bims-pimaco 2023-01-29 papers

on PI3K and MAPK signalling in colorectal cancer

Issue of 2023–01–29
eightteen papers selected by
Lucas B. Zeiger, CRUK Scotland Institute, Beatson Institute for Cancer Research

The KRAS crowd targets its next cancer mutations.
Structure of the lysosomal mTORC1-TFEB-Rag-Ragulator megacomplex.
Eliminating oncogenic RAS: back to the future at the drawing board.
A conformation-selective protein binder for a KRAS mutant inhibits the interaction between RAS and RAF.
Lipid raft protein flotillin-1 is important for the interaction between SOS1 and H-Ras/K-Ras, leading to Ras activation.
Annual review of KRAS inhibitors in 2022.
New developments in targeted therapy for metastatic colorectal cancer.
Inhibition of autophagy and MEK promotes ferroptosis in Lkb1-deficient Kras-driven lung tumors.
Destabilizing NF1 variants act in a dominant negative manner through neurofibromin dimerization.
Crosstalk between protein kinases AKT and ERK1/2 in human lung tumor-derived cell models.
EGOC inhibits TOROID polymerization by structurally activating TORC1.
TORC1 phosphorylates and inhibits the ribosome preservation factor Stm1 to activate dormant ribosomes.
Mapping lesion-specific response and progression dynamics and inter-organ variability in metastatic colorectal cancer.
Molecular Characteristics of Early-Onset Colorectal Cancer According to Detailed Anatomical Locations: Comparison With Later-Onset Cases.
Cancer stem cells, not bulk tumor cells, determine mechanisms of resistance to SMO inhibitors.
Combined PD-1, BRAF and MEK inhibition in BRAFV600E colorectal cancer: a phase 2 trial.
An mTOR feedback loop mediates the 'flare' ('rebound') response to MET tyrosine kinase inhibition.
Transferrin Receptor-Mediated Iron Uptake Promotes Colon Tumorigenesis.

Nat Rev Drug Discov. 2023 Jan 23.

The KRAS crowd targets its next cancer mutations.

Asher Mullard.

DOI: https://doi.org/10.1038/d41573-023-00015-x
Nature. 2023 Jan 25.

Structure of the lysosomal mTORC1-TFEB-Rag-Ragulator megacomplex.

Zhicheng Cui, Gennaro Napolitano, Mariana E G de Araujo, Alessandra Esposito, Jlenia Monfregola, Lukas A Huber, Andrea Ballabio, James H Hurley.

The transcription factor TFEB is a master regulator of lysosomal biogenesis and autophagy1. The phosphorylation of TFEB by the mechanistic target of rapamycin complex 1 (mTORC1)2-5 is unique in its mTORC1 substrate recruitment mechanism, which is strictly dependent on the amino acid-mediated activation of the RagC GTPase activating protein FLCN6,7. TFEB lacks the TOR signalling motif responsible for the recruitment of other mTORC1 substrates. We used cryogenic-electron microscopy to determine the structure of TFEB as presented to mTORC1 for phosphorylation, which we refer to as the 'megacomplex'. Two full Rag-Ragulator complexes present each molecule of TFEB to the mTOR active site. One Rag-Ragulator complex is bound to Raptor in the canonical mode seen previously in the absence of TFEB. A second Rag-Ragulator complex (non-canonical) docks onto the first through a RagC GDP-dependent contact with the second Ragulator complex. The non-canonical Rag dimer binds the first helix of TFEB with a RagCGDP-dependent aspartate clamp in the cleft between the Rag G domains. In cellulo mutation of the clamp drives TFEB constitutively into the nucleus while having no effect on mTORC1 localization. The remainder of the 108-amino acid TFEB docking domain winds around Raptor and then back to RagA. The double use of RagC GDP contacts in both Rag dimers explains the strong dependence of TFEB phosphorylation on FLCN and the RagC GDP state.

DOI: https://doi.org/10.1038/s41586-022-05652-7
Biochem Soc Trans. 2023 Jan 23. pii: BST20221343. [Epub ahead of print]

Eliminating oncogenic RAS: back to the future at the drawing board.

Candy Laura Steffen, Pelin Kaya, Elisabeth Schaffner-Reckinger, Daniel Abankwa.

