Marion de Jong

The sick euthyroid syndrome: changes in thyroid hormone serum parameters and hormone metabolism

Multiple alterations in the serum concentration of the iodothyronines have been recognized in patients with systemic non-thyroidal illnesses (NTI). Most prominent are the low serum 3,5,3’-triiodothyronine (T3) and elevated 3,3’,5’triiodothyronine (reverse T3, rT3) concentrations, leading to the generally used name ‘low T3 syndrome’ to describe these changes in the serum thyroid hormone parameters (Wartofsky & Burman, 1982). However, a more appropriate description would be ‘sick euthyroid syndrome’, while not only serum T3 concentrations, but all thyroid hormone parameters, including TSH, are often affected. Since the carly description of this syndromc in ill patients (Carter et al., 1974; Bermudez et al., 1975), low serum T3 concentrations have also been found in patients with liver disease (Chopra et d., 1974; Nomura et al., 19751, after stress or surgery (Burr et al., 1975), in patients with chronic renal failure (Finucane et al., 19771, in the elderly sick (Burrows et al., 1977), and after the ingestion of a number of drugs (Table 1). Of course, these changes have to be attributed to the illness only in the absence of an underlying disorder of the hypothalamicpituitary-thyroid axis, and their complete reversal must accompany recovery from the causal illness. The alterations may rcflcct changes in production of thyroid hormone by affecting the thyroid itself, the hypothalamic-pituitarythyroid axis, the peripheral tissue metabolism of the hormoncs, or by a combination of these effects. In practice, the clinician must differentiate the changes in the serum thyroid hormone lcvels induced by illness from those caused by treatable disorders of thyroid function.

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

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

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

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

Peptide Receptor Radionuclide Therapy with radiolabelled somatostatin analogues in patients with somatostatin receptor positive tumours

Peptide Receptor Radionuclide Therapy (PRRT) with radiolabelled somatostatin analogues is a promising treatment option for patients with inoperable or metastasised neuroendocrine tumours. Symptomatic improvement may occur with all of the various 111In, 90Y, or 177Lu-labelled somatostatin analogues that have been used. Since tumour size reduction was seldom achieved with 111Indium labelled somatostatin analogues, radiolabelled somatostatin analogues with beta-emitting isotopes like 90Y and 177Lu were developed. Reported anti-tumour effects of [90Y-DOTA0,Tyr3]octreotide vary considerably between various studies: Tumour regression of 50% or more was achieved in 9 to 33% (mean 22%). With [177Lu-DOTA0,Tyr3]octreotate treatments, tumour regression of 50% or more was achieved in 28% of patients and tumour regression of 25 to 50% in 19% of patients, stable disease was demonstrated in 35% and progressive disease in 18%. Predictive factors for tumour remission were high tumour uptake on somatostatin receptor scintigraphy and limited amount of liver metastases. The side-effects of PRRT are few and mostly mild, certainly when using renal protective agents: Serious side-effects like myelodysplastic syndrome or renal failure are rare. The median duration of the therapy response for [90Y-DOTA0,Tyr3]octreotide and [177Lu-DOTA0,Tyr3]octreotate is 30 months and more than 36 months respectively. Lastly, quality of life improves significantly after treatment with [177Lu-DOTA0,Tyr3]octreotate. These data compare favourably with the limited number of alternative treatment approaches, like chemotherapy. If more widespread use of PRRT is possible, such therapy might become the therapy of first choice in patients with metastasised or inoperable gastroenteropancreatic neuroendocrine tumours. Also the role in somatostatin receptor expressing non-GEP tumours, like metastasised paraganglioma/pheochromocytoma and non-radioiodine-avid differentiated thyroid carcinoma might become more important.

