Abstract
Background: Because clinical drug resistance is caused by low-grade expression of a responsible gene, highly sensitive methods are desirable for its detection in clinical settings. We developed a quantitative nucleic acid sequence-based amplification (NASBA) assay for multidrug resistance-1 ( MDR1) transcripts, and applied it to clinical samples. Method: MDR1 transcripts were amplified using the NASBA technique combined with sandwich hybridization of amplified MDR1 mRNA followed by chemiluminescence detection on an automated analyzer. Quantification of MDR1 mRNA was achieved through competitive coamplification of in vitro-generated RNA, which acts as an internal control. Results: The competitive NASBA assay exhibited higher sensitivity (reliable detection limit was 100 copies of MDR1 mRNA) and linearity over a broader dynamic range (7 logarithmic orders) than the competitive reverse transcription-polymerase chain reaction assay. All 33 clinical samples obtained from patients with leukemia were successfully assayed, demonstrating its feasibility. MDR1 expression—compensated with β-actin expression—ranged from 1.4×10 2 to 2.5×10 6 (median 4.8×10 5) copies/μg RNA, while the range of MDR1 expression in peripheral blood samples from 15 healthy adults was from 8.9×10 4 to 5.2×10 5 (median 2.2×10 5) copies/μg RNA. MDR1 expression in 8 of 33 clinical samples exceeded the median of healthy adult samples. Conclusions: The competitive NASBA assay is applicable to MDR1 mRNA quantification in clinical samples and would contribute to detection of clinical multidrug resistance.
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