Willem H. Bakker

Radiolabeled Somatostatin Analog [177Lu-DOTA0,Tyr3]Octreotate in Patients With Endocrine Gastroenteropancreatic Tumors

PURPOSE There are few treatment options for patients with metastasized or inoperable endocrine gastroenteropancreatic (GEP) tumors. Chemotherapy can be effective, but the response is usually less than 1 year. Here, we present the results of treatment with a radiolabeled somatostatin analog, [177Lu-DOTA0,Tyr3]octreotate (177Lu-octreotate). PATIENTS AND METHODS One hundred thirty-one patients with somatostatin receptor-positive tumors were treated with up to a cumulative dose of 600 to 800 mCi (22.2 to 29.6 GBq) of 177Lu-octreotate. RESULTS One patient developed renal insufficiency, and another patient developed hepatorenal syndrome. Creatinine clearance did not change significantly in the other patients. WHO hematologic toxicity grade 3 or 4 occurred after less than 2% of the administrations. We observed complete remission in three patients (2%), partial remission in 32 patients (26%), minor response (tumor diameter decrease of 25% to 50%) in 24 patients (19%), stable disease (SD) in 44 patients (35%), and progressive disease (PD) in 22 patients (18%). Higher remission rates were positively correlated with high uptake on pretherapy somatostatin receptor imaging and a limited number of liver metastases, whereas PD was significantly more frequent in patients with a low performance score and extensive disease. Median time to progression in 103 patients who either had SD or tumor regression was more than 36 months. CONCLUSION Treatment with 177Lu-octreotate results in tumor remission in a high percentage of patients with GEP tumors. Serious side effects are rare. The median time to progression compares favorably with chemotherapy. Results are better in patients with a limited tumor load. Therefore, early treatment, even in patients who have no PD, may be better.

LOCALISATION OF ENDOCRINE-RELATED TUMOURS WITH RADIOIODINATED ANALOGUE OF SOMATOSTATIN

Various endocrine-related tumours contain large numbers of high-affinity somatostatin receptors. 123I-labelled tyr-3-octreotide (tyr-3-SMS 201-995, a synthetic derivative of somatostatin) was used to localise such tumours in vivo with a gamma-camera. Positive scans were obtained for two meningiomas, two gastrinomas, and one carcinoid; negative scans were obtained for one insulinoma (in which unlabelled octreotide had no effect on insulin levels), one phaeochromocytoma, one adrenal carcinoma (octreotide had no effect on cortisol levels), and three medullary thyroid carcinomas (octreotide had no effect on calcitonin levels). Thus radioiodinated tyr-3-octreotide can label somatostatin receptors in endocrine-related tumours in vivo and can therefore be used for tumour localisation.

[111In-DTPA-D-Phe1]-octreotide, a potential radiopharmaceutical for imaging of somatostatin receptor-positive tumors: synthesis, radiolabeling and in vitro validation.

Somatostatin receptor-positive human tumors can be detected using radioiodinated analogues of somatostatin, both in vitro and in vivo. [123I-Tyr3]-octreotide has been successfully used in the visualization of somatostatin receptor-positive tumors by gamma camera scintigraphy, but this radiopharmaceutical has some major drawbacks, which can be overcome with other radionuclides such as 111In. As starting material for a potentially convenient radiopharmaceutical, a diethylenetriaminopentaacetic acid (DTPA) conjugated derivative of octreotide (SMS 201-995) was prepared. This peptide, [DTPA-D-Phe1]-octreotide (SDZ 215-811) binds more than 95% of added 111In in an easy, single-step labeling procedure without necessity of further purification. The specific somatostatin-like biologic effect of these analogues was proven by the inhibition of growth hormone secretion by cultured rat pituitary cells in a dose-dependent fashion by octreotide, [DTPA-D-Phe1]-octreotide and non-radioactive [115In-DTPA-D-Phe1]-octreotide. The binding of [111In-DTPA-D-Phe1]-octreotide to rat brain cortex membranes proved to be displaced similarly by natural somatostatin as well as by octreotide, suggesting specific binding of [111In-DTPA-D-Phe1]-octreotide to somatostatin receptors. The binding of the indium-labeled compound showed a somewhat lower affinity when compared with the iodinated [Tyr3]-octreotide, but indium-labeled [DTPA-D-Phe1]-octreotide still binds with nanomolar affinity. In conjunction with in vivo studies, these results suggest that [111In-DTPA-D-Phe1]-octreotide is a promising radiopharmaceutical for scintigraphic imaging of somatostatin receptor-positive tumors.

