Fragment-Based Approaches to Enhance GTP Competitive KRAS G12C Inhibitors

Principal Investigator: WESTOVER, KENNETH
Program: LCRP
Proposal Number: LC150042
Award Number: W81XWH-16-1-0106
Funding Mechanism: Idea Development Award - New Investigator Option
Partnering Awards:
Award Amount: $561,420.00


Objective and Rationale: One of the cancer-causing effects of cigarette smoke is a specific genetic mutation in the KRAS gene, which results in changes in the KRAS protein at codon 12 from glycine to cysteine (G12C). KRAS G12C mutations are a major driver of cigarette smoke-associated lung cancers, occurring in ~23,000 new cases of lung cancer per year. Indeed, KRAS G12C mutations are one of the most commonly observed genetic mutations found in lung cancer overall. Currently there are no effective therapies of any kind to target KRAS-driven cancers. The goal of this proposal is to further develop direct-acting KRAS G12C small molecule inhibitors that could be used as drugs to treat lung cancer and as "tool compounds" to enable scientific studies of how KRAS mutations cause cancer. The Westover lab and collaborators previously developed small molecule inhibitors such as SML-8-73-1 that, in a test tube, irreversibly attach to cysteine 12 and inactivate KRAS G12C protein. It is worth emphasizing that this targeting strategy is appealing because it exploits the very mutation that causes cancer. Therefore, these compounds are unlikely to affect healthy normal cells in the body that do not carry the KRAS G12C mutation. However, SML-8-73-1 is not suitable for use as a drug because it cannot pass through the cell membrane of cancer cells. The reason is that it contains chemical groups that are polar, meaning they carry a chemical charge and cannot pass through the non-polar cell membrane. We recently conducted a screen for small chemical fragments that could replace the polar portion of SML-8-73-1 and found several candidate compounds. For us to know how to replace the polar portion of SML-8-73-1 with the fragments from our screen, we need to obtain three-dimensional structures of KRAS G12C bound to the fragments. We will obtain such structures using a well-established technique that we have used to solve similar problems before called x-ray crystallography. This project addresses the following Lung Cancer Research Program areas of interest: (1) Understand the molecular mechanisms of progression to clinically significant lung cancer; (2) understand the molecular mechanisms that lead to various subtypes of lung cancer; and (3) identify innovative strategies for prevention and treatment of early and/or localized lung cancer.

Applicability of Research: What types of patients will this project help, and how will it help them? Cancer patients who have tumors bearing KRAS G12C mutations would benefit from this work because it would provide a medication to treat their cancer. KRAS G12C mutations occur most frequently in lung cancer (35% of non-small cell lung cancers contain KRAS mutations and ~50% of those are the G12C variety), but they are also found in colorectal, pancreatic, gynecological, and head and neck cancers. Also, if this work succeeds, it would represent a new paradigm in drug discovery and would likely motivate additional effort to therapeutically target other members of the KRAS protein superfamily that cause cancer.

What are the potential clinical applications, benefits, and risks? A KRAS G12C targeted drug could be used to treat cancer patients who have the KRAS G12C mutation. Most likely patients with advanced disease would benefit the most since early-stage patients are often treated adequately with surgery or ablative radiation such as Stereotactic Body Radiotherapy (SBRT). However, if KRAS G12C-targeted drugs turn out to be particularly non-toxic (because they target KRAS G12C, which is not found in normal healthy cells), giving these drugs to patients who have early-stage disease may also make sense to prevent metastases.

Describe the interim outcomes expected and their applicability to the field. A short-term outcome of this work would be development of effective "tool compounds" that target KRAS G12C. Consistent with the track record of our collaborative group, we would make such compounds freely available to the cancer research community. Tool compounds would assist in elucidating the complexities of how mutant KRAS functions in cancer, a topic that has occupied many researchers for the last 30 years.

What is the projected time it may take to achieve a clinically relevant outcome? "Tool compounds" would be completed by the end of the grant period. An additional 1-2 years beyond the grant period would be required for preclinical testing in animal cancer models, and an additional 1-2 years for further chemical optimization for use in humans. In a best case scenario, clinical trials in humans would require another 2-3 years to complete.

What are the likely contributions of this study to advancing the field of lung cancer research? Tool compounds that effectively inhibit KRAS G12C would enable multiple lines of research to help us understand how KRAS mutations cause lung cancer.

How is the project relevant to military Service members, Veterans, and their families? Exposure to cigarette smoke is common for members of the military and Veterans, resulting in high risks of lung cancer-associated mortality. Because the KRAS G12C mutation is one of the most common genetic mutations caused by smoking and because it results in cancer, developing drugs that hit this mutation would directly benefit military Service members, Veterans, and their families who struggle with the challenges of lung cancer.