Pathways In Head And Neck Squamous Cell Carcinoma Research Articles

Abstract 3102A: Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion through targeting laminin-332 in head and neck squamous cell carcinoma.

Abstract BACKGROUND: Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide. In spite of considerable advances in multimodality therapy including surgery, radiotherapy and chemotherapy, the overall five-year survival rate for patients with HNSCC is around 40%. Understanding of the molecular pathway underlying HNSCC could significantly improve diagnosis, therapy, and disease prevention. Recent our microRNA (miRNA) expression signature revealed that the expression of microRNA-218 (miR-218) was reduced in cancer tissues, suggesting a candidate of tumor suppressor in HNSCC. In this study, we investigated the functional significance of miR-218 and its mediated molecular pathways in HNSCC. METHODS: XTT, migration and invasion assays were performed following transient transfection of miR-218 in HNSCC cell lines (FaDu and SAS). Genome-wide gene expression analysis and GeneCodis software were used to analyze the pathways regulated by miR-218 or LAMB3. The expressions of miR-218 and lamini-332 genes were verified using qRT-PCR in HNSCC cells lines and clinical specimens. The luciferase reporter assay was used to identify the actual binding site of miR-218 in target gene. RESULTS: Restoration of miR-218 in cancer cells led to significant inhibition of cell migration and invasion activities in HNSCC cell lines (FaDu and SAS). Genome-wide gene expression analysis of miR-218 transfectants and in silico database analysis showed that focal adhesion pathway was a promising candidate of miR-218 target pathway. The laminins are an important and biologically active part of the basal lamina, the function of that are various such as influencing cell differentiation, migration and adhesion as well as proliferation and cell survival. Interestingly, all components of laminin-332 (LAMA3, LAMB3 and LAMC2) were downregulated and listed on the candidate genes in focal adhesion pathway. Furthermore, we focused on LAMB3 which has a miR-218 target site and gene expression studies and luciferase reporter assays showed that LAMB3 was directly regulated by miR-218. Silencing study of LAMB3 demonstrated significant inhibition of cell migration and invasion in HNSCC cells. In clinical specimens with HNSCC, the expression levels of laminin-332 were significantly upregulated in cancer tissues compared to adjacent non-cancerous tissues. CONCLUSIONS: These data showed that tumor suppressive miR-218 contributes to cancer cell migration and invasion through regulating focal adhesion pathway, especially laminin-332. Tumor suppressive miRNA-mediated novel cancer pathways provide new insights into the potential mechanisms of HNSCC oncogenesis. Citation Format: Takashi Kinoshita, Toyoyuki Hanazawa, Nijiro Nohata, Naoko Kikkawa, Noriko Yamamoto, Hideki Enokida, Hirofumi Yoshino, Takeshi Yamasaki, Hideo Hidaka, Masayuki Nakagawa, Yoshitaka Okamoto, Naohiko Seki. Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion through targeting laminin-332 in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3102A. doi:10.1158/1538-7445.AM2013-3102A

Molecular Pathways in Head and Neck Cancer: EGFR, PI3K, and More

The treatment of head and neck squamous cell carcinoma (HNSCC) is set to undergo rapid changes, as novel treatment targets informed by genomic profiling and novel molecularly targeted therapies continue to make strides. In this review we provide an overview of the latest developments regarding (1) EGFR targeting for HNSCC, (2) PI3K as a novel treatment target, and (3) newly described key genetic events in HNSCC such as NOTCH1 mutations and emerging candidate targets including ALK1 and hedgehog. The first molecular targeting strategy to demonstrate a survival advantage for patients with HNSCC has emerged in the context of EGFR biology. Cetuximab remains the only U.S. Food and Drug Administration (FDA)-approved targeted therapy available for HNSCC, but EGFR as a target has not been individualized in this disease. The PI3K-AKT pathway is downstream of EGFR and is emerging as potentially one of the most important pathways in HNSCC. PIK3CA is the most frequently mutated oncogene for HNSCC (approximately 20%) and may play a role for both HPV-negative and HPV-positive tumors. Multiple therapeutic strategies targeting PI3K are being explored, and multiple agents either alone or in combination are in development. NOTCH1 is a key tumor suppressor gene and its genetic alterations lead to abnormal pathway activation. ALK1 is a novel target involved in angiogenesis, and efficacy in patients with HNSCC was documented in an early inhibitor trial. The hedgehog pathway modulates EGFR dependence and epithelial to mesenchymal transition (EMT), a key invasion and drug-resistance mechanism in HNSCC.

Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion through targeting laminin-332 in head and neck squamous cell carcinoma

Recent our microRNA (miRNA) expression signature revealed that expression of microRNA-218 (miR-218) was reduced in cancer tissues, suggesting a candidate of tumor suppressor in head and neck squamous cell carcinoma (HNSCC). The aim of this study was to investigate the functional significance of miR-218 and its mediated moleculer pathways in HNSCC. Restoration of miR-218 in cancer cells led to significant inhibition of cell migration and invasion activities in HNSCC cell lines (FaDu and SAS). Genome-wide gene expression analysis of miR-218 transfectants and in silico database analysis showed that focal adhesion pathway was a promising candidate of miR-218 target pathways. The laminins are an important and biologically active part of the basal lamina, the function of that are various such as influencing cell differentiation, migration and adhesion as well as proliferation and cell survival. Interestingly, all components of laminin-332 (LAMA3, LAMB3 and LAMC2) are listed on the candidate genes in focal adhesion pathway. Furthermore, we focused on LAMB3 which has a miR-218 target site and gene expression studies and luciferase reporter assays showed that LAMB3 was directly regulated by miR-218. Silencing study of LAMB3 demonstrated significant inhibition of cell migration and invasion. In clinical specimens with HNSCC, the expression levels of laminin-332 were significantly upregulated in cancer tissues compared to adjacent non-cancerous tissues. Our analysis data showed that tumor suppressive miR-218 contributes to cancer cell migration and invasion through regulating focal adhesion pathway, especially laminin-332. Tumor suppressive miRNA-mediated novel cancer pathways provide new insights into the potential mechanisms of HNSCC oncogenesis.

Abstract 3113: Effects of an up-regulated ATR-CHEK1 pathway in head and neck squamous cell carcinomas

Abstract Background: The ATR-CHEK1 pathway is upregulated in a subset of head and neck squamous cell carcinoma (HNSCC) cell lines with loss of the G1 cell cycle checkpoint. We hypothesized that the upregulated ATR-CHEK1 pathway protects HNSCC from mitotic catastrophe (cell death) by enhancing the G2M phase checkpoint and that inhibition of this pathway may sensitize HNSCC to DNA damaging agents. Methods and Results: In HNSCC, we observed gain, amplification or translocation of the ATR gene in 8 of 20 cell lines studied; whereas the CHEK1 gene is partially lost in 12 of 20 cell lines. ATR and CHEK1 FISH in paraffin sections of primary head and neck squamous cell carcinomas confirmed our findings in HNSCC cell lines. We observed that both ATR and CHEK1 are overexpressed by quantitative PCR in five of eight HNSCC cell lines with loss of the G1 cell cycle checkpoint. Inhibition of ATR and CHEK1 with caffeine or specific inhibition with the respective siRNAs results in increased susceptibility of HNSCC to ionizing radiation by clonogenic cell survival assay. siRNA-mediated ATR or CHEK1 knockdown leads to loss of G2M checkpoint accumulation and increased sub-G0 apoptotic population by flow cytometric analysis. The mechanism of cell death after ATR and CHEK1 knockdown is by mitotic catastrophe, as evidenced by increased premature chromatin condensation. Conclusions: The ATR-CHEK1 pathway is up-regulated in a subset of HNSCC with loss of G1 phase cell cycle checkpoint. The up-regulated ATR-CHEK1 pathway protects these HNSCC from mitotic catastrophe by enhancing the G2M phase cell cycle checkpoints and inhibition of ATR and/or CHEK1 increase the sensitivity of the HNSCC to ionizing radiation. We conclude that inhibition of the up-regulated ATR-CHEK1 pathway in HNSCC may potentiate or increase the efficacy of the current therapeutic modalities for HNSCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3113. doi:1538-7445.AM2012-3113

Abstract LB-458: Cold plasma selectively affects HNSCC cell lines by non-apoptotic pathways

