Acquired doxorubicin-resistance in canine prostate cancer cell lines is MDR1-dependent

Abstract

Selection of resistant tumor cell clones during chemotherapy causes relapse and is often accompanied by multiresistance. In order to create a model system with acquired resistance towards doxorubicin, a frequently used chemotherapeutic, we selected resistant clones of six canine prostate adenocarcinoma and transitional cell carcinoma cell lines. Previous analyses showed an increased drug efflux in the resistant lines, which we herein characterized. Therefore, the expression of two doxorubicin efflux transporters (MDR1 and RALBP1) and topoisomerase 2A (TOP2A), its molecular target, were investigated by qPCR and Western blot in parental and resistant cell lines. Furthermore, metabolic activity at doxorubicin exposure was analyzed in presence or absence of the specific MDR1 inhibitor Tariquidar. While TOP2A expression was not altered and RALBP1 was upregulated in only one resistant prostate carcinoma cell line at protein level, MDR1 was upregulated by factors between 35 and 285 in Western blot. In qPCR, MDR1 was upregulated at significance levels between p=0.0338 in the cell line with the highest basal MDR1 expression and p<0.0001 in the cell line with the lowest abundance of MDR1 transcripts in the parental line. Tariquidar reversed the tolerability of highest achievable doxorubicin plasma concentrations in all resistant cell lines. Acquired doxorubicin resistance in canine tumor cell culture is MDR1-dependent. If this observation is transferable to in vivo, needs further investigation. However, as MDR1 function is vital for numerous physiologic functions, solely local inhibition might be of therapeutic relevance in case of MDR1 overexpression.