COORDINATION OF MANAGEMENT OF THE ACUTE RADIATION SYNDROME.

The acute radiation syndrome (ARS) constitutes the most challenging, immediate medical consequence of exposure to high doses of ionizing radiation in an emergency situation. This report highlights some of the currently available medical guidelines and recommendations on the clinical management of ARS, comments recent trends regarding the approval of targeted pharmaceuticals for ARS, and suggests further initiatives for international collaboration aiming at continuously updating the medical knowledge base of this syndrome.

Mitochondrial dysfunction is an essential step for killing of non-small cell lung carcinomas resistant to conventional treatment.

This corrects the article DOI: 10.1038/sj.onc.1205018.

Systems biology approaches to develop innovative strategies for lung cancer therapy.

Lung cancer (LC) is a number one killer of cancer-related death among men and women worldwide. Major advances have been made in the diagnosis, staging and use of surgery for LC, but systemic chemotherapy and radiotherapy alone or in combination with some targeted agents remains the core treatment of advanced LC. Unfortunately, in spite of improved diagnosis, surgical methods and new treatments, mortality is still extremely high among LC patients. To understand the precise functioning of signaling pathways associated with resistance to current treatments in LC, as well as to identify novel treatment regimens, a holistic approach to analyze signaling networks should be applied. Here, we describe systems biology-based approaches to generate biomarkers and novel therapeutic targets in LC, as well as how this may contribute to personalized treatment for this malignancy.

Harnessing the lysosome-dependent antitumor activity of phenothiazines in human small cell lung cancer.

Phenothiazines are a family of heterocyclic compounds whose clinical utility includes treatment of psychiatric disorders as well as chemotherapy-induced emesis. Various studies have demonstrated that these compounds possess cytotoxic activities in tumor cell lines of different origin. However, there is considerable confusion regarding the molecular basis of phenothiazine-induced cell death. Lung cancer (LC) remains one of the most prevalent and deadly malignancies worldwide despite considerable efforts in the development of treatment strategies, especially new targeted therapies. In this work, we evaluated the potential utility of phenothiazines in human LC. We show that phenothiazines as single treatment decreased cell viability and induced cell death preferentially in small cell lung carcinoma (SCLC) over non small cell lung carcinoma (NSCLC) cell lines. Sensitivity to phenothiazines was not correlated with induction of apoptosis but due to phenothiazine-induced lysosomal dysfunction. Interestingly, the higher susceptibility of SCLC cells to phenothiazine-induced cell death correlated with an intrinsically lower buffer capacity in response to disruption of lysosomal homeostasis. Importantly, this effect in SCLC occurred despite mutation in p53 and was not influenced by intrinsic sensitivity/resistance toward conventional chemotherapeutic agents. Our data thus uncovered a novel context-dependent activity of phenothiazines in SCLC and suggest that phenothiazines could be considered as a treatment regimen of this disease, however, extended cell line analyses as well as in vivo studies are needed to make such conclusion.

Resistance to DNA-damaging treatment in non-small cell lung cancer tumor-initiating cells involves reduced DNA-PK/ATM activation and diminished cell cycle arrest.

Increasing evidence suggests that tumor-initiating cells (TICs), also called cancer stem cells, are partly responsible for resistance to DNA-damaging treatment. Here we addressed if such a phenotype may contribute to radio- and cisplatin resistance in non-small cell lung cancer (NSCLC). We showed that four out of eight NSCLC cell lines (H125, A549, H1299 and H23) possess sphere-forming capacity when cultured in stem cell media and three of these display elevated levels of CD133. Indeed, sphere-forming NSCLC cells, hereafter called TICs, showed a reduced apoptotic response and increased survival after irradiation (IR), as compared with the corresponding bulk cell population. Decreased cytotoxicity and apoptotic signaling manifested by diminished poly (ADP-ribose) polymerase (PARP) cleavage and caspase 3 activity was also evident in TICs after cisplatin treatment. Neither radiation nor cisplatin resistance was due to quiescence as H125 TICs proliferated at a rate comparable to bulk cells. However, TICs displayed less pronounced G2 cell cycle arrest and S/G2-phase block after IR and cisplatin, respectively. Additionally, we confirmed a cisplatin-refractory phenotype of H125 TICs in vivo in a mouse xenograft model. We further examined TICs for altered expression or activation of DNA damage repair proteins as a way to explain their increased radio- and/or chemotherapy resistance. Indeed, we found that TICs exhibited increased basal γH2AX (H2A histone family, member X) expression and diminished DNA damage-induced phosphorylation of DNA-dependent protein kinase (DNA-PK), ataxia telangiectasia-mutated (ATM), Krüppel-associated protein 1 (KAP1) and monoubiquitination of Fanconi anemia, complementation group D2 (FANCD2). As a proof of principle, ATM inhibition in bulk cells increased their cisplatin resistance, as demonstrated by reduced PARP cleavage. In conclusion, we show that reduced apoptotic response, altered DNA repair signaling and cell cycle perturbations in NSCLC TICs are possible factors contributing to their therapy resistance, which may be exploited for DNA damage-sensitizing purposes.

