Abstract: Larotrectinib, a selective TRK tyrosine kinase inhibitor (TKI), has demonstrated histology-agnostic efficacy in patients with TRK fusion–positive cancers. Although responses to TRK inhibition can be dramatic and durable, duration of response may eventually be limited by acquired resistance. LOXO-195 is a selective TRK TKI designed to overcome acquired resistance mediated by recurrent kinase domain (solvent front and xDFG) mutations identified in multiple patients who have developed resistance to TRK TKIs. Activity against these acquired mutations was confirmed in enzyme and cell-based assays and in vivo tumor models. As clinical proof of concept, the first 2 patients with TRK fusion–positive cancers who developed acquired resistance mutations on larotrectinib were treated with LOXO-195 on a first-in-human basis, utilizing rapid dose titration guided by pharmacokinetic assessments. This approach led to rapid tumor responses and extended the overall duration of disease control achieved with TRK inhibition in both patients. Significance: LOXO-195 abrogated resistance in TRK fusion–positive cancers that acquired kinase domain mutations, a shared liability with all existing TRK TKIs. This establishes a role for sequential treatment by demonstrating continued TRK dependence and validates a paradigm for the accelerated development of next-generation inhibitors against validated oncogenic targets. Cancer Discov; 7(9); 963–72. ©2017 AACR. See related commentary by Parikh and Corcoran, p. 934. This article is highlighted in the In This Issue feature, p. 920

Abstract: Introduction: Bruton Tyrosine Kinase inhibitors (BTKis) have transformed the treatment of patients with chronic lymphocytic leukemia (CLL) and other B-cell malignancies by inducing durable responses, improving quality of life and prolonging overall survival. Prolonged use of BTKi in the real-world setting is limited by toxicity and acquired resistance. Discontinuation rates for BTKis may be as high as 40% in relapsed/refractory CLL, with BTK C481-mediated resistance evident in many progressing patients. Alternative therapies such as venetoclax are associated with on-target (BCL2) acquired resistance. We hypothesized that a selective, non-covalent BTKi would benefit patients with B-cell malignancies in the setting of acquired resistance and/ or unacceptable toxicities following an irreversible BTKi. LOXO-305 is a next-generation, highly selective, oral, non-covalent BTKi that inhibits wild-type and C481-mutated BTK preclinically. Here, we report results from a first-in-human, proof-of-concept phase 1 trial in patients with B-cell malignancies. Methods: This multicenter phase 1/2 trial (NCT 03740529) enrolled patients with advanced B-cell malignancies who had failed or were intolerant to & gt; 2 prior therapies. LOXO-305 was dosed orally in 28-day cycles, using a standard 3+3 dose-escalation design with a primary endpoint of MTD/RP2D identification. Results: As of 26 July 2019, 13 patients (9 CLL and 4 MCL) were enrolled to 3 dose levels: 25mg (n=5), 50mg (n=5) and 100mg (n=3) QD. Median age was 65 (range 51-79) years and the median number of prior therapies was 3 (range 2-6). 12 patients (8 CLL, 4 MCL) received prior chemotherapy + anti-CD20 antibody; 2 MCL patients underwent prior autologous stem cell transplantation; 5 CLL patients received prior umbralisib; 10 patients (7 CLL, 3 MCL) received prior ibrutinib (5 intolerant, 5 relapsed), including 1 who had also received venetoclax. 6 CLL patients displayed high-risk genetic features, including unmutated IGHV (4), complex karyotype (4) and del17p (3). Molecular characterization was available in 7 patients (6 CLL, 1 MCL) and revealed: BTK C481S mutations (in 2 CLL patients post-ibrutinib), a BCL2 G101V mutation (in a CLL patient post-venetoclax), and a TP53 mutation (in an MCL patient post-ibrutinib). At doses ≥50 mg QD, LOXO-305 exposure exceeded the calculated IC90 for wild-type and C481S mutated BTK. No DLTs were reported and all TEAEs are grade 1-2. Clinical activity was noted within the first cycle of therapy and at the first dose level of 25mg QD. The first eight patients were evaluable for initial response and 7 tumor responses (87.5%) were observed (by disease-defined criteria): 5/5 CLL patients (1 PR and 4 PR-L including one with BTK C481S mutation after ibrutinib and one with BCL2 G101V mutation after venetoclax) and 2/3 MCL patients (2 PR and 1 PD with a preexisting TP53 mutation). 