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

Positron emission tomography imaging of tumor angiogenesis and monitoring of antiangiogenic efficacy using the novel tetrameric peptide probe 64Cu-cyclam-RAFT-c(-RGDfK-)4

⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ is a novel multimeric positron emission tomography (PET) probe for α_Vβ₃ integrin imaging. Its uptake and α_Vβ₃ expression in tumors showed a linear correlation. Since α_Vβ₃ integrin is strongly expressed on activated endothelial cells during angiogenesis, we aimed to determine whether ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ PET can be used to image tumor angiogenesis and monitor the antiangiogenic effect of a novel multi-targeted tyrosine kinase inhibitor, TSU-68. Athymic nude mice bearing human hepatocellular carcinoma HuH-7 xenografts, which expressed negligible α_Vβ₃ levels on the tumor cells, received intraperitoneal injections of TSU-68 or the vehicle for 14 days. Antiangiogenic effects were determined at the end of therapy in terms of ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ uptake evaluated using PET, biodistribution assay, and autoradiography, and they were compared with microvessel density (MVD) determined by CD31 immunostaining. ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ PET enabled clear tumor visualization by targeting the vasculature, and the biodistribution assay indicated high tumor-to-blood and tumor-to-muscle ratios of 31.6 ± 6.3 and 6.7 ± 1.1, respectively, 3 h after probe injection. TSU-68 significantly slowed tumor growth and reduced MVD; these findings were consistent with a significant reduction in the tumor ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ uptake. Moreover, a linear correlation was observed between tumor MVD and the corresponding standardized uptake value (SUV) (r = 0.829, P = 0.011 for SUV_mean; r = 0.776, P = 0.024 for SUV_max) determined by quantitative PET. Autoradiography and immunostaining showed that the distribution of intratumoral radioactivity and tumor vasculature corresponded. We concluded that ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ PET can be used for in vivo angiogenesis imaging and monitoring of tumor response to antiangiogenic therapy.

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.

Oral gene delivery with cyclo-(D-Trp-Tyr) peptide nanotubes

The feasibility of cyclo-(D-Trp-Tyr) peptide nanotubes (PNTs) as oral gene delivery carriers was investigated in nude mice with eight 40 μg doses of pCMV-lacZ in 2 days at 3 h intervals. The association between DNA and PNTs, the DNase I stability of PNTs-associated DNA, and in vitro permeability of DNA were estimated. The results showed that the cyclo-(D-Trp-Tyr) PNTs self-associated at concentrations above 0.01 mg/mL. Plasmid DNA associated with PNTs with a binding constant of 3.2 × 10(8) M(-1) calculated by a fluorescence quenching assay. PNTs were able to protect DNA from DNase I, acid, and bile digestion for 50 min, 60 min, and 180 min, respectively. The in vitro duodenal apparent permeability coefficient of pCMV-lacZ calculated from a steady state flux was increased from 49.2 ± 21.6 × 10(-10) cm/s of naked DNA to 395.6 ± 142.2 × 10(-10) cm/s of pCMV-lacZ/PNT formulation. The permeation of pCMV-lacZ formulated with PNTs was found in an energy-dependent process. Furthermore, β-galatosidase (β-Gal) activity in tissues was quantitatively assessed using chlorophenol red-β-D-galactopyranoside (CPRG) and was significantly increased by 41% in the kidneys at 48 h and by 49, 63, and 46% in the stomach, duodenum, and liver, respectively, at 72 h after the first dose of oral delivery of pCMV-lacZ/PNT formulation. The organs with β-Gal activity were confirmed for the presence of pCMV-lacZ DNA with Southern blotting analysis and intracellular tracing the TM-rhodamine-labeled DNA and the presence of mRNA by reverse transcription-real time quantitative PCR (RT-qPCR). Another plasmid (pCMV-hRluc) encoding Renilla reniformis luciferase was used to confirm the results. An increased hRluc mRNA and luciferase in stomach, duodenum, liver, and kidney were detected by RT-qPCR, ex vivo bioluminescence imaging, luciferase activity quantification, and immunostaining, respectively.

