Feasibility and image quality of dual-isotope SPECT using 18F-FDG and (99m)Tc-tetrofosmin after acipimox administration

Currently, with the rapidly increasing number of patients with heart failure due to chronic coronary artery disease, the need for viability studies to guide treatment in these patients is increasing. The most accurate method for viability assessment is metabolic imaging with (18)F-FDG with PET or SPECT. To obtain excellent image quality in all patients, the (18)F-FDG studies should be performed during hyperinsulinemic euglycemic clamping. However, this approach is time-consuming and is not feasible in busy nuclear medicine laboratories. Recently, the use of a nicotinic acid derivative, acipimox, has been suggested, but limited data are available on the image quality of the (18)F-FDG studies using this approach.

METHODS

We evaluated the feasibility and image quality of (18)F-FDG SPECT (with dual-isotope simultaneous acquisition (DISA) using (99m)Tc-tetrofosmin to assess perfusion) after acipimox administration in 50 nondiabetic patients. The image quality of both (18)F-FDG and (99m)Tc-tetrofosmin was assessed visually and quantitatively using myocardium-to-blood-pool (M/B) ratios as a measure of target-to-background ratio. The image quality and diagnostic value of DISA (99m)Tc-tetrofosmin SPECT was compared with standard (99m)Tc-tetrofosmin SPECT at baseline.

RESULTS

After acipimox administration, the plasma levels of free fatty acids were extremely low (68 +/- 89 nmol/L). No severe side effects were observed, only paroxysmal flushing. The (18)F-FDG image quality was good in 46 patients (92%) and moderate but still interpretable in the other 4 patients (8%). The clinical information of the baseline (99m)Tc-tetrofosmin SPECT was retained in the DISA (99m)Tc-tetrofosmin SPECT images because we did observe no substantial fill-in of perfusion defects by high (18)F-FDG uptake in the same segment.

CONCLUSION

Cardiac (18)F-FDG SPECT after acipimox is safe and resulted consistently in good image quality; this simple approach may be the method of choice for routine cardiac metabolic imaging.

99mTc-tetrofosmin or 99mTc-sestamibi for double-phase parathyroid scintigraphy?

Several years ago technetium-99m tetrofosmin was reported to localise parathyroid adenomas. The aim of this study was to compare the sensitivity of this radiopharmaceutical with that of (99m)Tc-sestamibi using a double-phase parathyroid scintigraphy protocol. Scans of 12 patients were evaluated visually and lesion to thyroid ratios were calculated. Nine of the patients were subsequently operated on; a total of eight parathyroid adenomas or hyperplastic glands were histologically confirmed in seven of the patients, while in one patient a parathyroid carcinoma was histologically proven. All of these patients had positive (99m)Tc-sestamibi scintigrams, whereas only two (99m)Tc-tetrofosmin scintigrams were positive. With (99m)Tc-sestamibi there was a significant increase in the lesion to thyroid ratio from 10 min to 90 min and 150 min p.i. which was not seen on scintigraphy with (99m)Tc-tetrofosmin. This makes (99m)Tc-tetrofosmin less suitable for double-phase parathyroid scintigraphy.

The addition of DTPA to [177Lu-DOTA0,Tyr3]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.

Peptide receptor radionuclide therapy in vitro using [111In-DTPA0]octreotide

Peptide receptor radionuclide therapy (PRRT) using [(111)In-DTPA(0)]octreotide (where DTPA is diethylenetriaminepentaacetic acid) is feasible because, besides gamma-radiation, (111)In emits both therapeutic Auger and internal conversion electrons having a tissue penetration of 0.02-10 and 200-500 micro m, respectively. The aim of this study was to investigate the therapeutic effects of [(111)In-DTPA(0)]octreotide in a single-cell model including the effects of incubation time, radiation dose, and specific activity of [(111)In-DTPA(0)]octreotide. Finally, we discriminated between the effects of the Auger electrons and internal conversion electrons in PRRT.

METHODS

An in vitro, colony-forming assay to study cell survival after PRRT using the sst subtype 2-positive rat pancreatic tumor cell line CA20948 was developed.

RESULTS

In this in vitro system [(111)In-DTPA(0)]octreotide can control tumor growth to 0% survival, and the effects were dependent on incubation time, radiation dose, and specific activity used. Similar concentrations of (111)In-DTPA, which is not internalized into sst-positive tumor cells like [(111)In-DTPA(0)]octreotide, did not influence tumor survival. Excess unlabeled octreotide (10(-6) mol/L) could decrease tumor cell survival to 60% of control; the addition of radiolabeled peptide ([(111)In-DTPA(0)]octreotide [10(-9) mol/L] + 10(-6) mol/L octreotide) did not further decrease survival.