  RAS drug development has made enormous strides in the past ten years, with the first direct KRAS inhibitor being approved in 2021. However, despite the clinical success of covalent KRAS-G12C inhibitors, we are immediately confronted with resistances as commonly found with targeted drugs. Previously believed to be undruggable due to its lack of obvious druggable pockets, a couple of new approaches to hit this much feared oncogene have now been carved out. We here concisely review these approaches to directly target four druggable sites of RAS from various angles. Our analysis focuses on the lessons learnt during the development of allele-specific covalent and non-covalent RAS inhibitors, the potential of macromolecular binders to facilitate the discovery and validation of targetable sites on RAS and finally an outlook on a future that may engage more small molecule binders to become drugs. We foresee that the latter could happen mainly in two ways: First, non-covalent small molecule inhibitors may be derived from the development of covalent binders. Second, reversible small molecule binders could be utilized for novel targeting modalities, such as degraders of RAS. Provided that degraders eliminate RAS by recruiting differentially expressed E3-ligases, this approach could enable unprecedented tissue- or developmental stage-specific destruction of RAS with potential advantages for on-target toxicity. We conclude that novel creative ideas continue to be important to exterminate RAS in cancer and other RAS pathway-driven diseases, such as RASopathies.

Keywords:  RAS; cancer; drug development

DOI:  https://doi.org/10.1042/BST20221343
Biochem Biophys Res Commun. 2023 Jan 11. pii: S0006-291X(23)00042-6. [Epub ahead of print]645 110-117

A conformation-selective protein binder for a KRAS mutant inhibits the interaction between RAS and RAF.

Youn Hee Jung, Yoonjoo Choi, Hyo-Deok Seo, Moon-Hyeong Seo, Hak-Sung Kim.

  Small GTPases are key signaling nodes that regulate the cellular processes and subcellular events, and their abnormal activities and dysregulations are closely linked with diverse cancers. Here, we report the development of conformation-selective protein binders for a KRAS mutant. The conformation-specific protein binders were selected from a repebody scaffold composed of LRR (Leucine-rich repeat) modules through phage display and modular engineering against constitute active conformation of KRAS. Epitope of the selected binders was mapped to be located close to switch I of KRAS. The conformation-selective protein binders were shown to effectively block the interaction between active KRAS and RAS-binding domain of BRAF, suppressing the KRAS-mediated downstream signaling.

Keywords:  Conformational selectivity; KRAS; Repebody

DOI:  https://doi.org/10.1016/j.bbrc.2023.01.019
Int J Cancer. 2023 Jan 24.

Lipid raft protein flotillin-1 is important for the interaction between SOS1 and H-Ras/K-Ras, leading to Ras activation.

Hao Jin, Minsoo Koh, Hyesol Lim, Hae-Young Yong, Eun-Sook Kim, Sun Young Kim, Kyoungmee Kim, Joohee Jung, Won-Ji Ryu, Kang-Yell Choi, Aree Moon.

  Ras mutations have been frequently observed in human cancer. Although there is a high degree of similarity between Ras isomers, they display preferential coupling in specific cancer types. The binding of Ras to the plasma membrane is essential for its activation and biological functions. The present study elucidated Ras isoform-specific interactions with the membrane and their role in Ras-mediated biological activities. We investigated the role of a lipid raft protein flotillin-1 (Flot-1) in the activations of Ras. We found that Flot-1 was co-localized with H-Ras, but not with N-Ras, in lipid rafts of MDA-MB-231 human breast cells. The amino-terminal hydrophobic domain (1-38) of Flot-1 interacted with the hypervariable region of H-Ras. The epidermal growth factor-stimulated activation of H-Ras required Flot-1 which was not necessary for that of N-Ras in breast cancer cells. Flot-1 interacted with son of sevenless (SOS)1, which promotes the conversion of Ras-bound GDP to GTP. Notably, Flot-1 was crucial for the interaction between SOS1 and H-Ras/K-Ras in breast and pancreatic cancer cells. Stable knockdown of Flot-1 reduced the in vivo metastasis in a mouse xenograft model with human breast carcinoma cells. A tissue microarray composed of 61 human pancreatic cancer samples showed higher levels of Flot-1 expression in pancreatic tumor tissues compared to normal tissues, and a correlation between K-Ras and Flot-1. Taken together, our findings suggest that Flot-1 may serve as a membrane platform for the interaction of SOS1 with H-Ras/K-Ras in human cancer cells, presenting Flot-1 as a potential target for Ras-driven cancers. This article is protected by copyright. All rights reserved.

