The Genomic Landscape of Merkel Cell Carcinoma and Clinicogenomic Biomarkers of Response to Immune Checkpoint Inhibitor Therapy.

PURPOSE: Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy, which has demonstrated sensitivity to immune checkpoint inhibitor therapy. Here, we perform the largest genomics study in MCC to date to characterize the molecular landscape and evaluate for clinical and molecular correlates to immune checkpoint inhibitor response. EXPERIMENTAL DESIGN: Comprehensive molecular profiling was performed on 317 tumors from patients with MCC, including the evaluation of oncogenic mutations, tumor mutational burden (TMB), mutational signatures, and the Merkel cell polyomavirus (MCPyV). For a subset of 57 patients, a retrospective analysis was conducted to evaluate for clinical and molecular correlates to immune checkpoint inhibitor response and disease survival. RESULTS: Genomic analyses revealed a bimodal distribution in TMB, with 2 molecularly distinct subgroups. Ninety-four percent (n = 110) of TMB-high specimens exhibited an ultraviolet light (UV) mutational signature. MCPyV genomic DNA sequences were not identified in any TMB-high cases (0/117), but were in 63% (110/175) of TMB-low cases. For 36 evaluable patients treated with checkpoint inhibitors, the overall response rate was 44% and response correlated with survival at time of review (100% vs. 20%, P < 0.001). Response rate was 50% in TMB-high/UV-driven and 41% in TMB-low/MCPyV-positive tumors (P = 0.63). Response rate was significantly correlated with line of therapy: 75% in first-line, 39% in second-line, and 18% in third-line or beyond (P = 0.0066). PD-1, but not PD-L1, expression was associated with immunotherapy response (77% vs. 21%, P = 0.00598, for PD-1 positive and negative, respectively). CONCLUSIONS: We provide a comprehensive genomic landscape of MCC and demonstrate clinicogenomic associates of immunotherapy response.

Patient choice for high-volume center radiation impacts head and neck cancer outcome.

BACKGROUND: Studies suggest treatment outcomes may vary between high (HVC)- and low-volume centers (LVC). Radiation therapy (RT) for head and neck cancer (HNC) requires weeks of treatment, the inconvenience of which may influence a patient's choice for treatment location. We hypothesized that receipt of RT for HNC at a HVC would influence outcomes compared to patients evaluated at a HVC, but who chose to receive RT at a LVC. METHODS: From 1998 to 2011, 1930 HNC patients were evaluated at a HVC and then treated with RT at either a HVC or LVC. Time-to-event outcomes and treatment factors were compared. RESULTS: Median follow-up was 34 months. RT was delivered at a HVC for 1368 (71%) patients and at a LVC in 562 (29%). Patients were more likely to choose HVC-RT if they resided in the HVC's county or required definitive RT (all P < 0.001). HVC-RT was associated with a significant improvement in 3-year LRC (84% vs 68%), DFS (68% vs 48%), and OS (72% vs 57%) (all P < 0.001). On multivariate analysis (MVA), HVC-RT independently predicted for improved LRC, DFS, and OS (all P < 0.05). CONCLUSIONS: In patients evaluated at a HVC, the choice of RT location was primarily influenced by their residing distance from the HVC. HVC-RT was associated with improvements in LRC, DFS, and OS in HNC. As treatment planning and delivery are technically demanding in HNC, the choice to undergo treatment at a HVC may result in more optimal delivered dose, RT duration, and outcome.

Updated efficacy of avelumab in patients with previously treated metastatic Merkel cell carcinoma after ≥1 year of follow-up: JAVELIN Merkel 200, a phase 2 clinical trial.

