[177Lu-DOTA0,Tyr3]octreotate: comparison with [111In-DTPA0]octreotide in patients

The somatostatin analogue [DOTA⁰,Tyr³]octreotate has a nine-fold higher affinity for the somatostatin receptor subtype 2 as compared with [DOTA⁰,Tyr³]octreotide. Also, labelled with the beta- and gamma-emitting radionuclide lutetium-177, this compound has been shown to have a very favourable impact on tumour regression and animal survival in a rat model. Because of these reported advantages over the analogues currently used for somatostatin receptor-mediated radiotherapy, we decided to compare [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate (¹⁷⁷Lu-octreotate) with [¹¹¹In-DTPA⁰]octreotide (¹¹¹In-octreotide) in six patients with somatostatin receptor-positive tumours. Plasma radioactivity after ¹⁷⁷Lu-octreotate expressed as a percentage of the injected dose was comparable with that after ¹¹¹In-octreotide. Urinary excretion of radioactivity was significantly lower than after ¹¹¹In-octreotide, averaging 64% after 24 h. The uptake after 24 h, expressed as a percentage of the injected dose of ¹⁷⁷Lu-octreotate, was comparable to that after ¹¹¹In-octreotide for kidneys, spleen and liver, but was three- to fourfold higher for four of five tumours. The spleen and kidneys received the highest absorbed doses. The doses to the kidneys were reduced by a mean of 47% after co-infusion of amino acids. It is concluded that in comparison with the radionuclide-coupled somatostatin analogues that are currently available for somatostatin receptor-mediated radiotherapy, ¹⁷⁷Lu-octreotate potentially represents an important improvement. Higher absorbed doses can be achieved to most tumours, with about equal doses to potentially dose-limiting organs; furthermore, the lower tissue penetration range of ¹⁷⁷Lu as compared with ⁹⁰Y may be especially important for small tumours.     

Treatment of patients with gastro-entero-pancreatic (GEP) tumours with the novel radiolabelled somatostatin analogue [177Lu-DOTA(0),Tyr3]octreotate

Medical treatment and chemotherapy are seldom successful in achieving objective tumour reduction in patients with metastatic neuroendocrine tumours. Treatment with the radiolabelled somatostatin analogue [(90)Y-DOTA(0),Tyr(3)]octreotide may result in partial remissions in 10-25% of patients. The newer analogue [DOTA(0),Tyr(3)]octreotate (octreotate) has a ninefold higher affinity for the somatostatin receptor subtype 2 as compared with [DOTA(0),Tyr(3)]octreotide. Also, labelled with the beta- and gamma-emitting radionuclide (177)Lu, it has proved very successful in achieving tumour regression in animal models. The effects of (177)Lu-octreotate therapy were studied in 35 patients with neuroendocrine gastro-entero-pancreatic (GEP) tumours who underwent follow-up for 3-6 months after receiving their final dose. Patients were treated with doses of 100, 150 or 200 mCi (177)Lu-octreotate, to a final cumulative dose of 600-800 mCi, with treatment intervals of 6-9 weeks. Nausea and vomiting within the first 24 h after administration were present in 30% and 14% of the administrations, respectively. WHO toxicity grade 3 anaemia, leucocytopenia and thrombocytopenia occurred after 0%, 1% and 1% of the administrations, respectively. Serum creatinine and creatinine clearance did not change significantly. The effects of the therapy on tumour size were evaluable in 34 patients. Three months after the final administration, complete remission was found in one patient (3%), partial remission in 12 (35%), stable disease in 14 (41%) and progressive disease in seven (21%), including three patients who died during the treatment period. Tumour response was positively correlated with a high uptake on the octreoscan, limited hepatic tumour mass and a high Karnofsky Performance Score. Because of the limited efficacy of alternative therapies, many physicians currently adopt an expectant attitude when dealing with patients with metastatic GEP tumours. However, in view of the high success rate of therapy with (177)Lu-octreotate and the absence of serious side-effects, we advocate its use in patients with GEP tumours without waiting for tumour progression.     

