Ο ρόλος της κυκλοοξυγενάσης στην πειραματική καρκινογένεση

Abstract

Cancer is the main cause of death, followed by cardiovascular disease. Among thecategories of anticancer drugs tested so far, the non-steroidal anti-inflammatory drugs holda primary role. Furthermore, it is now clear that diet plays an important role incarcinogenesis. However, the effects of diet, of non-steroidal anti-inflammatory drugs ortheir combination, remain virtually unchartered as far as carcinogenesis is concerned,although significant progress has been made in this area in recent yearsThe purpose of this study is to elicit the therapeutic effect of the inhibitors ofcyclooxygenase (COX), in a rat experimental model of cancer, since there is strongevidence that cyclooxygenase inhibitors have indirect antitumor and anti-angiogenic activitywithin an experimental setting. In addition, the same experimental model was used to studycyclooxygenase alone, and in combination with aspirin, as an anti-inflammatory agent.Aspirin was selected because it has been observed that there are synergies between thecyclooxygenase inhibitor and aspirin. Finally, we examined the role of diet in cancer, whilean attempt was made at immune-histo-chemical detection of oncogene p53, and Bcl-2.For the experimental induction of cancer we used 7,12 - dimethylbenz-(a)-anthracene(DMBA) in rats because, despite the fact that spontaneous development of tumors inlaboratory animals is extremely rare, it has proved possible to induce such neoplasms byadministering chemical carcinogens. With regard to diet, during the last twenty years highfatdiets have been shown to increase the risk of various cancers. Hence, our study focusedon dietary fat.To achieve the objectives of our study we conducted two massive experiments in which ratswere used (a total of 480 animals or 240 in each experiment). The first experiment involvedthe investigation of the effect of the selective cyclooxygenase-2 inhibitors (Celebrex), andthree kinds of diet (high in animal fat, normal and low) in carcinogenesis which was inducedby one or two (double dose) doses of DMBA . The same experimental model used in thesecond experiment involved the action of cyclooxygenase, alone or in combination withaspirin as an anti-inflammatory agent. We completed our investigation with the use ofautopsy material obtained from two massively these experiments to determine the activity ofp53 and Bcl2 in the carcinogenesis model that we used.With regard to food, animals on restriction diet, consumed 40% less energy than animals onnormal diet. This was achieved by replacing the fat contained in the normal diet bycalorically inert material (fibers). Similarly, animals on high caloric content diet, consumed40% more calories with the corresponding increase in calories achieved by increasing thecontent of dietary fat at the expense of carbohydrates and fibers contained in the normaldiet. Otherwise, the food for all animals contained the same amounts of protein, vitaminsand minerals. Finally, to the feed of those animals who received aspirin or Celecoxib, weadded a daily dose of 1500 ppm Celecoxib and/or 350 ppm for aspirin. cancer. However, the reduction of fat (from the level corresponding to the "normal" diet) didnot improve significantly (either in absolute terms or in the sense of statistical significance)the potential for harm. We observed that Celebrex reduces cancer while it also preventspre-cancerous lung inflammation which can develop into cancer. Finally, we observed thatthe rich-in-fat diet worsens (increases) the chances of getting cancer or pre-cancerous lunginflammation.The data of the second experiment demonstrated a strong synergy between aspirin andCelebrex. Finally, with regard to the study of the DNA of tumor tissue which was undertakenin order to identify p53 and Bcl-2, we report that it was not possible to identify thecorresponding genes in any of our samples.Therefore, our results show that:1. The size of the administered dosage does not affect, at a statistically significant level, theDMBA potential for harm.2. High fat diet clearly affects, at a statistically significant level, the potential of DMBA forharm. In particular, it should be noted that the high-fat diet increases the chances ofdeveloping cancer or pre-cancerous lung inflammation. Thus, the probability of developingcancer in animals receiving a fat-rich-diet is, on average, about 2.5 times greater than forthe regular or for the reduced fat diet. However, the reduction of fat below the levelcorresponding to that of a "normal" diet, does not significantly improve the likelihood ofdamage.3. Treatment with Celecoxib protects against DMBA-induced tumors, in a statisticallysignificant way. Specifically, treatment with Celecoxib reduces the probability of cancer andprevents premalignant lesions (lung inflammation induced by DMBA) to develop into cancer.Without the administration of anti-inflammatory drugs the relative risk of cancer orinflammation of the lungs increases by 3.2 times. However, the relative effectiveness of theprotection provided by Celecoxib is significantly reduced when a doubling of the DMBAdose occurs.4. Finally, given the presence of p53 in all normal tissues, the absence of wild-type p53gene in all tumor samples shows that interference of DMBA in the function of p53 can beattributed to a mutation (and subsequent cloning of the mutated gene) rather than to anyexogenous or endogenous interfering with the protein p53. At the same time, the absenceof Bcl-2 gene in all the tumor samples, potentially increases the oncogenic activity of the mutated p53 gene.