We have shown previously that the
bleomycin (BLM)
carbohydrate moiety can recapitulate the
tumor cell targeting effects of the entire BLM molecule, that BLM itself is modular in nature consisting of
a DNA-cleaving aglycone which is delivered selectively to the interior of
tumor cells by its
carbohydrate moiety, and that there are
disaccharides structurally related to the BLM
disaccharide which are more efficient than the natural
disaccharide at
tumor cell targeting/uptake. Because BLM
sugars can deliver molecular cargoes selectively to
tumor cells, and thus potentially form the basis for a novel antitumor strategy, it seemed important to consider additional structural features capable of affecting the efficiency of
tumor cell recognition and delivery. These included the effects of
sugar polyvalency and net charge (at physiological pH) on
tumor cell recognition, internalization, and trafficking. Since these parameters have been shown to affect cell surface recognition, internalization, and distribution in other contexts, this study has sought to define the effects of these structural features on
tumor cell recognition by
bleomycin and its
disaccharide. We demonstrate that both can have a significant effect on
tumor cell binding/internalization, and present data which suggests that the
metal ions normally bound by
bleomycin following clinical administration may significantly contribute to the efficiency of
tumor cell uptake, in addition to their characterized function in DNA cleavage. A BLM
disaccharide-
Cy5** conjugate incorporating the positively charged
dipeptide d-Lys-d-Lys was found to associate with both the mitochondria and the nuclear envelope of DU145 cells, suggesting possible cellular targets for BLM
disaccharide-
cytotoxin conjugates.