Neuroprotective anticonvulsant and anxiolytic effects of octreotide in wistar rats

Somatostatin interneurons exhibited anti-epileptic activity. As a result, somatostatin agonists appear to be a promising target for antiepileptic drug development (AEDs). In this regard, we investigated the effects of octreotide, a somatostatin analog, on pentylenetetrazol (PTZ)-induced seizures in male Wistar rats. Animals were given octreotide at doses of 50 or 100 µg/kg for seven days. The anxiolytic effects of octreotide were then evaluated using open field and elevated plus-maze tests. Following that, mice were intraperitoneally given a single convulsive dosage of PTZ (60 mg/kg) and then monitored for 30 min for symptoms of seizures. Finally, the antioxidant capacity of brain tissue and histopathological changes in the hippocampus were investigated. Octreotide therapy for seven days at 50 or 100 µg/kg was more effective than diazepam in preventing acute PTZ-induced seizures (P < 0.05). Furthermore, both octreotide dosages revealed substantial anxiolytic effects in open-field and elevated plus-maze tests compared to untreated rats. Nonetheless, octreotide's anxiolytic impact was less effective than diazepam's. On the other hand, octreotide also suppressed neuronal apoptosis and attenuated oxidative stress. Our results suggest that chronic administration of octreotide has anticonvulsant, anxiolytic, and antioxidant activity in the male Wistar rat model.

Preclinical evaluation of [225Ac]Ac-DOTA-TATE for treatment of lung neuroendocrine neoplasms

PURPOSE

There is significant interest in the development of targeted alpha-particle therapies (TATs) for treatment of solid tumors. The metal chelator-peptide conjugate, DOTA-TATE, loaded with the β-particle emitting radionuclide ¹⁷⁷Lu ([¹⁷⁷Lu]Lu-DOTA-TATE) is now standard care for neuroendocrine tumors that express the somatostatin receptor 2 (SSTR2) target. A recent clinical study demonstrated efficacy of the corresponding [²²⁵Ac]Ac-DOTA-TATE in patients that were refractory to [¹⁷⁷Lu]Lu-DOTA-TATE. Herein, we report the radiosynthesis, toxicity, biodistribution (BD), radiation dosimetry (RD), and efficacy of [²²⁵Ac]Ac-DOTA-TATE in small animal models of lung neuroendocrine neoplasms (NENs).

METHODS

[²²⁵Ac]Ac-DOTA-TATE was synthesized and characterized for radiochemical yield, purity and stability. Non-tumor-bearing BALB/c mice were tested for toxicity and BD. Efficacy was determined by single intravenous injection of [²²⁵Ac]Ac-DOTA-TATE into SCID mice-bearing human SSTR2 positive H727 and H69 lung NENs. RD was calculated using the BD data.

RESULTS

[²²⁵Ac]Ac-DOTA-TATE was synthesized with 98% yield, 99.8% purity, and displayed 97% stability after 2 days incubation in human serum at 37 °C. All animals in the toxicity study appeared healthy 5 months post injection with no indications of toxicity, except that animals that received ≥111 kBq of [²²⁵Ac]Ac-DOTA-TATE had chronic progressive nephropathy. BD studies revealed that the primary route of elimination is by the renal route. RD calculations determined pharmacokinetics parameters and absorbed α-emission dosages from ²²⁵Ac and its daughters. For both tumor models, a significant tumor growth delay and time to experimental endpoint were observed following a single administration of [²²⁵Ac]Ac-DOTA-TATE relative to controls.

CONCLUSIONS

These results suggest significant potential for the clinical translation of [²²⁵Ac]Ac-DOTA-TATE for lung NENs.

Pituitary Function after High-Dose 177Lu-DOTATATE Therapy and Long-Term Follow-Up

INTRODUCTION

The pituitary gland has a high expression of somatostatin receptors and is therefore a potential organ at risk for radiation-induced toxicity after 177Lu-DOTATATE treatment.

OBJECTIVE

To study changes in pituitary function in patients with neuroendocrine tumors (NETs) treated with dosimetry-based 177Lu-DOTATATE to detect possible late toxicity.

