Abstract 3818: Therapeutic potential of blocking CCR5 by maraviroc in breast cancer bone metastasis

Introduction: Bone metastasis is a highly unfavorable condition observed in up to 70% of the patients with breast cancer. Treatment options for this condition are not curative, but palliative, only, which highlights the need for exploring new therapeutic options. In this study, we propose that targeting a chemokine receptor (CCR5), often upregulated in primary and secondary breast cancers, can contribute to a more successful treatment of breast cancer bone metastasis. Methodology: Following the blockage of CCR5 by maraviroc, cytotoxic effects were measured by MTT assay, while the migratory effects were determined by migration and scratch healing assays. Apoptosis related activities were investigated by nuclear staining and western blot analysis. Maraviroc mediated cytostatic changes were analyzed by a ready-made Human Cell Cycle Regulation Panel (Roche, Germany). In vivo experiments were performed by implanting MDA-MB-231 cells via the saphenous artery to the left hind limb of male nude rats (RNU strain) for inducing bone metastasis. Treatment with maraviroc was started from 2nd and 7th day of transplantation in two groups of rats (n = 6/group) designated as A and B, respectively, and was compared with an untreated control group (n = 8 rats). Results: CCR5 blockage by maraviroc (concentration > 100μM) induced concentration dependent cytotoxicity in MDA-MB-231 and MCF-7 cells. Maraviroc exposure also showed significant inhibition of migration of the cells, while nuclear staining indicated the condensation/fragmentation of nuclear content. Maraviroc exposure induced significant expression of cleaved caspase 7 and PARP, while real time RT-PCR showed pronounced inhibition of multiple genes (≥2fold) including cyclins, CDKs and their down-stream targets. Treatment of tumor bearing animals, with intra-peritoneal injections of maraviroc (25mg/kg, 3-4 weeks daily), reduced the tumor burden significantly (p < 0.05) in group A (50-75%), while the effects were minimal in group B (