687 BET inhibitor suppressed tumor growth and associated TME inflammation in mouse models of cutaneous T cell lymphoma

Abstract

Bromodomain and Extra-termial motif (BET) proteins epigenetically regulate gene expression critical for cell cycle and signaling pathways, implicating the potential for BET inhibitors as anticancer agents. We previously established a cutaneous T cell lymphoma (CTCL) model in mice, utilizing topical application of a skin sensitizer, 2,4-Dinitrofluorobenzene (DNFB), for inflammation dependent tumor induction. In this study we use this model to examine the function of OTX015, a potent BET inhibitor, in controlling the growth of MBL2 lymphoma cells and HH cells, a human CTCL cell line. Our studies showed that cell proliferation is significantly inhibited in cultured HH cells after incubation with OTX015 at lower concentrations (0.5 μM), while inhibition of MBL2 cells were observed at higher concentrations (2.5 μM). RT-PCR analysis showed significant inhibition of Ki-67, a gene marker of proliferation, in HH cells with OTX015, and decreased expression of IL-10 and IL-17 in MBL2 cells. In vivo, we administered OTX015 at low dosing (25 mg/kg) to mice inoculated with MBL2 cells. The MBL2 tumor microenvironment of OTX015 treated mice contained fewer CD45+ leukocytes and reduced inflammatory cytokine expression. In addition, strikingly smaller draining lymph nodes (1.3 vs. 0.1 cm, p=0.0105) as well as reduced spleen size were seen, suggesting a reduction in the metastatic properties of MBL2 T cells. Using the same dosing regimen, HH tumors inoculated in immunodeficient (NSG) mice were found to be significantly smaller (p<0.05) compared to vehicle-treated mice. Our studies suggest OTX015 as a potential new therapeutic agent for CTCL treatment via regulation of cancer-associated inflammation, reduced metastasis to regional LN and reduction of tumor size in syngeneic and xenograft, respectively.