Somatostatin receptor-targeted radionuclide therapy of tumors: preclinical and clinical findings

In preclinical studies in rats we evaluated biodistribution and therapeutic effects of different somatostatin analogs, [(111)In-DTPA]octreotide, [(90)Y-DOTA,Tyr(3)]octreotide and [(177)Lu-DOTA,Tyr(3)]octreotate, currently also being applied in clinical radionuclide therapy studies. [Tyr(3)]octreotide and [Tyr(3)]octreotate, chelated with DTPA or DOTA, both showed high affinity binding to somatostatin receptor subtype 2 (sst(2)) in vitro. The radiolabelled compounds all showed high tumor uptake in sst(2)-positive tumors in vivo in rats, the highest uptake being reached with [(177)Lu-DOTA,Tyr(3)]octreotate. In preclinical therapy studies in vivo in rats, excellent, dose dependent, tumor size responses were found, responses appeared to be dependent on tumor size at therapy start. These preclinical data showed the great promise of radionuclide therapy with radiolabelled somatostatin analogues. They emphasised the concept that especially the combination of somatostatin analogs radiolabeled with different radionuclides, like (90)Y and (177)Lu, is most promising to reach a wider tumor size region of high curability. Furthermore, different phase I clinical studies, using [(111)In-DTPA]octreotide, [(90)Y-DOTA,Tyr(3)]octreotide or [(177)Lu-DOTA, Tyr(3)]octreotate are described. Fifty patients with somatostatin receptor-positive tumors were treated with multiple doses of [(111)In-DTPA(0)]octreotide. Forty patients were evaluable after cumulative doses of at least 20 GBq up to 160 GBq. Therapeutic effects were seen in 21 patients: partial remission in 1 patient, minor remissions in 6 patients, and stabilization of previously progressive tumors in 14 patients. The toxicity was generally mild bone marrow toxicity, but 3 of the 6 patients who received more than 100 GBq developed a myelodysplastic syndrome or leukemia. Radionuclide therapy with [(90)Y-DOTA,Tyr(3)]octreotide started in 3 different phase I trials. Overall, antimitotic effects have been observed: about 20% partial response and 60% stable disease (N = 92) along with complete symptomatic cure of several malignant insulinoma and gastrinoma patients. Maximum cumulative [(90)Y-DOTA,Tyr(3)]octreotide dose was about 26 GBq, without reaching the maximum tolerable dose. New is the use of [(177)Lu-DOTA,Tyr(3)]octreotate, which shows the highest tumor uptake of all tested octreotide analogs so far, with excellent tumor-to-kidney ratios. Radionuclide therapy with this analog in a phase 1 trial started recently in our center in 63 patients (238 administrations), Interim analysis of 18 patients with neuroendocrine tumors was performed very recently. According to the WHO, toxicity criteria no dose limiting toxicity was observed. Minor CT-assessed tumor shrinkage (25% - 50% reduction) was noticed in 6% of 18 patients and partial remission (50% - 100% reduction, SWOG criteria) in 39%. Eleven percent of patients had tumor progression and in 44% no changes were seen. These data show that radionuclide therapy with radiolabelled somatostatin analogs, like [DOTA, Tyr(3)]octreotide and [DOTA, Tyr(3)octreotate is a most promising new treatment modality for patients who have sst(2)-positive tumors.     

Lutetium-labelled peptides for therapy of neuroendocrine tumours

Treatment with radiolabelled somatostatin analogues is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumours. Symptomatic improvement may occur with (177)Lu-labelled somatostatin analogues that have been used for peptide receptor radionuclide therapy (PRRT). The results obtained with (177)Lu-[DOTA(0),Tyr(3)]octreotate (DOTATATE) are very encouraging in terms of tumour regression. Dosimetry studies with (177)Lu-DOTATATE as well as the limited side effects with additional cycles of (177)Lu-DOTATATE suggest that more cycles of (177)Lu-DOTATATE can be safely given. Also, if kidney-protective agents are used, the side effects of this therapy are few and mild and less than those from the use of (90)Y-[DOTA(0),Tyr(3)]octreotide (DOTATOC). Besides objective tumour responses, the median progression-free survival is more than 40 months. The patients' self-assessed quality of life increases significantly after treatment with (177)Lu-DOTATATE. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with (177)Lu-DOTATATE. These findings compare favourably with the limited number of alternative therapeutic approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable neuroendocrine tumours.     

Therapy of neuroendocrine tumors with radiolabeled somatostatin-analogues.

