Cytotoxic/protective activity cancer

Cytotoxic/Protective Activity of Nitric Oxide in Cancer... 

Fig. 7.1 Schematic representation of the cytotoxic/protective roles of NO in cancer. The complicated outcome of cytotoxic/protective activity of NO depends on the concentration of NO and microenvironment with tumor cells and tumor-associated macrophages. High concentrations of NO, principally induced by iNOS, may induce anti-cancer effects in tumor cells, whereas low, but continuous, concentrations of NO, mainly induced by eNOS, may result in pro-cancer effects. NO has also the potential to enhance both radiotherapy and chemotherapy...

Abstract Nitric oxide (NO), synthesized from L-arginine by NO synthases, is a small, lipophilic, diffusible, highly reactive molecule with dichotomous regulatory roles in many biological events under physiological and pathological conditions. NO promotes apoptosis in some tumor cells, but provokes anti-apoptotic activity in other rnmor cells. For this reason, conflicting viewpoints have arisen as to whether nitric oxide is cytotoxic or protective in cancer cells. 

Constitutive activation of the P13-K - Akt/PKB survival signaling pathway is a likely mechanism by which many cancers become refractory to cytotoxic therapy. In LNCaP prostate cancer cells, the PTEN is inactivated, leading to constitutive activation of Akt/PKB and resistance to apoptosis. However, apoptosis and inactivation of Akt/PKB can be induced in these cells by treatment with P13-K inhibitors. Surprisingly, androgen, epidermal growth factor, or semm can protect these cells from apoptosis, even in the presence of P13-K inhibitors and without activation of Akt/PKB, indicating the activity of a novel, Akt/PKB-independent survival pathway. This pathway blocks apoptosis at a level prior to caspase 3 activation and release of cytochrome c from mitochondria (Carson et al, 1999)... 

Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and muagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented... 

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