We have synthesized a series of anti-cancer drug candidates known as arylated diazeniumdiolates that, by design, act by releasing cytolytic nitric oxide (NO) within the tumor cell on reaction with cellular nucleophiles such as glutathione, especially on catalysis by glutathione S-transferase. One of these, JS-K, has been reported not only to cut the growth rate of subcutaneously implanted HL-60 human leukemia cells by 50% in a mouse xenograft model, but also to induce significant necrosis in the remaining tumor mass. Similar activity was shown by JS-K in a prostate cancer mouse xenograft model, in a glioma xenograft, and in an orthotopic rat liver cancer model. JS-K was especially active against a multiple myeloma xenograft model in mice, greatly reducing the growth rate of the tumor and substantially prolonging the animals lifetime. More recently, JS-K was found to be active against lung cancer in mice, with the observed potency correlating significantly with the level of "reactive oxygen species" (ROS) produced within the cancer cells; lung tumor cell lines with the highest endogenous ROS output, lowest antioxidant defenses, and poorest DNA repair capacity were most susceptible to JS-K's toxic action, and tumors established with one of these cell lines had their growth rates cut by 85% relative to the vehicle-treated controls. The second-generation arylated diazeniumdiolate PABA/NO proved almost as potent as the clinically important drug cisplatin in slowing the growth of human ovarian cancer xenografts in mice. We believe that such evidence of broad-spectrum anti-cancer activity on the part of this novel drug class merits urgent followup aimed at exploiting any clinical benefits that may be inherent in this technology. Work continues to be focused on development issues, including testing different formulations for their ability to prolong the lifetime of the drugs in the blood stream (P. Shami) and designing molecular modifications that might lessen their reactivity (collaboration with X. Ji), thus decreasing their tendency to be activated and lose their NO before reaching the tumor site.