CONCLUSION

These in vitro studies show that the therapeutic effect of (111)In is dependent on internalization, enabling the Auger electrons with their very short particle range to reach the nucleus. Our results also indicate that the PRRT effects were receptor mediated.

Safe and effective inhibition of renal uptake of radiolabelled octreotide by a combination of lysine and arginine

As scintigraphy with [(111)In-DTPA(0)]octreotide has become a standard technique in analysing somatostatin receptor-receptor positive lesions such as neuroendocrine tumours, a logical next step is peptide receptor radionuclide therapy (PRRT). Initial studies on PRRT were performed with high doses of [(111)In-DTPA(0)]octreotide, and recently other radionuclides coupled to other somatostatin analogues have been used for this purpose. However, the dose delivered to the kidney is a major dose-limiting factor. Amino acid solutions have previously been used to reduce renal uptake of radioactivity, but these solutions have some disadvantages, i.e. their hyperosmolarity and their propensity to cause vomiting and metabolic changes. In this study we tested various amino acid solutions in patients receiving [(111)In-DTPA(0)]octreotide PRRT in order to assess their safety and their capacity to inhibit the renal uptake of radioactivity. Patients served as their own non-infused control. Renal radioactivity at 24 h following the injection of [(111)In-DTPA(0)]octreotide was inhibited by (1) a commercially available amino acid solution (AA) (21%+/-14%, P<0.02), (2) by 25 g (17%+/-9%, P<0.04), 50 g (15%+/-13%, P<0.04) or 75 g of lysine (44%+/-11%, P<0.001) and (3) by a combination of 25 g of lysine plus 25 g of arginine (LysArg) (33%+/-23%, P<0.01). Fluid infusion alone (500, 1,000 or 2,000 ml of saline/glucose) did not change renal uptake of radioactivity. In patients studied with 75 g of lysine (Lys75) and LysArg, serum potassium levels rose significantly. Maximal potassium levels were within the toxic range (6.3, 6.7 and 6.8 mmol/l) in three out of six patients infused with Lys75, whereas with LysArg the highest concentration measured was 6.0 mmol/l. Electrocardiographic analysis did not reveal significant changes in any of the patients. Vomiting occurred in 50% of patients infused with AA, but in only 6% of patients receiving no amino acid infusion (controls) and 9% of patients receiving LysArg. We conclude that co-infusion of Lys75 or LysArg results in a significant inhibition of renal radioactivity in PRRT, allowing higher treatment doses and thus resulting in higher tumour radiation doses. Because Lys75 produced serious hyperkalaemia, it is not suitable for clinical use. LysArg, however, is effective in offering renal protection in PRRT and is safe.

Preclinical comparison of (111)In-labeled DTPA- or DOTA-bombesin analogs for receptor-targeted scintigraphy and radionuclide therapy

The 14-amino-acid peptide bombesin (BN) has a high affinity for the gastrin-releasing peptide (GRP) receptor that is expressed by a variety of tumors. Recently, high densities of GRP receptors were identified by in vitro receptor autoradiography in human prostate and breast carcinomas using [(125)I-Tyr(4)]BN as radioligand. Radiometal-labeled diethylenetriaminepentaacetic acid (DTPA)-BN derivatives are potentially useful radioligands for receptor-targeted scintigraphy and radiotherapy of GRP receptor-expressing tumors.

METHODS

[DTPA-Pro(1),Tyr(4)]BN (A), [DOTA-Pro(1),Tyr(4)]BN (B), [DTPA-epsilon-Lys(3),Tyr(4)]BN (C), and [DOTA-epsilon-Lys(3),Tyr(4)]BN (D) (where DOTA is dodecanetetraacetic acid) were synthesized and studied for competition with binding of [(125)I-Tyr(4)]BN to the GRP receptor. The (111)In-labeled BN analogs were studied in vitro for binding and internalization by GRP receptor-expressing CA20948 and AR42J pancreatic tumor cells as well as in vivo for tissue distribution in rats. Specific tissue binding was tested by coinjection of 0.1 mg [Tyr(4)]BN.

