Neratinib is an irreversible tyrosine kinase inhibitor with IC₅₀s of 59 nM and 92 nM for HER2 and EGFR, respectively.
Neratinib has inhibition of tyrosine kinase KDR and Src with IC₅₀ of 0.8 μM and 1.4 μM, respectively. This compound is 14- and 24-fold less active compared with HER2. Furthermore, Neratinib displays no activity against other serine-threonine kinases such as Akt, cyclin D1/cdk4, cyclin E/cdk2, cyclin B1/cdk1, IKK-2, MK-2, PDK1, c-Raf, and Tpl-2, as well as the tyrosine kinase c-Met.
In 3T3 cells transfected with the HER2 (3T3/neu), Neratinib selectively inhibits the proliferation of 3T3 cells. At the same time, Neratinib inhibits SK-Br-3 and BT474 cell growth with IC₅₀ values of 2-3 nM.

Neratinib also inhibits the proliferation of EGFR -dependent A431 cells with an IC₅₀ of 81 nM. At the same time, It reduces HER2 receptor autophosphorylation in BT474 cells with an IC₅₀ of 5 nM, and EGF-dependent phosphorylation of EGFR in A431 cells with IC₅₀ of 3 nM.

What’s more, Blocking of HER-2 by Neratinib results in inhibition of downstream MAPK and Akt pathways with IC₅₀ of 2 nM. Neratinib inhibits the cyclin D1 expression and the phosphorylation of the Rb-susceptibility gene production in BT474 cells with IC₅₀ of 9 nM. As a result, Neratinib leads to G1-S arrest and ultimately decreased cell proliferation.

In vivo, Neratinib significantly inhibits the growth of xenografts with high levels of HER-2 and EGFR.

Neratinib significantly inhibits the growth of 3T3/neu xenografts. AT the dosage of 20, 40, and 80 mg/kg/day, Neratinib results in the inhibition of 53%, 98%, and 98%, respectively.
Additionally, Neratinib inhibits the growth of BT474 xenografts by 70-82%, 67%, and 93% at doses of 5, 10, and 40 mg/kg/day, respectively. Furthermore, Neratinib is also effective against SK-OV-3 xenografts with inhibition of 31% and 85% at 5 and 60 mg/kg/day, respectively.
However, Neratinib is less potent against EGFR -dependent A431 xenografts than HER-2-dependent tumors. It exhibits 32% and 44% inhibition at 5 and 20 mg/kg/day, respectively. However, Neratinib displays little activity against MCF-7 and MX-1 xenografts expressing low levels of HER-2 and EGFR. All above suggests that Neratinib has a selective activity for cells expressing HER-2 or EGFR.

In conclusion, Neratinib exhibits tyrosine kinase inhibition in vitro and in vivo.

Reference:

[1]. Rabindran SK, et al. Cancer Res, 2004, 64(11), 3958-3965.

[2]. Yoshioka T, et al. Cancer Sci. 2018 Apr;109(4):1166-1176.