A novel chemotherapeutic protocol for peritoneal metastasis and inhibition of relapse in drug resistant ovarian cancer.

The majority of ovarian cancer patients are diagnosed in late stages of the disease, in which the tumor cells have leaked into the peritoneum and are present as tumorspheres. These tumorspheres are rich in cancer stem-like cells (CSCs), which are resistant to therapy and are a major source of relapse. The purpose of this research was to identify a safe therapeutic approach that could eradicate the peritoneal CSC-rich tumorspheres and inhibit relapse. Highly metastatic ascitic cells (OVASC-1) that are resistant to standard-of-care chemotherapy due to upregulation of MDR1 gene were obtained from a patient with ovarian carcinoma and recurrent disease. CSC-rich tumorspheres were generated, characterized, and treated with different chemotherapeutics. The most effective drug combination that could eradicate tumorspheres at nanomolar levels despite upregulation of MDR1 gene was identified. Luciferase-expressing OVASC-1 cells were implanted in the peritoneum of nude mice and treated with the identified drug combination. The progression of disease, response to therapy and recurrence were studied by quantitative imaging. Toxicity to abdominal tissues was studied by histopathology. Mice implanted with intraperitoneal (IP) OVASC-1 xenografts showed limited response to combination therapy with cisplatin/paclitaxel at the maximum tolerated dose. Despite overexpression of MDR1 on OVASC-1 cells, mice treated with our combination IP low-dose MMAE and SN-38 chemotherapy showed complete response without relapse. No signs of toxicity to abdominal tissues were observed. While MMAE and SN-38 are not administered as free drugs due to their high potency and potential for systemic toxicity, our low-dose localized therapy approach effectively restricted the cytotoxic effects to the tumor cells in the peritoneum. Consequently, maximum efficacy with minimal adverse effects was achieved. These remarkable results with IP low-dose combination chemotherapy encourage investigation into its potential clinical application as either first-line therapy or in cases of acquired resistance to cisplatin and paclitaxel.