KRAS-mutant Cancer Cell Lines Research Articles

Dual inhibition of SUMOylation and MEK conquers MYC-expressing KRAS-mutant cancers by accumulating DNA damage

BackgroundKRAS mutations frequently occur in cancers, particularly pancreatic ductal adenocarcinoma, colorectal cancer, and non-small cell lung cancer. Although KRASG12C inhibitors have recently been approved, effective precision therapies have not yet been established for all KRAS-mutant cancers. Many treatments for KRAS-mutant cancers, including epigenome-targeted drugs, are currently under investigation. Small ubiquitin-like modifier (SUMO) proteins are a family of small proteins covalently attached to and detached from other proteins in cells via the processes called SUMOylation and de-SUMOylation. We assessed whether SUMOylation inhibition was effective in KRAS-mutant cancer cells.MethodsThe efficacy of the first-in-class SUMO-activating enzyme E inhibitor TAK-981 (subasumstat) was assessed in multiple human and mouse KRAS-mutated cancer cell lines. A gene expression assay using a TaqMan array was used to identify biomarkers of TAK-981 efficacy. The biological roles of SUMOylation inhibition and subsequent regulatory mechanisms were investigated using immunoblot analysis, immunofluorescence assays, and mouse models.ResultsWe discovered that TAK-981 downregulated the expression of the currently undruggable MYC and effectively suppressed the growth of MYC-expressing KRAS-mutant cancers across different tissue types. Moreover, TAK-981-resistant cells were sensitized to SUMOylation inhibition via MYC-overexpression. TAK-981 induced proteasomal degradation of MYC by altering the balance between SUMOylation and ubiquitination and promoting the binding of MYC and Fbxw7, a key factor in the ubiquitin–proteasome system. The efficacy of TAK-981 monotherapy in immunocompetent and immunodeficient mouse models using a mouse-derived CMT167 cell line was significant but modest. Since MAPK inhibition of the KRAS downstream pathway is crucial in KRAS-mutant cancer, we expected that co-inhibition of SUMOylation and MEK might be a good option. Surprisingly, combination treatment with TAK-981 and trametinib dramatically induced apoptosis in multiple cell lines and gene-engineered mouse-derived organoids. Moreover, combination therapy resulted in long-term tumor regression in mouse models using cell lines of different tissue types. Finally, we revealed that combination therapy complementally inhibited Rad51 and BRCA1 and accumulated DNA damage.ConclusionsWe found that MYC downregulation occurred via SUMOylation inhibition in KRAS-mutant cancer cells. Our findings indicate that dual inhibition of SUMOylation and MEK may be a promising treatment for MYC-expressing KRAS-mutant cancers by enhancing DNA damage accumulation.

Secretome of Cancer-Associated Fibroblasts (CAFs) Influences Drug Sensitivity in Cancer Cells.

Resistance is a major problem with effective cancer treatment and the stroma forms a significant portion of the tumor mass but traditional drug screens involve cancer cells alone. Cancer-associated fibroblasts (CAFs) are a major tumor stroma component and its secreted proteins may influence the function of cancer cells. The majority of secretome studies compare different cancer or CAF cell lines exclusively. Here, we present the direct characterization of the secreted protein profiles between CAFs and KRAS mutant-cancer cell lines from colorectal, lung, and pancreatic tissues using multiplexed mass spectrometry. 2573 secreted proteins were annotated, and differential analysis highlighted understudied CAF-enriched secreted proteins, including Wnt family member 5B (WNT5B), in addition to established CAF markers, such as collagens. The functional role of CAF secreted proteins was explored by assessing its effect on the response to 97 anticancer drugs since stromal cells may cause a differing cancer drug response, which may be missed on routine drug screening using cancer cells alone. CAF secreted proteins caused specific effects on each of the cancer cell lines, which highlights the complexity and challenges in cancer treatment and so the importance to consider stromal elements.

Design, synthesis, and bioevaluation of SOS1 PROTACs derived from pyrido[2,3-d]pyrimidin-7-one-based SOS1 inhibitor

Oncogenic KRAS mutations drive an approximately 25 % of all human cancers. Son of Sevenless 1 (SOS1), a critical guanine nucleotide exchange factor, catalyzes the activation of KRAS. Targeting SOS1 degradation has engaged as a promising therapeutic strategy for KRAS-mutant cancers. Herein, we designed and synthesized a series of novel CRBN-recruiting SOS1 PROTACs using the pyrido[2,3-d]pyrimidin-7-one-based SOS1 inhibitor as the warhead. One representative compound 11o effectively induced the degradation of SOS1 in three different KRAS-mutant cancer cell lines with DC50 values ranging from 1.85 to 7.53 nM. Mechanism studies demonstrated that 11o-induced SOS1 degradation was dependent on CRBN and proteasome. Moreover, 11o inhibited the phosphorylation of ERK and displayed potent anti-proliferative activities against SW620, A549 and DLD-1 cells. Further optimization of 11o may provide us promising SOS1 degraders with favorable drug-like properties for developing new chemotherapies targeting KRAS-driven cancers.

