Abstract 119: AR42, a histone deacetylase inhibitor (HDACI), increases microRNA (miR)-29b and sensitizes cells to decitabine (DAC) treatment: A novel epigenetic-targeting approach in acute myeloid leukemia (AML)

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL The outcome of the majority of older AML patients (pts) remains poor despite advances made in both pathogenesis and prognostication. Epigenetic gene silencing by DNA hypermethylation contributes to AML pathogenesis. Recently we reported promising results in older previously untreated AML pts receiving low-dose of hypomethylating agent DAC alone. However these results can be improved upon. In our study pts with higher miR-29b expression were more likely to respond to DAC therapy (P=.02). MiR-29b directly or indirectly targets and downregulates the DNA methyltransferases (i.e. DNMT1, DNMT3A and DNMT3B) and has hypomethylating and tumor suppressor activity in AML. We recently showed that miR-29b is repressed by a Sp1/NFkB/HDAC1 complex, and that the HDACI AR42 can increase miR-29b expression by disrupting this complex in AML. Thus we hypothesized that priming AML cells with AR42 would result in miR-29b upregulation and increased response to DAC in AML pts. Here we showed first that in three AML cell lines i.e. THP-1, NB4 & Kasumi-1, miR-29b is upregulated (1.7, 2.4 & 1.6, fold respectively) as early as 1h after 1 µM AR42 vs DMSO control treatment. Confirming the upregulation of miR-29b by AR42, we next tested if this would sensitize the cells to DAC treatment. Priming THP-1 cells with 1 µM AR42 (for 12h) followed by 2.5 µM DAC treatment (for 24h) decreased the cell viability (measured by MTS assays) by 7-fold when compared to cells that were treated with the reverse drug sequence i.e., 2.5 µM DAC (for 12h) followed by 1 µM AR42 (for 24h). The decrease of cell viability was also higher than for each drug alone; 1 µM AR42 (for 12h) followed by 2.5 µM DAC treatment (for 24h) decreased the cell viability by 5-fold compared to 1 µM AR42 alone (for 36h) and 2-fold compared to 2.5 µM DAC therapy alone (for 36h). To test this effect in vivo we utilized an AML model constituted by FDCP1 cells expressing mutant KIT (KITmut) that we engrafted in NOD/SCID mice. Mice developed AML at 4 weeks from inoculation. The sequential administration of AR42 followed by DAC resulted in longer overall survival (P<.001) of FDCP1-KITmut mice (60% alive at day 120) compared to mice treated with DAC followed by AR42 or either drug alone (0% alive at day 120 in each group). The sequence of “HDACIs followed by DAC” is novel as to our knowledge only the sequence of “hypomethylating agents followed by HDACIs” has been explored in the clinic. These preclinical results support AR42 as an effective compound to upregulate miR-29b and in turn the approach of priming AML blasts with HIDACIs in order to sensitize them to treatment with hypomethylating agents. Phase I trials with microRNA priming with AR42 prior to DAC treatment are presently underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 119. doi:1538-7445.AM2012-119