A peptide nucleic acid targeting nuclear RAD51 sensitizes multiple myeloma cells to melphalan treatment

摘要

RAD51-mediated recombinational repair is elevated in multiple myeloma (MM) and predicts poor prognosis. RAD51 has been targeted to selectively sensitize and/or kill tumor cells. Here, we employed a peptide nucleic acid (PNA) to inhibit RAD51 expression in MM cells. We constructed a PNA complementary to a unique segment of the RAD51 gene promoter, spanning the transcription start site, and conjugated it to a nuclear localization signal (PKKKRKV) to enhance cellular uptake and nuclear delivery without transfection reagents. This synthetic construct, (PNA(rad51_nls)), significantly reduced RAD51 transcripts in MM cells, and markedly reduced the number and intensity of de novo and melphalan-induced nuclear RAD51 foci, while increasing the level of melphalan-induced H2AX foci. Melphalan alone markedly induced the expression of 5 other genes involved in homologous-recombination repair, yet suppression of RAD51 by PNA(rad51_nls) was sufficient to synergize with melphalan, producing significant synthetic lethality of MM cells in vitro. In a SCID-rab mouse model mimicking the MM bone marrow microenvironment, treatment with PNA(rad51_nls) +/- melphalan significantly suppressed tumor growth after 2weeks, whereas melphalan plus control PNA(rad4 mu_nls) was ineffectual. This study highlights the importance of RAD51 in myeloma growth and is the first to demonstrate that anti-RAD51 PNA can potentiate conventional MM chemotherapy.