtDNA rNMP content has been identified in disease models. We investigated the effect of incorporated rNMPs on mtDNA stability over the mouse life span and found that the mtDNA rNMP content increased during early life. The rNMP content of mtDNA varied greatly across different tissues and was defined by the rNTP/dNTP ratio of the tissue. Accordingly, mtDNA rNMPs were nearly absent in SAMHD1 -/- mice that have increased dNTP pools. The near absence of rNMPs did not, however, appreciably affect mtDNA copy number or the levels of mtDNA molecules with deletions or strand breaks in aged animals near the end of their life span. The physiological rNMP load therefore does not contribute to the progressive loss of mtDNA quality that occurs as mice age.
    Keywords:  SAMHD1; dNTP pool; mitochondrial DNA; mtDNA; ribonucleotide incorporation
  5. Nat Commun. 2020 Jun 10. 11(1): 2935
    Narayan RS, Molenaar P, Teng J, Cornelissen FMG, Roelofs I, Menezes R, Dik R, Lagerweij T, Broersma Y, Petersen N, Marin Soto JA, Brands E, van Kuiken P, Lecca MC, Lenos KJ, In 't Veld SGJG, van Wieringen W, Lang FF, Sulman E, Verhaak R, Baumert BG, Stalpers LJA, Vermeulen L, Watts C, Bailey D, Slotman BJ, Versteeg R, Noske D, Sminia P, Tannous BA, Wurdinger T, Koster J, Westerman BA.
      Personalized cancer treatments using combinations of drugs with a synergistic effect is attractive but proves to be highly challenging. Here we present an approach to uncover the efficacy of drug combinations based on the analysis of mono-drug effects. For this we used dose-response data from pharmacogenomic encyclopedias and represent these as a drug atlas. The drug atlas represents the relations between drug effects and allows to identify independent processes for which the tumor might be particularly vulnerable when attacked by two drugs. Our approach enables the prediction of combination-therapy which can be linked to tumor-driving mutations. By using this strategy, we can uncover potential effective drug combinations on a pan-cancer scale. Predicted synergies are provided and have been validated in glioblastoma, breast cancer, melanoma and leukemia mouse-models, resulting in therapeutic synergy in 75% of the tested models. This indicates that we can accurately predict effective drug combinations with translational value.
  6. Nat Commun. 2020 Jun 11. 11(1): 2948
    Huang JW, Acharya A, Taglialatela A, Nambiar TS, Cuella-Martin R, Leuzzi G, Hayward SB, Joseph SA, Brunette GJ, Anand R, Soni RK, Clark NL, Bernstein KA, Cejka P, Ciccia A.
      Homologous recombination (HR) mediates the error-free repair of DNA double-strand breaks to maintain genomic stability. Here we characterize C17orf53/MCM8IP, an OB-fold containing protein that binds ssDNA, as a DNA repair factor involved in HR. MCM8IP-deficient cells exhibit HR defects, especially in long-tract gene conversion, occurring downstream of RAD51 loading, consistent with a role for MCM8IP in HR-dependent DNA synthesis. Moreover, loss of MCM8IP confers cellular sensitivity to crosslinking agents and PARP inhibition. Importantly, we report that MCM8IP directly associates with MCM8-9, a helicase complex mutated in primary ovarian insufficiency, and RPA1. We additionally show that the interactions of MCM8IP with MCM8-9 and RPA facilitate HR and promote replication fork progression and cellular viability in response to treatment with crosslinking agents. Mechanistically, MCM8IP stimulates the helicase activity of MCM8-9. Collectively, our work identifies MCM8IP as a key regulator of MCM8-9-dependent DNA synthesis during DNA recombination and replication.
  7. Proc Natl Acad Sci U S A. 2020 Jun 08. pii: 201920165. [Epub ahead of print]
    Saha LK, Wakasugi M, Akter S, Prasad R, Wilson SH, Shimizu N, Sasanuma H, Huang SN, Agama K, Pommier Y, Matsunaga T, Hirota K, Iwai S, Nakazawa Y, Ogi T, Takeda S.
      Nucleotide excision repair (NER) removes helix-destabilizing adducts including ultraviolet (UV) lesions, cyclobutane pyrimidine dimers (CPDs), and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs). In comparison with CPDs, 6-4PPs have greater cytotoxicity and more strongly destabilizing properties of the DNA helix. It is generally believed that NER is the only DNA repair pathway that removes the UV lesions as evidenced by the previous data since no repair of UV lesions was detected in NER-deficient skin fibroblasts. Topoisomerase I (TOP1) constantly creates transient single-strand breaks (SSBs) releasing the torsional stress in genomic duplex DNA. Stalled TOP1-SSB complexes can form near DNA lesions including abasic sites and ribonucleotides embedded in chromosomal DNA. Here we show that base excision repair (BER) increases cellular tolerance to UV independently of NER in cancer cells. UV lesions irreversibly trap stable TOP1-SSB complexes near the UV damage in NER-deficient cells, and the resulting SSBs activate BER. Biochemical experiments show that 6-4PPs efficiently induce stable TOP1-SSB complexes, and the long-patch repair synthesis of BER removes 6-4PPs downstream of the SSB. Furthermore, NER-deficient cancer cell lines remove 6-4PPs within 24 h, but not CPDs, and the removal correlates with TOP1 expression. NER-deficient skin fibroblasts weakly express TOP1 and show no detectable repair of 6-4PPs. Remarkably, the ectopic expression of TOP1 in these fibroblasts led them to completely repair 6-4PPs within 24 h. In conclusion, we reveal a DNA repair pathway initiated by TOP1, which significantly contributes to cellular tolerance to UV-induced lesions particularly in malignant cancer cells overexpressing TOP1.
    Keywords:  6–4PPs; UV damage; base excision repair; topoisomerase I
  8. Front Cell Dev Biol. 2020 ;8 324
    Hamadeh Z, Lansdorp P.
      Maintenance of genome stability is essential to prevent the accumulation of DNA mutations that can initiate oncogenesis and facilitate tumor progression. Studies of DNA repair genes have revealed a highly dynamic and redundant network of genes and proteins responsible for maintaining genome stability. Cancer cells are often deficient in DNA repair, and the resulting genome instability decreases their fitness but also allows for more rapid evolution under selective pressure. Of particular interest for genome stability are the RecQ class of helicases. Five genes in this class, RECQL1, BLM, WRN, RECQL4, and RECQL5, are unique to mammals, as simpler eukaryotes and bacteria appear to have only one homolog, RecQ. The precise role of each of the five mammalian RecQ helicases remains to be determined. Whereas loss of function mutations of BLM, WRN, and RECQL4 in humans are associated with specific diseases, RECQL1 and RECQL5 have not yet been associated with specific disorders. Mice deficient in Recql5 are more likely to develop cancer, and human cells deficient in RECQL5 display chromosomal instability and elevated sister chromatid exchange events, similar to cells deficient in any of the other RecQ helicases. Recent studies support the hypothesis that RECQL5 can resolve intermediate DNA repair structures resulting from the collision of DNA transcription and replication machinery. In this review, we aim to summarize current knowledge regarding RECQL5 in the context of DNA repair, replication, and transcription to help uncover the role of RECQL5 in the maintenance of genome stability.