Inhibition of Ephrin B3-mediated survival signaling contributes to increased cell death response of non-small cell lung carcinoma cells after combined treatment with ionizing radiation and PKC 412.

Radiation therapy is frequently used to treat non-small cell lung cancers (NSCLCs). We have previously shown that a combination of ionizing radiation (IR) and the staurosporine analog PKC 412, but not Ro 31-8220, increases cell death in NSCLC cells. To identify genes involved in the enhancement of cell death, a total gene profiling in response to co-administration of (i) PKC 412 with IR, or (ii) Ro 31-8220 with IR was implemented. These combined treatments caused upregulation of 140 and 179 genes and downregulation of 253 and 425 genes, respectively. Certain genes were selected and verified by real-time quantitative PCR and, of these genes, robust suppression of Ephrin B3 expression was suggested as a possible cell death-inducing mechanism of combined treatment with IR and PKC 412. Indeed, silencing of Ephrin B3 using siRNA in NSCLC cells resulted in a major alteration of their morphology with an elongated phenotype, decreased proliferation and increased cell death signaling. Moreover, silencing of Ephrin B3 in combination with IR caused a decrease in IR-mediated G(2)-arrest, induced cellular senescence, inhibited MAPK ERK and p38 phosphorylation, and caused an upregulation of p27(kip1) expression. Finally, silencing of Ephrin B3 in combination with IR sensitized U-1810 cells to IR-induced apoptosis. In conclusion, we identify and describe Ephrin B3 as a putative signaling molecule involved in the response of NSCLC cells to combined treatment with PKC 412 and ionizing radiation.

miRNA-214 modulates radiotherapy response of non-small cell lung cancer cells through regulation of p38MAPK, apoptosis and senescence.

BACKGROUND: Radio- and chemotherapy (RT/CT) resistance hampers success in combating small and non-small cell lung cancers (SCLC/NSCLC). The underlying molecular mechanisms of RT/CT resistance of LCs are multifactorial and have been understood in part hitherto. miRNAs, key regulators of mRNAs, are well-recognised oncomirs; however, their role in regulating RT response remains poorly understood. METHODS: Six human NSCLC and five SCLC cell lines with different SF2 values were investigated. Using microarray we examined whether expression of miRNAs is linked to the RT resistance of NSCLCs or SCLCs. Obtained data were validated by quantitative real-time PCR. Apoptosis and senescence were analysed using siRNA transfection, western blot and flow cytometry. RESULTS: miRNA-21, miRNA-1827, miRNA-214, miRNA-339-5p, miRNA-625, miRNA-768-3p, miRNA-523-3p, miRNA-1227, miRNA-324-5p, miRNA-423-3p, miRNA-1301 and miRNA-1249 are differentially expressed in LC cells. miRNA-214 is upregulated in RT-resistant NSCLC cells relative to radiosensitive counterparts. Considering miRNA-214 as a putative regulator of RT resistance, we demonstrate that knockdown of miRNA-214 in radioresistant NSCLCs sensitised them to RT by stimulation of senescence. Consistently, overexpression of miRNA-214 in radiosensitive NSCLCs protected against RT-induced apoptosis. Protection was mediated by p38MAPK, as downregulation of this kinase could reverse the miRNA-214 overexpression-induced resistance of NSCLC cells. CONCLUSION: miRNA profiling of LC revealed putative RT resistance signalling circuits, which might help in sensitisation of LC to RT.

Chemosensitization by phenothiazines in human lung cancer cells: impaired resolution of γH2AX and increased oxidative stress elicit apoptosis associated with lysosomal expansion and intense vacuolation.

