RB1 and melanoma: It is curious that, despite nearly complete inhibition of hyperphosphorylation of Rb S807/811 in response to 20 μM of PF-07104091 in B16F10 melanoma cells (Figure 2D), treatment with 10 μM of PF-07104091 for up to 48 hours had only a modest effect on cell viability (Figure 1A).