METHODS

68 patients from a phase II clinical trial of dosimetry-based, individualized 177Lu-DOTATATE therapy were included in this analysis. Patients had received a median of 5 (range 3-9) treatment cycles of 7.4 GBq/cycle. Median follow-up was 30 months (range 11-89). The GH/IGF-1 axis, gonadotropins, and adrenal and thyroid axes were analyzed at baseline and on a yearly basis thereafter. Percent changes in hormonal levels over time were analyzed statistically using a linear mixed model and described graphically using box plots. The absorbed radiation dose to the pituitary was estimated based on post-therapeutic imaging, and the results analyzed versus percent change in IGF-1 levels over time.

RESULTS

A statistically significant decrease in IGF-1 levels was found (p < 0.005), which correlated with the number of treatment cycles (p = 0.008) and the absorbed radiation dose (p = 0.03). A similar decrease, although non-significant, was seen in gonadotropins in postmenopausal women, while in men there was an increase during the first years after therapy, after which the levels returned to baseline. No change was observed in the adrenal or thyroid axes.

CONCLUSIONS

No signs of severe endocrine disorders were detected, although a significant decrease in the GH/IGF-1 axis was found, where dosimetric analyses indicated radiation-induced damage to the pituitary gland as a probable cause.

Octreotide-functionalized and resveratrol-loaded unimolecular micelles for targeted neuroendocrine cancer therapy

Medullary thyroid cancer (MTC) is a neuroendocrine tumor (NET) that is often resistant to standard therapies. Resveratrol suppresses MTC growth in vitro, but it has low bioavailability in vivo due to its poor water solubility and rapid metabolic breakdown, as well as lack of tumor-targeting ability. A novel unimolecular micelle based on a hyperbranched amphiphilic block copolymer was designed, synthesized, and characterized for NET-targeted delivery. The hyperbranched amphiphilic block copolymer consisted of a dendritic Boltorn® H40 core, a hydrophobic poly(l-lactide) (PLA) inner shell, and a hydrophilic poly(ethylene glycol) (PEG) outer shell. Octreotide (OCT), a peptide that shows strong binding affinity to somatostatin receptors, which are overexpressed on NET cells, was used as the targeting ligand. Resveratrol was physically encapsulated by the micelle with a drug loading content of 12.1%. The unimolecular micelles exhibited a uniform size distribution and spherical morphology, which were determined by both transmission electron microscopy (TEM) and dynamic light scattering (DLS). Cellular uptake, cellular proliferation, and Western blot analyses demonstrated that the resveratrol-loaded OCT-targeted micelles suppressed growth more effectively than non-targeted micelles. Moreover, resveratrol-loaded NET-targeted micelles affected MTC cells similarly to free resveratrol in vitro, with equal growth suppression and reduction in NET marker production. These results suggest that the H40-based unimolecular micelle may offer a promising approach for targeted NET therapy.

Amifostine protects rat kidneys during peptide receptor radionuclide therapy with [177Lu-DOTA0,Tyr3]octreotate

PURPOSE

In peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues, the kidneys are the major dose-limiting organs, because of tubular reabsorption and retention of radioactivity. Preventing renal uptake or toxicity will allow for higher tumour radiation doses. We tested the cytoprotective drug amifostine, which selectively protects healthy tissue during chemo- and radiotherapy, for its renoprotective capacities after PRRT with high-dose [(177)Lu-DOTA(0),Tyr(3)]octreotate.

METHODS

Male Lewis rats were injected with 278 or 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate to create renal damage and were followed up for 130 days. For renoprotection, rats received either amifostine or co-injection with lysine. Kidneys, blood and urine were collected for toxicity measurements. At 130 days after PRRT, a single-photon emission computed tomography (SPECT) scan was performed to quantify tubular uptake of (99m)Tc-dimercaptosuccinic acid (DMSA), a measure of tubular function.

RESULTS

Treatment with 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate resulted in body weight loss, elevated creatinine and proteinuria. Amifostine and lysine treatment significantly prevented this rise in creatinine and the level of proteinuria, but did not improve the histological damage. In contrast, after 278 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate, creatinine values were slightly, but not significantly, elevated compared with the control rats. Proteinuria and histological damage were different from controls and were significantly improved by amifostine treatment. Quantification of (99m)Tc-DMSA SPECT scintigrams at 130 days after [(177)Lu-DOTA(0),Tyr(3)]octreotate therapy correlated well with 1/creatinine (r(2)=0.772, p<0.001).

