Bis(Disulfide)-Bridged Somatostatin-14 Analogs and Their [111In]In-Radioligands: Synthesis and Preclinical Profile

The overexpression of one or more somatostatin receptors (SST1-5R) in human tumors has provided an opportunity for diagnosis and therapy with somatostatin-like radionuclide carriers. The application of "pansomatostatin" analogs is expected to broaden the clinical indications and upgrade the diagnostic/therapeutic efficacy of currently applied SST2R-prefering radioligands. In pursuit of this goal, we now introduce two bicyclic somatostatin-14 (SS14) analogs, AT5S (DOTA-Ala1-Gly2-c[Cys3-Lys4-Asn5-c[Cys6-Phe7-DTrp8-Lys9-Thr10-Cys11]-Thr12-Ser13-Cys14]) and AT6S (DOTA-Ala1-Gly2-c[Cys3-Lys4-c[Cys5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-Cys12]-Ser13-Cys14]), suitable for labeling with trivalent radiometals and designed to sustain in vivo degradation. Both AT5S and AT6S and the respective [111In]In-AT5S and [111In]In-AT6S were evaluated in a series of in vitro assays, while radioligand stability and biodistribution were studied in mice. The 8/12-mer bicyclic AT6S showed expanded affinity for all SST1-5R and agonistic properties at the SST2R, whereas AT5S lost all affinity to SST1-5R. Both [111In]In-AT5S and [111In]In-AT6S remained stable in the peripheral blood of mice, while [111In]In-AT6S displayed low, but specific uptake in AR4-2J tumors and higher uptake in HEK293-SST3R tumors in mice. In summary, high radioligand stability was acquired by the two disulfide bridges introduced into the SS14 motif, but only the 8/12-mer ring AT6S retained a pansomatostatin profile. In consequence, [111In]In-AT6S targeted SST2R-/SST3R-positive xenografts in mice. These results call for further research on pansomatostatin-like radioligands for cancer theranostics.

Glutathione analogues as substrates or inhibitors that discriminate between allozymes of the MDR-involved human glutathione transferase P1-1

Glutathione (GSH) structure-guided tripeptide analogues were designed and synthesized by solid phase technology, purified (≥95%) by RP and/or GF column chromatography, to identify those that, compared with GSH, exhibited similar or higher binding and catalytic efficiency toward the MDR-involved human GSTP1-1 isoenzyme, and could discriminate between the allozymic expression products of the polymorphic human GSTP1 gene locus, designated as hGSTP1*A (Ile(104) /Ala(113) ), hGSTP1*B (Val(104) /Ala(113) ), and hGSTP1*C (Val(104) /Val(113) ). The analogues bear single amino acid alterations as well as alterations in more than one position. Some analogues showed remarkable allozyme selectivity, binding catalytically to A (I, II, IV, XII), to C (V and XVI), to A and C (III, VII, XIV) or to all three allozymes (XV). A heterocyclic substituent at positions 1 or 2 of GSH favors inhibition of A, whereas a small hydrophobic/hydrophilic amide substituent at position 2 (Cys) favors inhibition of B and C. Heterocyclic substituents at position 1, only, produce catalytic analogues for A, whereas less bulky and more flexible hydrophobic/hydrophilic substituents, at positions 1 or 3, lead to effective substrates with C. When such substituents were introduced simultaneously at positions 1 and 3, the analogues produced have no catalytic potential but showed appreciable inhibitory effects, instead, with all allozymes. It is anticipated that when GSH analogues with selective inhibitory or catalytic binding, were conjugated to allozyme-selective inhibitors of hGSTP1-1, the derived leads would be useful for the designing of novel chimeric inhibitors against the MDR-involved hGSTP1-1 allozymes. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 330-344, 2016.

Structure-activity relationship study of angiotensin II analogs in terms of β-arrestin-dependent signaling to aldosterone production

The known angiotensin II (AngII) physiological effect of aldosterone synthesis and secretion induction, a steroid hormone that contributes to the pathology of postmyocardial infarction (MI) heart failure (HF), is mediated by both Gq/11 proteins and β-arrestins, both of which couple to the AngII type 1 receptors (AT1Rs) of adrenocortical zona glomerulosa (AZG) cells. Over the past several years, AngII analogs with increased selectivity ("bias") toward β-arrestin-dependent signaling at the AT1R have been designed and described, starting with SII, the gold-standard β-arrestin-"biased" AngII analog. In this study, we examined the relative potencies of an extensive series of AngII peptide analogs at relative activation of G proteins versus β-arrestins by the AT1R. The major structural difference of these peptides from SII was their varied substitutions at position 5, rather than position 4 of native AngII. Three of them were found biased for β-arrestin activation and extremely potent at stimulating aldosterone secretion in AZG cells in vitro, much more potent than SII in that regard. Finally, the most potent of these three ([Sar(1), Cys(Et)(5), Leu(8)]-AngII, CORET) was further examined in post-MI rats progressing to HF and overexpressing adrenal β-arrestin1 in vivo. Consistent with the in vitro studies, CORET was found to exacerbate the post-MI hyperaldosteronism, and, consequently, cardiac function of the post-MI animals in vivo. Finally, our data suggest that increasing the size of position 5 of the AngII peptide sequence results in directly proportional increases in AT1R-dependent β-arrestin activation. These findings provide important insights for AT1R pharmacology and future AngII-targeted drug development.

Involvement of angiotensin II type 2 receptor (AT2R) signaling in human pancreatic ductal adenocarcinoma (PDAC): a novel AT2R agonist effectively attenuates growth of PDAC grafts in mice

We have recently discovered the potential involvement of angiotensin II type 2 receptor (AT2R) signaling in pancreatic cancer using AT2R deficient mice. To examine the involvement of AT2R expression in human PDAC, expressions of AT2R as well as the major angiotensin II receptor (type 1 receptor, AT1R) in human PDAC and adjacent normal tissue was evaluated by immunohistochemistry and real time PCR using surgically dissected human PDAC specimens. In immunohistochemical analysis, relatively strong AT1R expression was detected consistently in both normal pancreas and PDAC areas, whereas moderate AT2R expression was detected in 78.5% of PDAC specimens and 100% of normal area of the pancreas. AT1R, but not AT2R, mRNA levels were significantly higher in the PDAC area than in the normal pancreas. AT2R mRNA levels showed a negative correlation trend with overall survival. In cell cultures, treatment with a novel AT2R agonist significantly attenuated both murine and human PDAC cell growth with negligible cytotoxicity in normal epithelial cells. In a mouse study, administrations of the AT2R agonist in tumor surrounding connective tissue markedly attenuated growth of only AT2R expressing PAN02 murine PDAC grafts in syngeneic mice. The AT2R agonist treatment induced apoptosis primarily in tumor cells but not in stromal cells. Taken together, our findings offer clinical and preclinical evidence for the involvement of AT2R signaling in PDAC development and pinpoint that the novel AT2R agonist could serve as an effective therapeutic for PDAC treatment.