Peptide receptor scintigraphy with the radioactive somatostatin-analogue [111In-DTPA0]octreotide (DTPA = diethylenetriaminepentaacetic acid) is a sensitive and specific technique to show in vivo the presence and abundance of somatostatin receptors on various tumors. With this technique primary tumors and metastases of neuroendocrine cancers as well as of many other cancer types can be localised. A new application is the use of peptide receptor radionuclide therapy, administrating high doses of 111In- or 90Y-labeled octreotide-analogues. PRECLINICAL: We investigated the radiotherapeutic effect of 90Y- and 111In-labeled [DOTA0,Tyr3]octreotide (DOTA = tetraazacyclododecanetetraacetic acid) or [111In-DTPA0]octreotide in Lewis rats bearing the somatostatin receptor-positive rat pancreatic tumor CA20948 in A) the flank or B) in the liver. PATIENTS: Thirty end-stage patients with mostly neuroendocrine progressing tumors were treated with [111In-DTPA0]octreotide, up to a maximal cumulative patient dose of about 74 GBq, in a phase 1 trial. PRECLINICAL RESULTS: A) Flank model: at least two 111MBq injections of [111In-DOTA0,Tyr3]octreotide were needed to reach tumor response, in 40% of the animals complete tumor remission was found after a follow-up period of 10 months. One or two injections of [90Y-DOTA0,Tyr3] octreotide yielded transient stable disease. B) Liver model: we found that peptide receptor radionuclide therapy is only effective if somatostatin receptors are present on the tumors, and is therefore receptor-mediated. High radioactive doses of 370 MBq [111In-DTPA0]octreotide or 93 MBq [90Y-DOTA0,Tyr3]octreotide can inhibit the growth of somatostatin receptor-positive metastases. CLINICAL RESULTS: There were no major clinical side effects after up to 2 years treatment, except that a transient decline in platelet counts and lymphocyte subsets can occur. Promising beneficial effects on clinical symptoms, hormone production and tumor proliferation were found. Of the 21 patients with progressive disease at baseline and who received a cumulative dose of more than 20 GBq [111In-DTPA0]octreotide, 8 patients showed stabilisation of disease and 6 other patients a reduction in size of tumors. There is a tendency towards better results in patients whose tumors have a higher accumulation of the radioligand. CONCLUSION: Radionuclide therapy with octreotide-derivatives is feasible, both with 111In and 90Y as radionuclides.     

Effects of therapy with [<Superscript>177</Superscript>Lu-DOTA<Superscript>0</Superscript>,Tyr<Superscript>3</Superscript>]octreotate on endocrine function

Purpose  

Peptide receptor radionuclide therapy (PRRT) with radiolabelled somatostatin analogues is a novel therapy for patients with somatostatin receptor-positive tumours. We determined the effects of PRRT with [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate (¹⁷⁷Lu-octreotate) on glucose homeostasis and the pituitary-gonadal, pituitary-thyroid and pituitary-adrenal axes.     

Localisation and mechanism of renal retention of radiolabelled somatostatin analogues

Purpose Radiolabelled somatostatin analogues, such as octreotide and octreotate, are used for tumour scintigraphy and radionuclide therapy. The kidney is the most important critical organ during such therapy owing to the reabsorption and retention of radiolabelled peptides. The aim of this study was to investigate in a rat model both the localisation and the mechanism of renal uptake after intravenous injection of radiolabelled somatostatin analogues. The multi-ligand megalin/cubilin receptor complex, responsible for reabsorption of many peptides and proteins in the kidney, is an interesting candidate for renal endocytosis of these peptide analogues.Methods For localisation studies, ex vivo autoradiography and micro-autoradiography of rat kidneys were performed 1–24 h after injection of radiolabelled somatostatin analogues and compared with the renal anti-megalin immunohistochemical staining pattern. To confirm a role of megalin in the mechanism of renal retention of [¹¹¹In-DTPA]octreotide, the effects of three inhibitory substances were explored in rats. Results Renal ex vivo autoradiography showed high cortical radioactivity and lower radioactivity in the outer medulla. The distribution of cortical radioactivity was inhomogeneous. Micro-autoradiography indicated that radioactivity was only retained in the proximal tubules. The anti-megalin immunohistochemical staining pattern showed a strong similarity with the renal [¹¹¹In-DTPA]octreotide ex vivo autoradiograms. Biodistribution studies showed that co-injection of positively charged d-lysine reduced renal uptake to 60% of control. Sodium maleate reduced renal [¹¹¹In-DTPA]octreotide uptake to 15% of control. Finally, cisplatin pre-treatment of rats reduced kidney uptake to 70% of control.Conclusion Renal retention of [¹¹¹In-DTPA]octreotide is confined to proximal tubules in the rat kidney, in which megalin-mediated endocytosis may play an important part.     

Gelatin-based plasma expander effectively reduces renal uptake of 111In-octreotide in mice and rats.