    Keywords:  DNA damage repair; DNA replication stress; RECQ5; RECQL5; cancer; genome stability; replication conflict; transcription
  9. Cancers (Basel). 2020 Jun 09. pii: E1503. [Epub ahead of print]12(6):
    Gomez MK, Illuzzi G, Colomer C, Churchman M, Hollis RL, O'Connor MJ, Gourley C, Leo E, Melton DW.
      High grade serous ovarian cancer (HGSOC) is a major cause of female cancer mortality. The approval of poly (ADP-ribose) polymerase (PARP) inhibitors for clinical use has greatly improved treatment options for patients with homologous recombination repair (HRR)-deficient HGSOC, although the development of PARP inhibitor resistance in some patients is revealing limitations to outcome. A proportion of patients with HRR-proficient cancers also benefit from PARP inhibitor therapy. Our aim is to compare mechanisms of resistance to the PARP inhibitor olaparib in these two main molecular categories of HGSOC and investigate a way to overcome resistance that we considered particularly suited to a cancer like HGSOC, where there is a very high incidence of TP53 gene mutation, making HGSOC cells heavily reliant on the G2 checkpoint for repair of DNA damage and survival. We identified alterations in multiple factors involved in resistance to PARP inhibition in both HRR-proficient and -deficient cancers. The most frequent change was a major reduction in levels of poly (ADP-ribose) glycohydrolase (PARG), which would be expected to preserve a residual PARP1-initiated DNA damage response to DNA single-strand breaks. Other changes seen would be expected to boost levels of HRR of DNA double-strand breaks. Growth of all olaparib-resistant clones isolated could be controlled by WEE1 kinase inhibitor AZD1775, which inactivates the G2 checkpoint. Our work suggests that use of the WEE1 kinase inhibitor could be a realistic therapeutic option for patients that develop resistance to olaparib.
    Keywords:  DNA repair; PARP inhibitor; WEE1 kinase; olaparib; ovarian cancer; resistance mechanism
  10. Expert Rev Mol Med. 2020 Jun 08. 22 e2
    Smith HL, Southgate H, Tweddle DA, Curtin NJ.
      DNA damage response (DDR) pathway prevents high level endogenous and environmental DNA damage being replicated and passed on to the next generation of cells via an orchestrated and integrated network of cell cycle checkpoint signalling and DNA repair pathways. Depending on the type of damage, and where in the cell cycle it occurs different pathways are involved, with the ATM-CHK2-p53 pathway controlling the G1 checkpoint or ATR-CHK1-Wee1 pathway controlling the S and G2/M checkpoints. Loss of G1 checkpoint control is common in cancer through TP53, ATM mutations, Rb loss or cyclin E overexpression, providing a stronger rationale for targeting the S/G2 checkpoints. This review will focus on the ATM-CHK2-p53-p21 pathway and the ATR-CHK1-WEE1 pathway and ongoing efforts to target these pathways for patient benefit.
    Keywords:  ATM; ATR; CDK1; CDK2; CHK1; CHK2; DNA damage response; WEE1; cell cycle; p53
  11. Cancers (Basel). 2020 Jun 09. pii: E1502. [Epub ahead of print]12(6):
    Peyraud F, Italiano A.
      Genomic instability is a hallmark of cancer related to DNA damage response (DDR) deficiencies, offering vulnerabilities for targeted treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) interfere with the efficient repair of DNA damage, particularly in tumors with existing defects in DNA repair, and induce synthetic lethality. PARPi are active across a range of tumor types harboring BRCA mutations and also BRCA-negative cancers, such as ovarian, breast or prostate cancers with homologous recombination deficiencies (HRD). Depending on immune contexture, immune checkpoint inhibitors (ICIs), such as anti-PD1/PD-L1 and anti-CTLA-4, elicit potent antitumor effects and have been approved in various cancers types. Although major breakthroughs have been performed with either PARPi or ICIs alone in multiple cancers, primary or acquired resistance often leads to tumor escape. PARPi-mediated unrepaired DNA damages modulate the tumor immune microenvironment by a range of molecular and cellular mechanisms, such as increasing genomic instability, immune pathway activation, and PD-L1 expression on cancer cells, which might promote responsiveness to ICIs. In this context, PARPi and ICIs represent a rational combination. In this review, we summarize the basic and translational biology supporting the combined strategy. We also detail preclinical results and early data of ongoing clinical trials indicating the synergistic effect of PARPi and ICIs. Moreover, we discuss the limitations and the future direction of the combination.
    Keywords:  CTLA-4; DNA damage response; PARP inhibitor; PD-1; PD-L1; combination therapy; immune checkpoint inhibitor; immunotherapy; solid tumors
  12. Trends Biochem Sci. 2020 Jun 06. pii: S0968-0004(20)30122-5. [Epub ahead of print]
    Ronato DA, Mersaoui SY, Busatto FF, Affar EB, Richard S, Masson JY.
      DNA double-strand break (DSB) resection, once thought to be a simple enzymatic process, is emerging as a highly complex series of coordinated activities required to maintain genome integrity. Progress in cell biology, biochemistry, and genetics has deciphered the precise resecting activities, the regulatory components, and their ability to properly channel the resected DNA to the appropriate DNA repair pathway. Herein, we review the mechanisms of regulation of DNA resection, with an emphasis on negative regulators that prevent single-strand (ss)DNA accumulation to maintain genome stability. Interest in targeting DNA resection inhibitors is emerging because their inactivation leads to poly(ADP-ribose) polymerase inhibitor (PARPi) resistance. We also present detailed regulation of DNA resection machineries, their analysis by functional assays, and their impact on disease and PARPi resistance.
    Keywords:  DNA double-strand break repair; DNA resection; DSB repair pathway choice; PARP inhibitors, genomic stability
  13. Cells. 2020 Jun 08. pii: E1423. [Epub ahead of print]9(6):
    Luzhin AV, Avanesyan B, Velichko AK, Shender VO, Ovsyannikova N, Arapidi GP, Shnaider PV, Petrova NV, Kireev II, Razin SV, Kantidze OL.
      Hyperthermia has been used as an adjuvant treatment for radio- and chemotherapy for decades. In addition to its effects on perfusion and oxygenation of cancer tissues, hyperthermia can enhance the efficacy of DNA-damaging treatments such as radiotherapy and chemotherapy. Although it is believed that the adjuvant effects are based on hyperthermia-induced dysfunction of DNA repair systems, the mechanisms of these dysfunctions remain elusive. Here, we propose that elevated temperatures can induce chromatin trapping (c-trapping) of essential factors, particularly those involved in DNA repair, and thus enhance the sensitization of cancer cells to DNA-damaging therapeutics. Using mass spectrometry-based proteomics, we identified proteins that could potentially undergo c-trapping in response to hyperthermia. Functional analyses of several identified factors involved in DNA repair demonstrated that c-trapping could indeed be a mechanism of hyperthermia-induced transient deficiency of DNA repair systems. Based on our proteomics data, we showed for the first time that hyperthermia could inhibit maturation of Okazaki fragments and activate a corresponding poly(ADP-ribose) polymerase-dependent DNA damage response. Together, our data suggest that chromatin trapping of factors involved in DNA repair and replication contributes to heat-induced radio- and chemosensitization.
