1142 - Focal Adhesion Kinase Targeting Enhances Anti-Tumor Immunity Following Conventionally Fractionated Radiation

Purpose/Objective(s): Focal adhesion kinase (FAK) is a driver of clinical radioresistance in p53 mutant, but not wild type, head and neck squamous cell carcinoma (HNSCC). This study examines whether FAK inhibition leads to laudatory effects on anti-tumor immunity when combined with conventionally fractionated radiation (IR).

Materials/Methods: MOC2 murine HNSCC cells (p53 mut, highly radio- and immune checkpoint inhibitor resistant) were used to generate flank tumors in immunocompetent (IC, C57BL/6) and immunodeficient (ID, Nu/Nu) mice (n=4-8) which were treated with FAK inhibitor (FAKi, defactinib, 25 mg/kg/d, i.p.) and conventionally fractionated radiation (IR). Tumor volume (day 18 post treatment shown) and tumor growth delay to 600mm³ (TDG₆₀₀) were evaluated. Tumor infiltrating lymphocytes (TILs) were measured via IHC in pre-clinical models and estimated using TIMER 2.0 in TCGA RNA Seq data. Unpaired t-test or ANOVA with post-hoc analysis was used where appropriate. A p/q <0.05 cutoff was used for statistical significance.

Results: MOC2 tumors generated in either ID or IC mice were treated with IR (2 Gy x 10 fx), FAKi, or both combined (FAKi 3 hr before each fraction). FAKi alone had no effect on tumor volume or TDG₆₀₀ in either model. IR alone led to a modest tumor volume reduction vs. control in the ID (p=0.09) and IC (p=2e^-6) models with no effect on TDG_600. FAKi + IR led to significant reductions in tumor volume vs. control in both ID (mean -999.3 mm³ ± 385.207, p=2.2e-7) and IC (mean -1462.1 mm³± 100.1, p=1e-15) models. Comparisons of TDG₆₀₀ between ID and IC models showed no significant differences between control, IR, or FAKi alone groups, however FAKi + IR TDG₆₀₀ was more than doubled in the IC model (ID: 10.9 d ± 0.5 vs. IC: 21.9 d ± 1.15, p=3.7e-10). Tumor volume was also significantly less in the FAKi + IR tumors from the IC group when evaluated as either raw values (mean -1271.9 mm3 ± 77.3 vs. ID, p=1e-15) or % change from baseline (mean -63.6% vs. ID, p=1e-15). We next examined the association between tumor immune microenvironment (TME) and FAK in HNSCC. PTK2 (gene encoding FAK) was significantly and negatively associated with CD8+ infiltrate in multiple platforms (ex. CD8+ via Cibersort Pearson r= -0.24, p=9e-8). Moreover, following treatment with IR + FAKi (~8 d post completion of IR), CD8+ TILs were significantly increased in MOC2 tumors compared to control (p=1.9e-8), FAKi alone (p=3.7e-9), or IR alone (3.2e-4).

Conclusion: The addition of FAKi to conventionally fractionated IR improves radiosensitivity and significantly enhances T cell infiltration into the TME in a highly treatment resistant mouse model of HNSCC. These findings suggest a potential new strategy for treatment of radioresistant p53 mutant tumors.