Gemtuzumab Ozogamicin In Combination With Vorinostat and Azacitidine In Older Patients With Relapsed Or Refractory Acute Myeloid Leukemia (AML): Final Results From A Phase 1/2 Study

Epigenetic therapeutics such as the histone deacetylase (HDAC) inhibitor, vorinostat, and the DNA methyltransferase (DNMT) I inhibitor, azacitidine, sensitize AML cells in vitro to the CD33-targeting immunoconjugate, gemtuzumab ozogamicin (GO). This observation, together with the improved clinical activity when HDAC inhibitors are used with DNMT inhibitors, prompted a phase 1/2 study (NCT00895934) of GO with vorinostat and azacitidine for primary refractory AML or AML in first relapse (remission duration ≤12 months) requiring 1^stsalvage therapy.

Patients aged ≥50 years were eligible if they had an ECOG performance status of 0-3 and had adequate organ function. Patients with prior hematopoietic stem cell transplantation (HCT) were eligible if relapse occurred 6-12 months post-transplant. Excluded were patients with a second active malignancy, prior treatment with any of the study drugs, or central nervous system disease. Hydroxyurea was given to reduce the total white blood cell count to <25,000/μL before treatment. If there was persistent leukemia on day 15, the first cycle was repeated, and patients came off study if, after repetition, there was disease progression. In all other patients, a second cycle was begun if peripheral blood counts had recovered (blood count recovery was not required for patients with persistent leukemia) and all toxicities had resolved to ≤grade 2. Patients came off study if a partial remission was not achieved by the end of cycle 3, or if a complete remission (CR) or CR with incomplete peripheral blood count recovery (CRi) was not achieved by the end of cycle 6. During phase 1, patients were assigned to therapy according to a “3+3” study design; dose-limiting toxicity (DLT) was defined as: 1) any grade 3 non-hematologic toxicity lasting >48 hours that results in >7 day delay of the subsequent treatment cycle, with the exception of febrile neutropenia or infection; 2) any grade ≥4 non-hematologic toxicity, with the exception of febrile neutropenia/infection or constitutional symptoms if recovery to grade ≤2 within 14 days; and 3) prolonged myelosuppression (platelet count <20,000/μL and/or absolute neutrophil count <500/μL at day 42 after treatment in patients without evidence of persistent leukemia). During phase 2, a Simon minimax two-stage design was to monitor whether a response rate of 0.34 was reached, with type I and II errors set at 0.1 and assuming a historical CR rate of 17% in these patients.

52 eligible patients, median age 64.8 (range, 50.2-78.9) years, with either primary refractory disease (n=29) or first relapse (n=23; median duration of first CR: 3 months) were enrolled and received a median of 2 (range, 1-4) cycles of therapy. During dose escalation, 1 DLT (death due to sepsis and respiratory failure) occurred at the 4^th tested dose level after cycle 1, identifying vorinostat (400 mg/day orally from days 1-9), azacitidine (75 mg/m²/day IV or SC from days 1-7), and GO (3 mg/m²/day IV on days 4 and 8) as the maximum tolerated dose (MTD). A total of 43 patients received therapy at the MTD level. Ten of these achieved CR, while 8 achieved CRi, for a CR/CRi rate of 18/43 (41.9%; exact 95% CI: 27.0-57.9%). Thirteen of the 18 patients that achieved CR/CRi were taken off protocol to receive additional, more intensive consolidative chemotherapy, including HCT (n=12). Of these 18 patients, 5 relapsed after a median of 122 (38-146) days, while 3 died while in remission after a CR duration of 46, 97, and 130 days, and 10 are in ongoing remission after a median of 326 (68- 710) days, respectively. Median overall survival for the 18 patients achieving CR/CRi was significantly longer than for those 21 patients who failed therapy but lived at least 29 days (i.e. did not experience treatment-related mortality) after treatment initiation (224.5 [range 70-798]) vs. 95 [36-900] days, log rank P-value=0.0023). Four patients died within 28 days of treatment initiation. Besides grade 3-4 cytopenias, infectious complications were the most common grade ³3 adverse events. Only 1 patient developed possible liver toxicity (abdominal pain/distention and mild ascites) after 4 cycles of therapy, although bilirubin and transaminases were only minimally elevated and doppler studies were unremarkable.

Our study indicates that GO in combination with vorinostat and azacitidine has encouraging anti-AML activity in older adults with relapsed/refractory AML.

Walter:Amgen, Inc: Research Funding; Seattle Genetics, Inc: Consultancy, Research Funding. Off Label Use: Use of vorinostat/azacitidine/gemtuzumab ozogamicin for the treatment of relapsed/refractory AML.