The irreversible FGFR inhibitor KIN-3248 overcomes FGFR2 kinase domain mutations

PURPOSE

FGFR2 and FGFR3 show oncogenic activation in many cancer types, often through chromosomal fusion or extracellular domain mutation. FGFR2 and FGFR3 alterations are most prevalent in intrahepatic cholangiocarcinoma (ICC) and bladder cancers, respectively, and multiple selective reversible and covalent pan-FGFR tyrosine kinase inhibitors (TKIs) have been approved in these contexts. However, resistance, often due to acquired secondary mutations in the FGFR2/3 kinase domain, limits efficacy. Resistance is typically polyclonal, involving a spectrum of different mutations that most frequently affect the molecular brake and gatekeeper residues (N550 and V565 in FGFR2).

EXPERIMENTAL DESIGN

Here we characterize the activity of the next-generation covalent FGFR inhibitor, KIN-3248, in preclinical models of FGFR2 fusion+ ICC harboring a series of secondary kinase domain mutations, in vitro and in vivo. We also test select FGFR3 alleles in bladder cancer models.

RESULTS

KIN-3248 exhibits potent selectivity for FGFR1-3 and retains activity against various FGFR2 kinase domain mutations, in addition to being effective against FGFR3 V555M and N540K mutations. Notably, KIN-3248 activity extends to the FGFR2 V565F gatekeeper mutation, which causes profound resistance to currently approved FGFR inhibitors. Combination treatment with EGFR or MEK inhibitors potentiates KIN-3248 efficacy in vivo, including in models harboring FGFR2 kinase domain mutations.

CONCLUSIONS

Thus, KIN-3248 is a novel FGFR1-4 inhibitor whose distinct activity profile against FGFR kinase domain mutations highlights its potential for the treatment of ICC and other FGFR-driven cancers.

Discovery of KIN-3248, An Irreversible, Next Generation FGFR Inhibitor for the Treatment of Advanced Tumors Harboring FGFR2 and/or FGFR3 Gene Alterations

Fibroblast growth factor receptor (FGFR) alterations are present as oncogenic drivers and bypass mechanisms in many forms of cancer. These alterations can include fusions, amplifications, rearrangements, and mutations. Acquired drug resistance to current FGFR inhibitors often results in disease progression and unfavorable outcomes for patients. Genomic profiling of tumors refractory to current FGFR inhibitors in the clinic has revealed several acquired driver alterations that could be the target of next generation therapeutics. Herein, we describe how structure-based drug design (SBDD) was used to enable the discovery of the potent and kinome selective pan-FGFR inhibitor KIN-3248, which is active against many acquired resistance mutations. KIN-3248 is currently in phase I clinical development for the treatment of advanced tumors harboring FGFR2 and/or FGFR3 gene alterations.

Abstract 4122: Occurrence of BRAF class II and III alterations is common across solid tumors and is associated with inferior clinical outcomes in NSCLC and melanoma

Background: Oncogenic BRAF alterations can be categorized by their distinct structural and signaling properties which lead to activation of the MAPK pathway: class I - kinase active signaling of BRAF mutant monomers; class II - kinase active signaling of BRAF mutant dimers; and class III - kinase impaired BRAF that signals via RAS-dependent, heterodimers containing wild-type RAF. There are currently no approved BRAF targeted therapies for patients whose tumors bear BRAF class II or III alterations. This research utilizes the GuardantINFORM࣪ clinical-genomic database to assess the real-world occurrence and outcomes of patients with oncogenic BRAF alterations by distinct classes across solid tumors.​

Methods: This observational study utilized a database containing clinical and genomic data from ~160,000 cancer patients with ctDNA profiling by the Guardant360 assay. Patients were categorized using a broad list of known and putative class I, II or III BRAF alterations compiled from published sources. Patients were stratified by BRAF mutant class for real-world overall survival analyses.

Results: The analysis identified a cohort of over 5,890 patients with oncogenic BRAF alterations. Class II and III alterations were present in more than 2% of all ctDNA positive patients and made up approximately 55% of all the oncogenic BRAF alterations. Class II and III accounted for 65%, 30% and 20% of oncogenic BRAF alterations in NSCLC, CRC and melanoma respectively. NSCLC and melanoma patients with class II or III BRAF alterations experienced shorter overall survival relative to patients with class I alterations.

Conclusions: The analysis of this large real-world dataset identified a substantial number of cancer patients with BRAF class II and III alterations. NSCLC and melanoma patients with BRAF class II and III alterations experienced inferior clinical outcomes and represent a population that could benefit from novel targeted therapies.

Overall survival in NSCLC and melanoma patients with BRAF class I, II or III alterations Cohort Median OS Months (%95 CI) Unadjusted P-value Class I Class II Class III I vs II I vs III II vs III NSCLC (n=938) 44.8 (37.5,52.8) 34.4 (27.5,41.5) 32.3 (28.4,40.9) 0.006 0.0126 0.6611 Melanoma (n=333) 46.5 (42.3,65.5) 28.5 (8.6,30.3) 30.5 (12.5,73.8) 0.0008 0.0165 0.6529

Citation Format: Paul L. Severson, Elifnur Yay Donderici, Nicole Zhang, Aleksandra Franovic, Nichol Miller, Eric Martin, Eric Murphy, Richard Williams. Occurrence of BRAF class II and III alterations is common across solid tumors and is associated with inferior clinical outcomes in NSCLC and melanoma [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 4122.

Design and rationale of a first-in-human (FIH) phase 1/1b study evaluating KIN-3248, a next-generation, irreversible (irrev), pan-FGFR inhibitor (FGFRi), in adult patients with solid tumors harboring FGFR2 and/or FGFR3 gene alterations (NCT05242822)

TPS9601

Background: FGFR1-4 gene alterations are observed in approximately 7% of all human cancers. There are currently 3 FDA-approved, reversible FGFRi for treatment of patients w/previously treated, locally advanced or metastatic (met) cholangiocarcinoma (CCA) harboring FGFR2 gene fusions/rearrangements (pemigatinib and infigratinib) or met urothelial carcinoma (UC) w/susceptible FGFR2 or FGFR3 genetic alterations (erdafitinib). A major limitation of approved and clinical-stage FGFRi is emergence of secondary, on-target resistance mutations (mutn) that reduce duration of response. Up to 67% of CCA patients treated with either reversible or irrev FGFRi exhibit secondary FGFR2 kinase domain resistance mutn at the time of relapse. KIN-3248 is a next-generation, selective, irrev, small molecule pan-FGFRi, structurally designed to inhibit primary FGFR oncogenic alterations as well as secondary kinase domain mutn associated w/disease progression. Preclinically, KIN-3248 has favorable pharmaceutical properties, is well-tolerated with continuous, daily oral administration in 28d GLP toxicology studies in rats and beagle dogs and is efficacious against primary FGFR2 and FGFR3 oncogenic driver alterations as well as secondary FGFR2 resistance mutn (e.g., gatekeeper and molecular brake) in human cancer cell and PDX models in vitro and in vivo. Methods: This is a FIH, multicenter, non-randomized Ph1 study of KIN-3248 in adult pts with advanced & metastatic solid tumors (AMST) harboring FGFR2 and/or FGFR3 gene alterations. KIN-3248 is given po qd continuously in 28-day cycles until drug intolerance or disease progression. Planned sample size is approx. 120 pts: Part A is a dose-escalation to MTD for pts w/AMST having either FGFR2 and/or FGFR3 alterations. Part A assesses single agent KIN-3248; Part B will evaluate a selected dose of KIN-3248 in 3 cohorts of pts (ICC, UC, or other AMST), each driven by specified FGFR alterations. Standard Ph1 enrollment criteria are required (ECOG PS 0-1, normal organ function, prior receipt of standard treatment or medical judgment that such is not appropriate). Pts may have measurable or evaluable disease. Key exclusion criteria include known active brain metastases and active/uncontrolled HBV/HCV. FGFRi-naïve & -pretreated patients are both eligible. Primary endpoints are safety/tolerability (Part A), and preliminary antitumor activity: objective response rate, disease control rate, duration of response, & duration of stable disease (Part B). Secondary objectives include pharmacokinetic and pharmacodynamic assessments including measures of FGFR pathway modulation. Enrollment is expected to commence in April 2022. Clinical trial information: NCT05242822.

