Targeting Hypoxia in Advanced Prostate Cancer Using Tirapazamine-Copper Nanoparticles

Introduction: Hypoxia is considered a hallmark of cancer and a common characteristic of locally advanced solid cancers, including prostate cancer. Tumor hypoxia plays a key role in promoting angiogenesis, metastasis, and drug... [ view full abstract ]

Introduction: Hypoxia is considered a hallmark of cancer and a common characteristic of locally advanced solid cancers, including prostate cancer. Tumor hypoxia plays a key role in promoting angiogenesis, metastasis, and drug resistance. Hypoxia-activated prodrugs have opened the door for specific treatment of the solid and metastatic tumors with lower side effects. Tirapazamine (TPZ) is the most advanced hypoxia-activated prodrug. TPZ has shown great specificity and potency in inhibiting tumor growth at moderate to severe hypoxic conditions. TPZ is currently in phase III clinical trials to treat cervical cancer, however its efficacy in vivo has been limited due to its poor penetration in tumor tissues. The present work aims to develop novel TPZ-copper nanoparticles to target and penetrate hypoxic prostate tumor mass, following systemic administration in vivo.

Methods: To improve the encapsulation of TPZ in nanoparticles, TPZ-copper complexes, Cu(TPZ)2, were prepared and characterized using different analytical techniques (HPLC, IR, UV/Vis, spectrofluorometry and MALDI-TOF). Next, a remote loading method was developed to encapsulate stable Cu(TPZ)2 complexes in different lipid-based nanoparticles. Cu(TPZ)2–nanoparticles were characterized using dynamic light scattering, spectrofluorometry and HPLC. The cytotoxicity of TPZ and Cu(TPZ)2 complexes, and Cu(TPZ)2–nanoparticles was assessed in vitro, using prostate cancer cells cultured under normoxia and hypoxia. The cytotoxicity was evaluated using resurazin cell viability assay.

Results: Cu(TPZ)2 complexes were more hydrophobic in nature, which led to an efficient drug loading in the lipid nanoparticles. The drug loading was dependent on the lipid composition, drug: lipid and the hydrating buffers used. Our results showed that the cytotoxicity of the Cu(TPZ)2–nanoparticles was highly selective to hypoxia. It was also dependent on the cell line, drug concentration, and the incubation time.

Conclusions: In this work, we showed that the complexation of TPZ with copper was an attractive approach to promote TPZ encapsulation in lipid nanoparticles. This novel nanomedicine could overcome TPZ shortcomings in vitro and in vivo, and offer a promising approach to target advanced prostate cancer in patients.

Acknowledgements: This work was supported by Prostate Cancer UK (Grant CDF-12-002), the Engineering and Physical Sciences Research Council (EPSRC) (EP/M008657/1), and University of East Anglia.