[CANCERRESEARCH56. 1823-1827.April 15.19961

ABSTRACT

Five somatostatin receptor subtypes (sat! to sst5) have been cloned. Wedemonstratedpreviouslythat sst2 and sst5 mediatethe antiproliferativeeffect of the somatostatin analogues octreotide and vapreotide. Using

reverse transcription-PCR, we investigated gene expression of the fivereceptors in 47 human normal and cancerous tissues or ceH lines frompancreatic and colorectal origin. mRNAs of somatostatin receptor subtypes were detected in 98% of samples, with more than two mRNAsubtypes being expressed in 55% of cases. sat!, sst4, and sst5 wereheterogeneously expressed in both normal and cancerous tissues; sst3 was

rarely or not expressed. sst2 was present in normal pancreatic tissues butwas absent in exocrine pancreatic carcinomas and their metastases. sst2mRNAs were detected in normal colon, sporadic polyadenomas, and 50%of Dukes' stage B and 20% of Dukes' stage C carcinomas but wereundetectable in Dukes' stage D carcinomas, hepatic metastases, and adenomas from familial adenomatous polyposis. The loss of sst2 expressioncould represent a growth advantage In these tumors and provide anexplanation for the lack of therapeutic effect of somatostatin analogues insuch adenocarcinomas.A subtypingof somatostatinreceptorsshouldbecarried out before considering a somatostatin analogue treatment inpatients with colorectal or pancreatic cancer.

INTRODUCTION

Somatostatinis a tetradecapeptidethat participatesin a variety ofbiological processes including inhibition of hormonal secretion andcell proliferation (1). These properties are used for the treatment ofhormone-producing pituitary or gastroenteropancreatic tumors by stable somatostatin analogues (2). Thus, hormonal suppression is produced in patients with acromegaly or with neuroendocrine tumorssuch as insulinoma, glucagonoma, gastrinoma, vipoma, or carcinoidsyndrome (2). In some patients, analogue therapy leads to an inhibition of tumor growth (2—4).Somatostatin exerts an antiproliferativeeffect by either indirectly inhibiting hormone and growth factor releaseor angiogenesis or by acting directly on neoplastic cells (1, 2, 4).The actionsof thepeptidearemediatedby specificreceptorsthathavebeen detected using binding assay or autoradiography in varioushuman normal and tumor tissues(1, 2). Scintigraphyby i.v. administration of radiolabeled analogue allowed the detection and localization of somatostatinreceptor-positivetumorsandtheir metastases(2).

Recently, five somatostatin receptor subtypes and one splice varianthave been cloned from humans, mice, and rats (5—10).After expression of sstl to sst53 gene clones in mammalian cell lines, we and

Received10/20/95;accepted2/14/96.The costsof publicationof this article weredefrayedin part by thepaymentof page

charges.This article mustthereforebe herebymarkedadvertisementin accordancewith18U.S.C.Section1734solely to indicatethis fact.

I Supported in part by Grant 6755 from the Association pour La Recherche contre Ic

Cancer,Grant9200045from theConseilRegionalMidi Pyrénées;agrantfrom theInstitutde Recherche des Maladies de l'Appareil Digestif; Grant SAL91-0873 from the PlanNacional I + D, Spain;and Grant FIS 94-0001-1from The Fondode InvestigacionesSanitarias, Spain.

2Towhomrequestsforreprintsshouldbeaddressed.Phone:(33)61322401;Fax:(33) 62 26 40 12.

3 The abbreviations used are: sst 1 to 5, cloned somatostatin receptor subtypes 1 to 5;

RT-PCR,reversetranscription-PCR;FAP,familialadenomatouspolyposis.

others demonstrated a distinct profile for binding of clinically usedsomatostatin analogues, SMS 201—995(octreotide), BIM 23014 (lanreotide), and RC-l60 (vapreotide). These analogues bind with highaffinity to sst2, sst3, and sst5 (IC50,0.1 to 22 nM) and with low affinityto sstl and sst4 (IC50, 200 to 1000 nM) (5—15).The biologicalfunctions mediated by the five sst(s) have not yet been establishedcompletely. Recently, after stable expression of sst(s), we demonstrated that only sst2 and sst5 mediated the antiproliferative effect ofthe somatostatinanaloguesoctreotideandvapreotide(1 1, 12). Recentstudies demonstrated that sst2mRNA was expressedpredominantly insomatotroph pituitary adenomas and gastro-entero-pancreatic neuroendocrine tumors (16—19).All of these results led some authors topostulate that sst2 could be a candidate for mediating the therapeuticeffect of analogues in these patients (16, 18).