BACKGROUND: Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer associated with poor survival outcomes in patients with distant metastatic disease (mMCC). In an initial analysis from JAVELIN Merkel 200, a phase 2, prospective, open-label, single-arm trial in mMCC, avelumab-a human anti-programmed death-ligand 1 (PD-L1) monoclonal antibody-showed promising efficacy and a safety profile that was generally manageable and tolerable. Here, we report the efficacy of avelumab after ≥1 year of follow-up in patients with distant mMCC that had progressed following prior chemotherapy for metastatic disease. PATIENTS AND METHODS: Patients received avelumab 10 mg/kg by 1-h intravenous infusion every 2 weeks until confirmed disease progression, unacceptable toxicity, or withdrawal. The primary endpoint was best overall response. Secondary endpoints included duration of response (DOR), progression-free survival (PFS), and overall survival (OS). RESULTS: Patients (N = 88) were followed for a minimum of 12 months. The confirmed objective response rate was 33.0% (95% CI, 23.3%-43.8%; complete response: 11.4%). An estimated 74% of responses lasted ≥1 year, and 72.4% of responses were ongoing at data cutoff. Responses were durable, with the median DOR not yet reached (95% CI, 18.0 months-not estimable), and PFS was prolonged; 1-year PFS and OS rates were 30% (95% CI, 21%-41%) and 52% (95% CI, 41%-62%), respectively. Median OS was 12.9 months (95% CI, 7.5-not estimable). Subgroup analyses suggested a higher probability of response in patients receiving fewer prior lines of systemic therapy, with a lower baseline disease burden, and with PD-L1-positive tumors; however, durable responses occurred irrespective of baseline factors, including tumor Merkel cell polyomavirus status. CONCLUSIONS: With longer follow-up, avelumab continues to show durable responses and promising survival outcomes in patients with distant mMCC whose disease had progressed after chemotherapy. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT02155647.

Nursing Management of Advanced Merkel Cell Carcinoma.

Merkel cell carcinoma (MCC) is a rare and lethal skin cancer with few known treatment options. Management of this disease is challenging, and oncology nurses must understand the medical, physical, and psychosocial burden that MCC places on the patient and family caregivers. Patients must navigate a complex medical and insurance network that often fails to support patients with rare cancers. Nurses must advocate for these patients to ensure quality comprehensive cancer care.

Profiling of 149 Salivary Duct Carcinomas, Carcinoma Ex Pleomorphic Adenomas, and Adenocarcinomas, Not Otherwise Specified Reveals Actionable Genomic Alterations.

PURPOSE: We sought to identify genomic alterations (GA) in salivary gland adenocarcinomas, not otherwise specified (NOS), salivary duct carcinomas (SDC), carcinoma ex pleomorphic adenoma (ca ex PA), and salivary carcinoma, NOS. EXPERIMENTAL DESIGN: DNA was extracted from 149 tumors. Comprehensive genomic profiling (CGP) was performed on hybridization-captured adaptor ligation-based libraries of 182 or 315 cancer-related genes plus introns from 14 or 28 genes frequently rearranged for cancer and evaluated for all classes of GAs. RESULTS: A total of 590 GAs were found in 157 unique genes (mean 3.9/tumor). GAs in the PI3K/AKT/mTOR pathway were more common in SDC (53.6%) than other histologies (P = 0.019) Cyclin-dependent kinase GAs varied among all histotypes: adenocarcinoma, NOS (34.6%); SDC (12.2%); ca ex PA (16.7%); carcinoma, NOS (31.2%; P = 0.043). RAS GAs were observed: adenocarcinoma, NOS (17.3%); SDC (26.8%); ca ex PA (4.2%); and carcinoma, NOS (9.4%; P = 0.054). ERBB2 GAs, including amplifications and mutations, were common: adenocarcinoma, NOS (13.5%); SDC (26.8%); ca ex PA (29.2%); carcinoma, NOS (18.8; P = 0.249). Other notable GAs include TP53 in >45% of each histotype; NOTCH1: adenocarcinoma, NOS (7.7%), ca ex PA (8.3%), carcinoma, NOS (21.6%); NF1: adenocarcinoma, NOS (9.6%), SDC (17.1%), carcinoma, NOS (18.8%). RET fusions were identified in one adenocarcinoma, NOS (CCDC6-RET) and two SDCs (NCOA4-RET). Clinical responses were observed in patients treated with anti-HER2 and anti-RET-targeted therapies. CONCLUSIONS: CGP of salivary adenocarcinoma, NOS, SDCs, ca ex PA, and carcinoma, NOS revealed diverse GAs that may lead to novel treatment options. Clin Cancer Res; 22(24); 6061-8. ©2016 AACR.

Institutional prevalence of malignancy of indeterminate thyroid cytology is necessary but insufficient to accurately interpret molecular marker tests.

