Safety and efficacy of gemtuzumab ozogamicin and venetoclax in patients with relapsed or refractory CD33+ acute myeloid leukemia: A phase Ib study.

Abstract

TPS7566

Background: AML is predominantly a disease of the elderly, yet outcomes remain dismal, especially 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)–that is linked to the cytotoxin calicheamicin. Recognized mechanisms of GO resistance include decreased (or aberrant) blast CD33 expression, upregulation of p-glycoprotein (re-exports calicheamicin), and decreased mitochondrial apoptosis. GO-induced apoptosis depends on pro-apoptotic Bax and Bak and is inhibited by overexpression of anti-apoptotic BCL-2 and BCL-XL. Venetoclax (VEN) is a BH3 mimetic, binding BCL-2, dislodging its binding to Bak/Bax, thus facilitating apoptosis. LSC uniquely overexpress BCL-2, however VEN 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 and CD33 expression (& sequencing for isoforms), MRD measurement at post-therapy timepoints using digital drop PCR technology, and quality of life assessments (EORTC QLQ-C30, FACT-Fatigue). Methods: 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, ≤2 lines of prior therapy, no prior use of GO or VEN, no previous VOD, no BMT within 2 months, no CNS disease, and no 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/m ² infused d 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/m ² on days 1 and 4 (Cycle 2). If BMT not applicable, and then in CR/CRi or PR (as above), 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, anti-leukemic activity, characterization of AEs, and estimates of RFS, EFS, and OS. This study is currently open and has to date enrolled 2 pts. Clinical trial information: NCT04070768 .