Molecular characterization of canine SHP2 mutants and anti‐tumour effect of SHP2 inhibitor, SHP099, in a xenograft mouse model of canine histiocytic sarcoma

Canine histiocytic sarcoma (HS) is an aggressive and highly metastatic neoplasm. Mutations in src homology 2 domain-containing phosphatase 2 (SHP2; encoded by PTPN11), which recently have been identified in canine HS tumour cells, could be attractive therapeutic targets for SHP099, an allosteric inhibitor of SHP2. Here, molecular characteristics of wild-type SHP2 and four SHP2 mutants (p.Ala72Gly, p.Glu76Gln, p.Glu76Ala and p.Gly503Val), including one that was newly identified in the present study, were investigated. Furthermore, in vivo effects of SHP099 on a HS cell line carrying SHP2 p.Glu76Ala were examined using a xenograft mouse model. While SHP2 Glu76 mutant cell lines and SHP2 wild-type/Gly503 mutant cell lines are highly susceptible and non-susceptible to SHP099, respectively, a cell line carrying the newly identified SHP2 p.Ala72Gly mutation exhibited moderate susceptibility to SHP099. Among recombinant wild-type protein and four mutant SHP2 proteins, three mutants (SHP2 p.Ala72Gly, p.Glu76Gln, p.Glu76Ala) were constitutively activated, while no activity was detected in wild-type SHP2 and SHP2 p.Gly503Val. Activities of these constitutively activated proteins were suppressed by SHP099; in particular, Glu76 mutants were highly sensitive. In the xenograft mouse model, SHP099 showed anti-tumour activity against a SHP2 p.Glu76Ala mutant cell line. Thus, there was heterogeneity in molecular characteristics among SHP2 mutants. SHP2 p.Glu76Ala and perhaps p.Glu76Gln, but not wild-type SHP2 or SHP2 p.Gly503Val, were considered to be oncogenic drivers targetable with SHP099 in canine HS. Further studies will be needed to elucidate the potential of SHP2 p.Ala72Gly as a therapeutic target of SHP099 in canine HS.