SEL24/MEN1703 Inhibits PIM/FLT3 Downstream Target in Acute Myeloid Leukemia (AML) Patients: Results of the Pharmacodynamics (PD) Assay and Genomic Profiling in the First-in-Human Diamond-01 Trial
Authors: Paoli Alessandro , Bellarosa Daniela , Bressan Alessandro , Bertolini Francesco , Solomon Scott R. , Montesinos Pau , Mukherjee Sudipto , Strickland Stephen A , Marconi Giovanni , Santoro Armando , Walter Roland B. , Cook Rachel J. , Calbacho Maria , Vives Susana , Fazal Salman , Ravandi Farhad , Brzozka Krzysztof , Rzymski Tomasz , Mazan Milena , Baldini Simone , Ravenni Niccolò , Binaschi Monica , Laurent Dirk , Pellacani Andrea 
Published: November 2021

Abstract
BACKGROUND. SEL24/MEN1703 is a first-in-class, orally available, dual PIM/FLT3 kinase inhibitor investigated in unselected AML patients in the First-in-Human, Dose Escalation (DE) and Cohort Expansion (CE) CLI24-001 trial (DIAMOND-01, ClinicalTrials.gov identifier: NCT03008187). The study has completed both the DE and CE part showing an acceptable safety profile up to the recommended dose (RD), with initial evidence of single agent efficacy particularly clustering in patients with IDH mutant disease. Previous studies conducted on a limited number of patients in the DE cohort indicated pS6, a downstream target in the PIM/FLT3 signaling pathway, as a biomarker of target engagement.
AIM. To assess the relevance of pS6 as a pharmacodynamic (PD) biomarker in SEL24/MEN1703-treated patients. Moreover, patients were characterized on the basis of genetic profile to identify mutations which might cluster in patients' samples that demonstrated significant target engagement. Finally, longitudinal assessment of Variant Allelic Frequency (VAF) has been implemented.
METHODS. S6 phosphorylation has been longitudinally monitored in the DIAMOND-01 study through an optimized assay for multiparametric analysis of phospho-protein activation. The assay allows a quantitative assessment of pS6 at the single cell level among blast cells as well as the identification of blast subpopulations in peripheral blood (PB). CD34+ Blast cells % was monitored to assess whether target engagement translated into blast reduction. Genotype analysis was performed by NGS using the Oncomine Myeloid Research Assay.
RESULTS. PB samples from DE and CE patients, treated at 125 mg (RD) were analyzed, for a total of n= 27 assessable patients. At screening, we observed a heterogeneous positivity for pS6 marker in blast cells (range: 0.9%-79%), consistent with the unselected AML patient population recruited in the trial. Overall, 14/27 (51.8%) patients showed pS6 inhibition in blast cells at the end of Cycle 1 in comparison with screening (range: 70%-94%) (Figure 1). When SEL24/MEN1703 treatment continued beyond Cycle 1 (n=11 patients), pS6 inhibition was maintained and long-lasting in 6/11 (54.5%) patients. While pS6 inhibition did not translate into CD34+ blast decrease in all patients, long-lasting pS6 inhibition was observed in 2 out of 3 responding patients (including CRi as best response) evaluable for pS6 levels. Genetic characterization of these two patients treated at 125 mg (RD) showed that they harbored IDH mutations.
CONCLUSIONS. The longitudinal PD assessment through the modulation of pS6 activation by flow cytometry confirmed that meaningful target engagement was achieved in more than 50% of patients treated with SEL24/MEN1703 at the RD. In most patients, including 2 out of 3 responders evaluable for pS6, its inhibition was maintained during the entire treatment. Preliminary genotyping showed that responding patients with strong pS6 inhibition harbored IDH mutations. In-depth analysis of genomic profiling and of the longitudinal assessment of VAF is ongoing in order to identify potential correlation with pS6 modulation and blast depletion in specific AML subsets, with the aim to define patient population(s) more likely to respond to SEL24/MEN1703.
Figure 1. pS6 (%pS6*MFI) assessment in peripheral blast cells at screening and at C1D14-4H in CE patients treated at RD of 125 mg.
Figure 1 Figure 1.

Disclosures
Paoli: Menarini Group: Current Employment. Bellarosa: Menarini Group: Current Employment. Bressan: Menarini Group: Current Employment. Bertolini: Gilead: Research Funding; Emercell: Research Funding. Montesinos: Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Stemline/Menarini: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics: Consultancy; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Glycomimetics: Consultancy; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Mukherjee: Eusa Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Teaching and Speaking; McGraw Hill: Honoraria, Other: Editor of Hematology Oncology Board Review (ongoing); Celgene Corporation: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Research/Independent Contractor, Research Funding; AAMDS in Joint Partnership with Cleveland Clinic Taussig Cancer Institute: Honoraria; Genentech: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Research Funding; BioPharm: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research/Independent Contractor, Research Funding; Bristol-Myers Squibb Co.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Acceleron: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Partnership for Health Analytic Research: Honoraria. Strickland: AbbVie, ArcherDx, Genentech, Incyte, Kura Oncology, Novartis, Pfizer, and Syros: Consultancy; Sunesis: Research Funding. Santoro: Takeda: Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy; Arqule: Consultancy, Speakers Bureau; Roche: Speakers Bureau; AbbVie: Speakers Bureau; Eli-Lilly: Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Speakers Bureau; Sandoz: Speakers Bureau; Eisai: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Speakers Bureau; Amgen: Speakers Bureau; Novartis: Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Walter: Jazz: Research Funding; Pfizer: Consultancy, Research Funding; Selvita: Research Funding; Amphivena: Consultancy, Other: ownership interests; Agios: Consultancy; Astellas: Consultancy; BMS: Consultancy; Genentech: Consultancy; Janssen: Consultancy; Kite: Consultancy; Macrogenics: Consultancy, Research Funding; Immunogen: Research Funding; Celgene: Consultancy, Research Funding; Aptevo: Consultancy, Research Funding; Amgen: Research Funding. Fazal: Taiho: Consultancy, Honoraria, Speakers Bureau; Stemline: Consultancy, Honoraria, Speakers Bureau; Sanofi Genzyme: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Karyopharm: Consultancy, Honoraria, Speakers Bureau; Jazz Pharma: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria, Speakers Bureau; Gilead: Consultancy, Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau; Agios: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau; Tolero: Consultancy. Ravandi: Novartis: Honoraria; AstraZeneca: Honoraria; Xencor: Honoraria, Research Funding; Astex: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Taiho: Honoraria, Research Funding; Prelude: Research Funding; Agios: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Syros Pharmaceuticals: Consultancy, Honoraria, Research Funding. Brzozka: Ardigen: Current Employment, Membership on an entity's Board of Directors or advisory committees; Ryvu Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Selvita SA: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Rzymski: Ryvu Therapeutics: Current Employment, Current equity holder in publicly-traded company. Mazan: Ryvu Therapeutics: Current Employment; Selvita SA: Current Employment. Baldini: Menarini Group: Current Employment. Ravenni: Menarini Group: Current Employment. Binaschi: Menarini Group: Current Employment. Laurent: Menarini Group: Current Employment. Pellacani: Menarini Group: Current Employment.