Introduction: Chemotherapy is often limited by resistant subpopulations of tumor cells. Tumor hypoxia contributes to resistance of tumor cells to clinical drugs via multiple mechanisms. Hypoxia-activated prodrugs selectively target hypoxic cells, among which SN30000 is a second generation of tirapazamine analogue with superior diffusion coefficient and hypoxia selectivity. Here we hypothesize that SN30000/chemotherapy drug combinations will provide improved activity.
Methods: HCT116 and SiHa spheroids were used to screen schedules of SN30000 in combination with 4 clinical drugs (cisplatin, doxorubicin, gemcitabine, paclitaxel) under 5% O2 and 20% O2, with endpoints of spheroid growth delay and clonogenic cell survival. The schedules were tested on HCT116 and SiHa monolayers under 5% O2. HCT116 monolayers and spheroids exposed to SN30000 or the clinical drugs were dissociated for clonogenic survival assay. Tumor growth delay using the same schedules of the most promising combination (SN30000 + gemcitabine) were then tested in HCT116 xenografts in NIH-III mice. Body weight loss and core body temperature of mice in response to the treatments were monitored. Results: Exposing to 25 µM SN30000 and 25 µM cisplatin/5 µM doxorubicin/10 µM gemcitabine simultaneously for 2 hr, and SN30000 3 hr before gemcitabine under 5% O2 significantly delayed HCT116 and SiHa spheroid growth, but their combined activity was compromised under 20% O2. Dosing SN30000 and cisplatin simultaneously, and SN30000 3 hr before gemcitabine significantly delayed HCT116 and SiHa monolayer growth. Clonogenic survival assay demonstrated that HCT116 monolayers were more sensitive than spheroids to doxorubicin, but not the other 3 clinical compounds, consistent with the known limited diffusion of doxorubicin into spheroids.Dosing SN30000 3 hr before gemcitabine or at the same time, but not SN30000 3 hr after gemcitabine significantly delayed tumor growth, which was consistent with the spheroid data. Body weight measurements showed that the combinations of SN30000 and gemcitabine added little additional toxicity while SN30000/doxorubicin was more toxic when administered simultaneously. SN30000 caused hypothermia in mice with recovery after 3 hr.
Discussion: Screening schedules of SN30000 in combination with 4 clinical drugs in HCT116/SiHa spheroids and monolayers demonstrated schedule and oxygen dependence of the activity of SN30000 and gemcitabine combinations, which was further demonstrated in HCT116 xenografts. The mechanism of the promising interaction between gemcitabine and SN30000 is being further investigated by flow cytometry and immunohistochemical staining to explore the hypoxic fraction and cell proliferation following treatments, and by evaluating the plasma pharmacokinetics of SN30000 and gemcitabine to investigate the implications of SN30000-induced hypothermia.
Citation Format: Xinjian Mao, Sarah McManaway, William Robert Wilson, Kevin Owen Hicks. Potentiation of the action of chemotherapeutic drugs by the hypoxia-activated prodrug SN30000 in multicellular tumor spheroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2440.