Activity of KIN-3248, a next-generation pan-FGFR inhibitor, against acquired FGFR-gatekeeper and molecular-brake drug resistance mutations

461

Background: Oncogenic FGFR (FGFR1, FGFR2, FGFR3, and FGFR4) gene alterations are observed in approximately 7% of all human cancers and present as point mutations, small intragenic deletions, genomic amplifications, or chromosomal rearrangements/ gene fusions. FGFR2 gene fusions and FGFR3 activating alterations are predicted oncogenic drivers in 10-20% of cholangiocarcinoma and 20-35% of urothelial cancers, respectively. While currently approved FGFR inhibitors (e.g., erdafitinib, pemigatinib, infigratinib) and those in development (e.g., futibatinib) provide clinical benefit in these cancer indications, disease progression typically occurs within 6-8 months of starting treatment and is often associated with the emergence of on-target resistance mutations within the FGFR kinase domain. KIN-3248 is a next-generation, irreversible, small molecule, pan-FGFR inhibitor designed to target clinically relevant primary FGFR driver alterations and secondary resistance mutations, including FGFR2 and FGFR3 gatekeeper, molecular brake, and activation loop mutations. Methods: KIN-3248 was evaluated across wild-type FGFR family members and clinically relevant fusions and kinase domain resistance mutations in vitro. In addition, KIN-3248 activity was assessed in FGFR-driven and FGFR inhibitor-resistant human gastrointestinal xenograft tumor models. Results: KIN-3248 exhibited low nanomolar biochemical potency against wild-type FGFR family members as well as mutants associated with resistance to FGFR inhibitors (IC50 3.9 – 24.1 nM). Consistently, KIN-3248 was active in human FGFR2-PHGDH fusion-positive CCLP-1 and FGFR2-OPTN fusion-positive ICC13-7 cholangiocarcinoma cell lines engineered to express wild-type or clinically relevant gatekeeper, molecular brake, and activation loop mutant alleles (EC50 2.4 – 9.9 nM). Lastly, KIN-3248 led to dose-dependent tumor growth inhibition and regressions in FGFR inhibitor-resistant, patient-derived gastric cancer and cholangiocarcinoma models harboring secondary FGFR2 kinase domain mutations. This efficacy was accompanied by both pharmacodynamic biomarker modulation, downstream pathway inhibition, and apoptotic cell death across models in vitro and in vivo. Conclusions: KIN-3248 is a next-generation, irreversible, orally available, small molecule pan-FGFR inhibitor that overcomes clinically observed secondary mutations in FGFR2 and FGFR3 known to drive resistance to both reversible and irreversible FGFR inhibitors and associated with disease progression. Its highly-selective, potent and broad-spectrum activity against mutations in both the FGFR2 and FGFR3 kinase domains – including gatekeeper, molecular brake, and activation loop alterations – is unique among FGFR inhibitors and has the potential to extend the clinical response of cancer patients with FGFR-altered tumors.

The next-generation pan-RAF inhibitor, KIN-2787, is active in class II and class III BRAF mutant models

3116

Background: Oncogenic BRAF gene alterations, leading to aberrantly activated BRAF monomers (Class I mutations) or dimers (Class II and Class III mutations), are observed in approximately 6% of all human cancers. First-generation BRAF inhibitors targeting Class I BRAF mutants, including dabrafenib, encorafenib, and vemurafenib, provide significant clinical benefit to patients with BRAF V600 mutation-driven melanoma and select solid tumors as monotherapies or in combination with other targeted therapies. The currently approved BRAF inhibitors have not, however, proven to be effective in patients with Class II or III BRAF alterations which account for a large proportion (34%) of BRAF mutations. KIN-2787 is an orally available, potent and selective small molecule pan-RAF inhibitor specifically designed to inhibit Class II and III BRAF dimers, in addition to Class I mutants. Methods: The efficacy and tolerability of the pan-RAF inhibitor, KIN-2787, was evaluated in vitro and in vivo in Class I, II, and III BRAF mutation-driven human cancer models. Results: In biochemical assays, KIN-2787 showed low nanomolar to picomolar potency against RAF1, BRAF, and ARAF (IC50 0.06-3.46 nM) with minimal activity towards non-RAF kinases. In cell-based assays, KIN-2787 inhibited RAF activity, as measured by inhibition of downstream ERK phosphorylation (pERK), across multiple BRAF mutant cancer cell lines. Class II and III BRAF mutant cell lines were the most responsive when treated with KIN-2787 (IC50 < 50 nM); 19- and 7-fold more sensitive compared to cells harboring wild-type BRAF, respectively. Dose-dependent inhibition of A-375 (Class I), BxPC-3 (Class II), and WM3629 (Class III) BRAF mutant human xenograft tumor growth was attained with daily KIN-2787 treatment and was well-tolerated. A trend towards greater tumor responses was observed with twice daily (BID) compared to once daily (QD) dosing of KIN-2787; however, the two dosing regimens led to similar tumor growth inhibition (TGI) and regressions (mean TGI up to 101-118%; p ≤0.0001) at equivalent total daily doses. Furthermore, KIN-2787 led to a significant in vivo pharmacodynamic response using either regimen, however, prolonged target coverage, as measured by pERK, was achieved with BID dosing. The impact of KIN-2787 treatment on additional biomarkers, including transcriptional changes and MAPK pathway modulation in cell-based models and patient-derived samples, will be presented at the meeting. Conclusions: KIN-2787 is a next-generation pan-RAF inhibitor with pronounced in vitro and in vivo activity against human cancers driven by Class II and III BRAF mutations. A phase 1 dose escalation and expansion clinical trial evaluating the safety and efficacy of KIN-2787 monotherapy in patients with advanced or metastatic solid tumors harboring BRAF gene alterations, including Class II and III mutations, is expected to initiate in 2021.

Mutant Isocitrate Dehydrogenase 1 Inhibitor Ivosidenib in Combination With Azacitidine for Newly Diagnosed Acute Myeloid Leukemia

PURPOSE

Ivosidenib is an oral inhibitor of the mutant isocitrate dehydrogenase 1 (IDH1) enzyme, approved for treatment of IDH1-mutant (mIDH1) acute myeloid leukemia (AML). Preclinical work suggested that addition of azacitidine to ivosidenib enhances mIDH1 inhibition-related differentiation and apoptosis.