RESULTS

All BN analogs competitively inhibited the binding of [(125)I-Tyr(4)]BN to the GRP receptor with 50% inhibitory concentration values in the range of 2-9 nmol/L. All (111)In-labeled analogs showed high and specific time- and temperature-dependent binding and internalization by CA20948 and AR42J cells. In in vivo studies, high and specific binding was found in GRP receptor-positive tissues such as pancreas (0.90, 1.2, 0.54, and 0.79 percentage injected dose per gram for A-D, respectively). In a rat model, the AR42J tumor could clearly be visualized by scintigraphy using [(111)In-DTPA-Pro(1),Tyr(4)]BN as the radioligand. Although [(111)In-DOTA-Pro(1),Tyr(4)]BN showed the highest uptake of radioactivity in GRP receptor-positive tissues as well as higher target-to-blood ratios, [(111)In-DTPA-Pro(1),Tyr(4)]BN was easier to handle and is more practical to use. Therefore, we decided to start phase I studies with this DTPA-conjugated radioligand.

CONCLUSION

[(111)In-DTPA-Pro(1),Tyr(4)]BN is a promising radioligand for scintigraphy of GRP receptor-expressing tumors. We are currently performing a phase I study on patients with invasive prostate carcinoma.

The inhibitory effect of (111)In-DTPA(0)-octreotide on intrahepatic tumor growth after partial hepatectomy

The aim of this animal study was to evaluate whether peptide receptor radionuclide therapy with (111)In-diethylenetriaminepentaacetic acid (DTPA)(0)-octreotide was able to reduce tumor growth even under tumor growth-stimulating conditions induced by partial hepatectomy (PHx).

METHODS

Rats underwent 70% PHx or sham operation. The development of hepatic metastases was determined 21 d after direct injection of somatostatin receptor (SS-R)-positive or SS-R-negative tumor cells into the portal vein. Groups of 8 or 9 animals that underwent PHx or sham operation were treated with octreotide 50 micro g/kg subcutaneously twice daily or with 370 MBq (111)In-DTPA(0)-octreotide intravenously on days 1 and 8. Both treatments were compared with control treatment. Forty non-tumor-bearing rats were used to determine the influence of (111)In-DTPA(0)-octreotide therapy on liver regeneration after PHx.

RESULTS

PHx induced an increase in tumor growth in all experiments (P < 0.01). Octreotide treatment did not influence tumor growth after PHx or sham operation. (111)In-DTPA(0)-octreotide could effectively reduce tumor growth in the liver of SS-R-positive tumors also under conditions of increased tumor growth as generated by PHx (P < 0.01). (111)In-DTPA(0)-octreotide was also effective on SS-R-negative tumors after PHx (P = 0.01) but not after sham operation. Furthermore, (111)In-DTPA(0)-octreotide therapy did not influence liver regeneration or liver function after PHx.

CONCLUSION

Peptide receptor radionuclide therapy with (111)In-DTPA(0)-octreotide is effective in SS-R-positive tumors. During liver regeneration, the growth of SS-R-negative tumors is also reduced. This effect is not induced by impairment of liver regeneration or liver function. Radionuclide therapy could therefore be a promising treatment modality for patients with symptomatic liver metastases of neuroendocrine tumors in combination with liver resection.

Efficacy of percutaneous intramyocardial injections using a nonfluoroscopic 3-D mapping based catheter system

BACKGROUND

Percutaneous transendomyocardial injection with an injection catheter is a new drug delivery method for e.g. therapeutic angiogenesis. Little is known about the efficacy of this drug delivery technique. We studied efficiency and retention of transendomyocardial injections with a NOGA guided injection catheter system by using scintigraphy with radio-labeled model drugs.

METHODS

Ten non-ischemic landrace pigs were used. In each animal 2-3 transendomyocardial injections were performed using a 3-D mapping based catheter system called NOGA. As a model for proteins like angiogenic growth factors we used (99m)Tc labeled albumin and as a model for small particles like microspheres or adenovirus we used (99m)Tc labeled colloid albumin. Efficiency of the injections and retention of the transendomyocardial deposited substance were evaluated by a gamma camera during and after injection of 0.1 or 0.2 ml.

RESULTS

All 29 injections showed scintigraphic proof of intramyocardial deposition. The average injection efficiency of all 29 injections was 26 +/- 23%. The average injection efficiency of 0.1 and 0.2 ml injections were 33 +/- 30% (n = 8) and 24 +/- 20% (n = 21), respectively (p = 0.33). Intramyocardial retention curves of albumin showed a rapid wash-out within the first 2 hours of the injection, whereas the retention of colloid albumin showed no decrease. In conclusion, transendomyocardial delivery of proteins or particles with an injection catheter show favorable efficiency rates, however the retention time of intramyocardial deposited small proteins like albumin is short. This may indicate the need for sustained release systems of angiogenic growth factors for intramyocardal injection in therapeutic angiogenesis.

