Degradation of MYC by the mutant p53 reactivator drug, COTI-2 in breast cancer cells

by Selleckchem | Sep 08 2023

TP53 (p53) and MYC are amongst the most frequently altered genes in cancer. Both are thus attractive targets for new anticancer therapies. Historically, however, both genes have proved challenging to target and currently there is no approved therapy against either. The aim of this study was to investigate the effect of the mutant p53 reactivating drug, COTI-2 on MYC. Total MYC, pSer62 MYC and pThr58 MYC were detected using Western blotting. Proteasome-mediated degradation was determined using the proteasome, inhibitor MG-132, while MYC half-life was measured using pulse chase experiments in the presence of cycloheximide. Cell proliferation was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Treatment of 5 mutant p53 breast cancer cell lines with COTI-2 resulted in dose-dependent MYC degradation. Addition of the proteasome inhibitor, MG132, rescued the degradation, suggesting that this proteolytic system was at least partly responsible for the inactivation of MYC. Using cycloheximide in pulse chase experiments, COTI-2 was found to reduce the half-life of MYC in 2 different mutant p53 breast cancer cell lines, i.e., from 34.8 to 18.6 min in MDA-MB-232 cells and from 29.6 to 20.3 min in MDA-MB-468 cells. Co-treatment with COTI-2 and the MYC inhibitor, MYCi975 resulted in synergistic growth inhibition in all 4 mutant p53 cell lines investigated. The dual ability of COTI-2 to reactivate mutant p53 and degrade MYC should enable this compound to have broad application as an anticancer drug.

Comments:

The study aimed to investigate the effects of COTI-2, a mutant p53-reactivating drug, on the MYC protein, which is frequently altered in cancer and considered an attractive target for anticancer therapies. The researchers performed various experiments to evaluate the impact of COTI-2 on MYC in breast cancer cell lines with mutant p53.

First, they treated five mutant p53 breast cancer cell lines with different concentrations of COTI-2 and observed that MYC protein levels decreased in a dose-dependent manner. They used Western blotting to detect total MYC levels as well as the phosphorylated forms of MYC at Ser62 and Thr58.

To determine the mechanism of MYC degradation, the researchers used MG-132, a proteasome inhibitor. They found that the addition of MG-132 rescued MYC degradation, indicating that the proteasome-mediated degradation pathway was involved in the inactivation of MYC induced by COTI-2.

To further investigate the stability of MYC, the researchers conducted pulse chase experiments using cycloheximide, a protein synthesis inhibitor. They found that COTI-2 reduced the half-life of MYC in two different mutant p53 breast cancer cell lines. In MDA-MB-232 cells, the half-life decreased from 34.8 to 18.6 minutes, while in MDA-MB-468 cells, it decreased from 29.6 to 20.3 minutes. This suggests that COTI-2 accelerates the turnover of MYC protein.

Additionally, the study explored the potential synergistic effect of combining COTI-2 with an MYC inhibitor called MYCi975. They found that co-treatment with COTI-2 and MYCi975 resulted in enhanced growth inhibition in all four mutant p53 cell lines investigated, indicating a synergistic effect between the two compounds.

Based on these findings, the researchers concluded that COTI-2 has a dual ability to reactivate mutant p53 and degrade MYC protein. This dual action suggests that COTI-2 could have broad applications as an anticancer drug, particularly in cancers with both mutant p53 and dysregulated MYC. However, further research and clinical studies would be needed to validate these findings and determine the therapeutic potential of COTI-2 in cancer treatment.