MYC and HIF1α are among the most important oncoproteins whose pharmacologic inhibition has been challenging for the diverse mechanisms driving their abnormal expression and because of the challenge in blocking protein-DNA interactions. Surprisingly, we found that MYC and HIF1α proteins in echinomycin-treated cells were degraded through proteasome dependent pathways, respectively by the β-TrCP- or VHL-dependent mechanisms. The degradation is induced in a variety of cancer types, including those with mutations in the p53 tumor and LKB tumor suppressors and the KRAS oncogene. Consistent with inhibition of MYC and HIF1α, administration of echinomycin inhibited growth of lung adenocarcinoma xenograft and a syngeneic lymphoma model in mice. Furthermore, echinomycin efficiently induced regression of syngeneic mouse lymphoma driven by MYC over-expression. Our data demonstrated a new mechanism by which echinomycin simultaneously targets MYC and HIF1α for degradation to inhibit growth of lung cancer and lymphoma. Given the broad impact of β-TrCP or VHL in stability of oncogenic proteins, echinomycin may emerge as a non-PROTAC (proteolysis targeting chimera) degrader of oncogenic proteins.
Keywords: HIF1α; MYC; lung cancer; lymphoma; proteasome; protein degradation.