Abstract Plasma is an ionized gas that is typically generated in high temperature laboratory conditions. Recent progress in atmospheric plasmas has led to the creation of cold plasmas with ion temperature close to room temperature. We recently examined the therapeutic potential of a cold plasma jet in cancer cell lines and tumors, showing selective tumor eradication capabilities and apoptotic signaling pathway deregulation in melanoma cell lines. We now wanted to examine cold plasma selectivity in Head and Neck Squamous Cell Carcinoma (HNSCC) cell lines and identify signaling pathway deregulation leading to selectivity in HNSCC. We choose four HNSCC cell lines (022, 028, 029, SCC25) and two normal oral cavity epithelium cell lines (OKF6 and NOKsi) to carry out this experiment. Cold plasma treatments were carried out at 8 kV, using a helium flow of 20 liters/min-1, with a distance from plasma source to cells of 3 cm, and treatment durations of 10s, 30s, and 45s. We exposed cells in 96 well plates to cold plasma treatment durations of 10s, 30s, and 45s and a helium flow of 20 liters/min-1 for 10s as a positive treatment control. After treatment we transferred the cell lines to two sets of six well plates per cell line. To examine selective cell viability and growth in HNSCC following cold plasma application we performed the MTT assay to plated cells 48 hours after cold plasma application. Clonogenic or colony formation assays were performed to determine cell reproductive death seven days after treatment with cold plasma. Western blot analysis of PARP cleavage was perfomed 48 hours after treatment to determine if cold plasma application leads to selective cell death via apoptotic pathways in HNSCC. The MTT assay results revealed that cold plasma selectively diminished cell viability in SCC25 and O28, in a dose response manner. O22 and O29 cell lines showed diminished cell viability only after 30s and 45s treatments. The viability of OKF6 cells was not affected by cold plasma, while the viability of NOKsi cell lines was slightly diminished after 30s and 45s treatments. The results of the colony formation assay also revealed a cell specific response to cold plasma application. Exposure to helium flow for 10s did not impede colony formation. O28 and O29 cell lines did not form any colonies after the three cold plasma treatment periods. O22, SCC25 and OKF6 only formed colonies after cold plasma treatment for 10s. NOKsi formed colonies after all three cold plasma treatment periods. Western blot analysis did not show evidence that PARP cleavage is taking place after cold plasma treatment. Our preliminary results indicate that cold plasma application selectively affects some HNSCC cell lines more than other, while having minimal effect on normal oral cavity epithelium cell lines. We plan further to perform examination of cold plasma selectivity in HNSCC, to examine the in vitro effects of using different voltage, helium flow conditions and application distance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-458. doi:1538-7445.AM2012-LB-458

Abstract B40: micro-RNA-128 regulated gene expression in head and neck squamous cell carcinoma

Abstract Purpose: Each year in the United States there are more than 65,000 Americans diagnosed with head and neck cancer and 25,000 die from this disease. Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous disease with complex molecular abnormalities. African Americans have an incidence approximately twice higher than Caucasian men. The overexpression of BMI1 polycomb ring finger oncogene (BMI-1) and epidermal growth factor receptor (EGFR) in HNSCC cases has been shown to be an indicator of poor prognosis and survival in HNSCC. MicroRNAs are a class of posttranslational regulators of gene expression and have been shown to regulate a number of biological processes. In this study, we investigate that mechanism of microRNA-128 (miR-128) involved the regulation of BMI-1 and EGFR gene expressions in HNSCC. Methods: We generated stably expressing exogenous miRNA-128 in HNSCC of the Larynx (JHU-22) using lentivirus infection, performed colony formation assays to determine cell growth and proliferation, QRT-PCR to analyze gene expression, and western blot analysis to evaluate protein expression. Results: The transfected JHU-22miR-128 cell line stably expressed exogenous miR-128 in vitro and in vivo tumor xenografts. Compared with the control vector cells, the cell growth and proliferation decreased significantly in JHU-22miR-128 cells and JHU-22miR-128 tumor xenografts. However, the level of BMI-1proteins was decreased more than EGFR in transfected JHU-22miR-128 cells. Conclusion: miR-128 is able to significantly inhibit BMI-1protein expression, partially affects EGFR protein expression. miR-128 has a putative target site within the mRNA 3′UTR of Bmi-1 and EGFR. Therefore, miR-128 regulates the proliferative pathway in HNSCC. MiR −128 have potential to serve as a therapeutic approach to specifically target EGFR in HNSCC. This work was supported in part by grants P20 CA118770 from National Cancer Institute. Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B40.