Collagen Ialpha1 polymorphism is associated with bone characteristics in Caucasian children and young adults

A large proportion of the variation in bone mass can be explained by genetic factors. We analyzed the G to T substitution in the Sp1 binding site in the first intron of the collagen type Ialpha1 (COLIA1) gene in relation to bone mass. The genotypes GG, GT, and TT were determined in 148 Caucasian children and young adults. We performed dual energy X-ray absorptiometry twice (mean follow-up time 4.4 years), and speed of sound (SOS) was assessed by tibial ultrasonometry at follow-up. Genotype distribution was 104 (70%) GG, 40 (27%) GT and 4 (3%) TT. Carriers of the T-allele had a 0.5 SDS (standard deviation score) decreased bone mineral content (BMC) of total body (P = 0.001), and a 0.4 SDS decreased bone mineral density (BMD) for both lumbar spine (P = 0.04) and total body (P = 0.05). The genotype effect on BMD and BMC decreased after adjustment for height or body mass index. When we calculated apparent BMD, these differences diminished to 0.1 SDS and were no longer significant. T-allele carriers had shorter stature (0.4 SDS; P = 0.04) and smaller bones (0.5 SDS lower width of the lumbar vertebral body; P = 0.01). The T-allele was also associated with lower SOS (P = 0.03), independent of BMD and BMC, and lower lean body mass. Similar associations were found at follow-up. The change in BMD and BMC SDS between the first and second measurement did not differ between the GG and GT&TT group. In conclusion, the COLIA1 polymorphism in children and young adults is associated with several bone characteristics. However, at least a part of the COLIA1 effect on bone mass may be related to differences in frame size.

Reference data for bone density and body composition measured with dual energy x ray absorptiometry in white children and young adults

AIMS

To obtain normative data on bone mineral density and body composition measured with dual energy x ray absorptiometry (DXA) from early childhood to young adulthood.

METHODS

Cross sectional results from 444 healthy white volunteers (4-20 years) in the Netherlands were combined with the results from 198 children who agreed to participate in the follow up study approximately four years later. DXA (Lunar, DPXL) of lumbar spine and total body was performed to assess bone density and body composition.

RESULTS

Bone density and lean body mass (LBM) increased with age. Maximal increase in bone density and LBM occurred around the age of 13 years in girls and approximately two years later in boys. Bone density of total body and lumbar spine showed an ongoing slight increase in the third decade. Mean fat percentage in boys remained at 10.5% throughout childhood, but increased in girls.

CONCLUSIONS

Most of the skeletal mass in lumbar spine and total body is reached before the end of the second decade, with a slight increase thereafter. This study provides reference values for bone density and body composition measured with DXA for children and young adults.

Tissue distribution of octreotide binding receptors in normal mice and strains prone to autoimmunity

Somatostatin has diverse functions, including immunomodulatory functions. In humans, sites of active inflammation can be visualized by the administration of 111In-DTPA(0)-octreotide, a radiolabelled somatostatin analogue. We wished to establish an animal model for preclinical evaluation of the effects of somatostatin analogues on the immune system. However, most animal models for immunological diseases are murine. This report is a preliminary study of the distribution of somatostatin receptors in mouse tissues, with emphasis on the immune system. Tissue distribution of octreotide binding receptors in normal (BALB/c) mice was determined in vivo by receptor binding of 111In-DTPA(0)-octreotide and in vitro and ex vivo by receptor autoradiography. Additionally, we investigated the tissue distribution of octreotide binding receptors in inflammatory lesions in a murine model of immune mediated disease, i.e. pre-diabetic pancreatic infiltration in the non-obese diabetic mouse strain. High specific uptake of radioactivity was seen in the thymus (range 1-1.7% ID/g) and the pituitary (1-1.6% ID/g) in all mouse strains. Specific uptake was also found in the stomach (0.1-0.7% ID/g), in the adrenal glands (0.1-0.3% ID/g) and in the pancreas (0.1-0.3% ID/g). However, we did not detect increased uptake of radiolabelled octreotide in the pancreas of pre-diabetic NOD mice. Autoradiography on tissue sections confirmed the presence of octreotide binding sites in the tissues that showed specific uptake. Moreover, by using autoradiography we could localize the cortex of the thymus and the anterior part of the pituitary as the localization of specific and high affinity, octreotide binding sites. A high, but not a receptor mediated, uptake of radioactivity was seen in the kidneys and was significantly higher in females than in males (12-19% vs 4% ID/g, respectively). Our results point to profound species differences in the tissue distribution of octreotide binding receptors. Of particular interest is the high uptake of 111In-DTPA(0)-octreotide in the cortex of the mouse thymus. This offers perspectives for the use of this animal in studies concerning the effect of somatostatin analogues on the immune system. To our knowledge, this is the first report on the tissue distribution of octreotide binding receptors in mice.

