bims-pimaco Biomed News
on PI3K and MAPK signalling in colorectal cancer
Issue of 2020‒12‒27
ten papers selected by
Lucas B. Zeiger
Beatson Institute for Cancer Research

  1. Adv Drug Deliv Rev. 2020 Dec 17. pii: S0169-409X(20)30281-7. [Epub ahead of print]
      The canonical Wnt pathway is one of the key cellular signaling cascades that regulates, via the transcriptional co-activator β-catenin, numerous embryogenic developmental processes, as well as tissue homeostasis. It is therefore not surprising that misregulation of the Wnt/β-catenin pathway has been implicated in carcinogenesis. Aberrant Wnt signaling has been reported in a variety of malignancies, and its role in both hereditary and sporadic colorectal cancer (CRC), has been the subject of intensive study. Interestingly, the vast majority of colorectal tumors harbor mutations in the tumor suppressor gene adenomatous polyposis coli (APC). The Wnt pathway is complex, and despite decades of research, the mechanisms that underlie its functions are not completely known. Thus, although the Wnt cascade is an attractive target for therapeutic intervention against CRC, one of the malignancies with the highest morbidity and mortality rates, achieving efficacy and safety is yet extremely challenging. Here, we review the current knowledge of the Wnt different epistatic signaling components and the mechanism/s by which the signal is transduced in both health and disease, focusing on CRC. We address some of the important questions in the field and describe various therapeutic strategies designed to combat unregulated Wnt signaling, the development of targeted therapy approaches and the emerging challenges that are associated with these advanced methods.
    Keywords:  Colonic delivery; Colorectal cancer; Wnt signalling
  2. Mol Cell. 2020 Dec 10. pii: S1097-2765(20)30836-4. [Epub ahead of print]
      Mechanistic target of rapamycin complex 1 (mTORC1) controls cell growth and proliferation by sensing fluctuations in environmental cues such as nutrients, growth factors, and energy levels. The Rag GTPases (Rags) serve as a critical module that signals amino acid (AA) availability to modulate mTORC1 localization and activity. Recent studies have demonstrated how AAs regulate mTORC1 activity through Rags. Here, we uncover an unconventional pathway that activates mTORC1 in response to variations in threonine (Thr) levels via mitochondrial threonyl-tRNA synthetase TARS2. TARS2 interacts with inactive Rags, particularly GTP-RagC, leading to increased GTP loading of RagA. mTORC1 activity in cells lacking TARS2 is resistant to Thr repletion, showing that TARS2 is necessary for Thr-dependent mTORC1 activation. The requirement of TARS2, but not cytoplasmic threonyl-tRNA synthetase TARS, for this effect demonstrates an additional layer of complexity in the regulation of mTORC1 activity.
    Keywords:  Rag GTPases; TARS2; amino acid; aminoacyl-tRNA synthetase; mTORC1; threonine
  3. Front Oncol. 2020 ;10 581365
      Colorectal cancer (CRC) is a disease with constantly increasing incidence and high mortality. The treatment efficacy could be curtailed by drug resistance resulting from poor drug penetration into tumor tissue and the tumor-specific microenvironment, such as hypoxia and acidosis. Furthermore, CRC tumors can be exposed to different pH depending on the position in the intestinal tract. CRC tumors often share upregulation of the Akt signaling pathway. In this study, we investigated the role of external pH in control of cytotoxicity of perifosine, the Akt signaling pathway inhibitor, to CRC cells using 2D and 3D tumor models. In 3D settings, we employed an innovative strategy for simultaneous detection of spatial drug distribution and biological markers of proliferation/apoptosis using a combination of mass spectrometry imaging and immunohistochemistry. In 3D conditions, low and heterogeneous penetration of perifosine into the inner parts of the spheroids was observed. The depth of penetration depended on the treatment duration but not on the external pH. However, pH alteration in the tumor microenvironment affected the distribution of proliferation- and apoptosis-specific markers in the perifosine-treated spheroid. Accurate co-registration of perifosine distribution and biological response in the same spheroid section revealed dynamic changes in apoptotic and proliferative markers occurring not only in the perifosine-exposed cells, but also in the perifosine-free regions. Cytotoxicity of perifosine to both 2D and 3D cultures decreased in an acidic environment below pH 6.7. External pH affects cytotoxicity of the other Akt inhibitor, MK-2206, in a similar way. Our innovative approach for accurate determination of drug efficiency in 3D tumor tissue revealed that cytotoxicity of Akt inhibitors to CRC cells is strongly dependent on pH of the tumor microenvironment. Therefore, the effect of pH should be considered during the design and pre-clinical/clinical testing of the Akt-targeted cancer therapy.