OBJECTIVE: Several molecular marker tests are available to refine the diagnosis of thyroid nodules. Knowing the true prevalence of malignancy (PoM) within each cytological category is considered necessary to select the most appropriate test and to interpret results accurately. We describe our institutional PoM among cytological categories and report our experience with molecular markers. DESIGN: Single-center retrospective study. METHODS: We calculated the institutional PoM for each category of the Bethesda system (Bethesda) on all thyroid nodules with cytological evaluation from October 2008 to May 2014. We estimated the predictive values for Afirma, miRInform, and ThyroSeq v2, based on published sensitivity and specificity. Finally, we assessed our own experience with miRInform. RESULTS: The PoMs for Bethesda III and IV categories were 21 and 28%, respectively. ThyroSeq v2 achieves the highest theoretical negative and positive predictive values (NPV and PPV) in Bethesda III (98 and 75%) and Bethesda IV categories (96 and 83%). At our institution, miRInform detected a mutation in 16% of 109 indeterminate nodules tested, all in Bethesda IV specimens. Histology was available in 56 (51%) nodules. The observed sensitivity and specificity in Bethesda IV specimens were 63 and 86%, yielding an NPV and a PPV of 75 and 77%, respectively. CONCLUSIONS: For our current Bethesda III and IV PoM, the actual performance of miRInform was worse than expected. Theoretically ThyroSeq v2 should have the best performance, but it could be affected in the same way as miRInform, given the similarities between the tests. Assessing the institutional performance of each test is necessary along with PoM individualization.

Determining optimal follow-up in the management of human papillomavirus-positive oropharyngeal cancer.

BACKGROUND: Determining the optimal follow-up for patients can help maximize the use of health care resources. This is particularly true in a growing epidemic such as human papillomavirus-positive oropharyngeal squamous cell carcinoma (HPV+OPSCC). The objective of the current study was to evaluate time to disease recurrence or late toxicity in this cohort of patients to optimize patient management. METHODS: An institutional database identified 232 patients with biopsy-proven, nonmetastatic HPV+OPSCC who were treated with radiotherapy. A retrospective review was conducted in patients who were followed every 3 months for the first year, every 4 months in year 2, and every 6 months in years 3 to 5. Late toxicity (grade ≥ 3; toxicity was scored based on National Cancer Institute Common Terminology Criteria for Adverse Events [version 4]), locoregional control, distant control, and overall survival were assessed. RESULTS: The median follow-up was 33 months. Based on Radiation Therapy Oncology Group (RTOG) 0129 study risk groupings, patients were either considered to be at low (162 patients; 70%) or intermediate (70 patients; 30%) risk. Concurrent systemic therapy was used in 85% of patients (196 patients). The 3-year locoregional control, distant control, and overall survival rates were 94%, 91%, and 91%, respectively. Late toxicity occurred in 9% of patients (21 patients). Overall, 64% of toxicity and failure events occurred within the first 6 months of follow-up, with a < 2% event incidence noted at each subsequent follow-up. Only 4 patients experienced their first event after 2 years. CONCLUSIONS: HPV+OPSCC has a low risk of disease recurrence and late toxicity after treatment; approximately two-thirds of events occur within the first 6 months of follow-up. These data suggest that it may be reasonable to reduce follow-up in patients with HPV+OPSCC to every 3 months for the first 6 months, every 6 months for the first 2 years, and annually thereafter.

Comparison of every 3 week cisplatin or weekly cetuximab with concurrent radiotherapy for locally advanced head and neck cancer.

BACKGROUND: Cisplatin dosed every 3 weeks (CIS) or weekly cetuximab (CTX) concurrent with radiotherapy are standards of care for locally advanced head and neck squamous cell carcinoma (LAHNC). Retrospective comparisons of CIS and CTX have offered mixed conclusions. We compared outcomes between CIS and CTX in this patient population. METHODS: Between January 2006 and December 2011, we identified 279 patients who underwent definitive radiotherapy and concurrent systemic therapy for LAHNC. The median age difference between the CIS and CTX groups was relatively small (58 vs. 62 years, respectively) and CIS patients had a slightly higher rate of N2 disease than CTX patients (74% vs. 61%, respectively). RESULTS: Median follow-up was 27 months. Systemic therapy consisted of CIS in 241 (86.4%) and CTX in 38 (13.6%). Actuarial locoregional control of the CIS and CTX groups at 2 years were 91% and 90% (p=0.74), respectively. Actuarial 2 year distant metastasis rates between the groups were 8% and 12%, respectively (p=0.55), and actuarial 2 year overall survival between the groups were 87% and 89%, respectively (p=0.47). CONCLUSIONS: We found no difference in locoregional control, distant metastasis rate, or overall survival between patients treated with concurrent CIS or CTX.

