Search

Imbalances in cancer cell redox homeostasis provide a platform for new opportunities in the development of anticancer drugs. The control of severe dose-limiting toxicities associated with redox regulation, including myelosuppression and immunosuppression, remains a challenge. Recent evidence implicates a critical role for redox regulation and thiol balance in pathways that control myeloproliferation, hematopoietic progenitor cell mobilization, and immune response. Hematopoietic stem cell (HSC) self-renewal and differentiation are dependent upon levels of intracellular reactive oxygen species (ROS) and niche microenvironments. Redox status and the equilibrium of free thiol:disulfide couples are important in modulating immune response and lymphocyte activation, proliferation and differentiation. This subject matter is the focus of the present review. The potential of redox modulating chemotherapeutics as myeloproliferative and immunomodulatory agents is also covered., (Copyright © 2010 Elsevier Inc. All rights reserved.)

A variety of cell biological, pharmacological, crystallographic and clinical approaches have indicated that the antimitotic drug estramustine has interesting and unusual properties. Although designed as an alkylating agent, the marked stability of the carbamate linkage to the steroid carrier molecule prevents the formation of alkylating intermediates. The affinity of the parent molecule for microtubule associated proteins and the concomitant antimicrotubule activity have cytotoxic consequences in tumor cells. Both preclinical and clinical studies of estramustine in combination with other antimicrotubule agents have shown that this approach has great potential to achieve therapeutic advantage, especially in disease states such as hormone refractory prostate cancer.

Incubation of 100 microM chlorambucil (CMB) with 1 mM glutathione (GSH) in 0.1 M potassium phosphate buffer yielded a mixture of GSH conjugates and hydrolytic products that were separable by HPLC. The appearance in HPLC analysis of four of these products was GSH-dependent. 35S-Label from 35S-GSH eluted with all four chemical species that also gave UV spectra characteristic of CMB-containing compounds. Mass spectral analysis of three of these compounds gave molecular weights consistent with the following adducts: adduct 2: diglutathionyl CMB; adduct 3: monohydroxy monochloroglutathionyl CMB; adduct 4: monochloro monoglutathionyl CMB. Purified GST alpha and partially pure GST pi and mu class protein prepared from adult male mouse liver cytosol significantly increased the formation of the monoglutathionyl CMB adduct. At 5 min incubations, this adduct was quantitatively most important and was increased 4.4-fold by the addition of GST alpha isozymes. At 1 hr incubations, all four adducts were measurable, although enzymes primarily affected the formation of adduct 4. At 1 hr, addition of GST alpha, pi, or mu protein increased the production of monochloro monoglutathionyl CMB 2-fold, 1.5-fold, and 1.7-fold, respectively, demonstrating that CMB is indeed a substrate for GST isozymes in vitro.

Friend erythroleukemia cells (FLC) selected by exposure to Adriamycin (doxorubicin) express an approximate 2.5-fold (ARN1) or 13-fold (ARN2) resistance to the drug with various degrees of cross-resistance to other anthracyclines, vinca alkaloids, and epipodophyllotoxins. Because the redox cycling of the quinone moiety of Adriamycin is known to produce oxidative stress, however, an analysis of glutathione (GSH) and related enzyme systems was undertaken in the wild-type and selected resistant cells. In ARN1 and ARN2, superoxide dismutase (SOD) and catalase activities were slightly decreased, intracellular GSH and GSH reductase were essentially unchanged, and total GSH peroxidase, glutathione S-transferase (GST), and DT-diaphorase activities were slightly elevated. In each case there was no stoichiometric relationship between degree of resistance and level of activity. GST isozymes were purified from each cell line by HPLC GSH affinity column chromatography. Two-dimensional gel electrophoresis and western blot immunoreactivity against a battery of GST isozyme polyclonal antibodies determined that both the resistant and sensitive cells expressed isozymes of the alpha, pi, and mu classes (alternative murine nomenclature: M1, M2, M3). Of significance, both ARN1 and ARN2 cell lines expressed a unique alpha subunit which was absent from the parent FLC cell line. This isozyme presumably accounted for the increased GSH peroxidase activity (cumene hydroperoxide as substrate) found in ARN1 and ARN2 and may play a role in the small incremental resistance to melphalan found for both resistant lines. Expression of the isozyme was not stoichiometric with respect to degree of resistance. The presence of this isozyme may contribute to the resistant phenotype or may be the consequence of a more general cellular response to oxidative stress.