Improved quality of life in patients treated with Peptide radionuclides

Peptide receptor radionuclide therapy (PRRT) has recently been established as an important treatment modality for somatostatin receptor (SSTR)-positive tumors. The purpose of this study was to evaluate the clinical response, side-effects as well as the quality of life following ⁹⁰Y-DOTA-lanreotide (DOTALAN) and/or ⁹⁰Y-DOTA-Tyr ³-DPhe¹-octreotide (DOTATOC) therapy in patients with progressive metastatic disease during a 6-year follow-up period. Following dosimetric evaluation with ¹¹¹In-DOTALAN and ¹¹¹In-DOTATOC, 13 patients with estimated absorbed tumor doses of >5 Gy/GBq (carcinoid, n = 5; radioiodine-negative thyroid cancer, n = 4; gastrinoma, n = 1; insulinoma, n = 1; glucagonoma, n = 1; glomus jugularis tumor, n = 1) were assigned for PRRT. A dose of 925 MBq of ⁹⁰Y-DOTALAN (four patients) or 1.85–3.7 GBq of ⁹⁰Y-DOTATOC (10 patients) was administered intravenously and repeated every 4–8 weeks. Tumor dosimetry was performed prior to and under therapy, re-staging every 2–3 months. Pain intensity, Karnofsky score and general symptoms were evaluated in order to determine quality of life. Patients were followed until death. Altogether, 53 infusions of PRRT (1.85–14.1 GBq) were administered. After the first follow-up of 3 months of ⁹⁰Y-DOTALAN therapy, stable disease (SD) was observed in one patient and progressive disease (PD) in three patients. With ⁹⁰Y-DOTATOC therapy, SD was found in all 10 patients. During the re-evaluation period (4–27 months), one patient had to be shifted from ⁹⁰Y-DOTALAN to ⁹⁰Y-DOTATOC therapy due to reduced ¹¹¹In-DOTALAN uptake after 5.5 GBq. In the first 6 months after PRRT with DOTATOC, SD was found in nine of 10 patients and PD in one patient. Thereafter, SD was observed in two patients and PD in eight patients. Nine of 13 patients after PRRT with either DOTALAN or DOTATOC died. None of the patients had experienced severe acute hematological side-effects. Transient thrombocytopenia or lymphocytopenia was seen in 10 patients after 3.7 GBq, and a skin reaction in one patient. Total accumulated kidney dose ranged between 4 and 64 Gy, with reduced creatinine clearance in two patients. Pain relief was achieved in three of three patients after ~3.7 GBq ERT within 4–6 months. Appetite, weight, Karnofsky score and general well-being had improved in patients with SD during and after therapy. Based on the results of this study conducted on a small group of patients, we conclude that PRRT may offer an alternative treatment option for SSTR-positive tumors, with only mild transient side-effects and a marked improvement in the quality of life.

Experience with indium-111 and yttrium-90-labeled somatostatin analogs

The high level expression of somatostatin receptors (SSTR) on various tumor cells has provided the molecular basis for successful use of radiolabeled octreotide / lanreotide analogs as tumor tracers in nuclear medicine. Other (nontumoral) potential indications for SSTR scintigraphy are based on an increased lymphocyte binding at sites of inflammatory or immunologic diseases such as thyroid-associated ophthalmology. The vast majority of human tumors seem to over-express the one or the other of five distinct hSSTR subtype receptors. Whereas neuroendocrine tumors frequently overexpress hSSTR2, intestinal adenocarcinomas seem to overexpress more often hSSTR3 or hSSTR4, or both of these hSSTR. In contrast to In-DTPA-DPhe(1)-octreotide (OctreoScan(R)) which binds to hSSTR2 and 5 with high affinity (Kd 0.1-5 nM), to hSSTR3 with moderate affinity (K(d) 10-100 nM) and does not bind to hSSTR1 and hSSTR4, (111)In / (90)Y-DOTA-lanreotide was found to bind to hSSTR2, 3, 4, and 5 with high affinity, and to hSSTR1 with lower affinity (K(d) 200 nM). Based on its unique hSSTR binding profile, (111)In-DOTA-lanreotide was suggested to be a potential radioligand for tumor diagnosis, and (90)Y-DOTA-lanreotide suitable for receptor-mediated radionuclide therapy. As opposed to (111)In-DTPA-DPhe(1)-octreotide and (111)In-DOTA-DPhe(1)-Tyr(3)-octreotide, discrepancies in the scintigraphic results were seen in about one third of (neuroendocrine) tumor patients concerning both the tumor uptake as well as detection of tumor lesions. On a molecular level, these discrepancies seem to be based on a "higherrdquuo; high-affinity binding of (111)In-DOTA-DPhe(1)-Tyr(3)-octreotide to hSSTR2 (K(d) 0.1-1 nM). Other somatostatin analogs with divergent affinity to the five known hSSTR subtype receptors have also found their way into the clinics, such as (99m)Tc-depreotide (NeoSpect(R); NeoTect(R)). Most of the imaging results are reported for neuroendocrine tumors (octreotide analogs) or nonsmall cell lung cancer ((99m)Tc-depreotide), indicating high diagnostic cabability of this type of receptor tracers. Consequently to their use as receptor imaging agents, hSSTR recognizing radioligands have also been implemented for experimental receptor-targeted radionuclide therapy. Beneficial results were reported for high-dose treatment with (111)In-DTPA-DPhe(1)-octreotide, based on the emission of Auger electrons. The Phase IIa study "MAURITIUS" (Multicenter Analysis of a Universal Receptor Imaging and Treatment Initiative, a eUropean Study) showed in progressive cancer patients (therapy entry criteria) with a calculated tumor dose > 10 Gy / GBq (90)Y-DOTA-lanreotide, the proof-of-principle for treating tumor patients with peptide receptor imaging agents. In the "MAURITIUS" study, cummulative treatment doses up to 200 mCi (90)Y-DOTA-lanreotide were given as short-term infusion. Overall treatment results in 70 patients indicated stable tumor disease in 35% of patients and regressive tumor disease in 10% of tumor patients with different tumor entities expressing hSSTR. No acute or chronic severe hematological toxicity, change in renal or liver function parameters due to (90)Y-DOTA-lanreotide treatment, were reported. (90)Y-DOTA-DPhe(1)-Tyr(3)-octreotide may show a higher tumor uptake in neuroendocrine tumor lesions and may therefore be superior for treatment in patients with neuroendocrine tumors. However, there is only limited excess to long-term and survival data at present. Potential indications for (90Y-DOTA-lanreotide are radioiodine-negative thyroid cancer, hepatocellular cancer and lung cancer. Besides newer approaches and recent developments of 188)Re-labeled radioligands, no clinical results on the treatment response are yet available. In conclusion, several radioligands have been implemented on the basis of peptide receptor recognition throughout the last decade. A plentitude of preclinical data and clinical studies confirm their potential use in diagnosis as well as "proof-of-principle" for therapy of cancer patients. However, an optimal radiopeptide formulatioents. However, an optimal radiopeptide formulation does not yet exist for receptor-targeted radionuclide therapy. Ongoing developments may result in peptides more suitable for this kind of receptor-targeted radionuclide therapy.