Phosphoproteomic Analysis of Signaling Pathways in Head and Neck Squamous Cell Carcinoma Patient Samples

Molecular targeted therapy represents a promising new strategy for treating cancers because many small-molecule inhibitors targeting protein kinases have recently become available. Reverse-phase protein microarrays (RPPAs) are a useful platform for identifying dysregulated signaling pathways in tumors and can provide insight into patient-specific differences. In the present study, RPPAs were used to examine 60 protein end points (predominantly phosphoproteins) in matched tumor and nonmalignant biopsy specimens from 23 patients with head and neck squamous cell carcinoma to characterize the cancer phosphoproteome. RPPA identified 18 of 60 analytes globally elevated in tumors versus healthy tissue and 17 of 60 analytes that were decreased. The most significantly elevated analytes in tumor were checkpoint kinase (Chk) 1 serine 345 (S345), Chk 2 S33/35, eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) S65, protein kinase C (PKC) ζ/ι threonine 410/412 (T410/T412), LKB1 S334, inhibitor of kappaB alpha (IκB-α) S32, eukaryotic translation initiation factor 4E (eIF4E) S209, Smad2 S465/67, insulin receptor substrate 1 (IRS-1) S612, mitogen-activated ERK kinase 1/2 (MEK1/2) S217/221, and total PKC ι. To our knowledge, this is the first report of elevated PKC ι in head and neck squamous cell carcinoma that may have significance because PKC ι is an oncogene in several other tumor types, including lung cancer. The feasibility of using RPPA for developing theranostic tests to guide personalized therapy is discussed in the context of these data.

Microenvironmental genomic alterations reveal signaling networks for head and neck squamous cell carcinoma

BackgroundAdvanced stage head and neck squamous cell carcinoma (HNSCC) is an aggressive cancer with low survival rates. Loss-of-heterozygosity/allelic imbalance (LOH/AI) analysis has been widely used to identify genomic alterations in solid tumors and the tumor microenvironment (stroma). We hypothesize that these identified alterations can point to signaling networks functioning in HNSCC epithelial-tumor and surrounding stroma (tumor microenvironment).ResultsUnder the assumption that genes in proximity to identified LOH/AI regions are correlated with the tumorigenic phenotype, we mined publicly available biological information to identify pathway segments (signaling proteins connected to each other in a network) and identify the role of tumor microenvironment in HNSCC. Across both neoplastic epithelial cells and the surrounding stromal cells, genetic alterations in HNSCC were successfully identified, and 75 markers were observed to have significantly different LOH/AI frequencies in these compartments (p < 0.026). We applied a network identification approach to the genes in proximity to these 75 markers in cancer epithelium and stroma in order to identify biological networks that can describe functional associations amongst these marker-associated genes.ConclusionsWe verified the involvement of T-cell receptor signaling pathways in HNSCC as well as associated oncogenes such as LCK and PLCB1, and tumor suppressors such as STAT5A, PTPN6, PARK2. We identified expression levels of genes within significant LOH/AI regions specific to stroma networks that correlate with better outcome in radiation therapy. By integrating various levels of high-throughput data, we were able to precisely focus on specific proteins and genes that are germane to HNSCC.

Curcumin Inhibits Carcinogen and Nicotine-Induced Mammalian Target of Rapamycin Pathway Activation in Head and Neck Squamous Cell Carcinoma

