PGP and cancer: We reported that naturally-occurring shikonin and its analogues (Fig. 1) could circumvent cancer drug resistance mediated by drug transporters P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), and brest cancer resistance protein (BCRP1), and by antiapoptotic proteins Bcl-2 and Bcl-xL, by induction of necroptosis [22], [23], [24], [25], [26], a cell death recently defined and studied in depth by Degterev A and Yuan J [27], [28], [29].