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Open Access Publications from the University of California

Bioengineering Novel Chimeric microRNA-34a for Prodrug Cancer Therapy: High-Yield Expression and Purification, and Structural and Functional Characterization.

  • Author(s): Wang, Wei-Peng
  • Ho, Pui Yan
  • Chen, Qiu-Xia
  • Addepalli, Balasubrahmanyam
  • Limbach, Patrick A
  • Li, Mei-Mei
  • Wu, Wen-Juan
  • Jilek, Joseph L
  • Qiu, Jing-Xin
  • Zhang, Hong-Jian
  • Li, Tianhong
  • Wun, Theodore
  • White, Ralph DeVere
  • Lam, Kit S
  • Yu, Ai-Ming
  • et al.

Development of anticancer treatments based on microRNA (miRNA/miR) such as miR-34a replacement therapy is limited to the use of synthetic RNAs with artificial modifications. Herein, we present a new approach to a high-yield and large-scale biosynthesis, in Escherichia coli using transfer RNA (tRNA) scaffold, of chimeric miR-34a agent, which may act as a prodrug for anticancer therapy. The recombinant tRNA fusion pre-miR-34a (tRNA/mir-34a) was quickly purified to a high degree of homogeneity (>98%) using anion-exchange fast protein liquid chromatography, whose primary sequence and post-transcriptional modifications were directly characterized by mass spectrometric analyses. Chimeric tRNA/mir-34a showed a favorable cellular stability while it was degradable by several ribonucleases. Deep sequencing and quantitative real-time polymerase chain reaction studies revealed that tRNA-carried pre-miR-34a was precisely processed to mature miR-34a within human carcinoma cells, and the same tRNA fragments were produced from tRNA/mir-34a and the control tRNA scaffold (tRNA/MSA). Consequently, tRNA/mir-34a inhibited the proliferation of various types of human carcinoma cells in a dose-dependent manner and to a much greater degree than the control tRNA/MSA, which was mechanistically attributable to the reduction of miR-34a target genes. Furthermore, tRNA/mir-34a significantly suppressed the growth of human non-small-cell lung cancer A549 and hepatocarcinoma HepG2 xenograft tumors in mice, compared with the same dose of tRNA/MSA. In addition, recombinant tRNA/mir-34a had no or minimal effect on blood chemistry and interleukin-6 level in mouse models, suggesting that recombinant RNAs were well tolerated. These findings provoke a conversation on producing biologic miRNAs to perform miRNA actions, and point toward a new direction in developing miRNA-based therapies.

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