DNA double strand break repair defect and sensitivity to poly ADP-ribose polymerase (PARP) inhibition in human papillomavirus 16-positive head and neck squamous cell carcinoma

Patients with human papillomavirus-positive (HPV+) head and neck squamous cell carcinomas (HNSCCs) have increased response to radio- and chemotherapy and improved overall survival, possibly due to an impaired DNA damage response. Here, we investigated the correlation between HPV status and repair of DNA damage in HNSCC cell lines. We also assessed in vitro and in vivo sensitivity to the PARP inhibitor veliparib (ABT-888) in HNSCC cell lines and an HPV+ patient xenograft. Repair of DNA double strand breaks (DSBs) was significantly delayed in HPV+ compared to HPV- HNSCCs, resulting in persistence of γH2AX foci. Although DNA repair activators 53BP1 and BRCA1 were functional in all HNSCCs, HPV+ cells showed downstream defects in both non-homologous end joining and homologous recombination repair. Specifically, HPV+ cells were deficient in protein recruitment and protein expression of DNA-Pk and BRCA2, key factors for non-homologous end joining and homologous recombination respectively. Importantly, the apparent DNA repair defect in HPV+ HNSCCs was associated with increased sensitivity to the PARP inhibitor veliparib, resulting in decreased cell survival in vitro and a 10-14 day tumor growth delay in vivo. These results support the testing of PARP inhibition in combination with DNA damaging agents as a novel therapeutic strategy for HPV+ HNSCC.

Combining Chk1/2 Inhibition with Cetuximab and Radiation Enhances In Vitro and In Vivo Cytotoxicity in Head and Neck Squamous Cell Carcinoma

EGFR inhibition and radiotherapy are potent inducers of DNA damage. Checkpoint kinases 1 and 2 (Chk1/2) are critical regulators of the DNA-damage response, controlling cell-cycle checkpoints that may permit recovery from therapy-associated genomic stress. We hypothesized that Chk1/2 inhibition (CHKi) with prexasertib may enhance cytotoxicity from EGFR inhibition plus radiotherapy in head and neck squamous cell carcinoma (HNSCC). In this study, we found that the addition of CHKi to the EGFR inhibitor cetuximab with and without radiotherapy significantly decreased cell proliferation and survival fraction in human papillomavirus virus (HPV)-positive and HPV-negative HNSCC cell lines. Reduced proliferation was accompanied by decreased checkpoint activation, induced S-phase accumulation, persistent DNA damage, and increased caspase cleavage and apoptosis. Importantly, a significant tumor growth delay was observed in vivo in both HPV-positive and HPV-negative cell line xenografts receiving triple combination therapy with CHKi, cetuximab, and radiotherapy without a concomitant increase in toxicity as assessed by mouse body weight. Taken together, the combination of CHKi with cetuximab plus irradiation displayed significant antitumor effects in HNSCCs both in vitro and in vivo, suggesting that this combination therapy may increase clinical benefit. A clinical trial to test this treatment for patients with head and neck cancer is currently ongoing (NCT02555644).

MARCKS phosphorylation is modulated by a peptide mimetic of MARCKS effector domain leading to increased radiation sensitivity in lung cancer cell lines

Lung cancer is the leading cause of cancer-associated mortality in the United States. Kinase hyperactivation is a known mechanism of tumorigenesis. The phosphorylation status of the plasma membrane-associated protein myristoylated alanine rich C-kinase substrate (MARCKS) effector domain (ED) was previously established as being important in the sensitivity of lung cancer to radiation. Specifically, when MARCKS ED was in a non-phosphorylated state, lung cancer cells were more susceptible to ionizing radiation and experienced prolonged double-strand DNA breaks. Additional studies demonstrated that the phosphorylation status of MARCKS ED is important for gene expression and in vivo tumor growth. The present study used a peptide mimetic of MARCKS ED as a therapeutic intervention to modulate MARCKS phosphorylation. Culturing A549, H1792 and H1975 lung cancer cell lines with the MARCKS ED peptide led to reduced levels of phosphorylated MARCKS and phosphorylated Akt serine/threonine kinase 1. Further investigation demonstrated that the peptide therapy was able to reduce lung cancer cell proliferation and increase radiation sensitivity. In addition, the MARCKS peptide therapy was able to prolong double-strand DNA breaks following ionizing radiation exposure. The results of the present study demonstrate that a peptide mimetic of MARCKS ED is able to modulate MARCKS phosphorylation, leading to an increase in sensitivity to radiation.