PATIENTS AND METHODS

This was an open-label, multicenter, phase Ib trial comprising dose-finding and expansion stages to evaluate safety and efficacy of combining oral ivosidenib 500 mg once daily continuously with subcutaneous azacitidine 75 mg/m² on days 1-7 in 28-day cycles in patients with newly diagnosed mIDH1 AML ineligible for intensive induction chemotherapy (ClinicalTrials.gov identifier: NCT02677922).

RESULTS

Twenty-three patients received ivosidenib plus azacitidine (median age, 76 years; range, 61-88 years). Treatment-related grade ≥ 3 adverse events occurring in > 10% of patients were neutropenia (22%), anemia (13%), thrombocytopenia (13%), and electrocardiogram QT prolongation (13%). Adverse events of special interest included all-grade IDH differentiation syndrome (17%), all-grade electrocardiogram QT prolongation (26%), and grade ≥ 3 leukocytosis (9%). Median treatment duration was 15.1 months (range, 0.3-32.2 months); 10 patients remained on treatment as of February 19, 2019. The overall response rate was 78.3% (18/23 patients; 95% CI, 56.3% to 92.5%), and the complete remission rate was 60.9% (14/23 patients; 95% CI, 38.5% to 80.3%). With median follow-up of 16 months, median duration of response in responders had not been reached. The 12-month survival estimate was 82.0% (95% CI, 58.8% to 92.8%). mIDH1 clearance in bone marrow mononuclear cells by BEAMing (beads, emulsion, amplification, magnetics) digital polymerase chain reaction was seen in 10/14 patients (71.4%) achieving complete remission.

CONCLUSION

Ivosidenib plus azacitidine was well tolerated, with an expected safety profile consistent with monotherapy with each agent. Responses were deep and durable, with most complete responders achieving mIDH1 mutation clearance.

Margetuximab plus pembrolizumab in patients with previously treated, HER2-positive gastro-oesophageal adenocarcinoma (CP-MGAH22-05): a single-arm, phase 1b-2 trial

BACKGROUND

Margetuximab, a novel, investigational, Fc-engineered, anti-HER2 monoclonal antibody, is designed to more effectively potentiate innate immunity than trastuzumab. We aimed to evaluate the safety, tolerability, and antitumour activity of margetuximab plus pembrolizumab (an anti-PD-1 monoclonal antibody) in previously treated patients with HER2-positive gastro-oesophageal adenocarcinoma.

METHODS

CP-MGAH22-05 was a single-arm, open-label, phase 1b-2 dose-escalation and cohort expansion study done at 11 academic centres in the USA and Canada and 15 centres in southeast Asia (Korea, Taiwan, and Singapore) that enrolled men and women aged 18 years or older with histologically proven, unresectable, locally advanced or metastatic, HER2-positive, PD-L1-unselected gastro-oesophageal adenocarcinoma, with an Eastern Cooperative Oncology Group performance status of 0 or 1, who had progressed after at least one previous line of therapy with trastuzumab plus chemotherapy in the locally advanced unresectable or metastatic setting. In the dose-escalation phase, nine patients were treated: three received margetuximab 10 mg/kg intravenously plus pembrolizumab 200 mg intravenously every 3 weeks and six received the recommended phase 2 dose of margetuximab 15 mg/kg plus pembrolizumab 200 mg intravenously every 3 weeks. An additional 86 patients were enrolled in the phase 2 cohort expansion and received the recommended phase 2 dose. The primary endpoints were safety and tolerability, assessed in the safety population (patients who received at least one dose of either margetuximab or pembrolizumab) and the objective response rate as assessed by the investigator according to both Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, in the response-evaluable population (patients with measurable disease at baseline and who received the recommended phase 2 dose of margetuximab and pembrolizumab). This trial is registered with ClinicalTrials.gov, NCT02689284. Recruitment for the trial has completed and follow-up is ongoing.

FINDINGS

Between Feb 11, 2016, and Oct 2, 2018, 95 patients were enrolled. Median follow-up was 19·9 months (IQR 10·7-23·1). The combination therapy showed acceptable safety and tolerability; there were no dose-limiting toxicities in the dose-escalation phase. The most common grade 3-4 treatment-related adverse events were anaemia (four [4%]) and infusion-related reactions (three [3%]). Serious treatment-related adverse events were reported in nine (9%) patients. No treatment-related deaths were reported. Objective responses were observed in 17 (18·48%; 95% CI 11·15-27·93) of 92 evaluable patients.

INTERPRETATION

These findings serve as proof of concept of synergistic antitumour activity with the combination of an Fc-optimised anti-HER2 agent (margetuximab) along with anti-PD-1 checkpoint blockade (pembrolizumab).

FUNDING

MacroGenics.

Effect of enasidenib (ENA) plus azacitidine (AZA) on complete remission and overall response versus AZA monotherapy in mutant-IDH2 (mIDH2) newly diagnosed acute myeloid leukemia (ND-AML)

7501

Background: ENA and AZA each induce overall response rates (ORR) of ~30% and complete remission (CR) rates of ~20% in ND-AML. In vitro, combining ENA + AZA enhances cell differentiation. We report results of the phase II portion of an open-label, randomized phase I/II study of ENA + AZA (“E+A”) vs. AZA monotherapy (“A”) in patients (pts) with m IDH2 ND-AML (NCT02677922). Methods: Pts age ≥ 18 years ineligible for intensive chemotherapy, with ECOG PS ≤ 2 and intermediate- or poor-risk cytogenetics, were randomized 2:1 to E+A or A in 28-day (d) cycles. All pts received SC AZA 75 mg/m2/d x 7 d/cycle; pts randomized to E+A also received ENA 100 mg QD. The primary endpoint was ORR (CR, CR with incomplete recovery, partial remission, morphologic leukemia-free state). Other endpoints include duration of response (DOR), overall and event-free survival (OS, EFS), safety, and m IDH2 VAF. Results: 101 pts received E+A (n = 68) or A (n = 33). Median age was 75 years (57–85); most pts (83%) had intermediate-risk cytogenetics. 21 pts in the E+A arm and 1 in the A arm were ongoing at data cutoff (Aug 2019). Most common reason for discontinuation was disease progression (E+A 31%, A 52%). Median number Tx cycles was 10 (1–26) in the E+A arm and 6 (1–28) in the A arm. 7 pts (21%) in the A arm received subsequent Tx with ENA. ORR, CR rate and DOR were significantly improved with E+A vs. A (Table). Median OS was 22 mo in both arms (HR 0.99 [95%CI 0.52, 1.87]; P = 0.97). Median EFS was 17.2 and 10.8 mo in the E+A and A arms, respectively (HR 0.59 [95%CI 0.30, 1.17]; P = 0.13). Maximal m IDH2 VAF change from BL was –83.4% with E+A vs. –17.7% with A ( P < 0.01). No baseline co-mutation predicted primary resistance. Common Tx-related grade 3–4 AEs in the E+A arm were thrombocytopenia (37%), neutropenia (35%), anemia (19%), and febrile neutropenia (15%); these occurred in 19%, 22%, 22%, and 16% in the A arm. Grade 3–4 infections occurred in 18% of E+A pts and 31% of A pts. IDH differentiation syndrome occurred in 12 pts (18%) in the E+A arm. 5 E+A pts (7%) and 1 A pt (3%) died in the first 60 d. Conclusions: Combining ENA + AZA resulted in significantly improved response rates and durations, and was generally well-tolerated in older patients with m IDH2 ND-AML. The impact of subsequent Tx on OS/EFS and new translational data will be presented at the meeting. Clinical trial information: NCT02677922 . [Table: see text]

Abstract 2509: Analysis of clonal hematopoiesis-associated mutations in the cell-free DNA of advanced cancer patients

Background: Clonal hematopoiesis (CH) is the acquisition of mutations in hematopoietic progenitor cells that can lead to clonal expansion. Recent studies suggest that CH-derived mutations can confound interpretation of cell-free DNA (cfDNA) sequencing results. To better understand the contribution of CH to cfDNA analysis in the metastatic cancer setting, we characterized CH-associated alterations observed in the cfDNA of late-stage cancer patients.