Keywords:  H-Ras; K-Ras; flotillin-1; son of sevenless 1; triple-negative breast cancer

DOI:  https://doi.org/10.1002/ijc.34443
Eur J Med Chem. 2023 Jan 16. pii: S0223-5234(23)00039-9. [Epub ahead of print]249 115124

Annual review of KRAS inhibitors in 2022.

Hao Wang, Lingling Chi, Fuqiang Yu, Honglin Dai, Chao Gao, Xiaojie Si, Zhengjie Wang, Limin Liu, Jiaxin Zheng, Lihong Shan, Hongmin Liu, Qiurong Zhang.

  Kirsten rat sarcoma viral (KRAS) oncogene is the most commonly mutated isoform of RAS, accounting for 85% of RAS-driven human cancers. KRAS functioning as a signaling hub participates in multiple cellular signaling pathways and regulates a variety of critical processes such as cell proliferation, differentiation, growth, metabolism and migration. Over the past decades, KRAS oncoprotein has been considered as an "undruggable" target due to its smooth surface and high GTP/GDP affinity. The breakthrough in directly targeting G12C mutated-KRAS and recently approved covalent KRASG12C inhibitors sotorasib and adagrasib broke the myth of KRAS undruggable and confirmed the directly targeting KRAS as one of the most promising strategies for the treatment of cancers. Targeting KRASG12C successfully enriched the understanding of KRAS and brought opportunities for the development of inhibitors to directly target other KRAS mutations. With the stage now set for a new era in the treatment of KRAS-driven cancers, the development of KRAS inhibitors also enters a booming epoch. In this review, we overviewed the research progress of KRAS inhibitors with the potential to treat cancers covering articles published in 2022. The design strategies, discovery processes, structure-activity relationship (SAR) studies, cocrystal structure analysis as well as in vitro and in vivo activity were highlighted with the aim of providing updated sight to accelerate the further development of more potent inhibitors targeting various mutated-KRAS with favorable drug-like properties.

Keywords:  Irreversible inhibitors; KRAS; PROTACs; Peptides; Reversible inhibitors

DOI:  https://doi.org/10.1016/j.ejmech.2023.115124
Ther Adv Med Oncol. 2023 ;15 17588359221148540

New developments in targeted therapy for metastatic colorectal cancer.

Ambrose H N Wong, Brigette Ma, Rashid N Lui.

  Colorectal cancer (CRC) is the second most lethal cancer worldwide and the prognosis of metastatic CRC (mCRC) remains poor. Recent advancements in translational research have led to the identification of several new therapeutic targets and improved the treatment outcome of patients with tumours harbouring BRAF V600E mutation, (HER2) ErBB2 alterations, NTRK gene fusions and KRAS(G12C) mutation. Improved understanding towards the mechanism of resistance to targeted therapy such as anti-epidermal growth factor receptor antibodies and the evolving role of therapeutic monitoring with circulating tumour DNA (ctDNA) has enabled the longitudinal tracking of clonal evolution during treatment and the individualization of subsequent treatments. To broaden the community-based implementation of precision oncology in directing targeted therapies for patients with gastrointestinal cancers including mCRC, the feasibility of 'Master Protocols' that utilizes ctDNA-based genotyping platforms is currently being evaluated. Such protocols encompass both observational and interventional clinical trials of novel targeted therapies conducted within a large clinical trial network. In this review, we will discuss the latest developments in targeted therapies, and therapeutic strategies for overcoming acquired drug resistance in patients with mCRC.

Keywords:  BRAF inhibitor; EGFR inhibitor; colorectal cancer; personalized medicine; precision oncology; targeted therapy

DOI:  https://doi.org/10.1177/17588359221148540
Cell Death Dis. 2023 Jan 26. 14(1): 61

Inhibition of autophagy and MEK promotes ferroptosis in Lkb1-deficient Kras-driven lung tumors.