Renal Toxicity of Radiolabeled Peptides and Antibody Fragments: Mechanisms, Impact on Radionuclide Therapy, and Strategies for Prevention

Peptide-receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs such as octreotide is an effective therapy against neuroendocrine tumors. Other radiolabeled peptides and antibody fragments are under investigation. Most of these compounds are cleared through the kidneys and reabsorbed and partially retained in the proximal tubules, causing dose-limiting nephrotoxicity. An overview of renal handling of radiolabeled peptides and resulting nephrotoxicity is presented, and strategies to reduce nephrotoxicity are discussed. Modification of size, charge, or structure of radiolabeled peptides can alter glomerular filtration and tubular reabsorption. Coinfusion of competitive inhibitors of reabsorption also interferes with the interaction of peptides with renal endocytic receptors; coinfusion of basic amino acids is currently used for kidney protection in clinical PRRT. Furthermore, nephrotoxicity may be reduced by dose fractionation, use of radioprotectors, or use of mitigating agents. Decreasing the risk of nephrotoxicity allows for administration of higher radiation doses, increasing the effectiveness of PRRT.

Peptide-receptor radionuclide therapy for endocrine tumors

Peptide-receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs is a promising option for the treatment of somatostatin-receptor-positive endocrine tumors. Treatment with somatostatin analogs labeled with 111In, 90Y or 177Lu can result in symptomatic improvement, although tumor remission is seldom achieved with 111In-labeled analogs. In this Review, the findings of several studies on the use of PRRT for endocrine tumors are evaluated. Large variation in the antitumor effects of 90Y-octreotide was reported between studies: an objective response (≥50% tumor regression) was achieved in 9–33% of patients. After treatment with 177Lu-octreotate, an objective response was achieved in 29% of patients and a minor response (25–50% tumor regression) was achieved in 16% of patients; stable disease was present in 35% of patients. Treatment with 177Lu-octreotate resulted in a survival benefit of several years and markedly improved quality of life. Serious, delayed adverse effects were rare after PRRT. Although randomized, clinical trials have not yet been performed, data on the use of PRRT compare favorably with those from other treatment approaches, such as chemotherapy. If these results can be replicated in large, controlled trials, PRRT might become the preferred option in patients with metastatic or inoperable gastroenteropancreatic neuroendocrine tumors.

Radiolabelled peptides for tumour therapy: current status and future directions. Plenary lecture at the EANM 2002.

On their plasma membranes, cells express receptor proteins with high affinity for regulatory peptides, such as somatostatin. Changes in the density of these receptors during disease, e.g. overexpression in many tumours, provide the basis for new imaging methods. The first peptide analogues successfully applied for visualisation of receptor-positive tumours were radiolabelled somatostatin analogues. The next step was to label these analogues with therapeutic radionuclides for peptide receptor radionuclide therapy (PRRT). Results from preclinical and clinical multicentre studies have already shown an effective therapeutic response when using radiolabelled somatostatin analogues to treat receptor-positive tumours. Infusion of positively charged amino acids reduces kidney uptake, enlarging the therapeutic window. For PRRT of CCK-B receptor-positive tumours, such as medullary thyroid carcinoma, radiolabelled minigastrin analogues are currently being successfully applied. The combination of different therapy modalities holds interest as a means of improving the clinical therapeutic effects of radiolabelled peptides. The combination of different radionuclides, such as 177Lu- and 90Y-labelled somatostatin analogues, to reach a wider tumour region of high curability, has been described. A variety of other peptide-based radioligands, such as bombesin and NPY(Y1) analogues, receptors for which are expressed on common cancers such as prostate and breast cancer, are currently under development and in different phases of (pre)clinical investigation. Multi-receptor tumour targeting using the combination of bombesin and NPY(Y1) analogues is promising for scintigraphy and PRRT of breast carcinomas and their lymph node metastases.

