Reducing the renal uptake of radiolabeled antibody fragments and peptides for diagnosis and therapy: present status, future prospects and limitations

Abstract

Elevated renal uptake and prolonged retention of radiolabeled antibody fragments and peptides is a problem in the therapeutic application of such agents. Over recent years, one of the focuses of research has therefore been to develop suitable methods to reduce this renal uptake, and to evaluate whether the resulting methodology will benefit therapy with antibody fragments and peptides. In these studies it has been shown that the kidney uptake of antibody fragments in animals can be reduced in a dose-dependent manner by almost one order of magnitude by the systemic administration of cationic amino acids and their derivatives, whereas the uptake in all other organs, as well as the tumor, remains unaffected. A similar reduction in renal retention is achieved for all intracellularly retained radionuclides (e.g., radiometals) or radioiodinated immunoconjugates, as well as for smaller peptides. Lysine is usually the preferred agent, and its d- and l-isomers are equally effective whether given intraperitoneally or orally. Amino sugars are effective, but their N-acetyl derivatives, lacking the positive charge, are not. Basic polypeptides are also effective, and their potency increases with increasing molecular weight (i.e., the amount of positive charges per molecule). Urine analysis of treated individuals shows the excretion of unmetabolized, intact fragments or peptides, in contrast to mostly low-molecular-weight metabolites in untreated controls. In therapy studies using radiometal-conjugated Fab fragments, the kidney is the first dose-limiting organ. Administration of cationic amino acids results in a substantial increase in the maximum tolerated dose of such Fab fragments. No biochemical or histological evidence of renal damage has been observed under these conditions. As was the case in animal studies, in pilot clinical trials the renal uptake in patients injected with Fab' fragments and given amino acids could be decreased significantly, whereas the uptake by all other organs remained unaffected. These recent studies indicate that a variety of basic compounds are capable of inhibiting the tubular reabsorption of peptides and proteins, thus significantly lowering the renal uptake of antibody fragments or peptides in both animals and patients. On a molecular basis, the effect seems to rely essentially on the presence of a positively charged amino group. Thus, radiation nephrotoxicity of antibody fragments and peptides can be overcome successfully; this may provide new prospects for cancer therapy with radiolabeled antibody fragments and peptides.

Comparison of the Biodistribution and Tumor Targeting of Two 99mTc-Labeled Anti-EGFR Nanobodies in Mice, Using Pinhole SPECT/Micro-CT

“…Renal uptake was high for both compounds; this property is typical for peptides and small proteins whose molecular weight is below the threshold that can be filtered by the glomerular membrane (,60 kDa) (14). It is believed that nonspecific renal activity accumulation is caused by the electrostatic interactions between positively charged peptides and the negatively charged surface of tubular cells as peptides are filtered in the glomerulus and reabsorbed in the cells of the proximal tubuli (15).…”

“…Elevated renal uptake and prolonged retention of radiolabeled Nanobodies might be problematic not only for imaging lesions in the vicinity of the kidneys but also for the therapeutic application of such agents. However, encouraging results have recently been achieved in reducing radiation nephrotoxicity by infusion of cationic or polycationic amino acids before the administration of the radiolabeled compounds (14,16,17). Renal uptake was high for both compounds but was significantly higher for 99m Tc-7C12 than for 99m Tc-7D12.…”

Localization, mechanism and reduction of renal retention of technetium‐99m labeled epidermal growth factor receptor‐specific nanobody in mice

“…This problem is common to most small proteins or peptide tracers. The kidney retrieves useful substances from the glomerular filtrate and radiometal-chelated amino acids are trapped, leading to high absorbed doses of radiation (12). Since the radiation dose to the kidney might be a dose-limiting factor in Blood samples were collected at indicated time points, their activity was determined with a gamma-counter and expressed as percentage of the administered activity per total blood volume (%IA/TBV).…”

“…It is believed to be related to the extensive apical endocytic apparatus of the renal proximal tubule that is responsible for reabsorption of molecules filtered in the glomeruli. Several key receptors appear to be involved in this function with megalin receptor as probably the most important receptor in the endocytosis process (12). Megalin is a 600 kDa multiligand endocytic recepor belonging to the lowdensity lipoprotein receptor.…”

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

“…The receptor involved in the renal uptake of radioactive peptides binds various structurally different proteins, including albumin and β 2 microglobulin [8]. Basic amino acids, including arginine and lysine, bind to megalin via their cationic sites and therefore competitively inhibit renal reabsorption of radioactive peptide used in TRT [8][9][10][11][12][13]. The reduction in renal uptake induced by cationic amino acids ranges between 15% and 60% depending on the amount of amino acids being used and on the experimental design [9][10][11][12][13].…”