Vrushank Bhatt, Taijin Lan, Wenping Wang, Jerry Kong, Eduardo Cararo Lopes, Jianming Wang, Khoosheh Khayati, Akash Raju, Michael Rangel, Enrique Lopez, Zhixian Sherrie Hu, Xuefei Luo, Xiaoyang Su, Jyoti Malhotra, Wenwei Hu, Sharon R Pine, Eileen White, Jessie Yanxiang Guo.

LKB1 and KRAS are the third most frequent co-mutations detected in non-small cell lung cancer (NSCLC) and cause aggressive tumor growth. Unfortunately, treatment with RAS-RAF-MEK-ERK pathway inhibitors has minimal therapeutic efficacy in LKB1-mutant KRAS-driven NSCLC. Autophagy, an intracellular nutrient scavenging pathway, compensates for Lkb1 loss to support Kras-driven lung tumor growth. Here we preclinically evaluate the possibility of autophagy inhibition together with MEK inhibition as a treatment for Kras-driven lung tumors. We found that the combination of the autophagy inhibitor hydroxychloroquine (HCQ) and the MEK inhibitor Trametinib displays synergistic anti-proliferative activity in KrasG12D/+;Lkb1-/- (KL) lung cancer cells, but not in KrasG12D/+;p53-/- (KP) lung cancer cells. In vivo studies using tumor allografts, genetically engineered mouse models (GEMMs) and patient-derived xenografts (PDXs) showed anti-tumor activity of the combination of HCQ and Trametinib on KL but not KP tumors. We further found that the combination treatment significantly reduced mitochondrial membrane potential, basal respiration, and ATP production, while also increasing lipid peroxidation, indicative of ferroptosis, in KL tumor-derived cell lines (TDCLs) and KL tumors compared to treatment with single agents. Moreover, the reduced tumor growth by the combination treatment was rescued by ferroptosis inhibitor. Taken together, we demonstrate that autophagy upregulation in KL tumors causes resistance to Trametinib by inhibiting ferroptosis. Therefore, a combination of autophagy and MEK inhibition could be a novel therapeutic strategy to specifically treat NSCLC bearing co-mutations of LKB1 and KRAS.

DOI: https://doi.org/10.1038/s41419-023-05592-8
Proc Natl Acad Sci U S A. 2023 Jan 31. 120(5): e2208960120

Destabilizing NF1 variants act in a dominant negative manner through neurofibromin dimerization.

Lucy C Young, Ruby Goldstein de Salazar, Sae-Won Han, Zi Yi Stephanie Huang, Alan Merk, Matthew Drew, Joseph Darling, Vanessa Wall, Reinhard Grisshammer, Alice Cheng, Madeline R Allison, Matthew J Sale, Dwight V Nissley, Dominic Esposito, Jana Ognjenovic, Frank McCormick.

  The majority of pathogenic mutations in the neurofibromatosis type I (NF1) gene reduce total neurofibromin protein expression through premature truncation or microdeletion, but it is less well understood how loss-of-function missense variants drive NF1 disease. We have found that patient variants in codons 844 to 848, which correlate with a severe phenotype, cause protein instability and exert an additional dominant-negative action whereby wild-type neurofibromin also becomes destabilized through protein dimerization. We have used our neurofibromin cryogenic electron microscopy structure to predict and validate other patient variants that act through a similar mechanism. This provides a foundation for understanding genotype-phenotype correlations and has important implications for patient counseling, disease management, and therapeutics.

Keywords:  NFI; cryo-EM; neurofibromatosis type I

DOI:  https://doi.org/10.1073/pnas.2208960120
Front Oncol. 2022 ;12 1045521

Crosstalk between protein kinases AKT and ERK1/2 in human lung tumor-derived cell models.

Aurimas Stulpinas, Matas Sereika, Aida Vitkeviciene, Ausra Imbrasaite, Natalija Krestnikova, Audrone V Kalvelyte.

