Immune profiles in primary squamous cell carcinoma of the head and neck.

OBJECTIVES: In this study we describe the tumor microenvironment, the signaling pathways and genetic alterations associated with the presence or absence of CD8+ T-cell infiltration in primary squamous cell carcinoma of the head and neck (SCCHN) tumors. MATERIALS AND METHODS: Two SCCHN multi-analyte cohorts were utilized, the Cancer Genome Atlas (TCGA) and the Chicago Head and Neck Genomics (CHGC) cohort. A well-established chemokine signature classified SCCHN tumors into high and low CD8+ T-cell inflamed phenotypes (TCIP-H, TCIP-L respectively). Gene set enrichment and iPANDA analyses were conducted to dissect differences in signaling pathways, somatic mutations and copy number aberrations for TCIP-H versus TCIP-L tumors, stratified by HPV status. RESULTS: TCIP-H SCCHN tumors were enriched in multiple immune checkpoints irrespective of HPV-status. HPV-positive tumors were enriched in markers of T-regulatory cells (Tregs) and HPV-negative tumors in protumorigenic M2 macrophages. TCIP-L SCCHN tumors were enriched for the ß-catenin/WNT and Hedgehog signaling pathways, had frequent mutations in NSD1, amplifications in EGFR and YAP1, as well as CDKN2A deletions. TCIP-H SCCHN tumors were associated with the MAPK/ERK, JAK/STAT and mTOR/AKT signaling pathways, and were enriched in CASP8, EP300, EPHA2, HRAS mutations, CD274, PDCD1LG2, JAK2 amplifications. CONCLUSIONS: Our findings support that combinatorial immune checkpoint blockade and depletion strategies targeting Tregs in HPV-positive and M2 macrophages in HPV-negative tumors may lead to improved antitumor immune responses in patients with TCIP-H SCCHN. We highlight novel pathways and genetic events that may serve as candidate biomarkers and novel targeted therapies to enhance the efficacy of immunotherapy in SCCHN patients.

Bifunctional immune checkpoint-targeted antibody-ligand traps that simultaneously disable TGFß enhance the efficacy of cancer immunotherapy.

A majority of cancers fail to respond to immunotherapy with antibodies targeting immune checkpoints, such as cytotoxic T-lymphocyte antigen-4 (CTLA-4) or programmed death-1 (PD-1)/PD-1 ligand (PD-L1). Cancers frequently express transforming growth factor-ß (TGFß), which drives immune dysfunction in the tumor microenvironment by inducing regulatory T cells (Tregs) and inhibiting CD8+ and TH1 cells. To address this therapeutic challenge, we invent bifunctional antibody-ligand traps (Y-traps) comprising an antibody targeting CTLA-4 or PD-L1 fused to a TGFß receptor II ectodomain sequence that simultaneously disables autocrine/paracrine TGFß in the target cell microenvironment (a-CTLA4-TGFßRIIecd and a-PDL1-TGFßRIIecd). a-CTLA4-TGFßRIIecd is more effective in reducing tumor-infiltrating Tregs and inhibiting tumor progression compared with CTLA-4 antibody (Ipilimumab). Likewise, a-PDL1-TGFßRIIecd exhibits superior antitumor efficacy compared with PD-L1 antibodies (Atezolizumab or Avelumab). Our data demonstrate that Y-traps counteract TGFß-mediated differentiation of Tregs and immune tolerance, thereby providing a potentially more effective immunotherapeutic strategy against cancers that are resistant to current immune checkpoint inhibitors.

In silico analysis of pathways activation landscape in oral squamous cell carcinoma and oral leukoplakia.

