POS-378 SELECTIVE ETA ANTAGONIST ATRASENTAN, RAPIDLY REDUCES ALBUMINURIA AND DOWNREGULATES INTRA-RENAL PRO-INFLAMMATORY AND PRO-FIBROTIC TRANSCRIPTIONAL NETWORKS IN THE GDDY MOUSE MODEL OF SPONTANEOUS IGA NEPHROPATHY

Abstract

Endothelin pathway activation has been observed in kidney biopsies from IgA nephropathy (IgAN) patients which may be an important driver of disease progression by promoting proteinuria along with kidney inflammation and fibrosis via ETA receptor activation. Atrasentan is a potent and selective ETA antagonist which has demonstrated rapid and sustained reductions in proteinuria, preservation of kidney function and improved kidney outcomes in diabetic kidney disease patients. However, the effects of atrasentan have not been previously investigated in IgAN. The objective of this study was to evaluate the effect of short-term treatment of varying doses of atrasentan in the gddY mouse model of spontaneous IgAN, with a focus on dynamic changes in the intra-renal transcriptional profile. 6-week-old male gddY mice were administered atrasentan (10, 20 or 30 mg/kg/day, n=3/group or 0 mg/kg/day, n=2/group) in drinking water for 5 days. Urine albumin to creatinine ratio (UACR) was measured at baseline and on Day 4 of treatment. On Day 5, a terminal plasma sample was collected for the measurement of atrasentan plasma concentrations and kidney cortex was flash-frozen for RNA-seq which was analyzed by pairwise differential gene expression using edgeR’s quasi-likelihood F-test (FDR adjusted p-value < 0.05) and gene pathway analysis (FDR adjusted p-value filter of < 0.001). At baseline, gddY mice had substantial albuminuria, with a mean UACR of 293.1 ± 16 mg/g. Atrasentan reduced UACR from baseline by 28 ± 44 % (p=ns), 62 ± 8 % (p=0.0498) and 63 ± 6 % (P=0.029) at 10, 20 and 30 mg/kg/day, respectively. Free terminal atrasentan plasma concentrations were 90 pM, 100 pM and 207 pM at the 10, 20 and 30 mg/kg/day doses respectively, providing free atrasentan concentrations 2.6-fold, 2.9-fold and 6.1-fold above the atrasentan ETA Ki (34 pM), respectively and in the same range as observed clinically at the optimized atrasentan dose of 0.75 mg. High quality RNA sequencing reads revealed dose-dependent effects of atrasentan on differential gene expression compared to untreated control ddY mice, including reductions in known ETA target genes ET-1 and ETA. Ingenuity Pathway Analysis to calculate enrichment scores showed that atrasentan produced prominent, dose-dependent downregulation of inflammatory, proliferative, and fibrotic gene networks. Atrasentan was observed to downregulate signaling pathways previously implicated in IgAN pathogenesis including the PDGF, NF-κB, IL-6 and TNF pathways. In the gddY mouse model of spontaneous IgAN, selectively blocking ETA with atrasentan leads to rapid reductions in albuminuria and results in intra-renal transcriptional downregulation of inflammatory and fibrotic signaling. The dynamic transcriptional changes in the kidney, including downregulation of known direct ETA receptor target genes, following only 5 days of treatment and prior to sustained long-term reductions in albuminuria and blood pressure that could mediate this benefit, is consistent with direct anti-inflammatory and antifibrotic effects of ETA blockade in IgAN. These results support further characterization of the effects of long-term treatment of atrasentan in the gddY mouse model and also support the therapeutic potential of atrasentan in IgAN patients to reduce proteinuria and kidney inflammation and fibrosis, key drivers of IgAN progression.