Therapeutic implications of activating noncanonical PIK3CA mutations in head and neck squamous cell carcinoma
Nan Jin, … , Daniel E. Johnson, Jennifer R. Grandis
Nan Jin, … , Daniel E. Johnson, Jennifer R. Grandis
Published November 15, 2021
Citation Information: J Clin Invest. 2021;131(22):e150335. https://doi.org/10.1172/JCI150335.
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Research Article Oncology

Therapeutic implications of activating noncanonical PIK3CA mutations in head and neck squamous cell carcinoma

Abstract

Alpelisib selectively inhibits the p110α catalytic subunit of PI3Kα and is approved for treatment of breast cancers harboring canonical PIK3CA mutations. In head and neck squamous cell carcinoma (HNSCC), 63% of PIK3CA mutations occur at canonical hotspots. The oncogenic role of the remaining 37% of PIK3CA noncanonical mutations is incompletely understood. We report a patient with HNSCC with a noncanonical PIK3CA mutation (Q75E) who exhibited a durable (12 months) response to alpelisib in a phase II clinical trial. Characterization of all 32 noncanonical PIK3CA mutations found in HNSCC using several functional and phenotypic assays revealed that the majority (69%) were activating, including Q75E. The oncogenic impact of these mutations was validated in 4 cellular models, demonstrating that their activity was lineage independent. Further, alpelisib exhibited antitumor effects in a xenograft derived from a patient with HNSCC containing an activating noncanonical PIK3CA mutation. Structural analyses revealed plausible mechanisms for the functional phenotypes of the majority of the noncanonical PIK3CA mutations. Collectively, these findings highlight the importance of characterizing the function of noncanonical PIK3CA mutations and suggest that patients with HNSCC whose tumors harbor activating noncanonical PIK3CA mutations may benefit from treatment with PI3Kα inhibitors.

Authors

Nan Jin, Bhumsuk Keam, Janice Cho, Michelle J. Lee, Hye Ryun Kim, Hayarpi Torosyan, Natalia Jura, Patrick K.S. Ng, Gordon B. Mills, Hua Li, Yan Zeng, Zohar Barbash, Gabi Tarcic, Hyunseok Kang, Julie E. Bauman, Mi-Ok Kim, Nathan K. VanLandingham, Danielle L. Swaney, Nevan J. Krogan, Daniel E. Johnson, Jennifer R. Grandis

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Figure 2

The Q75E PIK3CA mutation exhibits an activating phenotype in an HNSCC platform.

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The Q75E PIK3CA mutation exhibits an activating phenotype in an HNSCC pl...
(A) Generation of isogenic models in PCI-52-SD1 cells. Immunoblot analysis of the indicated proteins using extracts from cells expressing LUC, WT PIK3CA, canonical E545K mutant, or noncanonical Q75E mutant, following growth in the presence or absence of doxycycline (Dox, 1 μg/mL) for 24 hours. GAPDH, loading control. The fold-changes of the ratio of pAKT/(total AKT) were quantified by densitometry 3 times independently and normalized to no Dox treatment (n = 3). Data are shown as mean ± SD. (B) Serum-dependence assays. Cells were cultured for 72 hours in medium containing Dox with either normal FBS (10%) or low FBS (1%–2%) followed by crystal violet staining. The cell growth rate in low FBS was normalized to the individual control of normal FBS (n = 6). Data are shown as the mean ± SD. The experiment was repeated 3 times with similar results. (C) Colony formation assays. Cells were cultured in the absence or presence of Dox for 3 weeks followed by crystal violet staining. Colonies were quantified using ImageJ and the relative colony counts were normalized to no Dox treatment (n = 3). Data are shown as the mean ± SD. (D) Cell migration assays. Cells were applied to Boyden chambers and incubated for 48 hours in the absence or presence of Dox followed by crystal violet staining. Images were taken from the bottom side of transmembrane chambers. Scale bar: 100 μm. The migrated cells were quantified using ImageJ and the relative cell migration level was normalized to no Dox treatment (n = 3). Data are shown as the mean ± SD. The experiments in C and D were repeated twice with similar results. In all bar graphs, *P < 0.05, **P < 0.01, ***P < 0.001, NS ≥ 0.05 for 1-tailed Student’s pairwise t test.