    Keywords:  Akt kinase; alkalization; colorectal cancer; lactic acidosis; mass spectrometry imaging; perifosine; signal co-registration; tumor environment
  4. Nat Commun. 2020 Dec 21. 11(1): 6422
      Wnt/β-catenin signaling is crucial for intestinal carcinogenesis and the maintenance of intestinal cancer stem cells. Here we identify the histone methyltransferase Mll1 as a regulator of Wnt-driven intestinal cancer. Mll1 is highly expressed in Lgr5+ stem cells and human colon carcinomas with increased nuclear β-catenin. High levels of MLL1 are associated with poor survival of colon cancer patients. The genetic ablation of Mll1 in mice prevents Wnt/β-catenin-driven adenoma formation from Lgr5+ intestinal stem cells. Ablation of Mll1 decreases the self-renewal of human colon cancer spheres and halts tumor growth of xenografts. Mll1 controls the expression of stem cell genes including the Wnt/β-catenin target gene Lgr5. Upon the loss of Mll1, histone methylation at the stem cell promoters switches from activating H3K4 tri-methylation to repressive H3K27 tri-methylation, indicating that Mll1 sustains stem cell gene expression by antagonizing gene silencing through polycomb repressive complex 2 (PRC2)-mediated H3K27 tri-methylation. Transcriptome profiling of Wnt-mutated intestinal tumor-initiating cells reveals that Mll1 regulates Gata4/6 transcription factors, known to sustain cancer stemness and to control goblet cell differentiation. Our results demonstrate that Mll1 is an essential epigenetic regulator of Wnt/β-catenin-induced intestinal tumorigenesis and cancer stemness.
  5. ACS Pharmacol Transl Sci. 2020 Dec 11. 3(6): 1176-1187
      Single-agent drug treatment of KRASmut colorectal cancers is often ineffective because the activation of compensatory signaling pathways leads to drug resistance. To mimic cyclic chemotherapy treatments of patients, we showed that intermittent treatments of 3D tumor spheroids of KRASmut colorectal cancer cells with inhibitors of mitogen-activated protein kinase (MAPK) signaling pathway temporarily suppressed growth of spheroids. However, the efficacy of successive single-agent treatments was significantly reduced. Molecular analysis showed compensatory activation of PI3K/AKT and STAT kinases and EGFR family proteins. To overcome the adaptation of cancer cells to MAPK pathway inhibitors, we treated tumor spheroids with a combination of MEK and EGFR inhibitors. This approach significantly blocked signaling of MAPK and PI3K/AKT pathways and prevented the growth of spheroids, but it was not effective against STAT signaling. Although the combination treatment blocked the matrix invasion of DLD1 cells, additional treatments with STAT inhibitors were necessary to prevent invasiveness of HCT116 cells. Overall, our drug resistance model elucidated the mechanisms of treatment-induced growth and invasiveness of cancer cells and allowed design-driven testing and identifying of effective treatments to suppress these phenotypes.
  6. J Physiol. 2020 Dec 21.
      Contrary to Warburg's original thesis, accelerated aerobic glycolysis is not a primary, permanent and universal consequence of dysfunctional/impaired mitochondria compensating for poor ATP-yield per mole of glucose. Instead, in most tumours the Warburg effect is an essential part of a "selfish" metabolic reprogramming, which results from the interplay between (normoxic/hypoxic) HIF-1-overexpression, oncogene activation (cMyc, Ras), loss of function of tumour suppressors (mutant-p53, mutant-PTEN, microRNAs and sirtuins with suppressor functions), activated (PI3K/Akt/mTORC1, Ras/Raf/Mek/Erk/cMyc, Jak/Stat3) or deactivated (LKB1/AMPK) signalling pathways, components of the tumour microenvironment, and HIF-1-cooperations with epigenetic mechanisms. Molecular and functional processes of the Warburg effect include: (a) considerably accelerated glycolytic fluxes, (b) adequate ATP generation per unit time to maintain energy homeostasis and electrochemical gradients, (c) backup and diversion of glycolytic intermediates facilitating the biosynthesis of nucleotides, non-essential amino acids, lipids and hexosamines, (d) inhibition of pyruvate entry into mitochondria, (e) excessive formation and accumulation of lactate which stimulates tumour growth and suppression of anti-tumour immunity; in addition, lactate can serve as an energy source for normoxic cancer cells and drives malignant progression and resistances to conventional therapies, (f) cytosolic lactate is mainly exported through upregulated lactate-proton symporters (MCT4), working together with other H+ -transporters, and carbonic anhydrases (CAII, CAIX) which hydrate CO2 from oxidative metabolism to form H+ and bicarbonate, (g) in concert with poor vascular drainage these proton export mechanisms are responsible for extracellular acidification, driving malignant progression and resistances to conventional therapies, (h) maintenance of the cellular redox homeostasis and low ROS formation, and (i) HIF-1 overexpression, mutant-p53 and mutant-PTEN which inhibit mitochondrial biogenesis and functions, negatively impacting cellular respiration rate. The glycolytic switch is an early event in oncogenesis and primarily supports cell survival. All in all, the Warburg effect, i.e., aerobic glycolysis in the presence of oxygen and -in principle- functioning mitochondria, constitutes a major driver of the cancer progression machinery, resistance to conventional therapies, and poor patient outcome. However, as evidenced during the last two decades, in a minority of tumours primary mitochondrial defects can play a key role promoting the Warburg effect and tumour progression due to mutations in some Krebs cycle enzymes and mitochondrial ROS overproduction. Abstract figure legend Driving processes causing the Warburg effect during carcinogenesis (upper part), and mechanisms/consequences of metabolic reprogramming in Warburg phenotypes (lower part) leading to survival advantages, malignant progression and, ultimately, poor patient outcome. This article is protected by copyright. All rights reserved.
