JS-K, a GST-Activated Nitric Oxide Generator, Induces DNA-Double Strand Breaks and Inhibits Growth and Survival of Multiple Myeloma Cells In Vitro and In Vivo.

JS-K (O²-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate) is a diazeniumdiolate class of prodrug which is designed to release nitric oxide (NO^·) on reaction with glutathione S-transferases (GST). GST has been shown to be overexpressed in a broad spectrum of tumor cells. Therefore, JS-K can possibly turn GST overexpression to the tumor’s disadvantage by generating high intracellular concentrations of cytotoxic NO^·. Multiple myeloma (MM) is currently an incurable hematological malignancy where new treatment options are urgently needed. In this study we investigated the cytotoxicity of JS-K in MM in vitro and in vivo. JS-K showed significant cytotoxicity in both conventional therapy-sensitive and -resistant MM cell lines, as well as patient MM cells (IC₅₀: 0.3–2.5 mM). Importantly, no significant cytotoxic effects of JS-K at these doses were observed in normal peripheral blood mononuclear cells. JS-K treatment induced apoptosis in MM cells which was associated with PARP, caspase 8, and caspase 9 cleavage; increased cell surface expression of Fas/CD95; Mcl-1 cleavage; Bcl-2 phosphorylation; as well as mitochondrial cyt c, AIF, and EndoG release. Moreover, JS-K could overcome the survival and growth advantages conferred by exogenous IL-6 and IGF-1, or by adherence of MM cells to bone marrow stromal cells. Flow cytometry experiments revealed significant NO^· generation in JS-K-treated MM cells. Since NO^· is known to cause DNA double strand breaks (DSB), we hypothesized that JS-K induces DSB in MM cells and confirmed DSB formation by neutral comet assay. We further showed that JS-K also activated DNA damage response pathways as evidenced by H2AX, Chk2 and p53 phosphorylation. In addition, JNK was also activated by JS-K treatment in MM cells, and inhibition of JNK significantly decreased JS-K-induced cytotoxicity, suggesting that JS-K induced apoptosis is mediated via JNK signaling. Finally, JS-K was also significantly effective in inhibiting tumor growth and prolonging median survival (p < 0.01) in a human plasmacytoma xenograft mouse model. Analysis of tumors harvested from treated animals showed that JS-K induced apoptosis and decreased angiogenesis in vivo. Taken together, these data provide the preclinical rationale for the clinical evaluation of JS-K to improve patient outcome in MM.