Synthesis and beta-lactamase-mediated activation of a cephalosporin-taxol prodrug.
BACKGROUND
Enzyme-activatable prodrugs in conjunction with antibody-enzyme fusion proteins may enhance the anti-tumor efficacy of antibodies and reduce the toxic side effects of conventional chemotherapeutics. Cephalosporins have proven to be highly versatile triggers for the enzymatic activation of such prodrugs.


RESULTS
A cephem prodrug of taxol (PROTAX) was synthesized by substituting the C-3' position of cephalothin with 2'-(gamma-aminobutyryl) taxol. Hydrolysis of PROTAX by beta-lactamase rapidly released 2'-(gamma-aminobutyryl) taxol (kcat/K(M) = (1.4 +/- 0.1) x 10(5) s-1 M-1), which yielded taxol following intramolecular displacement. PROTAX is inactive in a microtubule assembly assay in vitro but has similar activity to taxol following prolonged activation with beta-lactamase. PROTAX is approximately 10-fold less toxic than taxol against SK-BR-3 breast tumor cells in vitro but has activity approaching that of taxol following prolonged activation with a fusion protein comprising beta-lactamase fused to a tumor-targeting antibody fragment.


CONCLUSIONS
Tubulin polymerization activity is abolished and cytotoxicity is reduced in the PROTAX prodrug compared to taxol. Activation of PROTAX by beta-lactamase followed by self-immolation restores the activity of PROTAX to that of free taxol.
Rodrigues
M L
ML
Department of Cell Genetics, Genentech Inc., South San Francisco, CA 94080-4990, USA.
Carter
P
P
Wirth
C
C
Mullins
S
S
Lee
A
A
Blackburn
B K
BK
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D001711:Biotransformation; D001923:Brain Chemistry; D001943:Breast Neoplasms / Q000378:metabolism; D002417:Cattle; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism; D017239:Paclitaxel / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D011355:Prodrugs / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D043823:Taxoids; D014407:Tumor Cells, Cultured; D001618:beta-Lactamases / Q000737:chemistry*
D000972:Antineoplastic Agents, Phytogenic; D011355:Prodrugs; D011993:Recombinant Fusion Proteins; D043823:Taxoids; C109632:protax; D001618:beta-Lactamases; D017239:Paclitaxel