Circulating mouse Flk1+/c-Kit+/CD45- cells function as endothelial progenitors cells (EPCs) and stimulate the growth of human tumor xenografts.

BACKGROUND: Endothelial progenitor cells (EPCs) have been demonstrated to have stem-cell like as well as mature endothelial functions. However, controversy remains as to their origins, immunophenotypic markings, and contribution to the tumor vascular network and tumor survival. METHODS: Flow cytometric analysis and sorting was used to isolate Flk-1+/c-Kit+/CD45- cells. Matrigel and methycellulose assays, flow cytometry, and gene array analyses were performed to characterize several murine EPC cell populations. Human tumor xenografts were used to evaluate the impact of EPCs on tumor growth and vascular development. RESULTS: Flk-1+/c-Kit+/CD45- cells were present at low levels in most murine organs with the highest levels in adipose, aorta/vena cava, and lung tissues. Flk-1+/c-Kit+/CD45- cells demonstrated stem cell qualities through colony forming assays and mature endothelial function by expression of CD31, uptake of acLDL, and vascular structure formation in matrigel. High passage EPCs grown in vitro became more differentiated and lost stem-cell markers. EPCs were found to have hemangioblastic properties as demonstrated by the ability to rescue mice given whole body radiation. Systemic injection of EPCs increased the growth of human xenograft tumors and vessel density. CONCLUSIONS: Flk-1+/C-Kit+/CD45- cells function as endothelial progenitor cells. EPCs are resident in most murine tissue types and localize to human tumor xenografts. Furthermore, the EPC population demonstrates stem-cell and mature endothelial functions and promoted the growth of tumors through enhanced vascular network formation. Given the involvement of EPCs in tumor development, this unique host-derived population may be an additional target to consider for anti-neoplastic therapy.

The irradiated tumor microenvironment: role of tumor-associated macrophages in vascular recovery.

Radiotherapy is an important modality used in the treatment of more than 50% of cancer patients in the US. However, despite sophisticated techniques for radiation delivery as well as the combination of radiation with chemotherapy, tumors can recur. Thus, any method of improving the local control of the primary tumor by radiotherapy would produce a major improvement in the curability of cancer patients. One of the challenges in the field is to understand how the tumor vasculature can regrow after radiation in order to support tumor recurrence, as it is unlikely that any of the endothelial cells within the tumor could survive the doses given in a typical radiotherapy regimen. There is now considerable evidence from both preclinical and clinical studies that the tumor vasculature can be restored following radiotherapy from an influx of circulating cells consisting primarily of bone marrow derived monocytes and macrophages. The radiation-induced influx of bone marrow derived cells (BMDCs) into tumors can be prevented through the blockade of various cytokine pathways and such strategies can inhibit tumor recurrence. However, the post-radiation interactions between surviving tumor cells, recruited immune cells, and the remaining stroma remain poorly defined. While prior studies have described the monocyte/macrophage inflammatory response within normal tissues and in the tumor microenvironment, less is known about this response with respect to a tumor after radiation therapy. The goal of this review is to summarize existing research studies to provide an understanding of how the myelomonocytic lineage may influence vascular recovery within the irradiated tumor microenvironment.

The use of epidermal growth factor receptor monoclonal antibodies in squamous cell carcinoma of the head and neck.

Targeting of the EGF receptor (EGFR) has become a standard of care in several tumor types. In squamous cell carcinoma of the head and neck, monoclonal antibodies directed against EGFR have become a regular component of therapy for curative as well as palliative treatment strategies. These agents have anti-tumor efficacy as a single modality and have demonstrated synergistic tumor killing when combined with radiation and/or chemotherapy. While cetuximab has been the primary anti-EGFR monoclonal antibody used in the US, variant anti-EGFR monoclonal antibodies have been used in several clinical studies and shown benefit with improved toxicity profiles. Next generation anti-EGFR monoclonal antibodies may demonstrate multi-target epitope recognition, enhanced immune cell stimulation, or conjugation with radioisotopes in order to improve clinical outcomes. Identification of the specific patient subset that would optimally benefit from anti-EGFR monoclonal antibodies remains an elusive goal.

Periprocedural complications by Child-Pugh class in patients undergoing transcatheter arterial embolization or chemoembolization to treat unresectable hepatocellular carcinoma at a VA medical center.

