A Novel Regimen for Acute Myeloid Leukemia with MLL Partial Tandem Duplication: Results of a Phase 1 Study NCI 8485

Background: MLL partial tandem duplication (MLL PTD) occurs in approximately 5-8% of patients with acute myeloid leukemia (AML) and is associated with an adverse prognosis. Our group has published that the MLL wild type (WT) allele is epigenetically silenced in MLL PTD; we showed that re-expression of this gene can be induced with methyltransferase (DNMT) and/or histone deacetylase (HDAC) inhibitors. Further, re-expression of MLL WT following combined decitabine and HDAC inhibitor treatment sensitized MLL PTD myeloid leukemia cells to chemotherapy in vitro. We hypothesized that epigenetic silencing of the MLL WT contributes to MLL PTD-associated leukemogenesis and that its pharmacologic re-expression with DNMT and HDAC inhibitors would activate apoptotic mechanisms important for chemo-response in the clinic. We aimed to develop a regimen to be tested in this unique molecular subset of disease. Because of the relatively low frequency of MLL PTD AML, this dose finding study was conducted in relapsed/refractory (R/R) AML regardless of molecular subtype but was enriched for MLLPTD.

Methods:In this phase 1 study, adults aged 18-59 years with R/R AML, ECOG 0-2, and preserved organ function were enrolled. Patients received decitabine 20mg/m² daily on days 1-10 and vorinostat 400mg daily on days 5-10 for all dose levels. Dose-escalated cytarabine was given on days 12, 14, 16 (six doses) according to the following schedule: dose level (DL) 1, 1.5g/m²/q12hr; DL 2, 2g/m²/q12hr; DL 3, 2.5g/m²/q12hr; and DL 4, 3g/m²/q12hr. Standard method 3+3 phase I design was used with the primary objective to determine the maximum tolerated dose and define specific toxicities with this combination therapy, in order to ultimately develop a regimen for MLLPTD AML.

Results:Seventeen adults with R/R AML and median age of 46 years (range, 21-59 years) enrolled. The median number of prior induction therapies was 2 (range, 1-4). European LeukemiaNet (ELN) genetic risk classification frequencies were: favorable (n=2), intermediate-I (n=3), intermediate-II (n=5), and adverse (n=7), respectively. Four patients had MLL PTD. A total of 6 patients were treated at DL 1 with no non-hematologic dose limiting toxicity (DLT). DL 1 was expanded after two patients experienced prolonged but uncomplicated myelosuppression. Since both patients achieved complete remission (CR) shortly after passing the day 42 DLT cut off for hematologic recovery, the protocol was amended to allow further time for count recovery (up to 56 days). Three patients each were treated on DL 2 and 3; 5 patients were treated on DL 4 with no other DLTs observed. Diarrhea, nausea, fatigue, febrile neutropenia, and elevated ALT were the most common toxicities (any grade, regardless of attribution), occurring in 41%, 29%, 29%, 35%, and 35% of patients, respectively, but none were DLTs. In regards to ≥ Grade 3 toxicities, febrile neutropenia and catheter-related infections were most common at 35% and 24%. Significant mucositis was not observed. DL 4 was the recommended phase 2 dose (RP2D). CR or CR with incomplete count recovery (CRi) was observed in 6/17 patients (35%, 5 with CR). Of 6 responders, all (n=4) patients with abnormal karyotype achieved cytogenetic remission. The median number of prior therapies for patients achieving CR/CRi was 2 (range, 1-3). Four patients subsequently received allogeneic transplantation. Of the four patients known to have MLL PTD mutations, two responded (1 with CR and 1 with CRi). It is interesting to note that the two patients with MLL PTD mutations who did not respond to treatment also had FLT3-ITD mutations, while this mutation was absent in the two responding patients who had MLLPTD.

Conclusions: We successfully determined the RP2D for this novel treatment regimen. The regimen had modest toxicities beyond uncomplicated (though prolonged) myelosuppression, and we propose that the study provides a framework for larger efficacy studies for AML patients with the uncommon but biologically distinct molecular feature of MLLPTD.

Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number U01CA076576. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Also supported by P30 CA016058/CA/NCI.