A sequential discrimination–amplification (SEDA) electrochemical strategy was constructed for the identification of single-copy circulating methylated DNA.
Circulating methylated DNA has been a new kind of cancer biomarker, yet its small fraction of trace total DNA from clinical samples impairs the accurate analysis. Though fluorescence methods based on quantitative methylation specific PCR (qMSP) have been adopted routinely, yet alternative electrochemistry assay of such DNA from clinical samples remains a great challenge. Herein, we report accurate electrochemistry analysis of circulating methylated DNA from clinical plasma samples based on a paired-end tagging and amplifications strategy. Two DNA primers each labeled with digoxigenin (Dig) and biotin are designed for the recognition and amplification of methylated DNA. Paired-end tagging amplicons and avidin-HRP molecules are successively captured on the electrode modified with Anti-Dig. Then HRP executes catalytic reaction to generate amplified signal. The design of paired-end tagging can readily integrate downstream electrochemical amplified reaction, and two heterogeneous amplifications enable high assay sensitivity. As little as 40 pg of methylated genomic DNA (∼10 genomic equivalents) is well identified, and our strategy can even distinguish as low as 1% methylation level. Tumor-specific methylated DNA is clearly detected in the plasma of 10 of 11 NSCLC patients. The high clinical sensitivity of 91% (10/11) indicates the good consistency with clinical diagnosis. Excellent spatial control of electrochemistry allows simpler detection of more methylation patterns compared to fluorescence methods. The developed electrochemical assay is a promising liquid biopsy tool for the analysis of tumor-specific circulating DNA.
The proteasome inhibitor bortezomib is the most successfully applied chemotherapeutic drug for treating multiple myeloma. However, its clinical efficacy reduced due to resistance development. The underlying molecular mechanisms of bortezomib resistance are poorly understood. In this study, by combining in silico analysis and sgRNA library based drug resistance screening assay, we identified SENP2 (Sentrin/SUMO-specific proteases-2) as a bortezomib sensitive gene and found its expression highly downregulated in bortezomib resistant multiple myeloma patient's samples. Furthermore, down regulation of SENP2 in multiple myeloma cell line RPMI8226 alleviated bortezomib induced cell proliferation inhibition and apoptosis, whereas, overexpression of SENP2 sensitized these cells to bortezomib treatment. We further demonstrate that knockdown of SENP2 in RPMI8226 cells increased SUMO2 conjugated IκBα that resulted in the activation of NF-κB. Taken together, we report that silencing of SENP2 and consequent activation of NF-κB through the modulation of IκBα sumoylation as a novel mechanism inducing bortezomib resistance in multiple myeloma. Multiple myeloma (MM) is a malignant plasma cell tumor that account for 12% of blood malignant tumors, which is the second most commonly diagnosed hematologic malignancy 1. Despite applying multiple therapeutic drugs such as, proteasome inhibitor bortezomib 2 and immunomodulator thalidomide 3 , the median MM patient survival was only slightly improved from 3-5 years to 5-7 years 4. Moreover, MM is still featured as a recurrence and insensitive to treatment due to drug resistance development 5. The bortezomib is the first class of proteasome inhibitor approved for the treatment of MM. Bortezomib is a dipeptidyl boronic acid that reversibly binds to chymotrypsin-like catalytic subunit of 20 S proteasome and inhibits its activity 6. Proteasome plays a critical role in cellular homeostasis by degrading unwanted cellular proteins 7. The imbalance between synthesis and degradation of proteins arises due to proteasome inhibition results in the accumulation of regulatory proteins causing endoplasmic reticulum stress and activation of the unfolded protein response leading to induction of apoptosis in malignant cells via multiple mechanisms 8,9 .
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