BACKGROUND: For patients with compensated cirrhosis, transcatheter arterial embolization with and without additive chemotherapy has been shown to improve survival. The aim of this study was to compare periprocedural complications in a population with hepatitis C virus-related hepatocellular carcinoma to evaluate for differences in complications by severity of liver disease. METHODS: Patients with unresectable hepatocellular carcinoma treated by transcatheter arterial embolization with or without additive chemotherapy procedures from 2003 to 2006 were retrospectively reviewed and compared by Child-Pugh (CP) class. A total of 141 embolizations were done in 76 patients. RESULTS: Complication rates were seen in 27% of CP class A and 17% of CP class B patients. There was no significant difference in the grade of complications between the 2 groups or between procedure types. Survival rate was dependent on the degree of liver dysfunction (3-year CP class A, 49%; CP class B, 13%; P = .0048). CONCLUSION: Embolization procedures to treat hepatitis C virus-related hepatocellular carcinoma can be performed safely with low morbidity and mortality rates, even in patients with a compromised hepatic reserve.

Flavopiridol enhances human tumor cell radiosensitivity and prolongs expression of gammaH2AX foci.

Flavopiridol is a cyclin-dependent kinase (CDK) inhibitor, which has recently entered clinical trials. However, when administered as a single agent against solid tumors, the antitumor actions of flavopiridol have been primarily cytostatic. Given its reported effects on cell cycle regulation, transcription, and apoptosis, flavopiridol may also influence cellular radioresponse. Thus, to evaluate the potential for combining this cyclin-dependent kinase inhibitor with radiation as a cancer treatment strategy, we have investigated the effects of flavopiridol on the radiation sensitivity of two human prostate cancer cell lines (DU145 and PC3). The data presented here indicate that exposure to flavopiridol (60-90 nM) after irradiation enhanced the radiosensitivity of both DU145 and PC3 cells. This sensitization occurred in the absence of significant reductions in cell proliferation, retinoblastoma protein phosphorylation, or P-TEFb activity. Moreover, the post-irradiation addition of flavopiridol had no effect on radiation-induced apoptosis or the activation of the G2 cell cycle checkpoint. However, flavopiridol did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, at 24 h after irradiation, the number of cells expressing gammaH2AX foci was significantly greater in the flavopiridol-treated cells. These results indicate that flavopiridol can enhance radiosensitivity of human tumor cells and suggest that this effect may involve an inhibition of DNA repair.

Gleevec-mediated inhibition of Rad51 expression and enhancement of tumor cell radiosensitivity.

Rad51 is an essential component of the homologous DNA repair pathway and has been implicated as a determinant of cellular radiosensitivity. Gleevec is a relatively specific inhibitor of c-Abl, a tyrosine kinase that can play a role in the regulation Rad51. The aim of this study was to determine the effects of Gleevec on Rad51 levels and the radiosensitivity of two human glioma cell lines and a nonimmortalized normal human fibroblast cell line. Exposure of both glioma cell lines to radiation resulted in an increase in Rad51 expression; Gleevec treatment alone reduced Rad51 expression. When glioma cells were pretreated with Gleevec, radiation-induced Rad51 expression and nuclear foci formation were reduced. Accordingly, pretreatment of the glioma cells with Gleevec resulted in an enhancement in their radiosensitivity. These data indicate that Gleevec enhances radiation-induced tumor cell killing and suggest that the mechanism involves the reduction in Rad51 levels. In contrast to the glioma cell lines, radiation or Gleevec treatments had no effect on Rad51 expression or foci formation in the normal fibroblast cells. Consistent with these observations, Gleevec did not modify the radiosensitivity of the normal cell line. These results suggest that Rad51 expression is subject to different regulatory processes in the glioma and normal cell lines and further suggest that Rad51 may be an appropriate target for selectively enhancing the radiosensitivity of brain tumor cells.

Enhanced cell killing induced by the combination of radiation and the heat shock protein 90 inhibitor 17-allylamino-17- demethoxygeldanamycin: a multitarget approach to radiosensitization.

