SPHK1 and infection: Specific inhibition of SPHK1 with SKI II also resulted in inhibition of infection (SKI II IC50 = 9.118 μM; P = 0.001 for 5 μM, P = 0.0005 for 10 μM, and P = 0.0156 for 20 μM) without a loss of viability at concentrations up to 10 μM (Fig. 1E to G).