Chemotherapy resistance poses severe limitations on the efficacy of anti-cancer medications. Recently, the notion of using novel combinations of 'old' drugs for new indications has garnered significant interest. The potential of using phenothiazines as chemosensitizers has been suggested earlier but so far our understanding of their molecular targets remains scant. The current study was designed to better define phenothiazine-sensitive cellular processes in relation to chemosensitivity. We found that phenothiazines shared the ability to delay γH2AX resolution in DNA-damaged human lung cancer cells. Accordingly, cells co-treated with chemotherapy and phenothiazines underwent protracted cell-cycle arrest followed by checkpoint escape that led to abnormal mitoses, secondary arrest and/or a form of apoptosis associated with increased endogenous oxidative stress and intense vacuolation. We provide evidence implicating lysosomal dysfunction as a key component of cell death in phenothiazine co-treated cells, which also exhibited more typical hallmarks of apoptosis including the activation of both caspase-dependent and -independent pathways. Finally, we demonstrated that vacuolation in phenothiazine co-treated cells could be reduced by ROS scavengers or the vacuolar ATPase inhibitor bafilomycin, leading to increased cell viability. Our data highlight the potential benefit of using phenothiazines as chemosensitizers in tumors that acquire molecular alterations rendering them insensitive to caspase-mediated apoptosis.

Radioresistant cervical cancer shows upregulation of the NHEJ proteins DNA-PKcs, Ku70 and Ku86.

BACKGROUND: Radiotherapy is central in the treatment of cervical cancer. The formation of DNA double-strand breaks is considered to be critical for the radiotherapeutic effect. The non-homologous end joining (NHEJ) proteins DNA-PKcs, Ku70 and Ku86 have a major role in repairing DNA lesions. The objective of this study was to analyse if the expression of DNA-PKcs, Ku70 and Ku86 and their downstream signalling molecules p53, p21 and Mdm-2 are altered in residual cervical tumours after radiotherapy. METHODS: Retrospective analysis of 127 patients with cervical cancer stage IB-IIA treated with preoperative radiotherapy and radical surgery, revealed residual tumour in the cervical specimen in 30 patients. In 22 cases tumour material from residual and corresponding primary tumour were retrieved and the expression of DNA-PKcs, Ku86, Ku70, p53, p21 and Mdm-2 were assessed by immunohistochemistry. RESULTS: Residual tumours showed increased frequency of DNA-PKcs (P=0.037), Ku70 (P=0.018), Ku86 (P=0.008) positive cells. A correlation in DNA-PKcs expression between primary and residual tumours was found. The frequency of p21-positive cells was decreased (P=0.007) in residual tumours whereas no change in p53 or Mdm-2-positive cells were observed. CONCLUSION: Our results show that cervical carcinoma surviving radiotherapy have an increased DNA-PK expression. Studies on larger patient cohorts are needed to allow an interpretation that an upregulation of DNA-PK function may be part of a radioresistance mechanism within this tumour type.

Significantly higher levels of vascular endothelial growth factor (VEGF) and shorter survival times for patients with primary operable triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer (TNBC) lacking expression of steroid receptors and human epidermal growth factor receptor 2, having chemotherapy as the only therapeutic option, is characterised by early relapses and poor outcome. We investigated intratumoural (i.t.) levels of the pro-angiogenic cytokine vascular endothelial growth factor (VEGF) and survival in patients with TNBC compared with non-TNBC. PATIENTS AND METHODS: VEGF levels were determined by an enzyme immunosorbent assay in a retrospective series consisting of 679 consecutive primary breast cancer patients. RESULTS: Eighty-seven patients (13%) were classified as TNBC and had significantly higher VEGF levels; median value in TNBC was 8.2 pg/microg DNA compared with 2.7 pg/microg DNA in non-TNBC (P < 0.001). Patients with TNBC had statistically significant shorter recurrence-free survival [hazard ratio (HR) = 1.8; P = 0.0023], breast cancer-corrected survival (HR = 2.2; P = 0.004) and overall survival (HR = 1.8; P = 0.005) compared with non-TNBC. Patients with TNBC relapsed earlier than non-TNBC; mean time from diagnosis to first relapse was 18.8 and 30.7 months, respectively. The time between first relapse and death was also shorter in TNBC: 7.5 months versus 17.5 months in non-TNBC (P = 0.087). CONCLUSIONS: Our results show that TNBC have higher i.t. VEGF levels compared with non-TNBC. Ongoing clinical trials will answer if therapy directed towards angiogenesis may be an alternative way to improve outcome in this poor prognosis group.