  There is no doubt that cell signaling manipulation is a key strategy for anticancer therapy. Furthermore, cell state determines drug response. Thus, establishing the relationship between cell state and therapeutic sensitivity is essential for the development of cancer therapies. In the era of personalized medicine, the use of patient-derived ex vivo cell models is a promising approach in the translation of key research findings into clinics. Here, we were focused on the non-oncogene dependencies of cell resistance to anticancer treatments. Signaling-related mechanisms of response to inhibitors of MEK/ERK and PI3K/AKT pathways (regulators of key cellular functions) were investigated using a panel of patients' lung tumor-derived cell lines with various stemness- and EMT-related markers, varying degrees of ERK1/2 and AKT phosphorylation, and response to anticancer treatment. The study of interactions between kinases was the goal of our research. Although MEK/ERK and PI3K/AKT interactions are thought to be cell line-specific, where oncogenic mutations have a decisive role, we demonstrated negative feedback loops between MEK/ERK and PI3K/AKT signaling pathways in all cell lines studied, regardless of genotype and phenotype differences. Our work showed that various and distinct inhibitors of ERK signaling - selumetinib, trametinib, and SCH772984 - increased AKT phosphorylation, and conversely, inhibitors of AKT - capivasertib, idelalisib, and AKT inhibitor VIII - increased ERK phosphorylation in both control and cisplatin-treated cells. Interaction between kinases, however, was dependent on cellular state. The feedback between ERK and AKT was attenuated by the focal adhesion kinase inhibitor PF573228, and in cells grown in suspension, showing the possible role of extracellular contacts in the regulation of crosstalk between kinases. Moreover, studies have shown that the interplay between MEK/ERK and PI3K/AKT signaling pathways may be dependent on the strength of the chemotherapeutic stimulus. The study highlights the importance of spatial location of the cells and the strength of the treatment during anticancer therapy.

Keywords:  AKT; ERK (extracellular signal-regulated kinase); cancer cell; cell signaling; cellular resistance; kinase inhibitors; lung cancer; targeted drugs

DOI:  https://doi.org/10.3389/fonc.2022.1045521
Nat Struct Mol Biol. 2023 Jan 26.

EGOC inhibits TOROID polymerization by structurally activating TORC1.

Manoël Prouteau, Clélia Bourgoint, Jan Felix, Lenny Bonadei, Yashar Sadian, Caroline Gabus, Savvas N Savvides, Irina Gutsche, Ambroise Desfosses, Robbie Loewith.

Target of rapamycin complex 1 (TORC1) is a protein kinase controlling cell homeostasis and growth in response to nutrients and stresses. In Saccharomyces cerevisiae, glucose depletion triggers a redistribution of TORC1 from a dispersed localization over the vacuole surface into a large, inactive condensate called TOROID (TORC1 organized in inhibited domains). However, the mechanisms governing this transition have been unclear. Here, we show that acute depletion and repletion of EGO complex (EGOC) activity is sufficient to control TOROID distribution, independently of other nutrient-signaling pathways. The 3.9-Å-resolution structure of TORC1 from TOROID cryo-EM data together with interrogation of key interactions in vivo provide structural insights into TORC1-TORC1' and TORC1-EGOC interaction interfaces. These data support a model in which glucose-dependent activation of EGOC triggers binding to TORC1 at an interface required for TOROID assembly, preventing TORC1 polymerization and promoting release of active TORC1.

DOI: https://doi.org/10.1038/s41594-022-00912-6
EMBO J. 2023 Jan 24. e112344

TORC1 phosphorylates and inhibits the ribosome preservation factor Stm1 to activate dormant ribosomes.

Sunil Shetty, Jon Hofstetter, Stefania Battaglioni, Danilo Ritz, Michael N Hall.

  Target of rapamycin complex 1 (TORC1) promotes biogenesis and inhibits the degradation of ribosomes in response to nutrient availability. To ensure a basal supply of ribosomes, cells are known to preserve a small pool of dormant ribosomes under nutrient-limited conditions. However, the regulation of these dormant ribosomes is poorly characterized. Here, we show that upon inhibition of yeast TORC1 by rapamycin or nitrogen starvation, the ribosome preservation factor Stm1 mediates the formation of nontranslating, dormant 80S ribosomes. Furthermore, Stm1-bound 80S ribosomes are protected from proteasomal degradation. Upon nutrient replenishment, TORC1 directly phosphorylates and inhibits Stm1 to reactivate translation. Finally, we find that SERBP1, a mammalian ortholog of Stm1, is likewise required for the formation of dormant 80S ribosomes upon mTORC1 inhibition in mammalian cells. These data suggest that TORC1 regulates ribosomal dormancy in an evolutionarily conserved manner by directly targeting a ribosome preservation factor.

