William C. Rose

Novel Strategies for the Discovery of Plant-Derived Anticancer Agents.

Work has continued on the investigation of plants, collected mainly from tropical rainforests, as potential sources of new cancer chemotherapeutic agents. About 400 primary samples are obtained each year, with the chloroform-soluble extract of each being screened against a battery of in vitro assays housed at the three consortial sites in our current National Cooperative Drug Discovery Group (NCDDG) research project. An HPLC-MS dereplication procedure designed to screen out “nuisance” compounds has been refined. Several hundred secondary metabolites that are active in one or more of the primary assays utilized have been obtained in the project to date, and are representative of wide chemical diversity. Some of these are also active in various in vivo assays, inclusive of the hollow fiber assay, which was installed recently as part of our collaborative research effort. A number of bioactive compounds of interest to the project are described.

Preclinical antitumor and toxicologic profile of carboplatin

Carboplatin, an analog of the antitumor drug Platinol, was selected for clinical evaluation on the basis of its experimental antitumor and toxicologic profile in animal models. Described in this review is a detailed summary of selected preclinical data accumulated on carboplatin as well as data obtained concomitantly using Platinol. The predominant result gleaned from the experimental antitumor data is that of comparability between the two compounds, a finding which we feel best reflects the emerging clinical data. With respect to the preclinical toxicology, carboplatin was found to be less nephrotoxic and less emetic than Platinol. This pattern of toxicity for carboplatin appears to be substantiated in the clinical setting.

Novel water soluble phosphate prodrugs of taxol® possessing in vivo antitumor activity☆

Abstract Synthesis and biological evaluation of novel taxol derivatives having a phosphonoxyphenylpropionate ester group at the 2′-position or at the 7-position of taxol are described. These were found to have much improved water solubility and both were found to generate taxol upon exposure to alkaline phosphatase. A particular derivative, 7-phosphonoxyphenylpropionate of taxol 3b exhibited antitumor activity comparable to that of taxol against the ip/ip M109 murine tumor model.

Discovery of anticancer agents of diverse natural origin.

A collaborative multidisciplinary research project is described in which new natural product anticancer drug leads are obtained from a diverse group of organisms, constituted by tropical plants, aquatic cyanobacteria, and filamentous fungi. Information is provided on how these organisms are collected and processed. The types of bioassays are indicated in which crude extracts of these acquisitions are tested. Progress made in the isolation of lead bioactive secondary metabolites from three tropical plants is discussed.

Cetuximab preclinical antitumor activity (monotherapy and combination based) is not predicted by relative total or activated epidermal growth factor receptor tumor expression levels

Although Erbitux (cetuximab) has proven therapeutic benefit in the clinical setting, the molecular determinants predicting responsiveness to this agent are still not very well understood. Here, we assessed the relationship between basal total and activated (pY1068) epidermal growth factor receptor (EGFR) levels in a tumor and the responsiveness to cetuximab monotherapy or combination-based treatment using human xenograft models. Cetuximab treatment alone (0.25–1 mg/mouse/injection, q3d, i.p.) effectively delayed the growth of GEO and L2987 tumors by a minimum of 10 days corresponding to log cell kill values of ≥1.0. Borderline activity was seen in the A549 and WiDr xenografts. However, cetuximab failed to show any significant antitumor activity in the HT29, HCT116, LOVO, Colo205, LX-1, HCC70, and N87 models. All of the studied tumors had detectable yet variable levels of EGFR. For combination regimens, cetuximab (1 mg/mouse/injection, q3dx5, i.p.) and cisplatin (4.5 mg/kg/injection, q3dx5, i.v.) proved to be significantly more efficacious than individual monotherapies in the cisplatin-refractory yet cetuximab-responsive GEO tumor model (P < 0.001). However, no therapeutic enhancement was observed in the cisplatin and cetuximab weakly responsive A549 xenograft. Similarly, combinations of CPT-11 (48 mg/kg/injection, q3dx5, i.v.) with cetuximab (1 mg/mouse/injection, q3dx5, i.p.) failed to show any improvements over individual monotherapies in the cetuximab resistant/weakly responsive HT29, A549, and WiDr models. We conclude that preclinical activity associated with cetuximab monotherapy does not correlate directly with relative basal levels of total or activated (pY1068) EGFR in a tumor. Moreover, robust single-agent activity by cetuximab may be the best predictor for this agent to potentiate chemotherapy-mediated antitumor activities. [Mol Cancer Ther 2006;5(1):104–13]