    Keywords:  DNA repair; DNA replication; PARP; chromatin; hyperthermia
  14. J Exp Clin Cancer Res. 2020 Jun 09. 39(1): 105
    Hu L, Li B, Chen G, Song D, Xu Z, Gao L, Xi M, Zhou J, Li L, Zhang H, Feng Q, Wang Y, Lu K, Lu Y, Bu W, Wang H, Wu X, Zhu W, Shi J.
      BACKGROUND: DCZ3301, a novel aryl-guanidino compound previously reported by our group, exerts cytotoxic effects against multiple myeloma (MM), diffused large B cell lymphoma (DLBCL), and T-cell leukemia/lymphoma. However, the underlying mechanism of its action remains unknown.METHODS: We generated bortezomib (BTZ)-resistant cell lines, treated them with various concentrations of DCZ3301 over varying periods, and studied its effect on colony formation, cell proliferation, apoptosis, cell cycle, DNA synthesis, and DNA damage response. We validated our results using in vitro and in vivo experimental models.
    RESULTS: DCZ3301 overcame bortezomib (BTZ) resistance through regulation of the G2/M checkpoint in multiple myeloma (MM) in vitro and in vivo. Furthermore, treatment of BTZ-resistant cells with DCZ3301 restored their drug sensitivity. DCZ3301 induced M phase cell cycle arrest in MM mainly via inhibiting DNA repair and enhancing DNA damage. Moreover, DCZ3301 promoted the phosphorylation of ATM, ATR, and their downstream proteins, and these responses were blocked by the ATM specific inhibitor KU55933.
    CONCLUSIONS: Our study provides a proof-of-concept that warrants the clinical evaluation of DCZ3301 as a novel anti-tumor compound against BTZ resistance in MM.
    Keywords:  Cell cycle; DNA damage response; Drug-resistance; Multiple myeloma
  15. Oncogene. 2020 Jun 12.
    Prendergast L, Hong E, Safina A, Poe D, Gurova K.
      The histone chaperone FACT is upregulated during mammary tumorigenesis and necessary for the viability and growth of breast tumor cells. We established that only proliferating tumor cells are sensitive to FACT knockdown, suggesting that FACT functions during DNA replication in tumor cells but not in normal cells. We hypothesized that the basal level of replication stress defines the FACT dependence of cells. Using genetic and chemical tools, we demonstrated that FACT is needed to overcome replication stress. In the absence of FACT during replication stress, the MCM2-7 helicase dissociates from chromatin, resulting in the absence of ssDNA accumulation, RPA binding, and activation of the ATR/CHK1 checkpoint response. Without this response, stalled replication forks are not stabilized, and new origin firing cannot be prevented, leading to the accumulation of DNA damage and cell death. Thus, we propose a novel role for FACT as a factor preventing helicase dissociation from chromatin during replication stress.
  16. Genes (Basel). 2020 Jun 10. pii: E642. [Epub ahead of print]11(6):
    Wilhelm T, Said M, Naim V.
      Chromosomal instability (CIN) is associated with many human diseases, including neurodevelopmental or neurodegenerative conditions, age-related disorders and cancer, and is a key driver for disease initiation and progression. A major source of structural chromosome instability (s-CIN) leading to structural chromosome aberrations is "replication stress", a condition in which stalled or slowly progressing replication forks interfere with timely and error-free completion of the S phase. On the other hand, mitotic errors that result in chromosome mis-segregation are the cause of numerical chromosome instability (n-CIN) and aneuploidy. In this review, we will discuss recent evidence showing that these two forms of chromosomal instability can be mechanistically interlinked. We first summarize how replication stress causes structural and numerical CIN, focusing on mechanisms such as mitotic rescue of replication stress (MRRS) and centriole disengagement, which prevent or contribute to specific types of structural chromosome aberrations and segregation errors. We describe the main outcomes of segregation errors and how micronucleation and aneuploidy can be the key stimuli promoting inflammation, senescence, or chromothripsis. At the end, we discuss how CIN can reduce cellular fitness and may behave as an anticancer barrier in noncancerous cells or precancerous lesions, whereas it fuels genomic instability in the context of cancer, and how our current knowledge may be exploited for developing cancer therapies.
    Keywords:  DNA replication stress; aneuploidy; cancer; chromosomal instability; chromosome segregation; mitosis
  17. Mol Cancer Res. 2020 Jun 11. pii: molcanres.0214.2020. [Epub ahead of print]
    Nishimoto K, Niida H, Uchida C, Ohhata T, Kitagawa K, Motegi A, Suda T, Kitagawa M.
      Recent studies have demonstrated that lysine acetylation of histones is crucial for nucleotide excision repair (NER) by relaxing the chromatin structure, which facilitates the recruitment of repair factors. However, few studies have focused on the contribution of histone deacetylases (HDACs) to NER. Here, we found that histone H3 Lys14 (H3K14) was deacetylated by HDAC3 after UV irradiation. Depletion of HDAC3 caused defects in cyclobutene pyrimidine dimer excision and sensitized cells to UV irradiation. HDAC3-depleted cells had impaired unscheduled DNA synthesis, but not recovery of RNA synthesis, which indicates that HDAC3 was required for global genome NER. Moreover, Xeroderma pigmentosum, complementation group C (XPC) accumulation at the local UV-irradiated area was attenuated in HDAC3-depleted cells. In addition to the delay of XPC accumulation at DNA damage sites, XPC ubiquitylation was inhibited in HDAC3-depleted cells. These results suggest that the deacetylation of histone H3K14 by HDAC3 after UV irradiation contributes to XPC recruitment to DNA lesions to promote global genome NER. Implications: Involvement of histone deacetylation for XPC accumulation after UV irradiation indicates conversion of chromatin structure is essential for nucleotide excision repair in human cancer cells.
  18. Cell Rep. 2020 Jun 09. pii: S2211-1247(20)30725-7. [Epub ahead of print]31(10): 107745
    Zhu C, Rogers A, Asleh K, Won J, Gao D, Leung S, Li S, Vij KR, Zhu J, Held JM, You Z, Nielsen TO, Shao J.
      Spatiotemporal protein reorganization at DNA damage sites induced by genotoxic chemotherapies is crucial for DNA damage response (DDR), which influences treatment response by directing cancer cell fate. This process is orchestrated by valosin-containing protein (VCP), an AAA+ ATPase that extracts polyubiquinated chromatin proteins and facilitates their turnover. However, because of the essential and pleiotropic effects of VCP in global proteostasis, it remains challenging practically to understand and target its DDR-specific functions. We describe a DNA-damage-induced phosphorylation event (Ser784), which selectively enhances chromatin-associated protein degradation mediated by VCP and is required for DNA repair, signaling, and cell survival. These functional effects of Ser784 phosphorylation on DDR correlate with a decrease in VCP association with chromatin, cofactors NPL4/UFD1, and polyubiquitinated substrates. Clinically, high phospho-Ser784-VCP levels are significantly associated with poor outcome among chemotherapy-treated breast cancer patients. Thus, Ser784 phosphorylation is a DDR-specific enhancer of VCP function and a potential predictive biomarker for chemotherapy treatments.
    Keywords:  DNA damage response; K48-linked polyubiquitin; VCP; biomarker; cancer; chemotherapy; chromatin-associated degradation; nucleus; phosphorylation; proteostasis
  19. Genes (Basel). 2020 Jun 09. pii: E635. [Epub ahead of print]11(6):
    Whalen JM, Freudenreich CH.
