Clinical Radioresistance Research Articles

Genome-scale CRISPR-Cas9 knockout screening in nasopharyngeal carcinoma for radiosensitive and radioresistant genes

BackgroundGenome-scale CRISPR-Cas9 knockout screening may provide new insights into the mechanism underlying clinical radioresistance in nasopharyngeal carcinoma (NPC), which is remain largely unknown. Our objective was to screen the functional genes associated with radiosensitivity and radioresistance in NPC, laying a foundation for further research on its functional mechanismand. MethodsCRISPR-Cas9 library lentivirus screening in radiation-treated NPC cells was combined with second-generation sequence technology to identify functional genes, which were further validated in radioresistant NPC cells and patient tissues. ResultsEleven radiosensitive and radioresistant genes were screened. Among these genes, the expression of FBLN5, FAM3C, MUS81, and DNAJC17 were significantly lower and TOMM20, CDKN2AIP, SNX22, and SP1 were higher in the radioresistant NPC cells (C666-1R, 5-8FR) (p < 0.05). CALD1 was highly expressed in C666-1R. Furthermore, we found knockout of FBLN5, FAM3C, MUS81 and DNAJC17 promoted the proliferation of NPC cells, while CDKN2AIP and SP1 had the opposed results (p < 0.05). This result was verified in NPC patient tissues. Meanwhile, KEGG analysis showed that the Fanconi anemia pathway and the TGF-β signaling pathway possibly contributed to radiosensitivity or radioresistance in NPC. ConclusionsNine genes involved in the radiosensitivity or radioresistance of NPC: four genes for radiosensitivity (FBLN5, FAM3C, MUS81, and DNAJC17), two genes for radioresistance (CDKN2AIP, SP1), two potential radioresistant genes (TOMM20, SNX22), and a potential radiosensitive gene (CALD1). Genome-scale CRISPR-Cas9 knockout screening for radiosensitive and radioresistant genes in NPC may provide new insights into the mechanisms underlying clinical radioresistance to improve the efficacy of radiotherapy for NPC.

Hyperbaric oxygen enhances X-ray induced ferroptosis in oral squamous cell carcinoma cells.

The objective of this study was to investigate the combined effect of X-ray radiation (IR) and hyperbaric oxygen (HBO) on oral squamous cell carcinoma (OSCC) cells and to explore the possible molecular mechanism. The OSCC cells were treated with or without IR, together with or without HBO co-exposure. Cells were transfected with specific plasmids using Lipofectamine 2000. The cell varieties, apoptosis markers, and ferroptosis markers were determined by using appropriate method. OSCC xenograft mice model was categorized into several subgroups according to the specific treatement. GPX4 expressions were determined by immunohistochemistry (IHC) in OSCC tissues and were tested by ELISA in serums from OSCC patients. The co-exposure of IR and HBO significantly strengthened the cytotoxicity of IR on SCC15-S cells in ferroptosis-dependent manner. The regulated GPX4/ferroptosis mediated the HBO function on re-sensitizing the radio-resistant OSCC cells to IR. In xenograft mice, co-exposure of IR and HBO can significantly reduce the tumor under IR activation compared with IR alone. Clinical data indicated that high GPX4 levels were associated with poor chemo-radiotherapy outcome. HBO could re-sensitize radio-resistant OSCC cells through GPX4/ferroptosis regulation. These results provide a potential therapeutic strategy for clinical radio-resistance.

A Review of the Role of Hypoxia in Radioresistance in Cancer Therapy.

Hypoxia involves neoplastic cells. Unlike normal tissue, solid tumors are composed of aberrant vasculature, leading to a hypoxic microenvironment. Hypoxia is also known to be involved in both metastasis initiation and therapy resistance. Radiotherapy is the appropriate treatment in about half of all cancers, but loco-regional control failure and a disease recurrence often occur due to clinical radioresistance. Hypoxia induces radioresistance through a number of molecular pathways, and numerous strategies have been developed to overcome this. Nevertheless, these strategies have resulted in disappointing results, including adverse effects and limited efficacy. Additional clinical studies are needed to achieve a better understanding of the complex hypoxia pathways. This review presents an update on the mechanisms of hypoxia in radioresistance in solid tumors and the potential therapeutic solutions.

KEAP1/NFE2L2 Mutations Predict Lung Cancer Radiation Resistance That Can Be Targeted by Glutaminase Inhibition.

