Defining the boundaries and expanding the utility of head and neck cancer patient derived xenografts.

BACKGROUND: Patient derived xenografts (PDXs) represent an essential tool in oncologic research, and we sought to further expand our repertoire of head and neck squamous cell carcinoma (HNSCC) while determining potential boundaries for this system. METHODS: We consented new patients for PDX development and determined if a 24-h time delay from tumor excision to xenograft implantation affected PDX establishment. We developed a tissue microarray (TMA) from formalin fixed, paraffin embedded PDXs and their subsequent passages and carried out quantitative immunohistochemistry for EGFR, pEGFR, pAkt, pERK and ERCC1. First and last passaged PDXs were compared via a paired t-test to examine for the stability of protein expression across passages. We performed a similar comparison of the mutational profile of the patient tumor and resulting xenografts using a targeted sequencing approach. RESULTS: No patient/tumor characteristics influenced PDX take rate and the 24-h time delay from tumor excision to xenograft implantation did not affect PDX establishment, growth or histology. There was no significant difference in biomarker expression between the first and last passaged PDXs for EGFR, pEGFR, pAkt, and ERCC1. For pERK there was a significant difference (p=0.002), but further analysis demonstrated this only arose in three of 15 PDXs. Targeted sequencing revealed striking stability of passenger and likely driver mutations from patient to xenograft. CONCLUSIONS: The stability of protein expression across PDX passages will hopefully allow greater investigation of predictive biomarkers in order to identify ones for further pre-clinical and clinical investigation.

Cotargeting mTORC and EGFR Signaling as a Therapeutic Strategy in HNSCC.

Head and neck squamous cell carcinomas (HNSCC) are frequently altered along the PI3K/AKT/mTORC signaling axis. Despite excellent preclinical data, the use of compounds targeting this pathway as monotherapy has been underwhelming in initial clinical trials, and identification of predictive biomarkers remains challenging. To investigate mTORC-specific inhibition, we tested catalytic mTORC (AZD8055) and PI3K/mTORC (NVP-BEZ-235) inhibitors ± cetuximab in a panel of HNSCC cell lines and patient-derived xenografts (PDX). Cell lines were assayed for response to all agents and siRNA knockdown of targets by multiple approaches. All cell lines showed similar response to both drug and siRNA inhibition of both PI3K and mTORC pathways, with anti-EGFR combination producing modest additive effect. Five PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and AZD8055. In vivo single-agent mTORC inhibition inhibited growth of one PIK3CA-mutant cancer, but had little effect on any PIK3CAWT or a second PIK3CA-mutant model. In all models, the combination therapy showed greater growth delay than monotherapy. The uniform ability of PI3K and mTORC inhibition to suppress the growth of HNSCC cells highlights the pathway's role in driving proliferation. Although single-agent therapy was largely ineffective in vivo, improved response of combination treatment in an array of PDXs suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy. Overall, these results add to a growing body of evidence, suggesting that approaches that attempt to match biomarkers to the optimal therapy in HNSCC remain complex and challenging. Mol Cancer Ther; 16(7); 1257-68. ©2017 AACR.

Radiosensitization of Adenoid Cystic Carcinoma with MDM2 Inhibition.

Purpose: Adenoid cystic carcinoma (ACC) is a rare cancer arising from the major or minor salivary gland tissues of the head and neck. There are currently no approved systemic agents or known radiosensitizers for ACC. Unlike the more common head and neck squamous cell carcinomas that frequently harbor TP53 mutations, ACCs contain TP53 mutations at a rate of <5%, rendering them an attractive target for MDM2 inhibition.Experimental Design: We report the successful establishment and detailed characterization of a TP53-WT ACC patient-derived xenograft (PDX), which retained the histologic features of the original patient tumor. We evaluated this model for response to the MDM2 inhibitor AMG 232 as monotherapy and in combination with radiotherapy.Results: AMG 232 monotherapy induced modest tumor growth inhibition, and radiation monotherapy induced a transient tumor growth delay in a dose-dependent fashion. Strikingly, combination treatment of AMG 232 with radiotherapy (including low-dose radiotherapy of 2 Gy/fraction) induced dramatic tumor response and high local tumor control rates 3 months following treatment. Posttreatment analysis revealed that although both AMG 232 and radiotherapy alone induced TP53 tumor-suppressive activities, combination therapy amplified this response with potent induction of apoptosis after combination treatment.Conclusions: These data identify that MDM2 inhibition can provide potent radiosensitization in TP53-WT ACC. In light of the absence of effective systemic agents for ACC, the powerful response profile observed here suggests that clinical trial evaluation of this drug/radiotherapy combination may be warranted to improve local control in this challenging malignancy. Clin Cancer Res; 23(20); 6044-53. ©2017 AACR.

Targeting the HER Family with Pan-HER Effectively Overcomes Resistance to Cetuximab.

Cetuximab, an antibody against the EGFR, has shown efficacy in treating head and neck squamous cell carcinoma (HNSCC), metastatic colorectal cancer, and non-small cell lung cancer (NSCLC). Despite the clinical success of cetuximab, many patients do not respond to cetuximab. Furthermore, virtually all patients who do initially respond become refractory, highlighting both intrinsic and acquired resistance to cetuximab as significant clinical problems. To understand mechanistically how cancerous cells acquire resistance, we previously developed models of acquired resistance using the H226 NSCLC and UM-SCC1 HNSCC cell lines. Cetuximab-resistant clones showed a robust upregulation and dependency on the HER family receptors EGFR, HER2, and HER3. Here, we examined pan-HER, a mixture of six antibodies targeting these receptors on cetuximab-resistant clones. In cells exhibiting acquired or intrinsic resistance to cetuximab, pan-HER treatment decreased all three receptors' protein levels and downstream activation of AKT and MAPK. This correlated with decreased cell proliferation in cetuximab-resistant clones. To determine whether pan-HER had a therapeutic benefit in vivo, we established de novo cetuximab-resistant mouse xenografts and treated resistant tumors with pan-HER. This regimen resulted in a superior growth delay of cetuximab-resistant xenografts compared with mice continued on cetuximab. Furthermore, intrinsically cetuximab-resistant HNSCC patient-derived xenograft tumors treated with pan-HER exhibited significant growth delay compared with vehicle/cetuximab controls. These results suggest that targeting multiple HER family receptors simultaneously with pan-HER is a promising treatment strategy for tumors displaying intrinsic or acquired resistance to cetuximab. Mol Cancer Ther; 15(9); 2175-86. ©2016 AACR.