ABSTRACT
The remarkable anticancer drug dolastatin 10 (1a) from the Indian Ocean sea hare Dolabella auricularia is currently undergoing phase I clinical trials. Thirty-eight new structural modifications of this unusual peptide have been synthesized and evaluated against a variety of human and murine cancer cell lines, and for their ability to inhibit tubulin polymerization and vinblastine and GTP binding to tubulin. Dolastatin 10 and one structural modification was found to have antifungal activity, while one other structural modification of the parent compound exhibited antibacterial activity. Some of the new peptides approximated the antineoplastic potency of dolastatin 10, especially those based on replacement of the Doe unit with Met, Phe or an appropriately substituted phenylethylamide.
Subject(s)
Antineoplastic Agents/pharmacology , Oligopeptides/pharmacology , Animals , Anti-Bacterial Agents , Anti-Infective Agents/chemistry , Anti-Infective Agents/pharmacology , Antineoplastic Agents/chemistry , Cryptococcus neoformans/drug effects , Depsipeptides , Drug Design , Drug Screening Assays, Antitumor , Female , Humans , Mice , Microbial Sensitivity Tests , Micrococcus luteus/drug effects , Oligopeptides/chemical synthesis , Oligopeptides/chemistry , Structure-Activity Relationship , Tubulin/chemistry , Tumor Cells, Cultured/drug effectsABSTRACT
Dolastatins 10 and 15 are small peptides isolated from the marine sea hare Dolabella auricularia that have been shown to interact with tubulin. Their growth-inhibitory properties were compared using panels of human ovarian and colon-carcinoma cell lines. Both agents were very potent inhibitors of cell growth, with dolastatin 10 being an average of 9.1-fold more potent than dolastatin 15 [mean 50% inhibitory concentrations (IC50 values) 2.3 x 10(-10) and 2.1 x 10(-9) M, respectively; P < 0.05] and more potent than paclitaxel or vinblastine. While neither dolastatin exhibited marked cross-resistance in cisplatin- or etoposide-resistant cell lines, contrasting effects were observed using an acquired doxorubicin-resistant (CH1doxR, 100-fold resistant, P-glycoprotein overexpressing) cell line. Resistance was significantly higher to dolastatin 15 (12.7-fold) than to dolastatin 10 (only 3.2-fold; P < 0.05) and was reversible in both cases by verapamil. In vivo, using a s.c. advanced-stage human ovarian carcinoma xenograft and equitoxic doses, greater activity was observed with dolastatin 10 (6.1-day growth delay) versus 0.4 days for dolastatin 15. A radioimmunoassay for dolastatin 10 (limit of detection in mouse plasma 5 ng/ml) was developed. The rabbit antiserum aslo cross-reacted by 65% with dolastatin 15. Comparative mouse pharmacokinetics following i.v. administration of 1 mg/kg showed that both compounds are rapidly eliminated, but with a shorter second-phase half-life (t1/2 beta) being observed for dolastatin 15 (being detectable for only up to 4 h post-administration), the t1/2 beta being 3 times longer for dolastatin 10. In addition, areas under the plasma concentration-time curve (AUC values) were 1.6-fold higher for dolastatin 10 (333 versus 208 ng ml-1 h). Plasma binding of dolastatin 10 exceeded 90%. The highly sensitive RIA will be useful for pharmacokinetic studies in conjunction with the planned phase I clinical trials of these novel, extremely potent, tubulin-binding agents, of which dolastatin 10 appears to possess the more promising preclinical features.
Subject(s)
Antineoplastic Agents/therapeutic use , Depsipeptides , Oligopeptides/therapeutic use , Animals , Antineoplastic Agents/administration & dosage , Antineoplastic Agents/blood , Antineoplastic Agents/pharmacology , Carcinoma/drug therapy , Carcinoma/pathology , Cell Division/drug effects , Colonic Neoplasms/drug therapy , Colonic Neoplasms/pathology , Cross Reactions , Drug Resistance, Multiple/genetics , Female , Half-Life , Humans , Injections, Intravenous , Mice , Mice, Inbred BALB C , Neoplasm Transplantation , Oligopeptides/administration & dosage , Oligopeptides/blood , Oligopeptides/pharmacology , Ovarian Neoplasms/drug therapy , Ovarian Neoplasms/pathology , Rabbits , Radioimmunoassay , Random Allocation , Transplantation, Heterologous , Tumor Cells, Cultured/drug effects , Verapamil/pharmacologyABSTRACT
New structural modifications of the marine shell-less mollusk peptide constituent dolastatin 10 (1) have been synthesized, and evaluated against a variety of cancer cell lines and for their ability to inhibit tubulin polymerization. A number of useful structure-activity relationships were uncovered. The most important observation was that the dolaphenine unit of dolastatin 10 could be satisfactorily replaced with a phenethylamine. Peptide 11C, designated auristatin PE, was found to exhibit inhibition of cancer cell growth and tubulin assembly comparable to that of dolastatin 10.
