Head And Neck Squamous Cell Carcinoma Patient-derived Xenografts Research Articles

Therapeutic implications of transcriptomics in head and neck cancer patient-derived xenografts.

There are currently no clinical strategies utilizing tumor gene expression to inform therapeutic selection for patients with head and neck squamous cell carcinoma (HNSCC). One of the challenges in developing predictive biomarkers is the limited characterization of preclinical HNSCC models. Patient-derived xenografts (PDXs) are increasingly recognized as translationally relevant preclinical avatars for human tumors; however, the overall transcriptomic concordance of HNSCC PDXs with primary human HNSCC is understudied, especially in human papillomavirus-associated (HPV+) disease. Here, we characterized 64 HNSCC PDXs (16 HPV+ and 48 HPV-) at the transcriptomic level using RNA-sequencing. The range of human-specific reads per PDX varied from 64.6%-96.5%, with a comparison of the most differentially expressed genes before and after removal of mouse transcripts revealing no significant benefit to filtering out mouse mRNA reads in this cohort. We demonstrate that four previously established HNSCC molecular subtypes found in The Cancer Genome Atlas (TCGA) are also clearly recapitulated in HNSCC PDXs. Unsupervised hierarchical clustering yielded a striking natural division of HNSCC PDXs by HPV status, with C19orf57 (BRME1), a gene previously correlated with positive response to cisplatin in cervical cancer, among the most significantly differentially expressed genes between HPV+ and HPV- PDXs. In vivo experiments demonstrated a possible relationship between increased C19orf57 expression and superior anti-tumor responses of PDXs to cisplatin, which should be investigated further. These findings highlight the value of PDXs as models for HPV+ and HPV- HNSCC, providing a resource for future discovery of predictive biomarkers to guide treatment selection in HNSCC.

STAT3 Activation as a Predictive Biomarker for Ruxolitinib Response in Head and Neck Cancer.

Increased activity of STAT3 is associated with progression of head and neck squamous cell carcinoma (HNSCC). Upstream activators of STAT3, such as JAKs, represent potential targets for therapy of solid tumors, including HNSCC. In this study, we investigated the anticancer effects of ruxolitinib, a clinical JAK1/2 inhibitor, in HNSCC preclinical models, including patient-derived xenografts (PDX) from patients treated on a window-of-opportunity trial. HNSCC cell lines were treated with ruxolitinib, and the impact on activated STAT3 levels, cell growth, and colony formation was assessed. PDXs were generated from patients with HNSCC who received a brief course of neoadjuvant ruxolitinib on a clinical trial. The impact of ruxolitinib on tumor growth and STAT3 activation was assessed. Ruxolitinib inhibited STAT3 activation, cellular growth, and colony formation of HNSCC cell lines. Ruxolitinib treatment of mice bearing an HNSCC cell line-derived xenograft significantly inhibited tumor growth compared with vehicle-treated controls. The response of HNSCC PDXs derived from patients on the clinical trial mirrored the responses seen in the neoadjuvant setting. Baseline active STAT3 (pSTAT3) and total STAT3 levels were lower, and ruxolitinib inhibited STAT3 activation in a PDX from a patient whose disease was stable on ruxolitinib, compared with a PDX from a patient whose disease progressed on ruxolitinib and where ruxolitinib treatment had minimal impact on STAT3 activation. Ruxolitinib exhibits antitumor effects in HNSCC preclinical models. Baseline pSTAT3 or total STAT3 levels in the tumor may serve as predictive biomarkers to identify patients most likely to respond to ruxolitinib.

Dose predictions for [177Lu]Lu-DOTA-panitumumab F(ab\u2032)2 in NRG mice with HNSCC patient-derived tumour xenografts based on [64Cu]Cu-DOTA-panitumumab F(ab\u2032)2 \u2013 implications for a PET theranostic strategy

