Lung cancer is still the leading cause of death amongst the various types of cancers.This study researched the influence of a combined therapy, consisting of a multi-kinase inhibitor and a specific phosphodiesterase 5 inhibitor, compared with that of a single inhibitor used in mono-therapies and compared with that in a placebo.On the day the experiment commenced, all the animals received a subcutaneous injection of isolated A549 cells just above the muscle of the right buttock.Each of the seven animal test groups consisted of 6-10 laboratory animals (nude mice). For the duration of the experiment of 28 days, the animals were treated with different inhibitors in the form of oral medication: sildenafil, a specific PDE5 inhibitor, sorafenib and sunitinib as multi-kinase inhibitors, the combined therapy groups sorafinib + sildenafil and sunitinib + sildenafil, the placebo groups (these laboratory animals received an oral dose of methylcellulose), and finally the control group there was no intervention with these animals.The animals received the same dosage of medication. The size of the tumor was measured every four days.The largest increase in volume occurred, as expected, in the control and the placebo groups. The smallest increase in volume occurred in the combined-therapy groups. The most constant was, however, for the combination of sunitinib + sildenafil.The mRNA expression of individual growth factor receptors from tissues of the control group was examined with the help of real-time PCR. In order to capture the influence of tumor stroma, the following were also examined: human fibroblasts, monocytes, macrophages, lymphocytes, donor lung tissue, and, for comparison, isolated and cultivated A549 cells. The receptors cKIT, RET, CSF-1R, Flt3, PDGF-alpha, PDGF-beta, EGF, VEGF3 and also the receptor for PDE5a showed an expression in every sample examined. Flt.1 and KDR showed no expression in isolated A549 cells; however, they did show expressions in the rest of the tissues.Furthermore, some of these factors were compared among themselves and examined for their expression in the tumors of the individual groups by means of immunohistochemical quantification. At the end of the experiment, the resulting tumor was dissected from the attached tissue and, after the usual preparation, cut for the immunohistochemical examination. We could demonstrate a decrease in the expression of the various growth factor receptors that were inhibited. In particular, PDGFR-beta, Flt-1 and EGFR showed a significant decline in the density of receptors.Additionally, the active rate of cell division (PCNA) and the existing section of the vessels were stained and compared with one another. It was interesting to note, that the one with the smallest increase in tumor volume had the largest number of vessel sections and a slightly higher active rate of cell division, in comparison to the mono-therapy group.The combined therapy of a multi-kinase inhibitor and the specific PDE5 inhibitor appears to be a good therapy option for NSCLC, as the tumor growth is delayed and so the chance of survival increased. The influence of the factors studied provided no detailed information about the mode of action effective in this kind of therapy, in particular with regards to angiogenesis. This needs to be examined in further studies.
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