C. PURINE ANALOGUES : 6-MERCAPTOPURINE (6-MP), 6-THIOGUANINE (6-TG)
Resistance
- changes in target enzymes
-
decreased ability to inhibit PNP and HGPRT
-
- decreased activation of prodrugs
-
decreased expression of activation enzymes (esp. HGPRT)
-
- increased inactivation
-
increased rates of degradation of the drugs or their "activated" analogues
-