Ritonavir inhibits HIF-1α-mediated VEGF expression in retinal pigment epithelial cells in vitro

Purpose Retinal hypoxia-mediated activation of the hypoxia-inducible factor (HIF pathway) leading to angiogenesis is a major signaling mechanism underlying a number of sight-threatening diseases. Inhibiting this signaling mechanism with an already approved therapeutic molecule may have promising anti-angiogenic role with fewer side effects. Hence, the primary objective of this study was to examine the expression of HIF-1 alpha and VEGF in human retinal pigment epithelial cells treated with ritonavir under hypoxic and normoxic conditions. Methods ARPE-19 and D407 cells were cultured in normoxic or hypoxic conditions, alone or in the presence of ritonavir. Quantitative real-time polymerase chain reaction, immunoblot analysis, sandwich ELISA, endothelial cell proliferation, and cytotoxicity were performed. Results A 12-h hypoxic exposure resulted in elevated mRNA expression levels of both HIF-1a and VEGF in ARPE-19 and D407 cells. Hence, this time point was selected for subsequent experiments. Presence of ritonavir in the culture medium strongly inhibited VEGF expression in a concentration-dependent manner under hypoxic conditions. Immunoblot analysis demonstrated a substantially reduced protein expression of HIF-1a in the presence of ritonavir. Further, hypoxic exposure-induced VEGF secretion was also inhibited by ritonavir, as demonstrated using ELISA. Finally, ritonavir significantly diminished the proliferation of choroid-retinal endothelial (RF/6A) cells demonstrating potential anti-angiogenic activity. Cytotoxicity studies showed that ritonavir is non-toxic to RPE cells. Conclusions This study demonstrates for the first time that ritonavir can inhibit HIF-1a and VEGF in ARPE-19 and D407 cells. Such inhibition may form a platform for application of ritonavir in the treatment of various ocular diseases.