Current status of prognostic immunohistochemical markers for urothelial bladder cancer.

The management and prognostication of patients with urothelial carcinomas (UCs), the most common histological type of bladder cancer, is mainly based on clinicopathological parameters. Several markers have been proposed to monitor this disease, including individual cell cycle-related proteins such as p53, pRb, p16, p21 and p27. Other putative markers are the oncogene products of FGFR3 and the ErbB family, proliferation markers including Ki-67, Aurora-A and survivin and different components within the immune system. In this review, a total of 12 parameters were evaluated and their discriminatory power compared. It is concluded that, in single-marker analyses, the proliferation markers Ki-67, survivin and Aurora-A offer the best potential to predict disease progression since they were all able to demonstrate independent prognostic power in repeated studies. Markers related to the immune system (e.g. CD8+ cells, regulatory T cells and cyclooxygenase-2 expression) or oncogene products of the ErbB family and FGFR3 are less powerful predictors of outcome or have not been equally well studied. The cell cycle-related proteins p53, pRb, p16, p21 and p27 have been extensively studied, but their usefulness as single prognostic markers remains unclear. However, in multimarker analyses, these markers appear to add prognostic information, indicating that they may contribute to more accurate treatment of UC.

Ionizing radiation activates IGF-1R triggering a cytoprotective signaling by interfering with Ku-DNA binding and by modulating Ku86 expression via a p38 kinase-dependent mechanism.

Ionizing radiation exposure results in the activation of several tyrosine kinase receptors that participate in radiation-induced DNA damage response and radioresistance. We previously showed that insulin-like growth factor 1 receptor (IGF-1R) inhibition enhanced radiosensitivity of non-small-cell lung cancer (NSCLC) cells. In this paper, we demonstrate that in U1810 NSCLC cells gamma-radiation activates IGF-1R within 10 min, with a maximal activation effect 2 h post-irradiation. Impairment of IGF-1R tyrosine kinase activity enhances human lung cancer cells radiosensitivity by a mechanism that involves phosphatidylinositol 3-kinase (PI3-K) and p38 kinase. In an active form, IGF-1R binds and activates p38 kinase, promoting receptor signaling. Conversely, inhibition of IGF-1R phosphorylation results in IGF-1R/p38 complex disruption and p38 kinase inactivation. We have also demonstrated that in insulin-like growth factor-1-stimulated cells, Ku-DNA-binding activation is induced by ionizing radiation within 4 h, reaches a maximum level at 12 h and remains active up to 72 h. Blockade of IGF-1R activity or its downstream signaling through p38 kinase induces a decrease in radiation-mediated Ku-DNA-binding activation and downregulates the level of Ku86, without affecting Ku70 expression in the nucleus of U1810 cells. The IGF-1R signaling via PI3-K does not interfere with the p38 signaling, the Ku-DNA-binding activity or the level of Ku86. Our present study demonstrates for the first time that ionizing radiation activates IGF-1R. Inhibition of IGF-1R signaling via p38 kinase induces radiosensitivity by a novel mechanism involving nuclear Ku86.

Expression of DNA damage response proteins and complete remission after radiotherapy of stage IB-IIA of cervical cancer.

The primary aim of this study was to investigate if the expression of the DNA damage identifying protein DNA-PKcs known to be involved in DNA repair after treatment with ionising radiation can be used as a predictive marker for radiotherapy (RT) response in cervical cancer. Formalin-fixed primary tumour biopsies from 109 patients with cervical cancer, FIGO-stage IB-IIA, treated with preoperative brachytherapy followed by radical surgery were analysed by immunohistochemistry. In addition, correlation studies between early pathological tumour response to radiation and expression of Ku86, Ku70, Mdm-2, p53 and p21 in primary tumours were also performed. We found that tumour-transformed tissue shows positive immunostaining of DNA-PKcs, Ku86 and Ku70, while non-neoplastic squamous epithelium and tumour-free cervix glands show negative immunoreactivity. Expression of DNA-PKcs positively correlated with both Ku86 and Ku70, and a statistically significant correlation between the Ku subunits was also found. After RT, 85 patients demonstrated pathologic complete remission (pCR), whereas 24 patients had residual tumour in the surgical specimen (non-pCR). The main finding of our study is that there was no correlation between the outcome of RT and the expression of DNA-PK subunits. Positive p53 tumours were significantly more common among non-pCR cases than in patients with pCR (P=0.031). Expression of p21 and Mdm-2 did not correlate with the outcome of RT.