Although somatostatin analogue administration is now consideredas an accepted treatment for neuroendocrine tumors of the gut (2, 4),it is still unclear whether analogue therapy is effective against nonendocrine carcinomas such as colorectal and pancreatic cancers. Numerous studies conducted on experimental neoplasms in vitro and invivo demonstrated that somatostatin analogues inhibit growth of cob

rectalandexocrinepancreaticcancers(4, 20—22).In contrast,clinicalstudies revealed that somatostatin analogue therapy does not producean adequate clinical response in patients suffering from an advancedtumor stage of pancreatic or colon carcinomas (21, 23—25).Somatostatin binding sites were poorly or not detected in these tumors (2,26, 27); this could be one of the explanations for a lack of directantiproliferative effect of analogue therapy. Moreover, consideringthe differences in the pharmacological profile and the biologicalfunction mediated by somatostatin receptor subtypes, the therapeuticresponse may depend on the subtype expression for a given tumor.Finally, it is not known whether the presenceof somatostatin receptorsin pancreatic or colorectal cancers may influence their growth behav

ior or their prognosis. To gain more insight into somatostatin receptorexpression in such adenocarcinomas,we examined simultaneously thedifferential mRNA expression of the five receptor subtypes on specimens obtained from primary tumors or metastasesfrom coborectalorexocrine pancreatic cancer patients.

MATERIALS AND METHODS

Tissue Samples. Tissue samples were obtained from 38 patients at surgery.

Noneof thesepatientsreceivedsomatostatinanalogueor antitumortreatmentbefore or during surgery.All tumors were histopathologicallydiagnosed.Individualcoloncarcinomaswerestagedaccordingto theDukes'classificationsystem modified by Astler and Coller (28). Six pancreatic cancer specimenswereanalyzed,andall wereof ductalappearance.Fiveof themwereanalyzedafter intrapancreaticxenograftsin nudemice from threeprimary tumorsandtwo metastases, obtained as described (29, 30). Samples analyzed from xcnograftscorrespondedto the first passageafter implantation.Specimensfromnormalcolonor pancreaswereobtainedfrom organdonors.All sampleswereimmediatelyfrozenin liquid nitrogenandstoredat —80°Cuntil use.Thestudyprotocolwasapprovedby the hospitalethicalcommittees.

Cell Lines. The establishedhumanpancreaticcancercell lines BxPC3,Capan-1,Capan-2,Mia Paca-2,PANC Tu II, 818—1,and 818—7and the

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Loss of sst2 Somatostatin Receptor Gene Expression in Human Pancreatic andColorectal Cancer'

Louis BUSCaII,2 Nathalie Saint-Laurent, Eric Chastre, Jean-Christophe Vaillant, Christian Gespach, Gabriel Capellà,

Holger Kaithoff, Felix Lluis, Nicole Vaysse, and Christiane Susini

INSERM U151, Institut Louis Bugnard, I avenue J. Poulhès, CHU Rangueil, 31054 Toulouse, Cédex,France fL B., N. S-L, N. V., C. S.); INSERM USS and Service de ChirurgieDigestive, Hôpital Saint Antoine, 75012 Paris, France fE. C., f-C. V., C. G.j; Laboratori d'Invesrigacio Gastrointestinal, Institut de Recerca, Hospital de Ia Santa Creu I San:Pau, 08025 Barcelona, Spain 1G. C.. F. Li; and Research Unit Molecular Oncology, University Hospital. 24105 Kiel, Germany [H. K.]

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Table 1 SomatostatinreceptorsubtypemRNA expressionin normal orcanceroushumanexocrine pancreas and derived celllinesNormal

humanexocrinepancreatictissueswere sampledfrom nonpathologicalorgans.Primaryhumanpancreaticcarcinomas2, 3, and 4 were sampledafter orthotopic xc

nograltsin nudemice, and metastatictumors from humanpancreaticcarcinomaswerefromperitoneal(case1)andhepatic(case2) origins,respectively,andweresampledafterintrapancreatic

xenograft in nudemice.Cases

sstl sst2 550 sst4sst5Normal(I)

+ + — ++(2)+ + — ++(3)+ + — ++(4)+ + — ++(5)+ + — ++(6)+ + — ++(7)+ + — ++CarcinomasPrimary(1)

— — — +—(2)+ — — ++(3)+ — — ++(4)+ — — ++Metastases(1)