Electronic sculpting of ligand-GPCR subtype selectivity: the case of angiotensin II

GPCR subtypes possess distinct functional and pharmacological profiles, and thus development of subtype-selective ligands has immense therapeutic potential. This is especially the case for the angiotensin receptor subtypes AT1R and AT2R, where a functional negative control has been described and AT2R activation highlighted as an important cancer drug target. We describe a strategy to fine-tune ligand selectivity for the AT2R/AT1R subtypes through electronic control of ligand aromatic-prolyl interactions. Through this strategy an AT2R high affinity (K_i = 3 nM) agonist analogue that exerted 18,000-fold higher selectivity for AT2R versus AT1R was obtained. We show that this compound is a negative regulator of AT1R signaling since it is able to inhibit MCF-7 breast carcinoma cellular proliferation in the low nanomolar range.

[DOTA]Somatostatin-14 analogs and their (111)In-radioligands: effects of decreasing ring-size on sst1-5 profile, stability and tumor targeting

Multiple somatostatin receptor (sst)-subtype expression has been manifested in several human tumors. Hence, the availability of radiopeptides retaining the full pansomatostatin profile of the native hormone (SS14) is expected to increase the sensitivity and broaden the clinical indications of currently applied sst2-preferring cyclic octapeptide radioligands, like OctreoScan(®) ([(111)In-DTPA]octreotide). On the other hand, SS14 has been excluded from clinical use due to its rapid in vivo degradation. We herein present a small library of seven novel cyclic SS14-mimics carrying at their N-terminus the universal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) for stable binding of medically useful radiometals, like (111)In. By decreasing the number of amino acids composing the ring in their structure from 12 up to 6 AA, we induced important changes in key-biological parameters in vitro and in vivo. In particular, we observed unexpected changes and even total loss of sst1-5-affinity (6AA-ring), as well as weaker sst2-internalization efficacy as the ring size decreased. In contrast, in vivo stability increased with decreasing ring size, reaching its maximum in the 6AA-ring analogs. Interestingly, only the 12AA- and 9AA-ring members of this series showed sst2-specific uptake in AR4-2J tumors in mice revealing the prominent role of ring size on the biological response of tested SS14-derived radioligands.

Structure-activity studies of lGnRH-III through rational amino acid substitution and NMR conformational studies

Lamprey gonadotropin-releasing hormone type III (lGnRH-III) is an isoform of GnRH isolated from the sea lamprey (Petromyzon marinus) with negligible endocrine activity in mammalian systems. Data concerning the superior direct anticancer activity of lGnRH-III have been published, raising questions on the structure-activity relationship. We synthesized 21 lGnRH-III analogs with rational amino acid substitutions and studied their effect on PC3 and LNCaP prostate cancer cell proliferation. Our results question the importance of the acidic charge of Asp⁶ for the antiproliferative activity and indicate the significance of the stereochemistry of Trp in positions 3 and 7. Furthermore, conjugation of an acetyl-group to the side chain of Lys⁸ or side chain cyclization of amino acids 1-8 increased the antiproliferative activity of lGnRH-III demonstrating that the proposed salt bridge between Asp⁶ and Lys⁸ is not crucial. Conformational studies of lGnRH-III were performed through NMR spectroscopy, and the solution structure of GnRH-I was solved. In solution, lGnRH-III adopts an extended backbone conformation in contrast to the well-defined β-turn conformation of GnRH-I.

[111In-DOTA]Somatostatin-14 analogs as potential pansomatostatin-like radiotracers - first results of a preclinical study

Background

In this study, we report on the synthesis, radiolabeling, and biological evaluation of two new somatostatin-14 (SS14) analogs, modified with the universal chelator DOTA. We were interested to investigate if and to what extent such radiotracer prototypes may be useful for targeting sst_1-5-expressing tumors in man but, most importantly, to outline potential drawbacks and benefits associated with their use.

Methods

AT1S and AT2S (DOTA-Ala¹-Gly²-c[Cys³-Lys⁴-Asn⁵-Phe⁶-Phe⁷-Trp⁸/DTrp⁸-Lys⁹-Thr¹⁰-Phe¹¹-Thr¹²-Ser¹³-Cys¹⁴-OH], respectively) were synthesized on the solid support and labeled with ¹¹¹In. The sst_1-5 affinity profile of AT1S/AT2S was determined by receptor autoradiography using [Leu⁸,dTrp²²,¹²⁵I-Tyr²⁵]SS28 as radioligand. The ability of AT2S to stimulate sst₂ or sst₃ internalization was qualitatively analyzed by an immunofluorescence-based internalization assay using hsst₂- or hsst₃-expressing HEK293 cells. Furthermore, the internalization of the radioligands [¹¹¹In]AT1S and [¹¹¹In]AT2S was studied at 37 °C in AR4-2J cells endogenously expressing sst₂. The in vivo stability of [¹¹¹In]AT1S and [¹¹¹In]AT2S was tested by high-performance liquid chromatography analysis of mouse blood collected 5 min after radioligand injection, and biodistribution was studied in normal mice. Selectively for [¹¹¹In]AT2S, biodistribution was further studied in SCID mice bearing AR4-2J, HEK293-hsst_2A⁺, -hsst₃⁺ or -hsst₅⁺ tumors.

Results

The new SS14-derived analogs were obtained by solid phase peptide synthesis and were easily labeled with ¹¹¹In. Both SS14 conjugates, AT1S, and its DTrp⁸ counterpart, AT2S, showed a pansomatostatin affinity profile with the respective hsst_1-5 IC₅₀ values in the lower nanomolar range. In addition, AT2S behaved as an agonist for sst₂ and sst₃ since it stimulated receptor internalization. The ¹¹¹In radioligands effectively and specifically internalized into rsst_2A-expressing AR4-2J cells with [¹¹¹In]AT2S internalizing faster than [¹¹¹In]AT1S. Ex vivo mouse blood analysis revealed a rapid degradation of both radiopeptides in the bloodstream with the DTrp⁸ analog showing higher stability. Biodistribution results in healthy mice were consistent with these findings with only [¹¹¹In]AT2S showing specific uptake in the sst₂-rich pancreas. Biodistribution of [¹¹¹In]AT2S in tumor-bearing mice revealed receptor-mediated uptake in the AR4-2J (1.82 ± 0.36 %ID/g - block 0.21 ± 0.17 %ID/g at 4 h post injection (pi)), the HEK293-hsst_2A⁺ (1.49 ± 0.2 %ID/g - block 0.27 ± 0.20 %ID/g at 4 h pi), the HEK293-hsst₃⁺ (1.24 ± 0.27 %ID/g - block 0.32 ± 0.06 %ID/g at 4 h pi), and the HEK293-hsst₅⁺ tumors (0.41 ± 0.12 %ID/g - block 0.22 ± 0.006 %ID/g at 4 h pi). Radioactivity washed out from blood and background tissues via the kidneys.