Comparative somatostatin receptor scintigraphy using in-111-DOTA-lanreotide and in-111-DOTA-Tyr3-octreotide versus F-18-FDG-PET for evaluation of somatostatin receptor-mediated radionuclide therapy

BACKGROUND

Based on the high number of somatostatin (SST) receptors expressed by neuroendocrine tumors, long-acting SST analogs have been successfully used for tumor detection. New developments point to the potential use of these types of radioligands for tumor-specific radionuclide therapy.

PATIENTS AND METHODS

We have comparatively investigated the diagnostic capacity of the SST analog. 111In-DOTA-lanreotide (LAN), as opposed to 111ln-DOTA-DPhe1-Tyr3-octreotide (TOCT) in tumor patients. This article gives an overview of recent scintigraphic results compared to CT/MRI, 18F-FDG-PET, endoscopy and/or surgery in a threshold of 218 tumor patients.

RESULTS

As opposed to radiology, previously unknown tumor lesions were demonstrable by either SST radioligand in about one third of patients. In carcinoid patients, the SST scan sensitivity was 64% for LAN (18 of 28) and 87% (34 of 39) for TOCT, whereas the sensitivity was 100% in patients with (radioiodine-negative) thyroid cancer (17 of 17) for LAN and 95% for TOCT (20 of 21). Discordant scintigraphic results between LAN and TOCT (higher tumor uptake and/or visualisation of different lesions in the same patient) were also seen in patients with lymphoma, lung cancer and intestinal adenocarcinoma. In a direct comparison of both SST tracers in 38 tumor patients, LAN gave positive results in 35 of 38, TOCT in 36 of 38 and 18F-FDG-PET in 14 of 22 of the same patients. SST scan results obtained by both tracers were equivocal in 23 of 38 patients, but were better in 10 patients withTOCTand in 5 patients with LAN.

CONCLUSIONS

We conclude that both SST radioligands are suitable tracers for tumor imaging, but may give significantly different uptake results for different tumor types. Since the uptake is most important for tumor therapy, using either longacting SSTanalogs, and/or 90Y-labeled analogs, careful evaluation should be made prior to therapy.

New trends in peptide receptor radioligands

The high level expression of somatostatin receptors (SSTR) on various tumor cells has provided the molecular basis for successful use of radiolabeled octreotide/lanreotide analogs as tumor tracers in nuclear medicine. The vast majority of human tumors seem to overexpress the one or the other of five distinct hSSTR sub-type receptors. Whereas neuroendocrine tumors frequently overexpress hSSTR2, intestinal adenocarcinomas seem to over-express more often hSSTR3 or hSSTR4, or both of these hSSTR. In contrast to 111In-DTPA-DPhe1-octreotide (OCTREOSCAN) which binds to hSSTR2 and 5 with high affinity (Kd 0.1-5 nM), to hSSTR3 with moderate affinity (Kd 10-100 nM) and does not bind to hSSTR1 and hSSTR4, 111In/90Y-DOTA-lanreotide was found to bind to hSSTR2, 3, 4, and 5 with high affinity, and to hSSTR1 with lower affinity (Kd 200 nM). Based on its unique hSSTR binding profile, 111In-DOTA-lanreotide was suggested to be a potential radioligand for tumor diagnosis, and 90Y-DOTA-lanreotide suitable for receptor-mediated radionuclide therapy. As opposed to 111In-DTPA-DPhe1-octreotide and 111In-DOTA-DPhe1-Tyr3-octreotide, discrepancies in the scintigraphic results were seen in about one third of (neuroendocrine) tumor patients concerning both the tumor uptake as well as detection of tumor lesions. On a molecular level, these discrepancies seem to be based on a "higher" high-affinity binding of 111In-DOTA-DPhe1-Tyr3-octreotide to hSSTR2. Other somatostatin analogs with divergent affinity to the five known hSSTR subtype receptors have also found their way into the clinics, including 99mTc-HYNIC-octreotide or 99mTc-depreotide (NEOSPECT; NEOTECT). Most of the imaging results are reported for neuroendocrine tumors (octreotide analogs) or non-small cell lung cancer (99mTc-depreotide), indicating high diagnostic capability of this type of receptor tracers. Consequently to their use as receptor imaging agents, hSSTR recognizing radioligands have also been implemented for experimental receptor-targeted radionuclide therapy. The study "MAURITIUS" (MulticenterAnalysis of a Universal Receptor Imaging and Treatment Initiative, a eUropean Study), a Phase IIa study, showed in patients with a calculated tumor dose >10 Gy/GBq 90Y-DOTA-lanreotide, the proof-of-principle for treating tumor patients with receptor imaging agents. Overall treatment results in >60 patients indicated stable tumor disease in roughly 35% of patients and regressive disease in 15% of tumor patients with different tumor entities. No acute or chronic severe hematological toxicity, change in renal or liver function parameters due to 90Y-DOTA-lanreotide, was reported. 90In-DOTA-DPhe1-Tyr3-octreotide may show a higher tumor uptake in neuroendocrine tumor lesions and may therefore provide even better treatment results in tumor patients, but there is only limited excess to long-term and survival data at present. Besides newer approaches and recent developments of 188Re-labeled radioligands no clinical results on the treatment response is available yet. In conclusion, several radioligands have been implemented on the basis of peptide receptor recognition throughout the last decade. A plentitude of preclinical data and clinical studies confirm "proof-of-principle" for their use in diagnosis as well as therapy of cancer patients. However, an optimal radiopeptide formulation does not yet exist for receptor-targeted radionuclide therapy.

