Internalization of sst2, sst3, and sst5 receptors: effects of somatostatin agonists and antagonists.

The uptake of radiolabeled somatostatin analogs by tumor cells through receptor-mediated internalization is a critical process for the in vivo targeting of tumoral somatostatin receptors. In the present study, the somatostatin receptor internalization induced by a variety of somatostatin analogs was measured with new immunocytochemical methods that allow characterization of trafficking of the somatostatin receptor subtype 2 (sst2), somatostatin receptor subtype 3 (sst3), and somatostatin receptor subtype 5 (sst5) in vitro at the protein level. METHODS: Human embryonic kidney 293 (HEK293) cells expressing the sst2, sst3, or the sst5 were used in a morphologic immunocytochemical internalization assay using specific sst2, sst3 and sst5 antibodies to qualitatively and quantitatively determine the capability of somatostatin agonists or antagonists to induce somatostatin receptor internalization. In addition, the internalization properties of a selection of these agonists have been compared and quantified in sst2-expressing CHO-K1 cells using an ELISA. RESULTS: Agonists with a high sst2-binding affinity were able to induce sst2 internalization in the HEK293 and CHO-K1 cell lines. New sst2 agonists, such as Y-DOTA-TATE, Y-DOTA-NOC, Lu-DOTA-BOC-ATE (where DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; TATE is [Tyr3, Thr8]-octreotide; NOC is [1-NaI3]-octreotide; and BOC-ATE is [BzThi3, Thr8]-octreotide), iodinated sugar-containing octreotide analogs, or BIM-23244 were considerably more potent in internalizing sst2 than was DTPA-octreotide (where DTPA is diethylenetriaminepentaacetic acid). Similarly, compounds with high sst3 affinity such as KE108 were able to induce sst3 internalization. In sst2- or sst3-expressing cell lines, agonist-induced receptor internalization was efficiently abolished by sst2- or sst3-selective antagonists, respectively. Antagonists alone had no effect on sst2 or sst3 internalization. We also showed that somatostatin-28 and somatostatin-14 can induce sst5 internalization. Unexpectedly, however, potent sst5 agonists such as KE108, BIM-23244, and L-817,818 were not able to induce sst5 internalization under the same conditions. CONCLUSION: Using sensitive and reproducible immunocytochemical methods, the ability of various somatostatin analogs to induce sst2, sst3, and sst5 internalization has been qualitatively and quantitatively determined. Whereas all agonists triggered sst2 and sst3 internalization, sst5 internalization was induced by natural somatostatin peptides but not by synthetic high-affinity sst5 agonists. Such assays will be of considerable help for the future characterization of ligands foreseen for nuclear medicine applications.     

Differences Between Treatment Seekers in an Obese Population: Medical Intervention vs. Dietary Restriction

This study examined two groups of people who were pursuing treatment for obesity: either medical intervention (a hospital group; N = 20) or support for dietary restriction (a community group; N = 18). This study addressed four questions: (1) Were there differences between the two groups in terms of their psychological distress (as measured by the Symptom Checklist)? (2) Does binge eating moderate psychological distress? (3) Do feelings of ineffectiveness moderate psychological distress? and (4) Which variables best accounted for group membership (i.e., type of treatment sought)? Results suggested that the hospital group was significantly more distressed than the community group. However, there were no differences between the two groups with respect to binge eating or feelings of ineffectiveness. These findings suggest that it is the effects of morbid obesity that are most likely to moderate psychological distress.     

New pansomatostatin ligands and their chelated versions: affinity profile, agonist activity, internalization, and tumor targeting.

PURPOSE: Somatostatin receptor (sst) targeting is an established method to image and treat sst-positive tumors. Particularly, neuroendocrine tumors express the receptor subtype 2 in high density, but sst1, sst3, sst4, and sst5 are also expressed to some extent in different human tumors. Currently used targeting peptides mainly have sst2 affinity. We aimed at developing (radio)peptides that bind with high affinity to all receptor subtypes. EXPERIMENTAL DESIGN: Carbocyclic octapeptides were coupled with macrocyclic chelators for radiometal labeling. Affinity, internalization, and agonist potencies were determined on sst1- to sst5-expressing cell lines. Biodistribution was determined on nude mice bearing HEK-sst2 or AR4-2J and HEK-sst3 tumors. RESULTS: High affinity to all receptor subtypes was found. Y(III)-KE88 showed agonistic properties at all five sst receptor subtypes as it inhibits forskolin-stimulated cyclic AMP production. Surprisingly, very low or even absent sst2 receptor internalization was found compared with currently clinically established octapeptides, whereas the sst3 internalization was very efficient. Biodistribution studies of [(111)In]KE88 and [(67)Ga]KE88/[(68)Ga]KE88 reflected the in vitro data. In nude mice with s.c. implanted sst2 (HEK-sst2, AR4-2J)-expressing and sst3 (HEK-sst3)-expressing tumors, high and persistent uptake was found in sst3-expressing tumors, whereas the uptake in the sst2-expressing tumors was lower and showed fast washout. The kidney uptake was high but blockable by coinjection of lysine. CONCLUSION: This peptide family shows pansomatostatin potency. As radiopeptides, they are the first to show a full pansomatostatin profile. Despite some drawback, they should be useful for imaging sst2-expressing tumors with short-lived radiometals, such as (68)Ga, at early time points and for sst3-expressing tumors at later time points with longer-lived radiometals, such as (64)Cu or (86)Y.     

