The Multi-Level Mechanism of Action of a Pan-Ras Inhibitor Explains its Antiproliferative Activity on Cetuximab-Resistant Cancer Cells.

Renata Tisi,Elisa Mazzoleni,Paolo Cazzaniga,Simone Arnhold,Marco Vanoni,Michela Spinelli,Francesco Peri,Luca De Gioia,Daniela Besozzi,Alessandro Palmioli,Cristina Airoldi,Rita Grandori,Elena Sacco,Marco S Nobile

doi:10.3389/fmolb.2021.625979

Abstract

Ras oncoproteins play a crucial role in the onset, maintenance, and progression of the most common and deadly human cancers. Despite extensive research efforts, only a few mutant-specific Ras inhibitors have been reported. We show that cmp4–previously identified as a water-soluble Ras inhibitor– targets multiple steps in the activation and downstream signaling of different Ras mutants and isoforms. Binding of this pan-Ras inhibitor to an extended Switch II pocket on HRas and KRas proteins induces a conformational change that down-regulates intrinsic and GEF-mediated nucleotide dissociation and exchange and effector binding. A mathematical model of the Ras activation cycle predicts that the inhibitor severely reduces the proliferation of different Ras-driven cancer cells, effectively cooperating with Cetuximab to reduce proliferation even of Cetuximab-resistant cancer cell lines. Experimental data confirm the model prediction, indicating that the pan-Ras inhibitor is an appropriate candidate for medicinal chemistry efforts tailored at improving its currently unsatisfactory affinity.

Highlights

Ras proteins are small guanine nucleotide-binding (G) proteins with low intrinsic GTPase activity, cycling between a GDP-bound inactive state and a GTP-bound active state
These results suggest that cmp4 binding to the Switch II extended pocket (SII-EP) counteracts nucleotide release, even in conditions favoring nucleotide release, as observed in HRasG13D (Johnson et al, 2019), and/or in the presence of EDTA or a Guanine nucleotide Exchange Factors (GEFs) catalytic domain
With its multi-level mechanism of action that is only minimally superimposed with that of Cetuximab, cmp4 is a good candidate for medicinal chemistry efforts tailored at improving its currently unsatisfactory affinity for Ras proteins

Summary

Introduction

Ras proteins are small guanine nucleotide-binding (G) proteins with low intrinsic GTPase activity, cycling between a GDP-bound inactive state and a GTP-bound active state. They act as molecular switches in signaling pathways regulating many cellular processes, including cell proliferation, growth, survival, adhesion, migration, energy, and redox homeostasis (Simanshu et al, 2017). Oncogenic Ras mutants contribute to tumor onset, maintenance, progression, and influence the efficacy of both cytotoxic and targeted therapies (Li et al, 2018). Many efforts, mostly promoted by the RAS initiative (https://www.cancer.gov/ research/key-initiatives/ras), have been devoted to investigating the mechanistic role of RAS oncogenes in cancer and to explore different strategies for attenuating the aberrant Ras oncoproteins signaling, as widely reviewed (Sacco et al, 2012c; Welsch et al, 2017; Gorfe and Cho, 2021; Ni et al, 2019; Spencer-Smith and O’Bryan, 2019; Khan et al, 2020; Tisi et al, 2020)

Methods

Discussion

Conclusion