Combining the Allosteric ABL1 Inhibitor Asciminib (ABL001) with Ponatinib Suppresses Emergence of and Restores Efficacy Against Highly Resistant BCR-ABL1 Compound Mutants
Authors: Eide Christopher A. , Zabriskie Matthew S. , Savage Samantha L. , Antelope Orlando , Vellore Nadeem A. , Than Hein , Reister Schultz Anna , Clair Phillip M. , Bowler Amber D. , Pomicter Anthony D. , Yan Dongqing , Senina Anna V. , Wang Qiang , Kelley Todd W. , Szankasi Philippe , Heinrich Michael C. , Tyner Jeffrey W. , Rea Delphine , Cayuela Jean-Michel , Kim Dong-Wook , Tognon Cristina E. , O'Hare Thomas , Druker Brian J. , Deininger Michael W. 
Published: February 2020

BCR-ABL1 point mutation-mediated resistance to tyrosine kinase inhibitor (TKI) therapy in Philadelphia chromosome-positive (Ph+) leukemia is effectively managed with several approved drugs, including ponatinib for BCR-ABL1T315I-mutant disease. However, for those patients who acquire BCR-ABL1 compound mutations (multiple mutations in the same BCR-ABL1 molecule), therapy options are extremely limited. Asciminib (formerly ABL001) is a recently developed allosteric inhibitor targeting the myristoyl-binding pocket of ABL1 kinase with activity against many imatinib-resistant BCR-ABL1 mutants, including T315I. We profiled asciminib against a panel of BCR-ABL1 single and compound mutants expressed in murine Ba/F3 cells. Asciminib potently inhibited the proliferation of most imatinib-resistant BCR-ABL1 point mutations tested, with the notable exception of substitutions at position F359, which conferred high levels of resistance. Consistent with this finding, next-generation sequencing of BCR-ABL1 in five patients with evidence of clinical resistance to asciminib revealed three patients with expansion of variants of position F359 on treatment. Cell-based mutagenesis screens starting from Ba/F3 cells expressing native BCR-ABL1 revealed a resistance profile for asciminib largely centered around residues of the myristoyl pocket, with these mutants remaining sensitive to approved ATP-site ABL1 TKIs. Combining asciminib with ATP-site TKIs enhanced target inhibition and suppression of resistant BCR-ABL1 point mutant outgrowth in Ph+ clinical isolates and cell lines. However, despite its unique binding mode, asciminib was ineffective against all tested BCR-ABL1 compound mutants. In contrast, combining asciminib with ponatinib re-sensitized even the problematic, currently untreatable T315I-inclusive compound mutants at clinically achievable concentrations, which was not achieved combining asciminib with other approved ATP-site TKIs. Additionally, the combination of asciminib with ponatinib resulted in suppression of T315I-inclusive compound mutant resistant clones using in vitro mutagenesis screens and significantly prolonged survival compared to either single agent in an in vivo T315I-inclusive compound mutant mouse xenograft model. Molecular dynamics-based structural modeling were performed and offer further insight into the mechanism of this combination's efficacy. Taken together, our findings support combining asciminib with ponatinib as a treatment strategy for improved management and mitigating the emergence of highly resistant BCR-ABL1 compound mutations in patients with Ph+ leukemia.

Disclosures
Heinrich: Deciphera Pharmaceuticals: Consultancy; Blueprint Medicines: Consultancy; Molecular MD: Consultancy, Equity Ownership; Novartis Pharmaceuticals: Consultancy, Patents & Royalties. Tyner:Seattle Genetics: Research Funding; Janssen: Research Funding; Array: Research Funding; Takeda: Research Funding; Syros: Research Funding; Aptose: Research Funding; Incyte: Research Funding; Genentech: Research Funding; Constellation: Research Funding; Petra: Research Funding; Syros: Research Funding; Gilead: Research Funding; Janssen: Research Funding; Seattle Genetics: Research Funding; Aptose: Research Funding; AstraZeneca: Research Funding; AstraZeneca: Research Funding; Constellation: Research Funding; Incyte: Research Funding; Agios: Research Funding; Gilead: Research Funding; Genentech: Research Funding; Petra: Research Funding; Agios: Research Funding; Array: Research Funding; Takeda: Research Funding. Rea:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte Biosciences: Honoraria; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria. Cayuela:Incyte: Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau. Kim:Il-Yang co.: Research Funding; Takeda: Research Funding; Pfizer: Research Funding; Novartis: Research Funding; BMS: Research Funding. Druker:OHSU (licensing fees): Patents & Royalties: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees ; Dana-Farber Cancer Institute (antibody royalty): Patents & Royalties: #2524, antibody royalty; Merck & Co: Patents & Royalties: Dana-Farber Cancer Institute license #2063, Monoclonal antiphosphotyrosine antibody 4G10, exclusive commercial license to Merck & Co; Pfizer: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding; Bristol-Myers Squibb: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Research Funding; Novartis: Other: PI or co-investigator on clinical trial(s) funded via contract with OHSU., Patents & Royalties: Patent 6958335, Treatment of Gastrointestinal Stromal Tumors, exclusively licensed to Novartis, Research Funding; Monojul: Other: former consultant; ICON: Other: Scientific Founder of Molecular MD, which was acquired by ICON in Feb. 2019; Gilead Sciences: Other: former member of Scientific Advisory Board; Celgene: Consultancy; CureOne: Membership on an entity's Board of Directors or advisory committees; Beat AML LLC: Other: Service on joint steering committee; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; The RUNX1 Research Program: Membership on an entity's Board of Directors or advisory committees; Patient True Talk: Consultancy; GRAIL: Equity Ownership, Other: former member of Scientific Advisory Board; Cepheid: Consultancy, Honoraria; Burroughs Wellcome Fund: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Beta Cat: Membership on an entity's Board of Directors or advisory committees, Other: Stock options; ALLCRON: Membership on an entity's Board of Directors or advisory committees; Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Aptose Biosciences: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Pfizer: Research Funding; Aileron Therapeutics: #2573, Constructs and cell lines harboring various mutations in TNK2 and PTPN11, licensing fees , Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Patents & Royalties, Research Funding. Deininger:Sangoma: Consultancy; Fusion Pharma: Consultancy; Ascentage Pharma: Consultancy, Honoraria; Adelphi: Consultancy; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Humana: Honoraria; Incyte: Honoraria; Novartis: Honoraria; Sangamo: Consultancy; TRM: Consultancy; Pfizer: Consultancy, Honoraria, Research Funding; Blueprint: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.