Aim: To evaluate the efficacy and the safety of azathioprine (AZA) and buthionine sulfoximine (BSO) by localized application into HepG2 tumor in vivo.
Methods: Different hepatoma and colon carcinoma cell lines (HepG2, HuH7, Chang liver, LoVo, RKO, SW-48, SW-480) were grown in minimal essencial medium supplemented with 10% fetal bovine serum and 1% antibiotic/antimycotic solution and maintained in a humidified 37 °C incubator with 5% CO₂. These cells were pretreated with BSO for 24 h and then with AZA for different times. We examined the effects of this combination on some proteins and on cellular death. We also studied the efficacy and the safety of AZA (6 mg/kg per day) and BSO (90 mg/kg per day) in HepG2 tumor growth in vivo using athymic mice. We measured safety by serological markers such as aminotransferases and creatine kinase.
Results: The in vitro studies revealed a new mechanism of action for the AZA plus BSO combination in the cancer cells compared with other thiopurines (6-mercaptopurine, 6-methylmercaptopurine, 6-thioguanine and 6-methylthioguanine) in combination with BSO. The cytotoxic effect of AZA plus BSO in HepG2 cells resulted from necroptosis induction in a mitochondrial-dependent manner. From kinetic studies we suggest that glutathione (GSH) depletion stimulates c-Jun amino-terminal kinase and Bax translocation in HepG2 cells with subsequent deregulation of mitochondria (cytochrome c release, loss of membrane potential), and proteolysis activation leading to loss of membrane integrity, release of lactate dehydrogenase and DNA degradation. Some of this biochemical and cellular changes could be reversed by N-acetylcysteine (a GSH replenisher). In vivo studies showed that HepG2 tumor growth was inhibited when AZA was combined with BSO.
Conclusion: Our studies suggest that a combination of AZA plus BSO could be useful for localized treatment of hepatocellular carcinoma as in the currently used transarterial chemoembolization method.
Keywords: Apoptosis; Azathioprine; Buthionine sulfoximine; Glutathione; Necrosis; Transarterial chemoembolization.