A subset of patients with oral squamous cell carcinoma (OSCC), the most common subtype of head and neck squamous cell carcinoma (HNSCC), harbor dysplastic lesions (often visually identified as leukoplakia) prior to cancer diagnosis. Although evidence suggest that leukoplakia represents an initial step in the progression to cancer, signaling networks driving this progression are poorly understood. Here, we applied in silico Pathway Activation Network Decomposition Analysis (iPANDA), a new bioinformatics software suite for qualitative analysis of intracellular signaling pathway activation using transcriptomic data, to assess a network of molecular signaling in OSCC and pre-neoplastic oral lesions. In tumor samples, our analysis detected major conserved mitogenic and survival signaling pathways strongly associated with HNSCC, suggesting that some of the pathways identified by our algorithm, but not yet validated as HNSCC related, may be attractive targets for future research. While pathways activation landscape in the majority of leukoplakias was different from that seen in OSCC, a subset of pre-neoplastic lesions has demonstrated some degree of similarity to the signaling profile seen in tumors, including dysregulation of the cancer-driving pathways related to survival and apoptosis. These results suggest that dysregulation of these signaling networks may be the driving force behind the early stages of OSCC tumorigenesis. While future studies with larger leukoplakia data sets are warranted to further estimate the values of this approach for capturing signaling features that characterize relevant lesions that actually progress to cancers, our platform proposes a promising new approach for detecting cancer-promoting pathways and tailoring the right therapy to prevent tumorigenesis.

SMAD4 Loss Is Associated with Cetuximab Resistance and Induction of MAPK/JNK Activation in Head and Neck Cancer Cells.

Purpose: We previously demonstrated an association between decreased SMAD4 expression and cetuximab resistance in head and neck squamous cell carcinoma (HNSCC). The purpose of this study was to further elucidate the clinical relevance of SMAD4 loss in HNSCC.Experimental Design: SMAD4 expression was assessed by IHC in 130 newly diagnosed and 43 patients with recurrent HNSCC. Correlative statistical analysis with clinicopathologic data was also performed. OncoFinder, a bioinformatics tool, was used to analyze molecular signaling in TCGA tumors with low or high SMAD4 mRNA levels. The role of SMAD4 was investigated by shRNA knockdown and gene reconstitution of HPV-negative HNSCC cell lines in vitro and in vivoResults: Our analysis revealed that SMAD4 loss was associated with an aggressive, HPV-negative, cetuximab-resistant phenotype. We found a signature of prosurvival and antiapoptotic pathways that were commonly dysregulated in SMAD4-low cases derived from TCGA-HNSCC dataset and an independent oral cavity squamous cell carcinoma (OSCC) cohort obtained from GEO. We show that SMAD4 depletion in an HNSCC cell line induces cetuximab resistance and results in worse survival in an orthotopic mouse model in vivo We implicate JNK and MAPK activation as mediators of cetuximab resistance and provide the foundation for the concomitant EGFR and JNK/MAPK inhibition as a potential strategy for overcoming cetuximab resistance in HNSCCs with SMAD4 loss.Conclusions: Our study demonstrates that loss of SMAD4 expression is a signature characterizing the cetuximab-resistant phenotype and suggests that SMAD4 expression may be a determinant of sensitivity/resistance to EGFR/MAPK or EGFR/JNK inhibition in HPV-negative HNSCC tumors. Clin Cancer Res; 23(17); 5162-75. ©2017 AACR.

Targeted sequencing reveals clonal genetic changes in the progression of early lung neoplasms and paired circulating DNA.

Lungs resected for adenocarcinomas often harbour minute discrete foci of cytologically atypical pneumocyte proliferations designated as atypical adenomatous hyperplasia (AAH). Evidence suggests that AAH represents an initial step in the progression to adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA) and fully invasive adenocarcinoma. Despite efforts to identify predictive markers of malignant transformation, alterations driving this progression are poorly understood. Here we perform targeted next-generation sequencing on multifocal AAHs and different zones of histologic progression within AISs and MIAs. Multiregion sequencing demonstrated different genetic drivers within the same tumour and reveal that clonal expansion is an early event of tumorigenesis. We find that KRAS, TP53 and EGFR mutations are indicators of malignant transition. Utilizing droplet digital PCR, we find alterations associated with early neoplasms in paired circulating DNA. This study provides insight into the heterogeneity of clonal events in the progression of early lung neoplasia and demonstrates that these events can be detected even before neoplasms have invaded and acquired malignant potential.

