Low concentrations of intravenous polygelines promote low-molecular weight proteinuria

Towards the Magic Radioactive Bullet: Improving Targeted Radionuclide Therapy by Reducing the Renal Retention of Radioligands

Targeted radionuclide therapy (TRT) is an emerging field and has the potential to become a major pillar in effective cancer treatment. Several pharmaceuticals are already in routine use for treating cancer, and there is still a high potential for new compounds for this application. But, a major issue for many radiolabeled low-to-moderate-molecular-weight molecules is their clearance via the kidneys and their subsequent reuptake. High renal accumulation of radioactive compounds may lead to nephrotoxicity, and therefore, the kidneys are often the dose-limiting organs in TRT with these radioligands. Over the years, different strategies have been developed aiming for reduced kidney retention and enhanced therapeutic efficacy of radioligands. In this review, we will give an overview of the efforts and achievements of the used strategies, with focus on the therapeutic potential of low-to-moderate-molecular-weight molecules. Among the strategies discussed here is coadministration of compounds that compete for binding to the endocytic receptors in the proximal tubuli. In addition, the influence of altering the molecular design of radiolabeled ligands on pharmacokinetics is discussed, which includes changes in their physicochemical properties and implementation of cleavable linkers or albumin-binding moieties. Furthermore, we discuss the influence of chelator and radionuclide choice on reabsorption of radioligands by the kidneys.

Exendin-4 analogs in insulinoma theranostics

Insulinomas, neuroendocrine tumors arising from pancreatic beta cells, often show overexpression of the glucagon‐like peptide‐1 receptor. Therefore, imaging with glucagon‐like peptide analog exendin‐4 can be used for diagnosis and preoperative localization. This review presents an overview of the development and clinical implementation of exendin‐based tracers for nuclear imaging, and the potential use of exendin‐4 based tracers for optical imaging and therapeutic applications such as peptide receptor radionuclide therapy or targeted photodynamic therapy.

Improving the Theranostic Potential of Exendin 4 by Reducing the Renal Radioactivity through Brush Border Membrane Enzyme-Mediated Degradation

As highly expressed in insulinomas, the glucagon-like peptide-1 receptor (GLP-1R) is believed to be an attractive target for diagnosis, localization, and treatment with radiolabeled exendin 4. However, the high and persistent radioactivity accumulation of exendin 4 in the kidneys limits accurate diagnosis and safe, as well as effective, radiotherapy in insulinomas. In this study, we intend to reduce the renal accumulation of radiolabeled exendin 4 through degradation mediated by brush border membrane enzymes. A new exendin 4 ligand NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 containing Met-Val-Lys (MVK) linker between the peptide and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) chelator was synthesized and labeled with ⁶⁸Ga. The in vitro mouse serum stability and cell binding affinity of the tracer were evaluated. Initial in vitro cleavage of the linker was determined by incubation of a model compound Boc-MVK-Dde with brush border membrane vesicles (BBMVs) with and without the inhibitor of neutral endopeptidase (NEP). Further cleavage studies were performed with the full structure of NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4. Kidney and urine samples were collected in the in vivo metabolism study after intravenous injection of ⁶⁸Ga-NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4. The microPET images were acquired in INS-1 tumor model at different time points; the radioactivity uptake of ⁶⁸Ga-NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 in tumor and kidneys were determined and compared with the control radiotracer without MVK linker. ⁶⁸Ga-NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 was stable in mouse serum. The MVK modification did not affect the affinity of NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 toward GLP-1R. The in vitro cleavage study and in vivo metabolism study confirmed that the MVK sequence can be recognized by BBM enzymes and cleaved at the amide bond between Met and Val, thus releasing the small fragment containing Met. MicroPET images showed that the tumor uptake of ⁶⁸Ga-NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 was comparable to that of the control, while the kidney uptake was significantly reduced. As a result, more favorable tumor to kidney ratios were achieved. In this study, a novel exendin 4 analogue, NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4, was successfully synthesized and labeled with ⁶⁸Ga. With the cleavable MVK sequence, this ligand could be cleaved by the enzymes on kidneys, and releasing the fragment of ⁶⁸Ga-NOTA-Met-OH, which will rapidly excrete from urine. As the high and consistent renal radioactivity accumulation could be significantly reduced, NOTA-MVK-Cys⁴⁰-Leu¹⁴-Exendin 4 shows great potential in the diagnosis and radiotherapy for insulinoma.

