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501 Results from a First-in-Human, Proof-of-Concept Phase 1 Trial in Pretreated B-Cell Malignancies for Loxo-305, a Next-Generation, Highly Selective, Non-Covalent BTK Inhibitor

Program: Oral and Poster Abstracts
Type: Oral
Session: 642. CLL: Therapy, excluding Transplantation: BTK Inhibitors and CAR T Cells in CLL
Hematology Disease Topics & Pathways:
Diseases, Leukemia, Follicular Lymphoma, Adult, CLL, Marginal Zone Lymphoma, Therapies, Non-Biological, Mantle Cell Lymphoma, Non-Hodgkin Lymphoma, DLBCL, B-Cell Lymphoma, Study Population, Lymphoid Malignancies
Sunday, December 8, 2019: 5:00 PM
Hall D, Level 2 (Orange County Convention Center)

Anthony R. Mato, MD MSCE1,2, Ian W. Flinn, MD, PhD3, John M. Pagel, MD, PhD, DSc4, Jennifer R Brown, MD, PhD5, Chan Y. Cheah6, Catherine C. Coombs, MD7, Manish R. Patel, MD8*, S. Michael Rothenberg, MD, PhD9, Donald E. Tsai, MD, PhD9, Nora C. Ku, MD9* and Michael L. Wang, MD10

1Center for CLL, Memorial Sloan-Kettering Cancer Center, New York, NY
2CLL Program, Leukemia Service, Hematologic Malignancies Division, Memorial Sloan Kettering Cancer Center, New York, NY
3Sarah Cannon Research Institute, Nashville, TN
4Center for Blood Disorders and Stem Cell Transplantation, Swedish Cancer Institute, Seattle, WA
5Dana-Farber Cancer Institute, Boston, MA
6NW Cancer Centre, Perth, WEA, Australia
7Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC
8Florida Cancer Specialists / Sarah Cannon Research Institute, Sarasota, FL
9Loxo Oncology, Stamford, CT
10U.T. M.D. Anderson Cancer Center, Houston, TX

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 > 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: Janssen: Consultancy; Acerta: Consultancy; Gilead: Research Funding; Pharmacyclics: Consultancy, Research Funding; AstraZeneca: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Sunesis: Consultancy, Research Funding; Celgene: Consultancy; Johnson & Johnson: Consultancy, Research Funding; TG Therapeutics: Consultancy, Other: DSMB member , Research Funding; LOXO: Consultancy, Research Funding; DTRM Biopharma: Research Funding; Genentech: Consultancy, Research Funding. Flinn: 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; 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; AbbVie, Seattle Genetics, TG Therapeutics, Verastem: Consultancy; 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; F. Hoffmann-La Roche Ltd: Research Funding. Pagel: AstraZeneca: Consultancy; Gilead Sciences: Consultancy; Pharmacyclics: Consultancy. Brown: Genentech/Roche: Consultancy; Gilead: Consultancy, Research Funding; Juno/Celgene: Consultancy; Kite, a Gilead Company: Consultancy, Research Funding; Loxo: Consultancy, Research Funding; Novartis: Consultancy; Pfizer: Consultancy; Pharmacyclics: Consultancy; Sunesis: Consultancy; TG Therapeutics: Consultancy; Verastem: Consultancy, Research Funding; Sun Pharmaceuticals: Research Funding; Janssen: Honoraria; Teva: Honoraria; Morphosys: Other: Data safety monitoring board; Invectys: Other: Data safety monitoring board; Octapharma: Consultancy; AbbVie: Consultancy; Acerta Pharma: Consultancy; AstraZeneca: Consultancy; BeiGene: Consultancy; Catapult Therapeutics: Consultancy; Dynamo Therapeutics: 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: Covance: Consultancy; Cowen & Co.: Consultancy; Dedham Group: Consultancy; H3 Biomedicine: Honoraria; Loxo: Honoraria; Medscape: Honoraria; 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.

*signifies non-member of ASH