BackgroundEpidermal growth factor receptors (EGFR) are overexpressed on many head and neck squamous cell carcinoma (HNSCC). Radioimmunotherapy (RIT) with F(ab')2 of the anti-EGFR monoclonal antibody panitumumab labeled with the β-particle emitter, 177Lu may be a promising treatment for HNSCC. Our aim was to assess the feasibility of a theranostic strategy that combines positron emission tomography (PET) with [64Cu]Cu-DOTA-panitumumab F(ab')2 to image HNSCC and predict the radiation equivalent doses to the tumour and normal organs from RIT with [177Lu]Lu-DOTA-panitumumab F(ab')2.ResultsPanitumumab F(ab')2 were conjugated to DOTA and complexed to 64Cu or 177Lu in high radiochemical purity (95.6 ± 2.1% and 96.7 ± 3.5%, respectively) and exhibited high affinity EGFR binding (Kd = 2.9 ± 0.7 × 10− 9 mol/L). Biodistribution (BOD) studies at 6, 24 or 48 h post-injection (p.i.) of [64Cu]Cu-DOTA-panitumumab F(ab')2 (5.5–14.0 MBq; 50 μg) or [177Lu]Lu-DOTA-panitumumab F(ab')2 (6.5 MBq; 50 μg) in NRG mice with s.c. HNSCC patient-derived xenografts (PDX) overall showed no significant differences in tumour uptake but modest differences in normal organ uptake were noted at certain time points. Tumours were imaged by microPET/CT with [64Cu]Cu-DOTA-panitumumab F(ab')2 or microSPECT/CT with [177Lu]Lu-DOTA-panitumumab F(ab')2 but not with irrelevant [177Lu]Lu-DOTA-trastuzumab F(ab')2. Tumour uptake at 24 h p.i. of [64Cu]Cu-DOTA-panitumumab F(ab')2 [14.9 ± 1.1% injected dose/gram (%ID/g) and [177Lu]Lu-DOTA-panitumumab F(ab')2 (18.0 ± 0.4%ID/g) were significantly higher (P < 0.05) than [177Lu]Lu-DOTA-trastuzumab F(ab')2 (2.6 ± 0.5%ID/g), demonstrating EGFR-mediated tumour uptake. There were no significant differences in the radiation equivalent doses in the tumour and most normal organs estimated for [177Lu]Lu-DOTA-panitumumab F(ab')2 based on the BOD of [64Cu]Cu-DOTA-panitumumab F(ab')2 compared to those estimated directly from the BOD of [177Lu]Lu-DOTA-panitumumab F(ab')2 except for the liver and whole body which were modestly underestimated by [64Cu]Cu-DOTA-panitumumab F(ab')2. Region-of-interest (ROI) analysis of microPET/CT images provided dose estimates for the tumour and liver that were not significantly different for the two radioimmunoconjugates. Human doses from administration of [177Lu]Lu-DOTA-panitumumab F(ab')2 predicted that a 2 cm diameter HNSCC tumour in a patient would receive 1.1–1.5 mSv/MBq and the whole body dose would be 0.15–0.22 mSv/MBq.ConclusionA PET theranostic strategy combining [64Cu]Cu-DOTA-panitumumab F(ab')2 to image HNSCC tumours and predict the equivalent radiation doses in the tumour and normal organs from RIT with [177Lu]Lu-DOTA-panitumumab F(ab')2 is feasible. RIT with [177Lu]Lu-DOTA-panitumumab F(ab')2 may be a promising approach to treatment of HNSCC due to frequent overexpression of EGFR.

Abstract A03: Predictors of HPV-related head and neck cancer progression identified through patient-derived models

