Summary N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino]-2-thenoyl)-L-glutamic acid (ICI D1694) is an analogue of the thymidylate synthase inhibitor, N'°-propargyl-5,8-dideazafolic acid (CB3717). CB3717 was found to be active in early clinical studies, but its use was limited by nephrotoxicity. ICI D1694 is a more potent antitumour agent than CB3717 and is also more water soluble. Previous studies have shown ICI D1694 to be non-toxic to the kidney following a single administration but its renal effects after chronic administration are unknown. To assess these effects, and further define the time course and dose relationship of CB3717-induced renal damage, an assay of glomerular filtration rate (GFR) has been developed which can be used in mice and hence in the screening of novel compounds. The '4C-inulin clearance assay developed was used to show a linear relationship between CB3717 dosage and renal damage (r=-0.989) following a single bolus dose (50-200mgkg-'), in mice. CB3717-induced renal damage is persistent (>6 weeks) and renal scarring was noted. ICI D1694 has been shown to be non-nephrotoxic following weekly administration of 250 mg kg-' for 6 weeks. Measurement of GFR has been shown to be a more sensitive indicator of impaired renal function than plasma urea and creatinine concentration, and the measurement of plasma creatinine concentration in particular, appears to be without value in the screening of potential nephrotoxins in certain mouse strains.Nl'-propargyl-5,8-dideazafolic acid (CB3717, Figure l.i.) is a folate based inhibitor of the enzyme thymidylate synthase (TS), which was found to be an active antitumour agent in early clinical trials in patients with breast, ovarian and hepatocellular carcinoma (Calvert et al., 1986;Cantwell et al., 1988; Bassendine et al., 1987). However, the clinical use of CB3717 was limited by its nephrotoxicity, which was observed in Phase I studies of both weekly (Vest et al., 1988) and 3-weekly administration schedules (Calvert et al., 1986;Sessa et al., 1988). Renal toxicity manifested primarily as a reduction in glomerular filtration rate (GFR). However, tubular damage was also identified by the measurement of the urinary enzymes, N-acetyl glucosaminidase (NAG) and leucine aminopeptidase (LAP). A >20% reduction in GFR was observed in seven of 12 (58%) patients receiving more than 400 mg m2 CB3717. In addition, urinary NAG and LAP levels were elevated in 50% of patients studied, although this elevation was not dose related (Calvert et al., 1986). CB3717-induced nephrotoxicity was thought to be due to the compound's relative insolubility at acid pH. However, despite adequate alkalinisation (pH ,8) of the urine, reductions in GFR (measured using creatinine clearance) of >20%, were still seen in 6/17 (35%) courses in patients treated at 400 mg m2 (Sessa et al., 1988). To circumvent toxicity related to drug precipitation in the kidney, a series of more soluble analogues of CB3717 have been synthesised. In addition to being devoid of renal toxic...

The comparative nephrotoxicity of i.v. cisplatin, i.v. carboplatin and six p.o. ammine/amine Pt(IV) dicarboxylates was studied in rodents following single MTD treatments. In mice, i.v. cisplatin caused proteinuria (1 g l-1), glycosuria (16.7 mM) and decreased GFR at 4 days, and histological kidney damage with onset at 6 days. In contrast, mice treated with i.v. carboplatin or p.o. ammine/amine Pt(IV) dicarboxylates had urinary glucose, urinary protein, GFR and kidney histology within the control range. In rats, i.v. cisplatin caused 5-fold elevations in plasma creatinine (188 +/- 33 microM) and urea (30.4 +/- 8.9 mM), a 10-fold fall in creatinine clearance (0.54 +/- 0.31 ml min-1 kg-1), a 25-fold elevation in urine/plasma glucose concentration ratio (3.28 +/- 0.17), a 20% increase in kidney weight (7.9 +/- 0.56 mg gm-1 body weight) and extensive histological damage 4 days after treatment. In contrast, i.v. carboplatin and p.o. JM216 (the lead compound of this series) caused neither abnormalities in renal function nor histological damage in rats. The nephrotoxicity of single MTD treatments of p.o. ammine/amine Pt(IV) dicarboxylate complexes appears less than i.v. cisplatin and comparable to i.v. carboplatin.