Discovery of antitumor indolocarbazoles: rebeccamycin, NSC 655649, and fluoroindolocarbazoles.

A fermentation directed product search for potential anticancer drugs conducted by Bristol-Myers in the 1970s and early 1980s resulted in the identification of a novel indolocarbazole (IC) rebeccamycin (RBM) as a potential drug development candidate. Subsequently, an analog program designed to impart distal site in vivo antitumor activity resulted in the discovery of diethylaminoethyl analog of RBM (DEAE-RBM), which is presently undergoing clinical evaluation as NSC 655649 and BMY-27557. Strong DNA intercalation is the primary mechanism of action of DEAE-RBM resulting in the potent catalytic inhibition of both topoisomerases I and II. Precursor feeding fermentation experiments with fluorine-substituted tryptophans yielded novel fluoroindolocarbazoles (FICs). These FICs were identified as targeting topoisomerase (topo) I in a mechanism-based screen and their action on topo I was confirmed by production of topo I-mediated single-strand breaks in DNA at sites essentially identical to those induced by camptothecin. Topo I dependent cytotoxicity was demonstrated for specific FICs using a P388 and camptothecin-resistant P388/CPT45 pair of cell lines, the latter expresses little or no functional topo I. For example, topo I selectivity was greatest with 3,9-difluoro substituted FIC and was least significant and least cytotoxic with 4,8-difluoro substituted FIC. The review focuses on the discovery of the rebeccamycin class of compounds and their structure-activity relationships leading to the development of the clinical candidate BMY-27557 (NSC 655649), as well as the lead identification of the fluoroindolocarbazole class of compounds.

ANTITUMOR ACTIVITY OF PLATINUM ANALOGS

Publisher Summary The antitumor drug cis-diamminedichloro platinum II (cis-DDP) is clinically active against many different neoplasms, most particularly bladder, ovarian, and testicular carcinomas. The drug, however, is not without its undesirable toxic side effects, which include renal toxicity, myelosuppression, and severe nausea and vomiting. In an attempt to improve upon the antitumor activity and/or lessen the unwanted toxic manifestations associated with using cis-DDP, many investigations have been undertaken to evaluate the analogs of this drug. Experimental studies involving platinum analogs have focused on the comparison of antitumor activity, toxic side effects, effectiveness in combination chemotherapy, and absence of cross-resistance. Several analogs have been found to have greater experimental antitumor activity than cis-DDP when evaluated against L1210 leukemia or ADJ/PC6 plasma cell tumor, and several congeners with 1, 2 diamino cyclohexane (DAC) substitutions have shown no cross-resistance to lines of P388 and L1210 leukemia resistant to cis-DDP. Clinical investigations involving some of the more active platinum analogs are also planned. The chapter presents the results of the testing of 74 analogs of cis-DDP for comparative antitumor activity in one to three experimental tumor systems.

Synthesis and antitumor evaluation of paclitaxel phosphonooxymethyl ethers: a novel class of water soluble paclitaxel pro-drugs

The synthesis, pharmacokinetic properties, and antitumor evaluation of novel paclitaxel phosphonooxymethyl ether derivatives 8–11 and salts thereof is described. These compounds exhibit improved water solubility as compared to paclitaxel (1) and upon incubation with plasma and alkaline phosphatase they readily release parent drug. The in vivo antitumor evaluation of compounds 8–11 established them as suitable pro-drugs of paclitaxel.

