Expression of an X-family DNA polymerase, pol lambda, in the respiratory epithelium of non-small cell lung cancer patients with habitual smoking

Translesion DNA Synthesis in Cancer: Molecular Mechanisms and Therapeutic Opportunities

The genomic landscape of cancer is one marred by instability, but the mechanisms that underlie these alterations are multifaceted and remain a topic of intense research. Cellular responses to DNA damage and/or replication stress can affect genome stability in tumors and influence the response of patients to therapy. In addition to direct repair, DNA damage tolerance (DDT) is an element of genomic maintenance programs that contributes to the etiology of several types of cancer. DDT mechanisms primarily act to resolve replication stress, and this can influence the effectiveness of genotoxic drugs. Translesion DNA synthesis (TLS) is an important component of DDT that facilitates direct bypass of DNA adducts and other barriers to replication. The central role of TLS in the bypass of drug-induced DNA lesions, the promotion of tumor heterogeneity, and the involvement of these enzymes in the maintenance of the cancer stem cell niche presents an opportunity to leverage inhibition of TLS as a way of improving existing therapies. In the review that follows, we summarize mechanisms of DDT, misregulation of TLS in cancer, and discuss the potential for targeting these pathways as a means of improving cancer therapies.

Not breathing is not an option: How to deal with oxidative DNA damage

Oxidative DNA damage constitutes a major threat to genetic integrity, and has thus been implicated in the pathogenesis of a wide variety of diseases, including cancer and neurodegeneration. 7,8-dihydro-8oxo-deoxyGuanine (8-oxo-G) is one of the best characterised oxidative DNA lesions, and it can give rise to point mutations due to its miscoding potential that instructs most DNA polymerases (Pols) to preferentially insert Adenine (A) opposite 8-oxo-G instead of the correct Cytosine (C). If uncorrected, A:8-oxo-G mispairs can give rise to C:G→A:T transversion mutations. Cells have evolved a variety of pathways to mitigate the mutational potential of 8-oxo-G that include i) mechanisms to avoid incorporation of oxidized nucleotides into DNA through nucleotide pool sanitisation enzymes (by MTH1, MTH2, MTH3 and NUDT5), ii) base excision repair (BER) of 8-oxo-G in DNA (involving MUTYH, OGG1, Pol λ, and other components of the BER machinery), and iii) faithful bypass of 8-oxo-G lesions during replication (using a switch between replicative Pols and Pol λ). In the following, the fate of 8-oxo-G in mammalian cells is reviewed in detail. The differential origins of 8-oxo-G in DNA and its consequences for genetic stability will be covered. This will be followed by a thorough discussion of the different mechanisms in place to cope with 8-oxo-G with an emphasis on Pol λ-mediated correct bypass of 8-oxo-G during MUTYH-initiated BER as well as replication across 8-oxo-G. Furthermore, the multitude of mechanisms in place to regulate key proteins involved in 8-oxo-G repair will be reviewed. Novel functions of 8-oxo-G as an epigenetic-like regulator and insights into the repair of 8-oxo-G within the cellular context will be touched upon. Finally, a discussion will outline the relevance of 8-oxo-G and the proteins involved in dealing with 8-oxo-G to human diseases with a special emphasis on cancer.

Combined heavy smoking and drinking predicts overall but not disease-free survival after curative resection of locoregional esophageal squamous cell carcinoma

INTRODUCTION

The prognostic impact of smoking and drinking on esophageal squamous cell carcinoma (ESCC) was scarcely discussed. We investigated the prognostic value of smoking and drinking and their relationships with clinicopathological characteristics in a large cohort of patients with locoregional ESCC.

PATIENTS AND METHODS

We retrospectively analyzed 488 patients who underwent curative treatment at a single institution between January 2007 and December 2008. A chi-square test was used to evaluate the relationships between smoking and drinking and clinicopathological variables, the Kaplan-Meier method was used for 5-year overall survival (OS) and disease-free survival, and Cox proportional hazards models were applied for univariate and multivariate analyses of variables with respect to OS and disease-free survival.