Keywords:  SERBP1; Stm1; TORC1; dormant ribosomes; proteasome

DOI:  https://doi.org/10.15252/embj.2022112344
Nat Commun. 2023 Jan 26. 14(1): 417

Mapping lesion-specific response and progression dynamics and inter-organ variability in metastatic colorectal cancer.

Jiawei Zhou, Amber Cipriani, Yutong Liu, Gang Fang, Quefeng Li, Yanguang Cao.

Achieving systemic tumor control across metastases is vital for long-term patient survival but remains intractable in many patients. High lesion-level response heterogeneity persists, conferring many dissociated responses across metastatic lesions. Most studies of metastatic disease focus on tumor molecular and cellular features, which are crucial to elucidating the mechanisms underlying lesion-level variability. However, our understanding of lesion-specific heterogeneity on the macroscopic level, such as lesion dynamics in growth, response, and progression during treatment, remains rudimentary. This study investigates lesion-specific response heterogeneity through analyzing 116,542 observations of 40,612 lesions in 4,308 metastatic colorectal cancer (mCRC) patients. Despite significant differences in their response and progression dynamics, metastatic lesions converge on four phenotypes that vary with anatomical site. Importantly, we find that organ-level progression sequence is closely associated with patient long-term survival, and that patients with the first lesion progression in the liver often have worse survival. In conclusion, our study provides insights into lesion-specific response and progression heterogeneity in mCRC and creates impetus for metastasis-specific therapeutics.

DOI: https://doi.org/10.1038/s41467-023-36121-y
Am J Gastroenterol. 2023 Jan 30.

Molecular Characteristics of Early-Onset Colorectal Cancer According to Detailed Anatomical Locations: Comparison With Later-Onset Cases.

Tomotaka Ugai, Koichiro Haruki, Tabitha A Harrison, Yin Cao, Conghui Qu, Andrew T Chan, Peter T Campbell, Naohiko Akimoto, Sonja Berndt, Hermann Brenner, Daniel D Buchanan, Jenny Chang-Claude, Kenji Fujiyoshi, Steven J Gallinger, Marc J Gunter, Akihisa Hidaka, Michael Hoffmeister, Li Hsu, Mark A Jenkins, Roger L Milne, Victor Moreno, Polly A Newcomb, Reiko Nishihara, Rish K Pai, Lori C Sakoda, Martha L Slattery, Wei Sun, Efrat L Amitay, Elizabeth Alwers, Stephen N Thibodeau, Amanda E Toland, Bethany Van Guelpen, Michael O Woods, Syed H Zaidi, John D Potter, Marios Giannakis, Mingyang Song, Jonathan A Nowak, Amanda I Phipps, Ulrike Peters, Shuji Ogino.

INTRODUCTION: Early-onset colorectal cancer diagnosed before the age of 50 years has been increasing. Likely reflecting the pathogenic role of the intestinal microbiome, which gradually changes across the entire colorectal length, the prevalence of certain tumor molecular characteristics gradually changes along colorectal subsites. Understanding how colorectal tumor molecular features differ by age and tumor location is important in personalized patient management.
METHODS: Using 14,004 cases with colorectal cancer including 3,089 early-onset cases, we examined microsatellite instability (MSI), CpG island methylator phenotype (CIMP), and KRAS and BRAF mutations in carcinomas of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum and compared early-onset cases with later-onset cases.
RESULTS: The proportions of MSI-high, CIMP-high, and BRAF-mutated early-onset tumors were lowest in the rectum (8.8%, 3.4%, and 3.5%, respectively) and highest in the ascending colon (46% MSI-high; 15% CIMP-high) or transverse colon (8.6% BRAF-mutated) (all Ptrend <0.001 across the rectum to ascending colon). Compared with later-onset tumors, early-onset tumors showed a higher prevalence of MSI-high status and a lower prevalence of CIMP-high status and BRAF mutations in most subsites. KRAS mutation prevalence was higher in the cecum compared with that in the other subsites in both early-onset and later-onset tumors (P < 0.001). Notably, later-onset MSI-high tumors showed a continuous decrease in KRAS mutation prevalence from the rectum (36%) to ascending colon (9%; Ptrend <0.001), followed by an increase in the cecum (14%), while early-onset MSI-high cancers showed no such trend.
DISCUSSION: Our findings support biogeographical and pathogenic heterogeneity of colorectal carcinomas in different colorectal subsites and age groups.

