Modulators of multidrug resistance PSC 833 and CsA show differential capacity to induce apoptosis independently of the MDR phenotype in lymphoid leukemia cell lines

LOPES EC; GARCÍA MG; BENAVIDES F; SHEN J; ALVAREZ E; HAJOS S

Orlando, Florida- USA

Congreso; 38th Annual Meeting of American Society of Clinical Oncology (ASCO); 2002

ASCO

Most anticancer drugs exert their cytotoxic action by inducing apoptosis, a gene-activated program for cell death. Previous investigations strongly suggest that inhibition of the apoptotic pathway can lead to cytotoxic drug resistance. We demonstrated CsA as well as its analogue PSC 833 (0.1 mg/ml) reverted multidrug resistance phenotype (MDR) in murine cell lines resistant to either vincristine (LBR-V160) or doxorubicin (LBR-D160). We also showed that agents that presented cross-resistance with vincristine or doxorubicin were able to induce apoptosis preferentially on sensitive cell line (LBR-), showing correlation between the increase of MDR phenotype and the decrease apoptosis. The aim of this work was to evaluate the ability of PSC 833 and CsA to induce apoptosis in leukemia cell lines and to analyze the mechanisms involved. Apoptosis was evidenced by fluorescence microscopy, sub G1 accumulation and agarose gel electrophoresis while p53 (Trp53) gene phenotype was assayed by single stranded conformation polymorphisms (SSCP). The expression of Bcl2, Bax and Bcl2l proteins was analyzed by flow cytometry. Our results showed that CsA (1ug/ml) was able to induce apoptosis on all the cell lines, independently of their MDR phenotype: in 18.31% (± 4.46) for LBR-, 25.96% (± 5.24) for LBR-V160 and 27.36% (± 4.12) for LBR-D160. On the other hand, PSC 833 (1ug/ml) only induced apoptosis on LBR-V160 cell line 21.51% (± 5.73). High expression of Bcl2, Bax and Bcl2l proteins was found for the sensitive as well as for the resistant cell lines and was not modified after treatment with PSC 833 or CsA. No mutations were found in exons 5-8 of the tumor suppressor gene Trp53. We conclude that, depending on the concentration used, PSC 833 and CsA may act either modulating MDR (0.1 mg/ml) or inducing apoptosis (1 mg/ml), the latter through a mechanism not related with the Bcl2 proteins family. Besides, the resistant lines as well as the sensitive one presented Trp53 wild type phenotype, indicating that resistance induction through the continuous use of VCR or DOX failed to produce mutations of this tumor suppressor gene.