Volume Replacement Fluid Demarks Benign Insulinoma With 68Ga-DOTA-Exendin-4 PET/CT

Insulinomas are often difficult to localize. We present a 47-year-old woman who had recurrent neuroglycopenic symptoms and positive Whipple triad for 28 months. The 14 hours of fasting test confirmed the diagnosis of endogenous hyperinsulinemic hypoglycemia which is highly suspicious for the presence of an insulinoma. Previously performed MRI, endoscopic ultrasound, In-pentetreotide SPECT/CT, and Ga-DOTA-exendin-4 PET/CT did not show any evidence of an insulinoma. Subsequently, Ga-DOTA-exendin-4 PET/CT was repeated with the previous infusion of a colloidal volume replacement fluid (Gelofusine), known to reduce Ga-DOTA-exendin-4 accumulation in the kidneys. Consequently, the insulinoma was unmasked from the left kidney, allowing curative surgery.

Protective effect of Gelofusine against cRGD-siRNA-induced nephrotoxicity in mice

Based on successful targeting to the αvβ3 integrin of cyclic arginine–glycine–aspartic acid (cRGD), cRGD-conjugated small interfering RNA (siRNA) exhibits tumor targeting and has become a new treatment strategy for solid tumors. However, the nephrotoxicity caused by its renal retention limits its clinical application. Here, we evaluated the protective effect of Gelofusine against cRGD-conjugated siRNA-induced nephrotoxicity in mice. Male Kunming mice (six per group) were either co-injected with Gelofusine and cRGD-siRNA or injected with cRGD-siRNA alone. After administration of these treatments five times, creatinine and blood urea nitrogen (BUN) levels were determined. Hematoxylin–eosin staining (HE staining) and transferase dUTP nick end labeling (TUNEL) analysis were used to compare the difference in renal damage between the groups. Additionally, fluorescence imaging was used to observe the distribution of cRGD-siRNA in vivo. The group co-injected with Gelofusine and cRGD-siRNA displayed lower creatinine and BUN levels than the cRGD-siRNA-alone group and showed less renal damage upon HE staining and TUNEL analysis. Gelofusine decreased the retention time and accelerated the elimination of cRGD-siRNA from the organs, as observed in the fluorescence images. These data indicate that Gelofusine significantly increased the excretion of cRGD-conjugated siRNA and reduced the associated renal damage.

Gelofusine Attenuates Tubulointerstitial Injury Induced by cRGD-Conjugated siRNA by Regulating the TLR3 Signaling Pathway

Integrin αvβ3, which is selectively targeted by cyclic arginine-glycine-aspartic acid (cRGD) peptides, is significantly upregulated in tumors. Previous studies showed that small interfering RNA (siRNA) modified with cRGD (cRGD-siRNA) could significantly inhibit tumor growth through RNAi with oncogene expression. However, cRGD-siRNA is partially reabsorbed and trapped in the kidneys, causing renal injury in an unpredictable manner. This study aimed to investigate the influence of Gelofusine on tubulointerstitial injury induced by cRGD-siRNA in vitro and in vivo. The effect of Gelofusine on the distribution of cRGD-siRNA in tumor-bearing nude mice and wild-type mice was also explored. We found that Gelofusine inhibited apoptosis and activation of the innate immune response of human tubular epithelial cells induced by cRGD-siRNA in vitro. In addition, co-injection of Gelofusine efficiently reduced renal retention of cRGD-siRNA without affecting its tumor targeting in vivo. Further in vivo studies indicated that Gelofusine significantly attenuated tubulointerstitial injury induced by cRGD-siRNA through regulating Toll-like receptor 3 (TLR3)-mediated activation of the nuclear factor κ B (NF-κB) and caspase-3 apoptotic pathway. In conclusion, Gelofusine, acting as a novel and effective renal protective agent, could form a compound preparation with siRNA drugs for future clinical applications.