Abstract Purpose/Objectives: Therapeutic innovation for human papilloma virus-related (HPV+) head and neck squamous cell carcinomas (HNSCCs) is hindered by both inadequate biomarkers and a paucity of experimental models. To address these limitations, this study aimed to establish the first well-characterized panel of patient-derived xenografts (PDXs) and organoids from HPV+ HNSCCs, which typically grow poorly outside humans. The models were hypothesized to retain molecular hallmarks of HPV+ HNSCC that are lost in cell lines. In addition, genotype-phenotype correlations in the models were hypothesized to offer prognostic utility for patients. Materials/Methods: Whole-exome sequencing was performed on 20 HNSCC PDXs, including nine new HPV+ PDXs. Results were compared against the known genetic profiles of human HPV+ HNSCCs and their derivative cell lines. Genetic traits of the PDXs were subsequently evaluated relative to their growth properties and the outcomes of their patients of origin. Genotype-phenotype associations in the models were then tested for prognostic utility across multiple published patient cohorts. Results: Despite low engraftment rates, HPV+ PDXs retained multiple molecular features of HPV+ HNSCC lost in cell lines, including PIK3CA mutations, TRAF3 deletion, and absence of EGFR amplifications. Selective engraftment notably enriched for NOTCH1 mutants, thus providing new models for this negatively prognostic feature in HPV+ HNSCC. Observation of high tumor mutational burden (TMB) in faster-growing models facilitated detection of a novel association between TMB and local progression in both HPV+ and HPV- patients. Whereas TMB’s prognostic utility was limited to early stage HPV- tumors, outcomes prediction for HPV+ cases was served by features of an HPV+ PDX from an outlier case with lethal outcome. Reduced E7 and p16INK4A levels found in this PDX led to detection of similar profiles among recurrent HPV+ HNSCCs in two patient cohorts. Further analysis of the same cohorts revealed lower E2F target gene expression downstream of reduced E7 levels to be predictive of recurrence and mortality. Conclusions: Our PDXs are the first models systematically shown to retain the distinguishing genetic hallmarks of HPV+ HNSCC lost in cancer cell lines. Beyond bridging the critical gap in experimental models, these materials revealed novel applications for quantifying TMB and viral oncogene effects in biomarker development. Our findings suggest that E2F target transcript levels allow discrimination of HPV+ HNSCC patients at risk of treatment failure. Emerging evidence that low E2F target expression in poor-prognosis cases is part of a wider decrease in the viral imprint upon host gene expression holds promise for development of molecular risk stratifiers with clinical utility. Citation Format: Nicole D. Facompre, Pavithra Rajagopalan, Varun Sahu, Frederico O. Gleber-Netto, Joseph A. Califano, Curtis R. Pickering, Phyllis A. Gimotty, Devraj Basu. Predictors of HPV-related head and neck cancer progression identified through patient-derived models [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A03.

Establishment and characterization of patient-derived xenografts as paraclinical models for head and neck cancer

BackgroundWe investigated whether head and neck squamous cell carcinoma (HNSCC) patient-derived xenografts (PDXs) reaffirm patient responses to anti-cancer therapeutics.MethodsTumors from HNSCC patients were transplanted into immunodeficient mice and propagated via subsequent implantation. We evaluated established PDXs by histology, genomic profiling, and in vivo anti-cancer efficacy testing to confirm them as the authentic in vivo platform.ResultsFrom 62 HNSCCs, 15 (24%) PDXs were established. The primary cancer types were tongue (8), oropharynx (3), hypopharynx (1), ethmoid sinus cancer (1), supraglottic cancer (1), and parotid gland (1); six PDXs (40%) were established from biopsy specimens from advanced HNSCC. PDXs mostly retained donor characteristics and remained stable across passages. PIK3CA (H1047R), HRAS (G12D), and TP53 mutations (H193R, I195T, R248W, R273H, E298X) and EGFR, CCND1, MYC, and PIK3CA amplifications were identified. Using the acquisition method, biopsy showed a significantly higher engraftment rate when compared with that of surgical resection (100% [6/6] vs. 16.1% [9/56], P < 0.001). Specimens obtained from metastatic sites showed a significantly higher engraftment rate than did those from primary sites (100% [9/9] vs. 11.3% [6/53], P < 0.001). Three PDX models from HPV-positive tumors were established, as compared to 12 from HPV-negative (15.8% [3/19] and 27.9% [12/43] respectively, P = 0.311), suggesting that HPV positivity tends to show a low engraftment rate. Drug responses in PDX recapitulated the clinical responses of the matching patients with pan-HER inhibitors and pan-PI3K inhibitor.ConclusionsGenetically and clinically annotated HNSCC PDXs could be useful preclinical tools for evaluating biomarkers, therapeutic targets, and new drug discovery.

Inhibiting Translation Elongation with SVC112 Suppresses Cancer Stem Cells and Inhibits Growth in Head and Neck Squamous Carcinoma.