      Components of the nuclear pore complex (NPC) have been shown to play a crucial role in protecting against replication stress, and recovery from some types of stalled or collapsed replication forks requires movement of the DNA to the NPC in order to maintain genome stability. The role that nuclear positioning has on DNA repair has been investigated in several systems that inhibit normal replication. These include structure forming sequences (expanded CAG repeats), protein mediated stalls (replication fork barriers (RFBs)), stalls within the telomere sequence, and the use of drugs known to stall or collapse replication forks (HU + MMS or aphidicolin). Recently, the mechanism of relocation for collapsed replication forks to the NPC has been elucidated. Here, we will review the types of replication stress that relocate to the NPC, the current models for the mechanism of relocation, and the currently known protective effects of this movement.
    Keywords:  fork collapse; fork restart; nuclear pore complex; replication fork; replication fork barriers; sumoylation
  20. Proc Natl Acad Sci U S A. 2020 06 10. pii: 201921311. [Epub ahead of print]
    Tsutakawa SE, Sarker AH, Ng C, Arvai AS, Shin DS, Shih B, Jiang S, Thwin AC, Tsai MS, Willcox A, Her MZ, Trego KS, Raetz AG, Rosenberg D, Bacolla A, Hammel M, Griffith JD, Cooper PK, Tainer JA.
      Xeroderma pigmentosum group G (XPG) protein is both a functional partner in multiple DNA damage responses (DDR) and a pathway coordinator and structure-specific endonuclease in nucleotide excision repair (NER). Different mutations in the XPG gene ERCC5 lead to either of two distinct human diseases: Cancer-prone xeroderma pigmentosum (XP-G) or the fatal neurodevelopmental disorder Cockayne syndrome (XP-G/CS). To address the enigmatic structural mechanism for these differing disease phenotypes and for XPG's role in multiple DDRs, here we determined the crystal structure of human XPG catalytic domain (XPGcat), revealing XPG-specific features for its activities and regulation. Furthermore, XPG DNA binding elements conserved with FEN1 superfamily members enable insights on DNA interactions. Notably, all but one of the known pathogenic point mutations map to XPGcat, and both XP-G and XP-G/CS mutations destabilize XPG and reduce its cellular protein levels. Mapping the distinct mutation classes provides structure-based predictions for disease phenotypes: Residues mutated in XP-G are positioned to reduce local stability and NER activity, whereas residues mutated in XP-G/CS have implied long-range structural defects that would likely disrupt stability of the whole protein, and thus interfere with its functional interactions. Combined data from crystallography, biochemistry, small angle X-ray scattering, and electron microscopy unveil an XPG homodimer that binds, unstacks, and sculpts duplex DNA at internal unpaired regions (bubbles) into strongly bent structures, and suggest how XPG complexes may bind both NER bubble junctions and replication forks. Collective results support XPG scaffolding and DNA sculpting functions in multiple DDR processes to maintain genome stability.
    Keywords:  ERCC5; crystal structure; crystallography; electron microscopy; endonuclease
  21. Nat Commun. 2020 Jun 12. 11(1): 2971
    Jalili P, Bowen D, Langenbucher A, Park S, Aguirre K, Corcoran RB, Fleischman AG, Lawrence MS, Zou L, Buisson R.
      APOBEC3A is a cytidine deaminase driving mutagenesis, DNA replication stress and DNA damage in cancer cells. While the APOBEC3A-induced vulnerability of cancers offers an opportunity for therapy, APOBEC3A protein and mRNA are difficult to quantify in tumors due to their low abundance. Here, we describe a quantitative and sensitive assay to measure the ongoing activity of APOBEC3A in tumors. Using hotspot RNA mutations identified from APOBEC3A-positive tumors and droplet digital PCR, we develop an assay to quantify the RNA-editing activity of APOBEC3A. This assay is superior to APOBEC3A protein- and mRNA-based assays in predicting the activity of APOBEC3A on DNA. Importantly, we demonstrate that the RNA mutation-based APOBEC3A assay is applicable to clinical samples from cancer patients. Our study presents a strategy to follow the dysregulation of APOBEC3A in tumors, providing opportunities to investigate the role of APOBEC3A in tumor evolution and to target the APOBEC3A-induced vulnerability in therapy.
  22. Cancer Res. 2020 Jun 10. pii: canres.0057.2020. [Epub ahead of print]
    Qiu Z, Fa P, Liu T, Prasad CB, Ma S, Hong Z, Chan ER, Wang H, Li Z, He K, Wang QE, Williams TM, Yan C, Sizemore ST, Narla G, Zhang J.
      There is currently a lack of precise predictive biomarkers for patient selection in clinical trials of inhibitors targeting replication stress (RS) response proteins ATR and CHK1. The objective of this study was to identify novel predictive biomarkers for the response to these agents in treating non-small cell lung cancer (NSCLC). A genome-wide loss-of-function screen revealed that tumor suppressor PPP2R2A, a B regulatory subunit of protein phosphatase 2 (PP2A), determines sensitivity to CHK1 inhibition. A synthetic lethal interaction between PPP2R2A deficiency and ATR or CHK1 inhibition was observed in NSCLC in vitro and in vivo and was independent of p53 status. ATR and CHK1 inhibition resulted in significantly increased levels of RS and altered replication dynamics, particularly in PPP2R2A-deficient NSCLC cells. Mechanistically, PPP2R2A negatively regulated translation of oncogene c-Myc protein. c-Myc activity was required for PPP2R2A deficiency-induced alterations of replication initiation/RS and sensitivity to ATR/CHK1 inhibitors. We conclude that PPP2R2A deficiency elevates RS by upregulating c-Myc activity, rendering cells reliant on the ATR/CHK1 axis for survival. Our studies show a novel synthetic lethal interaction and identify PPP2R2A as a potential new predictive biomarker for patient stratification in the clinical use of ATR and CHK1 inhibitors.
  23. Elife. 2020 Jun 09. pii: e56611. [Epub ahead of print]9
    Srinivasan M, Fumasoni M, Petela NJ, Murray A, Nasmyth KA.
      Sister chromatid cohesion essential for mitotic chromosome segregation is thought to involve the co-entrapment of sister DNAs within cohesin rings. Although cohesin can load onto chromosomes throughout the cell cycle, it only builds cohesion during S phase. A key question is whether cohesion is generated by conversion of cohesin complexes associated with un-replicated DNAs ahead of replication forks into cohesive structures behind them, or from nucleoplasmic cohesin that is loaded de novo onto nascent DNAs associated with forks, a process that would be dependent on cohesin's Scc2 subunit. We show here that in S. cerevisiae, both mechanisms exist and that each requires a different set of replisome-associated proteins. Cohesion produced by cohesin conversion requires Tof1/Csm3, Ctf4 and Chl1 but not Scc2 while that created by Scc2-dependent de novo loading at replication forks requires the Ctf18-RFC complex. The association of specific replisome proteins with different types of cohesion establishment opens the way to a mechanistic understanding of an aspect of DNA replication unique to eukaryotic cells.
    Keywords:  S. cerevisiae; SMC; biochemistry; chemical biology; chromosomes; cohesin; gene expression; replication; replisome; shister chromatid cohesion
  24. Oncogene. 2020 Jun 10.
    Crawford LJ, Campbell DC, Morgan JJ, Lawson MA, Down JM, Chauhan D, McAvera RM, Morris TC, Hamilton C, Krishnan A, Rajalingam K, Chantry AD, Irvine AE.
