RESUMO
Health status is determined by the balance of oxidants and antioxidants which protects healthy cells against the threat of internal and external risk factors. Antioxidants such as ascorbate (vitamin C, ascorbic acid) are of fundamental importance in this respect. Ascorbate neutralizes potential damage caused by cellular oxidative stress which may be the greatest risk of damage to healthy tissue. Cellular oxidative stress is mediated by external factors (e.g. psychological stress, physical exertion, drugs, various diseases, environmental pollution, preservatives, smoking, and alcohol) and internal factors (products of cellular metabolism including reactive oxygen species). When the products of oxidative stress are not sufficiently neutralized, healthy cells are at risk for both mitochondrial and DNA damage. In the short term, cell function may deteriorate, while an increased production of proinflammatory cytokines over time may lead to the development of chronic inflammatory changes and diseases, including cancer. Although pharmaceutical research continues to bring effective chemotherapeutic agents to the market, a limiting factor is often the normal tissue and organ toxicity of these substances, which leads to oxidative stress on healthy tissue. There is increasing interest and imperative to protect healthy tissues from the negative effects of radio-chemotherapeutic treatment. The action of ascorbate against the development of oxidative stress may justify its use not only in the prevention of carcinogenesis, but as a part of supportive or complementary therapy during treatment. Ascorbate (particularly when administered parentally at high doses) may have antioxidant effects that work to protect healthy cells and improve patient tolerability to some toxic radio-chemotherapy regimens. Additionally, ascorbate has demonstrated an immunomodulatory effect by supporting mechanisms essential to anti-tumor immunity. Intravenous administration of gram doses of vitamin C produce high plasma levels immediately, but the levels drop rapidly. Following oral vitamin C administration, plasma levels increase slowly to relatively low values, and then gradually decay. With an oral liposomal formulation, significantly higher levels are attainable than with standard oral formulations. Therefore, oral administration of liposomal vitamin C appears to be an optimal adjunct to intravenous administration. In this review, the basic mechanisms and clinical benefits of ascorbate as an antioxidant that may be useful as complementary therapy to chemotherapeutic regimens will be discussed.
RESUMO
Acquired hormone resistance is an old hurdle and still represents to be a constant challenge in oncology for the medical community. Most recently, mainly following the results of BOLERO-2 study, the activation of the PI3K-AKT-mTOR pathway is considered clinically relevant for tumor escape from hormone dependence in breast cancer. In the BOLERO-2 trial, a combination of everolimus, mTOR inhibitor, and exemestane significantly prolonged the median progression free survival (PFS) compared to exemestane alone in advanced breast cancer patients with acquired endocrine resistance. Therefore, the inhibitors of the PI3K-AKT-mTOR pathway are a new class of drugs in great expansion joined with great expectation. This review article focuses on this special issue and briefly reports on the results of clinical trials using PI3K-AKT-mTOR inhibitors. However, the emergence of resistance to this new class of drugs, evidenced by the basic research and the relatively less benefit shown in the clinical trials, has been emerging as a new undesirable complication. Therefore, the principal elucidated mechanisms of the resistance to the inhibitors of the PI3K-AKT-mTOR pathway and the related potential therapeutic strategies are described. A more general immunological approach to delay acquired hormone resistance has also been considered and commented upon.