+ — — ++(2)+ — — +—Cell

linesBxPC3+ — — ++Capan-l+ — — ++Capan-2+ — — ++MiaPaca-2— + — ++PANCTumI— — — +—818-1+ — — +—818-7+ — — + +

SOMATOSTATIN RECEPTORS IN PANCREATIC AND COLON CANCER

absenceof reversetranscriptaseduring the reversetranscriptionprocedure.TheseproceduresandPCRreactionson waterwereusedasa negativecontrolof reaction.Positivecontrolswerealsousedif necessaryusingamplificationofhsst plasmids. To avoid cross contamination during PCR reaction, this procedurewasonly performedfor theconfirmationof negativeresults.Two separaterunsof PCRreactionwereperformedfor eachtissuespecimenandfor thefivesubtypes.

RESULTS

Before RT-PCR study of tumor specimens, specificity of the primers was verified for each receptor by PCR amplification of theplasmids containing hsst 1 to hsst3 cDNA(s) (5, 6). RT-PCR analysiswas also performed on CHO cells stably expressing hsst4 and hsst5(12, 14). The results of amplification are shown in Fig. 1. No PCRproduct was obtained when specific primers for a given subtype wasused to amplify the other receptor subtypes (data not shown).

The comparative distribution of the five sst(s) mRNA in 39 human

normal or tumor tissues from 38 patients or in 8 human cancer celllines is given in Tables 1 and 2. Representative results are shown in

Figs. 2 and 3 for pancreatic and colorectal specimens, respectively.Somatostatin receptor subtype mRNAs were present in 98% of cases,and all of the five subtypes were not expressed simultaneously. In55% of cases, more than two mRNA subtypes were present. Allsomatostatin receptor subtype mRNAs were expressed in normalhuman exocrine pancreasexcept sst3. In contrast, sst2 mRNA was notexpressed in human pancreatic adenocarcinomas, and sstl, sst4, andsst5 mRNA was detected in 83, 100, and 66% of cases,respectively.As in normal pancreas, neither primary tumors nor metastasesexpressed sst3 mRNA. In pancreatic cancer cell lines, sst2 mRNA waspresent in only 14% of cases,and sst3 mRNA was not detected; thethree other subtypes were detected in 71 to 100% of cases (Table 1;Fig. 2).

Normal colon mucosa and sporadic polyadenomas all expressedsst2, sst4, and sst5 mRNA but weakly expressedsstl and not sst3. sst2was not expressed in adenomas from FAP patients. In coborectal

@-

@ .

Fig. 1. Polyacrylamide/ethidiumbromide-stainedgel of PCR productsafter amplificationof plasmidDNAs containingsomatostatinreceptorsubtypes1 to 3 andRT-PCRanalysisof mRNA extractedfrom CHO cells stably expressinghsst4and hsst5.Theexpectedlengthsfor PCRproductswere415 bp (hsstl), 1104bp (hsst2),447 bp (hsst3),278bp(hsst4),and473bp(hsst5).DNA sizemarkers(pGEMmarkers;Promega)indicate2645, 1605, 1198, 676, 517, 460, 396, 350, and 222 bp from top to bottom.

1824

U)

a).@ 1•@@t._. —

(@ U)@ U)

(“l (() ‘@1' tO— — — —U) U) U) Cl)(I) U) U) Cl)

humancoloncarcinomacell line HT29wereinvestigatedfor theexpressionofsomatostatin mRNA.

RNA Isolation. Total RNA was extracted by the modified procedure ofChomczynskiandSacchi(31).Tissuewashomogenizedwith a Polytrontissuehomogenizer in RNAzoITMB (Bioprobe, Montreuil-sous-Bois, France). Cub

tured cells were grown in 5-cm-diameter dishes for 48 h and directly lysed in

RNAzol. Homogenized tissue or lysed cells were then incubated in RNAzol for10 mm at 4°C,and RNA was extracted as described (32).