CONCLUSION

Amifostine and lysine effectively decreased functional renal damage caused by high-dose [(177)Lu-DOTA(0),Tyr(3)]octreotate. Besides lysine, amifostine might be used in clinical PRRT as well as to maximise anti-tumour efficacy.

Long-term toxicity of [(177)Lu-DOTA (0),Tyr (3)]octreotate in rats

PURPOSE AND METHODS

Studies on peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues have shown promising results with regard to tumour control. The efficacy of PRRT is limited by uptake and retention in the proximal tubules of the kidney, which might lead to radiation nephropathy. We investigated the long-term renal toxicity after different doses of [(177)Lu-DOTA(0),Tyr(3)]octreotate and the effects of dose fractionation and lysine co-injection in two tumour-bearing rat models.

RESULTS

Significant renal toxicity was detected beyond 100 days after start of treatment as shown by elevated serum creatinine and proteinuria. Microscopically, tubules were strongly dilated with flat epithelium, containing protein cylinders. Creatinine levels rose significantly after 555 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate, but were significantly lower after 278 MBq (single injection) or two weekly doses of 278 MBq. Renal damage scores were maximal after 555 MBq and significantly lower in the 278 and 2x278 MBq groups. Three doses of 185 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate with intervals of a day, a week or a month significantly influenced serum creatinine (469+/-18, 134+/-70 and 65+/-15 micromol/l, respectively; p<0.001). Renal histological damage scores were not significantly influenced by dose fractionation. Lysine co-administration with three weekly treatments of 185 MBq significantly lowered serum creatinine and proteinuria.

CONCLUSION

Injection of high doses of [(177)Lu-DOTA(0),Tyr(3)]octreotate resulted in severe renal damage in rats as indicated by proteinuria, elevated serum creatinine and histological damage. This damage was dose dependent and became overt between 100 and 200 days after treatment. Dose fractionation had significant beneficial effects on kidney function. Also, lysine co-injection successfully prevented functional damage.

213Bi-[DOTA0, Tyr3]Octreotide Peptide Receptor Radionuclide Therapy of Pancreatic Tumors in a Preclinical Animal Model

PURPOSE

The somatostatin analogue [DOTA0, Tyr3]octreotide (DOTATOC) has previously been labeled with low linear energy transfer (LET) beta-emitters, such as 177Lu or 90Y, for tumor therapy. In this study, DOTATOC labeled with the high-LET alpha-emitter, 213Bi, was evaluated.

EXPERIMENTAL DESIGN

The radiolabeling, stability, biodistribution, toxicity, safety, and therapeutic efficacy of 213Bi-DOTATOC (specific activity 7.4 MBq/microg) were investigated. Biodistribution studies to determine somatostatin receptor specificity were done in Lewis rats at 1 and 3 hours postinjection. Histopathology of various organs was used to evaluated toxicity and safety. Therapeutic efficacy of 4 to 22 MBq 213Bi-DOTATOC was determined in a rat pancreatic carcinoma model.

RESULTS

Radiolabeling of the 213Bi-DOTATOC was achieved with radiochemical purity >95% and an incorporation yield > or = 99.9%. Biodistribution data showed specific binding to somatostatin receptor-expressing tissues. Administration of free 213Bi, compared with 213Bi-DOTATOC, resulted in higher radioactivity accumulation at 3 hours postinjection in the kidneys [34.47 +/- 1.40% injected dose/g (ID/g) tissue versus 11.15 +/- 0.46%, P < 0.0001] and bone marrow (0.31 +/- 0.01% ID/g versus 0.06 +/- 0.02%, P < 0.0324). A significant decrease in tumor growth rate was observed in rats treated with >11 MBq of 213Bi-DOTATOC 10 days postinjection compared with controls (P < 0.025). Treatment with >20 MBq of 213Bi-DOTATOC showed significantly greater tumor reduction when compared with animals receiving <11 MBq (P < 0.02).

