Exploiting MCL1 Dependency with Combination MEK + MCL1 Inhibitors Leads to Induction of Apoptosis and Tumor Regression in KRAS-Mutant Non–Small Cell Lung Cancer
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Published OnlineFirst September 25, 2018; DOI: 10.1158/2159-8290.CD-18-0277 RESEARCH ARTICLE Exploiting MCL1 Dependency with Combination MEK + MCL1 Inhibitors Leads to Induction of Apoptosis and Tumor Regression in KRAS-Mutant Non–Small Cell Lung Cancer Varuna Nangia1, Faria M. Siddiqui1, Sean Caenepeel2, Daria Timonina1, Samantha J. Bilton1, Nicole Phan1, Maria Gomez-Caraballo1, Hannah L. Archibald1, Chendi Li1, Cameron Fraser3, Diamanda Rigas2, Kristof Vajda1, Lorin A. Ferris1, Michael Lanuti4, Cameron D. Wright4, Kevin A. Raskin5, Daniel P. Cahill6, John H. Shin6, Colleen Keyes7, Lecia V. Sequist8,9, Zofia Piotrowska8,9, Anna F. Farago8,9, Christopher G. Azzoli8,9, Justin F. Gainor8,9, Kristopher A. Sarosiek3, Sean P. Brown10, Angela Coxon2, Cyril H. Benes1,9, Paul E. Hughes2, and Aaron N. Hata1,8,9 ABSTRACT BH3 mimetic drugs, which inhibit prosurvival BCL2 family proteins, have limited single-agent activity in solid tumor models. The potential of BH3 mimetics for these cancers may depend on their ability to potentiate the apoptotic response to chemotherapy and targeted therapies. Using a novel class of potent and selective MCL1 inhibitors, we demonstrate that concurrent MEK + MCL1 inhibition induces apoptosis and tumor regression in KRAS-mutant non–small cell lung cancer (NSCLC) models, which respond poorly to MEK inhibition alone. Susceptibility to BH3 mimetics that target either MCL1 or BCL-xL was determined by the differential binding of proapop- totic BCL2 proteins to MCL1 or BCL-xL, respectively. The efficacy of dual MEK+ MCL1 blockade was augmented by prior transient exposure to BCL-xL inhibitors, which promotes the binding of proapop- totic BCL2 proteins to MCL1. This suggests a novel strategy for integrating BH3 mimetics that target different BCL2 family proteins for KRAS-mutant NSCLC. SIGNIFICANCE: Defining the molecular basis for MCL1 versus BCL-xL dependency will be essential for effective prioritization of BH3 mimetic combination therapies in the clinic. We discover a novel strategy for integrating BCL-xL and MCL1 inhibitors to drive and subsequently exploit apoptotic dependencies of KRAS-mutant NSCLCs treated with MEK inhibitors. Cancer Discov; 8(12); 1–16. ©2018 AACR. See related commentary by Leber et al., p. 1511. 1Massachusetts General Hospital Cancer Center, Charlestown, Massa- Medicine, Harvard Medical School, Boston, Massachusetts. 10Department chusetts. 2Department of Oncology Research, Amgen, Thousand Oaks, of Medicinal Chemistry, Amgen, Thousand Oaks, California. 3 California. Department of Environmental Health, Harvard T. H. Chan Note: Supplementary data for this article are available at Cancer Discovery 4 School of Public Health, Boston, Massachusetts. Department of Surgery, Online (http://cancerdiscovery.aacrjournals.org/). Massachusetts General Hospital, Boston, Massachusetts. 5Department of Orthopaedics, Massachusetts General Hospital, Boston, Massachusetts. V. Nangia and F.M. Siddiqui contributed equally to this article. 6Department of Neurosurgery, Massachusetts General Hospital, Bos- Corresponding Author: Aaron N. Hata, Massachusetts General Hospital, ton, Massachusetts. 7Division of Pulmonary and Critical Care Medicine, 149 13th Street, Charlestown, MA 02129. Phone: 617-724-3442; Fax: Department of Medicine, Massachusetts General Hospital, Boston, Mas- 617-724-9648; E-mail: [email protected] 8 sachusetts. Division of Hematology Oncology, Department of Medicine, doi: 10.1158/2159-8290.CD-18-0277 Massachusetts General Hospital, Boston, Massachusetts. 9Department of ©2018 American Association for Cancer Research. OF1 | CANCER DISCOVERY DECEMBER 2018 www.aacrjournals.org Downloaded from cancerdiscovery.aacrjournals.org on September 27, 2021. © 2018 American Association for Cancer Research. Published OnlineFirst September 25, 2018; DOI: 10.1158/2159-8290.CD-18-0277 Combination MEK + MCL1 Inhibitors for KRAS-Mutant NSCLC RESEARCH ARTICLE INTRODUCTION (8, 9), although these have yet to be tested in the clinic. Thus, there remains an urgent need for new therapeutic strategies KRAS, a small GTPase that activates MAPK signaling, is that can target KRAS-mutant cancers. one of the most frequently mutated driver oncogenes (1). Several studies have shown that suppression of MAPK KRAS mutations, which are largely localized to residues G12, signaling, either by depletion of mutant KRAS or by phar- G13, and Q61, decrease either intrinsic and/or GAP-medi- macologic inhibition of downstream MEK1/2, is insufficient ated hydrolysis, causing constitutive activation of MAPK and to induce apoptosis in a significant number ofKRAS -mutant other downstream signaling pathways (2). Although effective