Conclusions

This study has revealed that the native SS14 structure can indeed serve as a motif for the development of promising pansomatostatin-like radiotracers. Further peptide stabilization is required to increase in vivo stability and, consequently, to enhance in vivo delivery and tumor targeting.

Pleiotrophin expression and role in physiological angiogenesis in vivo: potential involvement of nucleolin

Background

Pleiotrophin (PTN) is a heparin-binding growth factor with significant role(s) in tumour growth and angiogenesis. Although implication of endogenous PTN has been studied in several in vivo models of tumour angiogenesis, its role in physiological angiogenesis has not been addressed. In the present work, we studied expression and functional significance of endogenous PTN during angiogenesis in the chicken embryo chorioallantoic membrane (CAM).

Methods

Using molecular, cellular and biochemical assays, we studied the expression pattern of PTN in CAM and human endothelial cells and its possible interaction with nucleolin (NCL). CAM cells were transfected with a pCDNA3.1 vector, empty (PC) or containing full length cDNA for PTN in antisense orientation (AS-PTN). Angiogenesis was estimated by measuring total vessel length. In vitro, human endothelial cells migration was studied by using a transwell assay, and down-regulation of NCL was performed by using a proper siRNA.

Results

Endogenous PTN mRNA and protein levels, as well as protein levels of its receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) were maximal at early stages, when CAM angiogenesis is active. Application of AS-PTN onto CAM at days of active angiogenesis was not toxic to the tissue and led to dose-dependent decreased expression of endogenous PTN, ERK1/2 activity and angiogenesis. Interestingly, endogenous PTN was also immunolocalized at the endothelial cell nucleus, possibly through interaction with NCL, a protein that has a significant role in the nuclear translocation of many proteins. Down-regulation of NCL by siRNA in human endothelial cells significantly decreased nuclear PTN, verifying this hypothesis. Moreover, it led to abolishment of PTN-induced endothelial cell migration, suggesting, for the first time, that PTN-NCL interaction has a functional significance.

Conclusions

Expression of endogenous PTN correlates with and seems to be involved in angiogenesis of the chicken embryo CAM. Our data suggest that NCL may have a role, increasing the number of growth factors whose angiogenic/tumorigenic activities are mediated by NCL.

Enzymatic stability, solution structure, and antiproliferative effect on prostate cancer cells of leuprolide and new gonadotropin-releasing hormone peptide analogs

Analogs of GnRH, including [DLeu6, desGly1o]-GnRH-NHEt (leuprolide, commercial product), have been widely used in oncology to induce reversible chemical castration. Several studies have provided evidence that, besides their pituitary effects, GnRH analogs may exert direct antiproliferative effects on tumor cells. To study the effect of modifications in positions 4 and 6 of leuprolide on prostate cancer cell proliferation, we synthesized 12 new leuprolide analogs. All GnRH analogs lacked the carboxy-terminal Gly10-amide of GnRH, and an ethylamide residue was added to Pro9. Gly6 was substituted by DLys, Nepsilon-modified DLys, Glu, and DGlu. To improve the enzymatic stability, NMeSer was incorporated in position 4, and the rate of hydrolysis by alpha-chymotrypsin and subtilisin was investigated. Our results demonstrate that this incorporation increases enzymatic stability in all analogs of GnRH, whereas the antiproliferative effect on PC3 and LNCaP prostate cancer cells is similar to that of leuprolide. Conformational studies were performed to elucidate structural changes occurring on substitution of native residues and to study structure-activity relationship for these analogs. The solution models of [DLeu6, desGly10]-GnRH-NHEt (leuprolide), [NMeSer4, DGlu6, desGly10]-GnRH-NHEt, [Glu6, desGly10]-GnRH-NHEt, and [DGIu6, desGly10]-GnRH-NHEt peptides were determined through two-dimensional nuclear magnetic resonance spectroscopy in dimethylsulfoxide. Nuclear magnetic resonance data provide experimental evidence for the U-turn-like structure appeared in all four analogs, which could be characterized as beta-hairpin conformation. The most stable analog [NMeSer4, DGlu6, desGly10]-GnRH-NHEt against proteolytic cleavage forms a second extra backbone turn observed for residues 1-4.

Insights into ectopic estrogen receptor expression, nucleocytoplasmic distribution and interaction with chromatin obtained with new antibodies to estrogen receptors α and β

Recent reports have indicated that in cells ectopically expressing only ERα or the full-length hormone-binding isoform of ERβ (ERβ1), the receptors interact with chromatin with different efficacies and that antibodies capable of probing such interactions by chromatin immunoprecipitation (ChIP) are scarce. We therefore produced nine subtype and isoform-specific antibodies to ERα or ERβ and validated their performance in receptor probing in cell lines and tissue biopsies by various immunochemical methods, including ChIP. We also produced clones of HEK-293 cells stably transfected with an estrogen response element (ERE)-dependent luciferase reporter and ERα or ERβ1, in order to comparatively study their interaction with reporter ERE. We show that ERα was located in the nucleus and ERβ1 in the cytoplasm as well as the nucleus of the stably transfected cells, while both receptors were found predominantly in the nucleus in transiently transfected cells and in all estrogen target tissues examined using the same antibodies. The cells displayed wild-type transcriptional activity and canonical regulation of ERE-dependent luciferase expression by estrogen agonists and antagonists. However, unlike ERα, ERβ1 recruitment to the reporter ERE could be probed only by sequential ChIP with antibodies to receptor N- and C-terminus. These data suggest that in HEK-293 cells stably expressing ERα or ERβ1, ER subtype-specific constraints apply to ERβ1 nuclear entry; and that in cells displaying cytoplasmic as well as nuclear localization of ERβ1, sequential ChIP with different antibodies to the receptor is the method of choice for probing its interaction with chromatin.