PURPOSE: Current strategies for tumor cell radiosensitization focus on a target-based approach. However, the radioresponse of a tumor cell is influenced by a wide variety of signaling molecules existing in a number of different survival pathways. Therefore, in an attempt to increase the probability and/or degree of radiosensitization, we have begun to investigate a multitarget approach using the heat shock protein 90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG). EXPERIMENTAL DESIGN: The effect of 17AAG on the levels of three proteins (Raf-1, ErbB2, and Akt) previously implicated in the regulation of radiosensitivity was determined in four human tumor cell lines. Tumor cell survival after exposure to corresponding concentrations of 17AAG combined with clinically relevant doses of X-rays was then evaluated using a clonogenic assay. The radiosensitivity of a nonimmortalized, normal fibroblast cell line was also determined after exposure to 17AAG. RESULTS: Exposure to nanomolar concentrations of 17AAG reduced the levels of the three radiosensitivity-associated proteins in a cell type manner. Using corresponding concentrations, 17AAG enhanced the radiosensitivity of each of the tumor cell lines with enhancement factors ranging from 1.3 to 1.7. The enhancement appeared to be related to the number of radioresponse-regulatory proteins affected. In contrast to the tumor cell lines, 17AAG had no effect on the radiosensitivity of a normal, nonimmortalized human fibroblast cell line. CONCLUSIONS: These data suggest that heat shock protein 90 may be an appropriate target for selectively enhancing the radiosensitivity of tumor cells over normal cells. Furthermore, they illustrate the potential of a multitarget approach to radiosensitization.

Radiation-induced activation of nuclear factor-kappaB involves selective degradation of plasma membrane-associated I(kappa)B(alpha).

In contrast to nuclear factor-kappaB (NF-kappaB) activation by tumor necrosis factor-alpha (TNF-alpha), the specific processes involved in the activation of this transcription factor by ionizing radiation (IR) have not been completely defined. According to the classical paradigm, a critical event in NF-kappaB activation is the degradation of I(kappa)B(alpha). Data presented herein show that, in contrast to treatment with TNF-alpha, IR-induced NF-kappaB activation was not accompanied by degradation of I(kappa)B(alpha) in the U251 glioblastoma cell line as determined in whole cell lysates. However, treatment with the proteosome inhibitor MG-132 inhibited NF-kappaB activation induced by IR, suggesting that I(kappa)B(alpha) degradation was a critical event in this process. To reconcile these results, U251 cell lysates were separated into soluble and insoluble fractions and I(kappa)B(alpha) levels evaluated. Although I(kappa)B(alpha) was found in both subcellular fractions, treatment with IR resulted in the degradation of I(kappa)B(alpha) only in the insoluble fraction. Further subcellular fractionation suggested that the IR-sensitive, insoluble pool of I(kappa)B(alpha) was associated with the plasma membrane. These data suggest that the subcellular location of I(kappa)B(alpha) is a critical determinant in IR-induced NF-kappaB activation.

Inhibition of radiation-induced nuclear factor-kappaB activation by an anti-Ras single-chain antibody fragment: lack of involvement in radiosensitization.

We have shown previously that the transduction of a number of human tumor cell lines with an adenovirus (AV1Y28) expressing a single-chain antibody fragment (scFv) directed against Ras proteins results in radiosensitization. Because Ras is involved in the regulation of a number of transcription factors, we have determined the effects of this adenovirus on the activation of nuclear factor-kappaB (NF-kappaB), a radiation-responsive transcription factor associated with cell survival. In U251 human glioma cells, radiation-induced NF-kappaB was significantly attenuated by prior transduction of the anti-Ras scFv adenovirus. This effect appeared to involve an inhibition of IkappaB kinase activity and IkappaBalpha phosphorylation. Inhibitors to the Ras effectors mitogen-activated protein kinase kinase, phosphatidylinositol 3-kinase, and p38, however, did not reduce radiation-induced NF-kappaB. Whereas AV1Y28 inhibited NF-kappaB activation by hydrogen peroxide and ferricyanide, it had no effect of tumor necrosis factor-alpha-induced NF-kappaB activation. These results are consistent with a novel Ras-dependent, oxidant-specific signaling pathway mediating the activation of NF-kappaB. In additional cell lines radiosensitized by AV1Y28, radiation-induced NF-kappaB activation was also inhibited by the anti-Ras scFv, whereas in cell lines not radiosensitized, radiation did not activate NF-kappaB. This correlation suggested that AV1Y28-mediated radiosensitization involved the inhibition of radiation-induced NF-kappaB activation. However, inhibition of NF-kappaB activation via the expression of a dominant-negative form of IkappaBalpha in U251 cells had no effect on radiation-induced cell killing and did not influence AV1Y28-mediated radiosensitization. Therefore, whereas AV1Y28 inhibits radiation-induced NF-kappaB activation, this process does not appear to play a direct role in its radiosensitizing actions.