RESULTS

Heavy smokers were more likely to have advanced Tumor-Node-Metastases (TNM) stage and higher neutrophil/lymphocyte ratio at diagnosis (P<0.05). Drinkers were more likely to have advanced TNM stage, to present with a larger tumor, and to undergo multidisciplinary treatment (P<0.05). For patients who used neither heavy tobacco nor alcohol, used either tobacco or alcohol, and used both, the 5-year OS rates and OS times were 57.4%, 46.4%, and 39.1% (P<0.05) and not reached, 55.2 months, and 41.2 months (P<0.05), respectively. On multivariate analysis, patients who both heavily smoked and drank had 1.392 times the risk of dying during follow-up compared with neither-users (95% CI =1.020-1.901, P=0.037).

CONCLUSION

We identified that combined heavy smoking and drinking might predict poor prognosis in ESCC patients.

Predictors of pathological complete response to neoadjuvant chemoradiotherapy for esophageal squamous cell carcinoma

BACKGROUNDS

In this study, we evaluated the factors associated with a pathologic complete response (pCR) after neoadjuvant chemoradiotherapy (nCRT) for esophageal squamous cell carcinoma (ESCC).

METHODS

Pre-nCRT parameters in ESCC patients treated between 1999 and 2006 were analyzed to identify predictors of pCR. All patients received 5-fluorouracil/cisplatin-based chemotherapy and external beam radiation followed by scheduled esophagectomy. Variables were analyzed using univariate and multivariate analyses with pCR as the dependent variable. Estimated pCR rate was calculated with a regression model.

RESULTS

Fifty-nine (20.9%) of 282 patients achieved pCR. Univariate analysis identified four patient factors (age, smoking status, drinking history and hypertension), one pre-nCRT parameter (tumor length) as significant predictors of pCR (all P <0.05). On multivariate analysis, tumor length ≤3 cm (favorable, odds ratio (OR): 4.85, P = 0.001), patient age >55 years (favorable, OR: 1.95, P = 0.035), and being a non-smoker (favorable, OR: 3.6, P = 0.003) were independent predictors of pCR. The estimated pCR rates based on a logistic regression including those three predictors were 71%, 35 to approximately 58%, 19 to approximately 38%, and 12% for patients with 3, 2, 1 and 0 predictors, respectively.

CONCLUSION

Age, smoking habit and tumor length were important pCR predictors. These factors may be used to predict outcomes for ESCC patients receiving nCRT, to develop risk-adapted treatment strategies, and to select patients who could participate in trials on new therapies.

Involvement of AtPolλ in the repair of high salt- and DNA cross-linking agent-induced double strand breaks in Arabidopsis

DNA polymerase λ (Pol λ) is the sole member of family X DNA polymerase in plants and plays a crucial role in nuclear DNA damage repair. Here, we report the transcriptional up-regulation of Arabidopsis (Arabidopsis thaliana) AtPolλ in response to abiotic and genotoxic stress, including salinity and the DNA cross-linking agent mitomycin C (MMC). The increased sensitivity of atpolλ knockout mutants toward high salinity and MMC treatments, with higher levels of accumulation of double strand breaks (DSBs) than wild-type plants and delayed repair of DSBs, has suggested the requirement of Pol λ in DSB repair in plants. AtPolλ overexpression moderately complemented the deficiency of DSB repair capacity in atpolλ mutants. Transcriptional up-regulation of major nonhomologous end joining (NHEJ) pathway genes KU80, X-RAY CROSS COMPLEMENTATION PROTEIN4 (XRCC4), and DNA Ligase4 (Lig4) along with AtPolλ in Arabidopsis seedlings, and the increased sensitivity of atpolλ-2/atxrcc4 and atpolλ-2/atlig4 double mutants toward high salinity and MMC treatments, indicated the involvement of NHEJ-mediated repair of salinity- and MMC-induced DSBs. The suppressed expression of NHEJ genes in atpolλ mutants suggested complex transcriptional regulation of NHEJ genes. Pol λ interacted directly with XRCC4 and Lig4 via its N-terminal breast cancer-associated C terminus (BRCT) domain in a yeast two-hybrid system, while increased sensitivity of BRCT-deficient Pol λ-expressing transgenic atpolλ-2 mutants toward genotoxins indicated the importance of the BRCT domain of AtPolλ in mediating the interactions for processing DSBs. Our findings provide evidence for the direct involvement of DNA Pol λ in the repair of DSBs in a plant genome.

