Structural Investigation into RioK1 for Cancer Therapeutics

Abstract

Cancer was the second leading cause of death in the United States in 2020.1 Cancer shares many similarities with healthy cells, making it a difficult therapeutic target.2 Current developments of cancer therapeutics are governed by targeting key proteins responsible for distinct features in each type of cancer phenotype. (e.g. decreased apoptosis, metastasis, immortalization, etc.). However, finding a rational therapeutic target, engineering a lead compound, and lead compound optimization is time-consuming and expensive. With the use of high-throughput screens and structure-based drug design it is possible to design lead compounds in a more efficient manner. Techniques such as x-ray crystallography and cryo-electron microscopy are used to observe how compounds interact with the target protein at atomic resolution, which helps facilitate optimization.2-4 Kinases in particular, have benefitted greatly from these techniques.5 Kinases play key roles in signal transduction and its regulation in many cellular pathways. The catalytic active site is highly conserved among many kinase families, so designing drugs targeting a single enzyme’s catalytic site could have potential off target effects as many kinases could be inhibited. Strategies to target kinases therefore use distinct features of each kinase that take both conserved and nonconserved residues into consideration as well as for active and inactive forms of the kinase being targeted, so tailormade therapeutic solutions are derived, as with the case of reading open frame kinase 1 (RioK1).2, 4, 5 RioK1 was identified as a key enzyme in both lung and colorectal cancer, cancer subtypes with some of the most severe prognoses.6 In a study done by Kiburu et al., toyocamycin was demonstrated to bind tightly to RioK1 from archaeoglobus fulgidus (afRioK1), thereby discovering the first scaffold for RioK1.7 Toyocamycin is an adenosine analog, commonly used as inhibitor, and thus making this drug scaffold non-specific with off-target effects other than for RioK1.8-12 To address this issue, computer aided drug design was used to find toyocamycin-like compounds that have improved selectivity for afRioK1 inhibition. A series of these compounds were identified via screening approaches and then co-crystallized with afRioK1 with the goal of elucidating useful structure-activity relationship data for next stage drug-design. Furthermore, one of the most newly studied interactions of RioK1 is with protein arginine methyltransferase type 5 (PRMT5), so understanding the details of this interaction provides yet another means to develop afRioK1 inhibition strategies as part of an approach to block cancer progression.