Identification of a RIP1 Kinase Inhibitor Clinical Candidate (GSK3145095) for the Treatment of Pancreatic Cancer
Over the past decade, extensive resources have been dedicated to developing RIP1 inhibitors for treating several inflammatory and CNS diseases. However, inhibition of RIP1 kinases also differentiates T cells toward tumor suppressive phenotypes and can sensitize tumors to checkpoint blockade, thus providing promise for use in oncology.
In this month’s Featured Letter, Harris et al. (DOI: 10.1021/acsmedchemlett.9b00108) from GlaskoSmithKline and New York University School of Medicine report GSK3145095, a RIP1 clinical candidate, which exploits this pharmacology for treating pancreatic adenocarcinoma and other solid tumors. Developed from a DNA-encoded library hit, the optimized ligand exhibits exclusive selectivity in radioligand and competition binding assays, due to the unique ligand binding site that predominantly exploits a small allosteric lipophilic pocket adjacent to the ATP site. In vitro enzymatic, cellular, and whole-blood assays support a mechanism involving inhibition of TNF-stimulated necrosis through RIP1-dependent release of inflammatory cytokine MIP-1β. Further characterization using ex vivo tumor cultures indicate that treatment with GSK3145095 increases production of effector-memory T cells and immunogenic CD4+ T cells and may also increase CD8+ T cells and TNFα expression. Metabolite profiling and PK evaluation enabled progression to a phase I clinical trial. This novel pharmacology in combination with approved immunotherapies provides a promising opportunity for improving patient outcomes.
Do Zebrafish Obey Lipinski Rules?
The use of whole organism phenotypic assays can facilitate drug discovery by assessing biological effects, permeability, and toxicity in a single assay. In these studies, zebrafish are a popular model organism due to genetic, economic, and other practical considerations. However, despite these benefits, limited data indicates what types of molecules will permeate zebrafish. Thus, it is unclear whether an “inactive” compound (a) permeates the fish, but fails to regulate the biological pathway, or (b) does not permeate the fish, thus precluding biological changes.
To differentiate these possibilities, Huryn and collaborators (DOI: 10.1021/acsmedchemlett.9b00063) set out to establish a set of physicochemical descriptors that predict zebrafish permeability. The authors conducted a literature search to identify compounds exhibiting biological activity in zebrafish assays and compiled a list of 700 compounds. Comparison of various properties of these zebrafish-active molecules with well-known Lipinski parameters and two collections of small molecule approved drugs suggest that, statistically, zebrafish-active molecules tend to be smaller and have higher logP values, lower H-bond donor and acceptor counts, and lower polar surface areas. Further data supports use of standard Caco-2 and/or MDCK transwell assays for predicting zebrafish permeability. Though assessment of alternate data sets might further refine these “zebrafish rules,” the overall trends observed by the authors should facilitate interpreting data obtained from zebrafish models and help justify some “inactive” results produced from these assays.
DMSO-Perturbing Assay for Identifying Promiscuous Enzyme Inhibitors
Medicinal chemistry campaigns are dependent on identifying mechanistically characterized initial hits for subsequent development. Thus, the ability to differentiate inhibitors with good specificity, as opposed to promiscuous inhibitors, is essential for selecting appropriate lead compounds.
In this issue, Nose, Tomohara, and co-workers (DOI:10.1021/acsmedchemlett.9b00093) describe the use of DMSO as an assay-additive to identify nonspecific inhibitors. Using an extensive series of controls, the authors demonstrate that the addition of DMSO to the assay media increases the concentration of “non-productive but non-denatured” protein, which exhibits distinct binding kinetics relative to native protein or denatured protein. The systematic addition of increasing concentrations of DMSO causes a shift in inhibition curves of nonspecific inhibitors, while specific inhibitors display no such shift in the presence of DMSO. This simple protocol can be readily adapted to standard enzyme inhibitory assays that have already been optimized. Overall, the ability to rapidly identify promiscuous compounds while exerting minimal effort should accelerate lead selection and help put better compounds into the hands of medicinal chemists.
