Species, cell proliferation state and oxygen partial pressure are major factors in the in vitro toxicity of repurposed potential ADPKD drugs in human and murine renal proximal tubule cells

Abstract

Unexpected nephrotoxicity during clinical stages of drug development, due to undetected toxicity in in vitro and in vivo settings, can lead to drug attrition and jeopardize drug development. The latter highlights the importance of in vitro renal toxicity testing that can safely be translated to humans. Two factors commonly overlooked in the latter are the continuous cell proliferation that occurs in regeneration processes after renal insult and the physiological O₂ tension in the kidney. Autosomal Dominant Polycystic Kidney Disease is a genetic disorder characterized by the development of renal cysts and cellular changes, i.e. abnormal proliferation in conjunction with the Warburg effect. There is only one drug approved for the disease, tolvaptan, which, however, presents with liver toxicity and polyuria. In a quest for potential alternatives to tolvaptan, we compared the nephrotoxic and metabolic effects of four repurposed drugs, salicylic acid (up to 10 mM), birinapant (up to 100 µM), bardoxolone methyl (up to 1000 nM), and rapamycin (up to 160 nM) to tolvaptan (up to 100 µM) on human differentiated and proliferating (RPTEC/TERT1) and mouse proliferating (mProx24) renal proximal tubular epithelial cells at atmospheric (21%) and physiological (10%) O₂ tensions. The focus was on improved interpretation of in vitro test results for the detection of potential adverse effects. We found that cell proliferation and O₂ tension are major factors that determine the susceptibility of cells to compounds, while the drug effects on the metabolism and mitochondrial function provided further insight into the mechanisms underlying the observed in vitro toxicity.