A novel B-ring modified homocamptothecin, 12-Cl-hCPT, showing antiproliferative and topoisomerase I inhibitory activities superior to SN-38.
We report the synthesis and pharmacological evaluation of a novel homocamptothecin (hCPT) derivative, 12-Cl-hCPT, which contains a seven-membered beta-hydroxylactone in place of the conventional six-membered alpha-hydroxylactone found in camptothecin (CPT) and bears a chloro substituent at position 12. The capacity of 12-Cl-hCPT to inhibit DNA topoisomerase I was compared with that of SN-38, the active metabolite of the clinically used antitumour prodrug CPT-11. In the DNA relaxation assay, 12-Cl-hCPT proved to be slightly more potent than SN-38 at stimulating the formation of nicked plasmid DNA molecules. A series of radiolabelled DNA restriction fragments were employed to identify and compare the position of the DNA cleavage sites induced by topoisomerase I in the presence of 12-Cl-hCPT and SN-38. These sequencing studies confirm that both 12-Cl-hCPT and SN-38 strongly promote DNA cleavage by topoisomerase I and reveal that the majority of the cleavage sites are located at the same nucleotide positions for the two drugs. However, a certain number of DNA cleavage sites were found to be specific to 12-Cl-hCPT. These sites, previously characterized with unsubstituted hCPT, generally correspond to 5'-CG sites whereas the sites common to the 12-Cl-hCPT and SN-38 essentially correspond to 5'-TG sites. We also quantified the formation of drug-induced protein-DNA complexes formed in HT29 human colon carcinoma cells. Trapping of endogenous proteins onto DNA was found to be much more efficient with 12-Cl-hCPT than with SN-38. These data provide a molecular basis to account for the enhanced antiproliferative activity of 12-Cl-hCPT compared with that of SN-38. Biological evaluation on a panel of sensitive and drug-resistant cell lines revealed 12-Cl-hCPT to be more cytotoxic to tumour cells than SN-38. 12-Cl-hCPT proved 14- and 23-fold more active than SN-38 toward the K562adr and T24anp multidrug-resistant cell lines, respectively. The marked topoisomerase I inhibitory properties of 12-Cl-hCPT coupled with its interesting antiproliferative activity, in particular against cancer cells presenting multidrug resistance phenotype with overexpression of P-glycoprotein, makes 12-Cl-hCPT a valid candidate for subsequent preclinical evaluation. Collectively, the data strengthen homocamptothecin as an extremely promising template to generate novel and potent antitumour agents.
Bailly
C
C
Laboratoire de Pharmacologie Antitumorale du Centre Oscar Lambret, et INSERM U-524, IRCL, Lille, France. bailly@lille.inserm.fr
Laine
W
W
Baldeyrou
B
B
Demarquay
D
D
Huchet
M
M
Coulomb
H
H
Lanco
C
C
Lavergne
O
O
Bigg
D C
DC
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000302:isolation & purification / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D004278:DNA, Superhelical / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019073:HT29 Cells; D006801:Humans; D000077146:Irinotecan; D010957:Plasmids / Q000235:genetics / Q000302:isolation & purification; D059004:Topoisomerase I Inhibitors
D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D004278:DNA, Superhelical; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D004317:Doxorubicin; C120029:homocamptothecin; D002166:Camptothecin