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Updated: Aug 14, 2026
Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells In Vitro
Published on: March 18, 2014
Structure-guided discovery of small-molecule ICOS-ICOSL antagonists that remodel intratumoral immunity and enhance
Xianwen Yan1, Xuan Sun2, Ruixing Shui1
1Department of Spinal Surgery, Affiliated Hospital of Jiangsu University, Zhenjiang, Jiangsu 212016, China.
Abstract:
The inducible T‑cell co‑stimulator (ICOS)-ICOS ligand (ICOSL) axis shapes effector versus regulatory T‑cell programs in tumors, yet small‑molecule disruption of this protein-protein interaction remains underexplored. We used the ICOS-ICOSL complex to define an interfacial hotspot and applied DrugCLIP to screen approximately 5 × 108 compounds, followed by diversity clustering, developability triage, and AutoDock Vina docking. Five candidates were prioritized for experimental validation. In a TR‑FRET competition assay measuring ICOS-ICOSL complex formation, STK910592, STL167676, and OSSK‑026837 inhibited the interaction with IC50 values of 10.67, 12.59, and 14.37 μM, respectively. STK910592 and STL167676 showed favorable cellular tolerability and elicited functional immune modulation in parallel human and murine tumor-APC-T cell tri‑culture systems, increasing IL‑2, IFN‑γ, and TNF‑α secretion. In an immunocompetent orthotopic LM8 osteosarcoma model, both compounds produced dose‑dependent antitumor activity and were associated with immune remodeling, including increased CD8 infiltration, reduced FOXP3/ICOS immunoreactivity, and induction of innate‑priming and effector cytokine programs in tumor tissues. Notably, combining ICOS targeting with anti-PD-1 therapy yielded schedule‑dependent enhancement of efficacy and reduced pulmonary metastatic burden, with sequential dosing outperforming concomitant administration. These findings provide a preclinical rationale for developing ICOS-ICOSL small‑molecule antagonists and highlight temporal sequencing as an actionable parameter to optimize PD‑1-based combination immunotherapy in osteosarcoma.
Insights
Small molecules targeting the Inducible T-cell Co-stimulator (ICOS)-ICOS Ligand (ICOSL) axis show promise in cancer immunotherapy. These compounds demonstrated antitumor activity and enhanced efficacy when combined with anti-PD-1 therapy in osteosarcoma models.
Area of Science:
- Immunology
- Pharmacology
- Computational Chemistry
Background:
- The Inducible T-cell Co-stimulator (ICOS)-ICOS Ligand (ICOSL) axis plays a crucial role in regulating T-cell responses within the tumor microenvironment.
- Targeting protein-protein interactions, such as ICOS-ICOSL, with small molecules is an underexplored therapeutic strategy in cancer.
Purpose of the Study:
- To identify and validate small-molecule inhibitors of the ICOS-ICOSL interaction for potential cancer immunotherapy.
- To evaluate the efficacy of ICOS-ICOSL inhibitors alone and in combination with anti-PD-1 therapy in preclinical cancer models.
Main Methods:
- High-throughput virtual screening using DrugCLIP and AutoDock Vina to identify potential ICOS-ICOSL inhibitors from a large compound library.
- Experimental validation using TR-FRET assays to determine inhibitory concentrations (IC50).
- In vitro functional assays in human and murine tumor-APC-T cell co-cultures to assess immune modulation.
- In vivo efficacy studies in an orthotopic osteosarcoma mouse model and combination therapy studies with anti-PD-1.
Main Results:
- Three compounds (STK910592, STL167676, OSSK‑026837) inhibited ICOS-ICOSL interaction with IC50 values in the micromolar range.
- STK910592 and STL167676 demonstrated favorable tolerability and enhanced secretion of IL-2, IFN-γ, and TNF-α in vitro.
- In vivo, these compounds exhibited dose-dependent antitumor activity, increased CD8 infiltration, and modulated immune profiles in osteosarcoma.
- Combination therapy with anti-PD-1 showed enhanced efficacy and reduced metastasis, with sequential dosing being superior to concomitant administration.
Conclusions:
- Small-molecule inhibition of the ICOS-ICOSL axis is a viable strategy for cancer immunotherapy.
- ICOS-ICOSL antagonists can synergize with PD-1 blockade, and the timing of administration is critical for optimal outcomes.
- These findings provide a preclinical basis for developing ICOS-ICOSL inhibitors in combination with checkpoint inhibitors for osteosarcoma and potentially other cancers.
