Notably, the dual inhibition of IDO1 and PARP1/2 specifically reduced the expression of HR core genes and proteins, such as BRCA1 and RAD51, which may contribute to impaired DNA-damage repair and increased sensitivity to Olaparib. In summary, targeting both IDO1 and PARP1/2 represents a promising combination therapy for BRCA-proficient TNBC.

P3, N=855, Active, not recruiting, Bristol-Myers Squibb | Trial primary completion date: Nov 2025 --> Feb 2026

P2, N=10, Not yet recruiting, Tianjin Third Central Hospital; Tianjin Third Central Hospital

P2, N=9, Not yet recruiting, University Hospital, Basel, Switzerland

P3, N=89, Completed, Incyte Corporation | Active, not recruiting --> Completed

P2, N=51, Completed, Washington University School of Medicine | Active, not recruiting --> Completed | Trial completion date: Apr 2026 --> Oct 2025

By studying the turnover of IDO1 protein in human tumor cells exposed to various IDO1 catalytic inhibitors, such as epacadostat, linrodostat, and navoximod, we show here that these molecules stabilize a non-enzymatic protein conformation of IDO1, independently of their mechanism of inhibition. In the thyroid carcinoma cell line FTC-133, the stabilized and non-enzymatic IDO1 protein promotes the proliferation and migration of the tumor, resulting in an adverse pro-tumorigenic effect. These results uncover an unexpected adverse effect of IDO1 inhibitors in the tumor microenvironment that overcomes the enzymatic inhibition of IDO1, and suggest protein degradation, rather than enzymatic inhibition, as a more effective approach to target IDO1 in the tumor microenvironment.

These findings suggest a potential inhibitory mechanism for PF-06840003 and offer valuable structural insights for the rational design of potent IDO1 inhibitors. It should be noted that the inhibitory activity of the designed lead compounds is based solely on computational predictions; experimental validation through in vitro and in vivo studies is still required to confirm their actual inhibitory effects and pharmacokinetic properties.

P2, N=24, Active, not recruiting, Memorial Sloan Kettering Cancer Center | Trial completion date: Sep 2025 --> Sep 2026 | Trial primary completion date: Sep 2025 --> Sep 2026

CAFs suppressed T-cell proliferation and induced PD-1 expression in CD4+ and CD8+ T cells, effects reversed by epacadostat. IDO1 inhibition enhanced T-cell proliferation via AKT signaling, restored T-cell cytotoxicity, and increased ovarian cancer cell apoptosis. These findings suggest that targeting IDO1 may help counteract CAF-mediated immunosuppression and enhance antitumor immunity in HGSOC.

Cohort A received RT + nivolumab with escalating BMS-986205 doses in MGMT unmethylated GBM patients. Cohort B received the highest dose of BMS-986205 with nivolumab and standard RT/temozolomide (TMZ)

In vivo, a subcutaneous xenograft tumor model of nude mice was established by subcutaneously inoculating SK-HEP1 and treated with IDO1 catalytic inhibitor epacadostat (EPA) to observe the effect of IDO1 on tumor growth and immune cells infiltration...Targeting IDO1 may represent a promising immunotherapeutic strategy. However, its immunomodulatory effects must be validated in immunocompetent or humanized animal systems before clinical translation.