Exisulind, a novel proapoptotic drug, inhibits rat urinary bladder tumorigenesis

Exisulind (Aptosyn) is a novel antineoplastic drug being developed for the prevention and treatment of precancerous and malignant diseases. In colon t umor cells, the drug induces apoptosis by a mechanism involving cyclic GMP (cGMP) phosphodiesterase inhibition, sustained elevation of cGMP, and prote in kinase! G activation. We studied the effect of exisulind on bladder tumo rigenesis induced in rats by the carcinogen, N-butyl-N-(4-hydroxybutyl) nit rosamine. Exisulind at doses of 800, 1000, and 1200 mg/kg (diet) inhibited tumor multiplicity by 36, 47, and 64% and tumor incidence by 31, 38, and 61 %, respectively. Experiments on the human bladder tumor cell line, HT1376, showed that exisulind inhibited growth with a GI(50) of 118 muM, suggesting that the antineoplastic activity of the drug is vivo involved a direct eff ect on neoplastic urothelium. Exisulind also induced apoptosis as determine d by DNA fragmentation, caspase activation, and morphology. Analysis of pho sphodiesterase (PDE) isozymes in HT1376 cells showed PDE5 and PDE4 isozymes that were inhibited by exisulind with IC(50)s of 112 and 116 muM, respecti vely. Inhibition of PDES appears to be pharmacologically relevant, because treatment of HT1376 cells increased cGMP and activated protein kinase G at doses that induce apoptosis, whereas cyclic AMP levels were not changed. Im munocytochemistry showed that PDES was localized in discrete perinuclear fo ci in HT1376 cells. Immunohistochemistry showed that PDES was overexpressed in human squamous and transitional cell carcinomas compared with normal ur othelium. The data lead us to conclude that future clinical trials of exisu lind for human I,ladder cancer treatment and/or prevention should be consid ered and suggest a mechanism of action involving cGMP-mediated apoptosis in duction.