CONCLUSIONS

213Bi-DOTATOC showed dose-related antitumor effects with minimal treatment-related organ toxicity. No acute or chronic hematologic toxicities were observed. Mild, acute nephrotoxicity was observed without evidence of chronic toxicity. 213Bi-DOTATOC is a promising therapeutic radiopharmaceutical for further evaluation.

Induction of experimental allergic encephalomyelitis in a low-susceptible Albino Oxford rat strain by somatostatin analogue SMS 201-995

OBJECTIVE

The effect of the somatostatin analogue SMS 201-995 (octreotide; OCT) on the course of experimental allergic encephalomyelitis (EAE) in the relatively resistant Albino Oxford (AO) strain of rats was studied.

METHODS

Animals were actively immunized with bovine brain homogenate in complete Freund's adjuvant. OCT was given subcutaneously in the hind legs on days 7, 8 and 9 after immunization, at a dose of 3 x 5 microg/kg/day. Rats in control groups were treated with saline or were left untreated. EAE was scored clinically and immunophenotypically, estimating by flow cytometry the changes in the popliteal lymph nodes (PLN) and spleen and monitoring immunohistologically the brain sections of rats recovered from disease.

RESULTS

In control AO rats, EAE was induced in only 2 of 22 rats (9%). In OCT-treated rats, however, EAE developed in 11 of 20 rats (55%), in comparison with 3 of 17 saline-treated animals (17%) (p <0.05). In PLN of OCT-treated rats during the clinical course of EAE, a decreased proportion of OX8+ cells was seen, followed by increases in OX39+ and W3/25+ cells on days 17 and 26. In spleen, OCT decreased the proportion of OX1+, OX39+ and OX8+ cells (on days 12 and/or 17), and increased the proportion of OX39+ cells on days 26 and 31. In the brain sections of saline-treated rats recovered from EAE, numerous Mac-1+, Mac-3+ and OX8+ cells were found. These cells were, however, absent in OCT-treated rats; instead, several W3/25+ cells were noticed.

CONCLUSIONS

These data imply that OCT increases the susceptibility of AO rats to EAE, interfering with specific and/or nonspecific defense mechanisms operating in both the initial and recovery phase of EAE.

Receptor radionuclide therapy with 90Y-DOTATOC in patients with medullary thyroid carcinomas

Metastatic medullary thyroid cancer (MTC) shows a progressive course. Surgery is the only curative treatment. In advanced disease, chemo- and radiotherapy show poor results. Newly developed somatostatin analogue [DOTA0,Tyr3]octreotide (DOTATOC) labeled to 90Y is administered in patients with endocrine tumors expressing somatostatin receptors, like MTC. Preliminary studies demonstrated that 90Y-DOTATOC could be safely administered, resulting in objective responses in 27% of patients.

AIMS

To evaluate the efficacy of 90Y-DOTATOC therapy in metastatic MTC patients with positive OctreoScan, progressing after conventional treatments. Twenty-one patients were retrospectively evaluated after therapy, receiving 7.5-19.2 GBq in 2-8 cycles.

RESULTS

Two patients (10%) obtained a complete response (CR), as evaluated by CT, MRI and/or ultrasound, while a stabilization of disease (SD) was observed in 12 patients (57%); seven patients (33%) did not respond to therapy. The duration of the response ranged between 3-40 months. Using biochemical parameters (calcitonin and CEA), a complete response was observed in one patient (5%), while partial response in five patients (24%) and stabilization in three patients (14%). Twelve patients had progression (57%). Complete responses were observed in patients with lower tumor burden and calcitonin values at the time of the enrollment.

CONCLUSIONS

This retrospective analysis is consistent with the literature, regarding a low response rate in medullary thyroid cancers treated with 90Y-DOTATOC. Patients with smaller tumors and higher uptake of the radiopeptide tended to respond better. Studies with 90Y-DOTATOC administered in earlier phases of the disease will help to evaluate the ability of this treatment to enhance survival. New more specific peptides and new isotopes will also represent the key of a better treatment of MTC.

Ciliary body toxicity of cyclosporin A and octreotide acetate in rabbit eyes: a comparison with mitomycin C and 5-fluorouracil

PURPOSE

To compare the toxicities of cyclosporin A, octreotide acetate, mitomycin C and 5-fluorouracil to the ciliary body.