Kinase analysis of penile squamous cell carcinoma on multiple platforms to identify potential therapeutic targets

Penile squamous cell carcinoma (PSCC) is an orphan malignancy with poorly understood biology and suboptimal systemic therapy. Given that kinases may be drivers and readily actionable, we performed comprehensive multiplatform analysis of kinases in PSCC tumor and normal tissue. Fresh frozen tumors were collected from 11 patients with PSCC. After macrodissection to demarcate tumor from normal tissue, the samples underwent multiplatform analysis of kinases. Next Generation Sequencing (NGS) of 517 kinase genes was performed using Agilent Kinome capture and run on the Illumina MiSeq at PE150bp. The NanoString nCounter® platform analyzed the expression of 519 kinase genes. Kinase activity of tissue lysates was measured using PamStation®12 high-content phospho-peptide substrate microarray system. Network mapping was done with GeneGo MetaCore™ and upstream kinase prediction was performed with BioNavigator and the Kinexus database. Ingenuity pathway analysis was performed to integrate elevated kinase activity and gene over-expression with coexisting missense mutations at DNA level. Top pathways upregulated in both the kinase activity and gene expression platforms were PTEN, STAT3, GNRH, IL-8 and B cell receptor signaling. Potentially relevant missense mutations were seen in 176 kinase genes, with the top altered pathways overlapping with gene overexpression being GNRH, NF-kB and STAT3 signaling. ERBB2, ERBB3 and SYK were altered on NGS and also exhibited elevated kinase activity. To summarize, multiplatform comprehensive analysis of kinases discovered potential drivers of PSCC and actionable therapeutic targets. Translational studies are necessary to validate the functional relevance of our data to make advances in this rare malignancy.

Trastuzumab-Resistant HER2+ Breast Cancer Cells Retain Sensitivity to Poly (ADP-Ribose) Polymerase (PARP) Inhibition

HER2-targeted therapies, such as trastuzumab, have increased the survival rates of HER2⁺ breast cancer patients. However, despite these therapies, many tumors eventually develop resistance to these therapies. Our lab previously reported an unexpected sensitivity of HER2⁺ breast cancer cells to poly (ADP-ribose) polymerase inhibitors (PARPi), agents that target homologous recombination (HR)-deficient tumors, independent of a DNA repair deficiency. In this study, we investigated whether HER2⁺ trastuzumab-resistant (TR) breast cancer cells were susceptible to PARPi and the mechanism behind PARPi induced cytotoxicity. We demonstrate that the PARPi ABT-888 (veliparib) decreased cell survival in vitro and tumor growth in vivo of HER2⁺ TR breast cancer cells. PARP-1 siRNA confirmed that cytotoxicity was due, in part, to PARP-1 inhibition. Furthermore, PARP-1 silencing had variable effects on the expression of several NF-κB-regulated genes. In particular, silencing PARP-1 inhibited NF-κB activity and reduced p65 binding at the IL8 promoter, which resulted in a decrease in IL8 mRNA and protein expression. Our results provide insight in the potential mechanism by which PARPi induces cytotoxicity in HER2⁺ breast cancer cells and support the testing of PARPi in patients with HER2⁺ breast cancer resistant to trastuzumab. Mol Cancer Ther; 17(5); 921-30. ©2018 AACR.

