Antitumor activity of the dual PI3K/MTOR inhibitor, PF-04691502, in combination with radiation in head and neck cancer.

BACKGROUND AND PURPOSE

Head and neck squamous cell carcinoma (HNSCC) remains a clinical challenge where new treatments are required to supplement the current-standard-of care of concurrent chemoradiation. The PI3K/AKT/MTOR pathway has been identified from several next generation DNA sequencing studies to be commonly altered and activated in HNSCC.

MATERIAL AND METHODS

In this study we investigated the activity of PF-04691502, an orally active ATP-competitive, dual inhibitor of PI3K and mTOR, in combination with a clinically relevant fractionated radiation treatment in two contrasting, well characterized, low passage HNSCC models.

RESULTS

We found that PF-04691502 combined synergistically with radiation in the UT-SCC-14 model derived from a primary cancer but was ineffective in the UT-SCC-15 model which was derived from a nodal recurrence. Further examination of the status of key signaling pathways combined with next generation DNA sequencing of a panel of 160 cancer-associated genes revealed crucial differences between the two models that could account for the differential effect. The UT-SCC-15 cell line was characterized by a higher mutational burden, an excess of variants in the PI3K/AKT/MTOR pathway, increased constitutive activity of PI3K, AKT1 and 2 and MTOR and an inability to inhibit key phosphorylation events in response to the treatments.

CONCLUSION

This study clearly highlights the promise of agents such as PF-04691502 in selected HNSCCs but also emphasizes the need for molecular characterization and alternative treatment strategies in non-responsive HNSCCs.