SPHK1 and neoplasm: PF543 is the most potent inhibitor of SPHK1 known to date and it can be used for in vivo studies.[17] To determine the effects of pharmacological inhibition of SPHK1 on tumor growth and T cell activation, we orthotopically injected ID8 cells into C57BL/6 syngeneic mice and treated the animals with PF543 (ten mice per group).