Yttrium-90 and indium-111 labelling, receptor binding and biodistribution of [DOTA0,d-Phe1,Tyr3]octreotide, a promising somatostatin analogue for radionuclide therapy

In vitro octreotide receptor binding of [111In-DOTA0,d-Phe1,Tyr3]octreotide (111In-DOTATOC) and the in vivo metabolism of90Y or111In-labelled DOTATOC were investigated in rats in comparison with [111In-DTPA0]octreotide [111In-DTPAOC).111In-DOTATOC was found to have an affinity similar to octreotide itself for the octreotide receptor in rat cerebral cortex microsomes. Twenty-four hours after injection of90Y or111In-labelled DOTATOC, uptake of radioactivity in the octreotide receptor-expressing tissues pancreas, pituitary, adrenals and tumour was a factor of 2–6 that after injection of111In-DTPAOC. Uptake of labelled DOTATOC in pituitary, pancreas, adrenals and tumour was almost completely blocked by pretreatment with 0.5 mg unlabelled octreotide, indicating specific binding to the octreotide receptors. These findings strongly indicate that90Y-DOTATOC is a promising radiopharmaceutical for radiotherapy and that111In-DOTATOC is of potential value for diagnosis of patients with octreotide receptor-positive lesions, such as most neuroendocrine tumours.

[177LU-DOTA0, TYR3] OCTREOTATE FOR SOMATOSTATIN RECEPTOR-TARGETED RADIONUCLIDE THERAPY

Receptor‐targeted scintigraphy using radiolabeled somatostatin analogs such as octreotate is being used with great success to demonstrate the in vivo presence of somatostatin receptors on various tumors. A new and promising application for these analogs is radionuclide therapy. Radionuclides suitable for this application include the Auger electron‐emitter 111In and the β‐emitters 90Y (high energy) and 177Lu (low energy). We investigated [DOTA0,Tyr3]octreotate, labeled with the lanthanide 177Lu, in biodistribution and radionuclide therapy experiments using male Lewis rats bearing the somatostatin receptor‐positive rat CA20948 pancreatic tumor. Biodistribution studies in Lewis rats showed the highest uptake in the rat pancreatic CA20948 tumor and sst2‐positive organs, which include the adrenals, pituitary and pancreas, of [177Lu‐DOTA0,Tyr3]octreotate in comparison with 88Y‐ and 111In‐labeled analogs. Kidney uptake of [177Lu‐DOTA0,Tyr3]octreotate could be reduced by approximately 40% by co‐injection of 400 mg/kg D‐lysine. In radionuclide therapy studies, a 100% cure rate was achieved in the groups of rats bearing small (≤1 cm2) CA20948 tumors after 2 doses of 277.5 MBq or after a single dose of 555 MBq [177Lu‐DOTA0,Tyr3]octreotate. A cure rate of 75% was achieved after a single administration of 277.5 MBq. In rats bearing larger (≥1 cm2) tumors, 40% and 50% cure rates were achieved in the groups that received 1 or 2 277.5 MBq injections of [177Lu‐DOTA0,Tyr3]octreotate, respectively. After therapy with [177Lu‐DOTA0,Tyr3]octreotide in rats bearing small tumors, these data were 40% cure after 1 injection with 277.5 MBq and 60% cure after 2 repeated injections. In conclusion, [177Lu‐DOTA0,Tyr3]octreotate has demonstrated excellent results in radionuclide therapy studies in rats, especially in animals bearing smaller tumors. This candidate molecule shows great promise for radionuclide therapy in patients with sst2‐expressing tumors.

In vivo application of [111In-DTPA-D-Phe1]-octreotide for detection of somatostatin receptor-positive tumors in rats.

