Noncytotoxic Differentiation Treatment of Renal Cell Cancer

Current drug therapy for metastatic renal cell cancer (RCC) results in temporary disease control but not cure, necessitating continued investigation into alternative mechanistic approaches. Drugs that inhibit chromatin-modifying enzymes involved in transcription repression (chromatin-relaxing drugs) could have a role, by inducing apoptosis and/or through differentiation pathways. At low doses, the cytosine analogue decitabine (DAC) can be used to deplete DNA methyl-transferase 1 (DNMT1), modify chromatin, and alter differentiation without causing apoptosis (cytotoxicity). Noncytotoxic regimens of DAC were evaluated for in vitro and in vivo efficacy against RCC cell lines, including a p53-mutated RCC cell line developed from a patient with treatment-refractory metastatic RCC. The cell division-permissive mechanism of action-absence of early apoptosis or DNA damage, increase in expression of HNF4 alpha (hepatocyte nuclear factor 4 alpha), a key driver associated with the mesenchymal to epithelial transition, decrease in mesenchymal marker expression, increase in epithelial marker expression, and late increase in cyclin-dependent kinase inhibitor CDKN1B (p27) protein-was consistent with differentiation-mediated cell-cycle exit. In vivo blood counts and animal weights were consistent with minimal toxicity of therapy. The distinctive mechanism of action of a dose and schedule of DAC designed for noncytotoxic depletion of DNMT1 suggests a potential role in treating RCC. Cancer Res; 71(4); 1431-41. (C) 2011 AACR.