3111 - Exploiting Radiation-Activated Prodrugs to Target Antioxidant-Driven Radioresistance
Presenter(s)
S. Mohammadi1,2, J. Quintana1, M. Goemans1, T. S. C. Ng2, I. Banla1,3, and M. A. Miller1; 1Center for Systems Biology, Massachusetts General Hospital, Boston, MA, 2Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA
Purpose/Objective(s):
Radiation activated ProDrugs (RPDs) enable in-situ activation of potent cytotoxic and immunomodulatory drug payloads, and thus have the potential to improve the therapeutic index of systemic anti-cancer therapies. Radiation-generated radical species mediate chemical RPD activation, yet radioresistant cancer cells can harbor elevated antioxidants like glutathione (GSH), which impacts the availability of radical species and shifts the redox milieu from oxidizing towards reducing states. We hypothesized that RPDs could be tailored to exploit radioresistant cellular redox states, such that higher cellular concentrations of antioxidants could enhance the activation of RPDs reliant on reducing species. As a result, such RPDs may represent promising therapeutics for cancers that exhibit antioxidant-driven radioresistance.
Materials/Methods:
The chemical structures of radiation-activated probes were confirmed via NMR and mass spectrometry. Three distinct probes were examined, all based on radical-mediated phenyl azide (pAz) reduction, but each caging a separate payload: the microtubule inhibitor monomethyl auristatin E (pAz-MMAE), the immunostimulatory toll-like receptor 7/8 agonist resiquimod (pAz-Res), and the fluorochrome rhodamine 110 (pAz-R110). Radiation-dependent uncaging was assessed in phosphate-buffered saline (PBS) or in cell lysates. Radiation was applied using a 320kV X-ray irradiator.
Results:
All three prodrugs were more efficiently uncaged in the presence of GSH and NADPH. Cleavage efficiency was up to 33% higher in the presence of GSH and 65% higher with NADPH. Cleavage efficiency in cancer cell lysates was modulated by pretreatment with H2O2, which is known to deplete cellular antioxidants, decreased pAz-R110 activation efficiency from 159 nM/Gy to 72 nM/Gy. When cells were allowed to recover post-H2O2 treatment and replete their antioxidant stores, the release efficiency of RPDs recovered in a time-dependent fashion. We additionally probed the release efficiency in lysates of radioresistant cancer cell lines and observed prodrug activation was significantly higher in such cell lysates compared to PBS, suggesting that cellular antioxidant levels may enhance RPD activation.
Conclusion:
Cellular redox state modulates RPD activation. Elevated antioxidant levels, characteristic of radioresistant cancers, enhance the efficiency of reducing radical-dependent prodrug activation. This positions such RPDs as promising tools to overcome antioxidant-driven radioresistance.