      Proteasome inhibitors have provided a significant advance in the treatment of multiple myeloma (MM). Consequently, there is increasing interest in developing strategies to target E3 ligases, de-ubiquitinases, and/or ubiquitin receptors within the ubiquitin proteasome pathway, with an aim to achieve more specificity and reduced side-effects. Previous studies have shown a role for the E3 ligase HUWE1 in modulating c-MYC, an oncogene frequently dysregulated in MM. Here we investigated HUWE1 in MM. We identified elevated expression of HUWE1 in MM compared with normal cells. Small molecule-mediated inhibition of HUWE1 resulted in growth arrest of MM cell lines without significantly effecting the growth of normal bone marrow cells, suggesting a favorable therapeutic index. Studies using a HUWE1 knockdown model showed similar growth inhibition. HUWE1 expression positively correlated with MYC expression in MM bone marrow cells and correspondingly, genetic knockdown and biochemical inhibition of HUWE1 reduced MYC expression in MM cell lines. Proteomic identification of HUWE1 substrates revealed a strong association of HUWE1 with metabolic processes in MM cells. Intracellular glutamine levels are decreased in the absence of HUWE1 and may contribute to MYC degradation. Finally, HUWE1 depletion in combination with lenalidomide resulted in synergistic anti-MM activity in both in vitro and in vivo models. Taken together, our data demonstrate an important role of HUWE1 in MM cell growth and provides preclinical rationale for therapeutic strategies targeting HUWE1 in MM.
  25. Sci Rep. 2020 Jun 09. 10(1): 9343
    Duong VN, Zhou L, Martínez-Jiménez MI, He L, Cosme M, Blanco L, Paintsil E, Anderson KS.
      A key component of antiretroviral therapy (ART) for HIV patients is the nucleoside reverse transcriptase inhibitor (NRTI) is tenofovir. Recent reports of tenofovir toxicity in patients taking ART for HIV cannot be explained solely on the basis of off-target inhibition of mitochondrial DNA polymerase gamma (Polγ). PrimPol was discovered as a primase-polymerase localized to the mitochondria with repriming and translesion synthesis capabilities and, therefore, a potential contributor to mitochondrial toxicity. We established a possible role of PrimPol in tenofovir-induced toxicity in vitro and show that tenofovir-diphosphate incorporation by PrimPol is dependent on the n-1 nucleotide. We identified and characterized a PrimPol mutation, D114N, in an HIV+ patient on tenofovir-based ART with mitochondrial toxicity. This mutant form of PrimPol, targeting a catalytic metal ligand, was unable to synthesize primers, likely due to protein instability and weakened DNA binding. We performed cellular respiration and toxicity assays using PrimPol overexpression and shRNA knockdown strains in renal proximal tubular epithelial cells. The PrimPol-knockdown strain was hypersensitive to tenofovir treatment, indicating that PrimPol protects against tenofovir-induced mitochondrial toxicity. We show that a major cellular role of PrimPol is protecting against toxicity caused by ART and individuals with inactivating mutations may be predisposed to these effects.
  26. Trends Cancer. 2020 Jun 06. pii: S2405-8033(20)30166-7. [Epub ahead of print]
    Burdak-Rothkamm S, Mansour WY, Rothkamm K.
      Molecular-targeted therapies and treatment stratification based on molecular biomarkers have rapidly gained momentum in the therapeutic spectrum for patients with prostate cancer, particularly those with aggressive disease. DNA damage repair (DDR) pathways are commonly impaired in prostate cancer. Recent studies have detailed mechanisms interconnecting the DDR with the androgen receptor (AR) signaling pathway as well as its interplay with the immune response. The prominent role of DDR deficiency in prostate cancer development and treatment response encourages innovative strategies for the detection of DDR deficiency in individual tumors. In this review, we describe recent preclinical and early clinical data on the exploitation of DDR defects as predictive biomarkers and also as molecular therapeutic targets.
    Keywords:  DNA damage response; molecular biomarker; prostate cancer; targeted therapy
  27. Cancer Discov. 2020 Jun 12. pii: CD-20-0163. [Epub ahead of print]
    Yap TA, Kristeleit R, Michalarea V, Pettitt SJ, Lim JSJ, Carreira S, Roda D, Miller R, Riisnaes R, Miranda S, Figueiredo I, Nava Rodrigues D, Ward S, Matthews R, Parmar M, Turner A, Tunariu N, Chopra N, Gevensleben H, Turner NC, Ruddle R, Raynaud FI, Decordova SA, Swales KE, Finneran L, Hall E, Rugman P, Lindemann JPO, Foxley A, Lord CJ, Banerji U, Plummer R, Basu B, Lopez JS, Drew Y, de Bono JS.
      Preclinical studies have demonstrated synergy between poly(ADP-ribose) polymerase (PARP) and phosphatidylinositol-3-kinase (PI3K)/AKT pathway inhibitors in BRCA1 and BRCA2 (BRCA1/2)-deficient and BRCA1/2-proficient tumors. We conducted an investigator-initiated phase I trial utilizing a prospective intrapatient dose-escalation design to assess two schedules of capivasertib (AKT inhibitor) with olaparib (PARP inhibitor) in 64 patients with advanced solid tumors. Dose expansions enrolled germline BRCA1/2-mutant tumors, or BRCA1/2-wildtype cancers harboring somatic DNA damage response (DDR) or PI3K/AKT pathway alterations. The combination was well-tolerated. Recommended phase 2 doses for the two schedules were: olaparib 300mg BID with either capivasertib 400mg BID 4-days-on, 3-days-off, or capivasertib 640mg BID 2-days-on, 5-days-off. Pharmacokinetics were dose-proportional. Pharmacodynamic studies confirmed pGSK3β suppression, increased pERK and decreased BRCA1 expression. 25 (44.6%) of 56 evaluable patients achieved clinical benefit (RECIST CR/PR or stable disease ≥4 months), including patients with tumors harboring germline BRCA1/2-mutations and BRCA1/2-wildtype cancers with or without DDR and PI3K/AKT pathway alterations.
  28. J Biol Chem. 2020 Jun 09. pii: jbc.RA119.009981. [Epub ahead of print]
    Sayed IM, Sahan AZ, Venkova T, Chakraborty A, Mukhopadhyay D, Bimczok D, Beswick EJ, Reyes VE, Pinchuk I, Sahoo D, Ghosh P, Hazra TK, Das S.
      Infection with the Gram-negative, microaerophilic bacterium Helicobacter pylori induces an inflammatory response and oxidative DNA damage in gastric epithelial cells that can lead to gastric cancer (GC). However, the underlying pathogenic mechanism is largely unclear. Here, we report that the suppression of Nei-like DNA glycosylase 2 (NEIL2), a mammalian DNA glycosylase that specifically removes oxidized bases, is one mechanism through which H. pylori infection may fuel the accumulation of DNA damage leading to GC. Using cultured cell lines, gastric biopsies, primary cells, and human enteroid-derived monolayers from healthy human stomach, we show that H. pylori infection greatly reduces NEIL2 expression. The H. pylori infection-induced down-regulation of NEIL2 was specific, as Campylobacter jejuni had no such effect. Using gastric organoids isolated from the murine stomach in co-culture experiments with live bacteria mimicking the infected stomach lining, we found that H. pylori infection is associated with the production of various inflammatory cytokines. This response was more pronounced in Neil2-knockout (KO) mouse cells than in WT cells, suggesting that NEIL2 suppresses inflammation under physiological conditions. Notably, the H. pylori-infected Neil2-KO murine stomach exhibited more DNA damage than WT. Furthermore, H. pylori-infected Neil2-KO mice had greater inflammation and more epithelial cell damage. Computational analysis of gene expression profiles of DNA glycosylases in gastric specimens linked the reduced Neil2 level to GC progression. Our results suggest that NEIL2 down-regulation is a plausible mechanism by which H. pylori infection impairs DNA damage repair, amplifies the inflammatory response, and initiates GC.
