Fig. 1: Overview of N-alkylpyridinium reagents to achieve dual modification of functional proteins and proof-of-concept application with a toxin enzyme.

The tripeptide arginine-glycine-aspartic acid (RGD) has been selected as the targeting moiety that binds to the integrin receptors on the cancer cell’s surface. C3bot1 toxin (C3) from Clostridium botulinum that catalyzes ADP-ribosylation of Rho proteins was selected for dual modification with a fluorescent dye (Cy5) and a RGD peptide for in vitro imaging and concomitant inhibition of specific Rho-mediated cellular pathways.