Abstract LB220: Farnesyltransferase inhibitors show synergistic anticancer effects in combination with novel KRAS G12C inhibitors

Abstract Background. Farnesyltransferase inhibitors (FTI) failed as monotherapies for various cancer types until the discovery of their potency in HRAS mutant human head and neck and bladder cancers. On the other hand, RAS mutant cancers have been a great challenge for cancer research until the discoveries and approvals of several KRAS-G12C allele specific inhibitors. However, G12C inhibitors were effective mainly in lung cancer and de novo and acquired resistance prompted the development of various combinational modalities including immunotherapy as well as SOS- and SHP2-inhibitors. Based on in-silico analysis of drug sensitivities of KRAS mutant cancer cell lines treated with various drugs including FTIs, we have explored the possibility of the combination of FTIs with KRAS inhibitors.Methods. Clinically approved farnesyl-transferase inhibitors (tipifarnib and lonafarnib) were combined with, novel KRAS G12C inhibitors (sotorasib and adagrasib) using human lung-, pancreatic and colorectal- adenocarcinoma cells in vitro and in vivo. Antitumoral effects were evaluated for cell proliferation, apoptosis and migratory activity. Mechanisms of action were investigated by immunoblot analyzes of various farnesylated proteins, RAS activation and signaling, videomicroscopy and also by histopathology of xenograft tumors. Results. Synergistic anticancer effects were observed upon the combination of FTIs with G12C inhibitors in KRAS G12C mutant human cancer cell lines in vitro. We found that the combination interfered with the compensatory re-activation of HRAS, farnesylation of RHEB in the PI3K/mTOR pathway and lamin. Furthermore, we observed enhanced efficacy of sotorasib upon combination with tipifarnib in the xenograft models of lung adenocarcinoma affecting mitotic- and apoptotic rates and inducing necrosis.Discussion. Our findings suggest the potential clinical applicability of the combination of KRAS-G12C inhibitors and farnesyl-transferase inhibitors. Furthermore, our preliminary data suggest that the synergistic effect of FTIs on KRAS-G12C inhibitors can be projected to G12D inhibitors as well. Citation Format: Jozsef Timar, Marcell Baranyi, Eszter Molnar, Ivan Randelovic, Mihaly Cserepes, Jozsef Tovari, Balazs Hegedus. Farnesyltransferase inhibitors show synergistic anticancer effects in combination with novel KRAS G12C inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB220.

Abstract 6060: Discovery of potent SHP2 protein degraders with strong anti-tumor activities in KRAS mutant cancers

Abstract Background: SHP2 plays a pivotal role in modulating the RTK/RAS/MAPK signaling pathway, which is frequently dysregulated in various cancers. Multiple allosteric SHP2 inhibitors have been under active development for the treatment of RTK/RAS/MAPK-dependent cancers, while certain limitations have come to light, such as their inability to target the active form of SHP2 and narrow therapeutic index necessitating intermittent dosing to mitigate toxicity. To overcome these challenges, we have discovered SHP2 protein degraders as next generation SHP2 targeting agents. Here, we present compelling profiles of our SHP2 degraders. Methods: We employed a variety of cancer cell lines harboring mutations in RTK, KRAS, or SHP2 for assessing in vitro activity of SHP2 degraders. For in vivo assessment of pharmacological profile, we utilized an NCI-H358 KRAS G12C mutant NSCLC xenograft. SHP2 protein levels in cell lysates and tumors were analyzed to assess SHP2 degradation efficiency. Simultaneously, ERK phosphorylation and DUSP6 mRNA levels were analyzed to evaluate downstream effects. Immunoprecipitation assays were used to assess the impact on SHP2's scaffolding roles. Results: A series of SHP2 degraders have been identified, demonstrating highly efficient SHP2 degradation activity with DC50 values in subnanomolar ranges. Robust inhibition of ERK phosphorylation, followed by remarkable anti-cancer effects in multiple KRAS mutant cancer cell lines were observed. Interestingly, in vitro cell growth inhibition by SHP2 degraders are 10 times more potent than SHP2 inhibitors currently under clinical development. Further characterization reveals several advantages of SHP2 degraders compared to SHP2 inhibitors. First, we observed a more efficient disruption of SHP2 scaffolding function, such as the formation of the SHP2-GRB2-GAB1 complex. Second, we detected effective degradation of activating mutants of SHP2, such as E76K and T507K, which are typically not targeted by SHP2 inhibitors. Experiments using a KRAS mutant CDX model demonstrate compelling in vivo profiles. A single administration of lead compounds resulted in Dmax values exceeding 95% in tumors, accompanied by the significant reduction of downstream signaling markers, such as p-ERK and DUSP6 mRNA. Notably, the reduced levels of SHP2 and downstream markers persist for several days. This suggests that utilizing intermittent dosing could be a viable approach with SHP2 degraders. Once-weekly intravenous administration achieved strong tumor growth inhibition without causing significant body weight loss. Conclusion: We have successfully discovered novel SHP2 degraders exhibiting remarkable activities. We demonstrate that SHP2 degraders have potential to overcome the limitations associated with allosteric SHP2 inhibitors and provide a promising therapeutic option for RTK/RAS/MAPK-dependent cancer patients. Citation Format: So Hyun Kim, Jihye Lee, Jiyoung Song, Geon-Tae Park, Jieun Jung, Jungtae Na, Dong Ho Lee, Soohyun Lee, Ji Youn Park, Jiyoung Kim, Onnuri Bae, Jeonghwa Han, Ju Young Kang, Mijin Moon, Yongje Shin, Je Ho Ryu, Song Hee Lee, Sook-Kyung Park. Discovery of potent SHP2 protein degraders with strong anti-tumor activities in KRAS mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6060.

