Preclinical Development TPI-287, a New Taxane Family Member, Reduces the Brain Metastatic Colonization of Breast Cancer Cells

Brainmetastases of breast andother cancers remain resistant to chemotherapeutic regimens that are effective systemically, in part due to the blood–brain barrier. We report that TPI-287, a new microtubule-stabilizing agent, displays in vitro cytotoxic activity similar to taxanes and epothilones. Unlike the taxanes, TPI-287 is permeable through the blood–brain barrier. Brain-to-plasma ratios of TPI-287 after a single injection typically exceeded one and were as high as 63.8 in the rat and 14.1 in the mouse. A brain-tropic derivative of the MDAMB-231 triple-negative breast cancer cell line, 231-BR, was used to test whether TPI-287 may be efficacious at preventing or treating brain metastases. TPI-287 had growth inhibitory effects comparable with paclitaxel when 231-BR tumor cells were injected into the mammary fat pad. Brain metastatic colonization was determined by intracardiac injection of 231-BR cells, with treatment beginning on day 3 to 4 postinjection, culminating in a histologic count of brain metastases in brains necropsied days 25 to 28 postinjection. In this assay, paclitaxel, ixabepilone, and nab paclitaxel did not have significant inhibitory activity. TPI-287 was ineffective in the same assay using a 6 mg/kg every week schedule; however an 18 mg/kg dose delivered on days 3, 7, and 11 significantly reduced the outgrowth of brain metastases (55% reduction, P 1⁄4 0.028) and reduced proliferation in brain metastases (16% reduction, P 1⁄4 0.008). When TPI-287 treatment was delayed until days 18, 22, and 26postinjection, efficacywas reduced (17% reduction, not significant). These data suggest that TPI-287 may have efficacy when administered early in the course of the disease. Mol Cancer Ther; 11(9);