||Cryptofluorescent cobalamin bioconjugates were designed, synthesized, and evaluated for the potential to delineate tumor margins during surgical procedures, and therefore facilitate complete tumor resection. The fundamental hypotheses are that 1) Vitamin B12 (cobalamin) based fluorescent bioconjugates are safe as imaging agents that will preferentially accumulate at tumor margins, and 2) accumulation of these imaging agents will to aid in intraoperative tumor margin visualization and tumor resection. These hypotheses are based on the observations that cancer cells over-express the cell surface receptor for cobalamin, thereby exhibiting an increase in cobalamin uptake over normal cells; that appending a fluorescent moiety to cobalamin will allow for the visualization of cells; and that cobalamin-fluorophore conjugates display "cryptofluorescent" properties. The term cryptofluorescent describes a conjugate that displays little, or no fluorescent light emission while conjugated, but after cleavage of a linker between cobalamin and the fluorophore, strong fluorescence is observed. This drug delivery approach will in essence distribute a molecular beacon as conjugates are internalized and processed, that will reveal the location of transformed cells. As such, the experimental focus of this project is on the design, synthesis, and investigation of cryptofluorescent cobalamin-fluorophore conjugates to be used for in situ tumor margin visualization.