Gelofusine Ameliorates Colistin-Induced Nephrotoxicity

Colistin therapy is used as the last line of defense against life-threatening Gram-negative infections. Nephrotoxicity is the major dose-limiting side effect that impedes optimal dosing of patients. This study aims to examine the nephroprotective effect of the plasma volume expander gelofusine against colistin-induced nephrotoxicity. Renal protection was assessed in mice that were subcutaneously injected with colistin sulfate (14 mg/kg of body weight × 6 doses every 2 h; accumulated dose, 84 mg/kg) and simultaneously injected in the intraperitoneal region with gelofusine (75, 150, 300, or 600 mg/kg × 6). At 2 and 20 h after the last colistin dose, mice were euthanized, and the severity of renal alteration was examined histologically. Histological findings in mice revealed that colistin-induced nephrotoxicity was ameliorated by gelofusine in a dose-dependent manner, whereas significant histological abnormalities were detected in the kidneys of mice in the colistin-only group. The impact of coadministered gelofusine on colistin pharmacokinetics was investigated in rats. Rats were administered a single intravenous dose of gelofusine at 400 mg/kg 15 min prior to the intravenous administration of colistin (1 mg/kg). Gelofusine codosing did not alter the pharmacokinetics of colistin in rats; however, gelofusine did significantly lower the accumulation of colistin in the kidney tissue of mice. This is the first study demonstrating the protective effect of gelofusine against colistin-induced nephrotoxicity. These findings highlight the clinical potential of gelofusine as a safe adjunct for ameliorating the nephrotoxicity and increasing the therapeutic index of polymyxins.

Increased urinary excretion of albumin, hemopexin, transferrin and VDBP correlates with chronic sensitization to gentamicin nephrotoxicity in rats

Drug nephrotoxicity is a serious health and economic problem worldwide. Rats can be acutely sensitized to acute kidney injury (AKI) by subnephrotoxic treatments with potentially nephrotoxic drugs. Acquired sensitization to AKI poses a silent risk impossible to diagnose pre-emptively with the technology available at the clinical level. Herein, we hypothesized whether a chronic, subnephrotoxic insult to the kidneys might result in chronically acquired sensitization to AKI, and whether chronic sensitization might be detected through specific urinary markers. To this end, rats were treated with a subtoxic dosage of the experimental nephrotoxin uranyl nitrate (UN) in the drinking water for 21 weeks, or plain water (as control), and then with low-dose gentamicin for 7 days. Renal function and renal tissue damage were evaluated through the experiment. The mild renal damage caused by gentamicin was markedly magnified in rats having received UN chronically, which was evident both at the functional and histological level. Four proteins, namely albumin, hemopexin, transferrin and vitamin D binding protein were increased in the urine in temporal association with the appearance of chronic predisposition. Although further studies are necessary, our results suggest that these proteins might be potentially used as markers of hidden, chronic predisposition to gentamicin nephrotoxicity, in order to appropriately and pre-emptively stratify and handle individuals according to their specific risk in the long term, and to conveniently optimize their life conditions or additional clinical procedures or treatments that might trigger the disease. This might reduce AKI incidence and severity and the associated costs.

Reduction of renal uptake of 111In-DOTA-labeled and A700-labeled RAFT-RGD during integrin αvβ3 targeting using single photon emission computed tomography and optical imaging

Integrin α(v)β(3) expression is upregulated during tumor growth and invasion in newly formed endothelial cells in tumor neovasculature and in some tumor cells. A tetrameric RGD-based peptide, regioselectively addressable functionalized template-(cyclo-[RGDfK])4 (RAFT-RGD), specifically targets integrin α(v)β(3) in vitro and in vivo. When labeled with indium-111, the RAFT-RGD is partially reabsorbed and trapped in the kidneys, limiting its use for further internal targeted radiotherapy and imaging investigations. We studied the effect of Gelofusine on RAFT-RGD renal retention in tumor-bearing mice. Mice were imaged using single photon emission computed tomography and optical imaging 1 and 24 h following tracer injection. Distribution of RAFT-RGD was further investigated by tissue removal and direct counting of the tracer. Kidney sections were analyzed by confocal microscopy. Gelofusine significantly induced a >50% reduction of the renal reabsorption of (111)In-DOTA-RAFT-RGD and A700-RAFT-RGD, without affecting tumor uptake. Injection of Gelofusine significantly reduced the renal retention of labeled RAFT-RGD, while increasing the tumor over healthy tissue ratio. These results will lead to the development of future therapeutic approaches.

