Inhibiting Myc in cancer using Omomyc. From defining the fundamental mechanism of action to its pharmacological application

Abstract

Identifying and targeting cancer cell components that play non-degenerate and non-redundant functions within cancers could lead to the development of more effective therapies. Myc is considered a prime example of such a target, and has been characterized as a downstream effector of multiple oncogenic pathways. Indeed, several studies have shown that inhibiting Myc displays notable therapeutic potential against different types of cancer. However, targeting Myc pharmacologically – directly or indirectly – is still considered challenging. Use of the Myc dominant negative mutant termed Omomyc provided the first evidence of the efficacy and safety of targeting Myc and displayed one of the most outstanding anti-tumorigenic potentials to date. This thesis project is divided into two major tasks: firstly, we aimed to better determine the source of Omomyc’s therapeutic effect, which could provide clues on how to develop better Myc inhibitors; Secondly, despite the claims that Omomyc itself could not be used as a drug, we assessed different ways in which it could be effectively delivered to cancer cells to validate the first Omomyc-based drugs. In the context of our first task, by expressing Omomyc in a panel of lung cancer cells lines, we showed for the first time a gain-of-function of Omomyc, which intriguingly re-locates endogenous Max on Myc-unrelated DNA regions, thus potentially acting not only as a Myc inhibitor but also producing additional effects within cancer cells. Moreover, its dimerization with endogenous Max and the occupancy of DNA were identified as key effectors of Omomyc’s anti-tumorigenic efficacy. In the context of generating the first Omomyc-based pharmacological approaches, Omomyc was first produced as a polypeptide. Remarkably, we determined that its systemic administration is safe and effective against subcutaneously implanted lung cancer cells, both as monotherapy and in combination with standard chemotherapy. Second, we generated Omomyc-encapsulating liposomes, which are able to improve the cellular uptake of the polypeptide and its nuclear localization. Finally, we provided the first evidence that Omomyc could be delivered as mRNA into cells that will translate it into a functional nuclear peptide product. 6 Together, our results provide insights into Omomyc’s mechanism of action that might be used to develop new therapeutic approaches, including more effective Omomyc-derived drugs. Furthermore, we show that these could be delivered to cancer cells as cell-penetrating peptides (CPPs), liposomes and/or mRNA, providing an arsenal of tools to effectively and safely inhibit the Myc oncogene in the clinic.