Abstract A085: BI KRASmulti, a first-in-class, orally bioavailable and direct inhibitor of diverse oncogenic KRAS variants drives tumor regression in preclinical models and validates wild-type amplified KRAS as a therapeutic target

Abstract Alterations of KRAS are found in approximately one in seven of all human cancers, making KRAS one of the main oncogenic drivers in cancer. Gain-of-function missense mutations in KRAS are found in ~90% of pancreatic cancer, ~40% of colorectal cancer and ~30% of lung adenocarcinoma. In addition, focal high-level amplification of the KRAS wild-type (wt) allele, an alternative means of activating this oncoprotein, is observed in ~7% of cancers and lacks effective targeted therapies. Thus, there is an urgent need to identify effective therapies to address KRAS-driven tumors. Recently, we have reported the identification of compounds active against a broad range of oncogenic KRAS variants (KRASmulti) that selectively inactivate downstream signaling and tumor growth (Kim et al., Nature 2023). Herein we describe BI 3706674, a novel, potent and orally available small molecule inhibitor of the KRAS oncogene. BI 3706674 binds non-covalently to multiple KRAS mutant alleles, including the KRAS wt allele, in the GDP-bound state and thereby disrupts oncogenic signaling. Using several in vitro assays, we show that BI 3706674 is a) highly selective for KRAS vs HRAS or NRAS; b) blocks the interaction between KRAS mutant/wt and its guanidine exchange factor (GEF) SOS1 and c) shows potent antiproliferative activity in isogeneic cell lines that are dependent on various KRAS mutant alleles. In two large cancer cell line panels, BI 3706674 potently and selectively inhibits proliferation of KRAS mutant cancer cell lines as well as cancer cell lines with an amplification of the KRAS wt allele. Significant pharmacodynamic (PD) biomarker modulation (including inhibition of ERK1/2 phosphorylation and DUSP6 mRNA down-regulation) was observed in cell lines with a KRAS wt relative copy number (CN) > 10, treated with BI 3706674. Amplification of the KRAS wt allele is most frequently observed in gastric (~5%), esophageal (~13%) and gastroesophageal junction cancers (~12%). BI 3706674 was well-tolerated and showed dose-dependent efficacy in cell line-derived and patient-derived xenograft models (CDX and PDX) of human gastric cancer with a KRAS wt CN > 10. A twice daily oral dose of 30 mg/kg was sufficient to induce significant tumor regression. BI 3706674 treatment induced PD biomarker modulation (including inhibition of ERK1/2 phosphorylation, DUSP6 down-regulation, repression of the MAPK Pathway Activity Score (MPAS) signature and Ki67 reduction) in two KRAS wt amplified gastric cancer xenograft models. The depth and duration of PD biomarker responses following treatment correlated well with the doses used in the respective efficacy studies. Finally, these results support the clinical use of biomarkers such as the MPAS signature score and Ki67 to investigate treatment effects elicited by BI 3706674 in tumor biopsies. The KRASmulti inhibitor BI 3706674 is undergoing IND enabling studies and is intended to target tumors driven by KRAS wt amplifications as well as oncogenic KRAS missense mutations. Citation Format: Antonio Tedeschi, Lorenz Herdeis, Valeria Santoro, Fabio Savarese, Birgit Wilding, Matthias Treu, Julian Fuchs, Joachim Bröker, Tobias Wunberg, Michael Gmachl, Rumpel Klaus, Fiorella Schischlik, Jesse Lipp, David H. Peng, Mariah Williams, Charles Deckard, Vandhana Ramamoorthy, Joseph R. Daniele, Jaffer A. Ajani, Funda Meric-Bernstam, Christopher P. Vellano, Joseph R. Marszalek, Timothy P. Heffernan, Darryl McConnell, Mark Pearson, Norbert Kraut, Dorothea Rudolph. BI KRASmulti, a first-in-class, orally bioavailable and direct inhibitor of diverse oncogenic KRAS variants drives tumor regression in preclinical models and validates wild-type amplified KRAS as a therapeutic target [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A085.

Abstract A144: HM99462, a Novel & potent SOS1 inhibitor, induces tumor regressions in combination with KRAS G12C inhibitor, MEK inhibitor, or EGFR mutant inhibitor

Abstract Son of sevenless homolog 1 (SOS1) is one of guanine nucleotide exchange factor (GEF) responsible for a binary molecular switch to activate KRAS as well as a node in the negative feedback loop in the RTK-KRAS-MAPK signaling pathway. Therefore, combination strategies with a SOS1 inhibitor are being explored as a promising therapeutic options to target the MAPK-mediated bypass, which may improve antitumor activity or delay the induction of resistance after treatment. Herein, we presented a novel and potent SOS1 inhibitor, HM99462, which abrogates GTP-binding to KRAS and the profile of drug potency and mechanism of action was examined with in vitro and in vivo models. Biochemical activity on SOS1 was evaluated by a GTP-exchange assay on diverse KRAS G12X mutant types, NRAS Q61H, and HRAS G12V, and HM99462 showed excellent inhibitory activity, while SOS2 action was not affected. Moreover, HM99462 decreased ERK phosphorylation in various cancer cell lines harboring different major KRAS mutation statuses such as KRAS G12C, G12D, G12V, or G13D. Growth inhibition assay was performed using a three-dimensional (3D) conformation culture that mimics the complexity and heterogeneity of tumors and has elevated p-ERK. In this 3D spheroid growth inhibition assay, HM99462 demonstrated significantly effective GI50 against various KRAS mutant cancer cell lines. Additionally, HM99462 was evaluated in cancer cell xenograft mouse models harboring KRAS or EGFR mutation. The combination of HM99462 with KRAS G12C, MEK, or EGFR mutant inhibitor led to significantly synergistic anti-tumor activity in both in vitro and in vivo models with several KRAS or EGFR mutations. Based on our exploratory study, a novel and potent SOS1 inhibitor, HM99462 could be suggested as an appropriate therapeutic agent for diverse inhibitory activity against cancers causing by the hyperactivation of oncogenic KRAS or RTK signaling. And it has the potential to overcome the limitations of KRAS G12C, MEK or EGFR inhibitor through combination. IND enabling GLP-toxicity studies with HM99462 are currently underway, and we planned to initiate clinical study in early 2024. Citation Format: Jaeyul Choi, Seung Hyun Jung, Wongi Park, Jooyun Byun, Semi Lim, Youngjoo Lee, Soye Jeon, Yu-Yon Kim, Young Gil Ahn, Young Hoon Kim, Kwee Hyun Suh. HM99462, a Novel & potent SOS1 inhibitor, induces tumor regressions in combination with KRAS G12C inhibitor, MEK inhibitor, or EGFR mutant inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A144.