Dose-response effect of Gelofusine on renal uptake and retention of radiolabelled octreotate in rats with CA20948 tumours

Purpose

Peptide receptor radionuclide therapy using β-emitting radiolabelled somatostatin analogues like DOTA,Tyr³-octreotate shows beneficial results in patients suffering from somatostatin receptor overexpressing tumours. However, after high-dose therapy partial renal reabsorption of radiopeptides may lead to nephrotoxicity. Co-infusion of lysine/arginine lowers renal retention of these radiopeptides without affecting tumour uptake. Recently co-administration of Gelofusine has been described to have a comparable kidney-protecting effect in rats. In the present study optimal dosing of Gelofusine co-administration was studied in tumour-bearing rats.

Methods

Doses of 40, 80, 120 or 160 mg/kg Gelofusine were co-injected with 15 µg DOTA,Tyr³-octreotate, labelled with 3 MBq ¹¹¹In for biodistribution (24 h post-injection, n = 4 per group) and with 60 MBq ¹¹¹In for microSPECT imaging experiments at 3, 24 and 48 h post-injection. An additional group of rats received 80 mg/kg Gelofusine plus 400 mg/kg lysine co-injection. Biodistribution studies were performed both in older (475 g) and younger (300 g) rats, the latter bearing CA20948 tumours.

Results

Co-injection of 40 mg/kg Gelofusine resulted in 40–50% reduction of renal uptake and retention of ¹¹¹In-DOTA,Tyr³-octreotate, whereas higher doses further increased the reduction to 50–60% in both groups of rats. Combining Gelofusine and lysine caused 70% reduction of renal uptake. The uptake of radiolabelled octreotate both in somatostatin receptor-expressing normal tissues and tumours was not affected by Gelofusine co-injection.

Conclusion

In rats co-injection of 80 mg/kg Gelofusine resulted in maximum reduction of renal retention of ¹¹¹In-DOTA,Tyr³-octreotate, which was further improved when combined with lysine. Tumour uptake of radiolabelled octreotate was not affected, resulting in an increased tumour to kidney ratio.

Critical care "normality": individualized versus protocolized care

Patients with critical illness are heterogeneous, with differing physiologic requirements over time. Goal-directed therapy in the emergency room demonstrates that protocolized care could result in improved outcomes. Subsequent studies have confirmed benefit with such a "bundle-based approach" in the emergency room and in preoperative and postoperative scenarios. However, this cannot be necessarily extrapolated to the medium-term and long-term care pathway of the critically ill patient. It is likely that the development of mitochondrial dysfunction could result in goal-directed types of approaches being detrimental. Equally, arterial pressure aims are likely to be considerably different as the patient's physiology moves toward "hibernation." The agents we utilize as sedative and pressor agents have considerable effects on immune function and the inflammatory profile, and should be considered as part of the total clinical picture. The role of gut failure in driving inflammation is considerable, and the drive to feed enterally, regardless of aspirate volume, may be detrimental in those with degrees of ileus, which is often a difficult diagnosis in the critically ill. The pathogenesis of liver dysfunction may be, at least in part, related to venous engorgement that will contribute toward portal hypertension and gut edema. This, in association with loss of the hepatosplanchnic buffer response, it is likely to contribute to venous pooling in the abdominal cavity, impaired venous return, and decreased central blood volumes. Therapies such as those used in "small-for-size syndrome" may have a role in the chronic stages of septic vascular failure.

