In vitro metabolism of 5-fluoro-2-glutathionyl-nitrobenzene by kidney proximal tubular cells studied by 19F-NMR

Validation of Freshly Isolated Rat Renal Cells as a Tool for Preclinical Assessment of Radiolabeled Receptor-Specific Peptide Uptake in the Kidney

The synthetic analogs of regulatory peptides radiolabeled with adequate radionuclides are perspective tools in nuclear medicine. However, undesirable uptake and retention in the kidney limit their application. Specific in vitro methods are used to evaluate undesirable renal accumulation. Therefore, we investigated the usefulness of freshly isolated rat renal cells for evaluating renal cellular uptake of receptor-specific peptide analogs. Special attention was given to megalin as this transport system is an important contributor to the active renal uptake of the peptides. Freshly isolated renal cells were obtained from native rat kidneys by the collagenase method. Compounds with known accumulation in renal cells were used to verify the viability of cellular transport systems. Megalin expressions in isolated rat renal cells were compared to two other potential renal cell models by Western blotting. Specific tubular cell markers were used to confirm the presence of proximal tubular cells expressing megalin in isolated rat renal cell preparations by immunohistochemistry. Colocalization experiments on isolated rat kidney cells confirmed the presence of proximal tubular cells bearing megalin in preparations. The applicability of the method was tested by an accumulation study with several analogs of somatostatin and gastrin labeled with indium-111 or lutetium-177. Therefore, isolated rat renal cells may be an effective screening tool for in vitro analyses of renal uptake and comparative renal accumulation studies of radiolabeled peptides or other radiolabeled compounds with potential nephrotoxicity.

Detection of (19)F-labeled biopharmaceuticals in cell cultures with magnetic resonance

Magnetic resonance (MR) studies of the therapeutic efficacy of fluorinated drugs have recently become possible due to improvements in detection including the application of very strong magnetic fields up to 9.4Tesla (T). These advances allow tracking, identification, and quantification of (19)F-labeled biopharmaceuticals using (19)F MR imaging ((19)F MRI) and spectroscopy ((19)F MRS). Both techniques are noninvasive, are nondestructive, and enable serial measurements. They also allow for controlled and systematic studies of cellular metabolism in cancerous tissue in vivo (small animals and humans) and in vitro (body fluids, cells culture, tissue extracts and isolated tissues). Here we provide an overview of the (19)F MRI and (19)F MRS techniques used for tracking (19)F labeled anticancer chemotherapeutics and antibodies which allow quantification of drug uptake in cancer cells in vitro.

Transport and metabolism of glutathione conjugates of menadione and ethacrynic acid in confluent monolayers of rat renal proximal tubular cells

Confluent monolayers of primary rat renal proximal tubular (RPT) cells were used to compare transepithelial transport and concomitant metabolism of two different glutathione (GSH) S-conjugates. For the GSH-conjugated quinone compound, [35S]GSH-conjugated menadione (MGNQ), no specific transepithelial transport was observed. Most likely, [35S]MGNQ passed the monolayer via paracellular leakage as the result of a reduction in monolayer integrity due to toxicity via extensive redox cycling of the quinone under the culture conditions. RPT cell monolayers metabolise MGNQ into a cysteinylglycine conjugate, which after intramolecular cyclization yields 2H-(3-glycinyl)-9-hydroxy-10-methyl-1,4-naphthothiazine. Acivicin, an inhibitor of gamma-glutamyltranspeptidase, inhibited the formation of this 1,4-napthothiazine adduct. The second product formed is 1,4-napthothiazine formed by loss of glycine via the action of dipeptidases. Similarly, no basolateral (B) to apical (A) transport of a GSH-conjugated alpha, beta unsaturated ketone, [14C]ethacrynic acid (EASG), occurred. However, net transport of [14C] radioactivity could be observed from A=>B direction. After 8 h, 23% of total [14C] radioactivity was transported from the apical to the basolateral chamber. In both the apical and basolateral chambers, free, unconjugated ethacrynic acid (EA) was observed. gamma GT-mediated metabolism of EASG to the much more unstable cysteinylglycine conjugate leads to relatively large amounts of free EA. Thus, the GSH conjugate is not transported but rather the cysteine adduct and/or free, unconjugated EA. In agreement with this, acivicin reduced A=>B transport of EASG and inhibited the formation of free EA. In conclusion, the confluent monolayers of RPT cells do not or no longer possess active basolateral transport systems for GSH conjugates. However, they are still quite useful for studying biotransformation reactions of thioether conjugates.