A randomized phase II efficacy and correlative studies of cetuximab with or without sorafenib in recurrent and/or metastatic head and neck squamous cell carcinoma.

INTRODUCTION: A combination of cetuximab and sorafenib in patients with recurrent and/or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) were assessed for potential benefit. MATERIAL AND METHODS: In a randomized phase II study, R/M HNSCC patients were treated with cetuximab 400mg/m(2) IV on day 1 followed by 250mg/m(2) IV weekly (Arm A), or cetuximab at the same dose/schedule plus sorafenib 400mg PO twice-a-day (Arm B). Each cycle was 21days. Tumor p16 and HPV status, and plasma immunomodulatory cytokine levels were assessed. RESULTS: Of 55 patients enrolled (Arm A-27, Arm B-28), 52 patients received assigned treatments and 43 were evaluable for response. Overall response rate was 8% for both arms. Median overall survival (OS) and progression-free survival (PFS) were 9.0 and 3.0months in Arm A, and 5.7 and 3.2months in Arm B, respectively. Forty-four patients had tumors available for p16 staining (35-negative, 9-positive). Three of nine p16-positive tumors were also HPV positive. The p16-negative patients had significantly better PFS compared to the p16-positive patients (3.7 vs. 1.6months; p-value: 0.03), regardless of study arms. Twenty-four plasma samples were tested for 12 cytokine levels and patients with higher TGFß1 levels had inferior PFS compared to lower levels (1.9 vs. 4.7months; adjusted p-value: 0.015), regardless of study arms. CONCLUSIONS: A subset of R/M patients with p16-negative tumors or lower plasma TGFß1 levels had longer PFS given the cetuximab-based therapy. However, both arms showed only modest response and sorafenib given with cetuximab did not demonstrate clinical benefit.

The TGFß-miR200-MIG6 pathway orchestrates the EMT-associated kinase switch that induces resistance to EGFR inhibitors.

Although specific mutations in the tyrosine kinase domain of epidermal growth factor receptor (EGFR) identify tumors that are responsive to EGFR tyrosine kinase inhibitors (TKI), these genetic alterations are present in only a minority of patients. Patients with tumors expressing wild-type EGFR lack reliable predictive markers of their clinical response to EGFR TKIs. Although epithelial-mesenchymal transition (EMT) has been inversely correlated with the response of cancers to EGFR-targeted therapy, the precise molecular mechanisms underlying this association have not been defined and no specific EMT-associated biomarker of clinical benefit has been identified. Here, we show that during transforming growth factor ß (TGFß)-mediated EMT, inhibition of the microRNAs 200 (miR200) family results in upregulated expression of the mitogen-inducible gene 6 (MIG6), a negative regulator of EGFR. The MIG6-mediated reduction of EGFR occurs concomitantly with a TGFß-induced EMT-associated kinase switch of tumor cells to an AKT-activated EGFR-independent state. In a panel of 25 cancer cell lines of different tissue origins, we find that the ratio of the expression levels of MIG6 and miR200c is highly correlated with EMT and resistance to erlotinib. Analyses of primary tumor xenografts of patient-derived lung and pancreatic cancers carrying wild-type EGFR showed that the tumor MIG6(mRNA)/miR200 ratio was inversely correlated with response to erlotinib in vivo. Our data demonstrate that the TGFß-miR200-MIG6 network orchestrates the EMT-associated kinase switch that induces resistance to EGFR inhibitors, and identify a low ratio of MIG6 to miR200 as a promising predictive biomarker of the response of tumors to EGFR TKIs.

