Diagnostic imaging of dopamine receptors in pituitary adenomas

Dopamine D2 receptor scintigraphy of pituitary adenomas is feasible by single-photon emission computed tomography using (123)I-S-(-)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-hydroxy-3-iodo-6-methoxybenzamide ((123)I-IBZM) and (123)I-epidepride. (123)I-epidepride is generally superior to (123)I-IBZM for the visualization of D2 receptors on pituitary macroadenomas. However, (123)I-IBZM and (123)I-epidepride scintigraphy are generally not useful to predict the response to dopaminergic treatment in pituitary tumour patients. These techniques might allow discrimination of non-functioning pituitary macroadenomas from other non-tumour pathologies in the sellar region. Dopamine D2 receptors on pituitary tumours can also be studied using positron emission tomography with (11)C-N-raclopride and (11)C-N-methylspiperone.

Neuroendocrine tumors. Peptide receptor radionuclide therapy

Peptide receptor radionuclide therapy with radiolabelled somatostatin analogues is an emerging and convincing treatment modality for patients with unresectable, somatostatin-receptor-positive neuroendocrine tumours. Using radiolabelled somatostatin analogues for imaging became the gold standard for staging of neuroendocrine tumours. The somatostatin receptor is strongly over-expressed in most tumours, resulting in high tumour-to-background ratios. Consequently, the next step was to try to treat these patients by increasing the radioactivity of the administered radiolabelled somatostatin analogue in an attempt to bring about tumour cure. Many patients have been treated successfully with this approach, roughly 25% of them achieving objective tumour shrinkage >50%. Serious side-effects have been rare. This article reviews the effectiveness and safety of the different radiolabelled somatostatin analogues used. Furthermore, clinical issues--including indication and timing of therapy--are discussed. Finally, important directions for future research are mentioned to illustrate new strategies for increasing therapy efficacy.

Androgen-dependent expression of the gastrin-releasing peptide receptor in human prostate tumor xenografts

Human prostate cancers (PC) overexpress gastrin-releasing peptide (GRP) receptors. This observation suggests that GRP receptors may be used as new visualization and treatment modalities for these tumors. Radiolabeled GRP receptor-targeting analogs of GRP and bombesin (BN) have successfully been developed for these purposes. Expression of GRP receptors in human prostate tumors is, however, primarily evaluated in early stages of tumor development and information on expression in the more progressive prostate tumors is uncertain. To evaluate GRP receptor expression in all stages of PC, we investigated GRP receptor expression using a panel of 12 established human PC xenograft models representing the different stages of human PC and the effect of antiandrogen treatment (castration).

METHODS

Human PC xenografts were grown in male nude mice, and GRP receptor density in the tumors was evaluated using displacement receptor autoradiography with the universal BN receptor analog (125)I-[D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14) and the BN analog (111)In-[DTPA-Pro(1),Tyr(4)]BN (DTPA is diethylenetriaminepentaacetic acid) before and after castration.

RESULTS

Autoradiography showed high-density GRP receptor expression in the androgen-dependent tumors (3/12 models), whereas only very low receptor expression was found in the androgen-responsive and -independent tumors (9/12 models). Castration resulted in GRP receptor downregulation (11%-36% of initial values) in the 3 androgen-dependent tumors.

CONCLUSION

High GRP receptor density was only observed in androgen-dependent PC xenografts, indicating high GRP receptor expression in the early, androgen-dependent, stages of prostate tumor development and not in later stages. In addition, castration strongly reduced GRP receptor expression in androgen-dependent tumors, indicating that GRP receptor expression in human PC is androgen-regulated.

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.

Practical aspects of peptide receptor radionuclide therapy with [177Lu][DOTA0, Tyr3]octreotate