Cancer radioimmunotherapy

Targeting of radionuclides with antibodies, or radioimmunotherapy, has been an active field of research spanning nearly 50 years, evolving with advancing technologies in molecular biology and chemistry, and with many important preclinical and clinical studies illustrating the benefits, but also the challenges, which all forms of targeted therapies face. There are currently two radiolabeled antibodies approved for the treatment of non-Hodgkin lymphoma, but radioimmunotherapy of solid tumors remains a challenge. Novel antibody constructs, focusing on treatment of localized and minimal disease, and pretargeting are all promising new approaches that are currently under investigation.

Nephrotoxicity profiles and threshold dose values for [177Lu]-DOTATATE in nude mice

INTRODUCTION

In peptide receptor radionuclide therapy for neuroendocrine tumors the main dose-limiting tissue is found in the kidneys because of tubular reabsorption and retention of radioactivity. The aim of this study was to quantify late effects in renal cortex of nude mice exposed to high amounts of [(177)Lu]-DOTA-Tyr(3)-octreotate ([(177)Lu]-DOTATATE), and to determine whether a threshold dose value exists for these findings.

METHODS

Nude mice were exposed to 90, 120 or 150 MBq of [(177)Lu]-DOTATATE. Renal toxicity was evaluated up to 6 months after injection. Blood samples were collected to examine renal functional markers, and after sacrifice at 6 months changes in renal morphology were explored. Tissue damage was estimated by quantifying the relative area of the different subunits in the renal cortex using point counting. Additional morphological signs of radiation damage were also noted. The absorbed doses to the kidneys were estimated by previously determined kidney pharmacokinetics and Monte Carlo simulations for different assumptions regarding the activity distribution.

RESULTS

Increased serum creatinine and urea values indicated long-term renal toxicity. The tissue area occupied by proximal tubules decreased with increasing doses of [(177)Lu]-DOTATATE, whereas the other subunits in cortex slightly increased. The mean absorbed dose in the renal cortex for [(177)Lu]-DOTATATE was estimated to be 35-58 Gy for the different groups of animals. A dose-response relationship was observed for proximal tubular damage, and a threshold dose value of 24 Gy (BED 37 Gy) was determined.

CONCLUSIONS

Selective morphological changes in kidney cortex of nude mice were quantified and appeared in a dose dependent manner after injection of high amounts of [(177)Lu]-DOTATATE.

PLGA nanoparticles for peptide receptor radionuclide therapy of neuroendocrine tumors: a novel approach towards reduction of renal radiation dose

BACKGROUND

Peptide receptor radionuclide therapy (PRRT), employed for treatment of neuroendocrine tumors (NETs) is based on over-expression of Somatostatin Receptors (SSTRs) on NETs. It is, however, limited by high uptake and retention of radiolabeled peptide in kidneys resulting in unnecessary radiation exposure thus causing nephrotoxicity. Employing a nanocarrier to deliver PRRT drugs specifically to the tumor can reduce the associated nephrotoxicity. Based on this, (177)Lu-DOTATATE loaded PLGA nanoparticles (NPs) were formulated in the present study, as a potential therapeutic model for NETs.