Tumor genotyping is not routinely performed in localized non-small cell lung cancer (NSCLC) due to lack of associations of mutations with outcome. Here, we analyze 232 consecutive patients with localized NSCLC and demonstrate that KEAP1 and NFE2L2 mutations are predictive of high rates of local recurrence (LR) after radiotherapy but not surgery. Half of LRs occurred in tumors with KEAP1/NFE2L2 mutations, indicating that they are major molecular drivers of clinical radioresistance. Next, we functionally evaluate KEAP1/NFE2L2 mutations in our radiotherapy cohort and demonstrate that only pathogenic mutations are associated with radioresistance. Furthermore, expression of NFE2L2 target genes does not predict LR, underscoring the utility of tumor genotyping. Finally, we show that glutaminase inhibition preferentially radiosensitizes KEAP1-mutant cells via depletion of glutathione and increased radiation-induced DNA damage. Our findings suggest that genotyping for KEAP1/NFE2L2 mutations could facilitate treatment personalization and provide a potential strategy for overcoming radioresistance conferred by these mutations. SIGNIFICANCE: This study shows that mutations in KEAP1 and NFE2L2 predict for LR after radiotherapy but not surgery in patients with NSCLC. Approximately half of all LRs are associated with these mutations and glutaminase inhibition may allow personalized radiosensitization of KEAP1/NFE2L2-mutant tumors.This article is highlighted in the In This Issue feature, p. 1775.

Targeting HMGB3/hTERT axis for radioresistance in cervical cancer

BackgroundRadiotherapy is regarded as a milestone for the cure of cervical cancer. However, clinical outcome heavily be hindered by radioresistance. So, exploring the underlying mechanism of radioresistance, and find potential target, well deserve fully emphasis.MethodsIn this study, we developed two novel radiation resistance cervical cancer cell lines, which could mimic clinical radioresistance. In order to find new potential targets, RNA-Seq, database analysis, streptavidin-agarose and LC/MS were used. Pull-down, luciferase and rescue assays were conducted to explore the regulatory mechanisms. To further evaluate the correlation between therapeutic responses and HMGB3/hTERT expression, 172 cervical cancer patients were recruited.ResultsKnockdown of HMGB3 significantly inhibit the DNA damage repair and induced more γH2AX foci, leading to enhanced chemo- and radio-sensitivity in vitro and in vivo, whereas HMGB3 overexpression has the opposite effects. HMGB3 promotes cell growth and radioresistance by transcriptionally up-regulating hTERT via the specifical binding of HMGB3 at the hTERT promoter region from − 902 to − 321. HMGB3 knockdown-mediated radiosensitization could be reversed by the overexpressed hTERT in both cervical cancer cell lines and xenograft tumor mouse model. Furthermore, clinical data from 172 cervical cancer patients proved that there was a positive correlation between HMGB3 and hTERT expression, and high expression of HMGB3/hTERT predicted poor response to radiotherapy, worse TNM stages and shorter survival time.ConclusionHere, we have identified HMGB3/hTERT signaling axis as a new target for cervical cancer radioresistance. Our results provide new insights into the mechanism of cervical cancer radioresistance and indicate that targeting the HMGB3/hTERT signaling axis may benefit cervical cancer patients.

KEAP1/NFE2L2 mutations to predict local recurrence after radiotherapy but not surgery in localized non-small cell lung cancer.

9012 Background: Tumor genotyping in localized non-small cell lung cancer (NSCLC) is not broadly performed due to lack of actionable associations of mutations with treatment or outcome. We sought to identify recurrent mutations in localized NSCLC that are associated with local recurrence (LR) after radiotherapy (RT) or surgery. Methods: We identified consecutive patients with NSCLC treated with chemoradiotherapy (CRT), stereotactic ablative radiotherapy (SABR) or surgery from 2009-2018 at our institution with stage IA1-IIIC NSCLC who had genotyping performed on tumor tissue using a targeted gene panel. Our primary objective was to identify somatic tumor mutations that predicted LR after RT but not surgery. We also performed functional screening assays by expressing open reading frame constructs harboring patient-derived mutations in knock-out cell lines generated by CRISPR-Cas9 and evaluating effects on in vitro radioresistance. Results: We identified 232 consecutive patients with localized NSCLC (87.1% adenocarcinoma, 10.3% squamous, 2.3% other) who received tumor biopsy or resection specimen and underwent tumor genotyping. 47 patients with locally advanced NSCLC received CRT, 50 patients with early stage NSCLC received SABR, and 135 patients with early stage NSCLC underwent surgical resection. Of all recurrent mutations ( &gt; 5% mutation frequency), only mutations in Kelch-like ECH-associated protein 1 ( KEAP1) or Nuclear Factor Erythroid 2-Related Factor 2 ( NFE2L2) genes (K/NMUT) were significantly associated with LR after CRT or SABR, with 2-year LR in the combined RT cohort of 42.4% for K/NMUT versus 12.5% for wildtype (P = 0.005). Furthermore, K/NMUT were present in nearly half of all LR events. Strikingly, there was no significant difference in LR for K/NMUT tumors following CRT versus SABR (P = 0.47). Local recurrence was rare for patients who received surgery (n = 2) and was not associated with K/N mutation status (P = 0.60). Functional evaluation by expression of K/N mutations in knock-out cell lines revealed that LR only occurred in patients with mutations that induced radioresistance (i.e. pathogenic) but not passenger mutations (P = 0.04). In contrast to genotyping, NFE2L2 target gene expression analysis via RNA-seq did not predict LR (P = 0.93). Conclusions: Our findings suggest that KEAP1/NFE2L2 mutations are a predictive biomarker of clinical radioresistance and a dominant cause of LR after RT. Genotyping for KEAP1/NFE2L2 mutations could therefore facilitate treatment personalization in localized NSCLC.

