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Multidrug resistance (MDR) in small cell lung cancer is one of the major causes of failures of chemotherapy. MDR is a means of protection of tumor cells against chemotherapeutic drugs. Although the molecular basis of MDR is not fully understood, genes involved in apoptosis may be mutated. Recent finding of a link between over-expression of an apoptotic gene, cyclooxygenase 1 (cox 1), and MDR suggests that cox 1 is involved in the development of MDR phenotype. This research was an attempt to observe whether up-regulation of cox 1 contributes to the MDR phenotype in small cell lung cancer cells. This research ultimately may provide a mechanism to reverse the abberant up-regulation of apoptosis genes associated with multidrug resistance to either eliminate or control reproduction of cancer cells. Real time RT PCR was used to confirm the up-regulation of cox 1 in cultured MDR resistant small cell lung cancer cells (GLC4). The up-regulated cox 1 expression was down-regulated using RNA interference technology (RNAi) by transfection with an anti-cox 1 siRNA. More than 90% transfection of cells was confirmed using confocal microscopy. Down-regulation of cox 1 was validated as the protein expression significantly decreased (P=0.004) from multidrug resistant small cell lung cancer transfected cells compared to multidrug resistant nontransfected cells. There was decrease level of expression of cox 1 in multidrug resistant cells after the knockdown with siRNA specific to cox 1. The decreased level of cox 1 expression and, therefore, Cox 1 production increased the rate of apoptosis in small cell lung cancer cells as indicated by its sensitivity to the doxorubicin. / Department of Biology

The gene, cox-1, is over-expressed in cultured GLC4 small cell lung cancer cells concurrent with the development of multi-drug resistance (MDR) as a result of the use of the chemotherapeutic agent used to combat the cancer, doxorubicin. Prevention of MDR has been a tremendous challenge in cancer research and this research is concerned with abolishment of MDR as a cancer survival strategy. RNA-mediated interference technology (RNAi) was employed using siRNA to decrease cox-1 expression and temporarily restore the susceptibility of the cells to doxorubicin. GLC4 cells are of three types: S (sensitive cells never exposed to doxorubicin); ADR (MDR cells cultured in doxorubicin), and; REV (revertant cells previously cultured in presence of doxorubicin but no longer). REV and ADR cells were transfected with cox-1 siRNA. After 24 h, 1x106cells were used for RNA isolation and 1 μg of RNA was used for RT-PCR to assess down-regulation of cox-1 RNA. RT-PCR results indicated that cox-1 RNA was down-regulated to basal levels seen before exposure to doxorubicin. Ct values for GLC4/ADR and cox-1 down-regulated GLC4/ADR cells were 23 and 34, respectively. The result indicated abundant levels and moderate levels of cox-1 mRNA in the ADR cells and the transfected ADR cells respectively. The relative expression level of cox-1 mRNA was 33% higher in the non-transfected GLCR/ADR cells as compared to the transfected GLCR/ADR cells as shown by the curve. Two hundred thousand cells were used for hemacytometer cell counts in the presence of trypan blue to assess cell viability. cox-1 down-regulation in ADR cells resulted in a significantly higher percentage of non-viable cells (25.4%) as compared to its non-transfected control (20.5%) using a Student’s t-test (*P <0.05). Similarly, fluorescence microscopy confirmed that apoptosis was significantly increased in the ADR cells treated with doxorubicin and cox-1 siRNA simultaneously (69.4%) as compared to its non-transfected control (56.7%) (*= P <0.01). A Western blot analysis performed by Fernando Cuadrado indicated that siRNA transfection decreased the expression of COX-1 by 66% in GLC4/ ADR cells as compared to the non-transfected control using densitometry. However, no conclusive results were obtained using flow cytometry as the flow cytometer was incapable of analyzing the mixed cell population (adherent and suspension) which is a characteristic of this cell line, GLC4. Thus, we have clearly demonstrated that MDR cancer cells can be altered temporarily to become susceptible to doxorubicin, a potentially important finding for the treatment of cancer patients. / Department of Biology

published_or_final_version / abstract / toc / Medicine / Master / Master of Philosophy