METHODOLOGY AND FINDINGS

DOTATATE was labeled with Lutetium-177 ((177)Lu) (labeling efficiency 98%; R(f)∼0.8). Polyethylene Glycol (PEG) coated (177)Lu-DOTATATE-PLGA NPs (50:50 and 75:25) formulated, were spherical with mean size of 304.5±80.8 and 733.4±101.3 nm (uncoated) and 303.8±67.2 and 494.3±71.8 nm (coated) for PLGA(50:50) and PLGA(75:25) respectively. Encapsulation efficiency (EE) and In-vitro release kinetics for uncoated and coated NPs of PLGA (50:50 & 75:25) were assessed and compared. Mean EE was 77.375±4.98% & 67.885±5.12% (uncoated) and 65.385±5.67% & 58.495±5.35% (coated). NPs showed initial burst release between 16.64-21.65% with total 42.83-44.79% over 21 days. The release increased with coating to 20.4-23.95% initially and 60.97-69.12% over 21 days. In-vivo studies were done in rats injected with (177)Lu-DOTATATE and (177)Lu-DOTATATE-NP (uncoated and PEG-coated) by imaging and organ counting after sacrificing rats at different time points over 24 hr post-injection. With (177)Lu-DOTATATE, renal uptake of 37.89±10.2%ID/g was observed, which reduced to 4.6±1.97% and 5.27±1.66%ID/g with uncoated and coated (177)Lu-DOTATATE-NP. The high liver uptake with uncoated (177)Lu-DOTATATE-NP (13.68±3.08% ID/g), reduced to 7.20±2.04%ID/g (p = 0.02) with PEG coating.

CONCLUSION

PLGA NPs were easily formulated and modified for desired release properties. PLGA 50:50 NPs were a more suitable delivery vehicle for (177)Lu-DOTATATE than PLGA 75:25 because of higher EE and slower release rate. Reduced renal retention of (177)Lu-DOTATATE and reduced opsonisation strongly advocate the potential of (177)Lu-DOTATATE-PLGA-PEG NPs to reduce radiation dose in PRRT.

Cohort study of somatostatin-based radiopeptide therapy with [(90)Y-DOTA]-TOC versus [(90)Y-DOTA]-TOC plus [(177)Lu-DOTA]-TOC in neuroendocrine cancers

PURPOSE

Radiopeptide therapy is commonly performed with a single radioisotope. We aimed to compare the effectiveness of somatostatin-based radiopeptide therapy with a single versus a combination of radioisotopes.

PATIENTS AND METHODS

In a cohort study, patients with metastasized neuroendocrine cancer were treated with repeated cycles of (90)yttrium-labeled tetraazacyclododecane-tetraacetic acid modified Tyr-octreotide ([(90)Y-DOTA]-TOC) or with cycles alternating between [(90)Y-DOTA]-TOC and (177)lutetium-labeled DOTA-TOC ([(177)Lu-DOTA]-TOC) until tumor progression or permanent toxicity. Multivariable Cox regression and competing risk regression were used to study predictors of survival and renal toxicity in patients completing three or more treatment cycles.

RESULTS

A total of 486 patients completed three or more treatment cycles; 237 patients received [(90)Y-DOTA]-TOC and 249 patients received [(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC. Patients receiving [(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC had a significantly longer survival than patients receiving [(90)Y-DOTA]-TOC alone (5.51 v 3.96 years; hazard ratio, 0.64; 95% CI, 0.47 to 0.88; P = .006). The rates of severe hematologic toxicities (6.3% v 4.4%; P = .25) and severe renal toxicity (8.9% v 11.2%; P = .47) were comparable in both groups.

CONCLUSION

[(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC was associated with improved overall survival compared with [(90)Y-DOTA]-TOC alone in patients completing three or more cycles of treatment. Contrary to the current practice in radiopeptide therapy, our results suggest an advantage of using a combination of radioisotopes.

Engineering of affibody molecules for therapy and diagnostics

Affibody molecules are small and robust non-immunoglobulin affinity ligands capable of binding to a wide range of protein targets. They are selected from combinatorial libraries based on a 58 amino acid, three-alpha-helical Z-domain scaffold. They share no sequence or structural homologies to antibodies and in contrast to antibodies they can be functionally produced both by peptide synthesis and by recombinant expression in Escherichia coli. Protein engineering is used to adapt Affibody molecules binding to a target of interest to the specific demands imposed by the intended application. Obviously, the optimal molecule for molecular imaging will be different from the optimal molecule for therapy. Here, we describe general strategies to optimize Affibody molecules for diagnostic imaging and therapy applications.