DOI: https://doi.org/10.14309/ajg.0000000000002171
Cancer Res Commun. 2022 Jun;2(6): 402-416

Cancer stem cells, not bulk tumor cells, determine mechanisms of resistance to SMO inhibitors.

Joshy George, Yaohui Chen, Nourhan Abdelfattah, Keiko Yamamoto, Thomas D Gallup, Scott I Adamson, Brad Rybinski, Anuj Srivastava, Parveen Kumar, Min Gyu Lee, David S Baskin, Wen Jiang, Jong Min Choi, William Flavahan, Jeffrey H Chuang, Betty Ys Kim, Jiaqiong Xu, Sung Yun Jung, Kyuson Yun.

  The emergence of treatment resistance significantly reduces the clinical utility of many effective targeted therapies. Although both genetic and epigenetic mechanisms of drug resistance have been reported, whether these mechanisms are stochastically selected in individual tumors or governed by a predictable underlying principle is unknown. Here, we report that the dependence of cancer stem cells (CSCs), not bulk tumor cells, on the targeted pathway determines the molecular mechanism of resistance in individual tumors. Using both spontaneous and transplantable mouse models of sonic hedgehog (SHH) medulloblastoma (MB) treated with an SHH/Smoothened inhibitor, sonidegib/LDE225, we show that genetic-based resistance occurs only in tumors that contain SHH-dependent CSCs (SD-CSCs). In contrast, SHH MBs containing SHH-dependent bulk tumor cells but SHH-independent CSCs (SI-CSCs) acquire resistance through epigenetic reprogramming. Mechanistically, elevated proteasome activity in SMOi-resistant SI-CSC MBs alters the tumor cell maturation trajectory through enhanced degradation of specific epigenetic regulators, including histone acetylation machinery components, resulting in global reductions in H3K9Ac, H3K14Ac, H3K56Ac, H4K5Ac, and H4K8Ac marks and gene expression changes. These results provide new insights into how selective pressure on distinct tumor cell populations contributes to different mechanisms of resistance to targeted therapies. This insight provides a new conceptual framework to understand responses and resistance to SMOis and other targeted therapies.

Keywords:  Cancer stem cells; LDE225; SHH inhibitor; drug resistance mechanism; medulloblastoma

DOI:  https://doi.org/10.1158/2767-9764.crc-22-0124
Nat Med. 2023 Jan 26.

Combined PD-1, BRAF and MEK inhibition in BRAFV600E colorectal cancer: a phase 2 trial.

Jun Tian, Jonathan H Chen, Sherry X Chao, Karin Pelka, Marios Giannakis, Julian Hess, Kelly Burke, Vjola Jorgji, Princy Sindurakar, Jonathan Braverman, Arnav Mehta, Tomonori Oka, Mei Huang, David Lieb, Maxwell Spurrell, Jill N Allen, Thomas A Abrams, Jeffrey W Clark, Andrea C Enzinger, Peter C Enzinger, Samuel J Klempner, Nadine J McCleary, Jeffrey A Meyerhardt, David P Ryan, Matthew B Yurgelun, Katie Kanter, Emily E Van Seventer, Islam Baiev, Gary Chi, Joy Jarnagin, William B Bradford, Edmond Wong, Alexa G Michel, Isobel J Fetter, Giulia Siravegna, Angelo J Gemma, Arlene Sharpe, Shadmehr Demehri, Rebecca Leary, Catarina D Campbell, Omer Yilmaz, Gad A Getz, Aparna R Parikh, Nir Hacohen, Ryan B Corcoran.

