Disclosed are compounds for the selective labeling of cell-surface sugars in cancer cells. The compounds are activatable by triggers specific to cancer cells, and, when metabolized, label a cancer cell surface sugar with an azide chemical group. Facilitated by a click chemistry reaction, combination of the cell surface-expressed azide with a alkynyl-drug conjugate enables efficient targeted drug delivery to cancer cells with reduced toxicity. Also disclosed are compounds for delivering a drug to an azide-bearing cancer cell, and methods of treating cancer using the compounds of the invention.