Low and high LET radiation-induced apoptosis in M059J and M059K cells.

PURPOSE: To investigate and compare the ability of DNA-dependent protein kinase (DNA-PK)-deficient and -proficient cells to undergo apoptosis after exposure to low and high linear energy transfer (LET) radiation. MATERIALS AND METHODS: A human glioma cell line M059J lacking the catalytic subunit of DNA-PK (DNA-PKcs) and its DNA-PKcs-proficient counterpart, M059K, were exposed to 1 and 4 Gy of accelerated nitrogen ions (14N, 140 eV nm(-1), 8-12 Gy min(-1)) or 60Co gamma-rays (0.2 eV nm(-1), 0.7 Gy min(-1)). The induction of apoptosis was studied up to 144 h post-irradiation using two different methods: morphological characterization of apoptotic cells after fluorescent staining and cell size distribution analysis to detect apoptotic bodies. In parallel, protein expression of DNA-PKcs and poly(ADP-ribose) polymerase (PARP) as well as DNA-PK and caspase-3 activity were investigated. RESULTS: Low and high LET radiations (4 Gy) induced a time-dependent apoptotic response in both cell lines. Low LET radiation induced a significantly elevated apoptotic response in M059J as compared with M059K cells at 144 h post-irradiation. Following high LET radiation exposure, there was no difference between the cell lines at this time. PARP cleavage was detected in M059J cells following both low and high LET irradiation, while only high LET radiation induced PARP cleavage in M059K cells. These cleavages occurred in the absence of caspase-3 activation. CONCLUSIONS: M059J and M059K cells both display radiation-induced apoptosis, which occur independently of caspase-3 activation. The apoptotic course differs between the two cell lines and is dependent on the quality of radiation.

Difference in the induction, but not in the repair, of X-ray- and nitrogen ion-induced DNA single-strand breaks as measured using human cell extracts.

PURPOSE: To compare the repair efficiency of X-ray (low linear energy transfer [LET]) and nitrogen ion (high LET)-induced single-strand breaks (SSB) in a human cell-free end-joining system. MATERIALS AND METHODS: SSB were introduced into a bacterial plasmid, pBR322, by X-rays (4 MeV photons) and nitrogen ions with an LET=125 keV micro m(-1). Repair efficiency was studied under incubation with the protein extracts from human squamous carcinoma cells, UT-SCC-5. RESULTS: A several fold higher dose of nitrogen ion radiation compared with X-ray radiation was needed to induce a similar loss of supercoiled plasmid DNA. There was no difference in the repair efficiency of SSB induced by these two types of radiation. CONCLUSION: The data indicate that X-rays at 25 Gy and nitroging ions at 100 Gy radiation doses, under condition of low scavenging capacity (10 mM Tris), induce SSB of similar complexity or, alternatively, differences in SSB complexity do not alter the repair rate.

Pathologic complete remission after preoperative intracavitary radiotherapy of cervical cancer stage Ib and IIa is a strong prognostic factor for long-term survival: analysis of the Radiumhemmet data 1989-1991.

The purpose of this study was to evaluate the treatment results of preoperative brachytherapy and the prognostic value of pathologic complete remission after preoperative intracavitary irradiation in patients with stage Ib and IIa cervical carcinoma in relation to recurrence rate and survival. The clinical records of 185 patients with stage Ib (129 patients) and IIa (56 patients) cervical carcinoma, consecutively admitted to Radiumhemmet from January 1989 to December 1991 were reviewed. The median follow-up time was 71 months. In 121 patients the treatment consisted of uterovaginal intracavitary irradiation, according to the Stockholm technique, followed by surgery. Tumor remission assessed in the surgical specimen was classified as pathologic complete remission (pCR) if no microscopic tumor was found or incomplete pathologic remission (non-pCR) if microscopic residual tumor was found. Postoperative external beam radiation was added to cases with metastases in pelvic nodes or residual tumor in the resection margins. The disease-specific 5-year survival was 87% and 75% for stage Ib and IIa, respectively, for the patient population treated with preoperative intracavitary radiotherapy and surgery. After intracavitary radiation, 79% of the patients obtained pCR of the primary tumor. Five-year survival in those with pCR was 95%, compared with 46% in those with non-pCR (P < 0.0001). Patients with pCR and no lymph node metastases had a 98% 5-year survival as compared to a 5-year survival of 64% in patients with non-pCR and node negativity (P < 0.0001). Locoregional relapses were diagnosed in 2% of the patients with pCR compared to 54% in patients with non-pCR (P < 0.0001). Multivariate analysis revealed non-pCR (RR = 6.42) and node positivity (RR = 4.59) as nonfavorable factors for survival, while tumor size was not found to be of independent significance for survival. Pathologic complete remission after intracavitary irradiation is a strong favorable prognostic factor in node-negative patients. The combination of preoperative intracavitary radiotherapy and surgery results in a high cure rate and aids in identifying patients at risk for relapse who might be subject to adjuvant therapy.

