A novel temozolomide-perillyl alcohol conjugate exhibits superior activity against breast cancer cells in vitro and intracranial triple-negative tumor growth in vivo.

There is no effective therapy for breast cancer that has spread to the brain. A major roadblock is the blood-brain barrier (BBB), which prevents the usual breast cancer drugs from effectively reaching intracranial metastases. The alkylating agent temozolomide (TMZ) is able to penetrate the BBB and has become the gold standard for chemotherapeutic treatment of glioblastoma. However, when it was tested in clinical trials for activity against brain metastases of breast cancer, the results were mixed and ranged from "encouraging activity" to "no objective responses." In an effort to generate an agent with greater activity against intracranial breast metastases, we synthesized a TMZ analog where the natural product perillyl alcohol (POH) was covalently linked to TMZ's amide functionality. The resulting novel compound, called TMZ-POH (T-P), displayed greatly increased anticancer activity in a variety of breast cancer cell lines, inclusive of TMZ-resistant ones. It caused DNA damage and cell death much more efficiently than its parental compound TMZ, because linkage with POH increased its biologic half-life and thus provided greater opportunity for placement of cytotoxic DNA lesions. In an intracranial mouse tumor model with triple-negative breast cancer, T-P revealed considerably greater therapeutic efficacy than TMZ, where a single cycle of treatment extended median survival benefit from 6 days (in the case of TMZ) to 28 days. At the same time, T-P seemed to be well tolerated by the animals. Thus, T-P may have potential as a novel therapy for brain-targeted breast cancer metastases.