Discovery of Potent and Brain-Penetrable Tubulin Inhibitors that Effectively Suppress Breast Cancer Brain Metastasis

Breast cancer brain metastasis (BCBM) remains a clinical challenge marked by limited therapeutic options and poor survival rates. Approximately 30% of all metastatic breast cancer patients develop BCBM, with the highest incidence in patients with aggressive molecular subtypes, including triple-negative breast cancer (TNBC). TNBC patients with brain metastasis experience rapid disease progression and significantly reduced survival times due to a lack of targeted treatments that can penetrate the blood-brain barrier (BBB) and effectively control metastatic expansion. Current treatment options, such as whole-brain radiotherapy and chemotherapy, offer limited efficacy and are associated with significant toxicities, underscoring the urgent need for novel therapeutics that can target BCBM directly. We developed innovative colchicine binding site inhibitors (CBSIs) targeting tubulin, SB-216 and SP-1-39, that show potent preclinical efficacy against brain and extracranial metastases in BCBM models. Both CBSIs cross the BBB, inhibit cell growth and migration, and induce apoptosis with low nM potencies, similar to Azixa (MPC-6827), another CBSI previously evaluated in clinical trials. SB-216 reduced brain and concurrent extracranial metastases in a preventive dosing paradigm, extending overall survival. SB-216 also suppressed the expansion of pre-established brain lesions. In a taxane-refractory TNBC PDX model, SP-1-39 therapy markedly reduced brain and extracranial tumor burden. Together, these results highlight the promising therapeutic potential of SB-216 and SP-1-39 in treating taxane-sensitive or -resistant BCBM, filling a critical gap in TNBC management by offering targeted treatments that can cross the BBB and combat chemorefractory disease.