The relative expression of Mig6 and EGFR is associated with resistance to EGFR kinase inhibitors.

The sensitivity of only a few tumors to anti-epidermal growth factor receptor EGFR tyrosine kinase inhibitors (TKIs) can be explained by the presence of EGFR tyrosine kinase (TK) domain mutations. In addition, such mutations were rarely found in tumor types other than lung, such as pancreatic and head and neck cancer. In this study we sought to elucidate mechanisms of resistance to EGFR-targeted therapies in tumors that do not harbor TK sensitizing mutations in order to identify markers capable of guiding the decision to incorporate these drugs into chemotherapeutic regimens. Here we show that EGFR activity was markedly decreased during the evolution of resistance to the EGFR tyrosine kinase inhibitor (TKI) erlotinib, with a concomitant increase of mitogen-inducible gene 6 (Mig6), a negative regulator of EGFR through the upregulation of the PI3K-AKT pathway. EGFR activity, which was more accurately predicted by the ratio of Mig6/EGFR, highly correlated with erlotinib sensitivity in panels of cancer cell lines of different tissue origins. Blinded testing and analysis in a prospectively followed cohort of lung cancer patients treated with gefitinib alone demonstrated higher response rates and a marked increased in progression free survival for patients with a low Mig6/EGFR ratio (approximately 100 days, P = 0.01).

Inhibition of TGF-ß enhances the in vivo antitumor efficacy of EGF receptor-targeted therapy.

EGF receptor (EGFR)-targeted monoclonal antibodies (mAb), such as cetuximab, execute their antitumor effect in vivo via blockade of receptor-ligand interactions and engagement of Fcγ receptors on immune effector cells that trigger antibody-dependent cell-mediated cytotoxicity (ADCC). We show that tumors counteract the in vivo antitumor activity of anti-EGFR mAbs by increasing tumor cell-autonomous expression of TGF-ß. We show that TGF-ß suppresses the expression of key molecular effectors of immune cell-mediated cytotoxicity, including Apo2L/TRAIL, CD95L/FasL, granzyme B, and IFN-γ. In addition to exerting an extrinsic inhibition of the cytotoxic function of immune effectors, TGF-ß-mediated activation of AKT provides an intrinsic EGFR-independent survival signal that protects tumor cells from immune cell-mediated apoptosis. Treatment of mice-bearing xenografts of human head and neck squamous cell carcinoma with cetuximab resulted in emergence of resistant tumor cells that expressed relatively higher levels of TGF-ß compared with untreated tumor-bearing mice. Although treatment with cetuximab alone forced the natural selection of TGF-ß-overexpressing tumor cells in nonregressing tumors, combinatorial treatment with cetuximab and a TGF-ß-blocking antibody prevented the emergence of such resistant tumor cells and induced complete tumor regression. Therefore, elevated levels of TGF-ß in the tumor microenvironment enable tumor cells to evade ADCC and resist the antitumor activity of cetuximab in vivo. Our results show that TGF-ß is a key molecular determinant of the de novo and acquired resistance of cancers to EGFR-targeted mAbs, and provide a rationale for combinatorial targeting of TGF-ß to improve anti-EGFR-specific antibody therapy of EGFR-expressing cancers.

Adenylate kinase 3 sensitizes cells to cigarette smoke condensate vapor induced cisplatin resistance.

