| Objective:Cancer is a horrible threat to human health. Systemic chemotherapy forms the mainstay of cancer treatment. The spindle poison such as taxol and the vinca alkaloids are commonly used as the first-line drugs to treat a wide variety of cancers. They have proven succeeded in the clinic,and apoptosis induction is the important mechanism to kill tumor.But in the clinical work we noted that, some tumor was sensitive to these drugs,the tumor tissue disappeared in the experience of chemotherapy several times,While more common phenomenon were:The tumor tissue were sensitive to this type of drugs at the beginning of chemotherapy, but chemoresistance usually appeared after sevaral treatment cycles, or they had no obvious response to these drugs.The latter two phenomena are the root causes of out of control and tumor recurrence. According to statistics, more than90%of patients with cancer death attributed to the drug resistance in different degree.The study found that the spindle poison treated to cells, there were some of the cells occurs mainly apoptosis, some of the cells occurs mainly polyploidization. The foreign scholars also found that:Polyploid tumor are not sensitive to radiation and chemotherapy, polyploidy subclones have poorer prognosis. So, We propose that polyploidization might be account for this drug resistant after spindle poison used. For years, scientists have been trying to discuss the mechanisms of tumor resistance, and proposed a lot of theories and possible mechanism, but still did not find any fundamental solutions to this difficult clinical problem. With the continuous development of science, people gradually realized the reason of drug resistance is various, in addition to current Multidrug resistance genes related to drug resistance, we assume that the formation of polyploidy is probably an important reason for leading to the drug resistance after used the spindle poison, no one has been put forward the new possible mechanism of drug resistance yet. We took the formation of the polyploid tumor cells induced by spindle poison as the entry point, explored the relationship between polyploid formation and drug resistance by comparing the IC50s of the polyploid cloning and original tumor cells (before spindle poison application) to chemotherapy drugs commonly used,Possible mechanism of polyploidization was also investigated to find possible intervention point/method to solve this kind of drug resistance and put forward a new prevention strategy to suppress the formation of polyploid cloning.Methods:100ng/mL nocodazole induced the MDA-MB-231cells polyploidization, the polyploidy cells(T-MDA-MB-231) were sorted by flow cytometry. Morphology change and cell proliferation were compared between T-MDA-MB-231and MDA-MB-231. Cell growth inhibitory was evaluated with MTT assay, Cells were labeled with Annexin V-FITC/PI incorporation and analyzed with flow cytometry when these cells were treated with Paclitaxel, Docetaxel, Vincristine, Epirubicin,5-FU, VP16and Oxaliplatin individually. Bcl-2was knocked down using SiRNA in T-MDA-MB-231to evaluate its function on reversing drug resistance. Cell growth inhibitory was evaluated with MTT assay after knocked down the Bcl-2.Results:1. Polyploidy cells (T-MDA-MB-231) were able to grow continuously and maintain constant DNA content while they grew in vitro, and they were bigger in volume, and grew more slowly than MDA-MB-231cells.2. IC50(S) of Paclitaxel, Docetaxel, Vincristine, Oxaliplatin,5-FU, Epirubicin were (6.37±0.07)μmol/L,(32.98±1.48)μmol/L,(35.28±1.66)μmol/L,(19.07±0.45)μmol/L,(85.49±3.21)μmol/L and (0.53±0.06) μmol/L,respectively. T-MDA-MB-231was more resistant to Paclitaxel, Docetaxel, Epirubicin, Vincristine,5-FU, and Oxaliplatin when comparing with MDA-MB-231(P<0.01),but it significantly more sensitive than MDA-MB-231when exposed to VP16,(P<0.01), the IC50of VP16was (2.85±0.50)μmol/L3. T-MDA-MB-231has high expression of Bcl-2,it was relatively sensitive to Docetaxel after knocked down the Bcl-2(P<0.05) while it was more resistant to VP16,(P<0.05). The IC50(s) of Docetaxel and VP16were[(21.52±0.68)μmol/L] and[(19.59±0.48)μmol/L]. Conclusion:1. Polyploid tumor model provided a good platform for the further study of polyploid tumor2. Polyploidy tumor is more resistant to most of chemotherapeutic drugs, Polyploid tumor cells are relatively sensitive to VP16, VP16may be an effective drug to treat polyploid tumor.3. The formation of polyploidy is probably an important mechanism of the drug resistance after the spindle poison used, high expression of Bcl-2in polyploid tumor cells involved in the formation of resistant phenotype, down-regulation of Bcl-2may be solve this kind of drug resistance; Polyploidy tumor cells refered to multiple complicated drug resistance mechanism, not Bcl-2independent mediated;Defect of apoptosis is necessary for polyploidization,the Polyploidization might be a new mechanism of tumors resistance, the in-depth study of the nature of the polyploid tumor has important clinical value to control such resistance. |
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