Abstract A010: Using oncogenic pathway agonism to sensitize RAS-mutant cancers to immunotherapy

Abstract Overall, some 30% of human cancers are driven by mutant RAS proteins, which have proven relatively difficult to target. While immunotherapy is effective for NRAS-mutant melanoma, no options exist for resistant disease, and mutant KRAS-driven lung and pancreatic carcinomas are much less responsive overall. Oncogenic pathways are often key targets for inhibition. However, pathway agonism has not been systematically explored as a therapeutic approach. BRAF-mutant melanomas respond to BRAF inhibitors (BRAFi) due to decreased ERK signaling. They can recover signaling by acquiring activating RAS/MEK mutations, but exhibit decreased proliferation in the absence of inhibitor, suggesting that supraphysiologic ERK signaling also compromises fitness. In line with this, we observed that increasing ERK hyperactivation in RAS-mutant cancers, particularly in those with a high ERK activity, might elevate ERK signaling to a degree to induce senescence and also create an inflammatory tumor microenvironment. We have shown that a majority of RAS-mutant cancer cell lines we tested undergo senescence-like arrest following exposure to all FDA-approved BRAF inhibitors at clinically relevant doses. Simultaneous MEK or ERK inhibition allows the cells to recover proliferation, and a BRAFi which does not induce ERK activation fails to have any effect, confirming that ERK hyperactivation is the key driver of this response. Importantly, these findings generalize across NRAS-mutant and KRAS-mutant cancer cell lines including in fresh human pancreatic adenocarcinoma explants. Finally, our data in two novel genomically-characterized, immunocompetent models of NRAS-mutant melanoma and KRAS-mutant pancreatic adenocarcinoma support our in-vitro findings. Both RAS-mutant murine models demonstrate that anti-PD1 therapy is substantially more efficacious when mice are additionally treated with BRAFi. Molecular profiling of the tumor microenvironment reveals the expression of cytokines related to senescence and marked infiltration of activated CD8+ T-cells. In order to implement more potentially effective immunotherapies, we have analyzed the expression of different immune-checkpoint molecules and we have observed a high expression of LAG3 and TIM3 in the melanoma NRAS-mutant model. We will further analyze the effect of those checkpoints in combination with BRAFi to potentiate the anti-tumoral responses and tumor regression. We propose that oncogenic pathway agonism is a novel, effective, and untested strategy to induce proliferation arrest and sensitization to immunotherapy. The impact of this data is in the ability to broadly sensitize RAS-mutant cancers to immunotherapy in the settings of de-novo and acquired resistance. The direct connection between a tumor cell signaling vulnerability to immunotherapy response is a major point of novelty and provides a clear molecular rationale for pursuing combined targeted and immune-based therapy. Citation Format: Alvaro de Mingo Pulido, Charles Adelmann, Brittney Sell, Karol Prieto, Kimberly Nguyen, Cynthia Dixey, Ivannie Ortiz-Rivera, Marco Napoli, Elsa Flores, Jason Fleming, Karen Mann, Christin Burd, Kenneth Y. Tsai. Using oncogenic pathway agonism to sensitize RAS-mutant cancers to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr A010.

Abstract 5463: BPI-442096: A potent and selective inhibitor of SHP2 for the treatment of multiple cancers

Abstract Src homology region 2 domain-containing phosphatase-2 (SHP-2) is a key node in the RAS signaling pathway. Allosteric inhibition of SHP2 phosphatase is a potential therapeutic strategy for cancers harboring oncogenic mutations in the KRAS pathway. SHP2 also participates in the signal transduction downstream of regulatory immunoreceptors, and it has been shown in preclinical models that SHP2 inhibition drives anti-tumor immunity through modulation of both innate and adaptive mechanism. BPI-442096 is a potent, selective, and orally bioavailable small molecule SHP2 inhibitor. It exhibited significant anti-proliferation activities against multiple KRAS mutant cancer cell lines, including those from NSCLC, PDAC, CRPC, etc. BPI-442096 dose-dependently inhibited SHP2 phosphatase and downstream ERK phosphorylation in cancer cells, as well as NFAT reporter gene expression downstream of PD-1/PD-L1 signaling in immune cells. In vivo, BPI-442096 demonstrated strong tumor growth inhibition in KRASG12C, KRASG12D, and KRASG12V mutant xenograft mouse models. BPI-442096 also exhibited anti-tumor immunity in the MC38 syngeneic model, as a single agent or in combination with anti-PD1/PD-L1 drugs. Moreover, BPI-442096 combining with KRASG12C inhibitor may reverse intrinsic and acquired resistance to KRASG12C inhibition. Adequate oral exposure across multiple pre-clinical species and good ADME properties ensured the druggability of BPI-442096. In conclusion, BPI-442096 exhibits a robust anti-tumor effect in multiple KRAS mutant models and enhanced anti-cancer immunity in syngeneic mouse models, and it shows multiple combination potentials to overcome drug resistance. Phase 1 clinical trial is planned in early 2022. Citation Format: Ling Li, Bang Fu, Han Han, Zhongxin Sun, Xiangdong Zhao, Xuepeng Jv, Jun Tong, Jiayu Zhao, Zhengyao Zou, Haibo Chen, Xiaoyun Liu, Wei Ren, Yinlong Li, Wenmao Wu, Jing Guo, Dan Yan, Xiangyong Liu, Hong Lan, Hao Wu, Lieming Ding, Jiabing Wang. BPI-442096: A potent and selective inhibitor of SHP2 for the treatment of multiple cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5463.