Let-7 Status Is Crucial for PARP1 Expression in HER2-Overexpressing Breast Tumors

HER2⁺ breast tumors have been shown to express elevated levels of PARP1 protein. Yet, the mechanism by which PARP1 is upregulated in HER2⁺ breast cancer is unknown. Here, knockdown of HER2 (ERBB2) in HER2⁺ breast cancer cells resulted in a reduction in PARP1 protein. Conversely, ectopic overexpression of HER2 in a non-HER2-overexpressing cell line resulted in increased PARP1 protein levels. Alterations in HER2 expression had no significant effect on PARP1 transcript levels. Instead, HER2 mRNA status was inversely correlated with let-7a miRNA levels in breast cancer cells. Ectopic expression of let-7a miRNA resulted in downregulation of PARP1 protein, whereas expression of the let-7a anti-miRNA increased PARP1 protein. Furthermore, luciferase assays demonstrate that let-7a regulates PARP1 via its 3'UTR. Importantly, let-7a was significantly lower in human HER2⁺ breast tumors compared with HER2^- breast tumors and inversely correlated with PARP1 protein levels. Finally, HER2⁺ breast cancer cells exhibited similar cytotoxicity to ectopic let-7a expression as the PARP inhibitor veliparib (ABT-888). Collectively, these results reveal that increased PARP1 expression in HER2⁺ breast cancers is regulated by the let-7a miRNA, and that let-7a is a potential strategy to suppress PARP1 activity.Implications: This study reports the novel findings that HER2 increases PARP1 protein via suppression of the let-7a miRNA, which regulates the PARP1 3'-UTR. Moreover, HER2 status correlates with high PARP1 and low let-7a in breast cancer clinical specimens. Mol Cancer Res; 15(3); 340-7. ©2016 AACR.

DNA-PkCS expression in oropharyngeal squamous cell carcinoma: Correlations with human papillomavirus status and recurrence after transoral robotic surgery

BACKGROUND

Human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (SCC) has improved clinical outcomes compared to HPV-negative disease. However, the biology underlying differences in prognosis remains unclear.

METHODS

We characterized the expression of DNA-protein kinase catalytic subunit (DNA-Pk_CS ), a key DNA repair protein also associated with tumor progression, in 29 cases of oropharyngeal SCCs and correlated our findings with HPV status and disease recurrence. In addition, we assessed therapeutic response, migration, and invasion in head and neck cancer cell lines upon DNA-Pk_CS knockdown.

RESULTS

DNA-Pk_CS expression was significantly decreased in HPV-positive compared to HPV-negative oropharyngeal SCC samples. Within the HPV-positive subgroup, DNA-Pk_CS expression was inversely related to HPV E6 and E7 expression and trended toward significance as a predictor of recurrence. DNA-Pk_CS knockdown in cell lines resulted in increased sensitivity to cisplatin and radiotherapy and reduced cell migration and invasion.

CONCLUSION

These results suggest DNA-Pk_CS should be further studied as a potential marker of tumor progression in HPV-positive oropharyngeal SCCs. © 2016 Wiley Periodicals, Inc. Head Neck 39: 206-214, 2017.

Abstract A32: Upregulation of the Notch signaling pathway is associated with mortality and in vitro cell invasion in squamous cell carcinoma of the oral cavity