cell lines (10–12). Therapeutic strategies that cotarget kinase molecular targeted therapies that inhibit oncogenic mutant signaling pathways and apoptotic regulators may increase kinases in the RAS–MAPK pathway have been developed (e.g., apoptosis and convert cytostatic responses into tumor regres- EGFR inhibitors for EGFR-mutant NSCLC, BRAF inhibi- sions (13). Activated kinase signaling pathways such as MAPK tors for BRAF-mutant melanoma), there currently are no (RAS/RAF/MEK/ERK) and PI3K/AKT converge on the BCL2 approved targeted therapies for KRAS-mutant cancers. KRAS protein family, which regulates the mitochondrial or intrinsic mutations are found in 20% to 25% of patients with non– apoptotic response (14). In cells with MAPK activation, ERK small cell lung cancer (NSCLC) and predict lack of response phosphorylation suppresses the proapoptotic BH3 protein to EGFR inhibitors (3). Attempts to target downstream BIM by targeting it for degradation (15, 16). MEK inhibition MAPK signaling with inhibitors of MEK1/2 have yielded causes BIM to accumulate (16); however, BIM can be neutral- disappointing results (4, 5), and strategies that simultane- ized by prosurvival BCL2 family members such as BCL-xL or ously target multiple signaling pathways have been limited by MCL1. Combining MEK inhibitors with the BH3 mimetic toxicity (6, 7). Most recently, a novel class of KRAS inhibitors navitoclax (ABT-263), which prevents the binding of BIM that covalently bind to the G12C mutant has been described to BCL2 and BCL-xL, led to greater apoptosis and tumor DECEMBER 2018 CANCER DISCOVERY | OF2 Downloaded from cancerdiscovery.aacrjournals.org on September 27, 2021. © 2018 American Association for Cancer Research. Published OnlineFirst September 25, 2018; DOI: 10.1158/2159-8290.CD-18-0277 RESEARCH ARTICLE Nangia et al. regression in KRAS experimental models compared with MEK AM-8621 (Supplementary Fig. S1A–S1D). AM-8621 is the inhibitors alone (11), and a clinical trial evaluating this combi- prototypical member of a novel class of spiromacrocyclic nation is currently ongoing (NCT02079740; www.clinicaltrials. MCL1 inhibitors, which also includes the tool compound gov). To date, these approaches have been limited to target- AM-4907 and the clinical compound AMG 176, which exhibit ing BCL2 and BCL-xL due to the lack of selective and potent potent and selective MCL1 inhibition in vitro and in vivo inhibitors that target other members of the BCL2 family. (19). Synergistic drug combinations were determined using MCL1 is frequently amplified in lung cancers (17), and the a Loewe excess additivity model (20). A number of potential development of potent and selective MCL1 inhibitors has long clinically relevant synergistic combinations were identified, been of interest. Recently, a novel MCL1 inhibitor, S63845, with including conventional cytotoxic chemotherapeutic agents, in vivo activity was reported (18). Significant activity was observed HSP90 inhibitors, and BH3 mimetics targeting BCL-xL/BCL2 in leukemia, myeloma, and lymphoma models, and several dif- (Fig. 1A; Supplementary Fig. S1E). ferent MCL1 inhibitors are currently in clinical development To prioritize clinically promising MCL1 inhibitor com- for these malignancies (NCT02992483, NCT02979366, and binations, we considered the spectrum of oncogenic driver NCT02675452; www.clinicaltrials.gov). Single-agent activity of mutations present in the cell lines. One of the most nota- S63845 was limited in solid tumor models including NSCLC ble genotype-associated synergies was between AM-8621 and and breast cancers; however, combining S63845 with relevant drugs that inhibit the MAPK pathway (MEK and BRAF inhibi- kinase inhibitors led to decreased cell viability of BRAF-, EGFR-, tors) in cell lines with oncogenic MAPK pathway activation and HER2-addicted cell lines in vitro, providing proof of prin- (Fig. 1B). Six of 15 cell lines showed statistically significant ciple that MCL1 inhibition, similar to BCL-xL inhibition, may synergy with a majority of the MAPK pathway inhibitors potentiate the response to kinase inhibitor–targeted therapies. (MEK and BRAF) included in the screen, and eight cell lines However, due to the lack of studies that directly compare analo- showed statistically significant synergy with a majority of gous combination strategies that target either MCL1 or BCL- MEK inhibitors. Of these eight cell lines, five harbored muta- xL, the optimal pairing of kinase inhibitors with BH3 mimetics tions known to cause MAPK pathway activation (A427, H23: that target different BCL2 family proteins in specific subsets of KRAS; H1395, G-361: BRAF; H1437: MEK1). Additionally, cancer remains undefined. two of the three other cell lines that did not harbor MAPK- Here, we assessed the activity of a novel class of potent activating mutations have previously been demonstrated to and selective