Radioiodinated somatostatin analogues are useful ligands for the in vitro and in vivo detection of somatostatin receptors. [111In-DTPA-D-Phe1]-octreotide, a somatostatin analogue labeled with a different radionuclide, also binds specifically to somatostatin receptors in vitro. In this study we investigated its in vivo application in the visualization of somatostatin receptor-positive tumors in rats. The distribution of the radiopharmaceutical was investigated after intravenous injection in normal rats and in rats bearing the somatostatin receptor-positive rat pancreatic carcinoma CA 20948. After injection the radiopharmaceutical was rapidly cleared (50% decrease in maximal blood radioactivity in 4 min), predominantly by the kidneys. Excreted radioactivity was mainly in the form of the intact radiopharmaceutical. Ex vivo autoradiographic studies showed that specific accumulation of radioactivity occurred in somatostatin receptor-containing tissue (anterior pituitary gland). However, in contrast to the adrenals and pituitary, the tracer accumulation in the kidneys was not mediated by somatostatin receptors. Increasing radioactivity over the somatostatin receptor-positive tumors was measured rapidly after injection and the tumors were clearly visualized by gamma camera scintigraphy. In rats pretreated with 1 mg octreotide accumulation of [111In-DTPA-D-Phe1]-octreotide in the tumors was prevented. Because of its relatively long effective half-life, [111In-DTPA-D-Phe1]-octreotide is a radionuclide-coupled somatostatin analogue which can be used to visualize somatostatin receptor-bearing tumors efficiently after 24 hr, when interfering background radioactivity is minimized by renal clearance. This is an advantage over the previously used [123I-Tyr3]-octreotide which has a shorter effective half-life and shows high abdominal interference due to its hepato-biliary clearance. Therefore, [111In-DTPA-D-Phe1]-octreotide seems a better alternative for scintigraphic imaging of somatostatin receptor-bearing tumors.

Somatostatin analogue scintigraphy in carcinoid tumours

Scintigraphy with iodine-123 or indium-111 labelled somatostatin analogue (octreotide) was performed in 52 patients diagnosed as, suspected of, or at risk of having carcinoid tumours. In 32 of 37 (86%) patients in whom histologically proven carcinoids were still present, known tumour sites were visualized. Using 123I-coupled octreotide, 24 of 40 (60%) known extrahepatic sites were visualized, whereas all of 12 (100%) extrahepatic lesions were visualized after injection of 111In-coupled octreotide. Known liver metastases were not distinctly visualized with octreotide scintigraphy in 12 of 24 patients. In all but two of these cases, an even distribution of radioactivity in the liver was observed. This is most probably due to the fact that these liver metastases accumulated about as much radioactivity as does normal liver tissue. Previously unsuspected localizations or sites not recognized with other imaging techniques were found in 20 of the 37 patients. In 3 of 11 patients who were thought to have been surgically cured, and in 4 of 4 patients who were suspected of having carcinoids, octreotide scintigraphy showed abnormal accumulation of radioactivity. Histological or radiological evidence that additional sites noticed on octreotide scintigrams indeed represented tumour tissue was obtained in ten patients. Visualization of the carcinoids did not depend on the site of the tumour or on the presence or absence of hormonal hypersecretion, as measured by urinary 5-hydroxyindoleacetic acid and serum α-subunit concentrations. Apart from its use for tumour localization, octreotide scintigraphy, in consequence of its ability to demonstrate somatostatin receptor positive tumours, could be used to select those patients with the carcinoid syndrome who are likely to respond favourably to octreotide treatment.