111In-Diethylenetriaminepentaacetic acid-octreotide generally is used for the scintigraphic imaging of neuroendocrine and other somatostatin receptor-positive tumors. On the basis of the successful targeting of octreotide, radiolabeled somatostatin analogs, such as 90Y-(1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid [DOTA])0-Tyr3-octreotide and 177Lu-DOTA0-Tyr3-octreotate, were developed for peptide receptor radionuclide therapy. However, the maximum tolerated doses of these analogs are limited because of the high and persistent renal uptake that leads to relatively high radiation doses in the kidneys. Renal uptake can be reduced by coinfusion of basic amino acids or polypeptides. However, high doses of basic amino acids can induce severe side effects. It was reported that the infusion of gelatin-based plasma expanders resulted in increased low-molecular-weight proteinuria, suggesting that these plasma expanders interfere with the tubular reabsorption of peptides and proteins. In the present study, we analyzed the effects of several plasma expanders on the renal uptake of 111In-octreotide in rats and mice. METHODS: Wistar rats and BALB/c mice were injected with 0.5 or 0.1 mL of plasma expander, respectively. Thereafter, the animals received 111In-octreotide intravenously. Animals were killed at 20 h after the injection of the radiopharmaceutical. Organs were dissected, and the amount of radioactivity in the organs and tissues was measured. RESULTS: The administration of 20 mg of Gelofusine in rats or 4 mg in mice was as effective in reducing the renal uptake of 111In-octreotide as the administration of 80 or 20 mg of lysine in rats or mice, respectively, without reducing 111In-octreotide uptake in receptor-positive organs. Plasma expanders based on starch or dextran had no effect on the renal uptake of 111In-octreotide. CONCLUSION: The gelatin-based plasma expander Gelofusine significantly reduced the kidney uptake of 111In-octreotide as effectively as did lysine. Because Gelofusine is a well-known and generally used blood volume substitute that can be applied safely without the induction of toxicity, evaluation of this compound for its potential to reduce the kidney uptake of radiolabeled peptides in patients is warranted.     

[<Superscript>99m</Superscript>Tc]Demotate,a new <Superscript>99m</Superscript>Tc-based [Tyr<Superscript>3</Superscript>]octreotate analogue for the detection of somatostatin receptor-positive tumours: synthesis and preclinical results

Demotate is a new tetraamine-functionalised [Tyr3]octreotate derivative that binds technetium-99m with a high efficiency under mild conditions. The resulting radioligand, [99mTc]Demotate, forms in a high purity and is stable for at least 6 h after labelling. The affinity of the unlabelled peptide for somatostatin receptors is high (IC(50)=0.13 n M) and comparable to that of [Tyr3]octreotate or [Tyr3]octreotide, as demonstrated by competition binding experiments in rat brain cortex or AR42J cell membrane preparations. An equally very high affinity ( K(d)=0.07 n M) was exhibited by [99mTc/99gTc]Demotate during saturation binding experiments using rat brain cortex membrane homogenates. The radioligand resisted hydrolytic degradation in mouse plasma and was excreted intact in mouse urine. In vivo, [99mTc]Demotate cleared very rapidly from non-target tissues into the bladder via the kidneys, while radioactivity uptake in target organs was very high. In mice bearing the experimental AR42J tumour, [99mTc]Demotate demonstrated a very high tumour uptake at 1 h p.i. (25%ID/g) that remained high (20%ID/g) at 4 h p.i. This uptake could be effectively blocked by co-injection of a high dose of [Tyr3]octreotate together with the radioligand. High-quality planar and single-photon emission tomographic images were acquired 1 h after injection of [99mTc]Demotate in tumour-bearing mice, illustrating the excellent properties of this agent for somatostatin receptor tumour imaging.     

Tumour uptake of the radiolabelled somatostatin analogue [DOTA0, TYR3]octreotide is dependent on the peptide amount.

Radiolabelled tumour receptor-binding peptides can be used for in vivo scintigraphic imaging. Recently, the somatostatin analogue [Tyr3]octreotide (D-Phe-c(Cys-Tyr-D-Trp-Lys-Thr-Cys)-Thr(ol)) was derivatized with the chelator DOTA (tetra-azacyclododecane-tetra-acetic acid), enabling stable radiolabelling with both the high-energy beta particle-emitter yttrium-90 and the Auger electron-emitter indium-111. The thus produced radiolabelled compounds are promising for peptide receptor radionuclide therapy. Our previous in vitro and in vivo (rat) experiments with these radiolabelled compounds showed favourable binding and biodistribution characteristics with high uptake and retention in the target organs. We also demonstrated receptor-specific, time- and temperature-dependent internalization of radiolabelled [DOTA0,Tyr3]octreotide in somatostatin receptor subtype 2 (sst2)-positive rat pancreatic tumour cell lines. In this study we have investigated the effects of differences in the amount of injected peptide on tissue distribution of 111In-labelled [DOTA0, Tyr3]octreotide in normal, i.e. non-tumour-bearing, and CA20948 tumour-bearing rats. This was done in order to find the amount of peptide at which the highest uptake in target tissues is achieved, and thereby to increase the potential of radionuclide therapy while simultaneously ensuring the lowest possible radiotoxicity in normal organs. Uptake of radiolabelled [DOTA0,Tyr3]octreotide in sst2-positive organs showed different bell-shaped functions of the amount of injected peptide, being highest at 0.05 (adrenals), 0.05-0. 1 (pituitary and stomach) and 0.25 (pancreas) microg. Uptake in the tumour was highest at 0.5 microg injected peptide. The highest uptake was found at peptide amounts that were lower than those reported for [111In-DTPA0]octreotide ((D-Phe-c(Cys-Phe-D-Trp-Lys-Thr-Cys)-Thr(ol), DTPA = diethylene-triamine-penta-acetic acid), consistent with the higher receptor affinity of the first compound. Our observations of mass-dependent differences in uptake of radiolabelled [DOTA0, Tyr3]octreotide, being the resultant of a positive effect of increasing amounts of peptide on, for example, receptor clustering and a negative effect of receptor saturation, are of consequence for rat radionuclide therapy studies with radiolabelled peptides and may also be of consequence for human radionuclide therapy studies with this compound.     

