In vitro activity of PR-39, a proline-arginine-rich peptide, against susceptible and multi-drug-resistant Mycobacterium tuberculosis.

We have investigated the in vitro activity of antimicrobial peptides against Mycobacterium tuberculosis using a radiometric method and cfu determinations. PR-39, a proline-arginine-rich antibacterial peptide from porcine leucocytes, was found to be active against drug-susceptible as well as multi-drug-resistant (MDR) clinical isolates of M. tuberculosis. The activity of PR-39 was concentration dependent, with 80% growth inhibition of M. tuberculosis H37Rv at 50 mg/L. The MDR M. tuberculosis strains E1380/94 and P34/95 were less susceptible to PR-39, with 39 and 49% growth inhibition at 50 mg/L peptide, respectively, suggesting a lower susceptibility than strain H37Rv and drug-susceptible clinical isolates. Reduction of counts of M. tuberculosis H37Rv and the MDR M. tuberculosis strain E1380/94 by PR-39 indicated that the growth inhibition seen in the radiometric assay is due to a mycobactericidal effect of the peptide. These observations suggest that antimicrobial peptides may play an important role in host defence against MDR M. tuberculosis.

The somatostatin analogue octreotide inhibits neuroblastoma growth in vivo.

Neuroblastoma, a neural crest-derived childhood tumor of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. However, the majority of neuroblastomas are diagnosed as metastatic tumors with a poor prognosis despite intensive multimodal therapy. The neuropeptide somatostatin (SOM) has been shown to inhibit neuroblastoma growth and induce apoptosis in vitro. Therapeutic effects of SOM analogues are dependent on tumor expression of high-affinity receptors. In the present study, human neuroblastoma SH-SY5Y cells were grown as xenografts in nude rats. In vivo SOM receptor expression in the xenografts was identified using scintigraphy with 111In-pentetreotide. Rats were randomized to treatment with the long-acting SOM analogue octreotide (10 microg s.c. every 12 h), 13-cis-retinoic acid (4 mg orally every 24 h), or vasoactive intestinal peptide (40 microg s.c. every 24 h) and compared with controls. Tumor volume was assessed every second day and tumor weight after 10-12 d. Octreotide treatment inhibited neuroblastoma growth significantly with reduced tumor volumes at 10 and 12 d compared with untreated controls (mean 3.56 and 4.24 versus 6.48 and 8.01 mL, respectively; p < 0.01). Also, tumor weights after 10-12 d were reduced in octreotide-treated animals (n = 8, median weight 2.90 g, range 1.67-5.57 g) compared with untreated rats (n = 14, 7.54 g, 1.65-10.82 g, p = 0.005). Serum IGF-I decreased significantly over time both in rats treated with octreotide and in untreated controls. It is concluded that treatment with the SOM analogue octreotide may significantly decrease neuroblastoma tumor growth in vivo. Further studies are warranted to establish the role of SOM analogues in the treatment of children with unfavorable neuroblastoma.

In vivo dynamic distribution of 131I-glucagon-like peptide-1 (7-36) amide in the rat studied by gamma camera.

The in vivo distribution of glucagon-like peptide-1 (7-36) amide (GLP-1) was studied in a rat model using radiolabeled GLP-1 (131I-GLP-1) depicted by a gamma-camera. The dynamic scan showed a rapid clearance from the blood circulation after an intravenous (i.v.) injection of 131I-GLP-1. After 10 min, the major part of the radioactivity was accumulated in the kidneys, whereas about 9% (of the blood value) was found in the brain. The pharmacokinetic study using 125I-GLP-1 demonstrated a rapid elimination from plasma, with a half-life of 3.3 +/- 0.6 min, a clearance of 117 +/- 15 mL/min, and a distribution volume of 557 +/- 61 mL. The elimination half-lives for the intact 125I-GLP-1 in lungs and kidneys were determined to 3.7 and 3.9 min, respectively. The metabolite GLP-1 (9-36) amide was followed in blood, lung, and kidney. All other organs assumed to contain low molecular weight fragments of GLP-1. The present study suggest that GLP-1 and/or its labeled metabolites cross the blood-brain barrier. Also the kidney plays an essential role in GLP-1 elimination after an i.v. administration, which can be of clinical interest especially in patients with kidney insufficiency who are treated with GLP-1.