Short‐term dietary restriction and fasting precondition against ischemia reperfusion injury in mice

Dietary restriction (DR) extends lifespan and increases resistance to multiple forms of stress, including ischemia reperfusion injury to the brain and heart in rodents. While maximal effects on lifespan require long‐term restriction, the kinetics of onset of benefits against acute stress is not known. Here, we show that 2–4 weeks of 30% DR improved survival and kidney function following renal ischemia reperfusion injury in mice. Brief periods of water‐only fasting were similarly effective at protecting against ischemic damage. Significant protection occurred within 1 day, persisted for several days beyond the fasting period and extended to another organ, the liver. Protection by both short‐term DR and fasting correlated with improved insulin sensitivity, increased expression of markers of antioxidant defense and reduced expression of markers of inflammation and insulin/insulin‐like growth factor‐1 signaling. Unbiased transcriptional profiling of kidneys from mice subject to short‐term DR or fasting revealed a significant enrichment of signature genes of long‐term DR. These data demonstrate that brief periods of reduced food intake, including short‐term daily restriction and fasting, can increase resistance to ischemia reperfusion injury in rodents and suggest a rapid onset of benefits of DR in mammals.

Indication for different mechanisms of kidney uptake of radiolabeled peptides.

Nephrotoxicity due to renal reabsorption of radiolabeled peptides limits the tumor dose in peptide receptor radiotherapy (PRRT). Therefore, we evaluated the ability of several agents to inhibit the renal accumulation of different radiopeptides. Methods: Male Wistar rats (4 per group) were injected intravenously with 1 MBq of 111In-labeled octreotide (OCT), minigastrin (MG), bombesin (BOM), or exendin (EX), together with a potential inhibitor of renal uptake (lysine [Lys], poly-glutamic acid [PGA], and Gelofusine [GF], a gelatin-based plasma expander) or phosphate-buffered saline as a control. Organ uptake at 20 h after injection was determined as the percentage of injected activity per gram (%IA/g). Lys, PGA, and GF were also combined to determine whether an additive effect could be obtained. The localization of the peptides in the kidneys was investigated by autoradiography using a phosphor imager. Results: OCT accumulation in the kidney was inhibited by Lys and GF (40.7%–45.1%), whereas PGA was ineffective. On the other hand, renal uptake of BOM, MG, and EX was inhibited by PGA and GF (15.4%–85.4%), whereas Lys was ineffective. The combination of GF and Lys showed additive effects in inhibiting OCT uptake, whereas PGA and GF had additive effects for the inhibition of EX uptake. The amount of kidney uptake correlated with the number of charged amino acids. All radiopeptides were localized in the renal cortex, as indicated by autoradiography. Conclusion: Inhibition of renal accumulation of the radiopeptides tested could be achieved by either Lys or PGA but not by both at the same time, suggesting 2 different uptake mechanisms. The differences in renal accumulation of radiopeptides may be related to the number of charges of a molecule. GF is the only compound that inhibited renal accumulation of all radiopeptides tested. Additional experiments are needed to further elucidate these findings and to optimize inhibition of renal accumulation of radiopeptides to reduce the kidney dose in PRRT.

Of Mice and Humans: Are They the Same?—Implications in Cancer Translational Research

Animal models have been instrumental in elucidating key biochemical and physiologic processes of cancer onset and propagation in a living organism. Most importantly, they have served as a surrogate for patients in the evaluation of novel diagnostic and therapeutic anticancer drugs, including radiopharmaceuticals. Experimental tumors raised in rodents constitute the major preclinical tool of new-agent screening before clinical testing. Such models for oncologic applications today include solid tumors raised in syngeneic fully immunocompetent hosts and human xenografts induced in immunodeficient mouse strains, and tumors spontaneously growing in genetically engineered mice represent the newest front-line experimental modality. The power of these models to predict clinical efficacy is a matter of dispute, as each model presents inherent strengths and weaknesses in faithfully mirroring the extremely complex process of human carcinogenesis. Differences in size and physiology, as well as variations in the homology of targets between mice and humans, may lead to translational limitations. Other factors affecting the predictive power of preclinical models may be animal handling during experimentation and suboptimal compilation and interpretation of preclinical data. However, animal models will remain a unique source of in vivo information and the irreplaceable link between in vitro studies and our patients.