Abstract 1652: P16INK4a over-expression sensitizes HPV(-) HNSCC to radiation through down-regulation of USP7

Abstract Background: Head and neck squamous cell carcinoma (HNSCC) tumorigenesis induced by human papillomavirus (HPV) shows a greater clinical response to radiation therapy when compared to HPV negative patients. The underlying mechanism for this more favorable outcome is unknown, but the presumption is that DNA repair response must play a large role. P16INK4a is a known surrogate marker for HPV positivity; however the relationship between radiation sensitivity and P16INK4a has not been completely elucidated in this context. Ubiquitin specific protease 7 (USP7), also known as HAUSP, is a deubiquitylating enzyme that cleaves ubiquitin from substrates to stabilize target proteins. USP7 overexpression is a predictor of poor prognosis in lung carcinomas and correlates with disease progression and lower survival in gliomas. More recent studies have shown USP7 has a role in the stability of DNA damage response proteins such as RNF168, BRCA1 and Chk1; and USP7 knockdown has been shown to radio-sensitize breast cancer cells to radiation. We have investigated the possible role of USP7 in the radio-response of HNSCC cells in the context of HPV status. Methods: Four HPV(+) and four HPV(-) HNSCC were chosen for this study. The radio-response was determined by clonogenic survival assay. P16INK4a overexpression was generated using lentivirus. Western blot analysis was used for visualizing protein expression. The Cancer Genome Atlas was interrogated to examine the relationship between USP7 and clinical outcome. Results: Our data suggest P16INK4a negatively regulates USP7 and leads to the more radiosensitive phenotype associated with HPV(+)HNSCC. Radio-resistant HPV(-) HNSCC cell lines show higher levels of USP7 than HPV(+) lines and over-expression of P16INK4a in HPV(-) HN5 cells leads to down-regulation of USP7 and radio-sensitization. Conversely, P16INK4a siRNA knockdown in HPV(+) UMSCC-47 shows an increase of USP7 protein expression and radio-resistance. P22077, an inhibitor of USP7 activity, was also shown to radiosensitize a HPV(-) cell line. This shows proof of principle that inhibiting USP7 can be a viable approach to sensitizing HPV(-) HNSCC to radiation. USP7 overexpression was also associated with poorer overall survival in HNSCC. Conclusion: These results suggest that USP7 may be a marker of clinical radioresistance in HNSCC and that its inhibition has the potential to improve the treatment outcome of patients with HPV(-) HNSCC when combined with radiotherapy. Citation Format: David Molkentine, Li Wang, Kathleen Bridges, Kathy Mason, Raymond Meyn, Heath D. Skinner. P16INK4a over-expression sensitizes HPV(-) HNSCC to radiation through down-regulation of USP7. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1652.

IKKα-mediated biogenesis of miR-196a through interaction with Drosha regulates the sensitivity of cancer cells to radiotherapy.

