Synthetic Paclitaxel-octreotide Conjugate Reversing The Resistance Of A2780/Taxol To Paclitaxel In Xenografted Tumor In Nude Mice

Part 1 The targeting and efficacy of paclitaxel-octreotide conjugates to xenografted tumor in nude miceObjective:To investigate the targeting and inhibiting of paclitaxel-octreotide conjugate in xenografted tumor of paclitaxel-resistant ovarian cancer cells in nude mice.Methods:1. Xenograft models were established by s.c. injection of A2780/Taxol ovarian cancer cells into the right armpit of nude mice, and then averagely divided into five groups.2. The paclitaxel (150nmol/kg), octreotide (150nmol/kg), paclitaxel combined with octreotide (150nmol/kg), paclitaxel-octreotide conjugate (POC,150nmol/kg) or saline only were intravenously administrated on days 1,8 and 15 when the size of xenografts growing up to 1cm3 in each group.3. The targeting of conjugate was observed by using the automated In-Vivo Imaging through administrating of fluorescein-labeled paclitaxel-octreotide conjugates (FITC-POC) for 0.5h,8h,24h and 72h.4. The nude mice were sacrificed after one week of the last injection, and the inhibition rate was calculated by the measurements of varied volume and weight of xenografts.5. Morphological changes in various organs and xenografts were observed by HE staining.Results:1. The tumors grew up to about lcm3 in size after 10 days by s.c. injection of A2780/Taxol ovarian cancer cells in amount of 5 X106 into the right flanks of the nude mice. At this time, no symptoms of apathetic, diarrhea and poor vitality was observed in all of the nude mice.2. The significant aggregation of fluorescence into the xenografted tumor at 8h with reaching the peak at 24h indicate a favorable targeting of POC.3. POC presented the perfect efficancy in tumor growth inhibition with significant decrease of the tumor weight and size than any other treatments (P<0.05).4. The tumors showed the same morphology to the original human ovarian cancer by using HE staining. Furthermore, different degrees of necrosis, inflammatory cell infiltration and fibrosis, as well as a small amount of nuclear condensation, cracking were observed in all but control group. The appearance indicated the growth of tumor was significantly inhibited especially in PO group and POC group. In addition, unusual characteristics were not observed in the liver, kidney spleen and tail of the treated mice. Therefore, it is suggested POC had lower or none toxic to tissues outside of xenograftes.Conclusions:Paclitaxel-octreotide conjugate present better effects on targeting and inhibiting paclitaxel-resistant human ovarian cancer cells in nude mice.Part 2 The potential mechanisms of paclitaxel-octreotide conjugate on reversing the resistence of paclitaxel in xenograftObjective:To investigate the potential mechanisms of paclitaxel-octreotide conjugate on reveasing the resistence of A2780/Taxol to paclitaxel in xenografted tumor in nude mice.Methods:I. Immunohistochemistry was used to detect the SSTR2 expressing in xenografts.2. The mRNA and protein expression of SSTR2, MDR1, VEGF, MMP-9, a-tubulin and βⅢ-tubulin were investigated by Real-time PCR and Western Blot.Results:1. The SSTR2 expression was positively detected on tumor by using immunohistochemistry.2. The results of Real-time PCR and Western blot showed that the mRNA and protein expressions of SSTR2 in POC groups were significantly higher than the other groups (P<0.05), while MDRI, VEGF, MMP-9, a-tubulin and βⅢ-tubulin were obviously lower than the other groups (P<0.05).Conclusions:The inhibition of POC on tumors could be prabably resulted from a series of mechanisms, including specific binding of octreotide to the membrance receptor of SSTR2, up-regulated expression of SSTR2 as well as down-regulated expressions of MDRI (resistance reversing protein), α tubulin, βⅢ-tubulin (paclitaxel targeting proteins), VEGF and MMP-9(proliferation inhibiting proteins).