SYNTHESIS AND BETA-LACTAMASE-MEDIATED ACTIVATION OF A CEPHALOSPORIN-TAXOL PRODRUG

Background: Enzyme-activatable prodrugs in conjunction with antibody-e nzyme fusion proteins may enhance the anti-tumor efficacy of antibodie s and reduce the toxic side effects of conventional chemotherapeutics. Cephalosporins have proven to be highly versatile triggers for the en zymatic activation of such prodrugs. Results: A cephem prodrug of taxo l (PROTAX) was synthesized by substituting the C-3' position of cephal othin with 2'-(gamma-aminobutyryl) taxol. Hydrolysis of PROTAX by beta -lactamase rapidly released 2'-(gamma-aminobutyryl) taxol (k(cat)/K-M = (1.4 +/- 0.1) x 10(5) s(-1) M(-1)), which yielded taxol following in tramolecular displacement. PROTAX is inactive in a microtubule assembl y assay in vitro but has similar activity to taxol following prolonged activation with beta-lactamase. PROTAX is similar to 10-fold less tox ic than taxol against SK-BR-3 breast tumor cells in vitro but has acti vity approaching that of taxol following prolonged activation with a f usion protein comprising beta-lactamase fused to a tumor-targeting ant ibody fragment. Conclusions: Tubulin polymerization activity is abolis hed and cytotoxicity is reduced in the PROTAX prodrug compared to taxo l. Activation of PROTAX by beta-lactamase followed by self-immolation restores the activity of PROTAX to that free taxol.