Nanobody‐Mediated c‐MYC Degradation Inhibits Tumor Cell Progression

ABSTRACT 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.