Kidney protection during peptide receptor radionuclide therapy with somatostatin analogues

This review focuses on the present status of kidney protection during peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues. This treatment modality for somatostatin receptor-positive tumours is limited by renal reabsorption and retention of radiolabelled peptides resulting in dose-limiting high kidney radiation doses. Radiation nephropathy has been described in several patients. Studies on the mechanism and localization demonstrate that renal uptake of radiolabelled somatostatin analogues largely depends on the megalin/cubulin system in the proximal tubule cells. Thus methods are needed that interfere with this reabsorption pathway to achieve kidney protection. Such methods include coadministration of basic amino acids, the bovine gelatin-containing solution Gelofusine or albumin fragments. Amino acids are already commonly used in the clinical setting during PRRT. Other compounds that interfere with renal reabsorption capacity (maleic acid and colchicine) are not suitable for clinical use because of potential toxicity. The safe limit for the renal radiation dose during PRRT is not exactly known. Dosimetry studies applying the principle of the biological equivalent dose (correcting for the effect of dose fractionation) suggest that a dose of about 37 Gy is the threshold for development of kidney toxicity. This threshold is lower when risk factors for development of renal damage exist: age over 60 years, hypertension, diabetes mellitus and previous chemotherapy. A still experimental pathway for kidney protection is mitigation of radiation effects, possibly achievable by cotreatment with amifostine (Ethylol), a radiation protector, or with blockers of the renin-angiotensin-aldosterone system. Future perspectives on improving kidney protection during PRRT include combinations of agents to reduce renal retention of radiolabelled peptides, eventually together with mitigating medicines. Moreover, new somatostatin analogues with lower renal retention may be developed. Furthermore, knowledge on kidney protection from radiolabelled somatostatin analogues may be expanded to other peptides.

Renal uptake and metabolism of radiopharmaceuticals derived from peptides and proteins

Radiolabeled anti-CD20 antibodies have demonstrated impressive efficacy in the treatment of relapsed non-Hodgkin lymphoma. This encourages the treatment of solid tumor with radiolabeled antibody fragments and peptides. However, both preclinical and clinical studies revealed that persistent localization of radioactivity in the kidney constitutes a major obstacle that compromises therapeutic efficacy. Recent extensive studies show that long residence times of radiolabeled end products from lysosomes are responsible for the renal radioactivity levels. Recent studies have also elucidated the involvement of megalin-cubilin in renal tubular reabsorption of radiolabeled antibody fragments and peptides. In light of these findings, efforts are being made to block tubular reabsorption of radiolabeled antibody fragments and peptides by competitive inhibitors, charge modification, and PEGylation. An interposition of an enzyme-cleavable linkage between antibody fragments and radiolabels would constitute an alternative approach to reduce renal radioactivity levels. Recent findings of these studies will be described.

Renal impact of fluid management with colloids: a comparative review

BACKGROUND AND OBJECTIVES

Colloids such as hydroxyethyl starch (HES), gelatin, dextran and albumin are useful for maintaining renal perfusion and function. The comparative renal effects of colloids have not been previously reviewed.

METHODS

Computer searches of the MEDLINE and EMBASE bibliographic databases and the Cochrane Library were conducted using the search terms: colloids; hetastarch; gelatin; dextrans; serum albumin; kidney failure; cardiac surgical procedures; and kidney transplantation. Relevant studies were also sought through hand searching and examination of reference lists. Results of identified studies were qualitatively summarized with account taken for potential confounding factors.

RESULTS

The three artificial colloids HES, gelatin and dextran all exhibited troublesome renal side-effects. Randomized trials have demonstrated adverse renal effects of HES in sepsis and surgery. Undesirable renal effects are common to all available HES solutions regardless of molecular weight, substitution or C2/C6 ratio. While some of its effects may be less severe than those of HES, gelatin also can adversely affect the kidney. A negative renal impact of dextran is well-established, although this colloid is now less extensively used than formerly. As the normal endogenous colloid, albumin exhibits a wide margin of renal safety, although albumin overdose needs to be avoided. Albumin also appears to exert protective effects on the kidney such as inhibition of apoptosis and scavenging of reactive oxygen species.

CONCLUSIONS

Colloids display important differences in their actions on the kidney. These contrasting renal effects should be considered in making fluid management decisions.