A peptide corresponding to the C-terminal region of pleiotrophin inhibits angiogenesis in vivo and in vitro

Pleiotrophin (PTN) is a heparin-binding growth factor that plays a significant role in tumor growth and angiogenesis. We have previously shown that in order for PTN to induce migration of endothelial cells, binding to both α(ν) β(3) integrin and its receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) is required. In the present study we show that a synthetic peptide corresponding to the last 25 amino acids of the C-terminal region of PTN (PTN(112-136) ) inhibited angiogenesis in the in vivo chicken embryo chorioallantoic membrane (CAM) assay and PTN-induced migration and tube formation of human endothelial cells in vitro. PTN(112-136) inhibited binding of PTN to α(ν) β(3) integrin, and as shown by surface plasmon resonance (SPR) measurements, specifically interacted with the specificity loop of the extracellular domain of β(3) . Moreover, it abolished PTN-induced FAK Y397 phosphorylation, similarly to the effect of a neutralizing α(ν) β(3) -selective antibody. PTN(112-136) did not affect binding of PTN to RPTPβ/ζ in endothelial cells and induced β(3) Y773 phosphorylation and ERK1/2 activation to a similar extent with PTN. This effect was inhibited by down-regulation of RPTPβ/ζ by siRNA or by c-src inhibition, suggesting that PTN(112-136) may interact with RPTPβ/ζ. NMR spectroscopy studies showed that PTN(112-136) was characterized by conformational flexibility and absence of any element of secondary structure at room temperature, although the biologically active peptide segment 123-132 may adopt a defined structure at lower temperature. Collectively, our data suggest that although PTN(112-136) induces some of the signaling pathways triggered by PTN, it inhibits PTN-induced angiogenic activities through inhibition of PTN binding to α(ν) β(3) integrin.

Clinical outcome of patients with various advanced cancer types vaccinated with an optimized cryptic human telomerase reverse transcriptase (TERT) peptide: results of an expanded phase II study

BACKGROUND

TERT (telomerase reverse transcriptase) plays a critical role in tumor cell growth and survival. In an expanded phase II study, we evaluated the immunological and clinical responses to the TERT-targeting Vx-001 vaccine in patients with advanced solid tumors.

METHODS

HLA-A*0201-positive patients received two subcutaneous injections of the optimized TERT(572Y) peptide followed by four injections of the native TERT(572) peptide, every 3 weeks. Peptide-specific immune responses were evaluated by enzyme-linked immunosorbent spot at baseline, and after the second and the sixth vaccinations.

RESULTS

Fifty-five patients were enrolled and 34 (62%) completed the six vaccinations. A TERT-specific T-cell immune response was observed in 55% and 70% of patients after the second and the sixth vaccinations, respectively. The disease control rate (DCR) was 36% [95% confidence interval (CI) 24% to 49%], including one complete and one partial response. Immunologically responding patients had a better clinical outcome than nonresponders [DCR: 44% versus 14% (P = 0.047); progression-free survival (PFS): 5.2 versus 2.2 months (P = 0.0001) and overall survival: 20 versus 10 months (P = 0.041)]. Multivariate analysis revealed that the immunological response was an independent variable associated with increased PFS (hazard ratio = 3.35; 95% CI 1.7-6.7).

CONCLUSION

Vx-001 vaccine was well tolerated and induced a TERT-specific immunological response, which was significantly correlated with improved clinical outcome.

A new validated SPE-HPLC method for monitoring crocetin in human plasma--application after saffron tea consumption

Saffron (stigmas of Crocus sativus L.) is a well-known spice with many attributed therapeutic uses throughout centuries. Although studies have demonstrated that crocetin and crocins from saffron have various biological functions, issues concerning the route and way of saffron administration, the absorption and metabolism of saffron carotenoids in humans have not been answered yet. In the present study, an isocratic reversed-phase liquid chromatographic method was developed and validated for the determination of crocetin in plasma. Samples were pre-treated by solid phase extraction (recoveries >72%) and were chromatographed on a Luna C-18 column (4.6mm×250mm, 5μm) with a mobile phase consisting of methanol-water-trifluoroacetic acid (75.0:24.5:0.5, v/v/v) at a flow rate of 1.0mLmin(-1). The HPLC method developed resulted in sharp peaks at 10.7 (trans-crocetin) and 18.6min (cis-crocetin), whereas the calibration curve of total crocetin in plasma displayed a good linearity for concentrations of 0.020-20μM (R(2)=0.999). Specificity, precision, accuracy and stability were studied with spiked plasma samples and were acceptable. The developed method was applied to the determination of crocetin levels in plasma of four healthy human volunteers before and after consumption of one cup of saffron tea (200mg of saffron in 80°C water for 5min). Results showed that the concentration of crocetin was high after 2h (1.24-3.67μM) and still determined after 24h (0.10-0.24). Interestingly, the percentage of the cis-isomer ranges from 25 to 50%, suggesting in vivo isomerization.

Crocetin inhibits invasiveness of MDA-MB-231 breast cancer cells via downregulation of matrix metalloproteinases

Crocetin is a carotenoid dicarboxylic acid which, in nature, is esterified with glucose or gentiobiose units forming the crocins, abundant components of saffron (a spice with many reputed medicinal uses). We have previously reported that saffron, crocins and crocetin inhibit breast cancer cell proliferation. In order to further study the effect of crocetin on breast cancer cells, we used the highly invasive MDA-MB-231 cells and measured the viability with the WST-1 assay and the invasiveness through a reconstituted basement membrane. After 24 h incubation, crocetin significantly inhibited not only proliferation but also invasion at 1 and 10 µM. Cancer invasiveness and metastasis are associated with the expression of matrix metalloproteinases (MMPs). In order to study the molecular changes of MMP expression that might accompany the observed crocetin effects, gene expression of MMPs was studied by RT-PCR, whereas protein expression and gelatinolytic activity were determined with Western blotting and zymography, respectively. The gene and protein expression of pro-MT1-MMP and pro-MT2-MMP were greatly attenuated by both crocetin and all- TRANS-retinoic acid (ATRA, used as control). Incubation with 10 µM crocetin for 24 h in serum-free conditions reduced pro-MMP-9 activity and pro-MMP-2/MMP-2 protein levels. When cultured in media with sera 2 and 5 %, crocetin at 10 μΜ also reduced gelatinase activity. The above findings show that crocetin, the main metabolite of crocins, inhibits MDA-MB-231 cell invasiveness via downregulation of MMP expression.

Synthesis and Biological Evaluation of New CRH Analogues

A series of 7 new human/rat Corticotropin Releasing Hormone (h/r-CRH) analogues were synthesized. The induced alterations include substitution of Phe at position 12 with D-Phe, Leu at positions 14 and 15 with Aib and Met at positions 21 and 38 with Cys(Et) and Cys(Pr). The analogues were tested regarding their binding affinity to the CRH-1 receptor and their activity which is represented by means of percentage of maximum response in comparison to the native molecule. The results indicated that the introduction of Aib, or Cys derivatives although altering the secondary structure of the molecule, did not hinder receptor recognition and binding.

