Development of ITCH-activating IRAK4 degraders as dual-targeting drug candidates for the treatment of rheumatoid arthritis

The interleukin-1 receptor-activated kinase 4 (IRAK4) is a serine/threonine kinase mediating the innate immune and inflammatory response; it is expressed in numerous cell types. IRAKs are key regulators of inflammatory signaling elicited by Toll-like receptors (TLRs), interleukin-1 receptor (IL-1R) and interleukin-18 receptor (IL18R). Upon binding to the TLR, IRAK4 dimerizes and binds MyD88 adaptor protein to form a complex that facilitates IRAK autophosphorylation and activation. In turn, the NFkB and MAPK pathways are activated. Activated NFkB transcription factor regulates several proinflammatory cytokines, including IL-6 and IL-10. IRAK4 is critical to murine and human anti-inflammatory responses, as shown in experiments with knockout/knockin mice. IRAK4 knockout mice are resistant to septic shock, and their cytokine production is impaired, while IRAK4 kinase-dead knock-in mice are impaired in their ability to produce cytokines upon TLR agonist challenge. Thus, inhibition of IRAK4 is seen as a therapeutic avenue for treating conditions characterized by overactivation of innate immunity or inflammatory pathways, e.g., rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE). Several IRAK4 inhibitors have shown anti-inflammatory effects in preclinical models, and a few are in clinical trial for treatment of RA, SLE, and psoriasis. Targeted protein degradation using heterobifunctional molecules called PROTACs, which are composed of a target protein binder tethered to a ubiquitin E3 ligase binder, is a promising new therapeutic modality. PROTACs remove all the target protein in the cell by E3- directed degradation, and thus are more efficacious than simple pharmacological inhibitors, which can leave some target molecules intact or become susceptible to resistance. They have impressive preclinical profiles, and several are in clinical trial for cancer. Simple IRAK4 inhibitors have been reported, with three reaching clinical trials. A PROTAC that degrades IRAK4 employing the E3 ligase cereblon is in Phase I clinical trial for dermatitis and hidradenitis suppurativa. In the proposed project, Progenra will develop a novel IRAK-4 PROTAC using a different E3 ligase, ITCH; it will have improved pharmacology and therapeutic efficacy with broader applications, compared with the cereblon PROTAC and should be superior to the pharmacological inhibitors. ITCH-IRAK molecules designed to degrade IRAK4 efficiently will be synthesized and characterized biochemically and biophysically in vitro, and cellular proof of concept will be demonstrated using relevant cell models of inflammation. Chemical optimization and other aspects of preclinical development will be conducted in Phase II.