Effect of amino acid infusion on potassium serum levels in neuroendocrine tumour patients treated with targeted radiopeptide therapy

Treatment of neuroendocrine tumours with 177 Lu-peptide receptor radionuclide therapy: Challenging clinical scenarios and their management

Peptide receptor radionuclide therapy (PRRT) for the treatment of patients with neuroendocrine tumours is usually well tolerated, with selection based on existing guidelines. However, there are various scenarios where the risk-benefit analysis of PRRT needs to be evaluated to limit any complications associated with PRRT. This review looks at 11 key scenarios where the risk-benefit of PRRT needs to be closely evaluated.

Response to Single Low-dose 177Lu-DOTA-EB-TATE Treatment in Patients with Advanced Neuroendocrine Neoplasm: A Prospective Pilot Study

Objective:¹⁷⁷Lu-DOTA-EB-TATE is a theranostic agent based on octreotate that uses an Evans blue structure to bind albumin to improve the pharmacokinetics and pharmacodynamics. This pilot study aims to evaluate the efficacy of a single low-dose treatment using ¹⁷⁷Lu-DOTA-EB-TATE in patients with advanced neuroendocrine neoplasm (NEN).

Methods: With IRB approval and informed consent, 4 NEN patients were enrolled to undergo ¹⁷⁷Lu-DOTA-EB-TATE treatment with a single low dose of 0.66 ± 0.06 GBq (17.8 ± 1.7 mCi); 3 other NEN patients were enrolled as controls to undergo ¹⁷⁷Lu-DOTA-TATE treatment with administered activity of 3.98 ± 0.17 GBq (107.6 ± 4.6 mCi). One primary tumor and 62 metastatic lesions in the 7 patients were evaluated by ⁶⁸Ga-DOTA-TATE PET/CT immediately before and one or three months after the treatment. Maximum SUV (SUV_max) of the tumors ≥2.0 cm in diameter were measured and percentage of change (ΔSUV) after treatment were calculated.

Results: All 4 patients subjected to ¹⁷⁷Lu-DOTA-EB-TATE treatment tolerated the administered activity without significant adverse effects and showed symptomatic remission. Among the patients, 40 tumors were found with diameter ≥2.0 cm, with the baseline SUV_max varied from 1.5-82.9 (35.9 ± 21.0) and the ΔSUVs before and three months after the treatment from -75.1-26.3% (-38.9 ± 25.5%). Twenty-nine (72.5%) of the tumors showed >15% decrease of SUV_max (ΔSUV = -75.1%--17.1%). There was a significant negative correlation between the baseline SUV_max and the ΔSUV after treatment (r = -0.852, P < 0.001). Compared with the control ¹⁷⁷Lu-DOTA-TATE therapy, the ¹⁷⁷Lu-DOTA-EB-TATE treatment using approximately 1/6 the dose showed no significant difference in ΔSUV (-7.9 ± 5.4% vs. -5.8 ± 3.9%, P = 0.189) as demonstrated by the tumors with comparable baseline SUV_max from 10.0-35.0.

Conclusion: A single low-dose ¹⁷⁷Lu-DOTA-EB-TATE treatment appears to be safe and effective in the treatment of NENs with high ⁶⁸Ga-DOTA-TATE uptake. This pilot study merits further investigation with increased dose and frequency of ¹⁷⁷Lu-DOTA-EB-TATE administration with potential advantages over ¹⁷⁷Lu-DOTA-TATE.