Perfusion and contractile reserve in chronic dysfunctional myocardium: relation to functional outcome after surgical revascularization

BACKGROUND

Chronic dysfunctional but viable myocardium may exhibit contractile reserve and/or intact perfusion. Segments with intact perfusion without contractile reserve are frequently observed inpatients with ischemic cardiomyopathy. The clinical relevance of this observation is unclear; in particular, the functional outcome after revascularization is unknown. Thus, contractile reserve (using low-dose dobutamine echocardiography) and perfusion (using resting (99m)Tc tetrofosmin) were evaluated in 114 patients with ischemic cardiomyopathy and the findings were related to functional outcome (9 to 12 months after revascularization).

METHODS AND RESULTS

Patients (n=114) with ischemic cardiomyopathy undergoing surgical revascularization were evaluated for perfusion (using (99m)Tc tetrofosmin) and contractile reserve (using low-dose dobutamine echocardiography). Contractile function (two-dimensional echocardiography) was assessed before and 9 to 12 months after revascularization. In the 1 336 dysfunctional segments, perfusion was preserved in 51% of the segments and contractile reserve in 31% (P<.05); 47% of the segments with perfusion did not exhibit contractile reserve. The majority (66%) of segments with recovery of function postrevascularization had intact perfusion and contractile reserve; the majority (58%) of segments without functional recovery lacked both perfusion and contractile reserve. Interestingly, 22% of segments with functional recovery and 25% of segments without functional recovery showed intact perfusion without contractile reserve.

CONCLUSION

Segments with intact perfusion/contractile reserve have a high likelihood of recovery of function postrevascularization; segments without contractile reserve/perfusion have a low likelihood of recovery and segments with intact perfusion without contractile reserve have an intermediate likelihood of recovery.

Altered bone mineral density and body composition, and increased fracture risk in childhood acute lymphoblastic leukemia

OBJECTIVE

To evaluate fracture rate and bone mineral density (BMD) and body composition in children with acute lymphoblastic leukemia (ALL) treated with dexamethasone-based chemotherapy.

STUDY DESIGN

Children with ALL (n = 61) participated. At diagnosis, during therapy, and one year after cessation of therapy, BMD and body composition were measured using dual energy X-ray absorptiometry of lumbar spine (LS) and total body (TB). Serum markers of bone turnover were assessed.

RESULTS

BMD(LS) was significantly reduced at diagnosis, and remained low during therapy. BMD(TB) was normal at diagnosis, with a fast decrease in the first 32 weeks, in which chemotherapy was relatively intensive. Apparent ("volumetric") BMD(LS) was also reduced, but this did not reach significance at diagnosis and follow-up. Bone formation markers were reduced at diagnosis; formation as well as resorption markers increased during treatment. Fracture rate was 6 times higher in ALL patients compared with healthy controls. Lean body mass was decreased at baseline. Percentage of body fat increased significantly during therapy. After ALL treatment was completed, BMD and body composition tended to improve.

CONCLUSIONS

Children with ALL are at risk for osteopenia because of the disease itself and the intensive chemotherapy. Fracture rate increases substantially, not only during but also shortly after treatment.