Biodistribution of liposomal 131I-VIP in rat using gamma camera.

Vasoactive intestinal peptide (VIP), a 28 amino-acid peptide was labeled with 131I and encapsulated into liposomes. 131I-VIP or liposomal 131I-VIP was administered intravenously into the rats. The distribution was studied by a gamma camera and established by counting the radioactivity in the removed organs. The elimination half-life for the liposomal 131I-VIP in both blood and lungs was significantly longer (5.29 and 9.28 min, respectively) than that obtained after the administration of 131I-VIP (0.62 and 3.18 min, respectively). Dynamic scans using a gamma camera after the administration of liposomal 131I-VIP showed a higher uptake of the liposomal form into the lungs compared with 131I-VIP. The lack of VIP in asthmatics has been shown in previous studies. However, the clinical investigations using VIP were disappointing most probably due to the rapid degradation of the peptide in the bronchial tract. This in fact is supported by our previous study, in which we demonstrated that VIP had a half-life of 0.45 min in blood. We conclude that the encapsulation of VIP in liposomes prolongs its elimination half-life in plasma and enhances its uptake in lungs. This observation may increase the clinical use of VIP in both diagnostic and therapy.

Somatostatin in neuroblastoma and ganglioneuroma.

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. Somatostatin may inhibit neuroblastoma growth and induce apoptosis in vitro and was therefore investigated. Using a radioimmunoassay, we found that all ganglioneuromas contained high somatostatin concentrations (> 16 pmol/g), significantly higher than neuroblastomas (n = 117, median 2.8 pmol/g), healthy adrenals, Wilms' tumours, phaeochromocytomas and other neuroendocrine tumours (P < 0.001). Neuroblastomas contained more somatostatin than control tumours (P < 0.001-0.05). Neuroblastomas amplified for the MYCN oncogene contained less somatostatin than non-amplified tumours (1.2 pmol/g versus 4.0 pmol/g, respectively; P = 0.026). In a clinically unfavourable neuroblastoma subset (age > 12 months, stage 3 or 4) 16 children with high concentrations of somatostatin in primary tumours had a better prognosis than 23 with low somatostatin (46.7% versus 0% survival at 5 years, P < 0.005). Scintigraphy using 111In-pentetreotide identified tumours expressing high-affinity somatostatin receptors in vivo. However, no significant correlation was found between somatostatin receptor expression and peptide content in 15 tumours. Similarly, human SH-SY5Y neuroblastoma xenografts grown in nude rats showed low somatostatin concentrations, but were positive for somatostatin receptor scintigraphy. Treatment of these rats with the somatostatin analogue octreotide seemed to upregulate in vivo receptor expression of somatostatin and vasoactive intestinal peptide more effectively than 13-cis retinoic acid. In conclusion, somatostatin in neuroblastoma is associated with differentiation to benign ganglioneuromas in vivo and favourable outcome in advanced tumours. Furthermore, somatostatin receptor scintigraphy may identify tumours with high-affinity receptors in children that might benefit from targeted therapy using synthetic somatostatin analogues.

In vivo dynamical distribution of 131I-VIP in the rat studied by gamma-camera.

The in vivo distribution of vasoactive intestinal peptide (VIP) was studied for the first time using a rat model in combination with labeled VIP (131I-VIP) and a gamma-camera. A dynamic scan showed that 131I-VIP was cleared rapidly from the blood circulation. The radioactivity was taken up and accumulated in the lungs during the first minute. During the next 15 min, the radioactivity was slowly removed from the lungs and redistributed into the kidneys, gastric mucosa, liver and small intestine. However, the radioactivity extracted by the lungs was about 6-fold lower during the first minute when a large amount of the non iodinated VIP was coinjected with the 131I-VIP. 131I-VIP was eliminated rapidly from the blood with a half-life of 0.44 +/- 0.05 (min +/- SD) while in lung the elimination half-life was determined to 2.3 +/- 0.8 (min +/- SD). Of the radioactivity in the lungs, 2% was found to be intact 131I-VIP after 20 min. In all other organs the radioactivity found was assumed to be low molecular weight fragments of 131I-VIP. We suggest that lungs play an important role to extract VIP from the circulation after an i.v. administration. 131I-VIP degradation products are redistributed mostly to the kidneys and to the gastric mucosa to be excreted through urine and stomach contents, respectively.