Methods: We analyzed somatic variants from cfDNA profiles of over 62,000 patients in four late-stage cohorts: lung (&gt;35,000), gastro-intestinal (&gt;14,000), urogenital (&gt;4,700), breast (&gt;8,600). Matched white blood cell (WBC) and cfDNA was obtained for a subset of patient samples. Plasma cfDNA was processed using a 73-gene (150Kb, Guardant360TM) or 500-gene (2Mb, GuardantOMNITM) panel and sequenced to average depth of ~5000 molecules, with a 95% limit of detection (LOD) of 0.3-0.4% and 0.15-0.6% variant allele fraction (VAF) for SNVs, and 0.2%-0.7% and 0.4-0.8% for indels (for G360 and OMNI, respectively).

Results: In samples processed on the 500-gene panel, DNMT3A, TET2, PPM1D, ASXL1 and SF3B1 were the most frequently mutated CH-associated genes (75% of samples). While the majority (73%) of these mutations were at low variant allele fractions (VAF) of &lt;1%, CH VAFs ranged from 0.1% to 71.3%, and 20% of samples had ≥ 5 CH-associated variants. Tumor-associated VAFs across the same cohort ranged from 0.01% to 90.3%. In the 73-gene panel cohort of &gt;60,000 samples, JAK2 V617F, a known CH mutation, was observed in 927 samples with VAFs between 0.29% and 98%. Across the combined cohort, we found that in samples with a known CH variant (n=7,717), half of samples had a max CH VAF less than 50% of max tumor VAF. Interestingly, in &gt;25% of samples, the max CH VAF was higher than the max tumor VAF. Initial comparisons of matched plasma and WBC DNA show that 100% (16/16) of clinically relevant and 92% (84/91) of variants of unknown significance (VUSs) across the 73-gene panel were found exclusively in plasma DNA and not in WBC DNA testing.

Conclusions: We characterize the distribution of CH mutations across a large number of late-stage plasma samples and show that within highly pre-treated metastatic patients, the VAFs of CH mutations often differ from the tumor and can surpass the level of tumor shedding in circulation. Further investigation of these variants will enable improved understanding of CH in metastatic disease and its differentiation from the circulating tumor DNA.

Citation Format: Jennifer Yen, Katie Quinn, Elena Helman, Andrey Chursov, Tracy Nance, Ariel Jaimovich, Kimberly Banks, Aleksandra Franovic, Kristin Gleitsman, John Latham, Arielle Yablonovitch, Marcin Sikora, Stephen Fairclough, Darya Chudova, Richard B. Lanman, AmirAli Talasaz. Analysis of clonal hematopoiesis-associated mutations in the cell-free DNA of advanced cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2509.

Comprehensive genomic profiling of circulating cell-free DNA (cfDNA) distinguishes focal amplification (amp) from aneuploidy among MET amps in diverse advanced cancer types

3046

Background: MET amps can occur from focal gene copy number gain (e.g. MET-driven) or gain of chromosome 7 (e.g. aneuploidy); however, the contribution of each to MET amp is not well established. MET inhibitor-sensitive lung cancers harboring high-level MET amp have been reported in the absence of other sensitizing MET alterations (alts), e.g. exon 14 skipping, particularly among those with higher MET to chromosome 7 ratios. Methods: 3,114 samples from 2,902 Asian patients with advanced solid tumors were tested with a comprehensive cfDNA NGS panel (Guardant360) between Oct 2015-Dec 2018. This 70-73 gene assay evaluates single nucleotide variants (SNV), selected insertion-deletions (indels), fusions, and copy number gains. Focal amp was determined bioinformatically as having statistically higher copy number relative to other genes, such as BRAF, or CDK6, in the same chromosome arm. Results: MET alts associated with aberrant signaling were found in 223 pts (7.7%) with 18 different cancer types, most commonly lung (128/1,678), colorectal (36/349), and prostate (11/48). Among 223 pts, 189 pts (84.8%) had amps, 38(17.0%) had exon 14 skipping, and 8 (3.6%) had activating SNVs. 39.7% of MET amp was focal but differed by cancer type; highest prevalence was in gastroesophageal (80%) and lowest in prostate cancers (9%). Samples with focal MET amp had higher plasma copy number compared to those with non-focal MET amp (mean 5.8 vs. 2.5; p < 0.0001) and lower total number of alts per sample (8.8 vs. 11; p = 0.0122). Focal MET amp was more common than non-focal MET amp among 419 EGFR mutated samples (6.9% vs. 3.8%, p = 0.05) suggesting focal MET amp may be biologically more relevant as a mechanism of EGFR TKI resistance. Conclusions: This is the first study to use cfDNA to examine focal vs. non-focal MET amp. Focal MET amp accounted for ~40% of all MET amps, was found in 2.6% of pts with diverse cancers, was associated with higher plasma copy number, and found in a higher proportion of EGFR mutated lung cancer samples. The ability to differentiate may be clinically relevant given higher MET to chromosome 7 ratios have been associated with improved therapeutic response.

Detection of ERBB2 (HER2) Gene Amplification Events in Cell-Free DNA and Response to Anti-HER2 Agents in a Large Asian Cancer Patient Cohort

Background: HER2 antagonists have marked activity and are approved for the treatment of HER2 overexpressing breast and gastric cancers. Recent studies have shown that ERBB2 (HER2) gene amplification and overexpression may also be actionable in other tumor types. Inter- and intratumoral heterogeneity in HER2 status, however, poses a significant challenge in identifying patients that may benefit from HER2-targeted therapies. ERBB2 amplification as identified by circulating cell-free DNA (cfDNA), which circumvents tissue heterogeneity issues, is emerging as a robust biomarker predictive of response to anti-HER2 agents. Here, the prevalence and genomic landscape of ERBB2 alterations detectable by next-generation sequencing (NGS) of cfDNA was evaluated in a large cohort of Asian patients with advanced solid tumors. Methods: Results were queried for consecutive patients (n = 469) tested by a comprehensive 70/73-gene cfDNA NGS assay (Guardant360®) between November 2015 and June 2018. Patients with ERBB2 gene alterations including copy number amplifications (CNAs), single nucleotide variants (SNVs), and insertion-deletions (indels) were identified. Results: ERBB2 alterations were detected in 52 patients (11.1%); ERBB2 SNVs, CNAs, and indels were found in 27 (5.8%), 27 (5.8%), and 10 (2.1%) patients, respectively. ERBB2 amplification was most frequently identified in gastric (21.4%; 6/28), colorectal (11.1%; 5/45), lung (3.9%; 9/231), and breast (3.2%; 1/31) cancer patients. ERBB2 amplification was often mutually exclusive with other oncogenic alterations in gastric (83.3%; 5/6) and colorectal (60%; 3/5) cancer patients. ERBB2 copy number gains were also highest in gastric and colorectal cancers (median 4.8 and 6.6, respectively). We further report two cases of advanced gastric cancer patients, one treatment naïve, and the other having failed four lines of therapy, whose ERBB2 CNAs were identified by cfDNA and derived clinical benefit from HER2-based therapies. Conclusion: Our data indicate that ERBB2 amplification is a common event in solid tumors among Asian cancer patients. High ERBB2 incidence and copy number gains were observed in gastric and colorectal cancer patients, often in the absence of other oncogenic mutations, underscoring its likely role as the driver alteration in those settings. Finally, we show the potential of comprehensive cfDNA testing in identifying patients who are most likely to benefit from HER2-targeted therapies.