BACKGROUND: The major established etiologic risk factor for bladder cancer is cigarette smoking and one of the major antineoplastic agents used for the treatment of advanced bladder cancer is cisplatin. A number of reports have suggested that cancer patients who smoke while receiving treatment have lower rates of response and decreased efficacy of cancer therapies. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we investigated the effect of cigarette smoke condensate (CSC) vapor on cisplatin toxicity in urothelial cell lines SV-HUC-1 and SCaBER cells. We showed that chronic exposure to CSC vapor induced cisplatin resistance in both cell lines. In addition, we found that the expression of mitochondrial-resident protein adenylate kinase-3 (AK3) is decreased by CSC vapor. We further observed that chronic CSC vapor-exposed cells displayed decreased cellular sensitivity to cisplatin, decreased mitochondrial membrane potential (ΔΨm) and increased basal cellular ROS levels compared to unexposed cells. Re-expression of AK3 in CSC vapor-exposed cells restored cellular sensitivity to cisplatin. Finally, CSC vapor increased the growth of the tumors and also curtail the response of tumor cells to cisplatin chemotherapy in vivo. CONCLUSIONS/SIGNIFICANCE: The current study provides evidence that chronic CSC vapor exposure affects AK3 expression and renders the cells resistant to cisplatin.

Regulation of p53 family member isoform DeltaNp63alpha by the nuclear factor-kappaB targeting kinase IkappaB kinase beta.

The p53 family gene p63 plays an instrumental role in cellular stress responses including responses to DNA damage. In addition to encoding a full-length transcriptional activator, p63 also encodes several dominant inhibitory isoforms including the isoform DeltaNp63alpha, the function of which is not fully understood. DeltaNp63alpha is degraded in response to DNA damage, thereby enabling an effective cellular response to genotoxic agents. Here, we identify a key molecular mechanism underlying regulation of DeltaNp63alpha expression in response to chemotherapeutic agents or tumor necrosis factor-alpha. We found that DeltaNp63alpha interacts with IkappaB kinase (IKK), a multisubunit protein kinase that consists of two catalytic subunits, IKKalpha and IKKbeta, and a regulatory subunit, IKKgamma. The IKKbeta kinase promotes ubiquitin-mediated proteasomal degradation of DeltaNp63alpha, whereas a kinase-deficient mutant IKKbeta-K44A fails to do so. Cytokine- or chemotherapy-induced stimulation of IKKbeta caused degradation of DeltaNp63alpha and augmented transactivation of p53 family-induced genes involved in the cellular response to DNA damage. Conversely, IKKbeta inhibition attenuated cytokine- or chemotherapy-induced degradation of DeltaNp63alpha. Our findings show that IKKbeta plays an essential role in regulating DeltaNp63alpha in response to extrinsic stimuli. IKK activation represents one mechanism by which levels of DeltaNp63alpha can be reduced, thereby rendering cells susceptible to cell death in the face of cellular stress or DNA damage.

Resistance of cancers to immunologic cytotoxicity and adoptive immunotherapy via X-linked inhibitor of apoptosis protein expression and coexisting defects in mitochondrial death signaling.

The ability of cancers to evade immune surveillance and resist immunotherapy raises a fundamental question of how tumor cells survive in the presence of a competent immune system. Studies to address this question have primarily focused on mechanisms by which tumor cells avoid recognition by or induce tolerance in the immune system. However, little is known about whether cancer cells also acquire an intrinsic ability to resist killing by immune effectors. We find that cancer cells enhance their ability to withstand an attack by cytotoxic immune effector cells via acquisition of specific genetic alterations that interfere with the shared mitochondrial death signaling pathway entrained by granzyme B, IFN-gamma, and Apo2 ligand/tumor necrosis factor-related apoptosis inducing ligand (Apo2L/TRAIL), three key mediators of immunologic cell-mediated cytotoxicity. We show that the coexistence of specific mitochondrial signaling defects (either deletion of Bax, overexpression of Bcl-x(L), or deletion of Smac) with expression of X-linked inhibitor of apoptosis protein decreases the sensitivity of cancer cells to IFN-gamma/Apo2L/TRAIL- or granzyme B-induced apoptosis, lymphocyte-mediated cytotoxicity in vitro, and adoptive cellular immunotherapy in vivo. Conversely, negating X-linked inhibitor of apoptosis protein expression or function in tumor cells with defective mitochondrial signaling enables direct activation of caspase-3/-7 by granzyme B or Apo2L/TRAIL, and restores their susceptibility to immunologic cytotoxicity. These findings identify an important mechanism by which cancers evade elimination by immune effector cells and suggest that cancer immunotherapy might be improved by concurrent strategies to alleviate or circumvent the intrinsic mitochondrial death signaling defects that help cancer cells resist immunologic cytotoxicity.

