Chelsy Paulose

Recently, we reported that the ATP-binding cassette transporter 10 (ABCC10), also known as multidrug resistance protein 7 (MRP7), is able to confer resistance to a variety of anticancer agents, including taxanes. However, the in vivo functions of the pump have not been determined to any extent. In this study, we generated and analyzed Abcc10(-/-) mice to investigate the ability of Abcc10 to function as an endogenous resistance factor. Mouse embryo fibroblasts derived from Abcc10(-/-) mice were hypersensitive to docetaxel, paclitaxel, vincristine, and cytarabine (Ara-C) and exhibited increased cellular drug accumulation, relative to wild-type controls. Abcc10(-/-) null mice treated with paclitaxel exhibited increased lethality associated with neutropenia and marked bone marrow toxicity. In addition, toxicity in spleen and thymus was evident. These findings indicate that Abcc10 is dispensable for health and viability and that it is an endogenous resistance factor for taxanes, other natural product agents, and nucleoside analogues. This is the first demonstration that an ATP-binding cassette transporter other than P-glycoprotein can affect in vivo tissue sensitivity toward taxanes.

BACKGROUND: Resistance to chemotherapeutic agents is a major obstacle to cancer treatment. A group of ABC efflux pumps, the Multidrug Resistance Proteins, is a source of resistance. Herein, we investigated the role of ABCC10 in mammary tumours, given the important role we have defined for ABCC10 in transporting taxanes, and the recognition that some ABCC proteins have roles in tumour growth. METHODS: ABCC10 expression was correlated to human breast cancer subtype using breast tissue microarrays. Real-time quantitative PCR and western blot analysis were used to examine ABCC10 expression in human breast cancer lines. Abcc10(-/-) mice were crossed to MMTV-PyVmT mice to produce Abcc10(-/-) vs Abcc10(+/+) mammary tumours and derivative cell lines. We used allograft and cellular assays to perform baseline and drug sensitization analysis of tumours and cell lines. RESULTS: Clinical sample analyses indicated that ABCC10 was more highly expressed in Her2+ and ER+ than in Her2-, ER-, and triple-negative breast cancer. Unexpectedly, PyVmT; Abcc10(-/-) tumours grew more rapidly than PyVmT; Abcc10(+/+) tumours and were associated with significantly reduced apoptosis and metastasis. PyVmT; Abcc10(-/-) lines were less migratory than PyVmT; Abcc10(+/+) lines. Finally, we showed increased survival of docetaxel-treated MMTV-PyVmT; Abcc10(-/-) mice compared with wild-type mice. CONCLUSIONS: These data identify roles for Abcc10 in breast cancer pathogenesis and in vivo docetaxel resistance.

Supplementary Table 1 from Contribution of Abcc10 (Mrp7) to <i>In Vivo</i> Paclitaxel Resistance as Assessed in <i>Abcc10<sup>−/−</sup></i> Mice

Supplementary Figure Legend from Contribution of Abcc10 (Mrp7) to <i>In Vivo</i> Paclitaxel Resistance as Assessed in <i>Abcc10<sup>−/−</sup></i> Mice

Supplementary Figure 1 from Contribution of Abcc10 (Mrp7) to <i>In Vivo</i> Paclitaxel Resistance as Assessed in <i>Abcc10<sup>−/−</sup></i> Mice