Efecto paradójico de algunas sustancias radioprotectoras en la radiosensibilización de células de melanoma metastásico B16F10

Resumen

Introduction: An ideal chemical radioprotector should be highly effective against the biological damage caused by ionizing radiation while being void of toxicity. In Radiobiology, it is a permanent objective to search for specific protective mechanisms for each situation of human exposure that allows obtaining the desired benefits in exposures to ionizing radiation. Aims: to compare the genoprotective and radioprotective effects of certain antioxidative substances extracted from rosemary (Rosmarinus officinalis) (carnosic acid (CARN) and rosmarinic acid (AR)) with those of other antioxidative compounds and determine the possibly paradoxical effect of these substances that display an intense radiosensitizing action when applied to metastatic melanoma cells Material and method: the genoprotective effect of various substances was studied in two micronucleus assays in order to quantify the antimutagenic activity via micronucleus frequency reduction in vitro in irradiated Cytochalasin B-blocked human lymphocytes and in vivo in mouse bone marrow polychromatophilic erythrocytes. To determine the radioprotective effect on cellular survival, a cellular viability assay (MTT) was performed on PNT2 cell cultures (normal human prostate epithelial cells), TRAMP-C1 cells (transgenic murine prostate epithelial adenocarcinoma cells) and in B16F10 cells (metastatic murine melanoma), which were applied prior to exposure to a range of different X-ray doses (0Gy-10Gy). The statistical analysis of the genoprotective assays consisted of group comparisons whereby means contrasts were performed via analysis of variance. Likewise, a lineal and polynomic regression and correlation analysis was performed. Furthermore, the Magnitude of Protection or the protective capacity of the different substances has been determined A repeated measures ANOVA was performed for the radioprotection or cellular survival/viability assays in order to compare the percentages of cell survival for cultures containing different concentrations of the compounds, complemented by a paired-means contrast via Fisher&apos;s least-significant-difference method. These analyses were performed on data transformed logarithmically in order to adjust them to ANOVA requirements. Results: the results show that the substances tested have a genoprotective capacity with an emphasis on rosmarinic acid and carnosic acid which achieved a statistically significant reduction in micronuclei frequency (p<0.001), thus displaying their antimutagenic capabilities. The aforementioned substances presented a Protection Factor which reached a maximum of 62% in the case of pre-exposure application. Likewise, these substances, both alone and in the varying mixtures and concentrations at which they were utilized, a radioprotective capability was determined in terms of cell survival, which reached a Protection Factor of 100% at doses of 10 Gy, eliminating 40% of the radio-induced cell death in the PNT2 cells (p<0.001); as well as 77% of the radio-induced cell death in the TRAMPC1 cells (p<0.001) for which a Protection Factor of 334% was found. Conversely in the B16F10 cell line, while the remaining substances tested maintained an intense radioprotective activity, both CARN and AR completely lacked any radioprotective effect, causing aa significant decrease in cell survival was produced of 20-40% (p<0.01) and lacking of any Protective Magnitude, so they act as ow radiosensitizing substances for said cells Conclusions: one sole, unique, chemical structure or action mechanism related with radioprotective capacity does not exist among the substances tested. Antioxidant activity, biological availability, hydro- or liposolubility and its presence in the biological environment before exposure to ionizing radiation are characteristics related with the aforementioned protective activity. Nonetheless, certain substances, such as CARN and AR, which do display an intense radioprotective capacity, on occasion can produce increased radio-induced damage, and therefore, a paradoxically greater damage effect as occurs in melanoma cells, expressing specific mechanisms that would allow enhancing agents that protecting healthy cells can exclusively damage neoplastic cells, presenting a new strategy for cancer patients undergoing radiotherapy, even for the treatment of cancers considered radioresistant.