Abstract 1224: UMIBB: A novel nonparametric Bayesian method improves robustness and sensitivity of analysis in pooled CRISPR-Cas9 screens leveraging unique molecular identifiers

Abstract CRISPR-based functional genomics screens are a powerful tool for identifying synthetically lethal cancer drug targets. Current strategies for analyzing pooled CRISPR screens usually rely on signals from single guide RNAs (sgRNA) with differential relative abundance between two experimental conditions. However, conventional approaches are susceptible to false positives and false negatives driven by outlier cell clones, since the sgRNA abundance does not account for the heterogeneous phenotypes resulting from different editing outcomes of the same sgRNA. To overcome this, we added DNA barcodes to each sgRNA to create unique molecular identifiers (UMIs) for CRISPR libraries and developed a companion analytical platform that enables robust, industry-scale CRISPR screens. Here, we present UMIBB, a novel nonparametric Bayesian approach for analyzing UMI-CRISPR data. The number of UMIs with normalized count depletion or enrichment compared to the control experimental condition for each sgRNA is modeled by a beta-binomial distribution. The gene level statistics are derived by combining z-scores of the sgRNAs level posterior probabilities weighted by the number of UMIs in each sgRNA. This approach minimizes the impact of outlier cell clones on statistics and prioritizes genes with consistent count differentials across multiple UMIs in each gene. To assess the power of UMIBB, we benchmarked it on a low coverage (200X) genome-scale negative-selection screen, comparing with results from a high coverage (1000X) screen. These screens were conducted on KRAS mutant cancer celllines (A549) treated with trametinib or vehicle control. Despite the high noise level usually observed in lower coverage screens, our method was able to uncover most of the validated sensitizer genes for trametinib and achieved the highest sensitivity compared to conventional methods. Furthermore, we applied UMIBB on a genome-scale positive-selection screen and successfully identified novel genes (RAD18 and UBE2K) as key mediators of USP1 dependency in BRCA1 mutant cell lines. Our studies demonstrate that UMIBB is highly robust against false positives due to clonal heterogeneity and is more likely to identify true genetic interactions. Citation Format: Ashley Choi, Samuel Meier, Silvia Fenoglio, Tianshu Feng, Justin Engel, Binzhang Shen, Shangtao Liu, Teng Teng, Tenzing Khendu, Alan Huang, Jannik Andersen, Xuewen Pan, Yi Yu. UMIBB: A novel nonparametric Bayesian method improves robustness and sensitivity of analysis in pooled CRISPR-Cas9 screens leveraging unique molecular identifiers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1224.

Abstract P183: CRISPR screens identify sensitizers to trametinib in KRAS mutant cancer cell lines

Abstract KRAS is the most frequently mutated oncogene in human tumors and drives tumorigenesis across multiple lineages. Specifically, KRAS is mutated in about 30% of lung cancer and over 90% of pancreatic cancer. Despite recent progress in developing mutant selective KRASG12C inhibitors, patient treatment options for RAS activated cancers remain very limited. Targeting the MAPK pathway by means of MEK and ERK inhibitors has been explored as an alternative strategy for KRAS mutant cancer. However, the clinical benefit is modest due to drug resistance caused by reactivation of the MAPK pathway and potentially other pathways and/or bypass mechanisms. Here we used CRISPR-based screens to identify potential combination therapy targets to enhance trametinib response in KRAS mutant cancers. We screened in five KRAS mutant cell lines of lung and pancreatic lineages and identified both known as well as novel modulators of MEK inhibitor response. Consistent with previous reports, gene knockouts that impair the reactivation of ERK downstream of MEK inhibition scored as top hits in our drop-out screens. Knocking out MAPK1, RAF1, BRAF and PTPN11 sensitized all five cell lines to trametinib treatment supporting these as candidate drug combination targets for MAPK pathway inhibition. Our screens also identified multiple genes within the heparan sulfate pathway (EXT1, EXT2, EXTL3, XYLT2, ALG6, B3GAT3, B4GALT7 and HS2ST1) and the MAPK7 pathway (MAPK7 and MAP2K5) that sensitize multiple but not all cell lines to trametinib. As part of our target discovery platform, we further validated these screening results using various phenotypic assays. Altogether, our results suggest that resistance to MEK inhibitors is driven by reactivation of the MAPK pathway as previously demonstrated and that impairing such reactivation restores the sensitivity of KRAS mutant cancer cells to trametinib. The genetic mechanisms driving the MAPK pathway rebound are likely different in different cancers and understanding such mechanisms will be key for achieving clinical success. Citation Format: Silvia Fenoglio, Aileen M. Cristo, James Tepper, Teng Teng, Samuel R. Meier, Ashley Choi, Hongxiang Zhang, Shan-chuan Zhao, Shangtao Liu, Leanne G. Ahronian, Daniel Aird, Nikitha M. Das, Yi Yu, Robert Tjin Tham Sjin, Jannik N. Andersen, Alan Huang, Fang Li, Xuewen Pan. CRISPR screens identify sensitizers to trametinib in KRAS mutant cancer cell lines [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P183.