Lutetium-177 is increasingly used in patients for receptor-targeted radionuclide therapy with peptides such as [DOTA0,Tyr3]octreotate. In our therapy facility, we are performing yearly 400 treatments with each 7.4 GBq [177Lu][DOTA0,Tyr3]octreotate. Finger dosimetry data during radiolabeling reveal higher doses on the right hands of right-handed workers with the highest equivalent dose for the middle finger (53+/-12 microSv/GBq). Extrapolating dosimetry data, assuming 400 doses of 7.4 GBq per year performed by 4 workers, result in a mean equivalent dose of 23+/-11 mSv and 14+/-6 mSv for finger top and ring dose, respectively. Preparation of 400 doses will result in an effective dose of 0.5-1.5 mSv per year for these 4 workers. The extra radiation dose for workers during the radiolabeling of these doses thus remains below 10% of the legal annual limits, which is in accordance with the ALARA optimization principle. Based on measurements of the maximal radiation level at 1 m distance (7.5+/-3.6 microSv/h), patients treated with 7.4 GBq [177Lu][DOTA0,Tyr3]octreotate can already leave the therapy facility the next day. As radioactive waste streams are based on the half-lives of the used radionuclides, 177Lu-waste (t1/2=6.7 d) was initially collected along with the 131I-waste (t1/2=8 d). According to both manufacturers' specifications, 177Lu contains less than 0.4 kBq 177mLu/MBq 177Lu (at the end of neutron irradiation), when produced by the [176Lu n, gamma 177Lu] reaction via thermal neutron bombardment of enriched lutetium oxide. Unfortunately, because of the huge amounts of 177Lu used, contaminating 177mLu turned out to prevent the quick discharge of this waste, for some containers even after some years of storage. Therefore, a technique for calibrating 177mLu was developed, simultaneously confirming the manufacturer's specifications on the presence of 177mLu in 177Lu. Subsequently a reliable technique was developed to measure 177mLu in waste containers using a beta/gamma-contamination monitor. It is advised to collect 177mLu/177Lu-waste and certainly high-activity lutetium waste separated from 131I according the regulations in the country of use. Apart from the mentioned waste, excreta from patients are collected in decay tanks, where they are stored for 1-2 months before they are discarded into the general sewer within the overall tolerated discharge limit (150 radiotoxicity equivalents/year for our department).

Dopamine agonist therapy of clinically non-functioning pituitary macroadenomas. Is there a role for 123I-epidepride dopamine D2 receptor imaging?

OBJECTIVE

Clinically non-functioning pituitary adenomas (NFPAs) can express functional dopamine D2 receptors. Therapy with dopamine (DA) agonists may result in a NFPA size reduction. However, DA agonist-sensitive and -resistant NFPAs are clinically indistinguishable. We have studied the correlation between in vivo imaging of D2 receptors using (123)I-epidepride and the radiological response of NFPA to DA in 18 patients.

METHODS

Patients were treated with either cabergoline (1-2 mg/week) or quinagolide (150-300 mug/day) for a mean period of 89.7 months (range, 34-187 months).

RESULTS

Pituitary uptake of (123)I-epidepride varied from slight uptake classified as grade 0 to very high classified as grade 3. Grade 0 uptake was found in four patients; grade 1 in three; grade 2 in ten, and grade 3 in one. NFPA stabilization or shrinkage with DA agonist therapy showed no significant difference between grade 0, 1, and 2 tumors (mean tumor stabilization or shrinkage: 31, 30, and 36% respectively). However, when we considered a decrease in tumor size ranging from 0 to 20% as tumor stabilization and >20% decrease in tumor size as true shrinkage, one out of four NFPAs with grade 1 uptake, two out of three with grade 1 uptake, and eight out of ten with grade 2 uptake showed tumor shrinkage.

CONCLUSION

In conclusion, there is limited clinical usefulness of dopamine D2 receptor imaging for predicting the clinical efficacy of DA agonist in selected patients with NFPAs. DA agonist therapy in NFPAs can result in tumor stabilization and shrinkage.

Quantification of [3H]docetaxel in feces and urine: development and validation of a combustion method

Most radiolabeled biological samples require extensive sample preparation to reduce quenching interference before quantification of radioactivity is possible. Clearly, a more rapid and simple method ensuring a constant count rate and optimal counting efficiency has important advantages. We report on the development and analytical method validation of a rapid and simple combustion method to quantify [3H]docetaxel excreted in human feces and urine. A 3-day validation procedure was performed; quality control (QC) samples, prepared in blank feces and urine, were combusted 5 times and aliquots of the produced tritiated combustion water were counted in a liquid scintillation counter. The validation runs demonstrated adequate precision (below 7.6%) across all QC levels. Sensitivity at the lowest QC level was excellent and recovery of radioactivity constant (ranging from 85 to 91.8%). Clinical applicability of the method was tested in a cancer patient receiving docetaxel and a tracer amount of [3H]docetaxel; during the first 72 h after [3H]docetaxel infusion, 60% of total radioactivity was excreted in the collected feces and urine, which is within the expected range. Combustion of tritiated feces and urine samples is a simple, rapid, sensitive, precise and reproducible method with high recovery. It can be applied to quantify [3H]docetaxel excretion after i.v. administration.