Renal Function Assessment During Peptide Receptor Radionuclide Therapy

Theranostics labeled with Y-90 or Lu-177 are highly efficient therapeutic approaches for the systemic treatment of various cancers including neuroendocrine tumors and prostate cancer. Peptide receptor radionuclide therapy (PRRT) has been used for many years for metastatic or inoperable neuroendocrine tumors. However, renal and hematopoietic toxicities are the major limitations for this therapeutic approach. Kidneys have been considered as the "critical organ" because of the predominant glomerular filtration, tubular reabsorption by the proximal tubules, and interstitial retention of the tracers. Severe nephrotoxity, which has been classified as grade 4-5 based on the "Common Terminology Criteria on Adverse Events," was reported in the range from 0%-14%. There are several risk factors for renal toxicity; patient-related risk factors include older age, preexisting renal disease, hypertension, diabetes mellitus, previous nephrotoxic chemotherapy, metastatic lesions close to renal parenchyma, and single kidney. There are also treatment-related issues, such as choice of radionuclide, cumulative radiation dose to kidneys, renal radiation dose per cycle, activity administered, number of cycles, and time interval between cycles. In the literature, nephrotoxicity caused by PRRT was documented using different criteria and renal function tests, from serum creatinine level to more accurate and sophisticated methods. Generally, serum creatinine level was used as a measure of kidney function. Glomerular filtration rate (GFR) estimation based on serum creatinine was preferred by several authors. Most commonly used formulas for estimation of GFR are "Modifications of Diet in Renal Disease" (MDRD) equation and "Cockcroft-Gault" formulas. However, more precise methods than creatinine or creatinine clearance are recommended to assess renal function, such as GFR measurements using Tc-99m-diethylenetriaminepentaacetic acid (DTPA), Cr-51-ethylenediaminetetraacetic acid (EDTA), or measurement of Tc-99m-MAG3 clearance, particularly in patients with preexisting risk factors for long-term nephrotoxicity. Proximal tubular reabsorption and interstitial retention of tracers result in excessive renal irradiation. Coinfusion of positively charged amino acids, such as l-lysine and l-arginine, is recommended to decrease the renal retention of the tracers by inhibiting the proximal tubular reabsorption. Furthermore, nephrotoxicity may be reduced by dose fractionation. Patient-specific dosimetric studies showed that renal biological effective dose of <0Gy was safe for patients without any risk factors. A renal threshold value <28Gy was recommended for patients with risk factors. Despite kidney protection, renal function impairment can occur after PRRT, especially in patients with risk factors and high single or cumulative renal absorbed dose. Therefore, patient-specific dosimetry may be helpful in minimizing the renal absorbed dose while maximizing the tumor dose. In addition, close and accurate renal function monitoring using more precise methods, rather than plasma creatinine levels, is essential to diagnose the early renal functional changes and to follow-up the renal function during the treatment.

Targeted Radionuclide Therapy: An Evolution Toward Precision Cancer Treatment

OBJECTIVE

This article reviews recent developments in targeted radionuclide therapy (TRT) approaches directed to malignant liver lesions, bone metastases, neuroendocrine tumors, and castrate-resistant metastatic prostate cancer and discusses challenges and opportunities in this field.

CONCLUSION

TRT has been employed since the first radioiodine thyroid treatment almost 75 years ago. Progress in the understanding of the complex underlying biology of cancer and advances in radiochemistry science, multimodal imaging techniques including the concept of "see and treat" within the framework of theranostics, and universal traction with the notion of precision medicine have all contributed to a resurgence of TRT.

ENETS Consensus Guidelines for the Standards of Care in Neuroendocrine Neoplasia: Peptide Receptor Radionuclide Therapy with Radiolabeled Somatostatin Analogues

The purpose of these guidelines is to assist physicians caring for patients with neuroendocrine neoplasia in considering eligibility criteria for peptide receptor radionuclide therapy (PRRT) and in defining the minimum requirements for PRRT. It is not these guidelines' aim to give recommendations on the use of specific radiolabelled somatostatin analogues for PRRT as different analogues are being used, and their availability is governed by varying international regulations. However, a recent randomized controlled trial, NETTER-1, has provided evidence that may establish ¹⁷⁷Lu-DOTA-octreotate (LutaThera®) as the first widely approved agent. It also makes recommendations on what minimal patient, tumour, and treatment outcome characteristics should be reported for PRRT to facilitate robust comparisons between studies.