    Keywords:  Warburg effect; aerobic glycolysis; glycolytic phenotype; lactate accumulation; metabolic reprogramming; tumour acidosis; tumour glucose metabolism; tumour mitochondria
  7. Cancer Treat Rev. 2020 Dec 16. pii: S0305-7372(20)30175-4. [Epub ahead of print]92 102137
      The mitogen-activated protein kinase (MAPK) pathway plays a vital role in cellular processes such as gene expression, cell proliferation, cell survival, and apoptosis. Also known as the RAS-RAF-MEK-ERK pathway, the MAPK pathway has been implicated in approximately one-third of all cancers. Mutations in RAS or RAF genes such as KRAS and BRAF are common, and these mutations typically promote malignancies by over-activating MEK and ERK downstream, which drives sustained cell proliferation and uninhibited cell growth. Development of drugs targeting this pathway has been a research area of great interest, especially drugs targeting the inhibition of MEK. In vitro and clinical studies have shown promise for certain MEK inhibitors (MEKi) , and MEKi have become the first treatment option for certain cancers. Despite promising results, not all patients have a response to MEKi, and mechanisms of resistance typically arise in patients who do have a positive initial response. This paper summarizes recent developments regarding MEKi, the mechanisms of adaptive resistance to MEKi, and the potential solutions to the issue of adaptive MEKi resistance.
    Keywords:  Drug combination trials; MEK inhibitors; Mechanisms of Adaptive Resistance
  8. J Chemother. 2020 Dec 21. 1-7
      Panitumumab and cetuximab are monoclonal antibodies known to be effective in metastatic colorectal cancer (mCRC). Although the survival benefits when combined with chemotherapy have been determined, there are no studies comparing the two agents with chemotherapy in the second-line treatment. In this study, we aimed to compare the efficacy of cetuximab vs panitumumab in patients who previously received chemotherapy. Who progressed after first-line treatment for K-ras wild type mCRC were analyzed. The efficacy of cetuximab vs panitumumab on overall survival (OS) and progression-free survival (PFS) when combined with FOLFIRI regimen was compared retrospectively. Median PFS was 6.9 months in the cetuximab group and 4.7 months in the panitumumab group. Median OS cetuximab and panitumumab groups were 18.4 and 12.2 months, respectively. In the second-line treatment of K-ras wild type mCRC, both PFS and OS were found to be longer in patients receiving cetuximab than in patients receiving panitumumab, but no statistically significant difference was found.
    Keywords:  Colorectal cancers; K-ras; OS; PFS; cetuximab; panitumumab
  9. Cancers (Basel). 2020 Dec 17. pii: E3811. [Epub ahead of print]12(12):
      Intestinal epithelium architecture is sustained by stem cell division. In principle, stem cells can divide symmetrically to generate two identical copies of themselves or asymmetrically to sustain tissue renewal in a balanced manner. The choice between the two helps preserve stem cell and progeny pools and is crucial for tissue homeostasis. Control of spindle orientation is a prime contributor to the specification of symmetric versus asymmetric cell division. Competition for space within the niche may be another factor limiting the stem cell pool. An integrative view of the multiple links between intracellular and extracellular signals and molecular determinants at play remains a challenge. One outstanding question is the precise molecular roles of the tumour suppressor Adenomatous polyposis coli (APC) for sustaining gut homeostasis through its respective functions as a cytoskeletal hub and a down regulator in Wnt signalling. Here, we review our current understanding of APC inherent activities and partners in order to explore novel avenues by which APC may act as a gatekeeper in colorectal cancer and as a therapeutic target.
    Keywords:  APC; Wnt signalling; actin; cell division; cell migration; colorectal cancer; cytoskeleton; gut renewal; microtubules; spindle orientation; stem cells
  10. Front Oncol. 2020 ;10 602498
      The high heterogeneity of colorectal cancer (CRC) is the main clinical challenge for individualized therapies. Molecular classification will contribute to drug discovery and personalized management optimizing. Here, we aimed to characterize the molecular features of CRC by a classification system based on metabolic gene expression profiles. 435 CRC samples from the Genomic Data Commons data portal were chosen as training set while 566 sample in GSE39582 were selected as testing set. Then, a non-negative matrix factorization clustering was performed, and three subclasses of CRC (C1, C2, and C3) were identified in both training set and testing set. Results showed that subclass C1 displayed high metabolic activity and good prognosis. Subclass C2 was associated with low metabolic activities and displayed high immune signatures as well as high expression of immune checkpoint genes. C2 had the worst prognosis among the three subtypes. Subclass C3 displayed intermediate metabolic activity, high gene mutation numbers and good prognosis. Finally, a 27-gene metabolism-related signature was identified for prognosis prediction. Our works deepened the understanding of metabolic hallmarks of CRC, and provided valuable information for "multi-molecular" based personalized therapies.
    Keywords:  classification; colorectal cancer; immune signatures; metabolism; non-negative matrix factorization