    Keywords:  DNA damage; DNA repair; Helicobacter pylori; Nei-like DNA glycosylase; bacterial infection; base-excision repair; enteroids; gastric cancer; infection; inflammation; stem cells
  29. DNA Repair (Amst). 2020 Jul - Aug;91-92:pii: S1568-7864(20)30121-X. [Epub ahead of print]91-92 102873
    Rose E, Carvalho JL, Hecht M.
      Trypanosoma cruzi is the etiological agent of Chagas Disease, which affects 6-7 million people worldwide. Since the early stages of infection and throughout its life cycle, the parasite is exposed to several genotoxic agents. Furthermore, DNA damage is also part of the mechanism of action of at least a few trypanocidal drugs, including Benznidazole. Thus, it is paramount for the parasite to count on an efficient DNA repair machinery to guarantee genome integrity and survival. The present work provides an up-to-date review of both the conserved and peculiar DNA repair mechanisms described in T. cruzi against oxidative stress, ultraviolet and ionizing radiation, DNA adduct-inducing agents, and Benznidazole. The comprehension of the DNA repair mechanisms of the parasite may shed light on the parasite evolution and possibly pave the way for the development of novel and more effective trypanocidal drugs.
    Keywords:  DNA adduct-inducing agents; DNA repair; Ionizing radiation; Oxidative damage; Trypanosoma cruzi; UV light
  30. Genes (Basel). 2020 Jun 05. pii: E622. [Epub ahead of print]11(6):
    Debnath S, Sharma S.
      RECQ1 (also known as RECQL or RECQL1) belongs to the RecQ family of DNA helicases, members of which are linked with rare genetic diseases of cancer predisposition in humans. RECQ1 is implicated in several cellular processes, including DNA repair, cell cycle and growth, telomere maintenance, and transcription. Earlier studies have demonstrated a unique requirement of RECQ1 in ensuring chromosomal stability and suggested its potential involvement in tumorigenesis. Recent reports have suggested that RECQ1 is a potential breast cancer susceptibility gene, and missense mutations in this gene contribute to familial breast cancer development. Here, we provide a framework for understanding how the genetic or functional loss of RECQ1 might contribute to genomic instability and cancer.
    Keywords:  DNA repair; G4; breast cancer; cancer; genomic stability; helicase; replication; transcription
  31. Sci Transl Med. 2020 Jun 10. pii: eaay2163. [Epub ahead of print]12(547):
    Cissé MY, Pyrdziak S, Firmin N, Gayte L, Heuillet M, Bellvert F, Fuentes M, Delpech H, Riscal R, Arena G, Chibon F, Le Gellec S, Maran-Gonzalez A, Chateau MC, Theillet C, Carrere S, Portais JC, Le Cam L, Linares LK.
      Well-differentiated and dedifferentiated liposarcomas (LPSs) are characterized by a systematic amplification of the MDM2 oncogene, which encodes a key negative regulator of the p53 pathway. The molecular mechanisms underlying MDM2 overexpression while sparing wild-type p53 in LPS remain poorly understood. Here, we show that the p53-independent metabolic functions of chromatin-bound MDM2 are exacerbated in LPS and mediate an addiction to serine metabolism that sustains nucleotide synthesis and tumor growth. Treatment of LPS cells with Nutlin-3A, a pharmacological inhibitor of the MDM2-p53 interaction, stabilized p53 but unexpectedly enhanced MDM2-mediated control of serine metabolism by increasing its recruitment to chromatin, likely explaining the poor clinical efficacy of this class of MDM2 inhibitors. In contrast, genetic or pharmacological inhibition of chromatin-bound MDM2 by SP141, a distinct MDM2 inhibitor triggering its degradation, or interfering with de novo serine synthesis, impaired LPS growth both in vitro and in clinically relevant patient-derived xenograft models. Our data indicate that targeting MDM2 functions in serine metabolism represents a potential therapeutic strategy for LPS.
  32. Nat Commun. 2020 Jun 11. 11(1): 2950
    Ito K, Murayama Y, Kurokawa Y, Kanamaru S, Kokabu Y, Maki T, Mikawa T, Argunhan B, Tsubouchi H, Ikeguchi M, Takahashi M, Iwasaki H.
      During homologous recombination, Rad51 forms a nucleoprotein filament on single-stranded DNA to promote DNA strand exchange. This filament binds to double-stranded DNA (dsDNA), searches for homology, and promotes transfer of the complementary strand, producing a new heteroduplex. Strand exchange proceeds via two distinct three-strand intermediates, C1 and C2. C1 contains the intact donor dsDNA whereas C2 contains newly formed heteroduplex DNA. Here, we show that the conserved DNA binding motifs, loop 1 (L1) and loop 2 (L2) in site I of Rad51, play distinct roles in this process. L1 is involved in formation of the C1 complex whereas L2 mediates the C1-C2 transition, producing the heteroduplex. Another DNA binding motif, site II, serves as the DNA entry position for initial Rad51 filament formation, as well as for donor dsDNA incorporation. Our study provides a comprehensive molecular model for the catalytic process of strand exchange mediated by eukaryotic RecA-family recombinases.
  33. Mutat Res. 2020 May 26. pii: S0027-5107(20)30040-3. [Epub ahead of print]821 111707
    Shaban HA, Seeber A.
      DNA damage induced global chromatin motion has been observed in yeast and mammalian cells. Currently, it is unclear what mechanisms may be driving these changes in whole genome dynamics. Recent advances in live-cell microscopy now enable chromatin motion to be quantified throughout the whole nucleus. In addition, much work has improved quantification of single particle trajectories. This topic is particularly important to the field of DNA repair as there are a large number of unanswered questions that can be tackled by monitoring global chromatin movement. Foremost, is how local DNA repair mechanisms interact and change global chromatin structure and whether this impacts repair pathway choice or efficiency. In this review, we describe methodologies to monitor global chromatin movement putting them into context with the DNA repair field highlighting how these techniques can drive new discoveries.
    Keywords:  Chromatin motion; Correlated motion; DNA damage; Double-strand break; Microscopy
  34. Nat Commun. 2020 Jun 10. 11(1): 2926
    Verma K, Saxena K, Donaka R, Chaphalkar A, Rai MK, Shukla A, Zaidi Z, Dandage R, Shanmugam D, Chakraborty K.