Curcumin appears to be a safe, bioactive food compound that is a potential chemopreventive for patients at a high risk for head and neck squamous cell carcinoma (HNSCC). Identification and validation of intermediate endpoints is an important step in evaluating chemopreventive agents. AKT/MTOR pathway biomarkers are intrinsic to the carcinogenic process as well as the mechanism of intervention with curcumin. Antiproliferative effects of curcumin were assayed in 9 HNSCC and a keratinocyte cell line. Nicotine, a genotoxic alkaloid involved in tobacco addiction, forms DNA adducts and has been implicated in upper aerodigestive tract cancer promotion. The antiproliferative effects of curcumin were associated with inhibition of the AKT/MTOR pathway in presence and absence of nicotine, which also induced this pathway. Curcumin was highly effective at suppressing growth of SCC40 xenografts and its activity is associated with modulation of MTOR's downstream target pS6. Curcumin at 15 mg significantly increased survival (286 ± 37 vs. 350 days) in the 4NQO carcinogenic model survival study. A major cause of lethal progression of HNSCC is local regional migration and invasion of malignant cells, and curcumin significantly inhibited cancer cell migration and invasion in vitro and in vivo where downregulation of pS6 was associated with a significant decrease in MMP-9. This is the first study to demonstrate that curcumin inhibits the adverse effects of nicotine by blocking nicotine-induced activation of the AKT/MTOR pathway in HNSCC, which retards cell migration. These studies indicate that inhibiting the AKT/MTOR pathway with curcumin may be useful as an oral chemopreventive agent.

Expression of Stat3 and Notch1 is associated with cisplatin resistance in head and neck squamous cell carcinoma

Cisplatin is the most important chemotherapeutic agent involved in treatment of head and neck squamous cell carcinoma (HNSCC), but cisplatin resistance in HNSCC is still a serious problem in clinic. The reasons why patients fail chemotherapy are unclear. We examined 25 HNSCC patients who were all tested for cisplatin sensitivity by CD-DST (collagen gel droplet embedded culture-drug sensitivity) method and expression of Stat3 and Notch1. We found that high expression levels of Stat3 and Notch1 were closely associated with cisplatin resistance respectively (P=0.014, P=0.000). In addition, cisplatin resistance of HNSCC was decreased after inhibition of Stat3 or Notch signaling in vitro. Our results provide first evidence that both high Stat3 and Notch1 expression are associated with cisplatin resistance in HNSCC patients, supporting the hypothesis that co-activation of Stat3 and Notch1 by their crosstalk induces the reprogrammed survival pathways in HNSCC responding to chemotherapy.

Analysis of 724 cases of primary head and neck squamous cell carcinoma (HNSCC) with a focus on young patients and p53 immunolocalization

This study evaluated 724 primary head and neck squamous cell carcinoma (HNSCC) in young and old patients, with regard to clinical profile and immunohistochemical expression of p53 protein. Associations among age, epidemiological and clinicopathological parameters, and survival analysis were evaluated. HNSCC in young people occurred in 14.5% (median age 40.7years; male-to-female ratio 5.9:1). A statistical association was demonstrated between age and family history of cancer, and between age and anatomical site. Among older patients, a higher presence of disease was noted in posterior sites. Expression of p53 was found in 71.7% of the samples and a higher expression was noted in lesions of young patients. Survival analysis showed that the age parameter is not a reliable prognostic factor for HNSCC. Among young patients, cervical metastasis was associated with worse survival. The presence of a family history of cancer in young patients could indicate genetic susceptibility and molecular disturbances in the p53 pathway in HNSCC of young and older patients seem to be distinct.

Hypoxia-Induced Energy Stress Inhibits the mTOR Pathway by Activating an AMPK/REDD1 Signaling Axis in Head and Neck Squamous Cell Carcinoma

The mammalian target of rapamycin (mTOR) signaling network is frequently hyperactivated in patients with head and neck squamous cell carcinoma (HNSCC). Recent studies suggest that hypoxia, a common microenvironmental stress found in tumors, blocks this mitogenic pathway. Here, we demonstrate that in HNSCC cell lines, the expression of the phosphorylated forms of the mTOR downstream targets S6 kinase and S6 (pS6) decreased after hypoxia. These events were associated with a marked up-regulation of the regulated in development and DNA damage 1 (REDD1), a recently characterized hypoxia-induced protein that negatively controls mTOR activity. Conversely, pS6 levels were retained under hypoxia in REDD1 knock-down cells and in HNSCC cells lacking endogenous REDD1 expression. Furthermore, we observed that prolonged hypoxia induced an energy-depleting response as evidenced by decreased cellular ATP levels and AMP-activated protein kinase (AMPK) activation. Interestingly, AMPK inhibition before prolonged hypoxia prevented REDD1 expression, thereby sustaining mTOR activity. These results suggest a novel mechanism by which AMPK activation after hypoxia-induced energy stress may be crucial in regulating REDD1 expression to control the mTOR pathway in HNSCC. Furthermore, we found that, in some HNSCC cells, the reduced mTOR activity in response to hypoxia through AMPK/REDD1 was deregulated, which hence might contribute to the persistent activation of the mTOR pathway in this cancer type.

