Increased synthesis of the cell surface glycoprotein P-170
Anticancer drugs resistance can develop to a single drug or to a variety of drugs of different structures,
after the exposure to a single agent.
Single drug resistance can be due to:
1) Decreased sensitivity of a target enzyme
2) Decreased target receptor affinity to the drug
3) Increased inactivation of drugs
4) Decreased activation of prodrugs
Multidrug resistance can be due to:
1) Increased efflux of the drug from the cells, due to increased expression of a normal gene for a cell
surface glycoprotein (P-170) which uses the energy of ATP to expel a variety of foreign molecules (this
is the most common mechanism of multidrug resistance)
2) Increased DNA repair, due to increased activity of topoisomerase enzymes.
A) DNA repair is increased, not decreased, in case of multidrug resistance.
B) This can explain the resistance to methotrexate (the drug that inhibits dihydrofolate reductase) but
cannot account for multidrug resistance.
D, E) These events are decreased, not increased, in case of drug resistance.