Folding in solution of the C-catalytic protein fragment of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a key molecule of the renin-angiotensin-aldosterone system which is responsible for the control of blood pressure. For over 30 years it has become the target for fighting off hypertension. Many inhibitors of the enzyme have been synthesized and used widely in medicine despite the lack of ACE structure. The last 5 years the crystal structure of ACE separate domains has been revealed, but in order to understand how the enzyme works it is necessary to study its structure in solution. We present here the cloning, overexpression in Escherichia coli, purification and structural study of the Ala(959) to Ser(1066) region (ACE_C) that corresponds to the C-catalytic domain of human somatic angiotensin-I-converting enzyme. ACE_C was purified under denatured conditions and the yield was 6 mg/l of culture. Circular dichroism (CD) spectroscopy indicated that 1,1,1-trifluoroethanol (TFE) is necessary for the correct folding of the protein fragment. The described procedure can be used for the production of an isotopically labelled ACE(959-1066) protein fragment in order to study its structure in solution by NMR spectroscopy.

Sulphonamide-based bombesin prodrug analogues for glutathione transferase, useful in targeted cancer chemotherapy

Glutathione transferases (GSTs) are enzymes involved in cellular detoxification by catalysing the nucleophilic attack of glutathione (GSH) on the electrophilic centre of a number of toxic compounds and xenobiotics, including certain chemotherapeutic drugs. The encountered chemotherapeutic resistant of tumour cells, thus, has been associated with the increase of total GST expression. GSTs, in addition to GSH-conjugating activity, exhibit sulphonamidase activity, catalyzing the GSH-mediated hydrolysis of sulphonamide bonds. Such reactions are of interest as potential tumour-directed prodrug activation strategies. In the present work we report the design and synthesis of novel chimaeric sulphonamide derivatives of bombesin, able to be activated by the model human isoenzyme GSTA1-1 (hGSTA1-1). These derivatives bear a peptidyl-moiety (analogues of bombesin peptide: R-[Lue(13)]-bombesin, R-[Phe(13)]-bombesin and R-[Ser(3),Arg(10),Phe(13)]-bombesin, where R=C(6)H(5)SO(2)NH-) as molecular recognition element for targeting the drug selectively to tumour cells. The released S-alkyl-glutathione, after hGSTA1-1-mediated cleavage of the sulphonamide bond, provides an inhibitor of varied strength against GSTs from different sources. These prodrugs are envisaged as a plausible means to sensitize drug-resistant tumours that overexpress GSTs.

Effect of a polyphenol-rich wild blueberry extract on cognitive performance of mice, brain antioxidant markers and acetylcholinesterase activity

The aim of this study was to examine the effect of a polyphenol-rich extract (PrB) of Vaccinium angustifolium (wild blueberries) introduced intraperitoneally (i.p.) at 30 (PrB30) and 60 (PrB60) mg/kg body weight for 7 days, on cognitive performance, brain oxidative status and acetylcholinesterase activity in adult, male, 3-4-month-old Balb-c mice. Evaluation of rodent learning and memory was assessed by a step-through test on day 6 after a double training and an initial acquisition trial on day 5. Antioxidant status was determined by ferric reducing antioxidant power (FRAP), ascorbic acid concentration (FRASC), malondialdehyde and reduced glutathione levels in whole brain homogenates. Acetylcholinesterase (AChE) activity was determined by Ellman's colorimetric method. Results showed that the PrB60-treated mice exhibited a significant improvement in learning and memory (step-through latency time of 228+/-38 s compared to 101+/-32 s of the control group). PrB extract administration also resulted in reduced lipid peroxidation products (38 and 79%) and higher brain ascorbic acid levels (21 and 64%) in both PrB30 and PrB60-treated groups, respectively, and higher glutathione levels (28%) in the PrB60-treated group. Furthermore, salt- and detergent soluble AChE activity significantly decreased in both PrB-treated groups. Thus, the significant cognitive enhancement observed in adult mice after short-term i.p. supplementation with the blueberry extract concentrated in polyphenols, is closely related to higher brain antioxidant properties and inhibition of AChE activity. These findings stress the critical impact of wild blueberry bioactive components on brain function.

Diorganotin(IV) complexes of dipeptides containing the alpha-aminoisobutyryl residue (Aib): preparation, structural characterization, antibacterial and antiproliferative activities of [(n-Bu)2 Sn(H(-1)L)] (LH=H-Aib-L-Leu-OH, H-Aib-L-Ala-OH)

Two new organotin(IV) complexes with dianionic dipeptides containing the alpha-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)(2)Sn(H(-1)L(A))] x 2MeOH (1 x 2MeOH) (L(A)H=H-Aib-L-Leu-OH) and [(n-Bu)(2)Sn(H(-1)L(B))] x MeOH (2 x MeOH) (L(B)H=H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H(-1)L(2-) is the dianionic form of the corresponding dipeptide). Complexes 1 x 2MeOH and 2 x MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn(IV) atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and (119)Sn NMR data are discussed in terms of the nature of bonding and known structures. The antibacterial and antiproliferative activities as well as the effect of the new compounds on pDNA were examined. Complexes 1 and 2 are active against the gram-positive bacteria Bacillus subtilis and Bacillus cereus. The IC(50) values reveal that the two compounds express promising cytotoxic activity in vitro against a series of cell lines.

Helicobacter pylori neutrophil-activating protein activates neutrophils by its C-terminal region even without dodecamer formation, which is a prerequisite for DNA protection--novel approaches against Helicobacter pylori inflammation

Helicobacter pylori neutrophil-activating protein (HP-NAP) protects DNA from free radicals as a dodecamer through its ferroxidase activity without, however, directly binding to it. The retardation that was observed at pH 7.5 could be easily attributed to an iron effect, as it was revealed by experiments in the absence of HP-NAP. A total loss of ferroxidase activity, dodecamer formation and DNA protection in environments rich in free radicals was observed after replacement of His25, His37, Asp52 and Lys134, which are located within the ferroxidase site, with Ala. Molecular dynamics simulations revealed that dimer formation is highly unlikely following mutation of the above amino acids, as the Fe(2+) is no longer attracted with equal strength by both subunits. These findings probably indicate that iron plays an important role in the conformation of HP-NAP by initiating the formation of stable dimers that are indispensable for the ensuing dodecamer structure. Very surprisingly, neutrophil activation appeared to be stimulated by structural elements that are localized within the C-terminal region of both mutant HP-NAP and wild-type dodecamer HP-NAP. In particular, the dodecamer conformation does not seem to be necessary for activation, and helices H3 (Leu69-Leu75) and H4 (Lys89-Leu114) or the linking coils (His63-Thr68 and Thr76-Ser88) are probably critical in stimulating neutrophil activation.

Vaccination of patients with advanced non-small-cell lung cancer with an optimized cryptic human telomerase reverse transcriptase peptide

PURPOSE

To evaluate the immunological and clinical response as well as the safety of the optimized peptide telomerase reverse transcriptase p572Y (TERT572Y) presented by HLA-A*0201 in patients with advanced non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Twenty-two patients with advanced NSCLC and residual (n = 8) or progressive disease (PD; n = 14) following chemotherapy and/or radiotherapy received two subcutaneous injections of the optimized TERT572Y peptide followed by four injections of the native TERT572 peptide administered every 3 weeks. Peptide-specific immune responses were monitored by enzyme-linked immunosorbent spot assay and/or TERT572Y pentamer staining.