Cancer stem cells (CSC) drive growth, therapy resistance, and recurrence in head and neck squamous cell carcinoma (HNSCC). Regulation of protein translation is crucial for normal stem cells and CSCs; its inhibition could disrupt stemness properties, but translation inhibitors are limited clinically due to toxicity. SVC112 is a synthetic derivative of bouvardin, a plant-derived translation elongation inhibitor. SVC112 had greater antiproliferative effects on HNSCC cells compared with the FDA-approved translation inhibitor omacetaxine mepesuccinate (HHT). SVC112 preferentially inhibited cancer cells compared with patient-matched cancer-associated fibroblasts, whereas HHT was equally toxic to both. SVC112 reduced sphere formation by cell lines and CSCs. SVC112 alone inhibited the growth of patient-derived xenografts (PDX), and SVC112 combined with radiation resulted in tumor regression in HPV-positive and HPV-negative HNSCC PDXs. Notably, CSC depletion after SVC112 correlated with tumor response. SVC112 preferentially impeded ribosomal processing of mRNAs critical for stress response and decreased CSC-related proteins including Myc and Sox2. SVC112 increased cell-cycle progression delay and slowed DNA repair following radiation, enhancing colony and sphere formation radiation effects. In summary, these data demonstrate that SVC112 suppresses CSC-related proteins, enhances the effects of radiation, and blocks growth of HNSCC PDXs by inhibiting CSCs. SIGNIFICANCE: Inhibiting protein elongation with SVC112 reduces tumor growth in head and neck squamous cell carcinoma and increases the effects of radiation by targeting the cancer stem cell pool.

1139P - Sensitizing HRAS overexpressing head and neck squamous cell carcinoma (HNSCC) to chemotherapy

BackgroundHRAS is mutated or overexpressed in various cancers. Although numerous studies have demonstrated that HRAS mutations (HRASmut) promote chemoresistance in HNSCC, the effect of wild type HRAS overexpression (wtHRASov) on chemotherapy has not yet been studied. We sought: i. to investigate the repair capacity of wtHRASov tumors in cisplatin- induced damage and ii. to explore the cisplatin sensitizing effect of HRAS inhibitor tipifarnib. MethodsMutation/RNA and cisplatin IC50 data were retrieved from the Cancer Genome Atlas (TCGA) and COSMIC Cell Lines Project respectively. Modified Z-score was used to define HRAS overexpression. Patient derived xenografts (PDXs) were generated from treatment naïve HNSCC patients. Mutational and expression profile of tumor grafts was identified by whole exome sequencing, IHC, qRT-PCR and western blot analysis. Cisplatin or cisplatin combined with tipifarnib was used for PDX’s treatment. Therapy response was monitored by sequential tumor volume measurements over time. ResultsOur analysis of available RNA and cisplatin IC50 data from HNSCC cell lines demonstrated that wild type HRAS levels are positively correlated with cisplatin resistance. To identify resistance signatures in wtHRASov tumors, we compared the TCGA HNSCC transcriptomes of HRAS-altered (HRASmut or wtHRASov) and HRAS- unaltered tumors. Approximately 6% of HNSCCs were overexpressing HRAS, and there was only partial overlap with the 6% of HRASmut tumors. Moreover, ERCC1 was found highly upregulated in HRAS altered group and especially among wtHRASov subcluster. To further study the resistance of wtHRASov tumors, we generated a cohort of HNSCC PDXs and acquired their mutational, expression and chemosensitivity profile. PDX tumors harboring a profile similar to wtHRASov TCGA cluster exhibited a strong chemoresistant squamous phenotype associated with high ERCC1 levels. Interestingly, these tumors were resensitized to cisplatin when subjected to cisplatin/tipifarnib combinatorial treatment. ConclusionsERCC1 expression is a well-established biomarker for cisplatin resistance. Our study demonstrates that wtHRASov tumours represent a distinctive entity that strongly express ERCC1 and can be resensitized to cisplatin by tipifarnib. Legal entity responsible for the studyThe authors. FundingKura Oncology. DisclosureT. Rampias: Research grant / Funding (institution): Kura Oncology Company. All other authors have declared no conflicts of interest.

Wnt signaling dynamics in head and neck squamous cell cancer tumor-stroma interactions.