Antitumor activity of margetuximab (M) plus pembrolizumab (P) in patients (pts) with advanced HER2+ (IHC3+) gastric carcinoma (GC)

65

Background: Trastuzumab (T) + chemo is standard first-line therapy (tx) for HER2+ gastroesophageal adenocarcinoma (GEA) pts, though progression ensues in 6-8 months. The approved second-line tx is ramucirumab +/- paclitaxel (R+PAC). Pts with GC are less responsive to R+PAC than gastroesophageal junction (GEJ) pts, in particular HER2+ GC, and no anti-HER2 agents are approved in post-T setting. We report results of combination M+P in HER2+ GC pts and describe a biological rationale for this population. M is an anti-HER2 mAb Fc optimized for enhanced binding to activating FcgRIIIa (CD16A) and decreased binding to inhibitory FcgRIIb (CD32B). M demonstrated an enhanced Fc-dependent MoA, including enhanced ADCC. Methods: HER2+, PD-L1-unselected, second-line GEA pts post T progression received M (15 mg/kg) + P (200 mg) Q3wk. Safety, objective response rate (ORR), median overall & progression-free survival (mOS, mPFS), disease control rate (DCR), circulating tumor DNA, & tumor PD-L1 expression were assessed. Results: To date, 66 GEA pts were dosed; 35 (53%) GC and 31 (47%) GEJ. Overall, 12/66 (18.2%) had tx-related adverse events ≥ grade 3; 5 had drug-related SAEs: dehydration, diabetic ketoacidosis, hypotension and pneumonitis, each a single event, and 2 events of autoimmune hepatitis. Eligibility was based on archival HER2 expression; an exploratory endpoint measured retention of HER2 expression post-T by ERBB2 ctDNA. HER2 expression was lost in 23/56 (41.1%) of pts tested post T. HER2 retention was higher in pts with GC versus GEJ (65.8% vs. 44.8%) and in GEA pts with IHC 3+ vs 2+ archival tumors (61.7% vs 47.4%, respectively). Furthermore, GC had higher PD-L1 expression than GEJ, 53.3 vs. 33.3%, respectively. This coincided with more responses in IHC3+ GC pts, ORR 12/29 (41.4%; 95% CI 23.5-61.1), DCR 21/29 (72.4%; 95% CI 52.8-87.3), mPFS 5.5 months (95% CI 2.3-7.6), mOS not reached, with lower bound of 9.1 months for 95% CI. Enrollment of an additional 25 pts enriched for IHC3+ GC is ongoing. Conclusions: Results suggest that M+P, a chemo-free regimen, demonstrates acceptable tolerability and has encouraging preliminary activity in second-line HER2+ GEA, specifically in GC pts who retain ERBB2 amp prior to second-line tx. Clinical trial information: NCT02689284.

EGFR Genotyping of Matched Urine, Plasma, and Tumor Tissue in Patients With Non–Small-Cell Lung Cancer Treated With Rociletinib, an EGFR Tyrosine Kinase Inhibitor

Purpose

Liquid biopsies represent an attractive alternative to tissue biopsies, particularly rebiopsies, in determining patient eligibility for targeted therapies. Clinical utility of urine genotyping, however, has not been explored extensively. We evaluated epidermal growth factor receptor ( EGFR) T790M detection in matched urine, plasma, and tissue and the clinical outcomes of patients with advanced non–small-cell lung cancer treated with rociletinib.

Methods

Tissue (n = 540), plasma (n = 482), and urine (n = 213) were collected from evaluable patients enrolled in TIGER-X, a phase I/II study. Genotyping was performed by therascreen EGFR testing in tissue, BEAMing in plasma, and a quantitative short footprint assay (Trovera) in urine, which was used to further examine discordant samples.

Results

Positive percent agreement with tissue T790M results was similar for urine (82%; 142 of 173) and plasma (81%; 313 of 387) genotyping. Urine and plasma together identified more patients who were T790M positive (92%) than tissue alone (83%) among matched samples (n = 177). The ability to identify mutations in plasma was strongly associated with M stage ( P < .001); rate of T790M detection for patients with M1a/M0 disease increased from 54% for plasma alone to 85% when urine and plasma were both examined. Objective response rates of patients who were T790M positive were comparable between tumor (34%), plasma (32%), and urine (37%).

Conclusion

Clinical response to rociletinib was comparable irrespective of whether T790M status was identified by liquid or tissue biopsy. Combined, urine and plasma identified a higher percentage of patients who were T790M positive than tumor genotyping alone and improved detection of T790M, particularly in the absence of distant metastases. These findings support the noninvasive analysis of urine and plasma before tumor rebiopsy when assessing T790M status.

Abstract P3-06-05: Not presented

This abstract was not presented at the symposium.

Urine test for EGFR analysis in patients with non-small cell lung cancer

Precision medicine approaches in oncology are reliant on the accurate genomic characterization of tumors. While tissue remains the mainstay specimen for molecular testing, tumor biopsies are riddled with challenges and limitations due to their invasive and site-specific nature. Tumor inaccessibility and intratumoral heterogeneity, in particular, represent significant obstacles to the identification of actionable genetic alterations and hence effective mono- and combination therapy strategies. Proof-of-concept studies indicate that circulating tumor DNA (ctDNA) released from multiple tumor regions and anatomical locations is more reflective of intra- and intertumoral heterogeneity. Non-invasive liquid biopsy approaches that allow for the analysis of ctDNA are thus being increasingly implemented in routine patient care for the detection and monitoring of cancer-associated mutations. Indeed, the use of plasma testing to screen for epidermal growth factor receptor (EGFR) T790M mutant positive non-small cell lung cancer (NSCLC) patients eligible for treatment with third-generation EGFR inhibitors was recently approved by the U.S. Food and Drug Administration and is incorporated into the most recent version of the National Comprehensive Cancer Center guidelines as an alternative to tissue biopsy. Urine represents another liquid biopsy specimen that is distinguished by its ease of collection, option for home collection, and lack of temporal and volumetric collection restrictions. Importantly, there is an accumulating body of evidence supporting the clinical validity of urinary EGFR mutant testing for the identification and stratification of patients likely to benefit from EGFR-directed therapies and as a means to assess patient response, the presence of residual disease, and emergence of resistant tumor cell populations.