Radioresistance is a major obstacle in successful clinical cancer radiotherapy, and the underlying mechanisms are not clear. Here we show that IKKα-mediated miR-196a biogenesis via interaction with Drosha regulates the sensitivity of nasopharyngeal carcinoma (NPC) cells to radiotherapy. Phosphorylation of IKKα at T23 site (p-IKKαT23) promotes the binding of IKKα to Drosha that accelerates the processing of miR-196a primary transcripts, leading to increased expressions of both precursor and mature miR-196a. Dephosphorylation of p-IKKαT23 downregulates miR-196a expression and promotes the resistance of NPC cells to radiation treatment. The miR-196a mimic suppresses while its inhibitor promotes the resistance of NPC to radiation treatment. Importantly, the expression of p-IKKαT23 is positively related to the expression of miR-196a in human NPC tissues, and expression of p-IKKαT23 and miR-196a is inversely correlated with NPC clinical radioresistance. Thus, our studies establish a novel mechanistic link between the inactivation of IKKαT23-Drosha-miR-196a pathway and NPC radioresistance, and de-inactivation of IKKαT23-Drosha-miR-196a pathway would be an efficient way to restore the sensitivity of radioresistant NPC to radiotherapy.

Abstract 3441: Proteomic profiling identifies PTK2/FAK as a targetable marker of radioresistance in head and neck cancer

Abstract One of the primary treatments for head and neck squamous cell carcinoma (HNSCC) is radiotherapy. Despite decades of study, few if any targetable biomarkers for resistance to this modality. To systematically evaluate resistance to radiotherapy in HNSCC, we evaluated 50 HNSCC cell lines using reverse phase protein array (RPPA). Utilizing this method we identified 11 protein markers with altered expression in radioresistant HNSCC cell lines (FDR 1%), including PTK2/FAK. Both PTK2/Fak gene expression and copy number were highly correlated to PTK2/Fak protein expression and both were associated with radioresistance in these cell lines. Additionally, in clinical samples from the TCGA, PTK2/Fak copy number was highly associated with gene expression, with high expression levels in HNSCC tumors. To validate the association between PTK2/Fak and clinical radioresistance in HNSCC, we examined PTK2/FAK copy number in two separate cohorts of HNSCC patients treated uniformly with radiotherapy (n = 39 and n = 44). In both cohorts, PTK2/Fak amplification was associated with treatment failure following radiotherapy (p = 0.04 and p = 0.03 respectively and p = 0.004 for the combined population). Additionally, in a separate cohort of HNSCC patients treated with radiotherapy, high levels of PTK2/Fak gene expression were associated with failure following radiotherapy (p = 0.02). Additionally, in vitro pharmacologic inhibition of PTK2/FAK function led to radiosensitization in multiple HNSCC cell lines, primarily via induction of G2/M arrest, with minimal apoptosis observed. Taken together, these data identify a validated, targetable biomarker of radioresistance in HNSCC. Citation Format: Heath D. Skinner, Uma Giri, John S. Yordy, Michael D. Story, Jing Wang, Lauren A. Byers, Michelle D. Williams, Adel K. El-Naggar, Sang H. Woo, Liang P. Yang, You Fan, Curtis R. Pickering, Jeffrey N. Myers,, John V. Heymach. Proteomic profiling identifies PTK2/FAK as a targetable marker of radioresistance in head and neck cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3441. doi:10.1158/1538-7445.AM2015-3441

Abstract 3320: Identification of potential molecular targets related to radioresistance in human oral cancers

Abstract In India, oral cancer is the most common cancer in males and ranks third among females, attributed predominantly to the use of smokeless tobacco. Radiotherapy is an integral part of oral cancer treatment either alone or in combination with surgery and chemotherapy. However the development of radioresistance creates a hurdle in the efficacy of radiotherapy. Therefore, exploring the differential molecular profile of established radioresistant versus parental oral cancer cells may help in predicting the clinical effectiveness of radiotherapy. The present study aims to profile the radioresistant cell lines established by low dose radiation from their parental oral cancer cell lines, to identify the molecules and the possible mechanisms associated with radioresistance in oral cancer. We have established three radioresistant oral cancer cell lines i.e. 70Gy-AW13516, 70Gy-AW8507 and 70Gy-SCC029B derived from their parental AW13516, AW8507 and SCC029B cell lines respectively using in-vitro fractionated ionizing radiation (FIR). A clinically admissible 2Gy radiation dose was given using a 60Co-γ linear accelerator (Bhabhatron-2, ACTREC) upto 70Gy totally for each of the cell lines. The radioresistant character was determined by clonogenic cell survival assay and proteomic profiling of parental versus radioresistant cells was done by two-dimensional gel electrophoresis. Gels were analysed by PD-Quest software (Bio-Rad) and differential spot identities were revealed by MALDI-TOF/TOF (Bruker Ultra flex-II). To explore changes at transcript level; cDNA microarray was performed by Affymetirx Gene Chip array and analysed by Gene Spring GX-12.5 software. Mass spectrometry (MS) identified a total of 106 differentially expressed proteins among the three replicate sets of each parental and radioresistant 2-D gels with significant MS/MS score. Some of the differentially expressed proteins like Prohibitin, Moesin, PCNA, Keratin-8, Vimentin, HSP-70 and 14-3-3 sigma were validated by western blotting. We further, transiently knocked down Moesin expression by siRNA strategies and demonstrated a significant decrease in the radioresistant character of 70Gy-AW13516 cells as compared to control siRNA treated cells, indicating a role for Moesin in acquired radioresistance of oral cancer cells. Also differentially expressed genes (&amp;gt;3 fold) of radioresistant cells, were mapped by David (NIH) &amp; Panther (USC) functional tools. The pathway analysis revealed genes related to cell survival (PI3K, P38), Wnt and Apoptosis signalling. The proteomic and transcriptomic profiling of radioresistant oral cancer cell lines have revealed several radioresistance associated molecules that may be utilised in predicting cellular response to radiotherapy and the pathways identified may provide new insights in understanding the mechanism underlying clinical radioresistance in oral cancers. Citation Format: Tanuja R. Teni, Mohd Yasser, Sagar Pawar. Identification of potential molecular targets related to radioresistance in human oral cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3320. doi:10.1158/1538-7445.AM2015-3320

