MDR1 Inhibition Reverses Doxorubicin-Resistance in Six Doxorubicin-Resistant Canine Prostate and Bladder Cancer Cell Lines

by Selleckchem | Jul 13 2023

Acquired chemoresistance during chemotherapy, often accompanied by cross- and multi-resistance, limits therapeutic outcomes and leads to recurrence. In order to create in vitro model systems to understand acquired doxorubicin-resistance, we generated doxorubicin-resistant sublines of canine prostate adenocarcinoma and urothelial cell carcinoma cell lines. Chemoresistance to doxorubicin, cross-resistance to carboplatin, and the reversibility of the acquired resistance by the specific MDR1-inhibitor tariquidar were quantified in metabolic assays. Resistance mechanisms were characterized by expression of the efflux transporters MDR1 and RALBP1, as well as the molecular target of doxorubicin, TOP2A, with qPCR and Western blotting. Six out of nine cell lines established stable resistance to 2 µM doxorubicin. Drug efflux via massive MDR1 overexpression was identified as common, driving resistance mechanism in all sublines. MDR1 inhibition with tariquidar extensively reduced or reversed the acquired, and also partly the parental resistance. Three cell lines developed additional, non-MDR1-dependent resistance. RALBP1 was upregulated in one resistant subline at the protein level, while TOP2A expression was not altered. Combination therapies aiming to inhibit MDR1 activity can now be screened for synergistic effects using our resistant sublines. Nevertheless, detailed resistance mechanisms and maintained molecular target expression in the resistant sublines are still to be examined.

Comments:

The passage describes a study conducted to create in vitro models for understanding acquired resistance to the chemotherapy drug doxorubicin. The researchers generated doxorubicin-resistant sublines of canine prostate adenocarcinoma and urothelial cell carcinoma cell lines. They evaluated the resistance to doxorubicin and cross-resistance to carboplatin using metabolic assays. They also investigated the reversibility of acquired resistance by using the specific MDR1-inhibitor called tariquidar. The researchers examined the expression of MDR1, RALBP1, and the molecular target of doxorubicin (TOP2A) using quantitative PCR (qPCR) and Western blotting to understand the underlying resistance mechanisms.

The results showed that six out of nine cell lines established stable resistance to 2 µM doxorubicin. The researchers identified drug efflux, primarily driven by massive MDR1 overexpression, as a common resistance mechanism in all the resistant sublines. They found that inhibiting MDR1 with tariquidar significantly reduced or reversed both the acquired resistance and the inherent resistance observed in the parental cell lines. However, three cell lines developed additional resistance mechanisms that were not dependent on MDR1.

In one of the resistant sublines, RALBP1 was upregulated at the protein level, indicating its potential role in conferring resistance. However, there were no changes in TOP2A expression, which is the molecular target of doxorubicin.

The researchers concluded that their doxorubicin-resistant sublines can be used to screen combination therapies targeting MDR1 activity for synergistic effects. However, further investigations are needed to understand the detailed resistance mechanisms and to examine whether the molecular target expression is maintained in the resistant sublines.

Overall, this study provides insights into the mechanisms of acquired chemoresistance to doxorubicin and highlights the potential for developing strategies to overcome resistance in canine prostate adenocarcinoma and urothelial cell carcinoma.