Antitumor Activity of RXDX-105 in Multiple Cancer Types with RET Rearrangements or Mutations

Purpose: While multikinase inhibitors with RET activity are active in RET-rearranged thyroid and lung cancers, objective response rates are relatively low and toxicity can be substantial. The development of novel RET inhibitors with improved potency and/or reduced toxicity is thus an unmet need. RXDX-105 is a small molecule kinase inhibitor that potently inhibits RET. The purpose of the preclinical and clinical studies was to evaluate the potential of RXDX-105 as an effective therapy for cancers driven by RET alterations.Experimental design: The RET-inhibitory activity of RXDX-105 was assessed by biochemical and cellular assays, followed by in vivo tumor growth inhibition studies in cell line- and patient-derived xenograft models. Antitumor activity in patients was assessed by imaging and Response Evaluation Criteria in Solid Tumors (RECIST).Results: Biochemically, RXDX-105 inhibited wild-type RET, CCDC6-RET, NCOA4-RET, PRKAR1A-RET, and RET M918T with low to subnanomolar activity while sparing VEGFR2/KDR and VEGFR1/FLT. RXDX-105 treatment resulted in dose-dependent inhibition of proliferation of CCDC6-RET-rearranged and RET C634W-mutant cell lines and inhibition of downstream signaling pathways. Significant tumor growth inhibition in CCDC6-RET, NCOA4-RET, and KIF5B-RET-containing xenografts was observed, with the concomitant inhibition of p-ERK, p-AKT, and p-PLCγ. Additionally, a patient with advanced RET-rearranged lung cancer had a rapid and sustained response to RXDX-105 in both intracranial and extracranial disease.Conclusions: These data support the inclusion of patients bearing RET alterations in ongoing and future molecularly enriched clinical trials to explore RXDX-105 efficacy across a variety of tumor types. Clin Cancer Res; 23(12); 2981-90. ©2016 AACR.

Abstract A174: RXDX-105 demonstrates potent RET inhibitory activity with therapeutic potential in multiple preclinical models of RET-rearrangement driven cancer

Genomic alterations in RET, encoding the RET (rearranged in transformation) kinase, have been identified as bona fide oncogenic drivers in numerous tumor types. Activating RET point mutations are typically associated with multiple endocrine neoplasia (types A and B) and familial medullary thyroid carcinoma. Although activating RET rearrangements can be found in up to 40% of papillary thyroid cancers, they are only present in up to 2% of non-small cell lung cancers and at lower frequencies in multiple other malignancies. As a result of the relatively low prevalence of molecular alterations in multiple tumor types, diagnostics-driven therapeutic selection strategies are being developed to identify patients with RET alterations. There also remains a clinical need for a potent, selective and safe RET inhibitor that demonstrates robust efficacy in malignancies harboring RET rearrangements and other oncogenic alterations.

RXDX-105 (formerly CEP-32496) is a potent, orally available, small molecule kinase inhibitor that potently binds and antagonizes several known oncogenic driver proteins, including RET, while sparing VEGFR2. RXDX-105 is currently in clinical trial in patients with solid tumors. To evaluate the therapeutic potential of RXDX-105 in malignancies bearing RET alterations, we first assessed the ability of RXDX-105 to antagonize RET activity in vitro. In biochemical and cell based assays, RXDX-105 potently antagonizes the activity of RET-fusion proteins and RET activating point mutations, resulting in a dose dependent inhibition of downstream signaling events and cell proliferation. In vivo, RXDX-105 displays potent and dose dependent anti-tumor activity with significant tumor growth regressions in several patient derived xenograft models harboring RET-rearrangements.

These pre-clinical studies support the inclusion of patients bearing RET alterations in future diagnostics-based clinical trials exploring RXDX-105 efficacy across a variety of tumor types.

Citation Format: James Joseph, Aleksandra Franovic, Anni Schairer, Eric Martin, Ge Wei, Danielle Murphy, Jason Christiansen, Robert Shoemaker, Pratik Multani, Robert Wild, Gang Li. RXDX-105 demonstrates potent RET inhibitory activity with therapeutic potential in multiple preclinical models of RET-rearrangement driven cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A174.

Kinase-independent role for CRAF-driving tumour radioresistance via CHK2

Although oncology therapy regimens commonly include radiation and genotoxic drugs, tumour cells typically develop resistance to these interventions. Here we report that treatment of tumours with ionizing radiation or genotoxic drugs drives p21-activated kinase 1 (PAK1)-mediated phosphorylation of CRAF on Serine 338 (pS338) triggering a kinase-independent mechanism of DNA repair and therapeutic resistance. CRAF pS338 recruits CHK2, a cell cycle checkpoint kinase involved in DNA repair, and promotes CHK2 phosphorylation/activation to enhance the tumour cell DNA damage response. Accordingly, a phospho-mimetic mutant of CRAF (S338D) is sufficient to induce the CRAF/CHK2 association enhancing tumour radioresistance, while an allosteric CRAF inhibitor sensitizes tumour cells to ionizing radiation or genotoxic drugs. Our findings establish a role for CRAF in the DNA damage response that is independent from its canonical function as a kinase.

Tumors hijack cellular pathways to evade the effects of cancer therapy. Here, Advani et al. show that DNA damage-induced phosphorylation of CRAF Serine 338 triggers DNA repair by recruiting CHK2, highlighting a role for CRAF independent from its canonical function as a kinase.

Glioblastomas require integrin αvβ3/PAK4 signaling to escape senescence

Integrin αvβ3 has been implicated as a driver of aggressive and metastatic disease, and is upregulated during glioblastoma progression. Here, we demonstrate that integrin αvβ3 allows glioblastoma cells to counteract senescence through a novel tissue-specific effector mechanism involving recruitment and activation of the cytoskeletal regulatory kinase PAK4. Mechanistically, targeting either αvβ3 or PAK4 led to emergence of a p21-dependent, p53-independent cell senescence phenotype. Notably, glioblastoma cells did not exhibit a similar requirement for either other integrins or additional PAK family members. Moreover, αvβ3/PAK4 dependence was not found to be critical in epithelial cancers. Taken together, our findings established that glioblastomas are selectively addicted to this pathway as a strategy to evade oncogene-induced senescence, with implications that inhibiting the αvβ3-PAK4 signaling axis may offer novel therapeutic opportunities to target this aggressive cancer.

Abstract 4240: Targeting Galectin-3 to reverse tumor stemness and drug resistance

We have recently linked integrin αvβ3 expression to metastatic potential, stemness, and therapy resistance due to its capacity to couple to KRAS. This leads to the induction of RalB/TBK-1 and the activation of NFκB to shift tumor cells to a stem-like phenotype. To understand how integrin αvβ3 couples to KRAS, we generated β3 domain swap mutants containing either the intracellular or extracellular domains of β1 integrin. Each chimera partially reduced KRAS association with αvβ3, suggesting interactions on each side of the plasma membrane may contribute. Since the short β3 cytoplasmic tail has no putative KRAS binding regions, we considered Galectin-3 as a putative scaffolding partner to facilitate the αvβ3/KRAS association due to its reported binding to both KRAS and integrins. Indeed, treating cells with GCS-100, a complex polysaccharide that has the ability to bind to and block the effects of Galectin-3, decreased Galectin-3 surface expression, αvβ3 clustering, and αvβ3/KRAS association. Exposing cells to this drug also decreased tumor stem properties. Our observations provide a molecular basis for the αvβ3/KRAS/Galectin-3 complex and highlight the potential for Galectin-3 blockade as a therapeutic approach to reverse the aggressive behavior of αvβ3-expressing tumors.