Effects of therapy with [177Lu-DOTA0, Tyr3]octreotate in patients with paraganglioma, meningioma, small cell lung carcinoma, and melanoma

Therapy using the radiolabeled somatostatin analog [177Lu-DOTA0,Tyr3]octreotate (177Lu-octreotate) (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) has been used primarily in gastroenteropancreatic neuroendocrine tumors. Here we present the effects of this therapy in a small number of patients with metastasized or inoperable paragangliomas, meningiomas, small cell lung carcinomas (SCLCs), and melanomas.

METHODS

Twelve patients with paraganglioma, 5 with meningioma, 3 with SCLC, and 2 with eye melanoma were treated. Three meningiomas were very large and exophytic and all standard treatments had failed. Patients with melanoma had rapidly progressive disease (PD). The intended cumulative dose of 177Lu-octreotate was 22.2-29.6 GBq. Effects of the treatment on tumor size were evaluated using the Southwest Oncology Group criteria.

RESULTS

Two of 4 patients with progressive paraganglioma had tumor regression and 1 had stable disease (SD). Of 5 patients with stable paraganglioma, 2 had SD, 2 had PD, and in 1 patient treatment outcome could not be determined. Paraganglioma was stable in 3 patients in whom the disease status at the beginning of therapy was unknown. One of 4 patients with progressive meningioma had SD and 3 patients had PD. One patient with stable meningioma at the beginning of therapy had SD. All patients with SCLC or melanoma died within 5 mo after starting therapy because of tumor progression. Although not statistically significant, a positive trend was found between high uptake on pretherapy somatostatin receptor scintigraphy and treatment outcome.

CONCLUSION

177Lu-octreotate can be effective in patients with paraganglioma and meningioma. Response rates are lower than those in patients with gastroenteropancreatic neuroendocrine tumors. Most meningiomas were very large. Further studies are needed to confirm the treatment outcome because of the limited number of patients. 177Lu-octreotate did not have antitumor effects in patients with small lung carcinoma and melanoma.

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.

Survival and response after peptide receptor radionuclide therapy with [90Y-DOTA0,Tyr3]octreotide in patients with advanced gastroenteropancreatic neuroendocrine tumors

Because the role of chemotherapy, interferon, or somatostatin analogs as antiproliferative agents is uncertain, currently few treatment options exist for patients with metastatic or inoperable gastroenteropancreatic neuroendocrine tumors (GEP-NET). Fifty-eight patients with somatostatin receptor-positive GEP-NET were treated in a phase I dose-escalating study with cumulative doses of 47 mCi to 886 mCi of the radiolabeled somatostatin analog [(90)Y-DOTA(0),Tyr(3)]-octreotide. At baseline, 47 patients had progressive disease, and 36 were symptomatic. The extent of disease was: 4 patients without liver metastases and 52 patients with liver metastases, including 16 patients with very advanced disease, qualified as "end-stage," and 2 end-stage patients without liver metastases. The objective responses were 5 partial response (PR), 7 minor response (MR), 29 stable disease (SD), and 17 PD. Overall, 33 patients (57%) experienced some improvement in their disease status, including conversion from PD into SD and improvement from SD into MR. Accordingly, 21 of 36 patients (58%) had improvement in Karnofsky performance score or symptoms. The median overall survival (OS) was 36.7 months (95% confidence interval [CI] 19.4-54.1 months). The median progression-free survival in 41 patients who had at least stable disease at the end of the treatment period was 29.3 months (95% CI 19.3-39.3 months). Patients who had SD at baseline had a significantly better OS than patients who had PD at baseline. The extent of disease at baseline also was a significant predictive factor for OS. The OS after therapy with [(90)Y-DOTA(0),Tyr(3)]-octreotide was significantly better than in a historic control group of 32 comparable patients with GEP-NET who had been treated with another radiolabeled somatostatin analog, [(111)In-DTPA(0)]-octreotide (median OS 12.0 months, 95% CI 6.2-17.8 months). The difference in OS for both therapies remained highly significant in a multivariate Cox proportional hazard model including progression status and extent of disease at baseline as covariates. Although the objective response after therapy with [(90)Y-DOTA(0),Tyr(3)]-octreotide by standard criteria seems modest, the significantly longer OS compared with historic controls is most encouraging.