A proteomic and phosphoproteomic landscape of KRAS mutant cancers identifies combination therapies

KRAS mutant cancer, characterized by the activation of a plethora of phosphorylation signaling pathways, remains a major challenge for cancer therapy. Despite recent advancements, a comprehensive profile of the proteome and phosphoproteome is lacking. This study provides a proteomic and phosphoproteomic landscape of 43 KRAS mutant cancer cell lines across different tissue origins. By integrating transcriptomics, proteomics, and phosphoproteomics, we identify three subsets with distinct biological, clinical, and therapeutic characteristics. The integrative analysis of phosphoproteome and drug sensitivity information facilitates the identification of a set of drug combinations with therapeutic potentials. Among them, we demonstrate that the combination of DOT1L and SHP2 inhibitors is an effective treatment specific for subset 2 of KRAS mutant cancers, corresponding to a set of TCGA clinical tumors with the poorest prognosis. Together, this study provides a resource to better understand KRAS mutant cancer heterogeneity and identify new therapeutic possibilities.

Abstract 1962: Voruciclib, a CDK9 inhibitor, downregulates MYC and inhibits proliferation of KRAS mutant cancers in preclinical models

Abstract Mutations in KRAS at G12, G13, and Q61 are oncogenic drivers in many cancers, including lung, colorectal, pancreatic, multiple myeloma, and uterine carcinomas. KRAS mutations are frequently accompanied by stabilization of the MYC oncoprotein through increased MYC transcription and decreased protein degradation that is mediated by phosphorylation of MYC on Ser 62 by ERK and CDK9 kinases. Voruciclib is a novel oral inhibitor of CDKs 9, 4, 6, and 1 that is currently being tested in Phase 1B clinical trials for B-cell malignancies and acute myeloid leukemia. Voruciclib inhibition of CDK9 leads to decreased expression of transcriptional targets of RNA Pol II, such as Mcl1 and MYC. To test whether voruciclib could be effective in cancers driven by dysregulated KRAS-MYC signaling, ~20 cancer cell lines with KRAS mutations (G12A, G12C, G12D, G12S, G12V, G13C, G13D, Q61H) were treated in preclinical studies with voruciclib. MTS and Cell Titer Glo assays were used to monitor growth in vitro. Voruciclib decreased viability in all cell lines tested. To investigate MYC protein stability, MIA PACA-2 (G12C) cells were treated with 4 µM voruciclib for 5-240 min, followed by SDS-PAGE and Western Blotting analysis with α-MYC and α-pSer62-MYC antibodies. Voruciclib treatment resulted in a reduction in phosphorylation of MYC on Ser 62. A 60% decrease in pSer62 was observed after 5 min that reached 80% by 60 min. In contrast, there was no decrease in total MYC protein at either 5 or 15 min. A 10% reduction in total MYC was observed at 60 min that reached 50% at 240 min. The ability of voruciclib to inhibit tumor growth in vivo was also tested in murine xenograft models. KRAS mutant human cancer cells HCT-116 (CRC, KRAS G13D), SW-480 (CRC, KRAS G12V), and H-460 (NSCLC, KRAS Q61H) were injected subcutaneously into SCID mice. Once tumors reached 5-10 mm in diameter, voruciclib or vehicle were administered orally at 50, 100, or 200 mg/kg OD for 11-14 days. Tumors were measured every 2-3 days, and growth inhibition relative to control was calculated. Significant tumor growth inhibition (>50%) was observed at all doses of voruciclib tested. Collectively, these data demonstrate that voruciclib inhibition of CDK9 leads to reduced phosphorylation of MYC on Ser 62 followed by a decrease in total MYC protein in MIA PACA-2 cells and inhibition of growth in multiple KRAS mutant cancer cell lines in vivo and in vitro. This suggests that voruciclib could be an attractive therapeutic option for cancers driven by KRAS-MYC. Citation Format: Sandra E. Wiley, Yongwei Su, Yubin Ge. Voruciclib, a CDK9 inhibitor, downregulates MYC and inhibits proliferation of KRAS mutant cancers in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1962.

Comprehensive molecular and clinical characterization of SLC1A5 in human cancers

Although SLC1A5 has been reported to be closely associated with some cancer types, a comprehensive and systematic assessment of SLC1A5 across human cancers is lacking. Thus, Pan-cancer analysis of SLC1A5 was performed across 30 types of human cancers in this study. We examined mRNA expression, protein expression, copy number variation (CNV), DNA methylation, clinical relevance, cell functions, drug response and total immune infiltrates of SLC1A5 in more than 9000 patients across 30 human cancer types from The Cancer Genome Atlas (TCGA) dataset. Additionally, nine independent Gene Expression Omnibus datasets, more than 800 cancer cell lines from the Cancer Cell Line Encyclopedia dataset and the Project Achilles dataset were used to validate our findings in the TCGA dataset. Landscapes of SLC1A5 were established across multiple cancers. We showed that SLC1A5 is upregulated in multiple cancers, particularly in digestive and respiratory system cancers. SLC1A5 upregulation may be driven by CNV gain and DNA hypomethylation in human cancers. Furthermore, SLC1A5 overexpression is associated with tumor progression and poor survival in multiple cancers. Moreover, we systematically explored the potential effects of SLC1A5 expression on cell functions and drug response in human cancers. SLC1A5 knockdown showed significant proliferation-inhibiting effects in most human cancer types, especially in the digestive system and KRAS-mutant cancers. SLC1A5 expression is associated with proliferation activities of KRAS-mutant cancer cell lines and drug response of many anti-cancer drugs. Finally, we demonstrated that SLC1A5-realted tumor immune microenvironment characteristics showed strong heterogeneity in human cancers. Taken together, our findings highlight the important roles of SLC1A5 in tumorigenesis, progression, prognosis and therapy.