METHOD

We applied sponges soaked in these compounds to the open scleras of rabbit eyes. Histopathological specimens were obtained from the operation site and at 180 degrees from it on the 14th day after surgery.

RESULTS

Mean ciliary epithelial thickness in the study groups was as follows: 12.29 +/- 2.69 microm in group 1 (mitomycin C), 13.85 +/- 4.56 microm in group 2 (5-fluorouracil), 17.71 +/- 3.09 microm in group 3 (cyclosporin A), 11.64 +/- 2.92 microm in group 4 (octreotide acetate), 11.92 +/- 2.89 microm in group 5 (topically applied octreotide acetate) and 21.85 +/- 4.29 microm in group 6 (control). The ciliary epithelial thickness in groups 1, 2, 4 and 5 was statistically different from that in the control group. Intracellular vacuolisation and degenerative changes of the non-pigmented epithelium, and pigment loss of the pigmented epithelium, were found mostly in group 1 and moderately in group 2 and 3.

CONCLUSION

Octreotide acetate and cyclosporin A are less toxic alternatives to mitomycin C and 5-fluorouracil in glaucoma filtration surgery.

Toxicity and dosimetry of (177)Lu-DOTA-Y3-octreotate in a rat model

Radiolabeled somatostatin analogs have demonstrated effectiveness for targeted radiotherapy of somatostatin receptor-positive tumors in both tumor-bearing rodent models and humans. A radionuclide of interest for cancer therapy is reactor-produced (177)Lu (t(1/2) = 6.64 d; beta(-) [100%]). The high therapeutic efficacy of the somatostatin analog (177)Lu-DOTA-Tyr(3)-octreotate (DOTA-Y3-TATE, where DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) was previously demonstrated in a tumor-bearing rat model (Erion et al., J. Nucl. Med. 1999;40:223P; de Jong et al., Int. J. Cancer, 2001; 92:628-633). In the current study, the toxicity and dosimetry of (177)Lu-DOTA-Y3-TATE were determined in both normal and tumor-bearing rats. Doses of (177)Lu-DOTA-Y3-TATE ranging from 0 to 123 mCi/kg were administered to rats and complete blood counts (CBCs) and blood chemistries were analyzed out to 6 weeks. No overt signs of toxicity were observed with (177)Lu-DOTA-Y3-TATE (i.e., lethargy, weight loss, scruffy coat or diarrhea) at any of the dose levels. Blood chemistries and CBCs were normal except for the white blood cell counts, which showed a dose-dependent decrease. The maximum tolerated dose was not reached at 123 mCi/kg. The biodistribution of (177)Lu-DOTA-Y3-TATE was determined in CA20948 rat pancreatic tumor-bearing rats, and the data were used to estimate human absorbed doses to normal tissues. The dose-limiting organ was determined to be the pancreas, followed by the adrenal glands. The absorbed dose to the rat CA20948 tumor was estimated to be 336 rad/mCi (91 mGy/MBq). These data demonstrate that (177)Lu-DOTA-Y3-TATE is an effective targeted radiotherapy agent at levels that show minimal toxicity in this rat model.

Regression of U-87 MG human glioblastomas in nude mice after treatment with a cytotoxic somatostatin analog AN-238

Receptors for somatostatin (SST) found on brain tumors could be used for targeting of chemotherapeutic agents. This study was conducted to investigate the effects of targeted cytotoxic SST analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201), a potent derivative of doxorubicin (DOX) linked to somatostatin analogue RC-121, on the growth of SST receptor-positive U-87 MG human glioblastomas. Nude mice bearing U-87 MG xenografts received i.v. saline or equimolar doses of AN-238 or AN-201 (150 nmol/kg). Experiments also included groups that were administered RC-121 prior to the injection of AN-238, and groups injected with AN-162, a cytotoxic SST analogue similar to AN-238 but containing DOX instead of AN-201. Tumor volume, weight, and burden were determined. The effect of AN-238 and AN-201 on the survival time of nude mice bearing orthotopically implanted U-87 MG tumors was also evaluated. The binding of AN-238 to U-87 MG tumors was determined by radioreceptor assay and SST receptor (SSTR) subtype by reverse transcription-PCR. Nineteen days after a single administration of AN-238 the growth of U-87 MG tumors in nude mice was significantly inhibited (P = 0.00168), whereas two injections of AN-238 produced the regression of tumors (P = 0.0046). AN-201 was toxic and ineffective at the same dose. The antitumor effect on AN-238 could be blocked by pretreatment of the tumor-bearing mice with RC-121. The mean survival time of nude mice inoculated orthotopically with U-87 MG cells into the brain was significantly prolonged by treatment with AN-238 (P = 0.0099). AN-162 failed to inhibit significantly the growth of U-87 MG xenografts. High affinity binding sites for SST and mRNA for SST-2 receptor subtype were detected in U-87 MG tumors. Cytotoxic SST analogue AN-238 can be targeted to SST receptors on U-87 MG human glioblastomas to produce powerful inhibition of growth.