Comparison of [(177)Lu-DOTA(0),Tyr(3)]octreotate and [(177)Lu-DOTA(0),Tyr(3)]octreotide: which peptide is preferable for PRRT?

PURPOSE

Patients with somatostatin receptor subtype 2-positive metastasised neuroendocrine tumours can be treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [(177)Lu-DOTA(0),Tyr(3)]octreotide ((177)Lu-DOTATOC) and [(177)Lu-DOTA(0),Tyr(3)]octreotate ((177)Lu-DOTATATE), to see which peptide should be preferred for PRRT with (177)Lu.

METHODS

In the same patients, 3,700 MBq (177)Lu-DOTATOC and 3,700 MBq (177)Lu-DOTATATE was administered in separate therapy sessions. Amino acids were co-administered. Whole-body scanning was performed on days 1, 4 and 7 post therapy. Blood and urine samples were collected. We calculated residence times for tumours, spleen and kidneys.

RESULTS

All patients had longer residence times in spleen, kidneys and tumours after use of (177)Lu-DOTATATE (p=0.016 in each case). Comparing (177)Lu-DOTATATE with (177)Lu-DOTATOC, the mean residence time ratio was 2.1 for tumour, 1.5 for spleen and 1.4 for kidneys. Dose-limiting factors for PRRT are bone marrow and/or kidney dose. Although the residence time for kidneys was longer when using (177)Lu-DOTATATE, the mean administered dose to tumours would still be advantageous by a factor of 1.5, assuming a fixed maximum kidney dose is reached. Plasma radioactivity after (177)Lu-DOTATATE was comparable to that after (177)Lu-DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for (177)Lu-DOTATOC.

CONCLUSION

(177)Lu-DOTATATE had a longer tumour residence time than (177)Lu-DOTATOC. Despite a longer residence time in kidneys after (177)Lu-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.

In vivo radionuclide uptake quantification using a multi-pinhole SPECT system to predict renal function in small animals

PURPOSE

In vivo quantification of radiopharmaceuticals has great potential as a tool in developing new drugs. We investigated the accuracy of in vivo quantification with multi-pinhole single-photon emission computed tomography (SPECT) in rats.

METHODS

Fifteen male Lewis rats with different stages of renal dysfunction were injected with 50 MBq 99mTc-dimercaptosuccinic acid. Four to six hours after injection, SPECT of the kidneys was acquired with a new four-headed multi-pinhole collimator camera. Immediately after imaging the rats were sacrificed and the kidneys were counted in a gamma-counter to determine the absorbed activity. SPECT data were reconstructed iteratively and regions of interest (ROIs) were drawn manually. The absolute activity in the ROIs was determined.

RESULTS

Uptake values ranging from 0.71% to 21.87% of the injected activity were measured. A very strong linear correlation was found between the determined activity in vivo and ex vivo (r2=0.946; slope m=1.059).

CONCLUSION

Quantification in vivo using this multi-pinhole SPECT system is highly accurate.

The effect of etanercept on Graves' ophthalmopathy: a pilot study

PURPOSE

To assess the effect of etanercept, an antitumour necrosis factor (anti-TNF) drug, on clinical signs in Graves' ophthalmopathy (GO).

METHODS

A total of 10 consecutive patients (seven female, three male) with recent-onset, active, mildly-to-moderately severe GO were treated with subcutaneous injections of 25 mg etanercept (Enbrel) twice weekly during 12 weeks. The average age was 50 years (range: 39-59 years). The average duration of GO was 4 months (range: 2-6 months). All patients were at least 2 months euthyroid with medication. The mean pretreatment clinical activity score (CAS) was 4 (range: 3-6).

RESULTS

The mean CAS prior to treatment was 4, at 6 weeks 2.6, and at 12 weeks 1.6. The mean ophthalmopathy index (OI) prior to treatment was 5.8, at 6 weeks 4.8, and at 12 weeks 4.4. Thus, after 12 weeks of treatment the mean CAS had decreased by 2.4+/-1.3 (60%), and the mean OI had decreased by 1.4+/-1.2 (24%). The main decrease of the CAS and OI was noted at 6 weeks of treatment. The difference was particularly evident on soft-tissue changes, including periocular chemosis and redness. The mean exophthalmometry values did not change. In all, 60% percent of patients reported moderate to marked improvement. In three patients, the GO flared up again after cessation of treatment. There were no serious adverse events or side effects during a mean follow-up time of 18 months.