Value of peptide receptor scintigraphy using (123)I-vasoactive intestinal peptide and (111)In-DTPA-D-Phe1-octreotide in 194 carcinoid patients: Vienna University Experience, 1993 to 1998

PURPOSE

To report our experience with both (123)I-vasoactive intestinal peptide (VIP) and (111)In-DTPA-D-Phe(1)-octreotide for imaging to identify primary and metastatic tumor sites in carcinoid patients.

PATIENTS AND METHODS

One hundred ninety-four patients with a verified or clinically suspected diagnosis of a carcinoid tumor were injected with (111)In-DTPA-D-Phe(1)-OCT for imaging purposes, while 133 patients underwent scanning with both (123)I-VIP and (111)In-DTPA-D-Phe(1)-OCT in random order. Imaging results were compared with computed tomography scans, results of conventional ultrasound, endosonography, and endoscopy, and results of surgical exploration in case of inconclusive conventional imaging.

RESULTS

Primary or recurrent carcinoid tumors could be visualized with (111)In-DTPA-D-Phe(1)-OCT in 95 (91%) of 104 patients; metastatic sites were identified in 110 (95%) of 116 patients. In 11 (51%) of 21 patients with suggestive symptoms but without identified lesions by conventional imaging, focal tracer uptake located the carcinoid tumor. In addition, metastatic disease was demonstrated in three patients after resection. In a direct comparison in the 133 patients who underwent both imaging modalities, (111)In-DTPA-D-Phe(1)-OCT was found to be superior to (123)I-VIP, with 35 (93%) of 38 versus 32 (82%) of 38 scans being positive in primary or recurrent tumors, 58 (90%) of 65 versus 53 (82%) of 65 being positive in patients with metastatic sites, and seven (44%) of 16 versus four (25%) of 16 being positive in patients with symptoms but otherwise negative work-ups. Overall, additional lesions not seen on conventional imaging were imaged in 43 (41%) of 158 versus 25 (25%) of 103 scans with (111)In-DTPA-D-Phe(1)-OCT and (123)I-VIP, respectively.

CONCLUSION

Both peptide tracers have a high sensitivity for localizing tumor sites in patients with ascertained or suspected carcinoid tumors, with (111)In-DTPA-D-Phe(1)-OCT scintigraphy being more sensitive than (123)I-VIP receptor scanning. Both, however, had a higher diagnostic yield than conventional imaging, as verified by surgical intervention or long-term follow-up. The combination of both peptide receptor scans does not seem to further enhance diagnostic information.

New radiopharmaceuticals for receptor scintigraphy and radionuclide therapy

In vitro data have demonstrated a high amount of receptors for various hormones and peptides on malignant cells of neuroendocrine origin. Among these, binding sites for members of the SST-family (hSSTR1-5) are frequently found, and their expression has led to therapeutic and diagnostic attempts to specifically target these receptors. Receptor scintigraphy using radiolabeled peptide ligands has proven its effectiveness in clinical practice. In addition, initial results have indicated a clinical potential for receptor-targeted radiotherapy. Based on somatostatin (SST) receptor (R) recognition, the novel radiopharmaceuticals 111In/90Y-DOTA-lanreotide developed at the University of Vienna as well as 111In/90Y-DOTA-DPhe1-Tyr3-octreotide (NOVARTIS) both have provided promising data for diagnosis and treatment of hSSTR-positive tumors. SSTR scintigraphy using 111In-DTPA-DPhe1-octreotide has a high positive predictive value for the vast majority of neuroendocrine tumors and has gained its place in the diagnostic work-up as well as follow-up of patients. We have used 111In-DOTA-lanreotide scintigraphy in 166 patients since 1997 and have seen positive results in 93% of patients. In 42 patients with neuroendocrine tumors comparative data were obtained. As opposed to 111In-DTPA-DPhe1-octreotide and 111In-DOTA-DPhe1-Tyr3-octreotide, discrepancies in the scintigraphic results were seen in about one third of patients concerning both the tumor uptake as well as tumor lesion detection. Initial results both with 90Y-DOTA-lanreotide as well as 90Y-DOTA-DPhe1-Tyr3-octreotide has pointed out the clinical potential of radionuclide receptor-targeted radiotherapy. This new therapy could offer palliation and disease control at a reduced cost. The final peptide therapy strategy is most probably cheaper than conventional radiotherapies or prolonged chemotherapies. Overall, receptor-mediated radiotherapy with 90Y-DOTA-lanreotide/90Y-DOTA-DPhe1-Tyr3-octre otide might also be effective in patients refractory to conventional strategies.

DOTA-lanreotide: a novel somatostatin analog for tumor diagnosis and therapy

Long acting somatostatin-14 (SST) analogs are used clinically to inhibit tumor growth and proliferation of various tumor types via binding to specific receptors (R). We have developed a 111In-/90Y-labeled SST analog, DOTA-(D)betaNal1-lanreotide (DOTALAN), for tumor diagnosis and therapy. 111In-/90Y-DOTALAN bound with high affinity (dissociation constant, Kd, 1-12 nM) to a number of primary human tumors (n = 31) such as intestinal adenocarcinoma (n = 17; 150-4000 fmol/mg protein) or breast cancer (n = 4; 250-9000 fmol/mg protein). 111In-/90Y-DOTALAN exhibited a similar high binding affinity (Kd, 1-15 nM) for the human breast cancer cell lines T47D and ZR75-1, the prostate cancer cell lines PC3 and DU145, the colonic adenocarcinoma cell line HT29, the pancreatic adenocarcinoma cell line PANC1, and the melanoma cell line 518A2. When expressed in COS7 cells, 111In-DOTALAN bound with high affinity to hsst2 (Kd, 4.3 nM), hsst3 (Kd, 5.1 nM), hsst4 (Kd, 3.8 nM), and hsst5 (Kd, 10 nM) and with lower affinity to hsst1 (Kd, approximately 200 nM). The rank order of displacement of [125I]Tyr11-SST binding to hsst1 was: SST (IC50, 0.5 nM) >> DOTALAN (IC50, 154 nM) > lanreotide (LAN) approximate to Tyr3-octreotide (TOCT) approximate to DOTA-Tyr3-octreotide (DOTATOCT) approximate to DOTA-vapreotide (DOTAVAP; IC50, >1000 nM); that to hsst2 was: DOTATOCT approximate to TOCT approximate to DOTALAN approximate to SST approximately LAN approximate to DOTAVAP (IC50, 1.4 nM); that to hsst3 was: SST (IC50, 1.2 nM) > DOTALAN = LAN (IC50, 15 nM) approximate to TOCT (IC50, 20 nM) approximate to DOTAVAP (IC50, 28 nM) > DOTATOCT (IC50, 73 nM); that to hsst4 was: SST (IC50, 1.8 nM) approximate to DOTALAN (IC50, 2.5 nM) > LAN (IC50, 22 nM) >> DOTATOCT approximate to DOTAVAP approximate to TOCT (IC50, >500 nM); and that to hsst5 was: DOTALAN (IC50, 0.45 nM) > SST (IC50, 0.9 nM) > TOCT (IC50, 1.5 nM) > DOTAVAP (IC50, 5.4 nM) >> LAN (IC50, 21 nM) > DOTATOCT (IC50 260 nM). In Sprague Dawley rats (n = 10), 90Y-DOTALAN was rapidly cleared from the circulation and concentrated in hsst-positive tissues such as pancreas or pituitary. Taken together, our results indicate that 111In-/90Y-DOTALAN binds to a broad range of primary human tumors and tumor cell lines, probably via binding to hsst2-5. We conclude that this radiolabeled peptide can be used for hsst-mediated diagnosis (111In-DOTALAN) as well as systemic radiotherapy (90Y-DOTALAN) of human tumors.