Somatostatin receptor scintigraphy using [111In-DTPA0]RC-160 in humans: a comparison with [111In-DTPA0]octreotide

Somatostatin receptor-positive lesions can be visualized by scintigraphy using [¹¹¹In-DTPA⁰]octreotide. Recently, there have been reports of differences in receptor binding between somatostatin receptor subtypes and between somatostatin analogues, such as RC-160 and octreotide, as well as of differences in internalization between the somatostatin receptor subtypes. The possibility that certain somatostatin receptor-positive tissues and tumours which do not bind octreotide may bind and internalize RC-160 would open new scintigraphic or radiotherapeutic applications of radiolabelled RC-160. We investigated the metabolism and tissue distribution of [¹¹¹In-DTPA⁰]RC-160 in comparison with [¹¹¹In-DTPA⁰]octreotide in four patients after injection of 250 MBq (10 μg) of these radiopharmaceuticals. Patient 1 had a metastatic follicular thyroid carcinoma, patient 2 a metastatic medullary thyroid carcinoma, patient 3 tuberculosis and patient 4 an insulinoma. The plasma clearance of the [¹¹¹In-DTPA⁰]RC-160 was slower than that of [¹¹¹In-DTPA⁰]octreotide, with 5% and 2%, respectively, of the initial plasma radioactivity remaining at 10 h p.i. The urinary excretion of [¹¹¹In-DTPA⁰]RC-160 was initially also slower than that of [¹¹¹In-DTPA⁰]octreotide, but the cumulative excretion of radioactivity was not significantly different at 48 h p.i. Approximately 80% of injected radioactivity was cleared in the urine, while in one patient 20% of the injected dose was recovered in the faeces. The slower clearance of [¹¹¹In-DTPA⁰]RC-160 resulted in a higher background in all organs studied i.e. liver, spleen, kidneys and lungs, at 24 h p.i. Although the target to background ratio with [¹¹¹In-DTPA⁰]octreotide was higher, no differences were found between the two analogues with regard to their sensitivity in detecting lesions in these four patients. We conclude that although only four subjects were studied, [¹¹¹In-DTPA⁰]RC-160 does not appear to have additional value for scintigraphy and is associated with higher background activity. Received 20 October and in revised form 31 October 1997     

Optimising conditions for radiolabelling of DOTA-peptides with <Superscript>90</Superscript>Y, <Superscript>111</Superscript>In and <Superscript>177</Superscript>Lu at high specific activities

DOTA-conjugated peptides, such as [DOTA(0),Tyr(3)]octreotide (DOTATOC) and [DOTA(0),Tyr(3)]octreotate (DOTA-tate), can be labelled with radionuclides such as (90)Y, (111)In and (177)Lu. These radiolabelled somatostatin analogues are used for peptide receptor radionuclide therapy (PRRT). Radioligands for PRRT require high specific activities. However, although these radionuclides are produced without addition of carrier, contaminants are introduced during production and as decay products. In this study, parameters influencing the kinetics of labelling of DOTA-peptides were investigated and conditions were optimised to obtain the highest achievable specific activity. The effects of contaminants were systematically investigated, concentration dependently, in a test model mimicking conditions for labelling with minimal molar excess of DOTA-peptides over radionuclide. Kinetics of labelling of DOTA-peptides were optimal at pH 4-4.5; pH <4 strongly slowed down the kinetics. Above pH 5, reaction kinetics varied owing to the formation of radionuclide hydroxides. Labelling with (90)Y and (177)Lu was completed after 20 min at 80 degrees C, while labelling with (111)In was completed after 30 min at 100 degrees C. The effects of contaminants were systematically categorised, e.g. Cd(2+) is the target and decay product of (111)In, and it was found to be a strong competitor with (111)In for incorporation in DOTA. In contrast, Zr(4+) and Hf(4+), decay products of (90)Y and (177)Lu, respectively, did not interfere with the incorporation of these radionuclides. The following conclusions are drawn: (a) DOTA-peptides can be radiolabelled at high specific activity; (b) reaction kinetics differ for each radionuclide; and (c) reactions can be hampered by contaminants, such as target material and decay products.     

