We have recently shown increased sensitivity to IGF-I induced signal transduction in kidneys of diabetic mice. Accordingly we investigated the effects of PQ401, a novel diarylurea compound that inhibits IGF1R autophosphorylation in type I diabetes.Control (C) and Diabetic (D) mice were administered PQ401 (CP, DP) or vehicle (C, D) for 3weeks.CP animals showed a decrease in renal phosphorylated (p-)AKT and p-IGF1R. However, PQ401 had no effect on diabetic state (hyperglycemia, weight loss) or renal disease parameters (hypertrophy, hyperfiltration and albuminuria). Type IV collagen as well as TGF-β mRNA increased in DP and D compared to C. In the CP group renal hypertrophy with fat accumulation in proximal tubuli and increased renal IGF-I, collagen IV and TGF-β mRNA were seen.IGF1R inhibition by PQ401 exerted no significant effects on diabetic kidney disease parameters, arguing against a role for IGF-I in the pathogenesis of diabetic kidney disease. However, PQ401 affects normal kidneys, inducing renal hypertrophy as well as collagen and fat accumulation, with increased renal IGF-I mRNA, suggestive of a damage-regeneration process. Therefore, this diarylurea compound is not beneficial in early diabetic kidney disease. Its potential deleterious effects on kidney tissue need to be further investigated.