John P. O’Bryan, PhD
Associate Professor, Pharmacology
The University of Illinois at Chicago
For nearly 30 years, researchers have focused on identifying ways to pharmacologically inhibit RAS
, one of the most frequently activated oncogenes in human cancers.RAS
genes include 3 members, HRAS
, and NRAS
, each encoding proteins that function as regulated molecular switches, cycling between an “on” and “off” state. In cancer, mutations to RAS
lock the protein in an active, or “on,” state, leading to chronic activation of downstream signaling pathways that stimulate proliferation.
Unfortunately, direct RAS inhibitors have been elusive because, unlike many other drug targets, RAS proteins lack deep pockets where putative inhibitors can insert to block activity. While a number of RAS inhibitors have been isolated, none have reached FDA approval status due to issues with specificity or lack of activity toward mutant RAS
in tumors. Given the “addiction” of many tumors to mutant RAS
for their survival, there has been renewed interest in developing new ways to inhibit RAS in cancer. Indeed, the National Cancer Institute launched the RAS Initiative in 2013 to attack the problem of RAS inhibition specifically.
Our team of researchers at the University of Illinois at Chicago have discovered a previously unrecognized surface on RAS that is important for the signaling and transforming activity of this oncogene. Our findings, published in Nature Chemical Biology
, suggest a novel means of blocking the action of genetic mutations in cancer (2017;13:62-68). (Figure)
Figure. NS1 Monobody as Anticancer Agent
RAS proteins bind to the nucleotide guanosine diphosphate (GDP) in the “off” state and become “active” through aberrant signaling to bind with guanosine triphosphate (GTP). The monobody NS1 can disrupt RAS functions by binding to HRAS or KRAS proteins and inhibiting the hetreodimerization and activation of CRAF and BRAF proteins.
This method could potentially lead to new therapeutic approaches to treat cancers caused from a RAS
mutation, including pancreatic, lung, and colon cancers. Such approaches may also be of benefit in cancers that lack specific oncogenic mutations in RAS
but depend on RAS
activity for their survival. Targeting wild-type RAS
may also help unlock new therapeutic options.
Our strategy to studying RAS
was unique. We used monobody technology to identify regions of RAS
that are critical for its function. Monobodies are engineered, synthetic binding proteins designed to recognize a specific protein of interest.
Developed by Shohei Koide, PhD, of NYU Langone's Laura and Isaac Perlmutter Cancer Center, a collaborator on this study, this technology has been used to inhibit a diverse array of signaling proteins. Unlike conventional antibodies, monobodies are much smaller, are resistant to the reducing environment inside a cell, and can be readily used as genetically encoded inhibitors.
We isolated a monobody, termed NS1, which bound selectively and with high affinity to HRAS
, but not NRAS
. Using the NS1 monobody, we inhibited oncogenic HRAS and KRAS signaling and cellular transformation. This specificity was due to a minor sequence difference in NRAS
that prevented NS1 binding to the NRAS protein.
We found that NS1 blocks RAS
function by binding to a surface of the protein previously unrecognized as important for RAS
function. Further work revealed that this surface of RAS was critical for 2 RAS proteins interacting with each other in the process of activating their downstream targets.