[CANCER RESEARCH 58, 1850-1859. May 1. 1998] Somatostatin Receptor Subtype Specificity and in Vivo Binding of a Novel Tumor Tracer, 99mTc-P8291 Irene Virgolini,2 Maria Leimer, Hirsch Handmaker, Secondo Lastoria, Claudia Bischof, Pietro Muto, Thomas Pangerl, Doris Gludovacz, Markus Peck-Radosavljevic, John Lister-James, Gerhard Hamilton, Klaus Kaserer, Peter Valent, and Richard Dean Departments of Nuclear Medicine /I. V.. M. L. C. B.. T. P.. D. G.¡, Gastroenterologe ¡M.P-R.¡. Surgery ¡G.H.¡.Pathology ¡K.K.¡,and Internal Medicine I. Division of Hematolog\ [P. V.}, University of Vienna, A-1090 Vienna, Austria; Arizona Institute of Nuclear Medicine, Phoenix. Arizona 85016 [H. H.J; Department of Nuclear Medicine, National Cancer Institute, 80131 Naples, Italy ¡S.L, P. M.]: and Diatide, Inc.. Londonderry, New Hampshire 03053 ¡J.L-J., R. D.¡ ABSTRACT strated (1, 2, 5). In fact, such tumors frequently coexpress VIP and SST/OCT binding sites. Recent data suggest that somatostatin receptors (SSTRs) are expressed An interesting phenomenon is that VIP and OCT can cross-compete on various tumor cells. High-level expression of SSTR on the tumor cell for binding to tumor cell membrane receptors (2). The molecular basis surface provides the basis for the successful clinical use of radiolabeled of this phenomenon could not readily be explained thus far. However, ligands for the in vivo localization of tumor sites. We have characterized the in vitro binding properties of the novel SSTR ligand "mTc-P829 using the molecular cloning of SSTR and VIPR has recently provided new primary human tumors (carcinoids, breast cancers, intestinal adenocar- insights into the biology and interactions of VIP and SST. To date, cinomas, pheochromocytomas, small cell and non-small cell lung cancer, five different human SSTRs (6-13) and two different VIPRs (14-19) and melanomas; n = 28), various tumor cell lines, and COS7 cells trans- have been characterized in detail and have been cloned. Using trans fected with the human SSTR (hSSTR) subtypes 1, 2, 3, 4, and 5. """Tc- fected peptide receptors, hSSTRS has recently been identified as a P829 bound to primary tumor cells and tumor cell lines with high affinity potential common acceptor site for both SST/OCT and VIP (20). and high capacity. The dissociation constants (A,,I ranged between 1 and Several efforts have been undertaken to identify hSSTR subtypes 20 IIM. '"""Tc-1'829 also bound with high affinity to the transfected expressed in primary human cancers (for a review, see Ref. 21). A hSSTR2 (Ka, 2.5 nM), hSSTRS (Ad, 2 nM), and hSSTR3 (K¿,1.5 nM). Binding of "'""Tt-PH29 to hSSTR3 was found to be displaceable by unla- number of observations suggest that hSSTR2 is expressed in many different tumors, including neuroendocrine tumors and breast cancer beled P829/([ReO]-P829), SST-14, and vasoactive intestinal peptide (VIP; IC50, 2 nM) and, less effectively, by Tyr'-octreotide (IC50, 20 nM). In (22). However, other hSSTR subtypes have also been detected (23, contrast, the binding of 99mTc-P829 to hSSTR2 and hSSTRS could be 24). We recently have demonstrated expression of hSSTRS mRNA in displaced by P829/([ReO]-P829) and Tyr'-octreotide but not by VIP. a variety of human tumors, including breast cancers, melanomas, and 99l"Tc-P829 scintigraphy revealed in vivo binding to primary or metastatic neuroendocrine tumors (21, 25). Because this receptor (hSSTR3) was tumor sites in seven of eight patients with breast cancer and six of six found to bind both VIP and OCT (20), it was hypothesized that this patients with melanoma. In summary, our data show that 99n>Tc-P829 site is responsible for the observed cross-competition of these peptides binds with high affinity to many different types of primary and cloned in primary human tumors. tumor cells. Furthermore, our data identify hSS TK2. the VIP acceptor Despite the clinical usefulness of "'In-OCT (3) and 123I-VIP (4), hSSTR3, and hSSTRS as the respective target receptors. Because these several attempts have been made to label hSSTR ligands with 99mTc receptors are frequently expressed at high levels on primary tumor cells, because of its optimal decay properties and cost effectiveness (26- 99mTc-P829 appears to be a promising novel peptide tracer for tumor 28). Recently, P829, a peptide containing a sequence that mimics the imaging. binding domain of SST, has been identified as a suitable hSSTR ligand that can be labeled with 99mTc (29). However, the spectrum of human tumors that can be visualized by 99mTc-P829 has not been INTRODUCTION defined yet. Also, the binding behavior of this novel hSSTR ligand The high-level expression of peptide receptors on various tumor onto various subtypes of hSSTR is not known. The aims of the present cells as compared with normal tissue or blood (1,2) provides the study were to evaluate the binding characteristics and hSSTR subtype molecular basis for the successful use of radiolabeled SST* analogues specificity of 99mTc-P829, as well as the binding affinity of this