Sensitivity of 123I whole-body scan and thyroglobulin in the detection of metastases or recurrent differentiated thyroid cancer

Primary treatment of differentiated thyroid carcinoma consists of total thyroidectomy followed by ablation of thyroid tissue remnants and possible metastases by means of radioactive iodine. After complete destruction of remnants, metastases or recurrence can be detected by measurement of the serum thyroglobulin level as well as by radionuclide methods. Here we report on the sensitivity of diagnostic 123I scintigraphy and serum thyroglobulin measurement for tumour detection in patients with proven recurrence or metastases. Fifty-five patients who received their first high activity (1,850-5,550 MBq) of 123I therapy after total thyroidectomy and 131I ablation were included in the study. The thyroglobulin level was measured both during TSH-suppressive L-thyroxine therapy (Tg-on) and 4-6 weeks after L-thyroxine withdrawal (Tg-off, TSH>20 mU/l). Prior to treatment, whole-body scanning (WBS) was performed 24 h after the administration of 111-370 MBq 123I. The therapeutic activity of 1,850-5,550 MBq 131I was administered within 24 h after diagnostic scanning. The mean interval between 131I therapy and post-therapeutic WBS was 8.6 days (range 3-15 days). The sensitivity of WBS, Tg-on and Tg-off was 75%, 82% and 98%, respectively. The overall sensitivity of the combination of Tg-on with WBS and of Tg-off with WBS was 95% and 100%, respectively. In 12 out of 51 cases either Tg-off or Tg-on or both Tg-on and Tg-off levels were elevated while 123I-WBS was negative. More lesions were visible on the post-therapeutic 131I scan than on the corresponding diagnostic 123I scan (n=13). Tg values increased significantly (P<0.0001) after thyroid hormone withdrawal. Early treatment of distant metastases or tumour remnants of differentiated thyroid carcinoma is favoured and 131I treatment should also be considered in patients with a negative WBS but positive serum Tg level. The finding of a positive Tg-off level, which is clearly above the corresponding Tg-on value, is sufficient to make this decision. Additional diagnostic 123I WBS will not improve sensitivity.

Phase I study of peptide receptor radionuclide therapy with [In-DTPA]octreotide: the Rotterdam experience

Fifty patients with somatostatin receptor-positive tumors were treated with multiple doses of [(111)In-diethylenetriamine pentaacetic acid(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. Our results thus underscore the therapeutic potential of Auger-emitting radiolabelled peptides. 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. Therefore, we consider 100 GBq as the maximal tolerable dose. With a renal radiation dose of 0.45 mGy/MBq (based on previous studies) a cumulative dose of 100 GBq [(111)In-DTPA(0)]octreotide will lead to 45Gy on the kidneys, twice the accepted limit for external beam radiation. However, no development of hypertension, proteinuria, or significant changes in serum creatinine or creatinine clearance were observed in our patients including 2 patients who received 106 and 113 GBq [(111)In-DTPA(0)]octreotide without protection with amino acids, over a follow-up period of respectively 3 and 2 years. These findings show that the radiation of the short-range (maximal 10 microns) Auger electrons originating from the cells of the proximal tubules is not harmful for the renal function. The decrease in serum inhibin B and concomitant increase of serum FSH levels in men indicate that the spermatogenesis was impaired.

Somatostatin receptor imaging

[(111)In-DTPA(0)]octreotide is a radiopharmaceutical with a great potential for the visualization of somatostatin receptor-positive tumors. The overall sensitivity of Somatostatin Receptor Imaging (SRI) to localize neuroendocrine tumors is high. In a number of neuroendocrine tumor types, as well as in Hodgkin's disease, inclusion of SRI in the localization or staging procedure may be very rewarding, either in terms of cost-effectiveness, patient management, or quality of life. The value of SRI in patients with other tumors, like breast cancer, or in patients with granulomatous diseases, has to be established. The development of Peptide Receptor Radionuclide Therapy (PRRT) is expected to stimulate peptide receptor imaging.

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.

Longitudinal follow-up of bone density and body composition in children with precocious or early puberty before, during and after cessation of GnRH agonist therapy

We studied bone mineral density (BMD), bone metabolism, and body composition in 47 children with central precocious puberty (n = 36) or early puberty (n = 11) before, during, and after cessation of GnRH agonist. Bone density and body composition were measured with dual energy x-ray absorptiometry and expressed as SD scores. Bone age and biochemical parameters of bone turnover were assessed. Measurements were performed at baseline, after 6 months, and on a yearly basis thereafter. Mean lumbar spine BMD SD scores for chronological age were significantly higher than zero at baseline and decreased during treatment. Lumbar spine bone mineral apparent density and total body BMD did not differ from normal at baseline and showed no significant changes during treatment. In contrast, BMD SD scores for bone age were significantly lower than zero at baseline and at cessation of therapy. Two years after therapy, bone mineral apparent density and BMD SD scores for bone age and chronological age did not differ from normal. Markers of bone turnover decreased during treatment, mainly in the first 6 months. Patients had increased percentage of fat and lean body mass at baseline. After an initial increase of percentage body fat during treatment, percentage body fat decreased and normalized within 1 yr after cessation of treatment. Our longitudinal analysis suggests that peak bone mass or body composition will not be impaired in patients with precocious or early puberty after GnRH agonist therapy.

