Effect of various chemosensitizers on chemoresistance to adriamycin in MIP-101 cell line, a colon carcinoma cell line: analysis of glutathione and related enzymes

Strategies to enhance the response of liver cancer to pharmacological treatments

In contrast to other types of cancers, there is no available efficient pharmacological treatment to improve the outcomes of patients suffering from major primary liver cancers, i.e., hepatocellular carcinoma and cholangiocarcinoma. This dismal situation is partly due to the existence in these tumors of many different and synergistic mechanisms of resistance, accounting for the lack of response of these patients, not only to classical chemotherapy but also to more modern pharmacological agents based on the inhibition of tyrosine kinase receptors (TKIs) and the stimulation of the immune response against the tumor using immune checkpoint inhibitors (ICIs). This review summarizes the efforts to develop strategies to overcome this severe limitation, including searching for novel drugs derived from synthetic, semisynthetic, or natural products with vectorial properties against therapeutic targets to increase drug uptake or reduce drug export from cancer cells. Besides, immunotherapy is a promising line of research that is already starting to be implemented in clinical practice. Although less successful than in other cancers, the foreseen future for this strategy in treating liver cancers is considerable. Similarly, the pharmacological inhibition of epigenetic targets is highly promising. Many novel "epidrugs," able to act on "writer," "reader," and "eraser" epigenetic players, are currently being evaluated in preclinical and clinical studies. Finally, gene therapy is a broad field of research in the fight against liver cancer chemoresistance, based on the impressive advances recently achieved in gene manipulation. In sum, although the present is still dismal, there is reason for hope in the non-too-distant future.

Felbamate-induced apoptosis of hematopoietic cells is mediated by redox-sensitive and redox-independent pathways

Felbamate (FBM; 2-phenyl-1,3-propanediol dicarbamate) is an approved antiepileptic drug shown to be effective in a variety of seizure disorders refractory to other treatments. However, its use has been restricted because of association with occurrence of rare cases of aplastic anemia and hepatic failure. Since it was shown that FBM metabolism requires glutathione (GSH), we used two experimental protocols to determine if the effects of specific metabolites were sensitive to redox pathways. FBM and its metabolite W873 (2-phenyl-1,3-propanediol monocarbamate), at 0.1 mg/ml, induced increased apoptosis of bone marrow cells from B10.AKM mice as compared with B10.BR mice. Study of the effects of the drug on human promonocytic cell line U937 cells showed that FBM and the metabolite W2986 [2-(4-hydroxyphenyl)-1,3 propanediol dicarbamate], at higher concentrations (0.5 mg/ml), induced apoptosis in this cell line. We also observed that while FBM and its metabolites induced increased apoptosis of B cells with reduced intracellular GSH levels, addition of exogenous GSH decreased apoptosis induced by W873 but did not significantly affect apoptosis induced by FBM or W2986. Our results suggest that, at concentrations used during the present investigations, FBM metabolites induce apoptosis via redox-sensitive and redox-independent pathways.

Apoptosis or necrosis: intracellular levels of glutathione influence mode of cell death

The effect of lowering intracellular glutathione (GSH) concentrations on the toxicity of alkylating agents, and RNA synthesis inhibitor and topoisomerase 1 and 2 inhibitors to a number of human leukaemic cell lines were evaluated. By using the GSH synthesis inhibitor DL-buthionine-(S,R)-sulfoximine (BSO), GSH levels were artificially reduced. Cells with low GSH concentrations were exposed to a number of cytotoxic agents and the resultant mode of cell death was analysed using morphological and biochemical criteria. It was found that untreated cells exposed to the above drugs underwent apoptosis to varying extents. However, the toxicity of alkylating agents was dramatically increased to all cell lines on lowering GSH levels, with the mode of cell death switching from apoptosis to necrosis. The reduction of GSH levels had no effect on the toxicity of actinomycin-D, camptothecin or etoposide, nor did it affect the mode of cell death induced by these agents. These observations suggest that modulation of GSH levels effect the toxicity of alkylating agents and that GSH influences the mode of cell death induced by alkylating agents.

Comparative study of intracellular calcium and adenosine 3',5'-cyclic monophosphate levels in human breast carcinoma cells sensitive or resistant to Adriamycin: contribution to reversion of chemoresistance

Multidrug resistance (MDR) corresponds to the cross-over resistance of tumour cells to structurally unrelated cytotoxic chemotherapeutic drugs. One of the mechanisms causing this resistance is the enhanced expression of a transmembrane drug efflux pump P-glycoprotein (P-170). Reversal of P-glycoprotein-associated MDR has received much attention in recent years. In experimental cell lines, P-170 and the glutathione redox cycle seem to contribute to this phenomenon; P-170 may be inactivated by calcium and calmodulin antagonists and the glutathione redox cycle altered by buthionine sulphoximine (BSO). Treatment of human MCF-7 breast cancer cells with chemosensitizers (CS), such as verapamil, trifluoperazine or BSO, for 72 hr resulted in an enhanced sensitization of cells to Adriamycin, trifluoperazine being the most potent compound in the reversion of chemoresistance. In these Adriamycin sensitive or resistant cells, treated or not by the CS, the possible role of calcium and cyclic adenosine monophosphate (cAMP) in mediating the reversion of chemoresistance to Adriamycin was investigated. It was found that intracellular calcium was approximately 2-fold higher in resistant than in sensitive cells, the opposite was true for cAMP. Modifications in calcium and cAMP levels were observed in MCF-7 resistant cells after treatment with verapamil and BSO; trifluoperazine had no effect on these two parameters. These results seemed to rule out any implication of calcium and cAMP levels in the contribution of these three chemosensitizers in the mechanisms of reversion of chemoresistance to Adriamycin.