Indium-111 octreotide scintigraphy in patients with bone tumours of the extremities

Radiolabelled somatostatin analogues are of potential value in the imaging of somatostatin receptor-positive tumours. Recently, somatostatin receptors have been demonstrated in the osteoblast precursor cells. In this preliminary study, we evaluated the uptake characteristics of indium-111 octreotide in two benign and two malignant bone tumours. Tracer accumulation was observed in all four cases, and overall lesion to background ratio (mean±SD) was 2.74±0.84 and 2.98±1.49 at 4 h and 24 h, respectively. There was no clear relationship between I¹¹¹In-octreotide accumulation and the benign or malignant nature of the tumour. In one patient, tracer uptake was inhibited by unlabelled octreotide administration. These results suggest that¹¹¹In-octreotide can be taken up by benign and malignant bone tumours. The inhibition of tumour uptake by treatment with cold octreotide supports the concept that specific uptake mechanisms are responsible for¹¹¹In-octreotide deposition by bone tumours.     

A new radiolabelled somatostatin analogue [111In-DTPA-D-Phe1]RC-160: preparation,biological activity,receptor scintigraphy in rats and comparison with [111In-DTPA-D-Phe1]octreotide

We have evaluated the potential usefulness of indium-111 labelled [DTPA-D-Phe¹]RC-160, derived from the octapeptide somatostatin analogue RC-160, as a radiopharmaceutical for the in vivo detection of somatostatin receptor-positive tumours. For this purpose ¹¹¹In-and ¹¹¹In-labelled [DTPA-D-Phe¹]RC-160 was tested for its biological activity, and applied for somatostatin receptor scintigraphy in vivo to rats bearing the transplantable rat pancreatic tumour CA20948, which expresses somatostatin receptors. We previously described the development of the ¹¹¹In-labelled somatostatin analogue [DTPA-D-Phe¹]octreotide and its use in the in vivo visualization of somatostatin receptor-positive tumours in rats and in humans. Like [¹¹¹In-DTPA-D-Phe¹]octreotide, [¹¹¹In-DTPA-D-Phe¹]RC-160 showed uptake in and specific binding in vivo to somatostatin receptor-positive organs and tumours, and the tumours were clearly visualized by gamma camera scintigraphy. However, as compared to [¹¹¹In-DTPA-D-Phe¹]octreotide, blood radioactivity (background) was higher, resulting in a lower tumour to blood (background) ratio. Using this animal model we therefore conclude that [¹¹¹In-DTPA-DPhe¹]RC-160 has no advantage over [¹¹¹In-DTPA-DPhe¹]octreotide as a radiopharmaceutical in the visualization of somatostatin receptors which bind both analogues. However, recent reports suggest the existence of different somatostatin receptor subtypes on some human cancers, which differentially bind RC-160 and not octreotide. These tumours include cancers of the breast, ovary, exocrine pancreas, prostate and colon. [¹¹¹In-DTPA-D-Phe¹]RC-160 might be of interest for future use in such cancer patients as a radiopharmaceutical for imaging somatostatin receptor-positive tumours, which do not bind octreotide.     

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.     

Evaluation of [99mTc/EDDA/HYNIC0]octreotide derivatives compared with [111In-DOTA0,Tyr3, Thr8]octreotide and [111In-DTPA0]octreotide: does tumor or pancreas uptake correlate with the rate of internalization?