Biological and therapeutic relevance of nonreplicative DNA polymerases to cancer

Apart from surgical approaches, the treatment of cancer remains largely underpinned by radiotherapy and pharmacological agents that cause damage to cellular DNA, which ultimately causes cancer cell death. DNA polymerases, which are involved in the repair of cellular DNA damage, are therefore potential targets for inhibitors for improving the efficacy of cancer therapy. They can be divided, according to their main function, into two groups, namely replicative and nonreplicative enzymes. At least 15 different DNA polymerases, including their homologs, have been discovered to date, which vary considerably in processivity and fidelity. Many of the nonreplicative (specialized) DNA polymerases replicate DNA in an error-prone fashion, and they have been shown to participate in multiple DNA damage repair and tolerance pathways, which are often aberrant in cancer cells. Alterations in DNA repair pathways involving DNA polymerases have been linked with cancer survival and with treatment response to radiotherapy or to classes of cytotoxic drugs routinely used for cancer treatment, particularly cisplatin, oxaliplatin, etoposide, and bleomycin. Indeed, there are extensive preclinical data to suggest that DNA polymerase inhibition may prove to be a useful approach for increasing the effectiveness of therapies in patients with cancer. Furthermore, specialized DNA polymerases warrant examination of their potential use as clinical biomarkers to select for particular cancer therapies, to individualize treatment for patients.

Heavy smoking history interacts with chemoradiotherapy for esophageal cancer prognosis: a retrospective study

Smoking is a well-known risk factor for esophageal cancer. However, there are few reports that directly evaluate smoking as a prognostic factor for esophageal cancer. Moreover, scarce evidence is available on whether smoking interacts with major treatment modalities of esophageal cancer. In this study we retrospectively analyzed 364 patients with esophageal squamous cell cancer who were treated between 2001 and 2005 at our institution. Background characteristics, including smoking history, were analyzed as potential prognostic factors. Of the 363 patients, 76 patients (20.9%) were non-smokers or light smokers (non-heavy), whereas 287 patients (79.1%) were heavy smokers. The 5-year survival rate for non-heavy smokers and heavy smokers was 61.8% (95% confidence interval [CI]: 49.1-72.2) vs 44.6% (95% CI: 38.2-50.9), respectively. In a multivariate Cox model (adjusted for age, gender, performance status, alcohol consumption, histology, tumor length, International Union Against Cancer [UICC] stage, and treatment), the hazard ratio for heavy smokers in comparison with non-heavy smokers was 1.73 (95% CI: 1.12-2.68; P = 0.013). When we stratified by treatment method, heavy smoking was significantly associated with poor survival only in patients treated by chemoradiotherapy (hazard ratio, 2.43; 95% CI: 1.38-4.27; P = 0.002). More importantly, a statistically significant interaction between heavy smoking history and treatment modality was observed (P = 0.041). Our results indicated that smoking history is strongly associated with poor prognosis in patients with esophageal cancer, especially those treated by chemoradiotherapy. Further investigation is warranted to explain this different prognosis.

Interaction between DNA Polymerase lambda and anticancer nucleoside analogs

The anticancer activity of cytarabine (AraC) and gemcitabine (dFdC) is thought to result from chain termination after incorporation into DNA. To investigate their incorporation into DNA at atomic level resolution, we present crystal structures of human DNA polymerase lambda (Pol lambda) bound to gapped DNA and containing either AraC or dFdC paired opposite template dG. These structures reveal that AraC and dFdC can bind within the nascent base pair binding pocket of Pol lambda. Although the conformation of the ribose of AraCTP is similar to that of normal dCTP, the conformation of dFdCTP is significantly different. Consistent with these structures, Pol lambda efficiently incorporates AraCTP but not dFdCTP. The data are consistent with the possibility that Pol lambda could modulate the cytotoxic effect of AraC.