Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs

Area of Science:

• Oncology
• Radiotherapy
• Pharmacology

Background:

• Tumor hypoxia is a known factor in radiation resistance, prompting exploration of strategies to overcome it.
• Two main small molecule approaches target hypoxia: oxygen-mimetic radiosensitizers and hypoxia-activated prodrugs.
• Hypoxia-activated prodrugs are designed for selective activation in hypoxic tumor regions by reductases, releasing cytotoxic agents.

Purpose of the Study:

• To review and discuss the evolution, merits, and shortcomings of hypoxia-activated prodrug strategies in cancer therapy.
• To identify key issues hindering clinical success, including extravascular transport and micropharmacokinetic properties.
• To emphasize the critical need for co-developed biomarkers for patient selection and treatment optimization.

Main Methods:

• Review of preclinical and clinical efforts involving electron-affinic nitroheterocycles and hypoxia-activated prodrugs.
• Discussion of the transition from DNA-interactive cytotoxins to molecularly targeted agents in prodrug design.
• Analysis of factors limiting clinical efficacy, such as transport and pharmacokinetic properties.

Main Results:

• While hypoxia-activated prodrugs show promise for targeted delivery, clinical success has been limited.
• Failure to account for extravascular transport and micropharmacokinetics has compromised efficacy.
• Development of appropriate biomarkers for hypoxia, activating reductases, and drug sensitivity is crucial.

Conclusions:

• The field of hypoxia-targeted cancer therapy is evolving, with ongoing efforts to improve clinical outcomes.
• Future innovation may arise from integrating these strategies with advancements in radiation delivery and immuno-oncology.
• Addressing pharmacokinetic challenges and implementing robust biomarker strategies are essential for realizing the potential of hypoxia-activated prodrugs.