Specific inhibition of oncogenic RAS using cell-permeable RAS-binding domains

Oncogenic RAS proteins, common oncogenic drivers in many human cancers, have been refractory to conventional small-molecule and macromolecule inhibitors due to their intracellular localization and the lack of druggable pockets. Here, we present a feasible strategy for designing RAS inhibitors that involves intracellular delivery of RAS-binding domain (RBD), a nanomolar-affinity specific ligand of RAS. Screening of 51 different combinations of RBD and cell-permeable peptides has identified Pen-cRaf-v1 as a cell-permeable pan-RAS inhibitor capable of targeting both G12C and non-G12C RAS mutants. Pen-cRaf-v1 crosses the cell membrane via endocytosis, competitively inhibits RAS-effector interaction, and thereby exerts anticancer activity against several KRAS-mutant cancer cell lines. Moreover, Pen-cRaf-v1 exhibits excellent activity comparable with a leading pan-RAS inhibitor (BI-2852), as well as high target specificity in transcriptome analysis and alanine mutation analysis. These findings demonstrate that specific inhibition of oncogenic RAS, and possibly treatment of RAS-mutant cancer, is feasible by intracellular delivery of RBD.

Silencing of Oncogenic KRAS by Mutant-Selective Small Interfering RNA.

Oncogenic mutations in the KRAS gene are well-established drivers of cancer. While the recently developed KRASG12C inhibitors offer a targeted KRAS therapy and have shown success in the clinic, KRASG12C represents only 11% of all KRAS mutations. Current therapeutic approaches for all other KRAS mutations are both indirect and nonmutant-selective, largely focusing on inhibition of downstream KRAS effectors such as MAP kinases. Inhibition of KRAS downstream signaling results in a system-wide down-modulation of the respective targets, raising concerns about systemic cell toxicity. Here, we describe a custom short interfering RNA oligonucleotide (EFTX-D1) designed to preferentially bind mRNA of the most commonly occurring KRAS missense mutations in codons 12 and 13. We determined that EFTX-D1 preferentially reduced the mutant KRAS sequence versus wild-type at the levels of both transcription and translation and reversed oncogenic KRAS-induced morphologic and growth transformation. Furthermore, EFTX-D1 significantly impaired the proliferation of several KRAS mutant cancer cell lines in 2-D as well as 3-D assays. Taken together, our data indicate a novel use of RNA interference to target oncogenic KRAS-driven cancers specifically.

Abstract 1955: Inhibition of eIF4A by eFT226 blocks KRAS mutant tumor growth

Abstract Mutations in KRAS are among the most common oncogenic lesions across a variety of human cancers. Activation of KRAS directs signaling via the MAPK and PI3K pathways to promote tumor growth. One outcome of enhanced KRAS signaling is the induction of mRNA translation by eIF4A, eIF4E, and eIF4G, which together comprise the eIF4F complex. eIF4A is an RNA helicase that functions to unwind elements in the 5'-untranslated region (UTR) of mRNAs to facilitate scanning of the 40S ribosomal subunit. eFT226 is a highly potent and selective inhibitor of eIF4A that functions by forming a ternary complex between eIF4A, eFT226 and specific polypurine motifs in the 5'-UTR of select mRNAs, thus blocking ribosome scanning and inhibiting mRNA translation. This polypurine sequence motif is highly enriched in the 5'-UTR of eFT226 target genes, many of which are known proto-oncogenes. Translational profiling revealed KRAS to be a target of eFT226 and 5'-UTR sequence analysis of KRAS mRNA identified the polypurine regulatory motif, which imparts sensitivity to eFT226 mediated inhibition of translation. In cell-based reporter assays used to monitor translation, mutation of the KRAS 5'-UTR polypurine motifs resulted in a 10-fold decrease in sensitivity to eFT226 relative to the wild-type sequence. In a cell panel screen for in vitro apoptosis induction by eFT226, the most sensitive models were enriched for cell lines driven by KRAS mutations. Consistent with these results, treatment with eFT226 decreased KRAS protein levels, repressed downstream MAPK signaling, inhibited cell proliferation, and induced apoptosis in a collection of non-small cell lung, colorectal and pancreatic KRAS mutant cancer cell lines. The ability of eFT226 to block tumor cell growth and induce apoptosis is independent of the specific KRAS mutation present (e.g. G12C/V, G13D, Q61H/L) suggesting that eFT226 could be broadly efficacious in treating tumors with activating KRAS mutations. Treatment of KRAS mutant solid tumor xenografts with eFT226 as a monotherapy significantly inhibited tumor growth. Together, these results highlight the ability of eFT226 to inhibit growth and promote apoptosis in KRAS mutant tumors and support the clinical development of eFT226 in KRAS driven tumors. A clinical trial evaluating eFT226 in patients with solid tumor malignancies has initiated. Citation Format: Craig R. Stumpf, Vikas K. Goel, Joan Chen, Jocelyn Staunton, Emily M. Santori, Maria Barrera, Haleigh Howard, Kevin R. Webster, Gary G. Chiang, Peggy A. Thompson. Inhibition of eIF4A by eFT226 blocks KRAS mutant tumor growth [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1955.