Yttrium-90 DOTATOC: first clinical results

In a pilot study, DOTA-d-Phe(1)-Tyr(3)-octreotide (DOTATOC), which can be labelled with the beta-emitting radioisotope yttrium-90, has recently been used for the treatment of patients with advanced somatostatin receptor-positive tumours who had no other treatment option. The aim of the present study was to elucidate the therapeutic potential of (90)Y-DOTATOC in a larger number of patients employing a standardized treatment protocol. Careful attention was paid to any side-effects (renal and/or haematological toxicity). Of 44 patients with advanced somatostatin receptor-positive tumours of different histology, 29 could be included in the study. The 15 patients who were excluded from the study protocol were assigned to our institution for purely compassionate reasons. The 29 patients who were included received four or more single doses of (90)Y-DOTATOC with ascending activity at intervals of approximately 6 weeks (cumulative dose 6120+/-1347 MBq/m(2)) with the aim of performing an intra-patient dose escalation study. In total, 127 single treatments were given. In eight of these 127 single treatments, total doses of > or = 3700 MBq were administered. In an effort to prevent renal toxicity, two patients received Hartmann-Hepa 8% solution during all therapy cycles, while 13 patients did so during some but not all therapy cycles; in 14 patients no solution was administered during the therapy cycles. The treatment was monitored by computed tomography and indium-111 DOTATOC scintigraphy. Blood parameters were controlled weekly, while tumour markers and liver enzymes were controlled 6-weekly. Of the 29 patients, 24 patients showed no severe renal or haematological toxicity (toxicity < or = grade 2 according to the National Cancer Institute grading criteria). These 24 patients received a cumulative dose of < or = 7400 MBq/m(2). Five patients developed renal and/or haematological toxicity. All of these five patients received a cumulative dose of >7400 MBq/m(2) and had received no Hartmann-Hepa 8% solution during the therapy cycles. Four of the five patients developed renal toxicity; two of these patients showed stable renal insufficiency and two require haemodialysis. Two of the five patients exhibited anaemia (both grade 3) and thrombopenia (grade 2 and 4, respectively). To date, 20 of the 29 patients have shown a disease stabilization, two a partial remission, four a reduction of tumour mass <50% and three a progression of tumour growth. (90)Y-DOTATOC could be a powerful and promising new therapeutic agent for anti-cancer treatment - at least in terms of an adjuvant starting point of the disease. However, problems with toxicity have to be solved. Evaluation of the effect of amino acid infusions (e.g. Hartmann-Hepa 8% solution) during (90)Y-DOTATOC treatments with the aim of reducing renal toxicity is ongoing.

Octreotide stimulates Ca++ secretion by the gallbladder: a risk factor for gallstones

BACKGROUND

Gallstone formation during octreotide therapy has been linked to elevated levels of gallbladder bile Ca++, a well-known prolithogenic factor. Although the subcutaneous administration of octreotide raises gallbladder bile Ca++ in prairie dogs, the mechanism for this effect is unknown. Octreotide has been shown to increase gallbladder Na+ and water absorption in Ussing chamber studies. Given the known effects of octreotide on gallbladder ion transport, we hypothesized that octreotide may also promote gallstone formation by stimulating gallbladder Ca++ secretion, thereby raising the lumenal concentration of biliary Ca++.

METHODS

After cholecystectomy, prairie dog gallbladders were mounted in Ussing chambers, and standard electrophysiologic parameters were recorded. Unidirectional fluxes of Ca++ and Na+ were measured before and after serosal exposure to 50 nmol/L octreotide.

