Developing and taking a drug to market is a long and expensive path: on average it takes more than 12 years and $2 billion from research to development for public use. But even if a drug makes it to market, it doesn’t necessarily mean that it is safe for everyone.
A great option to speed up this process and search for safer drugs is to make use of structure-activity relationships (SAR). By relating the features of a chemical structure to its effect or biological activity in the body, SAR not only helps scientists reveal how the properties are relevant to the activity but also allows them to rationally decide how to tweak the structure of candidate molecules in order to improve their efficacy and decrease toxic effects.
In this work, a SAR analysis was used to guide the design of a peptide capable of triggering programmed cell death (PCD) in cancer cells, in which MicroScale Thermophoresis (MST) was vital for determining the changes in peptide structure that resulted in enhanced binding to its target.
Defining the candidate molecule for inducing suicide in cancer cells
PCD or apoptosis is a cellular process that helps keep the homeostatic cellular balance within the body. This normal homeostasis is not just a passive process but a tightly regulated one that is also triggered to eliminate damaged cells. Cancer cells, however, have found ways to escape this regulation by overexpressing anti-apoptotic proteins or down-regulating pro-apoptotic proteins. Therefore, targeting PCD then might be a viable therapeutic solution to fight cancer.
Based on this premise, studies have shown that the protein Thrombospondin-1 (TSP-1) — bound to its membrane receptor CD47 — induces PCD and plays an important antitumor role, defining TSP-1 as a potential target for therapeutic intervention.
Changing the structure of a drug to make it work better
After identifying the specific part of the TSP-1 molecule responsible for its biological effects in cancer, researchers then synthesized it for further testing. However, due to its poor solubility, potency, and metabolic stability, several chemical modifications were made to TSP-1 in order to enhance certain properties, resulting in a series of new and improved peptides.
Selecting peptides with improved affinity for its target
Since chemical modifications can influence the affinity of a drug for its target, a binding assay was developed to characterize the affinities of the different peptides to CD47, with the goal of selecting peptides with an improved affinity for CD47.
For this, two technologies were evaluated in parallel: MicroScale Thermophoresis (MST) with the Monolith NT.115 and Bio-Layer Interferometry (BLI) utilizing the OctetRed. Although both proved to be useful when analyzing the candidate peptides-CD47 interaction, MST showed a 10-fold affinity improvement — a difference most likely due to the fact that BLI requires the sample to be immobilized, which often leads to an unwanted orientation.
Using MST technology, the research team was able to easily characterize their cancer drug candidates in solution and produce highly-quality results, where other methods showed limitations. This study resulted in the design of the first serum stable TSP-1 mimetic agonist peptide that is able to selectively trigger PCD of cancer cells, opening new perspectives for the development of original anticancer therapies.