Response to treatment with yttrium 90-DOTA-lanreotide of a patient with metastatic gastrinoma

1,4,7,10-tetraazacyclododecane-N,N',N",N'''-tetraacetic acid (DOTA)-lanreotide is a universal somatostatin (SST) receptor subtype ligand that binds to a large variety of human tumors. We report the case of a patient with metastatic gastrinoma who was treated with 90Y-DOTA-lanreotide. Before treatment, dosimetry with 111In-DOTA-lanreotide (150 MBq, 10 nmol) indicated a dose of 5.8 mGy/MBq for the recurrent abdominal gastrinoma, and a mean dose of approximately 1.0 mGy/MBq for liver metastases (i.e., 56 and approximately 10 mGy/MBq for 90Y-DOTA-lanreotide, respectively). After four infusions of 90Y-DOTA-lanreotide (each 1 GBq, approximately 30 nmol) over a 6-mo period, the 111In-DOTA-lanreotide scintigraphy of the liver had returned to a nearly normal condition and a remarkably decreased uptake by the recurrent gastrinoma was calculated (approximately 5 mGy/MBq for 90Y-DOTA-lanreotide). The imaging results were well-correlated with a 25% regression of the liver metastases as indicated by CT. Blood, urine and whole-body clearances of 111In-DOTA-lanreotide and 90Y-DOTA-lanreotide were very similar. The DOTA-lanreotide promises to be useful for functional tumor diagnosis (111In-DOTA-lanreotide) and receptor-mediated tumor radiotherapy (90Y-DOTA-lanreotide).

Indium-111-DOTA-lanreotide: biodistribution, safety and radiation absorbed dose in tumor patients

Imaging with radiolabeled somatostatin/vasoactive intestinal peptide analogs has recently been established for the localization diagnosis of a variety of human tumors including neuroendocrine tumors, intestinal adenocarcinomas and lymphomas. This study reports on the biodistribution, safety and radiation absorbed dose of 111In-1,4,7,10-tetraazacyclododecane-N,N',N",N'''-tetraacetic acid (DOTA)-lanreotide, a novel peptide tracer, which identifies hSST receptor (R) subtypes 2 through 5 with high affinity, and hSSTR1 with low affinity.

METHODS

The tumor localizing capacity of 111In-DOTA-lanreotide was initially investigated in 10 patients (3 lymphomas, 5 carcinoids and 2 intestinal adenocarcinomas). Indium-111 -DOTA-lanreotide was then administered to 14 cancer patients evaluated for possible radiotherapy with 90Y-DOTA-lanreotide (8 neuroendocrine tumors, 4 intestinal adenocarcinomas, 1 Hodgkin lymphoma and 1 prostate cancer). After intravenous administration of 111In-DOTA-lanreotide (approximately = 150 MBq; 10 nmol/patient), sequential images over one-known tumor site were recorded during the initial 30 min after peptide application. Thereafter, whole-body images were acquired in anterior and posterior views up to 72 hr postinjection. Dosimetry calculations were performed on the basis of scintigraphic data, urine, feces and blood activities. A comparison with 111In-DTPA-D-Phe1-octreotide (111In-OCT) scintigraphy was performed in 8 of the patients.

RESULTS

After an initial rapid blood clearance [results of biexponential fits: T(eff1) 0.4 min (fraction a1 80%) and T(eff2) 13 min (fraction a2 14%)], the radioactivity was excreted into the urine and amounted to 42% +/- 3% of the injected dose (%ID) within 24 hr and 62% +/- 6%ID within 72 hr after injection of 111In-DOTA-lanreotide. In all patients, tumor sites were visualized during the initial minutes after injection of 111In-DOTA-lanreotide. The mean radiation absorbed dose amounted to 1.2 (range 0.21-5.8) mGy/MBq for primary tumors and/or metastases. The effective half-lives of 111In-DOTA-lanreotide in the tumors were T(eff1) 4.9 +/- 2.2 and T(eff2) 37.6 +/- 6.6 hr, and the mean residence time tau was 1.8 hr. The highest radiation absorbed doses were calculated for the spleen (0.39 +/- 0.13 mGy/MBq), kidneys (0.34 +/- 0.08 mGy/MBq), urinary bladder (0.21 +/- 0.03 mGy/MBq) and liver (0.16 +/- 0.04 mGy/MBq). The effective dose was 0.11 +/- 0.01 (range 0.09-0.12) mSv/MBq. During the observation period of 72 hr, no side effects were noted after 111In-DOTA-lanreotide application. The 111In-DOTA-lanreotide radiation absorbed tumor dose was significantly higher (ratio 2.25 +/- 0.60, p < 0.01) when directly compared with 111In-OCT.

CONCLUSION

Indium-111 -DOTA-lanreotide shows a high tumor uptake for a variety of different human tumor types, has a favorable dosimetry over 111In-OCT and is clinically safe.