While BRAF inhibitor combinations with EGFR and/or MEK inhibitors have improved clinical efficacy in BRAFV600E colorectal cancer (CRC), response rates remain low and lack durability. Preclinical data suggest that BRAF/MAPK pathway inhibition may augment the tumor immune response. We performed a proof-of-concept single-arm phase 2 clinical trial of combined PD-1, BRAF and MEK inhibition with sparatlizumab (PDR001), dabrafenib and trametinib in 37 patients with BRAFV600E CRC. The primary end point was overall response rate, and the secondary end points were progression-free survival, disease control rate, duration of response and overall survival. The study met its primary end point with a confirmed response rate (24.3% in all patients; 25% in microsatellite stable patients) and durability that were favorable relative to historical controls of BRAF-targeted combinations alone. Single-cell RNA sequencing of 23 paired pretreatment and day 15 on-treatment tumor biopsies revealed greater induction of tumor cell-intrinsic immune programs and more complete MAPK inhibition in patients with better clinical outcome. Immune program induction in matched patient-derived organoids correlated with the degree of MAPK inhibition. These data suggest a potential tumor cell-intrinsic mechanism of cooperativity between MAPK inhibition and immune response, warranting further clinical evaluation of optimized targeted and immune combinations in CRC. ClinicalTrials.gov registration: NCT03668431.

DOI: https://doi.org/10.1038/s41591-022-02181-8
Sci Rep. 2023 Jan 25. 13(1): 1378

An mTOR feedback loop mediates the 'flare' ('rebound') response to MET tyrosine kinase inhibition.

D M Altintas, M Cerqua, A De Laurentiis, L Trusolino, C Boccaccio, P M Comoglio.

Targeted therapy significantly impairs tumour growth but suffers from limitations, among which the 'flare' ('rebound') effect. Among cancers driven by tyrosine kinase receptors, those relying on alterations of the MET oncogene benefit from treatment by specific inhibitors. Previously, we reported that discontinuation of MET tyrosine kinase receptor inhibition causes 'rebound' activation of the oncogene, with a post-treatment transient hyperphosphorylation phase that culminates into a dramatic increase in cancer cell proliferation. The molecular mechanisms behind the 'MET burst' after treatment cessation are unknown but critically important for patients. Here we identify a positive feedback loop mediated by the AKT/mTOR pathway leading to (a) enhanced MET translation by activating p70S6K and 4EBP1 and (b) MET hyper-phosphorylation by inactivation of the tyrosine-phosphatase PTP1B. The latter effect is due to m-TOR-driven PTP1B phosphorylation of the inhibitory residues Ser50 and Ser378. These data provide in vitro evidence for the use of mTOR inhibitors to prevent the 'flare effect' in MET targeted therapy, with potential applicative ramifications for patient clinical management.

DOI: https://doi.org/10.1038/s41598-023-28648-3
Adv Sci (Weinh). 2023 Jan 26. e2207693

Transferrin Receptor-Mediated Iron Uptake Promotes Colon Tumorigenesis.

Hyeoncheol Kim, Luke B Villareal, Zhaoli Liu, Mohammad Haneef, Daniel M Falcon, David R Martin, Ho-Joon Lee, Michael K Dame, Durga Attili, Ying Chen, James Varani, Jason R Spence, Olga Kovbasnjuk, Justin A Colacino, Costas A Lyssiotis, Henry C Lin, Yatrik M Shah, Xiang Xue.

  Transferrin receptor (TFRC) is the major mediator for iron entry into a cell. Under excessive iron conditions, TFRC is expected to be reduced to lower iron uptake and toxicity. However, the mechanism whereby TFRC expression is maintained at high levels in iron-enriched cancer cells and the contribution of TFRC to cancer development are enigmatic. Here the work shows TFRC is induced by adenomatous polyposis coli (APC) gene loss-driven β-catenin activation in colorectal cancer, whereas TFRC-mediated intratumoral iron accumulation potentiates β-catenin signaling by directly enhancing the activity of tankyrase. Disruption of TFRC leads to a reduction of colonic iron levels and iron-dependent tankyrase activity, which caused stabilization of axis inhibition protein 2 (AXIN2) and subsequent repression of the β-catenin/c-Myc/E2F Transcription Factor 1/DNA polymerase delta1 (POLD1) axis. POLD1 knockdown, iron chelation, and TFRC disruption increase DNA replication stress, DNA damage response, apoptosis, and reduce colon tumor growth. Importantly, a combination of iron chelators and DNA damaging agents increases DNA damage response and reduces colon tumor cell growth. TFRC-mediated iron import is at the center of a novel feed-forward loop that facilitates colonic epithelial cell survival. This discovery may provide novel strategies for colorectal cancer therapy.

Keywords:  DNA damage response; TFRC; colon; iron; β-catenin

DOI:  https://doi.org/10.1002/advs.202207693