# Nanobody‐Mediated c‐MYC Degradation Inhibits Tumor Cell Progression

## TL;DR

A nanobody-based therapy called CPM4 effectively targets and degrades the c-MYC protein, reducing tumor growth in laboratory and animal models.

## Contribution

A cell-permeable nanobody (M4) was developed to specifically target and degrade the c-MYC oncoprotein via its PEST region.

## Key findings

- CPM4 induces c-MYC degradation by enhancing Thr58 phosphorylation and disrupting the c-MYC/MAX heterodimer.
- CPM4 causes apoptosis in MYC-expressing tumor cells and significantly reduces tumor growth in xenograft models.
- The nanobody M4 binds with high affinity to the PEST sequence (241–263) of c-MYC.

## 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.

A cell‐permeable nanobody strategy was developed to target the intrinsically disordered oncoprotein c‐MYC. A synthetic nanobody, M4, binds the central PEST region of c‐MYC (241–263) and promotes c‐MYC degradation by enhancing Thr58 phosphorylation. Conjugation of M4 to a cell‐penetrating peptide (CPP) generates CPM4, which efficiently accumulates in the nucleus, disrupts the c‐MYC/MAX heterodimer, downregulates MYC‐driven transcriptional programs, and induces apoptosis in MYC‐expressing tumor cells. Consequently, CPM4 suppresses tumor growth in vitro and in vivo, highlighting the therapeutic potential of nanobody‐based c‐MYC targeting.