Serum Ornithine Carbamoyl Transferase as a Surrogate Marker in Malaria

Ornithine carbamoyl transferase (OCT) activity and other liver function tests were studied in a total of 50 patients of clinical malaria and 15 controls. They were grouped as group I (positive for malarial parasite on peripheral blood smear, n=18), group II (negative for malarial parasite on peripheral blood smear (PBS) but responded to antimalarials, n=17) and group III (peripheral blood smear negative and did not respond to antimalarial therapy, n=15). The mean OCT levels were significantly raised in group I (6.79 ± 1.84 IU/L, p value = 0.006) and group II (5.0 ± 1.15 IU/L, p value = 0.014) as compared to controls (2.5 ± 1.13 IU/L) and returned to normal after treatment In contrast, group III had normal levels except in a case of kala azar and septicemia where OCT levels were high and increased further on treatment. Taking PBS positivity as a gold standard of diagnostic criteria, OCT had a sensitivity of 83% and specificity of 86% with a high positive predictive value of 88% as compared to ALT which had a lower sensitivity of 55% and specificity of 80%. The clinical response rate in PBS negative cases of fever having high OCT level was 83% as compared to 35% in cases with normal OCT level, making OCT a good surrogate marker of malaria. OCT levels could also be of prognostic significance as 2 cases of cerebral malaria had high OCT levels of 11.1 UAL and 10.7 IU/L, respectively.Key Words: Malaria, Ornithine carbamoyl transferase     

Preservation of the olfactory tract in bifrontal craniotomy

The bifrontal craniotomy approach used to be associated with a high percentage of olfactory tract damage. We present our experience with this technique, that was used with excellent results in a series of 11 patients that underwent the surgical approach described in this paper. We support the idea that bilateral subfrontal craniotomy allows a wide operative exposure as well as the complete anatomic and functional preservation of the olfactory tracts bilaterally.     

Novel sst(4)-selective somatostatin (SRIF) agonists. 3. Analogues amenable to radiolabeling