Hypoxia and cellular localization influence the radiosensitizing effect of gold nanoparticles (AuNPs) in breast cancer cells.

Hypoxia exists in all solid tumors and leads to clinical radioresistance and adverse prognosis. We hypothesized that hypoxia and cellular localization of gold nanoparticles (AuNPs) could be modifiers of AuNP-mediated radiosensitization. The possible mechanistic effect of AuNPs on cell cycle distribution and DNA double-strand break (DSB) repair postirradiation were also studied. Clonogenic survival data revealed that internalized and extracellular AuNPs at 0.5 mg/mL resulted in dose enhancement factors of 1.39 ± 0.07 and 1.09 ± 0.01, respectively. Radiosensitization by AuNPs was greatest in cells under oxia, followed by chronic and then acute hypoxia. The presence of AuNPs inhibited postirradiation DNA DSB repair, but did not lead to cell cycle synchronization. The relative radiosensitivity of chronic hypoxic cells is attributed to defective DSB repair (homologous recombination) due to decreased (RAD51)-associated protein expression. Our results support the need for further study of AuNPs for clinical development in cancer therapy since their efficacy is not limited in chronic hypoxic cells.

Abstract B49: Using ionizing radiation and primary human esophageal adenocarcinoma xenograft models to interrogate tumor cell characteristics associated with tumor-initiating cells

Abstract Radiotherapy is critical to the treatment of esophageal adenocarcinoma (EAC). However, with frequent recurrence and metastasis, five-year survival rates are only 13%. Clinical radioresistance is further evidenced by the fact that escalated doses increase toxicity without improving outcome. The cancer stem cell model may provide insight on the EAC cell of origin and thus, on clinically-observed radioresistance. Recent evidence has demonstrated a differential ability of EAC cells to seed tumors in mice, however a correlation between tumorigenicity and radioresistance in EAC has not been reported. Recently, sequencing and cross-checking of 14 commercially-available EAC cell lines revealed that these cell lines were in fact derived from other cancer types. These findings highlight the need for reliable models of EAC. We have developed mouse xenograft models of primary human EAC that recapitulated the original tumors in cellular differentiation and tumor architecture. Using these models, we compared the in vivo tumorigenicity of irradiated versus non-irradiated (control) tumors. We hypothesized that ionizing radiation would enrich the population of tumor-initiating cells (TIC) in xenograft tumors compared to non-irradiated tumors. Thus far, we are evaluating five primary xenograft models of human EAC that have been established in NODSCID mice. Treatment sensitivity testing has been performed on these five xenograft lines, and limiting dilution assays (LDA) have been performed on the first two. Initial experiments have revealed that xenograft Line 2 is significantly more radioresistant than the other four lines. LDA results on xenograft Line 1 revealed a TIC frequency of 1 in 20,089 in non-irradiated xenograft tumors and 1 in 40,620 in irradiated xenograft tumors. Line 2 revealed a TIC fraction of 1 in 434 non-irradiated tumors and 1 in 31,631 irradiated xenografts. These results suggest two Conclusions: (1) TIC frequency may be associated with relative radioresistance, since the radioresistant Line 2 appeared to be very tumorigenic; and (2) the comparison of TIC fractions in non-irradiated and irradiated xenograft tumors raises concerns that infiltrating mouse cells may dilute the TIC frequency through a radiation-induced inflammatory response. In subsequent LDAs, cells positive for the mouse-specific antigen H2k were depleted from the tumour cell suspension. Results from these LDAs are forthcoming, and will be presented at the meeting. In conclusion, preliminary LDA results have shown that the baseline TIC frequency in EAC xenografts is highly variable and might be related to radiosensitivity; our results suggest that this variability can be several orders of magnitude wider than previously reported. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B49.

