Background: MYCN gene amplification is found in ~25% of neuroblastoma patients and correlates with poor prognosis. Although development of MYCN inhibitor has been considered to be attractive, no drugs have yet progressed to clinical application due to lack of obvious surfaces of MYCN protein for small molecule binding. We have developed a novel MYCN-targeting DNA-alkylating drug using Pyrrole-Imidazole (PI) polyamide (MYCN-A3), designed to bind directly to minor groove of genomic DNA within the coding region of MYCN in a sequence-specific manner.
Methods: MYCN-A3 was designed to specifically alkylate on the template strand in 3’UTR of the MYCN gene and synthesized by an automated peptide synthesizer PSSM-8. To evaluate anticancer activity of MYCN-A3, we performed in vitro and in vivo assays using neuroblastoma cells and other type of cancer cells.
Results: Treatment of MYCN-amplified neuroblastoma cells with MYCN-A3 significantly suppressed MYCN expression at the mRNA and protein levels. Accordingly, MYCN-A3 induced apoptotic cell death and IC50 values of MYCN-amplified cells were lower than MYCN-non-amplified cells. Intriguingly, FISH analyses demonstrated that MYCN-A3 impaired the signal intensity of a probe specific for the MYCN gene loci (2p24.3), suggesting that MYCN-A3 directly binds to and alkylates the target sequence of the MYCN gene, interfering with the probe hybridization. Moreover, MYCN-A3 significantly inhibited tumor progression in human neuroblastoma xenograft mouse models.
Conclusion: MYCN-A3 is a promising and an innovative therapeutic drug candidate for aggressive neuroblastomas with MYCN amplification.