Radiolabeled somatostatin analogs are important tools for the in vivo localization and targeted radionuclide therapy of somatostatin receptor-positive tumors. The aim of this study was to compare 3 somatostatin analogs designed for the labeling with (99m)Tc (where HYNIC is 6-hydrazinopyridine-3-carboxylic acid): 6-hydrazinopyridine-3-carboxylic acid(0)-octreotide (HYNIC-OC/(99m)Tc-(1)), [HYNIC(0),Tyr(3)]octreotide (HYNIC-TOC/(99m)Tc-(2)), and [HYNIC(0),Tyr(3),Thr(8)]octreotide (HYNIC-TATE/(99m)Tc-(3)), using ethylenediamine-N,N'-diacetic acid (EDDA) as a coligand. In addition, we compared the (99m)Tc-labeled peptides [(111)In-diethylenetriaminepentaacetic acid(0)]octreotide ([(111)In-DTPA]-OC) and [(111)In-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid(0),Tyr(3),Thr(8)]octreotide ([(111)In-DOTA]-TATE) with regard to the rate of internalization and the biodistribution in AR4-2J (expressing the somatostatin receptor subtype 2) tumor-bearing rats. The main attention was directed toward a potential correlation between the rate of internalization and the tumor or pancreas uptake. METHODS: Synthesis was performed on solid phase using a standard Fmoc strategy. Internalization was studied in cell culture (AR4-2J) and biodistribution was studied using a Lewis rat tumor model (AR4-2J). RESULTS: The 5 radiopeptides showed a specific internalization into AR4-2J cells in culture (as shown by blocking experiments). The rate of internalization of the 5 radiopeptides differed significantly according to the following order: (99m)Tc-(1) approximately = [(111)In-DTPA]-OC < (99m)Tc-(2) < (99m)Tc-(3) approximately = [(111)In-DOTA]-TATE. All radiopeptides displayed a rapid blood clearance and a fast clearance from all somatostatin receptor-negative tissues predominantly via the kidneys. A receptor-specific uptake of radioactivity was observed for all compounds in somatostatin receptor-positive organs such as the pancreas, the adrenals, and the stomach. After 4 h, the uptake in the AR4-2J tumor was comparable for (99m)Tc-(2) (3.85 +/- 1.0 injected dose per gram tissue (%ID/g)), (99m)Tc-(3) (3.99 +/- 0.58%ID/g), and [(111)In-DOTA]-TATE (4.12 +/- 0.74%ID/g) but much lower for [(111)In-DTPA]-OC (0.99 +/- 0.08%ID/g) and (99m)Tc-(1) (0.70 +/- 0.13%ID/g). The specificity was determined by blocking experiments using a large excess of [Tyr(3)]octreotide. (99m)Tc-(3) displayed the highest tumor-to-kidney ratio (2.5:1), followed by (99m)Tc(2) (1.9:1) and [(111)In-DOTA]-TATE (1.7:1). CONCLUSION: These data show that the 5 radiopeptides are specific radioligands for the somatostatin receptor subtype 2. The rate of internalization correlates with the uptake in the tumor (R(2) = 0.75; P = 0.026) and pancreas (R(2) = 0.98; P = 7.4.10(-5)). [Tyr(3),Thr(8)]octreotide derivatives show superiority over the corresponding octreotide and [Tyr(3)]octreotide derivatives, indicating that [(111)In-DOTA]-TATE and [(99m)Tc/EDDA/HYNIC]-TATE are suitable candidates for clinical studies.     

Comparison of [177Lu-DOTA0,Tyr3]octreotate and [177Lu-DOTA0,Tyr3]octreotide: which peptide is preferable for PRRT?

Purpose Patients with somatostatin receptor subtype 2-positive metastasised neuroendocrine tumours can be treated with [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotide (¹⁷⁷Lu-DOTATOC) and [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate (¹⁷⁷Lu-DOTATATE), to see which peptide should be preferred for PRRT with ¹⁷⁷Lu.Methods In the same patients, 3,700 MBq ¹⁷⁷Lu-DOTATOC and 3,700 MBq ¹⁷⁷Lu-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 ¹⁷⁷Lu-DOTATATE (p=0.016 in each case). Comparing ¹⁷⁷Lu-DOTATATE with ¹⁷⁷Lu-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 ¹⁷⁷Lu-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 ¹⁷⁷Lu-DOTATATE was comparable to that after ¹⁷⁷Lu-DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for ¹⁷⁷Lu-DOTATOC.Conclusion ¹⁷⁷Lu-DOTATATE had a longer tumour residence time than ¹⁷⁷Lu-DOTATOC. Despite a longer residence time in kidneys after ¹⁷⁷Lu-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.     