2 additional CLL patients were awaiting initial radiologic assessment but had already demonstrated treatment-induced lymphocytosis. 12/13 patients remain on therapy, the longest 5+ months. Conclusion: Phase 1 data with LOXO-305 demonstrate a favorable safety profile and provide proof-of-concept evidence of efficacy in heavily pretreated CLL and MCL patients, including patients with acquired resistance to available BTKis and venetoclax. Disclosures Mato: DTRM Biopharma: Research Funding; Genentech: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding; Gilead: Research Funding; Acerta: Consultancy; Janssen: Consultancy; TG Therapeutics: Consultancy, Other: DSMB member , Research Funding; Celgene: Consultancy; Sunesis: Consultancy, Research Funding; AstraZeneca: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; LOXO: Consultancy, Research Funding; Johnson & Johnson: Consultancy, Research Funding. Flinn:F. Hoffmann-La Roche Ltd: Research Funding; Acerta Pharma, Agios, Calithera Biosciences, Celgene, Constellation Pharmaceuticals, Genentech, Gilead Sciences, Incyte, Infinity Pharmaceuticals, Janssen, Karyopharm Therapeutics, Kite Pharma, Novartis, Pharmacyclics, Portola Pharmaceuticals: Research Funding; TG Therapeutics, Trillum Therapeutics, Abbvie, ArQule, BeiGene, Curis, FORMA Therapeutics, Forty Seven, Merck, Pfizer, Takeda, Teva, Verastem, Gilead Sciences, Astra Zeneca (AZ), Juno Therapeutics, UnumTherapeutics, MorphoSys, AG: Research Funding; TG Therapeutics, Trillum Therapeutics, Abbvie, ArQule, BeiGene, Curis, FORMA Therapeutics, Forty Seven, Merck, Pfizer, Takeda, Teva, Verastem, Gilead Sciences, Astra Zeneca (AZ), Juno Therapeutics, UnumTherapeutics, MorphoSys, AG: Research Funding; AbbVie, Seattle Genetics, TG Therapeutics, Verastem: Consultancy. Pagel:AstraZeneca: Consultancy; Gilead Sciences: Consultancy; Pharmacyclics: Consultancy. Brown:Teva: Honoraria; Janssen: Honoraria; Sunesis: Consultancy; Juno/Celgene: Consultancy; Gilead: Consultancy, Research Funding; Dynamo Therapeutics: Consultancy; Genentech/Roche: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Loxo: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Sun Pharmaceuticals: Research Funding; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Octapharma: Consultancy; AstraZeneca: Consultancy; BeiGene: Consultancy; Catapult Therapeutics: Consultancy; Acerta Pharma: Consultancy; Invectys: Other: Data safety monitoring board; Morphosys: Other: Data safety monitoring board; AbbVie: Consultancy. Cheah:Roche, Janssen, MSD, Gilead, Loxo Oncology, Acerta, BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene, Roche, Abbvie: Research Funding; Roche: Other: Travel expenses. Coombs:Medscape: Honoraria; Covance: Consultancy; Cowen & Co.: Consultancy; H3 Biomedicine: Honoraria; Dedham Group: Consultancy; Loxo: Honoraria; Abbvie: Consultancy; Octopharma: Honoraria; Pharmacyclics: Honoraria. Rothenberg:LOXO Oncology Inc.: Employment. Tsai:Eli Lilly and Company: Employment. Ku:Eli Lilly and Company: Employment. Wang:BioInvent: Consultancy, Research Funding; VelosBio: Research Funding; Loxo Oncology: Research Funding; Guidepoint Global: Consultancy; Kite Pharma: Consultancy, Research Funding; Pharmacyclics: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Acerta Pharma: Consultancy, Research Funding; MoreHealth: Consultancy, Equity Ownership; AstraZeneca: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding; Juno Therapeutics: Research Funding; Dava Oncology: Honoraria; Aviara: Research Funding.