      Metabolic changes alter the cellular milieu; can this also change intracellular protein folding? Since proteostasis can modulate mutational buffering, if change in metabolism has the ability to change protein folding, arguably, it should also alter mutational buffering. Here we find that altered cellular metabolic states in E. coli buffer distinct mutations on model proteins. Buffered-mutants have folding problems in vivo and are differently chaperoned in different metabolic states. Notably, this assistance is dependent upon the metabolites and not on the increase in canonical chaperone machineries. Being able to reconstitute the folding assistance afforded by metabolites in vitro, we propose that changes in metabolite concentrations have the potential to alter protein folding capacity. Collectively, we unravel that the metabolite pools are bona fide members of proteostasis and aid in mutational buffering. Given the plasticity in cellular metabolism, we posit that metabolic alterations may play an important role in cellular proteostasis.
  35. J Med Chem. 2020 Jun 09.
    Jia X, Schols D, Meier C.
      The antiviral efficacy of many nucleoside analogues is strongly dependent on their intracellular activation by host cellular kinases to give ultimately the bioactive nucleoside analogue triphosphates (NTP). The metabolic conversion of nucleoside analogues into their triphosphates often proceeds insufficiently. We developed a nucleoside triphosphate (NTP) delivery system (TriPPPro-approach), in which the γ-phosphate is covalently modified by two different biodegradable masking units, one acyloxybenzyl- (AB) moiety and one alkoxycarbonyloxybenzyl- (ACB) group. Such compounds formed NTPs with high selectivity by an enzyme-triggered mechanism in human T-lymphocyte CEM cell extracts loosing first the AB group followed by the ACB moiety. This enables the bypass of all steps of the intracellular phosphorylation. This approach was applied here to convert some modestly active or even inactive nucleoside analogues into powerful biologically active metabolites. Potent antiviral activity profiles were obtained depending on the lipophilicity of the TriPPPro-NTP prodrugs against HIV-1 and HIV-2 replication in cultures of infected wild-type CD4+ CEM T-cells and more importantly in thymidine kinase-deficient CD4+ T-cells (CEM/TK-). This TriPPPro-strategy offers high potential for future antiviral and antitumoral chemotherapies.
  36. Ann Oncol. 2020 Jun 05. pii: S0923-7534(20)39869-0. [Epub ahead of print]
    Mauri G, Arena S, Siena S, Bardelli A, Sartore-Bianchi A.
      BACKGROUND: Colorectal cancer (CRC) represents a major cause of cancer deaths worldwide. Although significant progress has been made by molecular and immune therapeutic approaches, prognosis of advanced stage disease is still dismal. Alterations in the DNA damage response (DDR) pathways are emerging as novel targets for treatment across different cancer types. However, even though preclinical studies have shown the potential exploitation of DDR alterations in CRC, systematic and comprehensive testing is lagging behind and clinical development is based on analogies with other solid tumors according to a tissue-agnostic paradigm. Recently, functional evidence from patient-derived xenografts and organoids have suggested that maintenance with PARP-inhibitors might represent a therapeutic opportunity in CRC patients previously responsive to platinum-based treatment.DESIGN: In this review, we highlight the most promising preclinical data and systematically summarize published clinical trials in which DDR inhibitors have been used for CRC and provide evidence that disappointing results have been mainly due to a lack of clinical and molecular selection.
    CONCLUSIONS: Future preclinical and translational research will help in better understanding the role of DDR alterations in CRC and pave the way to novel strategies that might have a transformative impact on treatment by identifying new therapeutic options, including tailored use of standard chemotherapy.
    Keywords:  ATM; BRCA; Colon cancer; DNA Damage Response; Organoids; PARP-inhibitors; PARPness
  37. Curr Pharm Biotechnol. 2020 Jun 11.
    Kadir MFA, Othman S, Nellore K.
      BACKGROUND: The re-emerging of targeting dihydroorotate dehydrogenase (DHODH) in cancer treatment particularly acute myelogenous leukemia (AML) have corroborated the substantial role of DHODH in cancer and fascinated the attention of many pharmaceutical industries.OBJECTIVE: The effects brequinar sodium (BQR) and 4SC-101 in lymphoblastoid cell lines were investigated.
    METHOD: DHODH expression and cell proliferation inhibition of lymphoblastoid and lymphoma cell lines were analysed using Western blot analysis and XTT assay respectively. JC-1 probe and ATP biochemiluminescence kit was used to evaluate the mitochondrial membrane potential and ATP generation in these cell lines. Furthermore, we explored the cell cycle progression using Muse™ Cell Cycle Kit.
    RESULTS: Ramos, SUDHL-1 and RPMI-1788 cells are fast-growing cells with equal expression of DHODH enzyme and sensitivity to DHODH inhibitors that showed that the inhibition of DHODH was not cancer specific. In ATP depletion assay, the non-cancerous RPMI-1788 cells showed only a minor ATP reduction compared to Ramos and SUDHL-1 (cancer) cells. In the mechanistic impact of DHODH inhibitors on non-cancerous vs cancerous cells, the mitochondrial membrane potential assay revealed that significant depolarization and cytochrome c release occurred with DHODH inhibitors treatment in Ramos but not in the RPMI-1788 cells, indicating a different mechanism of proliferation inhibition in normal cells.
    CONCLUSION: The findings in this study provide evidence that DHODH inhibitors perturb the proliferation of non-cancerous cells via a distinct mechanism compared to cancerous cells. These results may lead to strategies for overcoming the impact on non-cancerous cells during treatment with DHODH inhibitors, leading to better therapeutic window in patients.
    Keywords:  4SC-101 ; ATP depletion; Dihydroorotate dehydrogenase; brequinar sodium; lymphoma; mitochondrial membrane potential; S-phase arrest
  38. Cancer Chemother Pharmacol. 2020 Jun 11.
    García-González X, Kaczmarczyk B, Abarca-Zabalía J, Thomas F, García-Alfonso P, Robles L, Pachón V, Vaz Á, Salvador-Martín S, Sanjurjo-Sáez M, López-Fernández LA.
      PURPOSE: Several clinical guidelines recommend genetic screening of DPYD, including coverage of the variants c.1905 + 1G>A(DPYD*2A), c.1679T>G(DPYD*13), c.2846A>T, and c.1129-5923C>G, before initiating treatment with fluoropyrimidines. However, this screening is often inadequate at predicting the occurrence of severe fluoropyrimidine-induced toxicity in patients.METHODS: Using a complementary approach combining whole DPYD exome sequencing and in silico and structural analysis, as well as phenotyping of DPD by measuring uracilemia (U), dihydrouracilemia (UH2), and the UH2/U ratio in plasma, we were able to characterize and interpret DPYD variants in 28 patients with severe fluoropyrimidine-induced toxicity after negative screening.
    RESULTS: Twenty-five out of 28 patients (90%) had at least 1 variant in the DPYD coding sequence, and 42% of the variants (6/14) were classified as potentially deleterious by at least 2 of the following algorithms: SIFT, Poly-Phen-2, and DPYD varifier. We identified two very rare deleterious mutations, namely, c.2087G>A (p.R696H) and c.2324T>G (p.L775W). We were able to demonstrate partial DPD deficiency, as measured by the UH2/U ratio in a patient carrying the variant p.L775W for the first time.
    CONCLUSION: Whole exon sequencing of DPYD in patients with suspicion of partial DPD deficiency can help to identify rare or new variants that lead to enzyme inactivation. Combining different techniques can yield abundant information without increasing workload and cost burden, thus making it a useful approach for implementation in patient care.
