QUANTITATION OF MULTIDRUG-RESISTANT MDR1 TRANSCRIPT IN ACUTE MYELOID-LEUKEMIA BY NONISOTOPIC QUANTITATIVE CDNA-POLYMERASE CHAIN-REACTION

Drug resistance in acute myeloid leukaemia (AML) may be caused by overexpression of the P glycoprotein (PGP), an efflux pump encoded by the multidrug resistance mdr1 gene. Previous studies have suggested that increased PGP expression in the leukaemic blasts is of prognostic significance, and that use of PGP antagonists may be beneficial in treatment. We describe preliminary results with a non-isotopic quantitative MDR1 cDNA-PCR assay, using an artificial RNA construct sharing primer recognition sites with the target MDR1 mRNA (MDR1 nucleic acids 483-504 and 624-644) as an internal control. KB 3.1 parent and KB 8.5 MDR positive cell lines expressed 0.004 and 1.96 molecules MDR1 mRNA/pg total RNA, Semiquantitative screening of 60 RNA samples from 53 AML cases detected MDR1 transcript ranging from 0 to 1.81 molecules per pg RNA, The median value at presentation (33 patients) was 0.055 and was higher in 14 patients at relapse (0.13) and in seven patients with refractory disease (0.14). Quantitation of MDR1 transcript in serial samples in seven treated patients between presentation and relapse showed the decrease in three patients (0.18-0.02 x) to be as marked as the increase in three other patients (3-16 x). The method described is well suited for the study of clinical samples because it is sensitive, specific, rapid and requires small amounts of clinical material.