IGF1R-targeted delivery of a bridged nucleic acid oligonucleotide-peptide conjugate for microRNA-21 inhibition in triple-negative breast cancer.

Triple-negative breast cancer (TNBC), defined by the absence of ER, PR, and Her2, impacts over 46 000 U.S. women annually, disproportionately affecting minority ethnic groups and individuals with BRCA mutations. Despite advancements such as PARP inhibitors, TNBC remains highly aggressive, with frequent recurrences and a 50% mortality rate within four years, underscoring the urgent need for more effective targeted therapies. MicroRNAs (miRNAs) represent a novel therapeutic approach. In TNBC, overexpressed miR-21 drives tumor progression, immune evasion, treatment resistance, and metastasis. Targeted miR-21 inhibition could curb these effects while minimizing harm to normal cells. We developed a peptide-conjugated miR-21 inhibitor targeting TNBC cells via the overexpressed IGF1 receptor (IGF1R), associated with poor prognosis. Using aminomethyl-bridged nucleic acid (BNA) chemistry, a serum-stable anti-miR-21 RNA analog was designed and tested for its effects on TNBC cell proliferation, apoptosis, tumor suppressor expression, and immune checkpoint regulation. Conjugation to an IGF1 peptide analog improved delivery, demonstrating tumor-specific biodistribution, efficacy, and safety in TNBC-bearing mice. The miR-21 inhibitor-peptide conjugate reduced proliferation, induced apoptosis, elevated tumor suppressors, and suppressed immune checkpoints in TNBC cell lines. In vivo, it concentrated in tumors, inhibited tumor growth, and showed no detectable liver or kidney toxicity at the tested dose, supporting therapeutic potential.