Location of a VIPoma by iodine-123-vasoactive intestinal peptide scintigraphy

A major problem in patients with small endocrine tumors is the difficulty in localizing the primary tumor site. Many endocrine tumors possess larger amounts of high affinity vasoactive intestinal peptide (VIP) binding sites compared with normal tissue or blood cells. We used radiolabeled VIP to localize the tumor site in a patient with Verner-Morrison syndrome (VMS). Under octreotide therapy, the VIP levels had declined in this patient, but a tumor site could not be detected by conventional techniques or by radiolabeled octreotide. However, using 123I-VIP, the tumor was detectable in the pancreatic tail. Surgical resection of the tumor was followed by complete remission of the VMS. Expression of VIP binding sites in the tumor was confirmed by a radioreceptor assay and showed cross-competition between VIP and octreotide. The identity of the VIP binding site in the tumor was analyzed by Northern blotting and revealed the expression of somatostatin receptor subtype 3, which binds both somatostatin-14 and VIP with higher affinity than octreotide. Iodine-123-VIP scintigraphy would be an effective tracer to identity the tumor site in VMS patients.

Somatostatin receptor subtype specificity and in vivo binding of a novel tumor tracer, 99mTc-P829

Recent data suggest that somatostatin receptors (SSTRs) are expressed on various tumor cells. High-level expression of SSTR on the tumor cell surface provides the basis for the successful clinical use of radiolabeled ligands for the in vivo localization of tumor sites. We have characterized the in vitro binding properties of the novel SSTR ligand 99mTc-P829 using primary human tumors (carcinoids, breast cancers, intestinal adenocarcinomas, pheochromocytomas, small cell and non-small cell lung cancer, and melanomas; n = 28), various tumor cell lines, and COS7 cells transfected with the human SSTR (hSSTR) subtypes 1, 2, 3, 4, and 5. 99mTc-P829 bound to primary tumor cells and tumor cell lines with high affinity and high capacity. The dissociation constants (Kd) ranged between 1 and 20 nM. 99mTc-P829 also bound with high affinity to the transfected hSSTR2 (Kd, 2.5 nM), hSSTR5 (Kd, 2 nM), and hSSTR3 (Kd, 1.5 nM). Binding of 99mTc-P829 to hSSTR3 was found to be displaceable by unlabeled P829/([ReO]-P829), SST-14, and vasoactive intestinal peptide (VIP; IC50, 2 nM) and, less effectively, by Tyr3-octreotide (IC50, 20 nM). In contrast, the binding of 99mTc-P829 to hSSTR2 and hSSTR5 could be displaced by P829/([ReO]-P829) and Tyr3-octreotide but not by VIP. 99mTc-P829 scintigraphy revealed in vivo binding to primary or metastatic tumor sites in seven of eight patients with breast cancer and six of six patients with melanoma. In summary, our data show that 99mTc-P829 binds with high affinity to many different types of primary and cloned tumor cells. Furthermore, our data identify hSSTR2, the VIP acceptor hSSTR3, and hSSTR5 as the respective target receptors. Because these receptors are frequently expressed at high levels on primary tumor cells, 99mTc-P829 appears to be a promising novel peptide tracer for tumor imaging.

Modified LDL decreases the binding of prostaglandin E2, I2, and E1 onto monocytes in patients with peripheral vascular disease

Recent data suggest that various eicosanoids including prostaglandins play an important regulatory role in the development of atherosclerotic lesions. Peripheral blood monocytes have been implemented in early atherogenesis because they express receptors specific for modified LDL. In this study we investigated the binding of tritium prostaglandins E2 (3H-PGE2), E1 (3H-PGE1) and I2 (3H-PGI2) onto intact peripheral monocytes isolated from 20 patients (32-71 years) with manifested ischemic peripheral vascular disease stage II according to Fontaine and compared the results with those obtained in 16 healthy volunteers (21-68 years). In control subjects, Scatchard analyses of the binding data indicated a single class of high-affinity binding sites for 3H-PGE2 (maximal binding capacity [Bmax] = 11,400 +/- 3200 sites/cell; dissociation constant [Kd] = 1.3 +/- 0.5 nmol/L) and two classes of binding sites for 3H-PGE1 (Bmax1 = 11,200 +/- 4900 sites/cell, Kd1 = 1.5 +/- 0.5 nmol/L; Bmax2 = 47,800 +/- 6100 sites/cell, Kd2 = 12.8 +/- 5.9 nmol/L) as well as for 3H-PGI2 (Bmax1 = 10,100 +/- 3700 sites/cell, Kd1 = 1.7 +/- 0.7 nmol/L; Bmax2 = 81,200 +/- 5200 sites/cell, Kd2 = 14.2 +/- 6.5 nmol/L). In the patients, an absence of the higher-affinity binding class and significantly (P < .01) fewer lower-affinity binding sites were found for each ligand (PGE2: Bmax = 6600 +/- 3600 sites/cell, Kd = 12.1 +/- 3.2 nmol/L; PGI2: Bmax = 6400 +/- 3100 sites/cell, Kd = 22.1 +/- 8.3; PGE1: Bmax = 5300 +/- 1700 sites/ cell, Kd = 20.5 +/- 7.0 nmol/L). After incubation of monocytes with modified LDL (oxidized LDL or acetylated LDL), the binding of prostaglandins was significantly (P < .01 to P < .001) decreased, whereas native VLDL, LDL, and HDL did not interfere with prostaglandin binding. Prostaglandin-induced adenosine 3'-5' cyclic monophosphate (cAMP) formation by monocytes was significantly (P < .01) lower in patients (the concentrations causing 50% elevation of basal cAMP formation [ED50] were 3.8 +/- 2.4 nmol/L for PGE2, 6.3 +/- 3.5 nmol/L for PGE1, and 5.6 +/- 4.1 nmol/L for PGI2) than in the control subjects (ED50 was 1.6 +/- 1.2 nmol/L for PGE2, 4.8 +/- 2.5 nmol/L for PGE1, and 3.1 +/- 1.4 nmol/L for PGI2). After preincubation with modified LDL, the PG-induced cAMP production by monocytes was remarkably decreased in both patients and control subjects (P < .05). Our results suggest a direct effect of modified LDL on PGE2, PGE1, and PGI2 binding onto monocytes by reducing the number of cell surface-expressed receptors available. Modified LDL also reduces the sensitivity of monocytes to prostaglandins, which results in decreased cAMP production. The complex interactions between prostaglandins and lipoproteins may play an important role during atherogenesis.

Inhalation scintigraphy with iodine-123-labeled interferon gamma-1b: pulmonary deposition and dose escalation study in healthy volunteers

Recent studies have suggested that recombinant interferon gamma (IFNg) may be useful in the treatment of various respiratory diseases, such as chronic inflammatory disease. This study was undertaken to investigate the dose response of escalating doses of inhaled 123I-labeled IFNg (123I-IFNg) and its safety, biodistribution and radiation absorbed doses in healthy volunteers.

