Abstract 4722: Selective inhibition of DNA methyltransferases and efficacy of novel DNMT inhibitors in leukemia xenografts

Abstract

Abstract Background. DNA methyltransferase (DNMT) 1 plays an important role in tumorigenesis and is responsible for maintenance and propagation of DNA methylation patterns, and DNMT3A and DNMT3B are involved in de novo DNA methylation. 4’-Thio-5-aza-2’-deoxycytidine (5-aza-T-dCyd) and 4’-thio-2’-deoxycytidine (T-dCyd) are novel DNMT inhibitors in development. In this investigation, we test the hypothesis that DNMTs are differentially modulated by DNMT inhibitors that may contribute to treatment efficacy. Methods. Animals (5 per group) bearing HL-60 leukemia cell xenografts were treated with saline or aza-T-dCyd at 2 mg/kg with and without 100 mg/kg tetrahydrouridine (ThU) for 5 days weekly for 2 weeks and cycle repeat after 9-day rest. Two other groups were dosed with T-dCyd at 4 mg/kg and decitabine at 0.75 mg/kg, respectively. Tumor growth was assessed by measuring tumor size. Expression of DNMT1, DNMT3A and DNMT3B was examined by immunohistochemistry in paraffin-embedded tumors resected at day 11. Results. Expression of DNMT1 was high, DNMT3B intermediate, and DNMT3A at low levels in saline control group. Significant growth delay was achieved in the aza-T-dCyd (86%) and aza-T-dCyd plus ThU cohorts (45%), compared with the controls. In the aza-T-dCyd treated xenografts, histological examination confirmed a significant reduction (77%) in tumor area (P = 0.002). Expression of DNMT1 and DNMT3B (n = 2 in aza-TdCyd group) was reduced in aza-T-dCyd cohort (P = 0.01 and P = 0.04) as well as aza-T-dCyd in combination with ThU group (P = 0.01 and P = 0.03). In contrast, no growth inhibition but decrease in DNMT3A and DNMT1 were observed by dosing with decitabine. There were neither delays for tumor growth nor changes of all three DNMTs by T-dCyd treatment with the dose administered. Conclusions. Aza-T-dCyd and aza-T-dCyd plus ThU treatments result in significant tumor growth inhibition in HL-60 leukemia xenografts. The anti-tumor activity is associated with simultaneous inhibition of the two drug targets — DNMT1 and DNMT3B. The preclinical results provide compelling evidence to advance aza-T-dCyd for clinical development and perhaps in the context of companion biomarker approach. Citation Format: Dat Nguyen, Melinda Hollingshead, Larry Rubinstein, James Doroshow, Sherry X. Yang. Selective inhibition of DNA methyltransferases and efficacy of novel DNMT inhibitors in leukemia xenografts. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4722.