RESULTS

Twelve (54.5%) of 22 patients completed the vaccination program. Toxicity consisted primarily of local skin reactions. TERT572-specific CD8+ cells were detected in 16 (76.2%) of 21 patients after the second vaccination, and 10 (90.9%) of 11 patients after the sixth vaccination. Stable disease (SD) occurred in eight (36.4%) of 22 vaccinated patients, with three (13.6%) having had PD before entering the study. The median duration of SD was 11.2 months. After a median follow-up of 10.0 months, patients with early developed immunological response (n = 16) had a significantly longer time to progression and overall survival (OS) than nonresponders (n = 5; log-rank tests P = .046 and P = .012, respectively). The estimated median OS was 30.0 months (range, 2.8 to 40.0 months) and 4.1 months (range, 2.4 to 10.9 months) for responders and nonresponders, respectively.

CONCLUSION

TERT572Y peptide vaccine is well tolerated and effective in eliciting a specific T cell immunity. Immunological response is associated with prolonged survival. These results are encouraging and warrant further evaluation in a randomized study.

Simulated Interactions between Angiotensin-Converting Enzyme and Substrate Gonadotropin-Releasing Hormone: Novel Insights into Domain Selectivity

Human angiotensin-I converting enzyme (ACE) is a central component of the renin-angiotensin system and a major target for cardiovascular therapies. The somatic form of the enzyme (sACE) comprises two homologous metallopeptidase domains (N and C), each bearing a zinc active site with similar but distinct substrate and inhibitor specificities. On the basis of the recently determined crystal structures of both ACE domains, we have studied their complexes with gonadotropin-releasing hormone (GnRH), which is cleaved releasing both the protected NH2- and COOH-terminal tripeptides. This is the first molecular modeling study of an ACE-peptide substrate complex that examines the structural basis of ACE's endopeptidase activity and offers novel insights into subsites that are distant from the obligatory binding site and were not identified in the crystal structures. Our data indicate that a bridging interaction between Arg500 of the N-domain and Arg8 of GnRH that involves a buried chloride ion may account for its role in the specificity of the N-domain for endoproteolytic cleavage of the substrate at the NH2-terminus in vitro. In support of this, the protected NH2-terminal dipeptide of GnRH exhibits stronger interactions than the protected COOH-terminal dipeptide with the N-domain of ACE. Further comparison of the models of ACE-substrate complexes promotes our understanding of how the two domains differ in their function and specificity and provides an extension of the pharmacophore model used for structure-based drug design up to the S7 subsite of the enzyme.

[99mTc]Demotensin 5 and 6 in the NTS1-R-targeted imaging of tumours: synthesis and preclinical results

PURPOSE

The aim of this study was to evaluate the applicability of [(99m)Tc]Demotensin 5 and 6 [Formula: see text] in the targeted diagnostic imaging of neurotensin subtype 1 receptor (NTS1-R)-expressing tumours.

METHODS

Labelling of Demotensin 5 and 6 with (99m)Tc was conducted by brief incubation with (99m)TcO(4) (-), SnCl(2) and citrate anions in alkaline medium at ambient temperature. Affinities of conjugates for the NTS1-R were determined by competition binding experiments in WiDr cell membranes using [(125)I-Tyr(3)]NT as the radioligand. Saturation binding assays were conducted for [(99m)Tc/(99g)Tc]Demotensin 6 in WiDr cell membranes. Internalisation of [(99m)Tc]Demotensin 5 and 6 was studied at 37 degrees C in WiDr cells. Biodistribution of [(99m)Tc]Demotensin 5 and 6 was performed in female Swiss nu/nu mice bearing human WiDr xenografts.

RESULTS

Unlabelled conjugates showed a high affinity for the human NTS1-R (Demotensin 5 IC(50)=0.03+/-0.01 nM; Demotensin 6 IC(50)=0.08+/-0.02 nM), while high affinity was also exhibited by (radio)metallated [(99m)Tc/(99g)Tc]Demotensin 6 (K (d)=0.13+/-0.01 nM). [(99m)Tc]Demotensin 5 and 6 internalised rapidly and specifically in WiDr cells. After injection in WiDr tumour-bearing mice, radiopeptides, and especially the doubly stabilised [(99m)Tc]Demotensin 6, showed NTS1-R-mediated uptake in the intestines and in the implanted tumour (4.30+/-0.45%ID/g at 1 h post injection) and rapid renal excretion from non-target tissues into the urine.

CONCLUSION

[(99m)Tc]Demotensin 6 shows a favourable preclinical profile and further testing in patients is warranted to monitor its eventual applicability as a radiotracer in the diagnostic imaging of NTS1-R-positive tumours.

Expression, purification, and physicochemical characterization of the N-terminal active site of human angiotensin-I converting enzyme

We have cloned, over expressed, and purified one of the two catalytic domains (residues Ala361 to Gly468, ACE-N) of human somatic angiotensin-I converting enzyme in Escherichia coli. This construct represents the N-catalytic domain including the two binding motifs and the 23 amino acid spacers as well as some amino acid residues before and after the motifs that might help in correct conformation. The overexpressed protein was exclusively localized to insoluble inclusion bodies. Inclusion bodies were solubilized in an 8-M urea buffer. Purification was carried out by differential centrifugation and gel filtration chromatography under denaturing conditions. About 12 mg of ACE-N peptide per liter of bacterial culture was obtained. The integrity of recombinant protein domain was confirmed by ESI/MS. Structural analysis using CD spectroscopy has shown that, in the presence of TFE, the ACE-N protein fragment has taken a conformation, which is consistent with the one found in testis ACE by X-ray crystallography. This purification procedure enables the production of an isotopically labeled protein fragment for structural studying in solution by NMR spectroscopy.

Synthesis and biological activity of oxytocin analogues containing conformationally-restricted residues in position 7

We report the solid-phase synthesis and some pharmacological properties of twenty oxytocin (OT) analogues. Basic modifications at position 7 (introduction of alpha-aminoisobutyric acid [Aib], L- or D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid [L/D-Tic], L-alpha-t-butylglycine [Gly(Bu(t))] and pipecolic acid [Pip]) were combined with D-Tyr(Et)(2), L/D-(pEt)Phe(2), D-Tic(2), and Mpa(1) modifications and their various combinations in a total of 14 analogues. Additionally, two analogues having one more modification in position 3, i.e. Gly(Bu(t)), and three analogues having glycine in position 9 substituted by d-Tic or Aib, were prepared. The analogues were tested for rat uterotonic activity in vitro, in the rat pressor assay and for binding affinity to human OT receptor. The analogue having the highest antioxytocic activity was [Mpa(1), D-Tyr(Et)(2), D-Tic(7), Aib(9)]OT having pA(2)=8.31+/-0.19; this analogue was also selective.

