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. Author manuscript; available in PMC: 2006 Jan 25.
Published in final edited form as: Trends Pharmacol Sci. 2005 Aug;26(8):385–387. doi: 10.1016/j.tips.2005.06.001

Figure 2.

Figure 2

Possible ways cells can develop P-glycoprotein (Pgp)-mediated multidrug resistance (MDR). (a) Tumor cells are either intrinsically resistant to drugs or acquire resistance on exposure to cytotoxic therapy. In both instances MDR is a consequence of the overexpression of the ABCB1 gene product. (b) Drug-sensitive (MDR−) cells acquire the MDR phenotype by the intercellular transfer of Pgp by an unknown mechanism but it is most probably mediated by relatively large (>0.8 μM) membrane microparticles (Figure 1c) and requires cell–cell contact with donor MDR+ cells [9] (for clarity only cell–cell contact is shown). It should be noted that the physiological relevance of this mechanism remains to be determined.