Tissue-specific regulation of potassium homeostasis by high doses of cationic amino acids

The administration of l-arginine hydrochloride has been used for testing pituitary secretion in humans, and as an experimental model for induction of acute pancreatitis in rats and mice. Whereas in the first case, the administration of the amino acid is associated with hiperkalemia, in the model of acute pancreatitis no data are available on possible changes in potassium homeostasis. The present study shows that the acute administration to mice of l-arginine hydrochloride or other cationic amino acids almost duplicate plasma potassium levels. This effect was associated to a marked decrease of tissue potassium in both pancreas and liver. No changes were found in other tissues. These changes cannot be ascribed to the large load of chloride ions, since similar effects were produced when l-ornithine aspartate was administered. The changes in potassium levels were dependent on the dose. The displacement of intracellular potassium from the liver and pancreas to the extracellular compartment appears to be dependent on the entry of the cationic amino acid, since the administration of an equivalent dose of alfa-difluoromethyl ornithine HCl (DFMO), a non physiological analog of l-ornithine, which is poorly taken by the tissues in comparison with the physiological cationic amino acids, did not produce any change in potassium levels in pancreas and liver. The analyses of the expression of cationic amino acid transporters (CAT) suggest that the CAT-2 transporter may be implicated in the potassium/cationic amino acid interchange in liver and pancreas. The possible physiological or pathological relevance of these findings is discussed.

Prediction of clinically relevant hyperkalemia in patients treated with peptide receptor radionuclide therapy

Background

Peptide receptor radionuclide therapy (PRRT) is applied in patients with advanced neuroendocrine tumors. Co-infused amino acids (AA) should prevent nephrotoxicity. The aims of this study were to correlate the incidence of AA-induced hyperkalemia (HK) (≥5.0 mmol/l) and to identify predictors of AA-induced severe HK (>6.0).

Methods

In 38 patients, standard activity of ¹⁷⁷Lu-labelled somatostatin analogs was administered. Pre-therapeutic kidney function was assessed by renal scintigraphy and laboratory tests. For kidney protection, AA was co-infused. Biochemical parameters (potassium, glomerular filtration rate, creatinine, blood urea nitrogen (BUN), sodium, phosphate, chloride, and lactate dehydrogenase (LDH)) were obtained prior to 4 and 24 h after the AA infusion. Incidence of HK (≥5.0) was correlated with pre-therapeutic kidney function and serum parameters. Formulas for the prediction of severe hyperkalemia (>6.0) were computed and prospectively validated.

Results

At 4 h, HK (≥5.0) was present in 94.7% with severe HK (>6.0) in 36.1%. Values normalized after 24 h in 84.2%. Pre-therapeutic kidney function did not correlate with the incidence of severe HK.

Increases in K⁺ were significantly correlated with decreases in phosphate (r = −0.444, p < 0.005) and increases in BUN (r = 0.313, p = 0.056). A baseline BUN of >28 mg/dl had a sensitivity of 84.6% and a specificity of 60.0% (AUC = 0.75) in predicting severe HK of >6.0 (phosphate, AUC = 0.37).

Computing of five standard serum parameters (potassium, BUN, sodium, phosphate, LDH) resulted in a sensitivity of 88.9% and a specificity of 79.3% for the prediction of severe HK >6.0 (accuracy = 81.6%).

Conclusions

A combination of serum parameters predicted prospectively the occurrence of relevant HK with an accuracy of 81.6% underlining its potential utility for identifying ‘high-risk’ patients prone to PRRT.

Influence of the amount of co-infused amino acids on post-therapeutic potassium levels in peptide receptor radionuclide therapy

Background

Peptide receptor radionuclide therapy (PRRT) is routinely used for advanced or metastasized neuroendocrine tumours (NET). To prevent nephrotoxicity, positively charged amino acids (AA) are co-infused. The aim of this study was to correlate the risk for therapy-related hyperkalaemia with the total amount of AA infused.

Methods

Twenty-two patients undergoing PRRT with standard activities of ¹⁷⁷Lu-DOTATATE/-TOC were monitored during two following treatment cycles with co-infusion of 75 and 50 g of AA (l-arginine and l-lysine), respectively. Mean serum levels of potassium and other parameters (glomerular filtration rate [GFR], creatinine, blood urea nitrogen [BUN], phosphate, chloride, lactate dehydrogenase) prior to, 4 h and 24 h after AA infusion were compared.

