Anti-Paclitaxel Resistance Effect Of Somatostatin Receptors Mediated Targeted Therapy On Non-small Cell Lung Cancer Cells And Its Possible Mechanisms

OBJECTIVE: The clinical relevance of the somatostatin receptor subtype 2 (SSTR2) and somatostatin receptor 5 (SSTR5) is well defined in neuroendocrine tumors but their expression and role in human non-small cell lung cancer (NSCLC) is not yet well studied. We investigated the expression of SSTR2 and SSTR5 in human NSCLC and its adjacent normal tissues, and explored their correlations with clinical staging and prognosis. The somatostatin analogue octreotide was conjugated to paclitaxel and two conjugates were synthesized: PTX-OCT and 2PTX-OCT. Furthermore, targeted therapy effect of the conjugates on paclitaxel-resistant NSCLC cell lines induced by different methods was evaluated and the possible mechanisms underlying anti-paclitaxel resistance were elucidated. Also we analyzed the expression of multidrug resistance related genes of NSCLC cells after treatment with paclitaxel and its octreotide conjugates in vitro and in vivo to find out whether the conjugates had low induction of drug resistance.METHODS: Immunohistochemical staining(S-P method) with specific antibodies was used to detect the expression of SSTR2 and SSTR5 in patients with NSCLC. The mRNA expression of somatostatin receptors (SSTRs) in human NSCLC cell line A549 and H157 cells was detected by reverse transcription-polymerase chain raction (RT-PCR). And the cell viability and apoptosis of A549 and H157 cells treated with paclitaxel and the paclitaxel-octreotide conjugates were measured by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and flow cytometry, respectively. Real-time PCR was also performed to evaluate the relative expression of multidrug related gene of A549 cells, A549 paclitaxel-resistant cells characterized by 3 different approaches, and A549 cells treated by paclitaxel and its octreotide conjugates in vitro and in vivo.RESULTS: The positive rates of SSTR2 and SSTR5 expression were 62.7% and 61.0% repectively in patients with NSCLC, which were higher than their expression in adjacent normal tissues (13.33% and 20.00%, respectively). The expression of SSTR2 and SSTR5 was significantly correlated with TNM stage and longer survival (P<0.05), but there was no relationship between the expression of SSTR2 and SSTR5 and other clinical characteristics of patients with NSCLC (P>0.05).The mRNA expression of 5 SSTR subtypes was all detected in A549 cells, while only mRNA expression of SSTR1 and SSTR4 was detected in H157 cells. Paclitaxel and the octreotide-paclitaxel conjugates effectively inhibited the growth of A549 cells in a concentration- and time-dependent manner.The conjugates were less cytotoxic than paclitaxel in SSTR2 and SSTR5-negative H157 cell. Three NSCLC paclitaxel-resistant cell lines A549-P,A549-PS and A549-S were established, and the resistance indexes (RI) were 6.84, 77.84 and 9.98,respectively. 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. The paclitaxel-octreotide conjugates effectively inhibited the growth of paclitaxel-resistant cells, and showed more cytotoxic effect than paclitaxel. Paclitaxel obviously induced the elevated expression of MDR-1,MRP-1 mRNAs in A549 cells and xenografted tumors, which was very higher than PTX-OCT and 2PTX-OCT treated groups.CONCLUSION: The expression of SSTR2 and SSTR5 was high in NSCLC tissues and low in adjacent normal tissues and the high expression of SSTR2 and SSTR5 in NSCLC was correlated with good prognosis and long survival. Both paclitaxel and its octreotide conjugates effectively inhibited the growth of SSTR2 and SSTR5 positive NSCLC cells in a concentration- and time-dependent manner, while the conjugates were less cytotoxic than paclitaxel in SSTR2 and SSTR5 negative NSCLC cells, which showed a SSTRs-mediated targeted therapy effect. The octreotide-paclitaxel conjugates more effectively inhibited the growth of paclitaxel-resistant cell lines and thus partially reversed the drug resistance to paclitaxel in NSCLC. Also octreotide-paclitaxel conjugates showed a low induction of multidrug resistance compared with treatment with paclitaxel in vitro and in vivo. Our results suggested that the octreotide-paclitaxel conjugates had a significant prospect in the targeted therapy mediated by SSTRs as well as reversing paclitaxel resistance and overcoming acquired paclitaxel resistance in human NSCLC.