Resistance mechanisms associated with altered intracellular distribution of anticancer agents

Pharmacol Ther. 2000 Mar;85(3):217-29. doi: 10.1016/s0163-7258(99)00073-x.


The resistance of tumor cells to anticancer agents remains a major cause of treatment failure in cancer patients. The term multidrug resistance (MDR) is used to define a resistance phenotype where cells are resistant to multiple drugs with no obvious structural resemblance and with different molecular targets. It is now clear that MDR is always multifactorial. The intracellular drug distribution is modified in many MDR cell lines, leading to increased drug sequestration in acidic vesicles, such as the trans-Golgi apparatus, recycling endosomes, and lysosomes, followed by transport to the plasma membrane and extrusion into the external medium. Since most anticancer agents target DNA or nuclear enzymes, sequestration of drug in cytoplasmic organelles will lead to decreased drug-target interaction and thereby, decreased cytotoxicity. Altered intracellular drug distribution is usually associated with the expression of drug efflux pumps, such as the P-glycoprotein and the multidrug resistance protein. Another common modification in MDR cells is alkalization of the intracellular pH. The relationship between these different resistance mechanisms is reviewed and a model proposed that suggests why these different resistance mechanisms are co-expressed in multiple cell lines.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • ATP-Binding Cassette Transporters / metabolism*
  • Antineoplastic Agents / pharmacokinetics
  • Antineoplastic Agents / pharmacology*
  • Biological Transport
  • DNA, Neoplasm / metabolism
  • Drug Resistance, Multiple*
  • Humans
  • Hydrogen-Ion Concentration
  • Neoplasm Proteins / metabolism
  • Organelles / chemistry*
  • Tumor Cells, Cultured
  • Vault Ribonucleoprotein Particles / metabolism


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • ATP-Binding Cassette Transporters
  • Antineoplastic Agents
  • DNA, Neoplasm
  • Neoplasm Proteins
  • Vault Ribonucleoprotein Particles
  • major vault protein