Patients with
breast cancer brain metastases have extremely limited survival and no approved systemic
therapeutics.
Triple-negative breast cancer (TNBC) commonly metastasizes to the brain and predicts poor prognosis. TNBC frequently harbors BRCA mutations translating to
platinum sensitivity potentially augmented by additional suppression of DNA repair mechanisms through PARP inhibition. We evaluated brain penetrance and efficacy of
carboplatin ± the
PARP inhibitor ABT888, and investigated gene-expression changes in murine intracranial TNBC models stratified by BRCA and molecular subtype status. Athymic mice were inoculated intracerebrally with BRCA-mutant: SUM149 (basal), MDA-MB-436 (
claudin-low); or BRCA-wild-type (wt): MDA-MB-468 (basal), MDA-MB-231BR (
claudin-low). TNBC cells were treated with PBS control [intraperitoneal (IP), weekly],
carboplatin (50 mg/kg/wk, IP),
ABT888 (25 mg/kg/d, oral gavage), or their combination. DNA damage (γ-H2AX), apoptosis (cleaved
caspase-3, cC3), and gene expression were measured in intracranial
tumors.
Carboplatin ±
ABT888 significantly improved survival in BRCA-mutant intracranial models compared with control, but did not improve survival in BRCA-wt intracranial models.
Carboplatin +
ABT888 revealed a modest survival advantage versus
carboplatin in BRCA-mutant models.
ABT888 yielded a marginal survival benefit in the MDA-MB-436, but not in the SUM149 model. BRCA-mutant SUM149 expression of γ-H2AX and cC3
proteins was elevated in all treatment groups compared with control, whereas BRCA-wt MDA-MB-468 cC3 expression did not increase with treatment.
Carboplatin treatment induced common gene-expression changes in BRCA-mutant models.
Carboplatin ±
ABT888 penetrates the brain and improves survival in BRCA-mutant intracranial TNBC models with corresponding DNA damage and gene-expression changes. Combination
therapy represents a potential promising treatment strategy for patients with TNBC
brain metastases warranting further clinical investigation.