RESULTS

Under basal conditions normal prairie dog gallbladder absorbed mucosal Ca++. Serosal octreotide converted the gallbladder from a state of basal Ca++ absorption to one of net Ca++ secretion by stimulating serosa to mucosa Ca++ flux. As anticipated, octreotide increased net Na+ absorption by stimulating mucosa to serosa Na+ flux and decreased tissue conductance and short-circuit current significantly compared with baseline values.

CONCLUSION

Fifty nanomoles per liter octreotide stimulated Ca++ secretion by gallbladder epithelium, a possible mechanism for increased biliary Ca++ in prairie dogs receiving subcutaneous injections. Ca++ secretion linked to octreotide therapy may induce gallstones by raising biliary levels of Ca++, a known prolithogenic factor.

Radiotherapy, toxicity and dosimetry of copper-64-TETA-octreotide in tumor-bearing rats

The efficacy of 64Cu [T1/2 = 12.7 hr; beta+ (0.655 MeV; 19%); beta- (0.573 MeV; 40%)] as a radioisotope for radiotherapy has been recently established. Here we demonstrate that 64Cu-1,4,8,11 -tetraazacyclotetradecane-N,N',N",N'''-tetraacetic acid (TETA)-octreotide, a somatostatin receptor ligand, inhibits the growth of CA20948 rat pancreatic tumors in Lewis rats at doses that cause minimal toxicity.

METHODS

Tumor-bearing rats were administered a single 15 mCi (555 MBq) dose, a fractionated dose of 15 mCi given in 2-3 doses over 2-8 days, or control agents of buffer, unlabeled octreotide or 64Cu-labeled TETA. In certain experiments, blood was removed at times from 4-23 days post-treatment, and a complete blood count along with blood chemistry analyses were obtained.

RESULTS

Tumor-growth inhibition was significantly greater in rats injected with a single 15 mCi dose than in rats injected with control agents (p < 0.05). Dose fractionation in two doses, either 1 or 2 days apart, induced significantly increased tumor-growth inhibition compared with rats given a single dose (p < 0.05). The only toxicity observed in treated rats was a decrease in the white blood cell count. This drop was more pronounced in rats treated with a single dose compared with those treated with a fractionated dose. Human absorbed doses of 64Cu-TETA-octreotide to normal organs were estimated from biodistribution data in Lewis rats, and these data indicate that radiotherapy with 64Cu-TETA-octreotide in humans would be feasible.

CONCLUSION

Copper-64-TETA-octreotide is a promising radiopharmaceutical for targeted radiotherapy of somatostatin receptor-positive tumors.

Retinal toxicity of intravitreous octreotide in the rabbit

OBJECTIVE

To evaluate the ocular toxicity of intravitreous octreotide.

DESIGN

New Zealand white rabbits weighing approximately 2 kg were given 5 mg (group 1, two eyes), 2 mg (group 2, four eyes), 1 mg (group 3, four eyes), 0.5 mg (group 4, two eyes), 0.3 mg (group 5, two eyes) or 0.1 mg (group 7, two eyes) of octreotide acetate, two doses of 0.3 mg 1 week apart (group 6, four eyes) or 0.1 mL of balanced salt solution (group 8 [control group], two eyes).

OUTCOME MEASURES

Findings on clinical examination and electroretinography, performed before and 10 days after injection, and on light microscopy.

RESULTS

Cataracts developed in groups 1 and 2. No clinical changes were found in groups 3 to 8. Electroretinography showed various degrees of decrease in the b-wave amplitude in groups 1 and 2; the results were normal in groups 3 to 8. Histologic examination showed macrophage and monocyte infiltration in the vitreous and retina in group 1. No histologic change was seen in the eyes in groups 2 to 8.

CONCLUSIONS

Octreotide injected intravitreally is safe at dosages of 1 mg or less.