Gene Expression Profiles as Markers of Aggressive Disease—EGFR as a Factor

We previously reported that 43 (58%) of 75 head and neck squamous cell carcinoma (HNSCC) tumors harbor increased epidermal growth factor receptor (EGFR) gene copy numbers as determined by fluorescent in situ hybridization. In this study, an increased EGFR copy number was associated with decreased progression-free survival and overall survival of HNSCC patients. However, activated EGFR protein levels are difficult to quantify by immunohistochemistry and are subject to dynamic regulation, specifically receptor downregulation on ligand binding. Therefore, we generated an activated EGFR gene expression signature in an in vitro HaCaT keratinocyte model system to further study genes involved in the EGFR signaling pathway in HNSCC. The results from this model system have suggested that the activated EGFR signature might reflect the activated state of the EGFR pathway in human HNSCC tumors and that it is associated with the increased EGFR gene copy number by fluorescent in situ hybridization. Furthermore, the activated EGFR signature has provided additional leads, because they are related to co-regulated molecular pathways and associated gene products on activation of EGFR. These could be exploited to refine and optimize combination therapies to be used in conjunction with available EGFR inhibitors in individual HNSCC patients.

Antitumor effects of combined bortezomib and tipifarnib in head and neck squamous cell carcinoma (HNSCC) cells

5581 Background: The dysregulation of the NF-κB and Ras/PI3K/AKT pathways in HNSCC supports our hypothesis that combined treatment with the proteasome inhibitor (PI) bortezomib (B) and the farnesyl transferase inhibitor (FTI) tipifarnib (T) leads to synergistic growth inhibition of HNSCC cells. Methods: Growth inhibitory effects of single agents (B 2.5–100 nM; T 0.625–5μM), combination (B+T) (B 12.5–17.5 nM; T 0.625–5 μM) or sequential treatment (B→T after 2h or T→B) were examined in three HNSCC lines (Tu212, 686LN and Sqcc/Y1) using a sulforrhodamine B assay after 72 h of drug exposure. Combination effect in cells treated concomitantly or sequentially was assessed using the combination index (C.I.: &lt; 1.0, synergy; &gt;1.0, antagonism; ≈1.0, additivity). Apoptosis was measured by flow cytometry. Relevant protein markers were evaluated by Western blot. Cell cycle analysis after flow cytometry used FlowJo software. Statistical analysis was done using a two-sided t-test. Results: Growth inhibition by B alone is very effective in all three lines (IC50 = 9–22nM). T used alone is active only in μM range (IC50 = 0.625–5 μM). The inhibitory effects of B and T were sequence dependent. Simultaneous treatment with 12.5 nM B and 5μM T showed synergistic growth inhibition in all 3 lines [C.I., 0.281–0.54]. B→T showed synergistic effects in all three cell lines [C.I., 0.36–0.76]. However, T→B was less synergistic in two of the three lines [Sqcc/Y1 C.I. = 0.404; Tu212 C.I. = 0.748]. Apoptosis was also sequence dependent with B+T or B→T treatment showing significantly more apoptosis than T→B (p = 0.03). Apoptosis induced by T→B was not different from treatment with single agent B (p = 0.22). Sqcc/Y1 cells treated with B and T showed accumulation in G2M phase and an increased percentage of cells in sub-G1. The observed synergistic inhibitory effect of B+T was associated with downregulation of p-AKT. Conclusions: We conclude that treatment with B+T and B→T synergistically enhances HNSCC growth inhibition and results in both significantly increased apoptosis and G2M arrest. These studies strongly support the clinical development of the sequential combination of a PI and a FTI. (Supported by Millenium Pharm. and the Georgia Cancer Coalition). [Table: see text]