Inhibition of breast cancer cell proliferation by style constituents of different Crocus species

Among the different species of Crocus, only C. sativus has been extensively studied for the composition and the biological properties of its styles, since these constitute the well-known spice saffron, which is widely used in the Mediterranean, Indian and Chinese diet. With high performance liquid chromatography (HPLC) and UV/vis spectroscopy, the presence of hydrophilic carotenoids in the styles of three other Crocus taxa, endemic in Greece, C. boryi ssp. tournefortii, C. boryi ssp. boryi and C. niveus, is reported for the first time. Incubation of MCF-7 and MDA-MB-231 breast cancer cells for 48 h with different concentrations of all four Crocus style extracts showed a dose-dependent inhibitory effect on cell proliferation measured by the MTT assay. The antiproliferative effect was not related to the presence of estrogen receptors. Studies on the effect of trans-crocin-4 (the main carotenoid constituent of C. sativus styles, digentibiosylester of crocetin), crocetin and safranal showed that the antiproliferative effect is attributed to the constituent crocins irrespective of the degree of glycosylation. These results show that the styles of the various Crocus taxa merit further investigation of their composition and mechanisms of action of their carotenoid constituents in order to establish if they could be used as chemopreventive or anticancer agents.

The phosphodiesterase 5 inhibitor sildenafil stimulates angiogenesis through a protein kinase G/MAPK pathway

cGMP-degrading pathways have received little attention in the context of angiogenesis. In the present study we set out to determine whether cGMP-specific phosphodiesterase 5 (PDE5) inhibition affects new blood vessel growth. Incubation of chicken chorioallantoic membranes (CAMs) in vivo with sildenafil increased vascular length in a dose-dependent manner. Moreover, incubation of cultured endothelial cells (ECs) with the PDE5 inhibitor promoted proliferation, migration, and organization into tube-like structures. The effects of sildenafil on the angiogenesis-related properties of EC could be blocked by pre-treatment with the soluble guanylyl cyclase (sGC) inhibitor ODQ or the protein kinase G (PKG) I inhibitor DT-3. In addition, over-expression of sGC in EC led to an enhanced growth and migratory response to sildenafil. To study the signaling pathways implicated in the sildenafil-stimulated angiogenic responses we determined the phosphorylation status of mitogen-activated protein kinase (MAPK) members. Incubation of cells with sildenafil increased both extracellular signal regulated kinase 1/2 (ERK1/2) and p38 phosphorylation in a time-dependent manner. Inhibition of MEK by PD98059 and p38 with SB203580 blocked sildenafil-induced proliferation and migration, respectively, suggesting that these MAPK members are downstream of PDE5 and mediate the angiogenic effects of sildenafil. PDE5 inhibitors could, thus, be used in disease states where neo-vessel growth is desired.

Amyloid fibril formation propensity is inherent into the hexapeptide tandemly repeating sequence of the central domain of silkmoth chorion proteins of the A-family

Peptide-analogues of the A and B families of silkmoth chorion proteins form amyloid fibrils under a variety of conditions [Iconomidou, V.A., Vriend, G. Hamodrakas, S.J. 2000. Amyloids protect the silkmoth oocyte and embryo. FEBS Lett. 479, 141-145; Iconomidou,V.A., Chryssikos, G.D.,Gionis, V., Vriend, G., Hoenger, A., Hamodrakas, S.J., 2001. Amyloid-like fibrils from an 18-residue peptide-analogue of a part of the central domain of the B-family of silkmoth chorion protein. FEBS Lett. 499, 268-273; Hamodrakas, S.J. Hoenger, A., Iconomidou, V. A., 2004 . Amyloid fibrillogenesis of silkmoth chorion protein peptide-analogues via a liquid crystalline intermediate phase. J. Struct. Biol. 145, 226-235.], which led us to propose that silkmoth chorion is a natural protective amyloid. In this study, we designed and synthesized two mutant peptide-analogues of the central conservative domain of the A family: (a) one, cA_m1, with a length half of that of the central domain of the A family, which folds and self-assembles, in various conditions, into amyloid fibrils very similar in properties and structure to the fibrils formed by the cA peptide, which corresponds to the entire length of the A family central domain [Iconomidou, V.A., Vriend, G. Hamodrakas, S.J. 2000. Amyloids protect the silkmoth oocyte and embryo. FEBS Lett. 479, 141-145.], in full support of our previous proposal, (b) the second, cA_m2, differing from cA_m1 at three positions, where three glutamates have replaced two valines and one alanine residues, does not form amyloid fibrils in any conditions. It appears that (a) the amyloidogenic properties of silkmoth chorion peptides are encoded into the tandemly repeating hexapeptides comprising the central domain of silkmoth chorion proteins, and, that (b) suitable mutations, properly and carefully designed, greatly affect the strong amyloidogenic properties inherent in certain aminoacid sequences and may inhibit amyloid formation.

Inhibitory activity on amyloid-beta aggregation and antioxidant properties of Crocus sativus stigmas extract and its crocin constituents

Crocus sativus stigmas are one of the widely known spices (saffron) and consist of unusually polar carotenoids. Alzheimer's disease is characterized pathologically by deposition of amyloid beta-peptide (Abeta) fibrils. Oxidation is thought to promote Abeta fibril formation and deposition. To identify agents inhibiting the pathogenesis of Alzheimer's disease, we examined in vitro the antioxidant properties of extract of C. sativus stigmas and its effect on Abeta(1-40) fibrillogenesis. The antioxidant properties were determined by measuring the ferric-reducing antioxidant power and Trolox-equivalent antioxidant capacity, while its effects on Abeta-aggregation and fibrillogenesis were studied by thioflavine T-based fluorescence assay and by DNA binding shift assay. The water:methanol (50:50, v/v) extract of C. sativus stigmas possesses good antioxidant properties, higher than those of tomatoes and carrots, and inhibited Abeta fibrillogenesis in a concentration and time-dependent manner. The main carotenoid constituent, trans-crocin-4, the digentibiosyl ester of crocetin, inhibited Abeta fibrillogenesis at lower concentrations than dimethylcrocetin, revealing that the action of the carotenoid is enhanced by the presence of the sugars. Our findings suggest the possible use of C. sativus stigma constituents for inhibition of aggregation and deposition of Abeta in the human brain.