METHODS

IFNg was labeled with 123I to produce a specific activity of 1800 MBq/mg of IFNg. The biological activities of 123I-IFNg, nebulized 123I-IFNg and unlabeled IFNg were evaluated in various functional in vitro tests. Ten healthy volunteers were enrolled in the in vivo dose escalation study (180 MBq of 123I-IFNg diluted with 0.1-2 mg of INFg). Inhalation scintigraphy, using a Pari-Master nebulizer, was performed for up to 37 min, during which dynamic posterior images of the lungs were obtained. Whole-body scanning was performed at various time points up to 24 hr postinjection, for biodistribution and dosimetry purposes. Blood, urine and feces were also collected over this 24-hr period. Lung perfusion scintigraphy with 99mTc-microspheres was performed at the end of the study for attenuation correction.

RESULTS

Inhaled nebulized IFNg showed a uniform deposition pattern in the lungs with deposition ratios of 0.74 (central-to-peripheral) and 0.78 (upper-to-lower). The lung deposition of IFNg was time-dependent, with a deposition half-time between 1 and 5 min. Despite a large interindividual variation, the total lung deposition was proportional to the nebulizer charge and was 53 +/- 12% of the inhaled dose and 19 +/- 7% of the initial nebulizer charge (between 0.1 and 2 mg of IFNg). The biological half-life in the lung could be fitted to a biexponential function, with resultant half-lives of 1 and 11 hr. Blood activity was maximal at 3.5 hr after inhalation and was due to free iodine. The radioactivity was excreted through both the urinary and intestinal tracts. Plasma IFNg levels did not significantly increase over time, and no significant HLA-DR induction on peripheral blood cells was detected. The highest radiation absorbed doses of 0.14 and 0.19 mGy/MBq were determined for the trachea and the lower intestines, respectively. The effective dose equivalent was 0.05 mSv/MBq.

CONCLUSION

After inhalation with the Pari-Master nebulizer, IFNg deposits normally in the lungs and shows no systemic effects in healthy volunteers.

Molecular and functional characterization of the urokinase receptor on human mast cells

The urokinase receptor system is involved in several biological processes including extracellular proteolysis, cell invasion, and chemotaxis. Mast cells are multifunctional perivascular cells that play an important role in the regulation of microenvironmental events. We report that primary human mast cells and the human mast cell line HMC-1 express the receptor for urokinase. As assessed by Northern blotting and reverse transcription polymerase chain reaction technique, purified human lung mast cells and HMC-1 cells expressed urokinase receptor mRNA in a constitutive manner. Using a toluidine blue/immunofluorescence double staining technique and monoclonal antibodies, surface expression of urokinase receptor was demonstrable in lung, skin, uterus, heart, and tonsil mast cells, whereas the low density lipoprotein receptor-related protein was not detectable. Binding of monoclonal antibody VIM5 (recognizing the urokinase binding domain of urokinase receptor) to HMC-1 could be blocked by high molecular weight but not low molecular weight urokinase. Binding analyses performed with 123I-urokinase revealed expression of 271,000 +/- 55,000 high affinity urokinase binding sites per HMC-1 cell, with a calculated dissociation constant of 1. 29 +/- 0.3 nM. Purified urokinase induced dose-dependent migration of primary mast cells and HMC-1 in a chemotaxis assay without inducing release of histamine. The mast cell agonist stem cell factor also induced migration of HMC-1 and caused up-regulation of expression of urokinase receptor mRNA. Together, our data show that human mast cells express functional receptors for urokinase. Expression of urokinase receptors on mast cells may have implications for mast cell-dependent microvascular processes associated with fibrinolysis, migration, or local tissue repair.

In vitro and in vivo studies of three radiolabelled somatostatin analogues: 123I-octreotide (OCT), 123I-Tyr-3-OCT and 111In-DTPA-D-Phe-1-OCT

Scintigraphy with long-acting somatostatin (SST) analogues may be useful for the localization of tumours expressing receptors (R) for SST. In this study we have analysed the in vitro and in vivo binding properties of three SST analogues, 123I-octreotide (OCT), 123I-Tyr-3-OCT and 111In-DTPA-d-Phe-1-OCT. In vitro binding studies performed with a variety of primary tumours (n=48) as well as with several tumour cell lines (A431, HT29, PANC1, COLO320, HMC1, KU812) indicated significant in vitro binding of these three radiolabelled SST analogues to two subpopulations of SSTR, high (Kd 0.2-2.0 nM) and low (Kd 5-15 nM) affinity ones. The number of SSTR on tumour cells was at least a 1000-fold higher as compared with normal peripheral blood cells. Comparative scintigraphic studies using 123I-OCT and/or 123I-Tyr-3-OCT and/or 111In-DTPA-d-Phe-1-OCT were performed in 21 patients with histologically verified intestinal carcinoid tumours. Corresponding scintigraphic results were obtained in 18 of 21 patients investigated with two different SSTR ligands, either 123I-OCT/123I-Tyr-3-OCT (four of five), 123I-OCT/111In-DTPA-d-Phe-1-OCT (eight of nine), or 123I-Tyr-3-OCT/111In-DTPA-d-Phe-1-OCT (six of seven). We conclude that various tumours express high amounts of SSTR which are recognized by three radiolabelled SST analogues: 123I-OCT, 123I-Tyr-3-OCT and 111In-DTPA-d-Phe-1-OCT. Differences between these SST analogues in their in vitro binding and/or in vivo scanning properties are observed in a minority of patients. Thus, the labelling of OCT with iodine may be an alternative approach for those nuclear medicine departments for which 111In-DTPA-d-Phe-1-OCT is not easily available, or is too expensive.