Fluorine-18 FDG imaging in hepatocellular carcinoma using positron coincidence detection and single photon emission computed tomography

BACKGROUND/AIMS

We prospectively evaluated whether fluorine-18 deoxyglucose (FDG) positron coincidence detection (PCD) or FDG single-photon emission computed tomography (SPECT) provides additional benefits to our conventional preoperative evaluation of lesion detection in patients suspected to have hepatocellular carcinoma (HCC).

METHODS

Thirteen consecutive patients with a suspected HCC underwent conventional preoperative evaluation with ultrasonography (US), triple-phase helical computed tomography (CT), superparamagnetic iron oxides (SPIO) enhanced magnetic resonance imaging (MRI) and serum alpha-fetoprotein (AFP) level. All 13 patients had an FDG-PCD and SPECT. These results were evaluated to assess the value of FDG-PCD and SPECT in addition to US, SPIO-enhanced MRI and triple-phase helical CT.

RESULTS

Ten of the 13 (77%) patients had at least one histologically confirmed HCC without extrahepatic abdominal spread. The tumors ranged in size from 1 to 8 cm and the serum AFP ranged from 3 to 30 000 microg/l. Of these 10 patients, two patients had an increased tumor F-FDG uptake (sensitivity of 20%); one patient with an AFP of 5 microg/l and a tumor size of maximum 4.5 cm and one patient with an AFP of 249 microg/l and a tumor size of maximum 2 cm. In three patients with a benign liver mass, FDG imaging with either PCD or SPECT was negative. There was no false positive finding.

CONCLUSIONS

We found poor sensitivity of FDG-PCD and FDG-SPECT for the detection of HCC. There were no clear relations between AFP or tumor size and FDG uptake. Therefore, we conclude that FDG imaging with PCD or SPECT has no value in the preoperative work-up for HCC in patients with cirrhosis.

Tumor response after [(90)Y-DOTA(0),Tyr(3)]octreotide radionuclide therapy in a transplantable rat tumor model is dependent on tumor size

A promising application of radiolabeled somatostatin analogs is peptide receptor-targeted radionuclide therapy of somatostatin receptor-expressing tumors. A suitable radionuclide is (90)Y, which emits high-energy beta-particles with a pathlength of several millimeters in tissue, making it especially promising for treatment of large tumors.

METHODS

We investigated the radiotherapeutic effect of different activities (111 and 370 MBq) of [(90)Y-1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA)(0),Tyr(3)]octreotide in Lewis rats bearing somatostatin receptor-positive rat pancreatic CA20948 tumors of different size (0.08-15 cm(2)) in their flank.

RESULTS

Dose-dependent radiotherapeutic effects of (90)Y-labeled octreotide in this rat tumor model were found. Tumor control (100% complete response) was found in animals bearing tumors of 3-9 cm(2) (mean, 7.8 cm(2)) after intravenous injection of the highest activity (370 MBq [(90)Y-DOTA(0),Tyr(3)]octreotide). In rats bearing tumors of < or =1 cm(2) or > or =14 cm(2), the effects were less pronounced (50% and 0% complete response, respectively). In tumors of < or =1 cm(2) the (90)Y radiation energy will not be absorbed completely in the tumor, whereas in tumors of > or =14 cm(2) the increased number of clonogenic and probably hypoxic tumor cells may explain the failure to reach a cure.

CONCLUSION

This study shows the ability of [(90)Y-DOTA(0),Tyr(3)]octreotide to control tumor growth, especially in medium-sized tumors. The effect of radionuclide therapy appeared to be dependent on tumor size at the onset of therapy.