Abstract: Background: Activating mutations and oncogenic fusions of the RET receptor tyrosine kinase have been identified in multiple tumor types, including thyroid, lung, breast and colon carcinoma. Furthermore, tyrosine kinase inhibitors (TKIs) with anti-RET activity have produced clinical responses in patients whose tumors harbor RET alterations. However, currently available RET inhibitors were initially developed to target kinases other than RET and are only moderately potent against RET, inhibit multiple kinases other than RET or poorly inhibit secondary resistance mutations (e.g. gatekeeper mutations) common to other TKIs. We have discovered novel, potent and selective RET inhibitors. The resulting compounds exhibit nanomolar potency against wild type RET and select RET mutants, including the KIF5B-RET fusion and V804M gatekeeper mutation, in both enzyme and cellular assays, with minimal activity against highly related kinases. AR025 is representative of this series; the activity of AR025 and related analogs in relevant in vitro and in vivo models will be presented here. Methods: In vitro and in vivo evaluations, including enzyme and cell-based assays, pharmacokinetic (PK)/pharmacodynamics (PD) correlations, drug metabolism characterization, and non-clinical safety evaluation, were conducted using standard methods. Tumor growth inhibition and PD studies were carried out using subcutaneous allografts of NIH-3T3 cells expressing KIF5B-RET in nude mice. Results: AR025 demonstrated nanomolar potency against both wild type and mutant RET proteins in enzyme and cellular assays. AR025 had minimal activity against an enzyme panel of & gt;200 diverse kinases and demonstrated & gt;50x cellular selectivity against VEGFR, with similar selectivity against other related kinases. AR025 possessed low intravenous clearance and high oral exposure in mice, rats and dogs. Finally, a single oral dose of 30mg/kg produced more than 90% inhibition of phospho-RET in NIH-3T3-KIF5B-RET mouse allografts, while twice-per-day continuous dosing resulted in greater than 90% tumor growth inhibition. Notably, AR025 was minimally toxic at doses up to 100mg/kg per day. Conclusions: We have identified a series of potent and selective RET inhibitors with high oral bioavailability and favorable PK properties in animals. One of these, AR025, demonstrated potent inhibition of RET in enzyme and cellular assays, with minimal activity against highly related kinases. In an NIH3T3-KIF5B-RET allograft model, AR025 effectively inhibited phospho-RET and caused dramatic tumor growth inhibition without significant toxicity. The identification of potent and selective RET inhibitors with significant in vivo activity and minimal toxicity may overcome the limitations of currently available inhibitors with anti-RET activity. Citation Format: Barbara J. Brandhuber, Nisha Nanda, Julia Haas, Karyn Bouhana, Lance Williams, Shannon Winski, Michael Burkard, Brian Tuch, Kevin Ebata, Jennifer Low, Francis Sullivan, Lauren Hanson, Tony Morales, Guy Vigers, Jessica Gaffney, Ross D. Wallace, James Blake, Yutong Jiang, S. Michael Rothenberg, Steven Andrews. Identification and characterization of highly potent and selective RET kinase inhibitors for the treatment of RET-driven cancers. [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 B192.

Abstract: Glioblastoma (GBM) is a highly aggressive brain cancer characterized by local invasion and angiogenic recruitment, yet metastatic dissemination is extremely rare. Here, we adapted a microfluidic device to deplete hematopoietic cells from blood specimens of patients with GBM, uncovering evidence of circulating brain tumor cells (CTC). Staining and scoring criteria for GBM CTCs were first established using orthotopic patient-derived xenografts (PDX), and then applied clinically: CTCs were identified in at least one blood specimen from 13 of 33 patients (39%; 26 of 87 samples). Single GBM CTCs isolated from both patients and mouse PDX models demonstrated enrichment for mesenchymal over neural differentiation markers compared with primary GBMs. Within primary GBMs, RNA in situ hybridization identified a subpopulation of highly migratory mesenchymal tumor cells, and in a rare patient with disseminated GBM, systemic lesions were exclusively mesenchymal. Thus, a mesenchymal subset of GBM cells invades the vasculature and may proliferate outside the brain. Significance: GBMs are locally invasive within the brain but rarely metastasize to distant organs, exemplifying the debate over “seed” versus “soil.” We demonstrate that GBMs shed CTCs with invasive mesenchymal characteristics into the circulation. Rare metastatic GBM lesions are primarily mesenchymal and show additional mutations absent in the primary tumor. Cancer Discov; 4(11); 1299–1309. ©2014 AACR. See related commentary by Seoane and De Mattos-Arruda, p. 1259 This article is highlighted in the In This Issue feature, p. 1243

