Targeted Octreotide-paclitaxel Conjugates Inhibit The Growth Of A549 And Its Paclitaxel-resistant Human Non-small Cell Lung Cancer Cells

OBJECTIVE: To investigate whether octreotide can potentiate the anti-proliferative effect of paclitaxel on non-small cell lung cancer and explore possible mechanisms.Three NSCLC drug-resistant cell lines were established by different approaches to compare their biological characteristics and elucidate possible mechanisms of drug resistance.METHODS: The mRNA expression of Somatostatin Receptor(SSTR)1-5 in non-small cell lung cancer cell lines A549 and H157 was evaluated by RT-PCR. The inhibitory effect of octreotide on the growth of A549 and H157 cells was evaluated by MTT assay and the morphological changes after octreotide treatment was observed by microscopy. MTT assay was also used to investigate whether combinations of octreotide and paclitaxel resulted in synergistic interactions. Cell apoptosis of A549 cell after treatment with paclitaxel, octroetide, and combinations of octreotide and paclitaxel was analysed by flow cytometry .The changes of MDR-1, MRP-1, BCRP mRNA expression of the cells after treatment with octreotide was evaluated by real time PCR.Three NSCLC paclitaxel-resistant cell lines:A549-P,A549-PS and A549-S were established respectively by high dose pulse, high dose pulse followed by low dose exposure in a stepwise manner and only low dose exposure in a stepwise manner. The biological characteristics of cell lines were determined by microscopy and cell count assay.The drug resistance to paclitaxel and cross resistance to adriamycin, vincristine and CDDP were determined by MTT assay. The cell cycle was detected by flow cytometry. The relative mRNA expression of MDR-1,MRP-1 and BCRP was evaluated by real time PCR.Three kinds of paclitaxel-octreotide conjugates were synthenized and their targeting inhibitory effects on the NSCLC paclitaxel-resistant cells were evaluated by MTT.RESULTS: The mRNA expression of SSTR1～SSTR5 was detected in A549 cells, while only mRNA expression of SSTR1 and SSTR4 was detected in H157 cells. Octreotide had an inhibitory effect on A549 cells in a time (24h, 48h, 72h) and dose(1～1000nmol/L)-dependent manner and morphological changes of the injured cells were observed; while it had no effect on H157 cells. The dose-dependent anti-proliferative effect of paclitaxel was synergistically enhanced by octreotide (125nmol/L, 250nmol/L, 500 nmol/L)on A549 cells(P<0.01); but for H157 cells , combination of octreotide and paclitaxel resulted in additive interactions. Cell apoptosis was induced by octreotide in A549 cells, but the apoptosis induced by paclitaxel was not promoted by octreotide in A549 cells. The mRNA expression of MDR-1, MRP-1 was down-regulated after octreotide treatment in A549 cells(P<0.05, P<0.01), while there were no changes in H157 cells.The resistance indexes of A549-P, A549-PS and A549-S were 6.48, 77.84 and 9.98 and there were changes in their biological characteristics. The mRNA expression of MDR-1, MRP-1 and BCRP were up-regulated in A549-S;and the mRNA expression of MDR-1 in A549-PS and MRP-1 in A549-P were also up-regulated.Other multidrug resistance genes were down-regulated.PTX-linker, PTX-OCT, and 2PTX-OCT were synthenized; and they had much stonger inhibitory effects on the NSCLC paclitaxel-resistant cells.CONCLUSION: Octreotide can promote the anti-proliferative effect of paclitaxel on SSTR-positive non-small cell lung cancer in synergy; and down-regulation of multidrug related genes may be the possible mechanism.There wad difference between three paclitaxel-resistant cell lines induced by different approaches and the changes of multidrug resistance genes may be involved in the mechanism of drug resistance.The paclitaxel-octreotide conjugates had targeted inhibitory effects on the NSCLC paclitaxel-resistant cells and might reverse the drug resistance of paclitaxel.