Thyroid hormone transport by the heterodimeric human system L amino acid transporter

Transport of thyroid hormone across the cell membrane is required for thyroid hormone action and metabolism. We have investigated the possible transport of iodothyronines by the human system L amino acid transporter, a protein consisting of the human 4F2 heavy chain and the human LAT1 light chain. Xenopus oocytes were injected with the cRNAs coding for human 4F2 heavy chain and/or human LAT1 light chain, and after 2 d were incubated at 25 C with 0.01-10 microM [(125)I]T(4), [(125)I]T(3), [(125)I]rT(3), or [(125)I]3,3'-diiodothyronine or with 10-100 microM [(3)H]arginine, [(3)H]leucine, [(3)H]phenylalanine, [(3)H]tyrosine, or [(3)H]tryptophan. Injection of human 4F2 heavy chain cRNA alone stimulated the uptake of leucine and arginine due to dimerization of human 4F2 heavy chain with an endogenous Xenopus light chain, but did not affect the uptake of other ligands. Injection of human LAT1 light chain cRNA alone did not stimulate the uptake of any ligand. Coinjection of cRNAs for human 4F2 heavy chain and human LAT1 light chain stimulated the uptake of phenylalanine > tyrosine > leucine > tryptophan (100 microM) and of 3,3'-diiodothyronine > rT(3) approximately T(3) > T(4) (10 nM), which in all cases was Na(+) independent. Saturation analysis provided apparent Michaelis constant (K(m)) values of 7.9 microM for T(4), 0.8 microM for T(3), 12.5 microM for rT(3), 7.9 microM for 3,3'-diiodothyronine, 46 microM for leucine, and 19 microM for tryptophan. Uptake of leucine, tyrosine, and tryptophan (10 microM) was inhibited by the different iodothyronines (10 microM), in particular T(3). Vice versa, uptake of 0.1 microM T(3) was almost completely blocked by coincubation with 100 microM leucine, tryptophan, tyrosine, or phenylalanine. Our results demonstrate stereospecific Na(+)-independent transport of iodothyronines by the human heterodimeric system L amino acid transporter.

Somatostatin receptor-mediated imaging and therapy: basic science, current knowledge, limitations and future perspectives

In vivo somatostatin receptor-mediated scintigraphy has proven to be a valuable method for the visualisation of neuroendocrine tumours and their metastases. A new application is the use of radiolabelled analogues for somatostatin receptor-mediated therapy. This paper presents a review on the basic science, historical background and current knowledge of somatostatin receptor subtypes and their expression in neuroendocrine tumours. New somatostatin analogues, new chelators, "new" radionuclides and combinations thereof are also discussed. Due attention is given to limitations and future perspectives of somatostatin receptor-mediated imaging and therapy.

[177Lu-DOTAOTyr3]octreotate: comparison with [111In-DTPAo]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.

Plasma membrane transport of thyroid hormones and its role in thyroid hormone metabolism and bioavailability

Although it was originally believed that thyroid hormones enter target cells by passive diffusion, it is now clear that cellular uptake is effected by carrier-mediated processes. Two stereospecific binding sites for each T4 and T3 have been detected in cell membranes and on intact cells from humans and other species. The apparent Michaelis-Menten values of the high-affinity, low-capacity binding sites for T4 and T3 are in the nanomolar range, whereas the apparent Michaelis- Menten values of the low-affinity, high-capacity binding sites are usually in the lower micromolar range. Cellular uptake of T4 and T3 by the high-affinity sites is energy, temperature, and often Na+ dependent and represents the translocation of thyroid hormone over the plasma membrane. Uptake by the low-affinity sites is not dependent on energy, temperature, and Na+ and represents binding of thyroid hormone to proteins associated with the plasma membrane. In rat erythrocytes and hepatocytes, T3 plasma membrane carriers have been tentatively identified as proteins with apparent molecular masses of 52 and 55 kDa. In different cells, such as rat erythrocytes, pituitary cells, astrocytes, and mouse neuroblastoma cells, uptake of T4 and T3 appears to be mediated largely by system L or T amino acid transporters. Efflux of T3 from different cell types is saturable, but saturable efflux of T4 has not yet been demonstrated. Saturable uptake of T4 and T3 in the brain occurs both via the blood-brain barrier and the choroid plexus-cerebrospinal fluid barrier. Thyroid hormone uptake in the intact rat and human liver is ATP dependent and rate limiting for subsequent iodothyronine metabolism. In starvation and nonthyroidal illness in man, T4 uptake in the liver is decreased, resulting in lowered plasma T3 production. Inhibition of liver T4 uptake in these conditions is explained by liver ATP depletion and increased concentrations of circulating inhibitors, such as 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid, indoxyl sulfate, nonesterified fatty acids, and bilirubin. Recently, several organic anion transporters and L type amino acid transporters have been shown to facilitate plasma membrane transport of thyroid hormone. Future research should be directed to elucidate which of these and possible other transporters are of physiological significance, and how they are regulated at the molecular level.