PP1 (Src Inhibitor)

PP1 is a potent, reversible, ATP-competitive, and selective inhibitor of the Src family of protein tyrosine kinases. It inhibits p56lck (IC₅₀ = 5 nM), p59fynT (IC₅₀ = 6 nM), Hck (IC₅₀ = 20 nM), and Src (IC₅₀ = 170 nM) without significantly affecting the activity of EGFR kinase (IC₅₀ = 250 nM), JAK2 (IC₅₀ = 50 µM), or ZAP-70 (IC₅₀ ≥ 0.6 µM).¹ PP1 inhibits anti-CD3-induced tyrosine phosphorylation of human T cells with an IC₅₀ value of 600 nM.¹ It exhibits antitumor activity by antagonizing both proliferation and the inhibition of apoptosis mediated by a stem cell factor/mast cell growth factor in hematopoietic and small cell lung cancer cell lines.^2,3 PP1 also blocks TGF-β-mediated cellular responses by directly inhibiting type I TGF-β receptors (IC₅₀ = 50 nM) in a manner unrelated to Src signaling.⁴

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1. Hanke, J.H., Gardner, J.P., Dow, R.L., et al. Discovery of a novel, potent, and Src family-selective tyrosine kinase inhibitor. Study of Lck- and FynT-dependent T cell activation. The Journal of Biological Chemisty 271(2), 695-701 (1996).

2. Krystal, G.W., DeBerry, C.S., Linnekin, D., et al. Lck associates with and is activated by kit in a small cell lung cancer cell line: Inhibition of SCF-mediated growth by the Src family kinase inhibitor PP1. Cancer Res. 58(20), 4660-4666 (1998).

3. Tatton, L., Morley, G.M., Chopra, R., et al. The Src-selective kinase inhibitor PP1 also inhibits kit and Bcr-Abl tyrosine kinases. The Journal of Biological Chemisty 278(7), 4847-4853 (2003).

4. Ungefroren, H., Sebens, S., Groth, S., et al. The Src family kinase inhibitors PP2 and PP1 block TGFβ-mediated cellular responses by direct and differential inhibition of type I and type II TGFβreceptors. Curr. Cancer Drug Targets 11(4), 524-535 (2011).

Callahan, A., Zhang, X., Wang, A., et al. CSF1R-CAR T cells induce CSF1R signaling and can promote target cell proliferation. Sci. Signal. 18(912), eadv4112 (2025).