The Study Of Targeted Therapy Of Somatostatin Receptor In Non-small Lung Cancer In Vivo

Background:Lung cancer is the leading course of cancer-related deaths in the world.About 80%of lung cancers arc non-small cell carcinomas.While 65%of the patients have advanced-stage,so chemotherapy is the main treatment for most patients.However,NSCLC(non-small lung cancer)is more resistant to chemotherapy than other forms of cancer.Recently,targeted chemotherapy is one of the novel approaches to the treatment of cancers,which would improve the efficacy of therapy and decrease the toxicity.SSTRs(Somatostatin receptors)as one of targets has been investigated,because of its overexpression on tumors.Some investigators had reported that cells of human NSCLC overexpressed SSTRs,so it is possible that SSTR will be a targeted treatment for NSCLC.Hung has coupled paclitaxel(PTX)to SSA(Somatostatin ananlogs),octreotide(OCT),and also has proved the cytotoxity in vitro.We have developed a series of cytotoxic octreotide conjugates,2PTX-OCT and PTX-OCT,that was made by coupling one or two moleculars cytotoxic paclixtel to one molecular somatostatin analog octreotide.We have evaluated their cytotoxicity in vitro.Objective:In this study,we investigated the efficacy of 2PTX-OCT and PTX-OCT in human NSCLC A549 xenografted into nude mice.Methods:Two cytotoxic somatostatin analog,PTX-OCT and 2PTX-OCT,were developed,in which paclixtel was linked to octreotide.Xenografts were initiated by s.c.injection of A549 cells into the right armpit.The nude mice that were xenografted were randomly divided into 8 groups. Three i.v.injections of PTX-OCT,2PTX-OCT,OP(mixture of OCT and PTX),PTX and OCT at 150nmol/kg,and PTX,2PTX-OCT at 300nmol/kg were given on days 1,7 and 21.By measuring the tumor volume and BW(body weight),calculating tumor volume doubling time,and observing histologic changes to evaluate the antitumor effects of the compounds.The white blood cells were counted by collecting blood from eye's endocanthion.The expression of messenger RNA(mRNA)for human somatostatin receptor subtypes1(SSTR1)to 5(SSTR5)were invistigated in tumors using reverse-transcription polymerase chain reaction(RT-PCR).Histologic apoptosis was detected by DNA ladder. Somatostatin receptors subtypes2 and 5(SSTR2 and 5)and tumor microvessel density(MVD)on A549 tumors were characterized by immunohistology.Results:Two cytotoxic somatostatin analog,PTX-OCT and 2PTX-OCT,were successfully developed.The conjugateswere purified by high-performance liquid chromato-graphy(HPLC). PTX-OCT(WP-06-2A)was the broad singlet product purifiedby HPLC (HPLC.15.67min.;MS.1998.7;MW.1996.27)and 2PTX-OCT(WP-06-2B)was a pure single productpurified by HPLC(HPLC.20.85min;MS.2892.8;MW.2890.19).Xenografts were initiated by s.c.injection of 5×10~6 A549 cells into the right flanks of 45 male nude mice.The study was started when tumors had grown to an average of 60 mm~3 in volume.150nmol/kg and 300nmol/kg 2PTX-OCT resulted in a significant tumor growth inhibition(P＜0.01),the final tumor volume being 60.7%and 70.3%smaller than in the controls,respectively;The tumor doubling time was also extended significantly(P＜0.01)from 9.07±0.61 days in the controls to 12.35±0.9.4days and 14.16±1.64 days,respectively;MVD were also significant(P＜0.01)decline.PTX was ineffective and more toxic,and the decline of body weight is significant on days 6,12,26(P＜0.05),contrasting to 2PTX-OCT.The counts of white blood cells(WBC)in the groups of PTX and 2PTX,which were 7610±780.54/mm~3, 6690±611.76/mm~3 at day 26 respectively,were declined significantly(P＜0.05)contrasting to control(10133±375.06/mm~3),2PTX-OCT group(9302±900.37/mm~3)and 2(2PTX-OCT) group(8931±717.93/mm~3).The mRNA for SSTR1,2,4,5 was found in A549 xenografts. SSTR2 were mainly found at tumor cell membrane by immunohistology;SSTR5 were found at tumor cell membrane and cytoplasm by immunohistology.More Histologic apoptosis bands were shown by DNA Ladder in 2PTX-OCT and double dose of 2PTX-OCT group.Conclusions:The targeting conjugate 2PTX-OCT that was made by coupling two moleculars cytotoxic paclixtel to one molecular somatostatin analog octreotide could enhance the effects,reduce microvessel and weaken the toxicity in comparison with the cytotoxic radical PTX.