Gonadotropin-releasing hormone analogues alter gene expression of metalloproteinases and their tissue inhibitors in human breast cancer epithelial cells

Luteinizing hormone-releasing hormone (LHRH or GnRH) is not only produced by hypothalamus, but also by other normal and cancer tissues. GnRH peptide agonists and antagonists inhibit the proliferation of breast cancer cells, but their effect on the expression of metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) has not been studied despite the fact that growth and invasiveness of breast cancer cells in adjacent and distant sites is associated with the expression of MMPs. In the present study, the effects of [D-Leu6, desGly10]GnRH-NHEt (commercially available) and [D-Tic3, Deg6, desGlyl0]GnRH-NHEt on gene expression of MMPs and TIMPs in the breast cancer cell line MCF-7 were examined with semi-quantitative RT-PCR. Results showed that incubation of MCF-7 cells with 30 microM of the synthetic GnRH analogues for 48 h in serum-containing medium resulted in a decrease of MMP-9 expression and increase in MT1- and MT2-MMP mRNA levels. Furthermore, both synthetic analogues induced a significant decrease in TIMP-1 and TIMP-3 mRNA levels and increase in TIMP-2 mRNA levels. The impact of the observed changes on the expression of MMPs and TIMPs warrants further investigation on the effects of GnRH analogues on the invasiveness and metastatic potential of breast cancer cells.

[99mTc]Demotate 2 in the detection of sst2-positive tumours: a preclinical comparison with [111In]DOTA-tate

PURPOSE

The aim of this study was to evaluate [(99m)Tc]Demotate 2 ([(99m)Tc-N(4) (0-1),Asp(0),Tyr(3)]octreotate) as a candidate for in vivo imaging of sst(2)-positive tumours and to compare it with [(111)In]DOTA-tate ([(111)In-DOTA(0),Tyr(3)]octreotate).

METHODS

Labelling of Demotate 2 with (99m)Tc was performed at room temperature using SnCl(2) as reductant in the presence of citrate at alkaline pH. Radiochemical analysis involved ITLC and HPLC methods. Peptide conjugate affinities for sst(2) were determined by receptor autoradiography on rat brain cortex sections using [DOTA(0),(125)I-Tyr(3)]octreotate as the radioligand. The affinity profile of Demotate 2 for human sst(1)-sst(5) was studied by receptor autoradiography in cell preparations using the universal somatostatin radioligand [(125)I][Leu(8),(D: )Trp(22),Tyr(25)]somatostatin-28. The internalisation rates of [(99m)Tc]Demotate 2 and [(111)In]DOTA-tate were compared in sst(2)-positive and -negative control cell lines. Biodistribution of radiopeptides was studied in male Lewis rats bearing CA20948 tumours.

RESULTS

Peptide conjugates showed selectivity and a high affinity binding for sst(2) (Demotate 2 IC(50)=3.2 nM and DOTA-tate IC(50)=5.4 nM). [(99m)Tc]Demotate 2, like [(111)In]DOTA-tate, internalised rapidly in all sst(2)-positive cells tested, but not in sst(2)-negative control cells. After injection in CA20948 tumour-bearing rats both radiopeptides showed high and specific uptake in the sst(2)-positive organs and in the implanted tumour and rapid excretion from non-target tissues via the kidneys.

CONCLUSION

[(99m)Tc]Demotate 2, similarly to the known sst(2)-targeting agent [(111)In]DOTA-tate, showed promising biological qualities for application in the scintigraphy of sst(2)-positive tumours.

Analysis of the CD2 and spliceosomal Sm B/B′ polyproline-arginine motifs defined by a monoclonal antibody using a phage-displayed random peptide library

The cytoplasmic region of the CD2 receptor of lymphocytes contains proline-rich motifs, which are involved in T cell activation and interleukin-2 production. An intracellular CD2 binding protein, CD2BP2, interacts with two tandem PPPPGHR segments of the CD2 tail. CD2BP2 contains a GYF (glycine-tyrosine-phenylalanine) domain that confers binding to these proline-rich sequences. Monoclonal antibody 3E10 that was previously raised against a peptide containing the CD2 PPPPGHR segment reacts with the native CD2 molecule and spliceosomal Sm B/B' proteins. To identify the exact epitope on the CD2 peptide recognized by 3E10, a phage-displayed combinatorial peptide library was used. Analysis of the selected clones revealed that the mAb 3E10 binds preferentially to the motif PxxPPGxR. Experiments using amino acid substitutions with synthetic peptides confirmed the reactivity of mAb 3E10 with this motif. In addition, we show that several similarities exist between this motif and the CD2BP2-GFY recognition motif PPGxR/K. Binding of antibody 3E10 indicates some degree of degeneracy, which is consistent with its ability to recognize structurally related polyproline-arginine motifs found in intracellular proteins including Sm B/B' proteins and other RNA binding proteins. Thus, mAb 3E10 can be used to specifically identify a sub-class of proline-rich motifs, and as such can be used to study the potential role of these proline-rich sequences in mediating protein-protein interactions.

Tetraamine-modified octreotide and octreotate: labeling with99mTc and preclinical comparison in AR4-2J cells and AR4-2J tumor-bearing mice

Two somatostatin analogues, [(99m)Tc]Demotide and [(99m)Tc]Demotate 4, were compared with [(99m)Tc]Demotate 1, a previously reported somatostatin receptor subtype 2 (sst(2)) targeting tracer. Conjugates were prepared by coupling an open-chain tetraamine chelator to D-Phe(1) of [Tyr(3)]-octreotide or [Tyr(3)]-octreotate, respectively, via a p-benzylaminodiglycolic acid spacer adopting solid-phase peptide synthesis techniques. Peptide conjugates were collected in a highly pure form after chromatographic purification. Eventually, [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 were obtained in approximately 1 Ci/micromol specific activity and >96% purity after labeling under alkaline conditions. Demotide and Demotate 4 exhibited similar high binding affinities for the sst(2) expressed in AR4-2J cells with IC(50) values 0.16 and 0.10 nM, respectively. The (radio)metallated analogues [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 showed equally high affinities to the sst(2) during saturation binding assays in AR4-2J cell membranes (K(d)s 0.08 and 0.07 nM, respectively). During incubation at 37 degrees C with AR4-2J cells, the radiopeptides internalized effectively via a receptor-mediated process, with [(99m)Tc]Demotate 4 exhibiting a faster internalization rate than [(99m)Tc]Demotide. After injection in athymic mice bearing sst(2)-expressing AR4-2J tumors, the radiotracers showed high and specific uptake in the tumor (>25%ID/g at 1 h) and in the sst(2)-positive organs. However, both [(99m)Tc]Demotide and [(99m)Tc]Demotate 4 showed unfavorably higher background activity, especially in the abdomen, in comparison to [(99m)Tc]Demotate 1 and are, therefore, less suited than [(99m)Tc]Demotate 1 for sst(2)-targeted tumor imaging in man.