Results

Self-limiting hyperkalaemia (>5.0 mmol/l) resolving after 24 h occurred in 91% (20/22) of patients in both protocols. Potassium levels, BUN, creatinine, GFR, phosphate, chloride and LDH showed a similar range at 4 h after co-infusion of 75 or 50 g of AA, respectively (p?>?0.05). Only GFR and creatinine levels at 24 h varied significantly between the two co-infusion protocols (p?<?0.05).

Conclusions

Hyperkalaemia is a frequent side effect of AA infusion in PRRT. Varying the dose of co-infused amino acids did not impact on the incidence and severity of hyperkalaemia.

68Gallium- and 90Yttrium-/ 177Lutetium: "theranostic twins" for diagnosis and treatment of NETs

Abundant expression of somatostatin receptors (SSTR) is frequently identified in differentiated neuroendocrine tumors and may serve as potential target for diagnostic imaging and treatment. This article discusses the “theranostic approach” of SSTR-targeting compounds including an overview of its role for diagnosis, staging and restaging, discussing its way to being established in clinical routine, and giving an outlook about further potentially relevant developments.

Neutrophil gelatinase associated lipocalin in acute kidney injury

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is a member of the lipocalin family of proteins. Usually, NGAL is produced and secreted by kidney tubule cells at low levels, but the amount produced and secreted into the urine and serum increases dramatically after ischemic, septic, or nephrotoxic injury of the kidneys. The purpose of our review article is to summarize the role of NGAL in acute kidney injury (AKI), emergent, and intensive care.

METHODS

A PubMed search was performed (only English-language articles concerning human subjects were considered) using each of the following search term combinations: neutrophil gelatinase-associated lipocalin OR NGAL and acute kidney injury OR AKI; cardiac surgery; heart failure OR cardiology; intensive care; emergency department OR emergency medicine; nephropathy OR nephrotoxicity and transplantation.

RESULTS

The results of our search yielded 339 articles. Of the 339 articles, 160 were eligible for review based on the predefined criteria for inclusion.

CONCLUSION

Based on the evidence reviewed, it is clear that patient NGAL level is an appropriate, sensitive, and specific early biomarker of AKI caused by a variety of different etiologies. It is advised that a multidisciplinary group of experts come together to make recommendations and propose a consensus of clinical procedures to advance the most efficacious NGAL monitoring protocol for early detection and treatment of patients with AKI.

Rapid blood clearance and lack of long-term renal toxicity of 177Lu-DOTATATE enables shortening of renoprotective amino acid infusion

PURPOSE

The aim of the study was to investigate the feasibility of shortening the recommended 4-h renoprotective amino acid infusion in patients receiving peptide receptor chemoradionuclide therapy (PRCRT) using radiosensitizing 5-fluorouracil. We evaluated the clearance of radiopeptide from the blood, long-term nephrotoxicity in patients undergoing PRCRT with the conventional 4-h amino acid infusion and renal uptake in patients receiving an abbreviated infusion.

METHODS

The whole-blood clearance of (177)Lu-DOTA-octreotate (LuTate) was measured in 13 patients receiving PRCRT. A retrospective analysis of short-term and long-term changes in glomerular filtration rate (GFR) in 96 consecutive patients receiving a 4-h infusion was performed. Renal LuTate retention estimated using quantitative SPECT/CT in 22 cycles delivered with a 2.5-h amino acid infusion was compared with that in 72 cycles with the 4-h infusion.

RESULTS

LuTate demonstrated biexponential blood clearance with an initial clearance half-time of 21 min. Approximately 88 % of blood activity was cleared within 2 h. With the 4-h protocol, there was no significant change in GFR (1.2 ml/min mean increase from baseline; 95 % CI -6.9 to 4.4 ml/min) and no grade 3 or 4 nephrotoxicity at the end of induction PRCRT. The long-term decline in GFR after a median follow up of 22 months was 2.2 ml/min per year. There was no significant difference in the renal LuTate retention measured in patients receiving a 2.5-h amino acid infusion compared to those who had a 4-h infusion.

CONCLUSION

The greatest renal exposure to circulating radiopeptide occurs in the first 1 - 2 h after injection. This, combined with the safety of LuTate PRCRT, allows consideration of an abbreviated amino acid infusion, increasing patient convenience and reducing human resource allocation.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.