Citation Format: Shumei Kato, Laetitia Seguin, Aleksandra Franovic, Hisashi Kato, Maria Camargo, Jay Desgrosellier, Sudarshan Anand, Sara Weis, Sanford Shattil, David A. Cheresh. Targeting Galectin-3 to reverse tumor stemness and drug resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4240. doi:10.1158/1538-7445.AM2014-4240

Abstract 1916: β3 integrin/KRAS/RalB complex drives tumor stemness and resistance to EGFR inhibition

Integrin αvβ3 expression is a marker of tumor progression for a wide range of histologically distinct cancers, yet the molecular mechanism by which αvβ3 influences the growth and malignancy of cancer is poorly understood. Here, we reveal that integrin αvβ3, in the unligated state on lung, breast and pancreatic cancer cells, recruits KRAS and RalB to the plasma membrane, leading to the activation of TBK-1/c-Rel. These events are both necessary and sufficient to promote tumor initiation, anchorage-independence, self-renewal, as well as resistance to nutrient deprivation and treatment with receptor tyrosine kinase (RTK) inhibitors such as erlotinib. Genetic or pharmacological inhibition of RalB or its effectors suppress tumor initiation, self-renewal, and re-sensitizes tumors to RTK inhibition. These findings not only identify ανβ3 as a marker/driver of tumor stemness but also provide a strategy to overcome tumor resistance to RTK Inhibition.

Citation Format: Laetitia Jocelyne Seguin, Shumei Kato, Aleksandra Franovic, Maria Fernanda Camargo, Katrhyn Elliott, Mayra Yebra, Jacqueline Lesperance, Ainhoa Mielgo, Jay Desgrosellier, Sudarshan Anand, Sara Weis, David Cheresh. β3 integrin/KRAS/RalB complex drives tumor stemness and resistance to EGFR inhibition. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1916. doi:10.1158/1538-7445.AM2014-1916

An integrin β₃-KRAS-RalB complex drives tumour stemness and resistance to EGFR inhibition

Tumour cells, with stem-like properties, are highly aggressive and often show drug resistance. Here, we reveal that integrin α(v)β₃ serves as a marker of breast, lung and pancreatic carcinomas with stem-like properties that are highly resistant to receptor tyrosine kinase inhibitors such as erlotinib. This was observed in vitro and in mice bearing patient-derived tumour xenografts or in clinical specimens from lung cancer patients who had progressed on erlotinib. Mechanistically, α(v)β₃, in the unliganded state, recruits KRAS and RalB to the tumour cell plasma membrane, leading to the activation of TBK1 and NF-κB. In fact, α(v)β₃ expression and the resulting KRAS-RalB-NF-κB pathway were both necessary and sufficient for tumour initiation, anchorage independence, self-renewal and erlotinib resistance. Pharmacological targeting of this pathway with bortezomib reversed both tumour stemness and erlotinib resistance. These findings not only identify α(v)β₃ as a marker/driver of carcinoma stemness but also reveal a therapeutic strategy to sensitize such tumours to RTK inhibition.

An oxygen-regulated switch in the protein synthesis machinery

Protein synthesis involves the translation of ribonucleic acid information into proteins, the building blocks of life. The initial step of protein synthesis consists of the eukaryotic translation initiation factor 4E (eIF4E) binding to the 7-methylguanosine (m⁷-GpppG) 5′cap of mRNAs^1,2. Low oxygen tension (hypoxia) represses cap-mediated translation by sequestering eIF4E through mammalian target of rapamycin (mTOR)-dependent mechanisms^3–6. While the internal ribosome entry site is an alternative translation initiation mechanism, this pathway alone cannot account for the translational capacity of hypoxic cells^7,8. This raises a fundamental question in biology as to how proteins are synthesized in periods of oxygen scarcity and eIF4E inhibition⁹. Here, we uncover an oxygen-regulated translation initiation complex that mediates selective cap-dependent protein synthesis. Hypoxia stimulates the formation of a complex that includes the oxygen-regulated hypoxia-inducible factor 2α (HIF-2α), the RNA binding protein RBM4 and the cap-binding eIF4E2, an eIF4E homologue. PAR-CLIP¹⁰ analysis identified an RNA hypoxia response element (rHRE) that recruits this complex to a wide array mRNAs, including the epidermal growth factor receptor (EGFR). Once assembled at the rHRE, HIF-2α/RBM4/eIF4E2 captures the 5′cap and targets mRNAs to polysomes for active translation thereby evading hypoxia-induced repression of protein synthesis. These findings demonstrate that cells have evolved a program whereby oxygen tension switches the basic translation initiation machinery.

Abstract LB-493: Blocking the integrin αvβ3-CRAF axis with Cilengitide arrests glioblastoma cells in pro-metaphase

Glioblastoma multiforme (GBM) is the most prevalent brain tumor subtype, with a particularly high mortality rate due to frequent recurrence and poor response to standard therapies. Improving outcome for these patients will require new therapies which target the unique features of this disease. One such approach is geared toward integrin αvβ3, as high-grade GBM tumors express both the extracellular matrix protein vitronectin and its receptor integrin αvβ3 which drive several key cell signaling pathways to promote cell invasion and survival. Blocking the function of integrin αvβ3 with the antagonist Cilengitide shows potent anti-tumor activity in preclinical models and is currently completing the first Phase III trial for newly-diagnosed GBM. Understanding the mechanisms of activity for Cilengitide will be critical as this drug nears FDA-approval for GBM. Since αvβ3 is highly expressed in both the brain tumor vasculature and on glioma cells, it is not clear whether Cilengitide exerts its effects by disrupting tumor angiogenesis, tumor cell invasion and survival, or other hallmark tumor traits. Focusing on GBM cells, we have made the novel observation that αvβ3 ligation leads to phosphorylation of CRAF on serine 338, an event which we have recently linked to cell survival and cell cycle progression. Pharmacological inhibition or knockdown of integrin αvβ3 reduces activated CRAF levels, causes tumor cells to arrest in pro-metaphase, and suppresses the growth of orthotopic GBM in mice. Activating this pathway by expression of a phospho-mimetic CRAF S338D mutant independently drives cell cycle progression in vitro, accelerates tumor growth in vivo, and renders tumors resistant to the effects of Cilengitide. These findings reveal a previously unappreciated mechanism of action for Cilengitide. In addition to its well-known anti-angiogenic function, it also directly induces cell cycle arrest in GBM cells. The clinical implications of this observation are two-fold as it: 1) provides important insight that could aid in the design of combination treatment regimes; and 2) points at integrin αvβ3 and phosphorylated CRAF S338 expression as potential biomarkers which could serve to help identify the patient populations most likely to benefit from Cilengitide.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-493. doi:1538-7445.AM2012-LB-493

A MEK-independent role for CRAF in mitosis and tumor progression

RAF kinases regulate cell proliferation and survival and can be dysregulated in tumors. The role of RAF in cell proliferation has been linked to its ability to activate mitogen-activated protein kinase kinase 1 (MEK) and mitogen-activated protein kinase 1 (ERK). Here we identify a MEK-independent role for RAF in tumor growth. Specifically, in mitotic cells, CRAF becomes phosphorylated on Ser338 and localizes to the mitotic spindle of proliferating tumor cells in vitro as well as in murine tumor models and in biopsies from individuals with cancer. Treatment of tumors with allosteric inhibitors, but not ATP-competitive RAF inhibitors, prevents CRAF phosphorylation on Ser338 and localization to the mitotic spindle and causes cell-cycle arrest at prometaphase. Furthermore, we identify phospho-Ser338 CRAF as a potential biomarker for tumor progression and a surrogate marker for allosteric RAF blockade. Mechanistically, CRAF, but not BRAF, associates with Aurora kinase A (Aurora-A) and Polo-like kinase 1 (Plk1) at the centrosomes and spindle poles during G2/M. Indeed, allosteric or genetic inhibition of phospho-Ser338 CRAF impairs Plk1 activation and accumulation at the kinetochores, causing prometaphase arrest, whereas a phospho-mimetic Ser338D CRAF mutant potentiates Plk1 activation, mitosis and tumor progression in mice. These findings show a previously undefined role for RAF in tumor progression beyond the RAF-MEK-ERK paradigm, opening new avenues for targeting RAF in cancer.