Elimination of hepatic metastases of colon cancer cells via p53-independent cross-talk between irinotecan and Apo2 ligand/TRAIL.

The majority of colorectal cancers have lost/inactivated the p53 tumor suppressor gene. Using isogenic human colon cancer cells that differ only in their p53 status, we demonstrate that loss of p53 renders tumor cells relatively resistant to the topoisomerase I inhibitor, irinotecan. Whereas irinotecan-induced up-regulation of the proapoptotic proteins PUMA and Noxa requires p53, we find that irinotecan inhibits Janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 and 5 (STAT3/5) signaling in both p53-proficient and p53-deficient tumor cells. We show that irinotecan inhibits JAK2-STAT3/5-dependent expression of survival proteins (Bcl-x(L) and XIAP) and cooperates with Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) to facilitate p53-independent apoptosis of colon cancer cells. Whereas xenografts of p53-deficient colon cancer cells are relatively resistant to irinotecan compared with their p53-proficient counterparts, combined treatment with irinotecan and Apo2L/TRAIL eliminates hepatic metastases of both p53-proficient and p53-deficient cancer cells in vivo and significantly improves the survival of animals relative to treatment with either agent alone. Although the synergy between chemotherapy and Apo2L/TRAIL has been ascribed to p53, our data demonstrate that irinotecan enhances Apo2L/TRAIL-induced apoptosis of tumor cells via a distinct p53-independent mechanism involving inhibition of JAK2-STAT3/5 signaling. These findings identify a novel p53-independent channel of cross-talk between topoisomerase I inhibitors and Apo2L/TRAIL and suggest that the addition of Apo2L/TRAIL can improve the therapeutic index of irinotecan against both p53-proficient and p53-deficient colorectal cancers, including those that have metastasized to the liver.

NF-kappaB in cancer--a friend turned foe.

The nuclear factor of kappaB (NF-kappaB) family of heterodimeric transcription factors plays an instrumental role in immune, inflammatory, and stress responses. NF-kappaB induces the expression of diverse target genes that promote cell cycle progression, regulate apoptosis, and facilitate cell adhesion, angiogenesis, and metastasis. Given the ability of NF-kappaB to influence these cardinal features of neoplastic transformation, it is no surprise that tumor cells of almost every tissue type acquire the ability to constitutively activate NF-kappaB via a host of diverse genetic alterations and viral proteins. The activation of NF-kappaB not only enables malignant transformation and tumor progression, but also provides a mechanism by which tumor cells escape immune surveillance and resist therapy. NF-kappaB may be inhibited by targeting either the apical signaling proteins responsible for its activation in specific types of cancer, the downstream kinases (IkappaB kinase and casein kinase 2) at which NF-kappaB-activating signaling pathways converge, the proteasome-mediated degradation of the inhibitor of kappaB (IkappaB) proteins, or the transcriptional activity of Rel proteins. Since NF-kappaB inhibitors can sensitize tumor cells to apoptosis signaling pathways activated by death receptors, interferons, and immune effector cells, they hold enormous promise for the development of effective combinatorial regimens against a wide spectrum of hematologic and epithelial malignancies.

Potential methods to circumvent blocks in apoptosis in lymphomas.

We review our current understanding of the molecular determinants and mechanisms of lymphocyte apoptosis and identify the key regulators of these death-signaling pathways. In addition, we describe the key molecular aberrations that underlie the resistance of lymphomas to conventional therapy, and highlight the enormous promise of potential therapeutic strategies that could circumvent or overcome these genetic impediments to apoptosis.