Preclinical antitumor activity of two novel taxanes

Abstract. Purpose: Two taxane analogs, BMS-184476 and -188797, were evaluated for their in vitro cytotoxicity and in vivo antitumor activity, and compared with paclitaxel and occasionally docetaxel (Taxotere). Methods: Cytotoxicity was assessed in vitro using a panel of human tumor cell lines. Several different murine and human tumor models were used in vivo to evaluate the taxane analogs. Results: Both compounds were found to have cytotoxic potency similar to paclitaxel and to partially overcome two different forms of paclitaxel resistance. BMS-184476 was found to be clearly superior to paclitaxel in three human xenograft tumor models: A2780 ovarian carcinoma; HCT/pk, a moderately paclitaxel-resistant colon carcinoma; and L2987 lung carcinoma. Additionally, in the clinically derived TAXOL-unresponsive ovarian carcinoma, HOC79, BMS-184476 performed slightly better than paclitaxel and Taxotere. BMS-184476 and paclitaxel were inactive in two murine model systems, M5076 sarcoma and the paclitaxel-resistant M109/txlr lung carcinoma. Against the parental M109 tumor, both BMS-184476 and paclitaxel performed comparably. BMS-184476 was never found to be inferior to paclitaxel. The other taxane analog, BMS-188797, displayed efficacy superior to paclitaxel in four in vivo tumor models: HOC79, HCT/pk, M109, and L2987 carcinomas. Like paclitaxel and BMS-184476, BMS-188797 was inactive versus M5076 sarcoma. Conclusions: Two new taxane analogs were characterized as superior to paclitaxel or Taxotere in several in vivo tumor models. Both BMS-184476 and -188797 are currently in phase I or II clinical trials.

Preclinical antitumor activity of water-soluble paclitaxel derivatives

Abstract Purpose: Five water-soluble paclitaxel derivatives were extensively evaluated for their antitumor activities relative to the parent drug. Methods: Both subcutaneous (s.c.) murine (M109 lung) and human (A2780 ovarian, L2987 lung) tumor models were used for this purpose. Results: Consecutive daily intravenous (i.v.) paclitaxel therapy of mice bearing s.c. M109, beginning on day 4 or 5 posttumor implant and continuing for 5 days, resulted in a range of maximum gross log cell kill (LCK) values (reflective of delays in tumor growth) and maximum relative median survival time (%T/C) values (reflective of increases in lifespan) of 1.0–2.1 and 132–162% (and one outlying result of 235%), respectively. Against the same tumor model, using the same treatment schedule, each of the water-soluble derivatives was active, with maximum LCK of 1.3–2.5 and T/C of 124–254%. These LCK and %T/C values were always within 0.5 LCK and 15%, respectively, of the concomitantly obtained maximum effects of paclitaxel. When tested in several experiments against staged (50–100 mg) s.c. A2780 tumors, using various i.v. treatment schedules, the water-soluble derivatives achieved a maximum LCK of 1.4–3.8. Evaluated in parallel, paclitaxel achieved a maximum LCK of 2.1–4.5 following every other day×5 i.v. therapy. When paclitaxel was assayed in several experiments using the staged (50–100 mg) s.c. L2987 tumor model, maximum LCK of 0.9–>4.1 were produced following every other day×5 i.v. therapy. Concomitant testing of the water-soluble derivatives, using the same i.v. treatment schedule, resulted in maximum LCK of 0.2–>4.1. In each of the tumor models used, the consistently active, and usually the most active, water-soluble derivative was BMS-185660. The levels of activity observed were comparable (within 1 LCK) to those achieved concomitantly using paclitaxel, and its potency was only slightly inferior to the parent drug. Conclusions: Based on the evaluations performed in three distal site tumor models, we conclude that BMS-185660 is a water-soluble paclitaxel derivative with preclinical antitumor activity comparable to that of the parent drug.