Head and neck squamous cell carcinomas (HNSCCs) 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 a 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. While 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 approaches that attempt to match biomarkers to the optimal therapy in HNSCC remains complex and challenging.

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, ACC 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 radiation (RT). Results AMG 232 monotherapy induced modest tumor growth inhibition and RT monotherapy induced a transient tumor growth delay in a dose dependent fashion. Strikingly, combination treatment of AMG 232 with RT (including low dose RT of 2 Gy/fraction) induced dramatic tumor response and high local tumor control rates three months following treatment. Post treatment analysis revealed that while both AMG 232 and RT 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/RT combination may be warranted to improve local control in this challenging malignancy.

PurposePatients with cancer receiving tumor-reactive humanized monoclonal antibody (mAb) therapy can develop a human antihuman antibody (HAHA) response against the therapeutic mAb. We evaluated for HAHA in patients with neuroblastoma treated in a phase I study of humanized anti-GD2 mAb (immunoglobulin (Ig)G1 isotype), hu14.18K322A (NCT00743496). The pretreatment sera (collected prior to mAb treatment) from 9 of 38 patients contained antitherapeutic antibodies, even though they had no prior mAb exposure. We sought to characterize these pre-existing antitherapeutic antibodies (PATA).Experimental designThe PATA+ pretreatment samples were characterized via ELISA; clinical associations with PATA status were evaluated.ResultsPretreatment sera from eight of nine PATA+ patients also bound rituximab and demonstrated preferential ELISA reactivity against the Fc portions of hu14.18K322A and rituximab as compared with the Fab portions of these mAbs. These PATA+ sera also recognized dinutuximab (human IgG1 isotype) and mouse IgG2a isotype mAbs, but not a mouse IgG1 isotype or the fully human panitumumab (IgG2 isotype) mAb. Of the 38 treated patients, only 4 patients (all in the PATA+ cohort) demonstrated no disease progression for>2.5 years without receiving further therapy (p=0.002).ConclusionsThis study demonstrates an association between clinical outcome and the presence of PATA against determinant(s) on the Fc component of the therapeutic mAb, suggesting that the PATA may be playing a role in augmenting mAb-based antitumor effects. Further analyses for the presence of PATA in a larger cohort of patients with relapsed neuroblastoma, analyses of their clinical correlates, identification of their immunological targets, and potential antitumor mechanisms are warranted.

e17509 Background: Head and neck squamous cell carcinomas (HNSCCs) are frequently altered along the PI3K/AKT/mTORC signaling axis leading to development of therapeutics targeting this pathway. Despite excellent preclinical data, the use of these compounds as monotherapy has been underwhelming in initial clinical trials and identification of predictive biomarkers remains challenging. The EGFR monoclonal antibody cetuximab remains the only approved targeted agent for HNSCC and has potential use in combination therapy. Methods: Both catalytic mTORC (AZD8055) and PI3K/mTORC(NVP-BEZ-235) inhibitors were tested +/- cetuximab in a panel of HNSCC cell lines and patient derived xenografts (PDX) evaluated for potential biomarkers of PI3K/AKT/mTORC pathway. Cell lines were assayed for response to all three agents by multiple approaches, and confirmed by siRNA knockdown. Five PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and AZD8055. Results: In HNSCC cells no likely sensitizing mutations were identified, whereas putative protein biomarkers were elevated in some lines. All lines showed similar response to both PI3K/mTORC and dual mTORC inhibition with cetuximab combination producing modest additive effect with similar results for siRNA knockdown. In PDX models, in vivo single agent mTORC inhibition inhibited growth of a 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. Conclusions: The uniform ability of PI3K and mTORC inhibition to suppress the growth of HNSCC cells highlights the pathway’s role in driving proliferation. In vivo, despite some PDX models meeting likely selection criteria, the single agent therapy was largely ineffective. Conversely improved response of combination treatment suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy. Overall, these results add to a growing body of evidence suggesting approaches that attempt to match biomarkers to the optimal therapy in HNSCC remains complex and challenging.

<div>Abstract<p><b>Purpose:</b> 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.</p><p><b>Experimental Design:</b> 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.</p><p><b>Results:</b> 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.</p><p><b>Conclusions:</b> 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. <i>Clin Cancer Res; 23(20); 6044–53. ©2017 AACR</i>.</p></div>