Sensitization of tumor cells to Apo2 ligand/TRAIL-induced apoptosis by inhibition of casein kinase II.

Tumor-cell death can be triggered by engagement of specific death receptors with Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL). Apo2L/TRAIL-induced apoptosis involves caspase-8-mediated cleavage of BID. The active truncated form of BID (tBID) triggers the mitochondrial activation of caspase-9 by inducing the activation of BAK or BAX. Although a broad spectrum of human cancer cell lines express death receptors for Apo2L/TRAIL, many remain resistant to TRAIL/Apo2L-induced death. A variety of human cancers exhibit increased activity of casein kinase II (CK2). Here we demonstrate that CK2 is at the nexus of two signaling pathways that protect tumor cells from Apo2L/TRAIL-induced apoptosis. We find that CK2 inhibits Apo2L/TRAIL-induced caspase-8-mediated cleavage of BID, thereby reducing the formation of tBID. In addition, CK2 promotes nuclear factor kappa B (NF-kappa B)-mediated expression of Bcl-x(L), which sequesters tBID and curtails its ability to activate BAX. Tumor cells with constitutive activation of CK2 exhibit a high Bcl-x(L)/tBID ratio and fail to activate caspase-9 or undergo apoptosis in response to Apo2L/TRAIL. Conversely, reduction of the Bcl-x(L)/tBID ratio by inhibition of CK2 renders such cancer cells sensitive to Apo2L/TRAIL-induced activation of caspase-9 and apoptosis. Using isogenic cancer cell lines that differ only in the presence or absence of either the p53 tumor suppressor or the BAX gene, we show that the enhancement of Apo2L/TRAIL-induced tumor-cell death by CK2 inhibitors requires BAX, but not p53. The identification of CK2 as a key survival signal that protects tumor cells from death-receptor-induced apoptosis could aid the design of Apo2L/TRAIL-based combination regimens for treatment of diverse cancers.

Requirement of BAX for TRAIL/Apo2L-induced apoptosis of colorectal cancers: synergism with sulindac-mediated inhibition of Bcl-x(L).

The cornerstone of the systemic treatment of advanced colorectal cancer is 5-fluorouracil.However, 5-fluorouracil-induced apoptosis is dependent on p53, a tumor suppressor gene that is lost or inactivated in at least 85% of human colorectal cancers. Here we show that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/Apo2L triggers caspase-8-mediated truncation of BID, mitochondrial activation of caspase-9, and apoptosis in both p53(+/+) or p53(-/-) isogenic HCT116 colorectal cancer cells. TRAIL/Apo2L also sensitizes both p53(+/+) or p53(-/-) colorectal cancer cells to ionizing radiation. In contrast, we find that TRAIL/Apo2L fails to activate caspase-9 or induce apoptosis in isogenic HCT116 colorectal cancer cells that are deficient in BAX, a proapoptotic gene that is mutated in >50% of colorectal cancers of the microsatellite mutator phenotype. Loss of BAX also renders colorectal cancer cells resistant to TRAIL/Apo2L-mediated radiosensitization. We additionally demonstrate that TRAIL/Apo2L-induced death of p53(+/+)- or p53(-/-)- BAX-proficient but not BAX-deficient colorectal cancer cells is augmented by reducing nuclear factor-kappaB-dependent expression of Bcl-x(L) with either a peptide that disrupts the inhibitor of kappaB kinase complex or the nonsteroidal anti-inflammatory drug, sulindac sulfide. These results indicate that the combination of TRAIL/Apo2L with either irradiation or sulindac may be highly effective against both p53-proficient and p53-deficient colorectal cancers; however, BAX-deficient tumors may evade elimination by TRAIL/Apo2L-based regimens. Our findings may aid the development and genotype-specific application of TRAIL/Apo2L-based combinatorial regimens for the treatment of colorectal cancers.