Interleukin 10 inhibits growth and granulocyte/macrophage colony-stimulating factor production in chronic myelomonocytic leukemia cells

Autonomous release of hematopoietic growth factors may play a crucial role in the pathogenesis of certain hematological malignancies. Because of its cytokine synthesis-inhibiting action, interleukin 10 (IL-10) could be a potentially useful molecule to affect leukemic cell growth in such disorders. Chronic myelomonocytic leukemia (CMML) cells spontaneously form myeloid colonies (colony-forming units-granulocyte/macrophage) in methylcellulose, suggesting an autocrine growth factor-mediated mechanism. We studied the effect of recombinant human IL-10 (rhIL-10) on the in vitro growth of mononuclear cells obtained from peripheral blood or bone marrow of patients with CMML. IL-10 specifically binding to leukemic cells had a profound and dose-dependent inhibitory effect on autonomous in vitro growth of CMML cells. IL-10 significantly inhibited the spontaneous growth of myeloid colonies in methylcellulose in 10/11 patients, and autonomous CMML cell growth in suspension in 5/5 patients tested. Spontaneous colony growth from CMML cells was also markedly reduced by addition of antigranulocyte/macrophage colony-stimulating factor (GM-CSF) antibodies, but not by addition of antibodies against G-CSF, IL-3, or IL-6, IL-10-induced suppression of CMML cell growth was reversed by the addition of exogenous GM-CSF and correlated with a substantial decrease in GM-CSF production by leukemic cells, both at the mRNA and protein levels. Our data indicate that IL-10 profoundly inhibits the autonomous growth of CMML cells in vitro most likely through suppression of endogenous GM-CSF release. This observation suggests therapeutic evaluation of rhIL-10 in patients with CMML.

Comparison of iodine-123-vasoactive intestinal peptide receptor scintigraphy and indium-111-CYT-103 immunoscintigraphy

Recently, we have shown that the expression of receptors for vasoactive intestinal peptide (VIP) on intestinal adenocarcinomas can be used for in vivo targeting of primary or metastatic tumor sites using 123I-labeled VIP. Several other receptors and antigens including the TAG-72 protein have also been implemented for in vivo localization purposes. In this study, we have compared the in vitro and in vivo binding of 123I-VIP and of the 111In-labeled monoclonal antibody (MAb) directed against TAG-72 (OncoScint; 111In-CR-103) in patients with intestinal adenocarcinomas in a single-blinded, prospectively randomized trial.

METHODS

Twenty patients were administered either 123I-VIP (150-200 MBq; 1 microgram) or 111In-CYT-103 (150 MBq; 1 mg) for one imaging study. After interim analysis demonstrated superior imaging with 123I-VIP, the next 10 patients (accounting for a total of 50 patients) enrolled in this trial underwent both studies in random order to allow for a direct comparison.

RESULTS

In total, 123I-VIP scans were true-positive in 28 of 30 patients (93%) versus 17 of 30 patients administered 111In-CYT-103 (56%). In the subgroup of 10 patients enrolled in the second part of the study, primary intestinal adenocarcinomas were imaged in five of five patients with 123I-VIP and in only two of these patients with 111In-CYT-103. Liver metastases were visualized in five of six patients by 123I-VIP receptor scanning and in four of these patients with 111In-CYT-103. The in vitro results indicated significant binding of 123I-VIP to primary colorectal tumors as well as to HT29 and COLO320 adenocarcinoma cells. In vitro, adenocarcinoma cells also expressed abundant numbers of the TAG-72 antigen.

CONCLUSION

Intestinal adenocarcinomas co-express VIP receptors and the IAG-72 antigen. Despite significant in vitro binding of both agents, however, the VIP receptor scan is more sensitive in localizing intestinal adenocarcinomas and metastatic spread.

123I-vasoactive intestinal peptide (VIP) receptor scanning: update of imaging results in patients with adenocarcinomas and endocrine tumors of the gastrointestinal tract

Recent data suggest that functional receptors (R) for vasoactive intestinal peptide (VIP) are expressed on various tumor cells. The high-level expression of VIPR on tumor cells provided the basis for the successful use of 123I-labeled VIP for the in vivo localization of intestinal adenocarcinomas and endocrine tumors. We here report an update of our imaging results using 123I-VIP (150-200 MBg/1 microgram/patient) in 169 patients. In patients with pancreatic adenocarcinomas without liver metastases, the primary/recurrent tumor was visualized in 16 of 18 patients (89%) and liver metastases were imaged in 15 of 16 patients. In 11 of 12 patients with colorectal adenocarcinomas, the primary/recurrent tumor (92%) was imaged by 123I-VIP. Also, in 21 of 25 patients, liver metastases (84%); in 3 of 6 patients, lung metastases (50%); and in 4 of 5 patients, lymph-node metastases (80%) were imaged by 123I-VIP. In 10 of 10 patients with gastric adenocarcinomas, the primary/recurrent tumor; in 3 of 4 patients, liver metastases; and in 2 of 2 patients, lymph-node metastases were visualized by 123I-VIP. 123I-VIP localized primary intestinal carcinoid tumors in 15 of 17 patients (88%) and 8 of 10 primary insulinomas (80%). We conclude that the 123I-VIPR scintigraphy localizes intestinal adenocarcinomas and endocrine tumors as well as metastatic tumor sites.

Combined use of 111In-DTPA-D-Phe-1-octreotide (OCT) and 123I-vasoactive intestinal peptide (VIP) in the localization diagnosis of medullary thyroid carcinoma (MTC)

Although serum calcitonin and CEA are sensitive indicators for the presence of medullary thyroid carcinoma (MTC), the localization of tumor sites may be very difficult. In an approach to localize MTC lesions we performed comparative in vivo studies in 12 patients with primary MTC and in 4 patients with suspected recurrent MTC using 123I-VIP (150 MBq/1 microgram) and 111In-DTPA-D-Phe-1-octreotide (111In-OCT; 150 MBq/1 microgram). Despite elevated calcitonin values in all patients with suspected recurrent or metastatic lesions, both ultrasound and computed tomography (CT) were unable to localize a tumor site. 111In-OCT localized the primary tumor in the thyroid gland in 7 of 11 patients (63.5%). In 2 of 4 patients (50%) with suspected recurrent MTC, pathological uptake of 111In-OCT in the mediastinum or liver was demonstrable. In none of the 11 patients did 123I-VIP-receptor scanning indicate primary, recurrent, or metastatic tumor lesions. In vitro binding studies showed an absence of high-affinity VIP receptors in MTC tissue, whereas high-affinity 111In-OCT receptors were present in 4 of 6, and low-affinity 123I-VIP as well as 111In-OCT receptors were present in 6 of 6 MTC tissue samples. We conclude that somatostatin receptor scanning using 111In-OCT may visualize primary MTC, but it has only a low sensitivity in the detection of recurrent disease. The 123I-VIP-receptor scan is not helpful in the localization diagnosis of primary or recurrent MTC.

Vasoactive intestinal peptide receptor scintigraphy

This study presents the biodistribution, safety and absorbed dose of 123I-VIP administered to 18 patients with intestinal adenocarcinomas or endocrine tumors.