RT-PCR.Beforereversetranscription,1 @tgof totalRNAwasfirstdenatsiredat94°Cfor 10mmandimmediatelychilledon ice.Reversetranscriptionwasthencarriedout in 50 mMTris-HCI buffer (pH 8.3) containing26.5 @Moligo d(T), I mMdeoxynucleotidetriphosphates,20 units RNasin(Promega,Charbonnières,France),10nmiDli', 75 mivtKC1,3 mi@iMgC12,and 1 @goftotaldenaturedRNA in a final volumeof 20gil.Priorto theadditionof reversetranscriptase, the reverse transcription mixture received 1 to 5 Hi of RNAsefree DNase I (Promega) and was incubated at 37°Cduring 30 mm to eliminategenomicDNA. The DNasewasinactivatedby incubationat 94°Cfor 5 mm.After a 10-mm incubation at 4°C,200 units of Moloney murine leukemia virus

reversetranscriptase(Life Technologies,Inc.) wasaddedto the reversetranscription mixture, which was incubated for 10 mm at 23°C,followed by 2 h at39°Cfor first-strand cDNA synthesis. The reverse transcription mixture was

then chilled on ice and diluted 2-fold with sterile water. PCR was thenperformed as described (32) in a final volume of 50 @.dcontaining 5 @.dof

reverse transcripted total RNA (125 ng of cDNA), 2.5 units of Taq polymerase(Beckman, Gagny, France), specific sense and antisense primers (2.2 @Mforsstl to sst5,and0.3 @Mfor (3-actin),and 250 @Mdeoxynucleotidetriphosphatesin a 10mMTris-HCI buffer (pH 9) containing1.5mi@tMgC12,50 nmiKCI, and 0.01% Triton X-l00. After denaturation of the sample at 94°Cfor 10

mm, the PCR was carriedout on a DNA Thermal Cycler (Techne)for 25cycles (/3-actin),32 cycles (hsst5), or 35 cycles (sstl to sst4) consisting of 1mm at 94°C(denaturation), annealing for 1 mm (56°Cfor sstl, 62°Cfor sst2,

70°Cfor sst3, 63°Cfor sst4, 60°Cfor sst5, and 54°Cfor @-actin),andextensionat 72°Cfor 90 s. The amplification was terminatedby a finalextensionstepat 72°Cfor 10mm.The conditionsof amplificationhavebeendeterminedas describedpreviously (33). The location of oligonucleotideprimer pairs used to amplify each cDNA is given with respect to the transla

tional start site in the DNA sequenceof sst(s)(5—8)and externalcontrolf3-actin (34) as follows: hsstl sense (nucleotide 622—636)and antisense(nucleotide 1022—1036)primers; hsst2 sense(1—23)and antisense(1081—1104) primers; hsst3 sense (721—741) and antisense (1148—1167) primers;

hsst4sense(843—862)andantisense(1099—1120)primers;hsst5sense(539—557) and antisense (994—1011) primers;and j3-actinsense (506—529)andantisense(998—1021)primers.PCR amplificationof both targetsampleand/3-actinwere run simultaneously.Only samplespositive for (3-actinwereconsideredfor somatostatinreceptorsubtypemRNA expression.Amplifiedfragments were separated by 7% PAGE and stained with ethidium bromide. To

confirmthatPCRproductsresultedfrom cDNA templatesratherthangenomicDNA, parallel RT-PCR reactionswere carried out for eachsamplein the

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Casessstlsst2sst3sst4sst5Normal°(I)—+—++Adenomas―(1)—+—++(2)++—++(3)FAP———÷—(4)FAP+——+—(5)FAP———++CarcinomasDukes'

B(1)+———+(2)—————(3)—++++(4)—+—++(5)———++(6)++—++Dukes'

C(1)++—+—(2)——+—+(3)———++(4)+——++(5)———++Dukes'

D(I)———+—(2)+—+—+(3)+-—NTCLiverMetastases(1)————+(2)+——++(3)+——+—(4)+————(5)+————(6)+———+Cell

lineHT29+———+

sstl

sst2

sstl

sst2

sst3

@ sst4

@ .. -.. , - ?,@@@@

@ sst5

a Colon from a nonpathological organ.

b Benign poly-adenomas from sporadic adenomas (1 and 2) and from FAP (3, 4, and5). Adenomas4 and5 werefrom the samepatient.

C NT, not tested.

M I 2 3 4 5 6 7 8 9 10 11

Fig. 2. Expressionof somatostatinreceptorgenessstl to sst5 in human normalexocrinepancreas.pancreaticadenocarcinomasand metastases,and derivedcell lines.Representative polyacrylamide/ethidium bromide-stained gels show sstl to sst5 mRNAexpression after RT-PCR analysis on total RNAs extracted from: Lane 1. normal pancreas;Lane 2, pancreaticcarcinoma;Lane 3, liver metastasis;Lane 4, pancreaticcarcinoma;celllines;Lane5, BxPC3;Lane6, Capan-l; Lane 7, Capan-2;Lane8, Mia Paca-2;Lane9,PANCTu II; Lane10,818—1;andLane11,818—7.LaneM, POEMmarkersasdescribedinFig.I.

