Applications of microwave-assisted organic synthesis on the multigram scale.

This review presents a summary of reactions performed using microwave irradiation on a multigram scale. Results are described in the context of existing equipment, and equipment currently in development, for the processing of multigram to kilogram quantities of materials including single- and multimode microwave reactors and batch, batch-flow and continuous-flow systems. Although limited in number, reports found in the literature to date suggest that with appropriate controls, reproducible scale-up of microwave reactions is feasible and requires minimal re-optimization of laboratory-scale reaction conditions. This feature, along with the dramatic reductions in reaction time generally observed for microwave reactions suggests that application of this technology in process research could be beneficial.

A prostate-specific antigen (PSA)-activated vinblastine prodrug selectively kills PSA-secreting cells in vivo.

Currently, there is no therapy for men with androgen-refractory prostate cancer that substantially extends survival. This report characterizes by in vitro and in vivo techniques a new chemotherapeutic that is composed of desacetyl-vinblastine covalently linked to a peptide that contains a peptide bond that can be hydrolyzed by prostate-specific antigen (PSA). This compound (referred to as vinblastine-conjugate) is minimally toxic to cells in culture which do not express PSA. In the presence of PSA, the peptide moiety is hydrolyzed, generating several highly toxic metabolites that contain vinblastine. Animals bearing PSA-positive human prostate tumors that were treated with the vinblastine-conjugate experienced a >99% reduction in PSA serum level. In contrast, animals bearing PSA-positive human prostate tumors treated with the cytotoxic metabolites derived from the PSA hydrolysis of the vinblastine-conjugate showed a nonsignificant change in both PSA and tumor weight values. The cell killing activity of the vinblastine-conjugate is PSA dependent because animals bearing non-PSA-producing human tumor xenografts had a nonsignificant increase in tumor weight after vinblastine-conjugate treatment. Exploratory efficacy/toxicity studies in LNCaP tumor-bearing nude mice were conducted with animals treated for 5 consecutive days with various doses of either the vinblastine-conjugate or a PSA-generated toxic metabolite (desacetyl-vinblastine). The desacetyl-vinblastine treatment resulted in 10-70% mortality with a very slight effect on tumor growth. In contrast, vinblastine-conjugate treatments resulted in no mortality, good to excellent antitumor efficacy, very slight to slight peripheral neuropathy and myelopathy, and slight to severe testicular degeneration. Similar treatment of beagle dogs with the vinblastine-conjugate showed even less toxicity. These data support the use of the PSA-hydrolyzable vinblastine-conjugate as an experimental therapy for prostate cancer in man.

Design and synthesis of a pro-drug of vinblastine targeted at treatment of prostate cancer with enhanced efficacy and reduced systemic toxicity.

Chemotherapy of prostate cancer with antimitotic agents such as vinblastine and doxorubicin is only marginally effective, due to dose-limiting systemic toxicity. Herein we report the development of peptidyl conjugate 5 of the cytotoxic agent vinblastine (1), along with the results of its in vitro and in vivo evaluation as a pro-drug targeted at prostate cancer cells. Prostate-derived tumors are known to produce significant amounts of prostate specific antigen (PSA), a serine protease with chymotrypsin-like properties. Earlier work in these laboratories established that an appropriately engineered peptidyl pro-drug will release active cytotoxic agent strictly within the microenvironment of the tumor tissue (Garsky, V. M., et al. J. Med.Chem. 2001, 44, 4216-4224). Conjugate 5, which features an octapeptide segment attached by an ester linkage at the 4-position of vinblastine (1), undergoes rapid cleavage by PSA (T(1/2) = 12 min) between the Gln and Ser residues. In nude mouse xenograft studies, 5 reduced circulating PSA levels by 99% and tumor weight by 85% at a dose just below its MTD. By contrast, the putative end-point metabolite, the cytotoxic agent des-acetyl vinblastine (1b), was ineffective in reducing PSA levels and tumor burden at its maximum tolerated doses. Additional data from metabolism studies on 5 support the supervention of a novel in vivo processing mechanism, the spontaneous release of 1b from a dipeptidyl intermediate driven by favorable diketopiperazine formation.