ABSTRACT
An effective approach for enhancing the selectivity of beta-site amyloid precursor protein cleaving enzyme (BACE 1) inhibitors is developed based on the unique features of the S1' pocket of the enzyme. A series of low molecular weight (<600) compounds were synthesized with different moieties at the P1' position. The selectivity of BACE 1 inhibitors versus cathepsin D and renin was enhanced 120-fold by replacing the hydrophobic propyl group with a hydrophilic propionic acid group.
Subject(s)
Alzheimer Disease/enzymology , Aspartic Acid Endopeptidases/antagonists & inhibitors , Drug Design , Enzyme Inhibitors/pharmacology , Amyloid Precursor Protein Secretases , Cathepsin D/antagonists & inhibitors , Endopeptidases , Enzyme Inhibitors/chemical synthesis , Humans , Molecular Structure , Molecular Weight , Propionates/chemistry , Renin/antagonists & inhibitors , Substrate SpecificityABSTRACT
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.
Subject(s)
Antineoplastic Agents, Phytogenic/therapeutic use , Prodrugs/therapeutic use , Prostate-Specific Antigen/metabolism , Prostatic Neoplasms/therapy , Vinblastine/therapeutic use , Animals , Antineoplastic Agents/therapeutic use , Antineoplastic Agents, Phytogenic/metabolism , Dogs , Doxorubicin/therapeutic use , Humans , Male , Mice , Mice, Nude , Models, Chemical , Neoplasm Transplantation , Prodrugs/metabolism , Prostatic Neoplasms/pathology , Species Specificity , Tissue Distribution , Tumor Cells, Cultured , Vinblastine/metabolismABSTRACT
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.
