Targeting Chemoresistance in Advanced Bladder Cancers with a Novel Adjuvant Strategy.

ABSTRACT

Advanced urinary bladder cancer is characterized by rapid progression and development of therapy resistance. About 30% of the patients are diagnosed with high-grade tumors (grade > T2a). A typical nonsurgical treatment is systemic chemotherapy using cisplatin (C) and gemcitabine (G). However, treatment failure and subsequent disease progression are common in treated patients, and adjuvant therapies are not significantly effective. The therapeutic potential of a molecular hybrid of ursolic acid (UA), a pentacyclic-triterpene conjugated to N-methyl piperazine (UA4), was tested on both naïve (WT) and gemcitabine-resistant (GemR) variants of two human invasive bladder cancer cell lines, 5637 and T24. UA4 killed 5637 (4 µmol/L), T24 (4 µmol/L) WT, and GemR cells in vitro at equal potency. Pretreatment with UA4 followed by G synergistically killed WT and GemR cells by >50% compared with G followed by UA4. Oral gavage of UA4 (100 mg/kg) inhibited WT and GemR tumor growth in athymic mice. UA4 + G was more effective against GemR tumors than either drug alone. Studies revealed cytotoxic autophagy as a mechanism of UA4 cytotoxicity. UA4 induced moderate apoptosis in T24 but not in 5637 cells. Mitochondrial integrity and function were most affected by UA4 because of high levels of reactive oxygen species, disruption of mitochondrial membrane, and cell cycle arrest. These effects were enhanced in the UA4 + G combination. UA4 was well-tolerated in mice, and oral gavage led to a serum level >1 µmol/L with no systemic toxicity. These results show the potential of UA4 as a nontoxic alternative treatment for high-grade bladder cancer.