Abstract LB-021: Focal adhesive kinase inhibitor IN10018 sensitizes KRAS mutant cancer and overcomes drug resistance of KRAS G12C inhibition

Abstract KRAS mutation is found in around 20-30% of human cancer. Previously, lack of targeting therapy limited the treatment outcomes. Recently, KRAS G12C inhibitors like AMG510, MRTX849, and MRTX1257 were developed and exhibited promising therapeutic outcomes targeting the mutation. However, a considerable amount of cases showed less sensitivity, indicating either intrinsic or adaptive resistance mechanisms. Other reports and our own data exhibited that Focal Adhesive Kinase (FAK) inhibition showed good treatment effects to KRAS mutant cancer. Interestingly, TCGA data analysis reveal that FAK mRNA expression level is significantly higher in KRAS mutant tumors. Considering that FAK is one predominant target for cancer treatment resistance, we hypothesize that FAK is one of mediator leading to resistance mechanism of KRAS G12C inhibition. To explore our hypothesis, we employed high potent FAK inhibitor IN10018, which is being tested in phase I clinical trial for different cancer types. First, we found that IN10018 is active in a series of KRAS mutated cancer xenograft models. The compound sharply decreased the level of phosphoFAK Y397, a direct marker for FAK activity. Then we investigated whether combination of IN10018 with KRAS G12C inhibitors can show synergic effects in vitro and in vivo. IN10018 in combination with either AMG510 or MRTX1257 showed better effects in killing KRAS G12C cancer cells than each single treatment. More importantly a significant synergy between IN10018 with KRAS G12C inhibitors against KRAS mutated cancer cell lines was observed in vivo. Further evidence showed that KRAS G12C inhibition can significantly increase the expression of phosphoFAK Y397, suggesting a possible underlying mechanism of resistance to KRAS G12C inhibitors. IN10018 significantly decreased the upregulated FAK Y397 phosphorylation in the combination treatments, underlying the mechanism of synergy between the two inhibitors. Our results indicate that KRAS G12C cancer patients can be better treated by the combination of IN10018 with KRAS G12C inhibitor. Citation Format: Baoyuan Zhang, Yan Zhang, Jiangwei Zhang, Ping Liu, Bo Jiao, Zaiqi Wang, Ruibao Ren. Focal adhesive kinase inhibitor IN10018 sensitizes KRAS mutant cancer and overcomes drug resistance of KRAS G12C inhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-021.

The protein kinase MAP3K19 phosphorylates MAP2Ks and thereby activates ERK and JNK kinases and increases viability of KRAS-mutant lung cancer cells

Identifying additional mitogen-activated protein kinase (MAPK) pathway regulators is invaluable in aiding our understanding of the complex signaling networks that regulate cellular processes, including cell proliferation and survival. Here, using in vitro kinase assays and by expressing WT or kinase-dead MAPK kinase kinase 19 (MAP3K19) in the HEK293T cell line and assessing activation of the extracellular signal-regulated kinase (ERK) and JUN N-terminal kinase (JNK) signaling pathways, we defined MAP3K19 as a novel regulator of MAPK signaling. We also observed that overexpression of WT MAP3K19 activates both the ERK and JNK pathways in a panel of cancer cell lines. Furthermore, MAP3K19 sustained ERK pathway activation in the presence of inhibitors targeting the RAF proto-oncogene Ser/Thr protein kinase (RAF) and MAPK/ERK kinase, indicating that MAP3K19 activates ERK via a RAF-independent mechanism. Findings from in vitro and in-cell kinase assays demonstrate that MAP3K19 is a kinase that directly phosphorylates both MAPK/ERK kinase (MEK) and MAPK kinase 7 (MKK7). Results from an short-hairpin RNA screen indicated that MAP3K19 is essential for maintaining survival in KRAS-mutant cancers; therefore, we depleted or inhibited MAP3K19 in KRAS-mutant cancer cell lines and observed that this reduces viability and decreases ERK and JNK pathway activation. In summary, our results reveal that MAP3K19 directly activates the ERK and JNK cascades and highlight a role for this kinase in maintaining survival of KRAS-mutant lung cancer cells.

Abstract A44: SHP2 inhibition overcomes RTK-mediated pathway reactivation in KRAS-mutant tumors treated with MEK inhibitors

Abstract FGFR1 was recently shown to be activated as part of a compensatory response to prolonged treatment with MEK inhibitor trametinib in several KRAS-mutant lung and pancreatic cancer cell lines. We hypothesize that other receptor tyrosine kinases (RTKs) are also feedback activated in this context. Herein, we profile a large panel of KRAS-mutant cancer cell lines for the contribution of RTKs to the feedback activation of phospho-MEK following MEK inhibition, using a SHP2 inhibitor (SHP099) that blocks RAS activation mediated by multiple RTKs. We find that RTK-driven feedback activation widely exists in KRAS mutant cancer cells and involves several RTKs including EGFR, FGFR, and MET. We further demonstrate this pathway feedback activation is mediated through mutant KRAS. Finally, SHP099 and MEK inhibitors exhibit combination benefits inhibiting KRAS mutant cancer cell proliferation in vitro and in vivo. These findings provide a rationale for exploration of combining SHP2 and MAPK pathway inhibitors for treating KRAS-mutant cancers in the clinic. Citation Format: Hengyu Lu, Chen Liu, Roberto Velazquez, Hongyun Wang, Lukas M. Dunkl, Malika Kazic-Legueux, Anne Haberkorn, Eric Billy, Eusebio Manchado, Saskia M. Brachmann, Susan Moody, Jeffrey A. Engelman, Peter S. Hammerman, Giordano Caponigro, Morvarid Mohseni, Huai-Xiang Hao. SHP2 inhibition overcomes RTK-mediated pathway reactivation in KRAS-mutant tumors treated with MEK inhibitors [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr A44.