To further evaluate the activity of the highly potent compounds 30 and 33, dose-dependent stabilization of HIF-1α and HIF-1α-OH was studied. HeLa (Figure ) and HEK293 cells (Figure ) were treated for 1 h with increasing concentrations of compounds 30 and 33, as well as compound 1 (VH298) as reference and levels of HIF-1α and HIF-1α-OH were independently monitored by immunoblotting. The PHD inhibitor daprodustat was included as additional positive control, and cisVH298, the stereoisomer of 1 with (S)-configuration at the hydroxy-substituted carbon, as negative control. A clear dependency of the compound concentrations ranging from 1 µM to 100 µM on the protein levels of HIF-1α and HIF-1α-OH was observed with all VHL inhibitors, while the non-binding epimer cisVH298 had no effect at 50 µM. As for VH298 (1), levels of HIF-1α and HIF-1α-OH were enhanced by compound 30 and 33 from as low as 10 µM concentration. At concentrations from 25 µM up to 100 µM, compounds 30 and 33 outperformed 1 (VH298), with compound 30 already inducing higher HIF-1α and HIF-1α-OH levels at 25 µM than compound 1 at 50 µM.