Developing microRNA therapeutics for triple negative breast cancer

Triple negative breast cancer (TNBC) lack estrogen and progesterone receptors, and Her2 protein, which could be targeted by specifically designed therapeutic agents. TNBC relapses after standard chemotherapy, leaving patients with a median survival of less than two years.;Tumor suppressor proteins are reduced in TNBC cells by pathogenic microRNAs. In TNBC, high levels of the miRNA guide strands miR-17-5p and miR-21 inhibit ribosomal translation of tumor suppressor mRNAs, such as programmed cell death 4 (PDCD4) or phosphatase and tensin homolog (PTEN ), the negative regulators of the PI3K/AKT/mTOR pathway. We hypothesized that knocking down the oncogenic miRNAs miR-17-5p and miR-21 might restore the expression levels of PDCD4 and PTEN tumor suppressor proteins, illustrating a route to oligonucleotide therapy of TNBC.;A more specific method of designing miRNA inhibitors was developed to avoid amplifying miRNA passenger strand activity. Conventional wisdom holds that only one of the two strands in a microRNA (miRNA) precursor duplex is selected as the active guide strand. The complementary passenger strand is thought to be inactive. Contrary to conventional wisdom, functional activities of miR-17-3p passenger strand were observed through changes in miR-17-3p target genes' protein expression and luciferase reporter signals when using a miR-17-3p mimic in MDA-MB-231 cells. Moreover, bioinformatics analysis, folding energy prediction, protein expression levels, and luciferase assays showed that antisense DNA-LNA against miR-17-5p guide strand mimicked miR-17-3p passenger strand, and targeted mRNAs of PDCD4 and PTEN, the same genes regulated by the guide strand.;To block oncogenic miRNAs such as miR-21 and miR-17-5p successfully, shorter guide strand specific antisense oligonucleotide inhibitors of miR-21 and miR-17-5p were designed and synthesized. The oligonucleotides were modified with a peptide nucleic acid backbone to increase binding affinity and resist degradation, and conjugated to an insulin-like growth factor 1 (IGF1) tetrapeptide analog to facilitate cancer specific cellular uptake through overexpressed IGF1 receptor (IGF1R). The anti-miR-21 PNA-tetrapeptide and anti-miR-17-5p PNA-tetrapeptide successfully raised PDCD4 and PTEN protein levels, and induced apoptosis in mesenchymal stem-like TNBC cells. The anti-miR-21 PNA-tetrapeptide also inhibited migration in these cells.;These results suggest that blocking cancer driving miRNAs, such as miR-21 and miR-17-5p, in TNBC is a promising therapeutic approach. Using PNA-IGF1 tetrapeptide agents provides the basis for potential targeted therapeutics for TNBC.