Liposome-mediated delivery of radionuclides to tumor models for cancer radiotherapy: A quantitative analysis

Towards the design of therapeutically effective liposome-radionuclide conju gates, the predominant focus should rest with the ability of such modalitie s to efficiently target tumor sites;md thus selectively deliver cytotoxic l evels of radiation doses. For this reason analytic dosimetric calculations were carried out to quantitatively examine the critical physical parameters for the potential clinical application of radionuclide-liposome conjugates in internal radiotherapy. The radiodosimetric model employed followed the mathematical formalism of the MIRD (Medical Internal Radiation Dose Committ ee) scheme. Analytic pharmacokinetic functions for a variety of liposome co nstructs coupled with the radiation properties of three of the most promisi ng particle emitting radionuclides: Cu-67, Re-188, At-211 and the most wide ly used in the clinic I-131, were used as input information to the model de veloped. Results are presented in the form of radiation absorbed doses and tumor-to-normal-tissue radiation ratios. It is concluded that liposome-medi ated radionuclide tumor targeting for radiotherapy is certainly promising, and critically dependent on the optimal matching between radionuclide half- life and the time range when the tumor-to-(critical)organ liposome accumula tion ratios become maximal. Liposome-mediated chemotherapy (drug targeting) is also comparatively discussed demonstrating the predominant importance o f "timing factors" in the case of radiotherapeutic (radionuclide targeting) applications.