Bone marrow dosimetry in peptide receptor radionuclide therapy with [177Lu-DOTA0,Tyr3]octreotate

Purpose  Adequate dosimetry is mandatory for effective and safe peptide receptor radionuclide therapy (PRRT). Besides the kidneys, the bone marrow is a potentially dose-limiting organ. The radiation dose to the bone marrow is usually calculated according to the MIRD scheme, where the accumulated activity in the bone marrow is calculated from the accumulated radioactivity of the radiopharmaceutical in the blood. This may underestimate the absorbed dose since stem cells express somatostatin receptors. We verified the blood-based method by comparing the activity in the blood with the radioactivity in bone marrow aspirates. Also, we evaluated the absorbed cross-dose from the source organs (liver, spleen, kidneys and blood), tumours and the so-called “remainder of the body” to the bone marrow. Methods  Bone marrow aspirates were drawn in 15 patients after treatment with [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate. Radioactivity in the bone marrow was compared with radioactivity in the blood drawn simultaneously. The nucleated cell fraction was isolated from the bone marrow aspirate and radioactivity was measured. The absorbed dose to the bone marrow was calculated. The results were correlated to the change in platelet counts 6 weeks after treatment. Results  A strong linear correlation and high agreement between the measured radioactivities in the bone marrow aspirates and in the blood was found (r=0.914, p<0.001). No correlation between the calculated absorbed dose in the bone marrow and the change in platelets was found. There was a considerable contribution from other organs and the remainder of the body to the bone marrow absorbed dose. Conclusion  (1) After PRRT with [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate, the radioactivity concentration in the bone marrow is identical to that in the blood; (2) There is no significant binding of the radiopharmaceutical to bone marrow precursor stem cells; (3) The contribution of the cross dose from source organs and tumours to the bone marrow dose is significant; and (4) There is considerable variation in bone marrow absorbed dose between patients. These findings imply that for individual dose optimization, individual calculation of the bone marrow absorbed dose is necessary.     

The addition of DTPA to [<Superscript>177</Superscript>Lu-DOTA<Superscript>0</Superscript>,Tyr<Superscript>3</Superscript>]octreotate prior to administration reduces rat skeleton uptake of radioactivity

Peptide receptor-targeted radionuclide therapy is nowadays also being performed with DOTA-conjugated peptides, such as [DOTA(0),Tyr(3)]octreotate, labelled with radionuclides like (177)Lu. The incorporation of (177)Lu is typically >/=99.5%; however, since a total patient dose can be as high as 800 mCi, the amount of free (177)Lu(3+) (= non-DOTA-incorporated) can be substantial. Free (177)Lu(3+) accumulates in bone with unwanted irradiation of bone marrow as a consequence. (177)Lu-DTPA is reported to be stable in serum in vitro, and in vivo it has rapid renal excretion. Transforming free Lu(3+) to Lu-DTPA might reroute this fraction from accumulation in bone to renal clearance. We therefore investigated: (a) the biodistribution in rats of (177)LuCl(3), [(177)Lu-DOTA(0),Tyr(3)]octreotate and (177)Lu-DTPA; (b) the possibilities of complexing the free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate to (177)Lu-DTPA prior to intravenous injection; and (c) the effects of free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate, in the presence and absence of DTPA, on the biodistribution in rats. (177)LuCl(3) had high skeletal uptake (i.e. 5% ID per gram femur, with localization mainly in the epiphyseal plates) and a 24-h total body retention of 80% injected dose (ID). [(177)Lu-DOTA(0),Tyr(3)]octreotate had high and specific uptake in somatostatin receptor-positive tissues, and 24-h total body retention of 19% ID. (177)Lu-DTPA had rapid renal clearance, and 24-h total body retention of 4% ID. Free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate could be complexed to (177)Lu-DTPA. Accumulation of (177)Lu in femur, blood, liver and spleen showed a dose relation to the amount of free (177)Lu(3+), while these accumulations could be normalized by the addition of DTPA. After labelling [DOTA(0),Tyr(3)]octreotate with (177)Lu the addition of DTPA prior to intravenous administration of [(177)Lu-DOTA(0),Tyr(3)]octreotate is strongly recommended.     

Amifostine protects rat kidneys during peptide receptor radionuclide therapy with [<Superscript>177</Superscript>Lu-DOTA<Superscript>0</Superscript>,Tyr<Superscript>3</Superscript>]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 [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate. Methods Male Lewis rats were injected with 278 or 555 MBq [¹⁷⁷Lu-DOTA⁰,Tyr³]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 ^99mTc-dimercaptosuccinic acid (DMSA), a measure of tubular function. Results Treatment with 555 MBq [¹⁷⁷Lu-DOTA⁰,Tyr³]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 [¹⁷⁷Lu-DOTA⁰,Tyr³]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 ^99mTc-DMSA SPECT scintigrams at 130 days after [¹⁷⁷Lu-DOTA⁰,Tyr³]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 [¹⁷⁷Lu-DOTA⁰,Tyr³]octreotate. Besides lysine, amifostine might be used in clinical PRRT as well as to maximise anti-tumour efficacy.