SOMATOSTATINRECEFFORSIN PANCREATICAND COLON CANCER

carcinomas, sst2 mRNA was detected in 50% of Dukes' B stage and20% of Dukes' C stagetumors but not in Dukes' D stagecarcinomas.The other subtypes were heterogeneously expressed, with sstl, sst3,sst4, and sst5 being expressed in 43, 23, 69, and 71%, respectively.Furthermore, in liver metastases, sst2 and sst3 were not expressed, and

Table 2 Somatostatin receptor subtype mRNA expression in human normal andcancerous human colon and derived cell line

r:-----

Fig. 3. Expressionof somatostatinreceptorgenessstl to sst5 in humannormalcolon,colorectalpolypsandcancers,liver mctastases,and HT29 colonic cells. Representativepolyacrylamide/ethidiumbromide-stainedgelsshowsstl to sst5mRNA expressionafterRT-PCR analysis on total RNAs extracted from: Lane 1. normal colon mucosa; Lane 2,sporadicpolyadenoma;Lane3. polyadenomafrom familial adenomatouspolyposis;Lane4, Dukes' stage B cancer; Lane 5, Dukes' stage C cancer; Lane 6, Dukes' stage D cancer;Lane 7, liver metastasis; and Lane 8, HT29 cell line. Lane M, PGEM markers as describedinFig.1.

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Ml 2 3 4 5 678

sstl, sst4, and sst5 mRNA was detected in 83, 33, and 50% of cases,respectively(Table 2; Fig. 3).

DISCUSSION

In the present study, RT-PCR was used to characterize simultaneously the geneexpression of the five somatostatin receptor subtypesin human normal tissues and adenocarcinomas from exocrine pancreasandcolon.Our resultsindicatethat, in contrastto thatobservedin normal tissue or benign lesions, there is a loss of gene expression

of sst2in pancreaticadenocarcinomas,in advancedcoborectalcancers,and their respectivemetastases.

Pancreatic cancer is the fourth leading cause of death from malignant diseasein Western countries.Unfortunately, late diagnosisbecauseof unspecific early symptoms is responsible for the fact that fewpatients can undergo curative surgical tumor resection.Numerousstudies showed that the somatostatin analogues octreotide or yapreotide significantly inhibited growth of pancreatic cancer cell lines invitro or in xenografts as well as in experimental neoplasms (4,20—22).The mechanism of action of the analogues may implicate theinhibition of release of growth factors and a direct antiproliferativeeffect throughhigh-affinity somatostatinreceptors(4, 20, 21). Amongthe recently cloned somatostatin receptor subtypes, sst2 displays thehighest affinity for analogues (5, 9—13,15). We demonstrated that thissubtypemediatesthe antiproliferativeeffect of the stableanaloguesoctreotide and vapreotide through the stimulation of a tyrosine phosphatase activity, both in rat pancreatic cells that endogenously cxpressed sst2 and in stably transfected cells with sst2 cDNA (11, 12,

sst3@ 35).

Pilot clinical trials using octreotide or vapreotide to treat patientssst4 withadvancedand/orunresectablepancreaticcancerfailedtodem

onstrate any significant benefit of analogue therapy (21, 23, 24). In thepresent study, we did not observe sst2 mRNA expression in pancreatic

sst5 adenocarcinomas and metastases; this subtype was present in all

normal pancreatic tissue samples. In addition, sst2 was not expressedin the pancreatic cancer cell lines, except in the Mia Paca-2 cells.Interestingly, RC-160 inhibited growth of this latter cell line both invitro and in vivo through binding of high-affinity sites and stimulation

of a tyrosinephosphataseactivity (36). All of theseobservationsarguein favor of the role of sst2 in the negative regulation of pancreatic cellgrowth. The loss of expressionof sst2in neoplasticpancreaticcells