CONCLUSIONS

This study strongly suggests that etanercept may suppress the clinical signs in GO, but randomized controlled trials are needed to further evaluate the effect of anti-TNF treatment and to compare its side-effects with those of corticosteroids.

[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.

Impact of diabetes mellitus on prediction of clinical outcome after coronary revascularization by 18F-FDG SPECT in patients with ischemic left ventricular dysfunction

Nuclear imaging using (18)F-FDG is an established method for the noninvasive assessment of myocardial viability. Data on the value of (18)F-FDG imaging in patients with diabetes mellitus are scarce. The aim of this study was to assess whether, in patients with diabetes mellitus and ischemic left ventricular (LV) dysfunction, (18)F-FDG imaging can predict improvement of LV function and heart failure symptoms after coronary revascularization.

METHODS

A total of 130 consecutive patients with ischemic LV dysfunction who were already scheduled for surgical revascularization were studied; 34 of the patients had diabetes mellitus. All patients underwent radionuclide ventriculography to assess left ventricular ejection fraction (LVEF), resting 2-dimensional echocardiography to identify dysfunctional myocardial tissue, and dual-isotope (18)F-FDG/(99m)Tc-tetrofosmin SPECT after oral administration of acipimox. Nine to 12 mo after coronary revascularization, radionuclide ventriculography and echocardiography were repeated. An improvement in LVEF by at least 5% was considered significant.

RESULTS

(18)F-FDG SPECT demonstrated that 610 (50%) of 1,212 dysfunctional segments were viable. Patients with and without diabetes mellitus had a comparable number of dysfunctional but viable segments per patient. Also, the number of patients with a substantial amount of dysfunctional but viable myocardium (>or=4 viable segments) was comparable between the groups with and without diabetes mellitus. The presence of substantial viability on (18)F-FDG SPECT was predictive of improvement in LVEF and heart failure symptoms postoperatively (sensitivity and specificity of 82% and 89%, respectively, in patients with diabetes and 83% and 93%, respectively, in patients without diabetes; not statistically significant).

CONCLUSION

(18)F-FDG SPECT is practical for routine assessment of myocardial viability in patients with ischemic LV dysfunction with or without diabetes mellitus. Patients with substantial myocardial viability on (18)F-FDG SPECT have a high probability of improvement of LV function and symptoms after coronary revascularization, irrespective of the absence or presence of diabetes mellitus.

Anticancer activity of targeted proapoptotic peptides

Tumor-induced angiogenesis can be targeted by RGD (Arg-Gly-Asp) peptides, which bind to alpha(v)beta(3)-receptors upregulated on angiogenic endothelial cells. RGD-containing peptides are capable of inducing apoptosis through direct activation of procaspase-3 to caspase-3 in cells. Additionally, tumor cells overexpressing somatostatin receptors can be targeted by somatostatin analogs. Radiolabeled somatostatin analogs are successfully used to image and treat such tumors via receptor-targeted scintigraphy and therapy. We combined these 2 peptides, RGD and somatostatin, to synthesize a new hybrid peptide, RGD-diethylenetriaminepentaacetic acid (DTPA)-octreotate (c(Arg-Gly-Asp-D-Tyr-Asp)-Lys(DTPA)-D-Phe-c(Cys-Tyr-D-Trp-Lys-Thr-Cys)-Thr). An earlier study showed that tumor-bearing rats had high receptor-specific uptake of RGD-(111)In-DTPA-octreotate in somatostatin receptor subtype 2-positive tissues and tumors. Furthermore, RGD-(111)In-DTPA-octreotate showed a pronounced tumoricidal effect, which is probably the result of increased apoptosis, as is shown by an increased caspase-3 activity after incubation with (111)In-labeled RGD-DTPA-octreotate in comparison with the 2 monopeptides (111)In-DTPA-RGD and (111)In-DTPA-Tyr(3)-octreotate. In this study, we evaluated the biodistributions of RGD-(111)In-DTPA-octreotate and (125)I-RGD-octreotate and investigated the caspase-3 activation of the unlabeled compound RGD-DTPA-octreotate in vitro.