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous disease with low survival rates, which have not significantly improved despite advances in surgery and radiotherapy. Although human papillomavirus is a strong predictor of outcomes in oropharyngeal tumors, other HNSCC subtypes lack reliable prognostic and therapeutic biomarkers. The purpose of this study was to identify molecular targets to improve the management of oral cavity SCC (OSCC). We isolated RNA from 19 OSCCs treated surgically at UAB and evaluated gene expression using the NanoString nCounter system and PanCancer Pathways analysis module. Results were confirmed using data from the oral cavity anatomic subdivision of the Head and Neck Squamous Cell Carcinoma cancer study generated by the TCGA Research Network. Associated in vitro phenotype was assessed in HNSCC cell lines UM-SCC1, UM-SCC6 and FaDu treated with the activating Notch ligand DLL4 and included evaluation of gene expression, proliferation, cell cycle, migration, invasion, and radiosensitivity. We identified a significant association between upregulation of the Notch pathway and mortality in both the UAB and TCGA OSCC sample sets. In vitro activation of Notch signaling altered transcription in a pattern similar to that found in patient samples from the mortality cohorts. HNSCC cells with Notch activation had increased expression of pro-invasive genes FGF1, IL1B, SIX1, and CCNA1. In addition, Notch activated cells displayed increased cell migration and invasion. Proliferation, cell cycle distribution, and radiosensitivity were unchanged in ligand-treated cells. Our results identify a subset of OSCC patients who have increased Notch pathway activity and worsened outcomes. These clinical findings may reflect a more invasive cell phenotype driven by Notch-mediated changes in transcription. Additional studies are needed to fully elucidate the mechanism underlying this association and to investigate the efficacy of therapies targeting Notch signaling in OSCC.

Citation Format: Alice N. Weaver, Tiffiny S. Cooper, Deborah Della Manna, Shi Wei, Eben L. Rosenthal, Eddy S. Yang. Upregulation of the Notch signaling pathway is associated with mortality and in vitro cell invasion in squamous cell carcinoma of the oral cavity. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Targeting the Vulnerabilities of Cancer; May 16-19, 2016; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(1_Suppl):Abstract nr A32.

Abstract A1-63: Characterizing the DNA damage repair defect in HPV-positive oropharyngeal squamous cell carcinoma

Although tobacco-associated head and neck cancers (HNCs) are declining in incidence, overall HNC rates are escalating due to increasing prevalence of human papillomavirus (HPV)-associated tumors, especially oropharyngeal squamous cell carcinomas (OPSCCs). Clinically, patients with HPV-associated OPSCCs have improved overall survival and increased response to therapy, especially agents which act by damaging DNA. Based on these observations, we hypothesized that HPV-positive OPSCCs harbor a defect in DNA repair activity and are sensitive to DNA repair-targeted therapy. We evaluated DNA repair activity by immunofluorescent staining for DNA damage-induced formation of DNA repair protein foci. Baseline expression of DNA repair proteins was determined by NanoString nCounter analysis of transcript levels and immunoblotting for protein levels. Therapeutic sensitivity was assessed in vitro using the colony formation assay and in vivo using both cell line-derived xenografts and a patient-derived xenograft. Consistent with our hypothesis, in vitro disease models demonstrated delayed resolution of radiation-induced DNA double strand breaks (DSBs) as assessed by γH2AX foci staining and neutral comet assay. Investigation of the two main DSB repair mechanisms, non-homologous end joining (NHEJ) and homologous recombination (HR), indicated intact activation of both pathways but strikingly diminished recruitment of downstream repair factors DNA-Pk (NHEJ) and BRCA2 (HR) to sites of damage. In addition, protein expression of both DNA-PK and BRCA2 was decreased in HPV-positive compared to HPV-negative HNC cell lines. We next studied susceptibility of HPV-positive OPSCCs to PARP inhibition, a class of anticancer agents which block DNA repair signaling pathways and have proven effective clinically in DNA repair-deficient cancers. In vitro colony formation assays revealed a negative effect on cell survival in HPV-positive but not HPV-negative HNCs treated with the PARP inhibitor veliparib. Importantly, these results were confirmed in vivo in both cell line-derived xenografts and a patient-derived xenograft. In summary, our findings demonstrate for the first time the presence of a significant DNA DSB repair defect in HPV-positive OPSCCs encompassing both NHEJ and HR repair, and suggest therapies targeting DNA repair pathways may help improve therapeutic ratio in this disease.

Citation Format: Alice N. Weaver, Tiffiny S. Cooper, Hoa Q. Trummell, James A. Bonner, Eben L. Rosenthal, Eddy S. Yang. Characterizing the DNA damage repair defect in HPV-positive oropharyngeal squamous cell carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Translation of the Cancer Genome; Feb 7-9, 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 1):Abstract nr A1-63.