Identification of differential gene expression profiles of radioresistant lung cancer cell line established by fractionated ionizing radiation in vitro

Radiotherapy plays a critical role in the management of non-small cell lung cancer (NSCLC). This study was conducted to identify gene expression profiles of acquired radioresistant NSCLC cell line established by fractionated ionizing radiation (FIR) by cDNA microarray. The human lung adenocarcinoma cell line Anip973 was treated with high energy X-ray to receive 60 Gy in 4 Gy fractions. The radiosensitivity of Anip973R and its parental line were measured by clonogenic assay. Gene expression profiles of Anip973R and its parental line were analyzed using cDNA microarray consisting of 21 522 human genes. Identified partly different expressive genes were validated by quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR). Fifty-nine upregulated and 43 downregulated genes were identified to radio-resistant Anip973R. Up-regulated genes were associated with DNA damage repair (DDB2), extracellular matrix (LOX), cell adhesion (CDH2), and apoptosis (CRYAB). Down-regulated genes were associated with angiogenesis (GBP-1), immune response (CD83), and calcium signaling pathway (TNNC1). Subsequent validation of selected eleven genes (CD24, DDB2, IGFBP3, LOX, CDH2, CRYAB, PROCR, ANXA1 DCN, GBP-1 and CD83) by Q-RT-PCR was consistent with microarray analysis. Fractionated ionizing radiation can lead to the development of radiation resistance. Altered gene profiles of radioresistant cell line may provide new insights into mechanisms underlying clinical radioresistance for NSCLC.

Hypoxic tumor cell radiosensitization: role of the iNOS/NO pathway.

Hypoxia is a common feature of the tumor microenvironment and a major cause of clinical radioresistance. During the last decades, several strategies to improve tumor oxygenation were developed such as breathing high oxygen content gas under hyperbaric conditions (3 atmosphere) and improving tumor perfusion by nicotinamide, in combination with carbogen breathing and accelerated radiotherapy to counteract tumor repopulation (ARCON). Other strategies to overcome hypoxia induced radioresistance are the use of hypoxic cell radiosensitizers, which mimic oxygen and enhance thereby radiation damage (e.g. the nitroimidazoles) and bioreductive drugs, which undergo intracellular reduction to form active cytotoxic species under low oxygen tension (e.g. mitomycin C and tirapazamine). A meta-analysis of all randomized trials in which some form of hypoxic modification was performed, showed an improved local control and survival, especially in cervix and head-and-neck cancer. Nevertheless, none of the discussed strategies are used in clinical routine because of feasibility and toxicity issues. We developed an alternative strategy that takes advantage of the microenvironment of solid tumors for tumor specific radiosensitization. The inducible isoform of nitric oxide synthase (iNOS) may be induced by bacterial LPS or its derivate lipid A, is expressed by a variety of solid tumors and generates NO at high rates inside tumor cells. This local production of NO results in efficient hypoxic tumor cell radiosensitization, at non-toxic extracellular concentrations of NO. In addition, iNOS is transcriptionally upregulated by hypoxia and proinflammatory cytokines such as interferon-gamma. Hence, we proposed the pro-inflammatory tumor infiltrate as a new target for radiosensitizing strategies and identified two mechanisms: First, tumor associated immune cells (macrophages, T/NK-cells) are a source of mediators that may induce the iNOS/NO pathway inside tumor cells. Second, tumor associated macrophages can produce high levels of NO that may radiosensitize bystander tumor cells. Our ongoing research is focused on combining immunostimulatory and radiosensitizing strategies.

Predicting the tumor response to radiotherapy using microarray analysis (Review)

Predicting the tumor response to radiotherapy is one of the major goals of human cancer treatment. Identification of the genes that are differentially expressed between radiosensitive and radioresistant cancers by global gene analysis may provide new insights into the mechanisms underlying clinical radioresistance and improve the efficacy of radiotherapy. In this study, we reviewed the published reports identifying sets of discriminating genes using microarray analysis that can be used for characterization and the prediction of response to radiotherapy in human cancers. These reports indicate that many of the identified genes were associated with DNA-repair, apoptosis, growth factor, signal transduction, cell cycle and cell adhesion. Several genes were found to be predictors of the radiation response with various cancers and certain sets of identified genes were also found to predict the radiation response by using clustering analysis. Global gene expression profiling of responders and non-responders can be useful in predicting responses to radiotherapy and may also provide insights into the development of individualized therapies and novel therapeutic targets.