METHODS

Biodistribution studies on tumor-bearing rats were performed with RGD-(111)In-DTPA-octreotate and (125)I-RGD-octreotate. The apoptotic activity, by activation of caspase-3 with RGD-DTPA-octreotate and RGD-octreotate, was examined using colorimetric and immunocytochemical assays.

RESULTS

The radiolabeled compound, RGD-(111)In-DTPA-octreotate, showed high uptake and retention in the rats in which rat pancreatic CA20948 tumor had been implanted. A major drawback was high renal uptake. In vitro, the unlabeled peptide RGD-DTPA-octreotate induced a significant increase in caspase-3 levels in various cell lines in comparison with RGD and Tyr(3)-octreotate (P < 0.01). Caspase-3 activation was time dependent. To alter the elimination route, we examined the biodistribution of radioiodinated RGD-octreotate without DTPA [c(Arg-Gly-Asp-D-Tyr-Asp)-D-Phe-c(Cys-Tyr-D-Trp-Lys-Thr-Cys)-Thr], as a model of unlabeled RGD-octreotate, in tumor-bearing rats. (125)I-RGD-octreotate showed a much lower renal uptake than did RGD-(111)In-DTPA-octreotate. Furthermore, the affinity of RGD-octreotate increased in comparison with RGD-DTPA-octreotate (values of 1.4 x 10(-8) mol/L vs. 9.4 x 10(-8) mol/L, respectively, for inhibitory concentration of 50%). Finally, RGD-octreotate was still able to activate caspase-3, as was indicated with immunocytochemistry.

CONCLUSION

Because of the high renal uptake, RGD-(111)In-DTPA-octreotate is unsuitable for radionuclide therapy. However, the unlabeled peptides, RGD-DTPA-octreotate and RGD-octreotate, also induced an increase in caspase-3 levels, indicating the therapeutic potential of this compound. Thus, the development of hybrid molecules can become a new approach in the treatment of cancer.

No difference between prednisolone and dexamethasone treatment in bone mineral density and growth in long term survivors of childhood acute lymphoblastic leukemia

BACKGROUND

Dexamethasone is known to have both more potent leukemic activity and is associated with a higher incidence of side effects than prednisolone. In this study, we compared the long-term effects of dexamethasone and prednisolone on bone mineral density (BMD), body composition and growth in long-term survivors of ALL in first complete remission.

PROCEDURE

Ninety patients (51 male, 49 female; 8.6-38.5 year), treated with either a prednisolone containing protocol (n = 47; n = 19 also with CNS-irradiation) or a dexamethasone containing protocol (n = 43; no cranial irradiation) participated in this cross-sectional single center study. Mean follow-up was 12.7 years (2.0-29.7 years). BMD of lumbar spine and total body, and body composition were expressed as standard deviation scores (SDS) using dual energy X-ray absorptiometry. Bone mineral apparent density of the lumbar spine (BMAD) was calculated to correct for bone size.

RESULTS

There was no difference in height, height corrected for target height, BMD, or lean body mass between prednisolone and dexamethasone treated patients. Prednisolone treated patients had an increased percentage body fat (SDS +0.46; P < 0.05) and increased body mass index (SDS 0.88; P < 0.01) compared to normal. Dexamethasone treated patients had only an increased body mass index (SDS 0.52; P < 0.05). Height, total body BMD, and lean body mass were lower in patients treated with cranial irradiation as compared to non-irradiated patients, but differences in the latter two disappeared when corrected for height. BMAD was normal after CNS-irradiation.

CONCLUSIONS

Long term survivors of ALL treated with prednisolone or dexamethasone containing regimens do not differ in height, BMD, or body composition.