    Keywords:  5-Fluoruracil; Adverse reaction; Capecitabine; Pharmacogenetics
  39. Med Oncol. 2020 Jun 11. 37(7): 61
    Kapacee ZA, Knox JJ, Palmer D, Blagden SP, Lamarca A, Valle JW, McNamara MG.
      BACKGROUND: Resistance to gemcitabine chemotherapy is common in patients with pancreatic ductal adenocarcinoma (PDAC), biliary tract cancer (BTC) and ovarian cancers (OC), conferring poor survival. Use of ProTide technology led to the development of a 'partially-activated' monophosphorylated gemcitabine compound, termed NUC-1031. NUC-1031 enters cancer cells independent of the human equilibrative nucleoside transporter, does not require deoxycytidine kinase-mediated activation and resists cytidine deaminase-mediated breakdown into toxic by-products.CURRENT FINDINGS: The phase I PRO-001 trial recruited 68 patients with advanced solid tumours; of the 49 patients that had response-evaluable disease, 5 (10%) had a partial response (PR) and 33 (67%) had stable disease (SD). Subsequently, the PRO-002 study assessed the safety and efficacy of NUC-1031 combined with carboplatin for patients with OC (n = 25); preliminary data from this study reported one (4%) unconfirmed complete response (CR), 8 (35%) PRs and 13 (57%) patients with SD, the final outcome data are awaited. The ABC-08 trial for advanced BTC assessed safety and efficacy of NUC-1031 combined with cisplatin; 14 patients were recruited with a 50% objective response rate in the intention to treat population at interim analysis. ACELARATE, the phase III trial in first-line advanced PDAC comparing NUC-1031 to gemcitabine monotherapy, recruited 200 patients but has been paused for futility analysis.
    CONCLUSION: Early studies demonstrate NUC-1031 is well tolerated with favourable pharmacokinetic profiles. NUC-1031 use in PDAC remains unclear, but encouraging results of disease control in BTC and OC has prompted phase II and III trial development. NuTide 121, is a phase III trial comparing cisplatin-NUC 1031 combination to the standard of care cisplatin-gemcitabine and recruitment is ongoing. Recruiting trials and mature data from existing studies will help inform on the impact of NUC-1031 on patient survival over standard gemcitabine.
    Keywords:  Acelarin; Biliary tract cancer; Gemcitabine resistance; NUC-1031; Ovarian cancer; Pancreatic ductal adenocarcinoma; Phase I trial
  40. Biochemistry. 2020 Jun 09.
    Beaupre BA, Forouzesh DC, Moran GR.
      Dihydropyrimidine dehydrogenase (DPD) catalyzes the initial step in the catabolism of the pyrimidines uracil and thymine. Crystal structures have revealed an elaborate subunit architecture consisting of two flavin cofactors, apparently linked by four Fe4S4 centers. Analysis of the DPD reaction(s) equilibrium position under anaerobic conditions revealed a reaction that favors dihydropyrimidine formation. Single-turnover analysis shows biphasic kinetics. The serine variant of the candidate general acid, cysteine 671, provided enhanced kinetic resolution for these phases. In the first event, one subunit of the DPD dimer takes up two electrons from NADPH in a reductive activation step. Spectrophotometric deconvolution suggests that thes electrons reside on one of the two flavins. That oxidation of the enzyme by dioxygen can be suppressed by the addition of pyrimidine, is consistent with these electrons residing on the FMN. The second phase involves further oxidation of NADPH and concomitant reduction of the pyrimidine substrate. During this phase no net reduction of DPD cofactors is observed indicating that the entire cofactor set acts as a wire, transmitting electrons from NADPH to the pyrimidine rapidly. This indicates that the availability of the proton from C671 general acid controls the transmittance of electrons from NADPH to the pyrimidine. Acid quench and HPLC product analysis of single-turnover reactions with limiting NADPH confirmed 2:1, NADPH:pyrimidine stoichiometry for the enzyme accounting for successive activation and pyrimidine reduction. These data support an alternating subunit model in which one protomer is activated and turns over before the other subunit can be activated and enter catalysis.
  41. Bioorg Chem. 2020 May 26. pii: S0045-2068(20)30727-6. [Epub ahead of print]101 103976
    Abdellatif KRA, Belal A, El-Saadi MT, Amin NH, Said EG, Hemeda LR.
      Multi-targeted anticancer drugs are in focus as a promising research topic. A new series of benzothiazoles hybridized with pyrimidine moiety was designed and synthesized using the lead compound 4a. Various chemical modifications on the pyrimidine ring of 4a at four different positions were done in a trial to get new multi-targeted anticancer agents. The structures of the newly synthesized compounds were established on their elemental analyses and spectral data. All final synthesized derivatives were submitted to the National Cancer Institute (NCI), USA, to be screened for their in vitro anticancer activity. Further evaluation for the cytotoxic activity of the most active compounds was performed using the MTT assay method. Compounds 4d, 8d, 8h, 8i and 17 were then selected for examining their in vitro enzyme inhibitory activities against EGFR, HER2 and TS enzymes using lapatinib and 5FU as standards. Furthermore, cell cycle analysis and apoptosis induction detection were also evaluated. Finally, molecular docking studies were carried out for compounds 4d, 8d, 8h, 8i and 17 to interpret their observed enzymatic activities based on the ligand-protein interactions.
    Keywords:  Antitumor activity; Benzothiazole; Cyano pyrimidine; Dual EGFR/HER2 inhibitor; Molecular docking; Multitarget; NCI; Thymidylate synthase
  42. J Clin Med. 2020 Jun 07. pii: E1772. [Epub ahead of print]9(6):
    Unseld M, Fischöder S, Jachs M, Drimmel M, Siebenhüner A, Bianconi D, Kieler M, Puhr H, Minichsdorfer C, Winder T, Prager GW.
      The nucleoside trifluridine/tipiracil (TAS-102) and the multikinase inhibitor regorafenib significantly improved survival in metastatic colorectal cancer patients (mCRC). Both treatments are characterized by different treatment-related adverse events but detailed analyses of predictive side effects are rare. In this retrospective, observational, real-life study, clinical data on mCRC patients treated with trifluridine/tipiracil or regorafenib at the Medical University of Vienna, Austria and the University Hospital Zurich, Switzerland were collected. The correlation between adverse events and response or survival rates were calculated performing Fisher's exact test and log-rank test, respectively. Common adverse events of any grade included fatigue (52%), nausea/vertigo (34%), anemia (26%), and leukopenia (22%) in trifluridine/tipiracil patients and fatigue (42%), hand-foot-skin syndrome (36%) and hoarseness (34%) in patients upon regorafenib treatment. In trifluridine/tipiracil patients the prevalence of leukopenia (p = 0.044) and weight loss (p = 0.044) was prognostic, whereas leukopenia (p = 0.044) and neutropenia (p = 0.043) predicted PFS. The disease control rate was not significantly affected. In regorafenib-treated patients, the prevalence of nausea (p = 0.001) was prognostic, while oral mucositis predicted PFS (p = 0.032) as well as the DCR (p = 0.039). In conclusion, we underline the efficacy of trifluridine/tipiracil and regorafenib in the real-life setting. We describe predictive adverse events like neutropenia/leukopenia, which might be used as surrogate marker in anticancer therapy beyond second line treatment.
    Keywords:  adverse events; late line therapy; metastatic colorectal cancer patients; regorafenib; trifluridine/tipiracil