Differential gene expression profiles of radioresistant pancreatic cancer cell lines established by fractionated irradiation

Identification of the genes that are differentially-expressed between radiosensitive and radioresistant cancer cells is important to the ability to predict the clinical effectiveness of radiotherapy. We established radioresistant human pancreatic cancer cell lines using fractionated irradiation in order to identify genes that are differentially-expressed between parental lines and radioresistant cell sublines. Six pancreatic cancer cell lines (PK-1, PK-8, PK-9, T3M4, MiaPaCa2 and PANC-1) were treated with 10 Gy fractionated irradiation at approximately two-week intervals (total dose 150-180 Gy). Five radioresistant sublines (PK-1, PK-8, PK-9, T3M4, and MiaPaCa2) were successfully established. Using oligonucleotide microarrays containing 17,086 genes, we identified 73 up-regulated genes and 55 down-regulated genes common to radioresistant sublines. Subsequent analysis by quantitative RT-PCR confirmed the reliability of our microarray strategy. Up-regulated genes were associated with growth factor (example, amphiregulin), cell-cycle check point (MAPKAPK2), intracellular signaling pathway (regucalcin), and angiogenesis stimulation (angiopoietin 2). Down-regulated genes were associated with apoptosis (caspase 8), retinoid esterification (lecithin retinol acyltransferase), and electron transport (calcium-activated chloride channel 1). Some of these genes have known association with response to radiation, such as caspase 8 and MAPKAPK2, but others are novel. Global gene analysis of radioresistant sublines may provide new insights into the mechanisms underlying clinical radioresistance and to improving the efficacy of radiotherapy for pancreatic cancer.

Constitutive mRNA expression of DNA repair-related genes as a biomarker for clinical radio-resistance: A pilot study in prostate cancer patients receiving radiotherapy

Purpose: Repair of radiation-induced DNA damage is believed to play a critical role in the development of adverse reactions in radiotherapy patients. Constitutive mRNA expression of repair genes was investigated in such patients to analyze whether expression patterns are predictive for therapy-related acute side effects.Materials and methods: Prostate cancer patients (n = 406) receiving intensity-modulated radiotherapy were recruited in a prospective epidemiological study. Adverse effects were monitored during therapy using common toxicity criteria. For expression analyses, samples from 58 patients were selected according to their observed grade of clinical side effects to radiotherapy. Expression profiles were generated from peripheral blood lymphocytes using customized cDNA-arrays which carried probes for 143 DNA repair or repair-related genes. In addition, expression of selected genes was confirmed by quantitative real-time reverse transcription PCR (RT-PCR). Constitutive mRNA expression profiles were analyzed for predicting acute clinical radiosensitivity or radio-resistance.Results: Cluster analysis identified 19 differentially expressed genes. Many of these genes are involved in DNA double strand break repair. Expression levels of these genes differed up to 7-fold from the mean of all patients whereas expression levels of housekeeping genes varied only up to 2-fold. High expression of the identified genes was associated with a lack of clinical radiation sensitivity thus indicating radio-resistance.Conclusions: Constitutive expression of DNA repair-related genes may affect the development of acute side effects in radiotherapy patients, and high expression levels of these genes seem to support protection from adverse reactions.

Intrinsic radiosensitivity by metallothionein expression has no great influence on clinical radiosensitivity in esophageal carcinoma

Several studies have shown that macroscopically infiltrative type of esophageal carcinoma generally has a poorer local response to radiation therapy than that of localized type. The aim of this study was to determine the role of metallothionein (MT) as a radioprotective agent in the difference of clinical radiosensitivities in esophageal carcinoma. A total of 45 surgically resected esophageal carcinoma tissues [20 macroscopically localized type without preoperative treatment (PT), 20 macroscopically infiltrative type without PT and 5 macroscopically infiltrative type with PT] were stained for MT by immunohistochemistry and were analyzed. MT expression level of macroscopically localized type of esophageal carcinoma was significantly higher than that of infiltrative type without PT (P=0.026) and was significantly higher than that of infiltrative type with PT (P=0.024). No significant difference was found between MT expression levels in infiltrative type of esophageal carcinoma without PT and that with PT. The results of this study suggest that there is less possibility that clinical radioresistance of the tumor is due to MT expression in esophageal carcinoma and also suggest that there is less possibility that MT synthesis is induced by fractionated irradiation of a moderate dose or by an anti-cancer agent during a course of treatment.