Wnt pathway activation maintains the cancer stem cell (CSC) phenotype and promotes tumor progression, making it an attractive target for anti-cancer therapy. Wnt signaling at the tumor and tumor microenvironment (TME) front have not been investigated in depth in head and neck squamous cell carcinoma (HNSCC). In a cohort of 48 HNSCCs, increased Wnt signaling, including Wnt genes (AXIN2, LGR6, WISP1) and stem cell factors (RET, SOX5, KIT), were associated with a more advanced clinical stage. Key Wnt pathway proteins were most abundant at the cancer epithelial-stromal boundary. To investigate these observations, we generated three pairs of cancer-cancer associated fibroblast (CAF) cell lines derived from the same HNSCC patients. 3D co-culture of cancer spheres and CAFs mimicked these in vivo interactions, and using these we observed increased expression of Wnt genes (eg, WNT3A, WNT7A, WNT16) in both compartments. Of these Wnt ligands, we found Wnt3a, and less consistently Wnt16, activated Wnt signaling in both cancer cells and CAFs. Wnt activation increased CSC characteristics like sphere formation and invasiveness, which was further regulated by the presence of CAFs. Time lapse microscopy also revealed preferential Wnt activation of cancer cells. Wnt inhibitors, OMP-18R5 and OMP-54F28, significantly reduced growth of HNSCC patient-derived xenografts and suppressed Wnt activation at the tumor epithelial-stromal boundary. Taken together, our findings suggest that Wnt signaling is initiated in cancer cells which then activate CAFs, and in turn perpetuate a paracrine signaling loop. This suggests that targeting Wnt signaling in the TME is essential.

MK2 Pathway Mediates Radiation-Induced Tumor Inflammation and Is a Poor Prognostic Factor in Head and Neck Cancer

Epithelial-to-mesenchymal transition (EMT) pathway is a known mechanism for tumor metastasis, invasion, proliferation and treatment resistance. We have identified the MAP kinase-activated protein kinase 2 (MK2) pathway as a regulator of inflammatory cytokine production and EMT pathway activation. However, no link has been established between radiotherapy (RT) and MK2 pathway, tumor inflammation, EMT and tumor repopulation in head and neck squamous cell carcinoma (HNSCC). We hypothesize that RT can activate MK2 signaling which in turn leads to increased tumor inflammation, EMT, tumor repopulation and high MK2 phosphorylation (pMK2) is a poor prognostic factor in HNSCC. A 180 patient oropharyngeal SCC (OSCC) tissue microarray, with annotated patient characteristics and survival outcomes, was stained for pMK2, p16, and HPV (ISH, RNA-seq). H-score was calculated for all samples and correlated to stage, HPV-p16 status and survival outcomes (OS and DSS) by log-rank analysis. For in vitro studies, HNSCC cell lines (SCC47, SCC90, TU167, HN11) were treated in 1 of 4 arms: control, MK2 inhibitor (MK2i), RT, or both. Intensity of pMK2 was assessed by immunoblot. Cytokine and EMT gene expression was evaluated by RT-qPCR. Cytokine production was assessed using a commercial kit. The siRNA experiments were performed to assess specificity of RT signaling through the MK2 pathway. For in vivo studies, HNSCC patient-derived xenografts (PDX) were treated and analyzed as the groups described above and survival studies performed. Patients bearing tumors with high pMK2 vs low pMK2 were associated with worse cancer-specific survival. This was more pronounced in p16-negative compared to p16-positive OSCC patients (p<0.0002). In vitro, RT increased TNFA (8-15x), IL6 (5-7x), VIM (4.5x), SNAI1 (2-5x) gene expression significantly. This effect was significantly reduced with the addition of MK2i prior to RT. MK2 siRNA successfully knocked down MK2 expression in all cell lines tested (to 7-14% of scramble). Similar to the small molecule inhibitor, MK2 siRNA could substantially reduce inflammatory cytokine production. The in vivo animal studies demonstrate that combined modality therapy was superior to monotherapy alone (p = 0.0123). Tumor PDX volumes captured at day 19 demonstrated the following average tumor sizes: control (994mm3), MK2i (440mm3), RT(479mm3), and RT+MK2i (185mm3). We observe that RT-induced inflammation, EMT and tumor regrowth appears to be regulated by MK2 pathway. OSCC patients who have p16-negative tumors with high pMK2 have a worse prognosis compared to patients with p16-positive tumors with low pMK2. We demonstrate for the first time that RT can induce MK2 phosphorylation in HNSCC leading to increased tumor inflammatory cytokine and EMT gene expression. Inhibition of the MK2 pathway may help to decrease RT resistance and improve HNSCC treatment outcomes.

Overcoming Resistance to Cetuximab with Honokiol, A Small-Molecule Polyphenol.

