HNMPA is a tyrosine kinase inhibitor that inhibited both the receptor serine and tyrosine phosphorylation, including insulin receptor tyrosine kinase activity [1].

Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for growth factors, cytokines, and hormones. The insulin receptor is one of a number of growth factor receptors with intrinsic tyrosine kinase activity that can be activated upon ligands binding [1].

HNMPA (Hydroxy-2-naphthalenylmethyl Phosphonic Acid) is a tyrosine kinase inhibitor that blocks receptor serine and tyrosine phosphorylation. HNMPA does not affect protein kinase C or cyclic AMP-dependent protein kinase activities. HNMPA inhibited tyrosine kinase activity of autophosphorylated insulin receptor towards poly (Glu4, Tyr) or insulin receptor-(1155-1165) peptide by 82% and 81%, respectively. HNMPA also inhibited autophosphorylation of insulin receptors by 13% + 4.6% in the presence of insulin. HNMPA not only inhibited insulin receptor tyrosine phosphorylation but also effectively decreased insulin receptor serine phosphorylation [1]. In β-cells exposed to high glucose, HNMPA was able to further increase the exe-4-induced insulin secretion [2].

References:
[1].  Baltensperger K, Lewis RE, Woon CW, et al. Catalysis of serine and tyrosine autophosphorylation by the human insulin receptor. Proc Natl Acad Sci U S A. 1992 Sep 1;89(17):7885-9.
[2].  Moon MJ, Kim HY, Park S, et al. Insulin contributes to fine-tuning of the pancreatic beta-cell response to glucagon-like peptide-1. Mol Cells. 2011 Oct;32(4):389-95.