Nanobody-Mediated c-MYC Degradation Inhibits Tumor Cell Progression.

The c-MYC oncogene, a critical driver of malignancies, is frequently associated with poor prognosis because it promotes unchecked cell proliferation and alters gene expression. Effective targeting of c-MYC using conventional therapeutic strategies has been difficult, largely because of its unstructured nature. In the present study, we identified a myc-binding nanobody named as M4 from a synthetic phage-display nanobody library. We conjugated M4 with a cell-penetrating peptide (CPP) to generate a molecule CPM4 and examined the effects and action mechanisms of CPM4 in inhibition of tumor cell growth in vitro and in vivo. CPM4 exhibited efficient nuclear localization, caused c-MYC reduction, and induced apoptosis in MYC-expressing cells. Hydrogen/deuterium exchange mass spectrometry revealed that CPM4 binds to the central PEST sequence (241-263 epitope) of c-MYC with high affinity. Further analysis revealed that CPM4 promotes c-MYC degradation via enhanced phosphorylation at Thr58, disrupts the c-MYC/MAX heterodimer, and downregulates c-MYC-targeted downstream genes. Xenograft studies further validated the therapeutic efficacy of CPM4, showing a significant reduction in tumor growth. These results underscore the therapeutic potential of CPM4 as an effective drug candidate for inhibiting c-MYC-driven tumor growth.