After our discovery that H-c[Cys-Phe-Phe-DNal-Lys-Thr-Phe-Cys]-OH (ODN-8) had high affinity and marginal selectivity for human sst(3) (part 2 of this series: Erchegyi et al. J. Med. Chem., preceding paper in this issue)(11) and that H-c[Cys-Phe-Phe-DTrp-Lys-Thr-Phe-Cys]-OH (ODT-8, 3) had high affinity and marginal selectivity for human sst(4), that H-c[Cys-Phe-Tyr-D-threo-beta-Me2Nal-Lys-Thr-Phe-Cys]-OH had high affinity for all sst's except for sst(1), and that H-c[Cys-Phe-Tyr-L-threo-beta-Me2Nal-Lys-Thr-Phe-Cys]-OH had high affinity for sst(4) (IC(50) = 2.1 nM), with more than 50-fold selectivity toward the other receptors (parts 1 and 2 of this series: Rivier et al. and Erchegyi et al. J. Med. Chem., preceding papers in this issue), we found H-c[Cys-Phe-Phe-Trp-Lys-Thr-Phe-Cys]-OH (OLT-8, 2), H-c[Cys-Phe-Phe-L-threo-beta-MeTrp-Lys-Thr-Phe-Cys]-OH (4) and H-c[Cys-Phe-Phe-D-threo-beta-MeTrp-Lys-Thr-Phe-Cys]-OH (5) to have very high affinity for sst(4) (IC(50) = 0.7, 1.8, and 4.0 nM, respectively) and 5- to 10-fold selectivity versus the other sst's. From earlier work, we concluded that an l-amino acid at position 8 and a tyrosine or 4-aminophenylalanine substitution at position 7 may lead to high sst(4) selectivity. In fact, [Tyr(7)]-2 (6) and [Tyr(7)]-3 (7) show ca. 5-fold selectivity for sst(4), and [Aph(7)]-2 (8) and [Aph(7)]-3 (9) have high sst(4) affinity (IC(50) = 1.2 and 0.88 nM, respectively) and selectivity, suggesting that indeed an l-residue at position 8 will direct selectivity toward sst(4). Unexpectedly, [Ala(7)]-2 (10) and [Ala(7)]-3 (11) have very high sst(4) affinity (IC(50) = 0.84 and 0.98 nM, respectively) and selectivity (>600- and 200-fold, respectively). The combination of Tyr(2) and dTrp(8) in analogues 14 and 22 did not affect the affinity of the analogues for sst(4) (IC(50) = 1.2 and 1.1 nM, respectively) but resulted in loss of selectivity, whereas the combination of Tyr(2) and LTrp(8) in H-Tyr-c[Cys-Phe-Aph-Trp-Lys-Thr-Phe-Cys]-OH (13) and H-Tyr-c[Cys-Phe-Ala-Trp-Lys-Thr-Phe-Cys]-OH(19) retained high affinity (IC(50) = 1.9 and 1.98 nM, respectively) and sst(4) selectivity (>50 and >250, respectively). Interestingly, the same substitutions at positions 2 and 7, with l-threo-beta-MeTrp at position 8, yielded a much less selective analogue (20). Carbamoylation of the N-terminus of most of these analogues resulted in slightly improved affinity, selectivity, or both. Other amino acid substitutions in this series, such as those with Amp (25, 26), Orn (27), or IAmp (29) at position 7, were also tolerated but with a 2- to 3-fold loss of affinity and concomitant loss of selectivity. Analogous peptides with a tyrosine at position 11 (31-36) were less selective than the corresponding peptides with a tyrosine at position 2. Several analogues in this series compared favorably with the non-peptide L-803,087 (37) in terms of affinity and selectivity. Analogues 8, 10, and 21 potently inhibited the forskolin-stimulated cAMP production in sst(4)-transfected cells, therefore acting as full agonists. Cold monoiodination of 19 yielded 21, with retention of high sst(4) selectivity and affinity (IC(50) = 3.5 nM). (125)Iodinated 19 selectively binds to sst(4)-transfected cells but not to sst(1-3)- or sst(5)-transfected cells. Binding in sst(4)-transfected cells was completely displaced by SRIF-28 or the sst(4)-selective L-803,087.     

Switch from antagonist to agonist after addition of a DOTA chelator to a somatostatin analog

Purpose  

Peptide receptor targeting has become an increasingly attractive method to target tumors diagnostically and radiotherapeutically. Peptides linked to a variety of chelators have been developed for this purpose. They have, however, rarely been tested for their agonistic or antagonistic properties. We report here on a somatostatin antagonist that switched to an agonist upon coupling to a DOTA chelator.     

Spectrin-alpha I/61: a new structural variant of alpha-spectrin in a double-heterozygous form of hereditary pyropoikilocytosis

Recent biochemical studies have led to the identification of abnormal spectrins in the erythrocytes of patients with hereditary pyropoikilocytosis (HPP) and hereditary elliptocytosis (HE). In this report we describe the biochemical characterization of the erythrocytes from a proband with severe HPP who is doubly heterozygous for two mutant spectrins (Sp): Sp alpha I/74 and a new, previously undetected, mutant of alpha-spectrin designated Sp alpha I/61. The proband's erythrocytes are unstable when exposed to 45 degrees C, and her membrane skeletons exhibit instability to shear stress. The content of spectrin in the proband's erythrocyte membranes is decreased to 75% of control values. The amount of spectrin dimers in crude 4 degrees C spectrin extracts is increased (58%) as compared with control values (6% +/- 4%). Limited tryptic digestion reveals a marked decrease in the normal 80,000-dalton alpha I domain, an increase in the 74,000-dalton fragment that is characteristic of Sp alpha I/74, and an increase in a series of new fragments of 61,000, 55,000, 21,000, and 16,000 daltons. Both parents are asymptomatic, but they have increased amounts of spectrin dimers (17% to 25%). Limited tryptic digestion of the father's spectrin demonstrates the presence of a previously identified abnormal spectrin (Sp alpha I/74) that is characterized by a decrease in content of the 80,000-dalton peptide and an increase in concentration of the 74,000-dalton peptide. The mother's spectrin digests show a decrease in the amount of 80,000-dalton peptide and the formation of new peptides of 61,000, 55,000, 21,000, and 16,000 daltons. The data indicate that this severe form of HPP is due to the inheritance of two distinct abnormal spectrins, Sp alpha I/74 and a new spectrin mutant, Sp alpha I/61.