PB1921: A RANDOMIZED, DOUBLE-BLIND, PHASE 3 STUDY OF TAMIBAROTENE/AZACITIDINE VERSUS PLACEBO/AZACITIDINE IN NEWLY DIAGNOSED ADULT PATIENTS SELECTED FOR RARA-POSITIVE HR-MDS (SELECT-MDS-1)

Abstract

Background: A novel genomically defined subset of higher-risk MDS (HR-MDS) patients with an actionable target characterized by overexpression of RARA has been identified (McKeown 2017). Approximately 30% of HR-MDS patients are RARA-positive (RARA+) by a blood-based biomarker test (Vigil, 2017). This RARA positivity enables biologically targeted therapy with tamibarotene (formerly SY-1425), an oral selective RARα agonist with potential to provide clinical benefit for HR-MDS patients, irrespective of mutation or cytogenetic risk. Initial Phase 2 clinical data in RARA+ relapsed/refractory HR-MDS patients treated with single agent tamibarotene showed myeloid differentiation, improved blood counts, and reduced bone marrow blasts, including one patient who achieved marrow complete remission with hematologic improvement (Jurcic 2017). Tamibarotene in combination with azacitidine (aza) demonstrated high complete response rates with rapid onset of response in RARA+ newly diagnosed (ND) unfit AML patients, including those with low blast count (≤ 30%) AML, and a majority of patients achieved or maintained transfusion independence (de Botton 2020). Tamibarotene plus aza was generally well tolerated with no increase in myelosuppression compared to single agent aza (de Botton 2020). HR-MDS and AML have common cytogenetic abnormalities and gene mutations present in the blast populations in each condition. The historical precedent demonstrating similar clinical outcomes among patients with HR-MDS and AML, particularly low blast count AML (Estey 2021), supports further development of the combination of tamibarotene plus aza in the HR-MDS population, with the opportunity to improve upon the clinical outcomes of standard of care treatment with hypomethylating agents (HMAs). Aims: This is a global Phase 3, multi-center, randomized, double-blind, placebo-controlled study comparing the activity of tamibarotene plus aza, to placebo plus aza in RARA+ patients with ND HR-MDS. The primary objective is to compare the complete remission rate of tamibarotene plus aza vs. placebo plus aza, with secondary objectives to compare objective response rate, event-free survival, overall survival, transfusion independence rate, time to and duration of initial and complete responses, and safety. Methods: Patients must be RARA+ based on the investigational biomarker test, ND with HR-MDS by WHO classification (Arber 2016), classified by IPSS-R risk category as very high, high, or intermediate risk with a bone marrow blast count > 5% at study entry. Patients suitable for allogeneic HSCT at the time of screening, or who received prior treatment for MDS with any HMA, chemotherapy or allogeneic HSCT are excluded. Aza will be administered at 75 mg/m2 IV/SC daily on days 1-7 (or days 1-5, 8-9) followed by tamibarotene/placebo at 6 mg BID orally days 8-28 of each 28-day cycle. Response will be assessed per the modified IWG MDS criteria (Cheson 2006). Results: Approximately 190 patients will be randomized 2:1 and stratified by IPSS-R risk group and geographic region, providing 90% power to detect the difference in CR rates between the experimental and control arms, respectively, with one-sided alpha of 0.025. Summary/Conclusion: The SELECT-MDS-1 trial opened to enrollment in February 2021, recruitment is ongoing, with sites located in North America, Israel, and Europe (NCT04797780).