METHODS

To achieve high-specific activity, 123I-VIP was purified by HPLC. Following intravenous administration of 123I-VIP (172 +/- 17 MBq (4.65 +/- 0.5 mCi); < 300 pmole ( < 1 microgram)/patient), sequential images were recorded during the initial 30 min. Thereafter, whole-body images were acquired in anterior and posterior views at various time points. Dosimetry calculations were performed on the basis of gamma camera data, urine, feces and blood activities.

RESULTS

After injection of labeled peptide, the lung was the primary site of 123I-VIP uptake. Peak lung activity represented 40% +/- 7% of the injected dose at 0.7 hr and declined to 21% +/- 7% at 3.5, to 14% +/- 3% at 7 and to 8% +/- 4% 22 hr postinjection. Radioactivity was excreted into the urine and amounted to 37% +/- 16% of the injected dose within 4, 68% +/- 12% within 8, 82% +/- 16% within 16 and 93% +/- 8% within 24 hr postinjection. The mean effective half-life of 123I-VIP in the lungs was 2.2 and 6 hr in the urinary bladder. The highest radiation absorbed doses were calculated for the lungs [67 muGy/MBq (248 mrad/mCi)], urinary bladder [77 muGy/MBq (284 mrad/mCi)] and thyroid gland [104 muGy/MBq (386 mrad/mCi)]. The effective dose was 28 muSv/MBq (104 mrem/mCi).

CONCLUSION

HPLC-purified 123I-VIP shows favorable dosimetry and is a safe and promising peptide tracer for localization of tumors expressing receptors for VIP.

Technetium-99m-galactosyl-neoglycoalbumin combined with iodine-123-Tyr-(A14)-insulin visualizes human hepatocellular carcinomas

Human hepatocellular carcinoma (HCC) is the most frequent primary hepatic malignancy and its diagnosis by conventional methods is still difficult. We hypothesized that the expression of specific receptors could possibly be used to improve in vivo localization of HCC with specific receptor-based radioligands.

METHODS

In initial in vitro studies, receptor binding of 99mTc-galactosyl-neoglycoalbumin (99mTc-NGA) and 123I-Tyr-(A14)-insulin to HCC was investigated. Scintigraphy was performed in 45 patients with histologically confirmed HCC using either 99mTc-NGA (75-150 MBq; 25-50 nmole, n = 27) and/or 123I-Tyr-(A14)-insulin (100-150 MBq; 7.5-10 micrograms, n = 30).

RESULTS

HCC (1256 +/- 290 pmole bound/mg protein, Kd = 3.4 +/- 2.9 nM) expressed a 1000-fold higher number of specific receptors for 123I-Tyr-(A14)-insulin compared to normal liver tissue (2.4 +/- 0.8 pmole bound/mg protein, Kd = 4.2 +/- 2.4 nM), whereas HCC did not express receptors specific for 99mTc-NGA. All HCC lesions were identified as cold spots after injection of 99mTc-NGA, whereas 123I-Tyr-(A14)-insulin accumulated in these lesions, indicating HCC-to-normal liver ratios of 1.6 +/- 0.4 in the mean. Subtraction images obtained from planar studies visualized 123I-Tyr-(A14)-insulin in HCC lesions detected by 99mTc-NGA as cold spots.

CONCLUSION

This hepatocyte receptor-specific, double-tracer method using 99mTc-NGA and 123I-Tyr-(A14)-insulin could become clinically useful in the diagnosis of HCC.

Characterization of LDL and VLDL binding sites on human basophils and mast cells

Recent data suggest that basophils and mast cells play a potential role in the processing and accumulation of plasma lipoproteins. This study investigated the interactions of 111In-low-density lipoprotein (LDL), 111In-acetyl-LDL, and 111In-very-low-density lipoprotein (VLDL) with purified primary human blood basophils, immortalized human basophils (KU812 cell line), and a human mast cell line, HMC-1. Binding sites for 111In-LDL resolved into curvilinear Scatchard plots indicating two classes of specific binding sites on primary basophils (Bmax1, 7404 sites/cell; Kd1, 1.9 nmol/L; Bmax2, 39,611 sites/cell; Kd2, 29 nmol/L), on KU812 cells (Bmax1, 8290 +/- 2690 sites/cell; Kd1, 2.4 +/- 0.6 nmol/L; Bmax2, 46,470 sites/cell; Kd2, 33.4 +/- 7.8 nmol/L), and on HMC-1 cells (Bmax1, 7840 +/- 360 sites/cell; Kd1, 1.8 +/- 0.8 nmol/L; Bmax2, 61,450 +/- 9900 sites/cell; Kd2, 28.4 +/- 9.4 nmol/L). On KU812 cells, binding of 111In-LDL was displaced by apolipoprotein (apo)-E-rich high-density lipoprotein (HDL) (IC50, 14 +/- 6 nmol/L), LDL (IC50, 29 +/- 11 nmol/L), VLDL (IC50, 55 +/- 21 nmol/L), HDL2 (IC50, 420 +/- 140 nmol/L), and heparin (IC50, 67 +/- 28 nmol/L), whereas no competition was produced by HDL, HDL3, or acetyl-LDL (IC50, > 1 mumol/L). Western blot analysis using the monoclonal antibody C7 confirmed the presence of the LDL receptor on human basophils and HMC-1 cells. 111In-acetyl-LDL binding sites (scavenger receptor) could be detected neither on human basophils nor on HMC-1 cells. 111In-VLDL bound to a single class of high-affinity binding sites on primary basophils (Bmax, 4320 sites/cell; Kd, 10 nmol/L), KU812 cells (Bmax, 4020 +/- 840 sites/cell; Kd, 8 +/- 3 nmol/L), and HMC-1 cells (Bmax, 6143 +/- 1866 sites/cell; Kd, 4 +/- 2 nmol/L). 111In-VLDL binding was displaced by VLDL > LDL > apoE-rich HDL but not by heparin (IC50 > 1 mmol/L). In the presence of prostaglandin E1, the number of 111In-LDL receptors increased by 150% (P < .05) in the high-affinity range and by 170% (P < .01) in the low-affinity range, whereas the number of 111In-VLDL binding sites remained unchanged. VLDL, LDL, HDL, and the subclasses HDL2 and HDL3 inhibited immunological histamine release by primary normal basophils (n = 3) and mast cells (n = 3). Our results provide evidence for the existence of LDL and VLDL binding sites on human basophils and HMC-1 mast cells. The exact biological and pathophysiological roles of these sites remain to be elucidated.