Lipid peroxidation, phosphoinositide turnover and protein kinase C activation in human platelets treated with anthracyclines and their complexes with Fe(III)

A critical evaluation of the mechanisms of action proposed for the antitumor effects of the anthracycline antibiotics adriamycin and daunorubicin

The mechanisms responsible for the antiproliferative and cytotoxic effects of the anthracycline antibiotics doxorubicin (Adriamycin) and daunorubicin (daunomycin) have been the subject of considerable controversy. This commentary addresses the potential role of DNA synthesis inhibition, free radical formation and lipid peroxidation, DNA binding and alkylation, DNA cross-linking, interference with DNA strand separation and helicase activity, direct membrane effects, and the initiation of DNA damage via the inhibition of topoisomerase II in the interaction of these drugs with the tumor cell. One premise underlying this analysis is that only studies utilizing drug concentrations that reflect the plasma levels in the patient after either bolus administration or continuous infusion are considered to reflect the basis for drug action in the clinic. The role of free radicals in anthracycline cardiotoxicity is also discussed.

Involvement of phosphorylation in doxorubicin-mediated myofibril degeneration. An immunofluorescence microscopy analysis

Loss of myofilaments has been observed in both adaptive cardiac responses (i.e., hypertrophy) as well as in chemotheraputic use of antineoplastic drugs with cardiotoxic side effects (i.e., doxorubicin). An understanding of the degenerative process is a prerequisite for determining approaches to limit the cardiomyopathic changes associated with chronic heart disease or long-term chemotheraputic treatments. However, little is known about the specific events and molecular changes that initiate the degenerative process. To study this process, neonatal rat cardiomyocytes were treated with doxorubicin, which induced rapid and widespread thin-filament degeneration as observed by fluorescence confocal microscopy. Which demonstrated deterioration of sarcomeric thin-filament structure. Changes in the spontaneous beating of cardiomyocytes corresponding with myofibrillar degeneration were apparent using differential interference contrast video microscopy. After finding induction of kinase activity by doxorubicin in cultured cardiomyocytes, the protective effects of specific inhibitors of kinase activity were assessed for their ability to inhibit doxorubicin-induced myofibrillar break-down. Doxorubicin-induced changes appeared similar to the degeneration observed after treatment with a protein kinase activator (phorbol 12-myristate 13-acetate) or a serine-threonine protein phosphatase inhibitor (okadaic acid). Collectively, these results indicate that activation of protein kinase is an important event in the initiation of myofibrillar degeneration by doxorubicin. Further analyses of myofibrillar proteins with respect to biochemical modifications will be necessary to determine if phosphorylation events transmit signal(s) to initiate degeneration.

Oxidative stress from environmental pollutants

Recently progress has been made on O2 toxicity and pathology related to numerous environmental contaminants in insects. The pro-oxidants studied included: dioxin, paraquat, and an assorted array of quinones, 8-methoxypsorlen, arsenic, and mercury. The responses to these oxidants are diverse, but they arise from the reactive oxygen species. These pro-oxidants in insects cause lipid peroxidation, protein and enzyme oxidation, and GSH depletion. Potentially, they may also cause DNA oxidation, and form DNA adducts. Oxidative challenge is alleviated by antioxidant compounds, but more importantly by the induction of antioxidant enzymes, which are crucial for the termination of O2 radical cascade and lipid peroxidation chain reaction. Insects exhibit a wasting syndrome under sub-acute stress. In acute toxicity vital physiological processes impaired are hemolymph melanization and diuresis. Thus, insects resemble vertebrates in both the response to oxidative stress and its pathological consequences. These results raise the prospect that insects may serve as non-mammalian model species for monitoring the oxidative-stress component of environmental toxicity.

Nuclear factor kappa B binding activity in mouse L1210 cells following photofrin II-mediated photosensitization

Clinical photodynamic therapy (PDT) uses the photosensitizer photofrin II to produce singlet molecular oxygen and other reactive oxygen intermediates for localized tumor tissue cytotoxicity. In this report, we show that PDT enhances the DNA binding activity of nuclear factor kappa B (NF kappa B), a transactivator of cytokine gene expression. Photosensitization following a 16 h incubation of photofrin II induced NF kappa B binding activity in mouse leukemia L1210 cells 10-fold above that observed in exponentially growing cultures. Serum starvation, as well as drug-alone and light-alone controls, elevated basal NF kappa B binding activity two- to three-fold. Upstream stimulatory factor binding activity was not modulated by any of the cell treatments and was used to standardize gel mobility shift data. This study identifies porphyrin-mediated PDT as an inducer of NF kappa B binding activity, extending recent findings that NF kappa B activation is a general response to oxidative stress.

The potential of protein kinase C as a target for anticancer treatment

Many investigators have embarked upon the search for novel cellular targets for the treatment of cancer. A popular therapeutic strategy is to intervene with the components of cellular signalling systems that are altered during malignancy. The molecular heterogeneity of the protein kinase C (PKC) family and their functional divergence make them attractive targets for anticancer drug development. PKC can also influence the sensitivity of tumor tissue to conventional cytotoxic drugs. As discussed in this review, a complete understanding of the PKC signal transduction pathway is obligatory for the selective destruction of tumor tissue by exploiting PKC as either a target or a modulator of cancer chemotherapeutic agents.