Phase Ib study of the safety and efficacy of Gemtuzumab Ozogamicin (GO) and Venetoclax in patients with relapsed or refractory CD33+ acute myeloid leukemia: Big Ten Cancer Research Consortium BTCRC-AML17-113

Arain, S.; Patel, P.; Sweiss, K.; Parkin, B.; Konig, H.; Calip, G.; Yavuz, B. G.; Quigley, J.

Background:AML is predominantly a disease of the elderly, yet outcomes remain dismal, particularly for relapsed/refractory (R/R) AML patients (pts). Gemtuzumab Ozogamicin (GO) is a monoclonal antibody targeting CD33-commonly expressed on AML blasts, and, critically, AML stem cells (LSC)-linked to the cytotoxin calicheamicin. GO resistance mechanisms include (i) decreased/aberrant blast CD33 expression, (ii) p-glycoprotein export of calicheamicin, and (iii) apoptosis resistance due to deficient activation of mitochondrial outer membrane permeabilization, a process highly dependent on BCL-2 expression. GO-induced apoptosis depends on the pro-apoptotic proteins Bax and Bak and is inhibited by overexpression of the anti-apoptotic proteins BCL-2 or BCL-XL. Venetoclax (VEN) is a BH3 mimetic, binding BCL-2, dislodging its binding to Bak/Bax, and thus facilitating apoptosis. LSC overexpress BCL-2, however VEN monotherapy is not effective in AML, as resistance develops rapidly. Hypothesis: VEN targeting of BCL-2 proteins that protect LSC from GO-induced apoptosis will synergistically increase GO efficacy. Correlative studies include pre-treatment AML blast BH3 profiling, CD33 expression (including sequencing for isoforms), and BCL-2, BCL-XL, and MCL-1 protein levels;MRD measurement at post-therapy time points using digital drop PCR technology;and quality of life assessments (EORTC QLQ-C30, FACT-Fatigue) MethodsThis is a single arm, open-label, multi-center (BTCRC), dose-escalation phase Ib study of combination of VEN and GO in R/R AML pts (18-75y), using a 3+3 design. Major eligibility: ECOG 0-2, adequate organ function, CD33+ in ≥ 20% AML blasts, ≤ 3 lines of prior therapy, and no prior use of GO or VEN, previous VOD, BMT within 2 months, CNS disease, or history of HIV. Induction: 3-day VEN ramp-up to the target dose of 200 (cohort i), 400 (ii), or 600 (iii) mg daily x 28 d, with GO 3mg/m2 infused days 1, 4, and 7. If CR/CRi achieved, pts proceed to BMT if applicable, otherwise, if in CR/CRi (provided ANC > 1000, plts > 100K) or PR (regardless of counts), they are consolidated with VEN at the prescribed dose x 28d and GO 3mg/m2 on days 1 and 4 (Cycle 2). If BMT not applicable, and pt remaining in CR/CRi or PR (as above), then proceed to VEN alone as Maintenance in cycles 3+ until progression or toxicity. The primary endpoint is MTD of VEN with GO. Secondary endpoints include ORR, antileukemic activity, characterization of AEs, and estimates of RFS, EFS, and OS. Progress: This study is currently open to its second dosing cohort and has enrolled 5 pts to date. No dose-limiting toxicities have been encountered. However, the COVID-19 pandemic has had a negative impact on enrollment, which is expected to improve as vaccinations expand. ClinicalTrials.gov NCT04070768.