676 Exploring novel therapeutic targets in the treatment of cutaneous T-cell lymphoma

Abstract

High throughput candidate exposure screening has emerged as a method for drug discovery and identification of novel therapeutics. Cutaneous T cell lymphoma (CTCL) is characterized by copy number variants clustering in pathways of T cell activation, cell cycle regulation, and DNA structural regulation. In particular, dysregulation of JAK/STAT signalling has been described in the pathogenesis of CTCL. Ruxolitinib is a small molecule inhibitor of JAK1/2 reported to inhibit in vitro proliferation of three CTCL cell lines. We sought to elucidate novel agents for the treatment of CTCL by high throughput drug screening. Additionally, we aimed to examine the effect of JAK inhibition on patient-derived CTCL cells in vitro and evaluate synergy with known CTCL therapies. CTCL cells purified from patients’ peripheral blood were exposed to high-throughput single and combination drug screening. Cytotoxic effects were evaluated as cell viability via ATP quantitation at 72h. Synergy was evaluated by the Chou-Talalay method. Screening of the Microsource GenPlus compound library yielded 19 compounds that had a significant effect on all samples tested, and also identified compounds with differential effects; several of these target pathways dysregulated in CTCL and are being investigated further as novel therapies. Purified cells showed differential responses to ruxolitinib. Of eight patient samples tested, five appeared resistant (mean IC50 121μM), while three were sensitive (mean IC50 0.3μM). Of these, three were exposed to drug combinations. They showed synergy when ruxolitinib was combined with either a BCL-2 inhibitor (venetoclax) or proteasome inhibitor (bortezomib) with a combination index<1. Although JAK targeting has differential response on the viability of CTCL cells, it shows synergistic effects when used in combination with a BCL-2 inhibitor or proteasome inhibitor. Thus, combination therapy with JAK inhibition may represent a novel therapeutic strategy in the treatment of CTCL.