PFI-1 (PF-6405761), a specific BET (bromodomain-containing protein) inhibitor for BRD4, is with the IC50 of 0.22 μM in a cell-free assay.

In rats, PFI-1, administered intravenously at a dose of 1 mg/kg, exhibits a distribution volume of 1 L/kg and a plasma clearance rate of 18 mL/kg per minute, with a half-life of 1 hour. Orally administered PFI-1 at a dose of 2 mg/kg demonstrates a low efficacy of 32%. When PFI-1 is administered subcutaneously to mice at a 2 mg/kg dose, the peak concentration (Cmax) reaches 58 ng/mL, the time to peak concentration (Tmax) is 1 hour, and the half-life is approximately 2 hours.

In human monocytes stimulated by lipopolysaccharides, PFI-1 (EC50=1.89 μM) suppresses the production of IL-6. It also inhibits cell proliferation in three NET cell lines (pancreatic NET-derived Bon-1 and lung NET-derived H727 and H720). In T4302 CD133+ cells, PFI-1 induces a dose-dependent decrease in cell viability. PFI-1 (KD=49 μM) binds to the cAMP response element-binding protein.

To determine dose response, cells are aliquoted into 96-well plate at 5 × 103 cells per well in triplicates. PFI-1 is added by 2- or 4-fold serial dilutions. Cell number is measured 5 days after plating using the CellTiter-Glo Kit and normalized to corresponding vehicle-treated groups. IC50 values are calculated by the GraphPad Prism 5 software using the 4-parameter logistic nonlinear regression model. To calculate the relative growth of cells, averaged cell titers of each group on day 1 are assigned a value of 1. All subsequent cell titer values are normalized accordingly. (Only for Reference)