Implantable polymers for tirapazamine treatments of experimental intracranial malignant glioma.

Malignant gliomas remain refractory to intensive radiotherapy and cellular hypoxia enhances clinical radioresistance. Under hypoxic conditions, the benzotriazine di-N-oxide (3-amino-1,2,4-benzotriazine 1,4-dioxide) (tirapazamine) is reduced to yield a free-radical intermediate that results in DNA damage and cellular death. For extracranial xenografts, tirapazamine treatments have shown promise. We therefore incorporated tirapazamine into the synthetic, biodegradable polymer, measured the release, and tested the efficacy both alone and in combination with external beam radiotherapy in the treatment of experimental intracranial human malignant glioma xenografts. The [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer was synthesized. The PCPP:SA polymer and solid tirapazamine were combined to yield proportions of 20% or 30% (wt/wt). Polymer discs (3 x 2 mm) (10 mg) were incubated (PBS, 37 degrees C), and the proportion of the drug released vs. time was recorded. Male nu/nu nude mice were anesthetized and received intracranial injections of 2 x 10(5) U251 human malignant glioma cells. For single intraperitoneal (i.p.) drug and/or external radiation treatments, groups of mice had i.p. 0.3 mmol/kg tirapazamine, 5 Gy cranial irradiation, or combined treatments on day 8 after inoculation. For fractionated drug and radiation treatments, mice had i.p. 0.15 mmol/kg tirapazamine, 5 Gy radiation, or combined treatments on days 8 and 9 after inoculation. For intracranial (i.c.) polymer treatments, mice had craniectomies and intracranial placement of polymer discs at the site of cellular inoculation. The maximally tolerated percentage loading of tirapazamine in the polymer.disc was determined. On day 7 after inoculation, groups of mice had i.c. empty or 3% tirapazamine alone or combined with radiation (5 Gy x 2 doses) or combined with i.p. drug (0.15 mmol/kg x 2 doses on days 8 and 9). Survival was recorded. Polymers showed controlled, protracted in vitro release for over 100 days. The 5 Gy x 1 treatment resulted in improved survival; 28.5 +/- 3.7 days (P = 0.01 vs. controls), while the single i.p. 0.3 mmol/kg tirapazamine treatment, 17.5 +/- 1.9 days (P = NS) and combined treatments; 21.5 +/- 5.0 days (P = NS) were not different. The fractionated treatments: 5 Gy x 2, i.p. 0.15 mmol/kg tirapazamine x 2 and the combined treatments resulted in improved survival: 44.5 +/- 3.9 (P < 0.001), 24.5 +/- 2.3 (P = 0.05) and 50.0 +/- 6.0 (P < 0.001), respectively. Survival after intracranial empty polymer was 16.5 +/- 3.0 days and increased to 31.0 +/- 3.0 (P = 0.003) days when combined with the 5 Gy x 2 treatment. The survival after the polymer bearing 3% tirapazamine alone vs. combined with radiation was not different. The combined 3% tirapazamine polymer, i.p. tirapazamine, and radiation treatments resulted in both early deaths and the highest long-term survivorship. The basis for potential toxicity is discussed. We conclude that implantable biodegradable polymers provide controlled intracranial release for treatment of experimental glioma. For treatment of malignant gliomas, the combination of continuous polymer-mediated delivery and fractionated systemic delivery of tirapazamine with external beam radiotherapy warrants further exploration.

Preferential Cytoplasmic Localization of p34 cdc2 in Recurrent Human Squamous Cell Carcinoma after Radiotherapy

Duration of the G2-phase delay and arrest after exposure to ionizing radiation is thought to influence radiosensitivity. The kinase activity of the p34cdc2-cyclin B complex and the p34cdc2-cyclin A complex is implicated in G2- to M-phase transition and in G2-phase arrest after exposure to ionizing radiation. We analyzed the expression level and the subcellular location of p34cdc2, cyclin A and cyclin B in head and neck squamous cell carcinoma (SCC) tumors; samples were obtained from patients with locally nonrecurrent and recurrent tumors that had been treated by surgery and radiotherapy. No significant difference was noticed in cyclin A, cyclin B and p34cdc2 expression. However, we noted a significant preferential cytoplasmic location of p34cdc2 in recurring tumors compared to the nonrecurring ones (P < 0.001). This abnormal location of p34cdc2 occurs even in primary tumors in patients with recurring tumors, suggesting that a default in the activation of p34cdc2 kinase could be implicated in clinical radioresistance.