Abstract: Rationally targeted therapies have transformed cancer treatment, but many patients develop resistance through bypass signaling pathway activation. PF-07284892 (ARRY-558) is an allosteric SHP2 inhibitor designed to overcome bypass-signaling-mediated resistance when combined with inhibitors of various oncogenic drivers. Activity in this setting was confirmed in diverse tumor models. Patients with ALK fusion–positive lung cancer, BRAFV600E-mutant colorectal cancer, KRASG12D-mutant ovarian cancer, and ROS1 fusion–positive pancreatic cancer who previously developed targeted therapy resistance were treated with PF-07284892 on the first dose level of a first-in-human clinical trial. After progression on PF-07284892 monotherapy, a novel study design allowed the addition of oncogene-directed targeted therapy that had previously failed. Combination therapy led to rapid tumor and circulating tumor DNA (ctDNA) responses and extended the duration of overall clinical benefit. Significance: PF-07284892–targeted therapy combinations overcame bypass-signaling-mediated resistance in a clinical setting in which neither component was active on its own. This provides proof of concept of the utility of SHP2 inhibitors in overcoming resistance to diverse targeted therapies and provides a paradigm for accelerated testing of novel drug combinations early in clinical development. See related commentary by Hernando-Calvo and Garralda, p. 1762. This article is highlighted in the In This Issue feature, p. 1749

Abstract: The RET proto-oncogene encodes a receptor tyrosine kinase that is activated by gene fusion in 1%–2% of non–small cell lung cancers (NSCLC) and rarely in other cancer types. Selpercatinib is a highly selective RET kinase inhibitor that has recently been approved by the FDA in lung and thyroid cancers with activating RET gene fusions and mutations. Molecular mechanisms of acquired resistance to selpercatinib are poorly understood. Patients and Methods: We studied patients treated on the first-in-human clinical trial of selpercatinib (NCT03157129) who were found to have MET amplification associated with resistance to selpercatinib. We validated MET activation as a targetable mediator of resistance to RET-directed therapy, and combined selpercatinib with the MET/ALK/ROS1 inhibitor crizotinib in a series of single patient protocols (SPP). Results: MET amplification was identified in posttreatment biopsies in 4 patients with RET fusion–positive NSCLC treated with selpercatinib. In at least one case, MET amplification was clearly evident prior to therapy with selpercatinib. We demonstrate that increased MET expression in RET fusion–positive tumor cells causes resistance to selpercatinib, and this can be overcome by combining selpercatinib with crizotinib. Using SPPs, selpercatinib with crizotinib were given together generating anecdotal evidence of clinical activity and tolerability, with one response lasting 10 months. Conclusions: Through the use of SPPs, we were able to offer combination therapy targeting MET-amplified resistance identified on the first-in-human study of selpercatinib. These data suggest that MET dependence is a recurring and potentially targetable mechanism of resistance to selective RET inhibition in advanced NSCLC.

Abstract: The RET receptor tyrosine kinase proto-oncogene is activated by somatic or germline mutations in a majority of medullary thyroid cancers (MTC). However, treatment of MTC has been challenging due to the lack of effective and tolerable RET-specific therapy, thus testing tumors for the presence of somatic RET mutation has not been warranted. In a first-in-human, phase 1/2 clinical trial (LIBRETTO-001, NCT03157128), selpercatinib (LOXO-292), an investigational, highly selective, potent small molecule RET kinase inhibitor, demonstrated significant and durable anti-tumor activity in patients with advanced RET-mutant MTC or with diverse RET fusion-positive cancers (1). Among the primary analysis set of patients with RET-mutant MTC previously treated with cabozantinib and/or vandetanib (N=55), the investigator-assessed objective response rate (ORR) per RECIST 1.1 was 56% (95% CI 42.3-69.7, n=31/55). Duration of response was not reached with a 10.6-months median follow-up (data cutoff date 17-Jun-2019). Here, we evaluated investigator-assessed ORR per RECIST 1.1 and clinical benefit rate (CBR) in this previously treated patient population by RET alteration and by germline or somatic testing used for enrollment. The ORR remained consistent across subgroups with RET M918T (49%, 95% CI 30.8-66.5, n=16/33), V804M/L gatekeeper mutations (60%, 95% CI 14.7-94.7, n=3/5), extracellular cysteine mutations (43%, 95% CI 9.9-81.6, n=3/7), other mutations (90%, 95% CI 55.5-99.7, n=9/10), and germline (50%, 95% CI 6.8-93.2, n=2/4) or somatic (57%, 95% CI 42.2-70.7, n=29/51) testing. The CBR, defined as the proportion of patients with best overall response of confirmed complete response, confirmed or unconfirmed partial response, or stable disease lasting 16 weeks or more, in this patient set was 87% (95% CI 75.5-94.7, n=48/55). The CBR remained consistent across subgroups with RET M918T (88%, 95% CI 71.8-96.6, n=29/33), V804M/L gatekeeper mutations (80%, 95% CI 28.4-99.5, n=4/5), extracellular cysteine mutations (71%, 95% CI 29.0-96.3, n=5/7), other mutations (100%, 95% CI 69.2-100.0, n=10/10), and germline (75%, 95% CI 19.4-99.4, n=3/4) or somatic (88%, 95% CI 76.1-95.6, n=45/51) testing. The primary technologies used to identify RET alterations were tumor next-generation sequencing (n=43) and polymerase chain reaction (n=9). As previously reported, selpercatinib was well tolerated with an acceptable safety profile (1). These results indicate broad anti-tumor activity for selpercatinib in patients with RET-mutant MTC irrespective of the specific RET mutation, and support implementation of RET mutation testing for patients with advanced MTC, including somatic testing, to identify patients who may benefit from selpercatinib. Reference: (1) Wirth et al., Ann Oncol. 2019 Oct; 30(supplement 5): v933.