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SOMATOSTATINRECEPTORSIN PANCREATICAND COLON CANCER

may provide a growth advantage for tumors and their metastases.Moreover, a direct antiproliferative effect of somatostatinand itsanalogues may thus be excluded in the absenceof sst2. Future studiesare necessary to determine if the loss of this negative regulation

contributes to pancreatic tumor development and progression.Experimental studies conducted in vitro and in vivo demonstrated

that somatostatin analogue treatment effectively reduced the growth

of colon cancers (4, 21,•22). Somatostatin receptors have been detected in normal colon mucosa as well as in colon adenomas or

carcinomas (2).@Clinical studies have been conducted using shortand long-term octreotide treatments in patients with advanced ormetastatic coborectal cancer, and analogue administration poorly influenced tumor growth (24, 25) The mechanism of action of the

analogue may implicate the inhibition of release of growth hormone,insulin, insulin-like growth factor I, or gastrmn; the inhibition ofautocrine secretion of growth factors; or a direct antiproliferativeeffect via the somatostatin receptors (2, 4, 22, 37). In the presentstudy, we found that sst2 mRNA was expressed in normal tissue andadenomasbut little was expressedor was absent in invasive coborectalcancers of Dukes' stageC or D and in metastases.Moreover, sst2 wasnot expressed in adenomas from FAP patients, which possessa hightransformation rate. The absenceof sst2 may explain, at least in part,the lack of local response to octreotide therapy in advanced or metastatic coborectal cancers (24, 25). As we postulated for pancreaticcancer, the decreaseof sst2 gene expression may be related to tumorlocal invasion and metastasis,and the loss of this receptor mayprovide a growth advantage in advanced cobomc tumors.

We found in this study that mRNAs of sstl, sst4, and sst5 subtypesare present both in normal and cancerous tissues from exocrine

pancreas and colon. We found previously that among these threesubtypes, sst5 also mediated the antiproliferative effect of somatosta

tin analogues (12). However, the mechanism implicated in the mcdiation of cell growth inhibition does not involve activation of tyrosine

phosphatase activity (12). In these conditions, and contrary to sst2,activation of sst5 cannot counteract the effect of growth factors actingvia tyrosine kinase-dependent receptors (12) such as epidermalgrowth factor, insulin-like growth factor, and insulin that are impli

cated in the growth of pancreatic and colon cancers (2, 4, 20, 35, 36).

sst5 may not necessarily regulate growth of these carcinomas. However, it is noteworthy that in two of the three Duke's D stagecarcinomas and in three of the six liver metastasis specimens, bothsst2 and sst5 were not expressed; the loss of sst5 could also conferadditional growth advantage to tumor cells in these cases. In thepresent study, the two subtypes sstl and sst4 are also heterogeneouslyexpressedin both normal and tumoral specimens; however, the role ofthese two subtypes remains unknown in human colon and pancreas.

Finally, sst3 mRNA was little or not detected, especially in exocrinepancreas. In contrast, this subtype seems to be present in endocrinepancreas because we and others could detect sst3 mRNA in bothfunctioning and nonfunctioning islet cell tumors (18, 19).@

In conclusion, the sst2 subtype that displays a high affinity forsomatostatin analogues and mediates their antiproliferative effect waspresent in normal tissues but was weakly or not expressed in pancreatic and coborectal carcinomas and their metastases.The loss of sst2gene expression and thus the mediation of negative regulation of cellproliferation in neoplastic tissues may provide a growth advantageforthese tumors and explain, in part, the lack of antigrowth effect ofsomatostatin analogues on advanced stage carcinomas. Conversely,sstl , sst4, and sst5 were heterogeneously expressed in both normaland cancerous tissues tested. The possibility that these subtypes may

4 L. Buscail et al., unpublished results.

act directly or indirectly as mediators of growth inhibition could notbe ruled out. Nevertheless, with regard to the heterogeneousdistribution of somatostatinmRNA, a rational receptorsubtypingshouldbecarried out before considering somatostatin analogues for the treatmentof patientswith coborectalor pancreaticcarcinomas.In parallel,the developmentof new analogueshighly selectivefor a given subtype could lead to a better diagnosis and treatment of somatostatinreceptor-positive human entero-pancreatic tumors.

ACKNOWLEDGMENTS

We thankDr. G. I. Bell (Howard HughesMedical Institute, Chicago,IL)for providing humansstl to sst4genesandDr. A. M. O'Carroll (NationalInstitute for Mental Health, Bethesda,MD) for providing the humansst5gene.We thank Drs. J. L. Gouzi, G. Fourtanier,and B. Suc for providingtissue specimens. We are indebted to Dr. R. Parc, Dr. S. Prévost,and thestaff of theCentrede Chirurgie Digestive (HôpitalSaintAntoine) for theircollaboration.

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1996;56:1823-1827. Cancer Res   Louis Buscail, Nathalie Saint-Laurent, Eric Chastre, et al.   Pancreatic and Colorectal CancerLoss of sst2 Somatostatin Receptor Gene Expression in Human

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