Epigenetic Targeting Via Transcriptional Inhibition of DNA Methyltransferase: a Phase I Study of Bortezomib in Combination with 5-Azacytidine in Adults with Relapsed or Refractory Acute Myeloid Leukemia (AML).

Hypomethylating agents have significant clinical activity in myelodysplastic syndromes (MDS) and AML. In AML, we recently demonstrated a novel epigenetic mechanism of action for the proteasome inhibitor bortezomib (Liu, Blood 2008). Bortezomib induced hypomethylation of leukemic cells in vitro and in vivo via depletion of the Sp1/NF-kB transcriptional activation complex on the DNA methyltransferase 1 (DNMT1) gene promoter, which results in down-regulation of DNMT1 mRNA and enzyme, DNA hypomethylation and re-expression of otherwise hypermethylated target genes. Based on this preclinical work, we designed a phase I dose escalation study of 5-azacytidine (AZA) in combination with bortezomib in AML.

Adults with relapsed or refractory AML by WHO criteria and preserved organ function with ECOG ≤2 were eligible. Previous decitabine or AZA was permitted. Patients received AZA at 75mg/m² IV daily for days (d) 1-7. Bortezomib was gradually dose escalated–dose level 1 (DL 1): 0.7mg/m² by IV push given immediately after AZA on d 2 and 5; DL 2: 0.7mg/m² on d 2, 5, 9, and 12; DL 3: 1.0mg/m² on d 2, 5, 9, and 12; and DL 4: 1.3mg/m² on d 2, 5, 9, and 12. Cycles were repeated every 28 d, regardless of count recovery or response at least until 3 cycles were administered. Responses were graded by International Working Group criteria for AML (Cheson, JCO 2003). Bortezomib was discontinued after 3 cycles if no objective response of complete remission (CR), CR with incomplete count recovery (CRi), or partial remission (PR) was achieved, but AZA could be continued beyond this timepoint in the absence of disease progression. For responding patients, 12 or more cycles of therapy were permitted. Dose limiting toxicities (DLT) were assigned for cycle 1 of therapy. Given the high likelihood of infection in this population regardless of therapy, infection was not considered a DLT. Six additional patients were treated at the recommended phase 2 dose (RP2D).

23 patients were enrolled with a median age of 65 years (range, 42-81) and had received a median of 2 prior inductions (range, 1-5). Median presenting WBC was 3,700/uL (500-59,100/uL); median BM blast was 26% (2-93%). 14 patients were refractory to last therapy received, including 4 with primary refractory AML. 9 patients had relapsed disease; all but 2 of these had prior CR duration <1 year. Patients received a median of 2 cycles of study therapy (range, 1-12+ cycles). Dose escalation was halted once the target bortezomib dose was reached; the RP2D was AZA at 75mg/m² d 1-7 plus bortezomib 1.3mg/m² d, 2, 5, 9, 12. Though no toxicities were considered to be DLT in this study, infection and/or febrile neutropenia were universal. Death within 8 weeks occurred in 5 patients (22%) due to pneumonia (1), sepsis (1), or progressive disease (3). Two patients had discontinuation of bortezomib after 2 cycles due to Grade 3 neuropathy; only 1 patient received bortezomib beyond 3 cycles. In 3 patients without objective response (and with no progression), AZA alone was continued after 3 cycles of combination therapy; each reported a subjective improvement in fatigue without bortezomib. Overall, the objective response rate was 26% (6/23). Responses were as follows: 3- CR, 2- CRi, and 1-PR. One CRi patient (in cytogenetic remission also) who discontinued study treatment after 2 cycles due to unrelated trauma subsequently had complete count recovery, but a repeat marrow examination was not performed. Three patients went on to allogeneic transplantation due to response achieved. Response followed the typical pattern of azanucleoside activity, requiring more than one cycle of therapy; the median number of cycles to initial response was 2 (range, 1-5). 5/6 responders had response to combination therapy; one patient responded following 5 cycles of treatment, the last 2 cycles with AZA as a single agent.

The combination of 5-azacytidine and bortezomib is well tolerated and active in this cohort of relapsed or refractory AML patients. Additional studies to further elucidate the role of proteasome inhibition as a mediator of hypomethylating activity in AML are warranted. Correlatives studies are ongoing.

Blum:Celgene: Research Funding.