Overexpression and activation of the EGFR have been linked to poor prognosis in several human cancers. Cetuximab is a mAb against EGFR that is used for the treatment in head and neck squamous cell carcinoma (HNSCC) and metastatic colorectal cancer. Unfortunately, most tumors have intrinsic or will acquire resistance to cetuximab during the course of therapy. Honokiol is a natural compound found in the bark and leaves of the Chinese Magnolia tree and is established to have several anticancer properties without appreciable toxicity. In this study, we hypothesized that combining cetuximab and honokiol treatments could overcome acquired resistance to cetuximab. We previously developed a model of acquired resistance to cetuximab in non-small cell lung cancer H226 cell line. Treatment of cetuximab-resistant clones with honokiol and cetuximab resulted in a robust antiproliferative response. Immunoblot analysis revealed the HER family and their signaling pathways were downregulated after combination treatment, most notably the proliferation (MAPK) and survival (AKT) pathways. In addition, we found a decrease in phosphorylation of DRP1 and reactive oxygen species after combination treatment in cetuximab-resistant clones, which may signify a change in mitochondrial function. Furthermore, we utilized cetuximab-resistant HNSCC patient-derived xenografts (PDX) to test the benefit of combinatorial treatment in vivo There was significant growth delay in PDX tumors after combination treatment with a subsequent downregulation of active MAPK, AKT, and DRP1 signaling as seen in vitro Collectively, these data suggest that honokiol is a promising natural compound in overcoming acquired resistance to cetuximab. Mol Cancer Ther; 17(1); 204-14. ©2017 AACR.

Barriers to generating PDX models of HPV-related head and neck cancer.

Delineate factors impacting the creation and use of patient-derived xenografts (PDXs) of human papilloma virus-related (HPV+) head and neck squamous cell carcinomas (HNSCCs). Laboratory-based translational study. Fifty-one surgically resected HNSCCs, including 31 HPV + cancers, were implanted into NOD/SCID/IL-2Rγ-/- (NSG) mice using standardized methodology. Clinical and pathologic factors were tested for association with engraftment. The gross, histologic, and molecular features of established HPV + PDXs were analyzed in comparison to their tumors of origin. Negative HPV status and perineural invasion (PNI) were independent, additive factors associated with increased PDX formation. Epstein-Barr virus-positive (EBV+) human large B-cell lymphomas grew from 32% of HPV + HNSCC cases that failed to engraft. Successfully established HPV + PDXs retained basaloid histology and often developed cystic growth patterns typical of HPV + nodal metastases. They also maintained elevated p16INK4A levels and expression of E6/E7 viral oncogene transcripts. Reduced engraftment by HPV + tumors lacking PNI likely results in selection biases in HNSCC PDX models. Formation of EBV + lymphomas in NSG mice further reduces the generation of HPV + models and must be ruled out before long-term use of PDXs. Nevertheless, the retention of distinctive pathologic traits and viral oncogene expression by HPV + PDXs provides a viable in vivo platform for basic and translational studies as well as a resource for generating advanced in vitro models. NA. Laryngoscope, 127:2777-2783, 2017.

AXL Is a Logical Molecular Target in Head and Neck Squamous Cell Carcinoma.

Head and neck squamous cell carcinoma (HNSCC) represents the eighth most common malignancy worldwide. Standard-of-care treatments for patients with HNSCC include surgery, radiation, and chemotherapy. In addition, the anti-EGFR monoclonal antibody cetuximab is often used in combination with these treatment modalities. Despite clinical success with these therapeutics, HNSCC remains a difficult malignancy to treat. Thus, identification of new molecular targets is critical. In the current study, the receptor tyrosine kinase AXL was investigated as a molecular target in HNSCC using established cell lines, HNSCC patient-derived xenografts (PDX), and human tumors. HNSCC dependency on AXL was evaluated with both anti-AXL siRNAs and the small-molecule AXL inhibitor R428. Furthermore, AXL inhibition was evaluated with standard-of-care treatment regimens used in HNSCC. AXL was found to be highly overexpressed in several models of HNSCC, where AXL was significantly associated with higher pathologic grade, presence of distant metastases, and shorter relapse-free survival in patients with HNSCC. Further investigations indicated that HNSCC cells were reliant on AXL for cellular proliferation, migration, and invasion. In addition, targeting AXL increased HNSCC cell line sensitivity to chemotherapy, cetuximab, and radiation. Moreover, radiation-resistant HNSCC cell line xenografts and PDXs expressed elevated levels of both total and activated AXL, indicating a role for AXL in radiation resistance. This study provides evidence for the role of AXL in HNSCC pathogenesis and supports further preclinical and clinical evaluation of anti-AXL therapeutics for the treatment of patients with HNSCC.