ETS-1 oncogenic activity mediated by transforming growth factor alpha

Inappropriate expression of Ets-1 is observed in a variety of human cancers, and its forced expression in cultured cells results in transformation, autonomous proliferation, and tumor formation. The basis by which Ets-1 confers autonomous growth, one of the primary hallmarks of cancer cells and a critical component of persistent proliferation, has yet to be fully explained. Using a variety of cancer cell lines, we show that inhibition of Ets-1 blocks tumor formation and cell proliferation in vivo and autonomous growth in culture. A screen of multiple diffusible growth factors revealed that inhibition of Ets-1 results in the specific downregulation of transforming growth factor alpha (TGFalpha), the proximal promoter region of which contains multiple ETS family DNA binding sites that can be directly bound and regulated by Ets-1. Notably, rescuing TGFalpha expression in Ets-1-silenced cells was sufficient to restore tumor cell proliferation in vivo and autonomous growth in culture. These results reveal a previously unrecognized mechanism by which Ets-1 oncogenic activity can be explained in human cancer through its ability to regulate the important cellular mitogen TGFalpha.

Translational up-regulation of the EGFR by tumor hypoxia provides a nonmutational explanation for its overexpression in human cancer

Overexpression of the EGF receptor (EGFR) is a recurrent theme in human cancer and is thought to cause aggressive phenotypes and resistance to standard therapy. There has, thus, been a concerted effort in identifying EGFR gene mutations to explain misregulation of EGFR expression as well as differential sensitivity to anti-EGFR drugs. However, such genetic alterations have proven to be rare occurrences in most types of cancer, suggesting the existence of a more general physiological trigger for aberrant EGFR expression. Here, we provide evidence that overexpression of wild-type EGFR can be induced by the hypoxic microenvironment and activation of hypoxia-inducible factor 2-alpha (HIF2alpha) in the core of solid tumors. Our data suggest that hypoxia/HIF2alpha activation represents a common mechanism for EGFR overexpression by increasing EGFR mRNA translation, thereby diminishing the necessity for gene mutations. This allows for the accumulation of elevated EGFR levels, increasing its availability for the autocrine signaling required for tumor cell growth autonomy. Taken together, our findings provide a nonmutational explanation for EGFR overexpression in human tumors and highlight a role for HIF2alpha activation in the regulation of EGFR protein synthesis.

Multiple Acquired Renal Carcinoma Tumor Capabilities Abolished upon Silencing of ADAM17

Malignancy is a manifestation of acquired defects in regulatory circuits that direct normal cell proliferation and homeostasis. Most of these circuits operate through cell autonomous pathways, whereas others potentially involve the neighboring microenvironment. We report that the metalloprotease ADAM17 plays a pivotal role in several acquired tumor cell capabilities by mediating the availability of soluble transforming growth factor-α, an epidermal growth factor receptor (EGFR) ligand, and thus the establishment of a key autocrine signaling pathway. Silencing of ADAM17 in human renal carcinoma cell lines corrects critical features associated with cancer cells, including growth autonomy, tumor inflammation, and tissue invasion. Highly malignant renal carcinoma cancer cells fail to form in vivo tumors in the absence of ADAM17, confirming the essential function of this molecule in tumorigenesis. These data show that ligand shedding is a crucial step in endogenous EGFR activation and endorse prospective therapeutic strategies targeting ADAM17 in human cancer. (Cancer Res 2006; 66(16): 8083-90)

Silencing of epidermal growth factor receptor suppresses hypoxia-inducible factor-2-driven VHL-/- renal cancer

Inactivating mutations in the von Hippel-Lindau (VHL) tumor suppressor gene are associated with clear cell renal cell carcinoma (VHL-/- RCC), the most frequent malignancy of the human kidney. The VHL protein targets the alpha subunits of hypoxia-inducible factor (HIF) transcription factor for ubiquitination and degradation. VHL-/- RCC cells fail to degrade HIF resulting in the constitutive activation of its target genes, a process that is required for tumorigenesis. We recently reported that HIF activates the transforming growth factor-alpha/epidermal growth factor receptor (TGF-alpha/EGFR) pathway in VHL-defective RCC cells. Here, we show that short hairpin RNA (shRNA)-mediated inhibition of EGFR is sufficient to abolish HIF-dependent tumorigenesis in multiple VHL-/- RCC cell lines. The 2alpha form of HIF (HIF-2alpha), but not HIF-1alpha, drives in vitro and in vivo tumorigenesis of VHL-/- RCC cells by specifically activating the TGF-alpha/EGFR pathway. Transient incubation of VHL-/- RCC cell lines with small interfering RNA directed against EGFR prevents autonomous growth in two-dimensional culture as well as the ability of these cells to form dense spheroids in a three-dimensional in vitro tumor assay. Stable expression of shRNA against EGFR does not alter characteristics associated with VHL loss including constitutive production of HIF targets and defects in fibronectin deposition. In spite of this, silencing of EGFR efficiently abolishes in vivo tumor growth of VHL loss RCC cells. These data identify EGFR as a critical determinant of HIF-2alpha-dependent tumorigenesis and show at the molecular level that EGFR remains a credible target for therapeutic strategies against VHL-/- renal carcinoma.

Hypoxia inducible factor activates the transforming growth factor-alpha/epidermal growth factor receptor growth stimulatory pathway in VHL(-/-) renal cell carcinoma cells

Bi-allelic-inactivating mutations of the VHL tumor suppressor gene are found in the majority of clear cell renal cell carcinomas (VHL(-/-) RCC). VHL(-/-) RCC cells overproduce hypoxia-inducible genes as a consequence of constitutive, oxygen-independent activation of hypoxia inducible factor (HIF). While HIF activation explains the highly vascularized nature of VHL loss lesions, the relative role of HIF in oncogenesis and loss of growth control remains unknown. Here, we report that HIF plays a central role in promoting unregulated growth of VHL(-/-) RCC cells by activating the transforming growth factor-alpha (TGF-alpha)/epidermal growth factor receptor (EGF-R) pathway. Dominant-negative HIF and enzymatic inhibition of EGF-R were equally efficient at abolishing EGF-R activation and serum-independent growth of VHL(-/-) RCC cells. TGF-alpha is the only known EGF-R ligand that has a VHL-dependent expression profile and its overexpression by VHL(-/-) RCC cells is a direct consequence of HIF activation. In contrast to TGF-alpha, other HIF targets, including vascular endothelial growth factor (VEGF), were unable to stimulate serum-independent growth of VHL(-/-) RCC cells. VHL(-/-) RCC cells expressing reintroduced type 2C mutants of VHL, and which retain the ability to degrade HIF, fail to overproduce TGF-alpha and proliferate in serum-free media. These data link HIF with the overproduction of a bona fide renal cell mitogen leading to activation of a pathway involved in growth of renal cancer cells. Moreover, our results suggest that HIF might be involved in oncogenesis to a much higher extent than previously appreciated.