A Swedish study of chemoradiation in squamous cell carcinoma of the esophagus.

This multicenter study describes the development of a chemoradiation protocol for the treatment of non-metastatic squamous cell carcinoma of the esophagus. Eighty patients were treated with three courses of chemotherapy (cisplatinum and 5-fluorouracil) with concomitant radiotherapy (40 Gy) during the last two courses of chemotherapy. Esophagectomy was performed, when feasible. If no operation was performed, patients were planned to receive a target dose of 64 Gy. Toxicity was mainly attributable to hematological impairment and led to two adjustments of the treatment protocol (addition of filgrastim and lowering of the 5-fluorouracil dose). These changes made it possible to administer the planned treatment in a gradually higher proportion of patients (13/23 [57%] before changes of treatment compared with 30/36 [83%] after changes). Treatment-related mortality was 3.75% (3 patients, associated with leucopenic septicemia after chemotherapy). Fifty-four patients were resected. No per- or postoperative mortality was encountered. The complete response (pathological CR) rate in operated patients was 46% (27/59 patients) after chemoradiation. In the whole series the CR rate (including clinical CR for non-resected patients) was 44%. With a minimum follow-up of 37 months, the 3-year survival for the whole group was 31% compared with 57% for the CR patients. Total 5-year survival thus far (July 1999) is 26%.

Defective caspase-3 relocalization in non-small cell lung carcinoma.

Many anticancer drugs exert their cytotoxicity through DNA damage and induction of apoptosis. Small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC) have different sensitivity to treatment with radiation and chemotherapeutic agents with SCLC being more sensitive than NSCLC both in vitro and in vivo. This difference might be related to the different susceptibility of small and non-small cell lung carcinoma to undergo apoptosis. The aim of this study was to investigate if deficiencies in the apoptotic pathways can explain the intrinsic resistance of NSCLC to anti-cancer treatment. Three different triggers were used to induce apoptosis. Etoposide and gamma-radiation, which are important parts of clinical lung cancer treatment, induce DNA-damage, whereas Fas ligation induces receptor-mediated apoptotic pathways. NSCLC cells were cross-resistant to all treatments, whereas SCLC cells, which do not express pro-caspase-8, were resistant to alphaFas-, but not to DNA-damage-induced apoptosis. Cytochrome c release, activation of caspase-9 and the executioner caspase-3 were observed in both types of lung cancer cells. However, cleavage of known nuclear substrates for caspase-3, such as PARP and DFF45/ICAD, was documented only in the sensitive SCLC cells but not in the resistant NSCLC cells. Moreover, relocalization of active caspase-3 from the cytosol into the nucleus upon treatment was observed only in the SCLC cell line. These results indicate that the inhibition of apoptosis in NSCLC occurs downstream of mitochondrial changes and caspase activation, and upstream of nuclear events.

DNA-dependent protein kinase is inhibited by trifluoperazine.

The DNA-dependent protein kinase (DNA-PK) is a serine/threonine nuclear kinase, important for the repair of DNA double strand breaks (DSB). Cells defective in DNA-PK show increased sensitivity to ionising radiation and different DNA-damaging drugs, such as cisplatinum. Increased sensitivity to cisplatinum has previously been noted in the presence of phenothiazines. We tested a panel of phenothiazines and one thioxanthen for any influence upon the activity and expression of DNA-PK in a nonsmall cell lung cancer cell line, U-1810. The activity of DNA-PK was completely inhibited in cell lysate and in purified enzyme by 200 microM TFP. DNA-PKcs and Ku86 cleavage were evident in U-1810 cells after 30 min incubation with 100 microM TFP, along with changes in the cells consistent with apoptosis. Our study suggests that phenothiazines and thioxanthens, acting through DNA-PK, have the potential to enhance the effects of DNA damaging agents.