In vitro and in vivo evaluation of melanin-binding decapeptide 4B4 radiolabeled with 177Lu, 166Ho, and 153Sm radiolanthanides for the purpose of targeted radionuclide therapy of melanoma

Melanoma is a malignancy with increasing incidence. Although primary tumors that are localized to the skin can be successfully treated by surgical removal, there is no satisfactory treatment for metastatic melanoma, a condition that has currently an estimated 5-year survival of just 6%. During the last decade, β- or α-emitter-radiolabeled peptides that bind to different receptors on a variety of tumors have been investigated as potential therapeutic agents in both the preclinical and clinical settings with encouraging results. A recent study demonstrated that 188-Rhenium ((188)Re)-labeled, via HYNIC ligand, fungal melanin-binding decapeptide 4B4 was effective against experimental MNT1 human melanoma and was safe to normal melanized tissues. The availability of radiolanthanides with diverse nuclear emission schemes and half-lives provides an opportunity to expand the repertoire of peptides for radionuclide therapy of melanoma. The melanin-binding decapeptide 4B4 was radiolabeled with (177)Lu, (166)Ho, and (153)Sm via a DO3A chelate. The stability studies of Ln*-DO3A-4B4 in phosphate-buffered saline, serum, and a hydroxyapatite assay demonstrated that (177)Lu-labeled peptide was more stable than (166)Ho- and (153)Sm-labeled peptides, most likely because of the smallest ionic radius of the former allowing for better complexation with DO3A. Binding of Ln*-DO3A-4B4 to the lysed highly melanized MNT1 melanoma cells demonstrated the specificity of peptides binding to melanin. In vivo biodistribution data for (177)Lu-DO3A-4B4 given by intraperitoneal administration to lightly pigmented human metastatic A2058 melanoma-bearing mice demonstrated very high uptake in the kidneys and low tumor uptake. Intravenous administration did not improve the tumor uptake. The plausible explanation of low tumor uptake of (177)Lu-DO3A-4B4 could be its decreased ability to bind to melanin during in vitro binding studies in comparison with (188)Re-HYNIC-4B4, exacerbated by the very fast clearance from the blood and the kidneys "sink" effect.

Rhenium-188 labeled recombinant human plasminogen kringle5 (rhk5) and preliminary biodistribution. Evaluation in mice bearing A549 tumours

AIM

Angiogenesis plays a critical role in tumour formation and metastasis. Suitable radiolabeled angiogenesis inhibitor can be used for noninvasive imaging of angiogenesis and radionuclide therapy. Here we prepare rhenium-188 labeled recombinant human plasminogen kringle5 (188Re-rhk5) in a convenient manner than evaluate its properties in A549 lung adenocarcinoma.

METHODS

188Re-rhk5 was obtained by conjugating His group at the C end of rhk5 with fac-[188Re(H2O)3(CO)3]+. Chelating efficiency of fac-[188Re(H2O)3(CO)3]+ and radiolabeling efficiency of 188Re-rhk5 were measured by radio thin-layer chromatography (RTLC). In vitro stability of 188Re-rhk5 was determined in human serum at 37°C and analyzed by RTLC. Competition test was also performed to verify the specificity of binding. A biodistribution study was carried out in nude mice bearing A549 lung adenocarcinoma.

RESULTS

188Re-rhk5 was obtained with a radiolabel efficiency of 66.1%, the radiochemical purity (RCP) can reach 95.2% after purification. 188Re-rhk5 showed high stability in human serum, the RCP was more than 80% even 12 h after incubation. Competition test showed a high binding specificity. Furthermore, this radio-complex was excreted mainly through kidneys and showed specific tumour uptake in mice bearing A549 tumours.

