Gamma-glutamyltranspeptidase expression regulates the growth-inhibitory activity of the anti-tumor prodrug gamma-L-glutaminyl-4-hydroxy-3-iodobenzene

Electrochemical Behavior and Direct Quantitative Determination of Paclitaxel

The electrochemical behavior and direct quantitative determination of paclitaxel, a poorly soluble drug made into microemulsion, were researched by cyclic voltammetry in acetate buffer solutions (pH = 4.0) at a glassy carbon electrode. The results show that the oxidation process is irreversible and controlled by diffusion. Moreover, the effects of anodic peak current (Ipa), anodic peak potential, scan rate, pH, and the electrochemical redox mechanism have been studied. The anodic peak current varied linearly with paclitaxel concentration in the range of 5 × 10-5 mol/L to 5 × 10-4 mol/L, and the detection limit was 9.15 × 10-8 mol/L. The results of RSD (0.90%) and recovery (99.22%-101.69%) were obtained. Additionally, it has been proved that one electron and one proton are involved in the electrochemical redox process. The present research has been successfully used to determine paclitaxel in pure and real samples, which further supported the electrochemical behavior investigation of paclitaxel and direct determination of micro-emulsion.

Glutathione S-conjugates as prodrugs to target drug-resistant tumors

Living organisms are continuously exposed to xenobiotics. The major phase of enzymatic detoxification in many species is the conjugation of activated xenobiotics to reduced glutathione (GSH) catalyzed by the glutathione-S-transferase (GST). It has been reported that some compounds, once transformed into glutathione S-conjugates, enter the mercapturic acid pathway whose end products are highly reactive and toxic for the cell responsible for their production. The cytotoxicity of these GSH conjugates depends essentially on GST and gamma-glutamyl transferases (γGT), the enzymes which initiate the mercapturic acid synthesis pathway. Numerous studies support the view that the expression of GST and γGT in cancer cells represents an important factor in the appearance of a more aggressive and resistant phenotype. High levels of tumor GST and γGT expression were employed to selectively target tumor with GST- or γGT-activated drugs. This strategy, explored over the last two decades, has recently been successful using GST-activated nitrogen mustard (TLK286) and γGT-activated arsenic-based (GSAO and Darinaparsin) prodrugs confirming the potential of GSH-conjugates as anticancer drugs.

Human melanocyte biology, toxicology, and pathology

The human melanocytes of the skin, hair, eyes, inner ears, and covering of the brain provide physiologic functions important in organ development and maintenance. Melanocytes develop from embryonic neural crest progenitors and share certain traits with other neural crest derivatives found in the adrenal medulla and peripheral nervous system. The distinctive metabolic feature of melanocytes is the synthesis of melanin pigments from tyrosine and cysteine precursors involving over 100 gene products. These complex biochemical mechanisms create inherent liabilities for melanocytic cells if intracellular systems necessary for compartmentalization, detoxification, or repair are compromised. Melanocyte disorders may involve pigmentation, sensory functions, autoimmunity, or malignancy. Environmental factors such as ultraviolet radiation and chemical exposures, combined with heritable traits, represent the principal hazards associated with melanocyte disorders.

Enzyme-catalyzed activation of anticancer prodrugs

The rationale fo the development of prodrugs relies upon delivery of higher concentrations of a drug to target cells compared to administration of the drug itself. In the last decades, numerous prodrugs that are enzymatically activated into anti-cancer agents have been developed. This review describes the most important enzymes involved in prodrug activation notably with respect to tissue distribution, up-regulation in tumor cells and turnover rates. The following endogenous enzymes are discussed: aldehyde oxidase, amino acid oxidase, cytochrome P450 reductase, DT-diaphorase, cytochrome P450, tyrosinase, thymidylate synthase, thymidine phosphorylase, glutathione S-transferase, deoxycytidine kinase, carboxylesterase, alkaline phosphatase, beta-glucuronidase and cysteine conjugate beta-lyase. In relation to each of these enzymes, several prodrugs are discussed regarding organ- or tumor-selective activation of clinically relevant prodrugs of 5-fluorouracil, axazaphosphorines (cyclophosphamide, ifosfamide, and trofosfamide), paclitaxel, etoposide, anthracyclines (doxorubicin, daunorubicin, epirubicin), mercaptopurine, thioguanine, cisplatin, melphalan, and other important prodrugs such as menadione, mitomycin C, tirapazamine, 5-(aziridin-1-yl)-2,4-dinitrobenzamide, ganciclovir, irinotecan, dacarbazine, and amifostine. In addition to endogenous enzymes, a number of nonendogenous enzymes, used in antibody-, gene-, and virus-directed enzyme prodrug therapies, are described. It is concluded that the development of prodrugs has been relatively successful; however, all prodrugs lack a complete selectivity. Therefore, more work is needed to explore the differences between tumor and nontumor cells and to develop optimal substrates in terms of substrate affinity and enzyme turnover rates fo prodrug-activating enzymes resulting in more rapid and selective cleavage of the prodrug inside the tumor cells.

Mapping of the active site of rat kidney gamma-glutamyl transpeptidase using activated esters and their amide derivatives

The enzyme gamma-glutamyl transpeptidase (GGT), implicated in many physiological processes, catalyses the transfer of a gamma-glutamyl from a donor substrate to an acyl acceptor substrate, usually an amino acid or a peptide. In order to investigate which moieties of the donor substrate are necessary for recognition by GGT, the structure of the well-recognized substrate L-gamma-glutamyl-p-nitroanilide was modified. Several activated esters and their amide derivatives were synthesized and used as substrates. Kinetic (K(m) and V(max)) and inhibition constants (K(i)) were measured and reveal that almost the entire gamma-glutamyl moiety is necessary for recognition in the binding site of the donor substrate. The implied presence of certain complementary amino acids in this substrate binding site will allow the more rational design of various substrate analogues and inhibitors.

Receptor-mediated and enzyme-dependent targeting of cytotoxic anticancer drugs

This review is a survey of various approaches to targeting cytotoxic anticancer drugs to tumors primarily through biomolecules expressed by cancer cells or associated vasculature and stroma. These include monoclonal antibody immunoconjugates; enzyme prodrug therapies, such as antibody-directed enzyme prodrug therapy, gene-directed enzyme prodrug therapy, and bacterial-directed enzyme prodrug therapy; and metabolism-based therapies that seek to exploit increased tumor expression of, e.g., proteases, low-density lipoprotein receptors, hormones, and adhesion molecules. Following a discussion of factors that positively and negatively affect drug delivery to solid tumors, we concentrate on a mechanistic understanding of selective drug release or generation at the tumor site.

Apoptosis in human lymphoblastoid cells induced by acivicin, a specific gamma-glutamyltransferase inhibitor

We examined the effects of acivicin, a specific inhibitor of the ectoenzyme gamma-glutamyltransferase (gamma-GT), on gamma-GT activity and apoptosis in 2 human T-lymphoblastoid CEM cell lines, CCRF and VBL-100. In both cell lines, acivicin was found to cause morphological and biochemical changes of apoptosis in a dose-dependent manner. There was a close correlation between inhibition of gamma-GT activity and the emergence of apoptotic cells. However, VBL-100 cells had a 50% higher gamma-GT basal activity than CCRF-CEM cells, their enzyme activity was more inhibited, and, they had a greater apoptotic response to acivicin. The gamma-GT-specific activity in apoptotic/dead cells was also almost totally inhibited, while that of cells that remained alive after 5 days of acivicin treatment was not. These findings confirm that gamma-GT is implicated in the process of apoptosis of CEM cells.