Background: IRF5 is a transcription factor and master regulator of pro-inflammatory immune responses activated downstream of specific pattern recognition receptors, like Toll-like receptors (TLRs). Downstream of TLR7, TL8 and TLR9 activation, IRF5 can act as a central node and regulate genes for pro-inflammatory cytokines (TNFα, IL-6, IL-12, IL-23), Type I IFN, and cellular functions such as B cell activation and antibody secretion. IRF5 is constitutively expressed and activated in immune cell types such as dendritic cells, monocytes, macrophages, and B cells. Human genetic and functional studies have linked IRF5 dysregulation to the pathogenesis of multiple autoimmune diseases, including SLE and Sjögren’s, and Irf5-deficient mice protect from lupus onset and severity. In SLE, endosomal TLRs recognize nuclear self-antigens, and can trigger IRF5 activation to drive the breakdown of immune tolerance via a cascade involving increased Type I IFN and pro-inflammatory cytokine production, and autoantibody production. Despite its strong mechanistic and genetic validation, IRF5 has historically remained undrugged likely due to its lack of catalytic activity, activation complexity and multiple functional isoforms. IRF5 is well suited for targeted protein degradation. KT-579, a potent and selective oral IRF5 degrader, offers a novel approach to modulating immune responses driven by IRF5.

Objectives: To evaluate the in vitro potency, selectivity, and functional activity of IRF5 degradation by KT-579 in human healthy or patient-derived cells or whole blood. In addition, to assess the in vivo therapeutic potential of the oral IRF5 degrader, KT-579, by evaluating its dose-dependent activity and immunomodulatory effects in the MRL.lpr and the NZB.W1, mouse models of lupus and compare the activity of an IRF5 degrader with targeted agents clinically being tested or approved in SLE treatment.

Methods: Peripheral blood mononuclear cells (PBMCs) derived from healthy or patient donors were cultured with KT-579 in the presence or absence of TLR7, TLR8 or TLR9 activation to evaluate KT-579 selectivity by global proteomics, potency to degrade IRF5 by flow cytometry or western methods, and functional activity via cytokine release, plasmablast differentiation and IgG release by flow cytometry or ELISA. Following daily oral administration of KT-579, plasma cytokines and IRF5 levels were measured in the spleen in mouse models of acute TLR7 or TLR9 systemic activation. KT-579 at doses of 5, 15, 50 and 200mg/kg were orally administered in the MRL.lpr lupus mouse model with relevant disease endpoints measured including urine proteinuria, anti-nuclear antibodies and splenic B cell subsets. Similar disease relevant endpoints were measured in the NZB.W1 mouse model treated with daily oral administration of an IRF5 degrader. In vivo , comparators were included that inhibit targets upstream of IRF5 (TLR7/8 inhibitor) or downstream of IRF5 activation and Type I IFN (anti-IFNRA1 biologic and TYK2 inhibitor).

Results: KT-579 was selective for IRF5 in the detectable proteome, including other IRF family proteins. KT-579 demonstrated nanomolar potencies across relevant cell types tested and inhibited pro-inflammatory cytokines and Type I IFN production (IFN-β) and reduced plasmablast and IgG levels following TLR7, TLR8 or TLR9 activation in healthy or patient-derived PBMCs. In vivo, KT-579 led to dose-dependent inhibition of both TLR7- or TLR9-induced cytokines including TNFα, IL-6,IL-12 and IFN-β. In the MRL.lpr lupus model, KT-579 doses achieving at least 50% degradation of IRF5 levels led to significant reduction of disease biomarkers such as proteinuria and anti-nuclear autoantibodies and at the top dose achieving >85% degradation led to 100% survival and significant reduction of disease activity including relevant end-organ weight, kidney disease progression and auto-antibody producing cells, better than comparators tested including a TLR7/8 small molecule inhibitor. In both lupus models, IRF5 degradation was well tolerated, and IRF5 degrader activity was superior or similar to approved or clinically active drugs. KT-579 achieved deep degradation (≥95%) across multiple species with oral doses and did not show adverse effects at concentrations up the projected human efficacious levels in preclinical safety studies.

Conclusions: We report here the first potent, selective, oral IRF5 degrader, KT-579, that inhibits in vitro and in vivo activity in endosomal TLR induced immune responses in human SLE patient derived cells and in lupus mouse models, demonstrating superior or similar activity to existing standards of care agents. These findings position KT-579 as a potential first-in-class approach capable of broadly modulating pathogenic pathways in SLE and other autoimmune diseases.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: Veronica Campbell Kymera Therapeutics, Erik Corcoran All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Emily Lurier All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Yi Zhang All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Virginia Massa All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Jordan Leedberg All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Chris Caroll All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Ryan Camire All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Chris Ho All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Dapeng Chen All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Matthew Lolande All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Revonda Mehovic All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Ziyan Zhao All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Charles Howarth All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Susanne Breitkopf All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Sarah Martinez All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Melissa Ford All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Xue Fei All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Murugappan Sathappa All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Matt Weiss All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Sushrut Kamerkar All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Juliet Williams All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners., Nello Mainolfi All authors are Kymera Therapeutics employees and equity owners., All authors are Kymera Therapeutics employees and equity owners.