CONCLUSION

188Re-rhk5 was prepared by a simple method. Preliminary biodistribution results showed its potential as an agent for possible tumour imaging, therapy and encouraged further investigation.

Immuno-imaging using nanobodies

Immuno-imaging is a developing technology that aims at studying disease in patients using imaging techniques such as positron emission tomography in combination with radiolabeled immunoglobulin derived targeting probes. Nanobodies are the smallest antigen-binding antibody-fragments and show fast and specific targeting in vivo. These probes are currently under investigation as therapeutics but preclinical studies indicate that nanobodies could also become the next generation of magic bullets for immuno-imaging. Initial data show that imaging can be performed as early as 1 hour post-injection enabling the use of short-lived radio-isotopes. These unique properties should enable patient friendly and safe imaging protocols. This review focuses on the current status of radiolabeled nanobodies as targeting probes for immuno-imaging.

Allosteric drugs: the interaction of antitumor compound MKT-077 with human Hsp70 chaperones

Hsp70 (heat shock protein 70 kDa) chaperones are key to cellular protein homeostasis. However, they also have the ability to inhibit tumor apoptosis and contribute to aberrant accumulation of hyperphosphorylated tau in neuronal cells affected by tauopathies, including Alzheimer's disease. Hence, Hsp70 chaperones are increasingly becoming identified as targets for therapeutic intervention in these widely abundant diseases. Hsp70 proteins are allosteric machines and offer, besides classical active-site targets, also opportunities to target the mechanism of allostery. In this work, it is demonstrated that the action of the potent anticancer compound MKT-077 (1-ethyl-2-[[3-ethyl-5-(3-methylbenzothiazolin-2-yliden)]-4-oxothiazolidin-2-ylidenemethyl] pyridinium chloride) occurs through a differential interaction with Hsp70 allosteric states. MKT-077 is therefore an "allosteric drug." Using NMR spectroscopy, we identify the compound's binding site on human HSPA8 (Hsc70). The binding pose is obtained from NMR-restrained docking calculations, subsequently scored by molecular-dynamics-based energy and solvation computations. Suggestions for the improvement of the compound's properties are made on the basis of the binding location and pose.

Phase II study of radiopeptide 177Lu-octreotate and capecitabine therapy of progressive disseminated neuroendocrine tumours

PURPOSE

In this phase II study we investigated the safety and efficacy of combination capecitabine and (177)Lu-octreotate for the treatment of disseminated, progressive, unresectable neuroendocrine tumours (NETs).

METHODS

Enrolled in the study were 33 patients with biopsy-proven NETs, positive (111)In-octreotide scintigraphy and progressive disease measurable by CT/MRI who were to receive four cycles of 7.8 GBq (177)Lu-octreotate 8-weekly, with 14 days of 1,650 mg/m(2) capecitabine per day.

RESULTS

Of the 33 patients, 25 completed four cycles. Minimal transient myelosuppression at 3-4 weeks caused grade 3 thrombocytopenia in one patient but no neutropenia. Nephrotoxicity was absent. Critical organ radiation dosimetry provided median estimates of the dose per cycle to the kidneys of 2.4 Gy and to the liver of 4.8 Gy, and showed cumulative doses all below toxic thresholds. Objective response rates (ORR) were 24% partial response (PR), 70% stable disease (SD) and 6% progressive disease. Median progression-free survival and median overall survival had not been reached at a median follow-up of 16 months (range 5-33 months). Survival at 1 and 2 years was 91% (95% CI 75-98%) and 88% (95% CI 71-96%), respectively.

CONCLUSION

The addition of capecitabine radiosensitizing chemotherapy does not increase the minimal toxicity of (177)Lu-octreotate radiopeptide therapy and led to an ORR of 24% PR and 70% minor response or SD in patients with progressive metastatic NETs. Tumour control and stabilization of disease was obtained in 94% of these patients.