novel (such as OCT) and VIP as tumor tracers in nuclear medicine (3, 4). tracer for primary human tumors. Thus, using primary tumor cells or cell lines, specific binding of both VIP and OCT to the cell surface of various tumors has been demon- MATERIALS AND METHODS Received 9/19/97; accepted 3/3/98. Synthesis and Labeling of P829. The peptide P829 was synthesized using The costs of publication of this article were defrayed in part by the payment of page solid-phase peptide synthesis techniques and /v'-(9-fluorenyl)methoxycarbonyl charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. chemistry and was purified by preparative high-performance liquid chroma- ' These studies have been supported in part by the Austrian National Bank (Jubiläums tography as described (29). [ReO]-P829 was prepared by ligand exchange fonds Projects 5460 and 6512) and by a Foundation of the Mayor of the City of Vienna. using tetrabutyl ammonium oxorhenium tetrabromide, which was prepared Parts of the studies were sponsored by Diatide. Inc. 2 To whom requests for reprints should be addressed, at Department of Nuclear according to Cotton and Lippard (30). For practical use, we formulated an Medicine. University of Vienna, Währinger Gürtel18-20. A-1090 Vienna. Austria. instant kit containing 50 /ig of the P829 peptide. This P829 kit was reconsti Phone/Fax: 43-1-40400-7835; E-mail: [email protected]. tuted with 500 MBq-3 GBq "'"Tc-pertechnetate (CIS Bio-International, Paris, 3 The abbreviations used are: SST, somatostatin; SSTR, SST receptor; hSSTR. human SSTR; VIP, vasoactive intestinal peptide; VIPR, VIP receptor; 123I-VIP, '"l-labeled VIP; France) in a final volume of 1-5 ml. The reconstituted product was heated for IC50, concentration of unlabeled ligand necessary to induce 50% inhibition of labeled 15 min and then kept at room temperature for 45 min. An aliquot of this ligand binding; Kd, dissociation constant (concentration of labeled ligand necessary to preparation was used for the in vitro series of experiments. The radiochemical produce half-maximal binding); LNN, lymph node métastases;NSCLC, non-small cell purity of the 99mTc-P829 product was determined by instant TLC (ITLC-SG; lung cancer; OCT, octreotide; "'In-OCT. '"In-labeled OCT: P829. novel SST-14 ana Gelman Sciences, Ann Arbor, MI) developed in saturated saline [99mTc-P829 logue; |ReO]-P829, oxorhenium complex of P829; PMNC, peripheral blood mononuclear and 99mTc-microcolloid, relative fraction (rf) 0-0.75] and ITLC-SG developed cell; SPECT, single-photon emission computed tomography; SSM, superficial spreading melanoma. in pyridine:acetic acid:water (5:3:1.5) for determination of "Tc-microcolloid 1850 Downloaded from cancerres.aacrjournals.org on September 26, 2021. © 1998 American Association for Cancer Research. BINDING PROPERTIES OF 'â„¢'"Tc-PK29 Table 1 Binding ¡if9v'"Tc-PH29. Approximately 500 MBq WmTc-P829 were injected i.V.. and planar and SPECT images were acquired within 24 h after injection. 99mTc-P829 identified primary tumors and métastasesas indicated in the Table. NP, not performed. Detection of tumor lesions by scintigraphy with Patient No./initials Site of disease" WmTc-P829 "in-OCT I-VIP BreastcancerI/EE2/SB3/RS4/JA5/HB6/BW''7/LT*8/CCfr9/SM'IO/NE'1 (right)Primarybreast cancer (right)Primarybreast cancer (left)NHLbreast cancer (left)Primary(MALToma) of the breast (left)Supraclavicularianductal breast cancer (left)Multiple LNN positive>l() tissueRecurrentLNN in bone, liver, soft positiveNegative1/1 (left)LNN. lobular breast cancer thoraxPrimaryleft lower positiveNPNPNPNPPositivePositive1/1 tumorPrimaryductal tumorPrimarylobular I/RE'12/TS''Melanomas1/LR'2/CF3/SA*4/VS"-'5/MR'"6/BMC'"''7/TJc8/KL''-'CarcinoidsI/RE*"2/TK"'rSCLCI/RM'NSCLC15/SP1" tumorPrimaryductal tumorPrimaryductal choroid)PrimarySSM (right toe)LNN SSM (left (leftgroin)LNN positive1/1 (leftaxilla)LNN positive>!(> groin)LNN(left and right positive1/1 (rightaxilla)s.c. positiveI/I metastasiss.c. positive3/3 métastasesLNN. positive1/1 rightaxillaBone positive5/5 métastasesLNN, positive4/4 groins.c.left, right positive2/2 métastasesLung positiveI/I positiveNPNPNPNPNPNPNP'smetastasisPrimary NMs.c. métastasesLNN métastasesLiver metastasisLNN (abdomen)Primarymétastases tumorPrimary tumorPositivePositivePositivePositiveNegative1/1 NHL,non-Hodgkin' melanoma:alreadylymphoma; MALToma. mucosa-associated lymphoid tissue tumor; NM. nodular small cell lung cancer;NPNPNPNPNPNPNPNPNPNPPositiveNPPositiveNPNPNPNPNPNPNPNPNPNPNPNPNPNPPositivePositivePositivePositiveNPNPNP.not performed. was'Primary tumor scintigraphy.,resected at the lime of From these patientsPrimary tissue specimens were obtained for in v/fm receptor analysis (seealso Table 2).NPNPNPNPNPNPNPNPNPPositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositivePositiveSCLC. (rf 0-0.25). The radiochemical purity of 99mTc-P829 was >90% in all exper Cell lines were cultured in RPMI 1640 (A431. HT29, T47D. BT20, ZR75-1. MCF7. and KU8I2) or in Iscove's modified Dulbecco's medium iments.