PKM and neoplasm: Another study reported that PKM2, but not PKM1 or PKL, was bound by shikonin, resulting in inhibition of PKM2 expression and suppression of mitochondrial function in tumor cells; shikonin showed a promising selectivity toward PKM2; shikonin at concentrations that resulted in over 50% inhibition of PKM2 activity did not inhibit PKM1 and PKL[15, 30].