Another resistance mechanism has been associated with ABCB1 (aka P-glycoprotein [Pgp] or multi-drug resistance-1 [MDR1]) levels, where Gupta et al.17 showed that inhibition of Pgp by verapamil, or suppression using siRNAs, re-sensitized acute lymphocytic leukemia cells to silvestrol. Here, ABCB1 is linked to acute lymphoblastic leukemia.