Cell-specific delivery of a transforming growth factor-beta type I receptor kinase inhibitor to proximal tubular cells for the treatment of renal fibrosis.

Purpose: Activation of tubular epithelial cells by transforming growth factor-beta (TGF-beta) plays an important role in the pathogenesis of renal tubulointerstitial fibrosis. We developed a renally accumulating conjugate of a TGF-beta type-I receptor kinase inhibitor (TKI) and evaluated its efficacy in vitro and in vivo.

Methods: TKI was conjugated to the protein Lysozyme (LZM) via a platinum-based linker. TKI-LZM was evaluated in human tubular cells (HK-2) for its anti-fibrotic activity. Plasma, kidney and urine drug levels after a single intravenous dose of TKI-LZM in rats were determined by HPLC or immunodetection. Anti-fibrotic effects of TKI-LZM were examined in the unilateral ureteral obstruction (UUO) model.

Results: TKI-LZM conjugate was successfully synthesized at an 1:1 drug/carrier ratio, and inhibited TGF-beta1-induced procollagen-1alpha1 gene expression in HK-2 cells. In vivo, TKI-LZM accumulated rapidly in tubular cells and provided a local depot for 3 days. Interestingly, a single dose of TKI-LZM inhibited the activation of tubular cells and fibroblasts in UUO rats and reduced renal inflammation. In contrast, free TKI at an equimolar (low) dosage exhibited little effects.

Conclusions: Inhibition of TGF-beta signaling by local drug delivery is a promising antifibrotic strategy, and demonstrated the important role of tubular activation in renal fibrosis.