2 P - Relationship between rTNF α-, Apoptosis- and Multidrug-Resistance in vitro

Abstract

Expression of both P-glycoprotein (P-gp) and multidrug-resistance-related protein (MRP) confers resistance to antineoplastic drugs (multidrug-resistance; MDR). Analogous to the MDR-phenomenon, tumor cells can also develop resistance to toxic impacts of TNFα (cytokine resistance). We investigated the relationship between these resistance types using either P-gp or MRP overexpressing cell lines (CCRF-CEM, HL-60, K562, KB, HeLa, LoVo, CHO, GLC4), selected by various drugs. Our data (MTT-assay) show that the drug-selection process can have an impact on rTNFα-responsiveness leading to both resistance and sensitivity even within the same cell model. A change in TNFα responsiveness was 1) not dependent on P-gp or MRP-expression, 2) not defined by the cell type but 3) more likely a consequence of the selection process. By means of the CCRF-CEM leukaemia model, including both rTNFα-resistant and-sensitive MDR-sublines, we studied whether the modulation of parameters causing rTNFα-resistance (p55, endogenous TNFα, MnSOD, HSP-70, HSP-27) or apoptosis-resistance (bc1-2, bcl-xl, c-myc) parallels rTNFα-responsivencss (RT-PCR, Western blot). Additionally, sensitivity to other apoptosis-inducers (H₂O₂, UV-light) was investigated. Results give evidence for a role of endogenous TNFα and MnSOD in rTNFα-responsiveness. rTNFα-resistance in CCRF-CEM cells implies no general "apoptosis resistance phenotype". We conclude that MDR phenotype and rTNFα-responsiveness are not directly linked. The rTNFα-hypersensitivity of some MDR cell lines implicate new therapeutic strategies against drug-resistant tumors.