Somatostatin receptor imaging for neuroendocrine tumors

Tumors and metastases that express the somatostatin receptor subtypes sst2 sst3 or sst5 can be visualized in vivo after injection of radiolabeled octapeptide somatostatin analogs, like (111)In-pentetreotide. (111)In-pentetreotide scintigraphy also allows for more accurate staging of the disease by demonstrating tumor sites, which were not shown by conventional imaging. (111)In-pentetreotide scintigraphy may also detect resectable tumors that would have remained unrecognized using conventional radiological imaging techniques; it may prevent surgery with curative intent in those patients whose tumors have metastasized to a greater extend than could be detected with conventional radiological imaging and it may be used to select patients for treatment with the currently available octapeptide somatostatin analogs or with tumor targeted radioactive treatment with radiolabelled somatostatin analogs. (111)In-pentetreotide scintigraphy has also been used to select patients with pituitary tumors for medical treatment with octapeptide analogs, but its clinical usefulness for this purpose seems to be limited. It further allows scar tissue to be differentiated from tumor recurrence after the pituitary surgery or radiotherapy. However, a large variety of lesions in and around the pituitary region also express somatostatin receptors and, therefore, can be visualized by (111)In-pentetreotide scintigraphy.

Staging and treatment of differentiated thyroid carcinoma with radiolabeled somatostatin analogs

In patients with progressive metastatic (or recurrent) differentiated thyroid carcinoma that either do not take up radioiodine or are unresponsive to continued radioiodine therapy, staging is difficult and treatment options are few. However, in most of these patients uptake of radiolabeled somatostatin analogs is evident on somatostatin-receptor scintigraphy (SRS). Using SRS, patients with sufficient uptake of radiolabeled somatostatin analogs can be selected for high-dose peptide receptor radionuclide therapy (PRRT) as an alternative targeted-treatment option. PRRT with the beta-particle-emitting radionuclides (90)yttrium ((90)Y) and (177)lutetium ((177)Lu) gives the best results in terms of objective tumor response. Promising, novel, radiolabeled somatostatin analogs that have a broader receptor affinity profile and, thus, a potentially wider therapeutic range are being tested clinically.

Prognostic implications of a normal stress technetium-99m-tetrofosmin myocardial perfusion study in patients with a healed myocardial infarct and/or previous coronary revascularization

Previous studies have shown a good outcome for patients who present with normal findings on stress myocardial perfusion imaging. Currently, the prognostic implications of a normal study in patients who have a history of coronary artery disease (CAD) are not clear. This study investigated the long-term prognosis after a normal finding on stress technetium-99m (Tc-99m)-tetrofosmin single-photon emission computed tomography in patients with a history of CAD. The study included 147 consecutive patients with a history of CAD (previous myocardial infarction and/or myocardial revascularization), who underwent exercise bicycle or high-dose dobutamine-atropine stress Tc-99m-tetrofosmin single-photon emission computed tomography, and had normal perfusion results during stress and at rest. Follow-up was completed in all patients. During a follow-up of 6.5 +/- 1.9 years, 20 patients (14%) died, 10 (7%) of whom died due to cardiac causes, and 12 (8%) had a nonfatal myocardial infarction. Annual cardiac death rates were 0.5% during the first 3 years of follow-up and 1.3% in the subsequent 3 years. Independent predictors of cardiac death were male gender, rate-pressure product at rest, and rate-pressure product at peak stress. In conclusion, patients who have a history of CAD have a very low cardiac death rate during the 3 years after a normal finding on stress Tc-99m-tetrofosmin single-photon emission computed tomography. Repeated testing should be reconsidered 3 years after the initial evaluation and when a change in symptoms or clinical condition occurs.

Oral versus intravenous administration of lysine: equal effectiveness in reduction of renal uptake of [111In-DTPA]octreotide

During tumor therapy with radiolabeled somatostatin analogs, the kidneys are dose limiting. Renal uptake in patients can effectively be reduced by a 4- to 10-h intravenous infusion of a lysine/arginine solution, thereby increasing the maximum radiation dose to the tumor without renal side effects. Oral administration of amino acids could facilitate this labor-intensive procedure. Therefore, the effects of oral versus intravenous administration of D-lysine were compared in rats injected with [111In-diethylenetriaminepentaacetic acid (DTPA)]octreotide.

METHODS

Rats were intravenously injected with 3 MBq/0.5 microg [111In-DTPA]octreotide and also received D-lysine intravenously or orally in various concentrations and following various time schedules. Twenty-four hours after injection, a biodistribution study and renal ex vivo autoradiography were performed.

RESULTS

Renal uptake was reduced significantly-up to 40%-in all lysine-treated groups, without affecting the uptake in other organs.

CONCLUSION

Renal uptake of this radiolabeled peptide can be reduced up to 40% both by oral and by intravenous administration of lysine in rats.