PIK3CA and head and neck squamous cell carcinoma: However, EHop-016 treatment only brought about moderate inhibition of the PI3K signaling proteins (24% and 23% inhibition of p-S6(Ser235/236) and total levels; Figure 4C) in RAC1-P29S-HNSCC xenografts, consistent with its minimal antitumor activity in vivo (Figure 4A).