Intravitreal injection of octreotide acetate

This study was conducted to determine the feasibility of injecting the somatostatin analogue, octreotide acetate (OA), into the vitreous cavity. Previous work suggests that octreotide effectively inhibits angiogenesis in vitro, thus its use in vivo may slow the progression of proliferative eye disease. Fifty micrograms of aqueous OA in 50 microliters aqueous solution was injected into the mid-vitreous of kitten eyes (n = 6), and OA levels were monitored over 4 days. A long-acting release form of octreotide (OA-LAR) was also injected into the mid-vitreous of rabbit eyes at doses of 0.36 (n = 16), 1.1 (n = 1), 2.1 (n = 1), 4.05 (n = 1), 8.2 (n = 1), and 36 mg (n = 3) in solution; and octreotide concentrations were measured at various time points over 42 days. OA concentrations were determined by a highly specific radioimmunoassay. Aqueous octreotide was eliminated rapidly (t1/2 = 16 hours) from the vitreous of the kitten eye, with only negligible amounts recoverable 4 days post-injection. In the long-acting form, OA in the rabbit eye reached peak levels at 28 days. By 42 days, OA levels had declined to the 14-day level. Doses of OA-LAR of 1.1 mg or less produced no gross evidence of clinical toxicity and elicited no grossly visible ocular side effects. Doses greater than 1.1 mg produced significant toxicity, including cataracts and rubeosis. The 28-day peak release for long-acting OA implies that monthly intravitreal injections could provide continual high levels of OA. Intravitreal injection of long-acting OA provides sustained, high concentrations of drug, and deserves further study as a potential treatment of proliferative eye diseases.

SMS 201-995 in the treatment of refractory prostatic carcinoma

The long-acting synthetic somatostatin analog, SMA 201-995, was used to treat patients with advanced hormonal-refractory prostate cancer. Twenty-two of 24 study patients treated are evaluable for toxicity and 20 are evaluable for response. The dose of SMS 201-995 was 100 mg subcutaneously every 8 hours for 6 weeks. Two patients suffered intolerable gastrointestinal complications requiring early cessation of therapy. No patient had objective evidence of tumor regression. After developing a clinical suspicion that tumor growth accelerated with SMS 201-995, we observed 10 patients closely for 2 months before beginning SMS 201-995 treatment and for the first 2 months on the therapy. In these 10 patients, the serum prostatic acid phosphatase level rose at an accelerated rate after 1 to 2 months of treatment. Among the 20 patients treated and evaluable for response, new osseous metastases developed in 12 and new visceral metastases in 4; 1 developed disseminated intravascular coagulation and 2 developed neurologic complications (mean time to objective progression, 5.6 weeks). Six patients received salvage chemotherapy after disease progressed on SMS 201-995 therapy, 5 of whom have achieved objective tumor regressions. We believe SMS 201995 stimulates prostatic tumor growth and may sensitize tumor cells to subsequent chemotherapy.

Why does somatostatin cause gallstones?

Long-term administration of the somatostatin analogue, octreotide, is complicated by gallstone formation. Somatostatin is known to inhibit hepatic bile secretion and gallbladder emptying. However, the effect of octreotide on gallbladder bile composition remains unknown. Therefore, we tested the hypothesis that octretide would alter hepatic bile composition and cause gallbladder stasis, thereby increasing gallbladder bile solute concentrations. Fourteen control prairie dogs received daily saline injections, whereas 10 animals received 1 micrograms of octreotide subcutaneously three times per day for 5 days. Cholecystectomy and common bile duct cannulation were then performed. Octreotide increased hepatic bile concentrations of bilirubin monoglucuronide (p less than 0.05), total bilirubin (p less than 0.05), and total protein (p less than 0.01). Rsa, an index of gallbladder stasis, was decreased (p less than 0.01) in the octreotide group. Gallbladder bile total calcium (p less than 0.05), bilirubin monoglucuronide (p less than 0.05), total bilirubin (p less than 0.01), total protein (p less than 0.05), and total lipids (p less than 0.05) were increased in the octreotide group. Animals receiving octreotide also had decreased hepatic (p less than 0.05) and gallbladder (p less than 0.001) bile pH. No differences in cholesterol saturation index were observed. These data suggest that in the prairie dog, octreotide (1) alters hepatic bile composition, (2) causes gallbladder stasis, and (3) increases gallbladder bile calcium, bilirubin, protein, lipid, and hydrogen ion concentrations. We conclude that octreotide causes alterations in gallbladder bile composition that increase the likelihood of cholesterol and calcium bilirubinate precipitation.