Drugging The “Undruggable” - A New Grant from Little Warrior

Little Warrior Foundation grants $130,000 to John Bushweller, PhD, Professor and Chemical and Structural Biologist at the University of Virginia, to further optimize a small molecule inhibitor for ETS-driven cancers like Ewing Sarcoma.

Ewing Sarcoma (EwS) has long been known to be driven by a single chromosomal translocation between DNA on Chromosomes 22 (EWS) and Chromosome 11 (FLI1). This somatic (non-heredity) mutation, often referred to as a fusion, gives rise through the process of transcription and translation to a specialized protein (i.e. an oncogene produces oncoprotein).

Proteins are a ubiquitous and essential part of life, to which both non-malignant and tumor cells alike could not survive without. From being critical components of the cell membrane, to various metabolic transporters, to enzymatic reactions, to presenting antigens on the cell surface -  all these processes (and many more) are mediated by specialized forms of proteins.

Moreover, EWS::FLI1, is a specialized protein that is known as a transcription Factor (TF). TFs bind and read specific DNA sequences (or code), resulting in the activation of genes that shouldn’t be turned on (like tumor enhancers) and conversely the repression of other genes that shouldn’t be off (like tumor suppression mechanisms).  You can think of TFs as the ultimate recruiter, assembling a team of key role players who are brought together to work towards a specific and common goal.  In the context of cancer, it is the worst type of recruiter, where the aim is to make sure that tumor cells proliferate.  To make matters worse, scientifically speaking, TFs are notoriously hard to target and drug because of their unique structural properties (or lack thereof). Even in 2024, scientists still don’t know the full structure of many of these TFs, because they are characterized as intrinsically disordered proteins (or IDP for short).  

As you can imagine, if a medicinal or pharmaceutical chemist doesn’t know the structure of a given protein, they are flying blind with regard to what to target.  Protein structure is akin to having a road map towards a new destination. Without this map in place, finding “druggable pockets” for inhibition becomes an almost impossible task, hence leading many scientists to deem TFs as “undruggable”.  This is also why in the past several decades, for hard-to-drug targets like EWS::FLI1, MYC, and P53-driven cancers (all TFs), there has been very little development of direct targeted approaches for these cancer drivers.

However, Dr. Bushweller, a chemical biology and structural biology researcher at the University of Virginia has been on the relentless pursuit of doing just that, tackling the impossible, by searching for druggable pockets in TFs. Stemming from his lab’s research in prostate cancer (a cancer where 50% of this patient population is driven by an ERG fusion), his lab developed a unique small-molecule inhibitor that inhibited the growth of ERG driven prostate cancer cells. In recognizing the homology (or similarity) between ERG and FLI1, Dr. Bushweller’s team further explored other cancer types that were related to ERG (ERG and FLI1 are in the same ETS subfamily): and lo and behold, they discovered a therapeutic that had scalability without compromising on therapeutic efficacy for both Prostate and Ewing Sarcoma cancer!

The key to Dr. Bushweller’s discovery is to take advantage of an inherent biological process called auto-inhibition. Auto-inhibition is a cellular regulatory system that acts as a type of “checks-and-balance” and is a brake system designed to stop a specific portion of a protein’s activity when that protein's function is no longer needed.  The first step to taking advantage of this unique regulatory process was to determine if these auto-inhibitory elements are present and functional on ERG (and FLI1) proteins. ✅ The second was to determine if these specific auto-inhibitory domains “protein pockets'' were druggable. 🔥 And lastly, by drugging these auto-inhibition domains, could it stop EWS::FLI1 from acting as a TF. 🏆  In summary, Dr. Bushweller’s unique workaround to stopping EWS::FLI1 TF activity, is to lock-it in an autoinhibited state, rendering it unable to bind to DNA and carry out its oncogenic program.  Here, a picture is worth a thousand words, see Fig.1 for a graphic representation of how this works.

Fig. 1. Graphic representation of the general mechanism of action.

With the support from Little Warrior Foundation, the Bushweller lab will continue to optimize its current lead molecule for EWS::FLI1 (and ERG) by increasing its therapeutic potency and validating the pharmacokinetics (stability) of the optimized drug in an in vivo (mouse model) setting.  If successful with these current aims, further in vivo tumor testing will be necessary before translating this targeted therapy approach. And with LWF’s powerful and committed community, we remain determined to be in lockstep with this promising research, ever hopeful that it has the chance to translate from the bench to the bedside and make a difference for those kids that need it most!

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