Somatostatin analogue scintigraphy in granulomatous diseases

Normal as well as activated lymphocytes and macrophages have previously been shown by radioreceptor analysis to express somatostatin receptors (SS-R). The somatostatin (SS) analogue [111In-DTPA-d-Phe1]octreotide (111In-octreotide) is already used successfully in the visualization of a variety of neuro-endocrine tumours and malignant lymphomas. In the present study 20 consecutive patients were investigated, 12 with sarcoidosis, one with both sarcoidosis and aspergillosis, four with tuberculosis and three with Wegeners granulomatosis. For in vivo SS-R imaging, total-body scintigraphy was performed 24 and 48 h after the administration of 111In-octreotide. Granuloma localizations could be visualized in all patients studied; additional sites were found in nine patients with sarcoidosis and in two patients with tuberculosis. In vitro autoradiography of fresh tissue biopsies, using the SS analogue [125I-Tyr3]octreotide, showed binding at sites that were microscopically identified as granulomatous inflammation. These observations demonstrate the expression of SS-R by human granulomas. This scintigraphy procedure may contribute to a more precise staging and evaluation of granulomatous diseases, but more importantly it may be a sensitive indicator of the efficacy of glucocorticoid and/or immunosuppressive therapy.

Internalization of radiolabelled [DTPA0]octreotide and [DOTA0,Tyr3]octreotide: peptides for somatostatin receptor-targeted scintigraphy and radionuclide therapy.

We compared the internalization of [90Y-DOTA0,Tyr3]octreotide and [111In-DOTA0,Tyr3]octreotide with that of [125I-Tyr3]octreotide and [111In-DTPA0]octreotide in the subtype 2 somatostatin receptor (sst2)-positive rat pancreatic tumour cell lines CA20948 and AR42J and in the somatostatin receptor-negative human anaplastic thyroid tumour cell line ARO. We demonstrated that [111In-DTPA0]octreotide, [90Y-DOTA0,Tyr3]octreotide and [111In-DOTA0,Tyr3]octreotide are internalized by a receptor-specific, time- and temperature-dependent process. The amount of [90Y-DOTA0,Tyr3]octreotide internalized was higher than that of [111In-DOTA0,Tyr3]octreotide and [111In-DTPA0]octreotide.

Pre-clinical comparison of [DTPA0] octreotide, [DTPA0,Tyr3] octreotide and [DOTA0,Tyr3] octreotide as carriers for somatostatin receptor-targeted scintigraphy and radionuclide therapy

We have evaluated the potential usefulness of radiolabelled [DTPA0,Tyr3]octreotide and [DOTA0,Tyr3]octreotide as radiopharmaceuticals for somatostatin receptor–targeted scintigraphy and radiotherapy. In vitro somatostatin receptor binding and in vivo metabolism in rats of the compounds were investigated in comparison with [111In‐DTPA0] octreotide. Comparing different peptide–chelator constructs, [DTPA0,Tyr3]octreotide and [DOTA0, Tyr3]octreotide were found to have a higher affinity than [DTPA0]octreotide for subtype 2 somatostatin receptors (sst2) in mouse AtT20 pituitary tumour cell membranes (all IC50 values obtained were in the low nanomolar range). In vivo studies in CA20948 tumor‐bearing Lewis rats revealed a significantly higher uptake of both 111In‐labelled [DOTA0,Tyr3]octreotide and [DTPA0,Tyr3]octreotide in sst2‐expressing tissues than after injection of [111In‐DTPA0]octreotide, showing that substitution of Tyr for Phe at position 3 in octreotide results in an increased affinity for its receptor and in a higher target tissue uptake. Uptake of 111In‐labelled [DTPA0]octreotide, [DTPA0,Tyr3]octreotide and [DOTA0,Tyr3]octreotide in pituitary, pancreas, adrenals and tumour was decreased to less than 7% of control by pre‐treatment with 0.5 mg unlabelled octreotide/rat, indicating specific binding to sst2. Comparing different radionuclides, [90Y‐DOTA0,Tyr3]octreotide had the highest uptake in sst2‐positive organs, followed by the [111In‐DOTA0,Tyr3]octreotide, whereas [DOTA0, 125I‐Try3]octreotide uptake was low compared to that of the other radiopharmaceuticals, when measured 24 hr after injection. Renal uptake of 111In‐labelled [DTPA0]octreotide, [DTPA0, Tyr3]octreotide and [DOTA0,Tyr3]octreotide was reduced over 50% by an i.v. injection of 400 mg/kg d‐lysine, whereas radioactivity in blood, pancreas and adrenals was not affected. Int. J. Cancer 75:406–411, 1998.