Abstract Background Tumor progression locus 2 (TPL2) is a cytoplasmic serine/threonine kinase broadly expressed in hematopoietic cells including myeloid cells. TPL2 is activated by inflammatory stimuli, such as bacterial cell wall components and TNFa, leading to activation of MAPK/ERK and downstream ERK-mediated gene expression changes. TPL2 expression is elevated in active ulcerative colitis (UC) and Crohn’s disease (CD), and several cytokines downstream of TPL2 activity are implicated in inflammatory bowel disease pathogenesis. GS-4875 is a highly selective, first-in-class small molecule inhibitor of TPL2, and tilpisertib fosmecarbil (TIP; GS-5290) is an intestinally cleaved prodrug of GS-4875 in development for moderately to severely active UC (NCT06029972). Methods In vitro, GS-4875 selectively inhibited LPS-stimulated phosphorylation of TPL2, MEK, and ERK in human monocytes. In preclinical models, GS-719201 (a tool TPL2 inhibitor) inhibited LPS-induced pro-inflammatory cytokine release (TNFa) and reduced tissue pERK levels, and ameliorated colitis disease pathology. To monitor pharmacodynamic (PD) changes mediated by GS-4875 or TIP dosing, a whole blood assay was developed which assessed inhibition of pERK in monocytes by flow cytometry after LPS stimulation of whole blood. In vitro, in rat whole blood, GS-4875 inhibited LPS-stimulated pERK with a blood-to-plasma-ratio adjusted EC50=400±121 nM. In healthy rats administered a single oral dose of GS-4875, whole blood LPS-stimulated pERK inhibition EC50=664 nM. High concordance was observed between in vitro and in vivo pERK EC50 values in rat, supporting clinical use of this PD assay to monitor pathway inhibition. Results In the first in human, healthy volunteer study of TIP, whole blood PD data were collected on Day 1 (single dose cohorts) and Days 1 and 10 (multiple dose cohorts). TIP demonstrated dose- and time-dependent inhibition of LPS-stimulated pERK in monocytes. At 300 mg QD or higher for 10 days, median inhibition exceeded 90% relative to pre-dose up to 24 h after the last dose. Specifically, on Day 10 at 24 h post dose, median inhibition (N = 5-8/cohort) was 3.9%, 39.8%, 91.6%, 98.5%, and 101.5% for placebo, 75 mg QD, 300 mg QD, 900 mg QD, and 600 mg BID, respectively. Conclusion Although ERK may be activated in a TPL2-independent manner, it is directly downstream of TPL2, and data supports the use of LPS-stimulated pERK as a PD biomarker for TPL2 inhibition. Given the durable and robust effect of TIP on inhibition of TPL2 pathway demonstrated in blood, and the elevated TPL2 pathway activity observed in UC and CD tissue, TPL2 inhibition represents a promising therapeutic strategy for IBD. TIP is currently in evaluation in a Phase 2 clinical trial in UC. Conflict of interest: Dr. Crellin, Natasha: Employee of Gilead Sciences. Liang, Yan: I am an employee of Gilead Sciences. Madia, Priyanka: I am employee of Gilead Sciences Canales, Eda: I am an employee of Gilead Sciences Arulmani, Udayasankar: Employee of Gilead Sciences
Crellin et al. (Thu,) studied this question.