Vitamin B12-Metal Conjugates for Targeted Chemotherapy and Diagnosis: Current Status and Future Prospects

Vitamin B-12 (cyanocobalamin) is a vital nutrient characterized by very low bioavailability. Owing to their extremely high proliferation rates, tumor cells show increased demand for nutrients in comparison with healthy ones, including the greater uptake of vitamin B-12. This avidity for cyanocobalamin can thus be exploited for the site-specific delivery of drugs directly into tumor cells by conjugation of vitamin B-12 (carrier) to either chemotherapeutic or diagnostic agents. In particular, tailored cobalamin-containing substrates can be conjugated to metal-based drugs to achieve targeted delivery into the affected tissues, thus accomplishing biomolecular recognition and tumor selectivity. Progress in the development of metalvitamin B-12 conjugates for medicinal applications is summarized and discussed.