Susanne M. Arnold

The intramitochondrial ATP/ADP-ratio controls cytochrome c oxidase activity allosterically1

Recently the signal transduction function for oxidative phosphorylation was found to be second order in ADP [Jeneson, J.A.L., Wiseman, R.W., Westerhoff, H.V. and Kushmerick, M.J. (1996) J. Biol. Chem. 271, 27995–27998], but the molecular mechanism of signal transduction remained unclear. Previously we described inhibition of cytochrome c oxidase by intramitochondrial ATP, accompanied by a change of hyperbolic into sigmoidal kinetics. The present study describes a sigmoidal relationship also between the ascorbate respiration of reconstituted cytochrome c oxidase and intraliposomal ADP concentration. Its possible role in the control of oxidative phosphorylation and cell respiration is discussed.

Obesity, metabolic factors and risk of different histological types of lung cancer: A Mendelian randomization study.

Background Assessing the relationship between lung cancer and metabolic conditions is challenging because of the confounding effect of tobacco. Mendelian randomization (MR), or the use of genetic instrumental variables to assess causality, may help to identify the metabolic drivers of lung cancer. Methods and findings We identified genetic instruments for potential metabolic risk factors and evaluated these in relation to risk using 29,266 lung cancer cases (including 11,273 adenocarcinomas, 7,426 squamous cell and 2,664 small cell cases) and 56,450 controls. The MR risk analysis suggested a causal effect of body mass index (BMI) on lung cancer risk for two of the three major histological subtypes, with evidence of a risk increase for squamous cell carcinoma (odds ratio (OR) [95% confidence interval (CI)] = 1.20 [1.01–1.43] and for small cell lung cancer (OR [95%CI] = 1.52 [1.15–2.00]) for each standard deviation (SD) increase in BMI [4.6 kg/m2]), but not for adenocarcinoma (OR [95%CI] = 0.93 [0.79–1.08]) (Pheterogeneity = 4.3x10-3). Additional analysis using a genetic instrument for BMI showed that each SD increase in BMI increased cigarette consumption by 1.27 cigarettes per day (P = 2.1x10-3), providing novel evidence that a genetic susceptibility to obesity influences smoking patterns. There was also evidence that low-density lipoprotein cholesterol was inversely associated with lung cancer overall risk (OR [95%CI] = 0.90 [0.84–0.97] per SD of 38 mg/dl), while fasting insulin was positively associated (OR [95%CI] = 1.63 [1.25–2.13] per SD of 44.4 pmol/l). Sensitivity analyses including a weighted-median approach and MR-Egger test did not detect other pleiotropic effects biasing the main results. Conclusions Our results are consistent with a causal role of fasting insulin and low-density lipoprotein cholesterol in lung cancer etiology, as well as for BMI in squamous cell and small cell carcinoma. The latter relation may be mediated by a previously unrecognized effect of obesity on smoking behavior.

New control of mitochondrial membrane potential and ROS formation--a hypothesis.

Abstract A new control of mitochondrial membrane potential ΔΨm and formation of reactive oxygen species (ROS) is presented, based on allosteric ATPinhibition of cytochrome c oxidase at high intramitochondrial ATP/ADP ratios. Since the rate of ATP synthesis by the ATP synthase is already maximal at low membrane potentials (100 120 mV), the ATP/ADP ratio will also be maximal at this ΔΨm (at constant rate of ATP consumption). Therefore the control of respiration by the ATP/ADPratio keeps ΔΨm low. In contrast, the known respiratory control leads to an inhibition of respiration only at high ΔΨm values (150 200 mV) which cause ROS formation. ATPinhibition of cytochrome c oxidase is switched on and off by reversible phosphorylation (via cAMP and calcium, respectively). We propose that stress hormones which increase intracellular [Ca 2+ ] also increase ΔΨm and ROS formation, which promote degenerative diseases and accelerate aging.

DIAGNOSIS AND MANAGEMENT OF BRAIN METASTASES

In the past 15 years, significant advancement has been made in the diagnosis and treatment of brain metastases. The distinction between the management of single and multiple brain metastases is an important one. Although radiotherapy remains a mainstay of treatment, especially in multiple brain metastases, surgical resection and stereotactic radiosurgery also have their place in the management of selected patients. Rarely, interstitial radiation or chemotherapy also may be used to treat brain metastases in the setting of relapse.

Human rRNA Gene Clusters Are Recombinational Hotspots in Cancer

The gene that produces the precursor RNA transcript to the three largest structural rRNA molecules (rDNA) is present in multiple copies and organized into gene clusters. The 10 human rDNA clusters represent <0.5% of the diploid human genome but are critically important for cellular viability. Individual genes within rDNA clusters possess very high levels of sequence identity with respect to each other and are present in high local concentration, making them ideal substrates for genomic rearrangement driven by dysregulated homologous recombination. We recently developed a sensitive physical assay capable of detecting recombination-mediated genomic restructuring in the rDNA by monitoring changes in lengths of the individual clusters. To prove that this dysregulated recombination is a potential driving force of genomic instability in human cancer, we assayed the rDNA for structural rearrangements in prospectively recruited adult patients with either lung or colorectal cancer, and pediatric patients with leukemia. We find that over half of the adult solid tumors show detectable rDNA rearrangements relative to either surrounding nontumor tissue or normal peripheral blood. In contrast, we find a greatly reduced frequency of rDNA alterations in pediatric leukemia. This finding makes rDNA restructuring one of the most common chromosomal alterations in adult solid tumors, illustrates the dynamic plasticity of the human genome, and may prove to have either prognostic or predictive value in disease progression.

The Assembly Pathway of Mitochondrial Respiratory Chain Complex I.

Mitochondrial complex I is the largest integral membrane enzyme of the respiratory chain and consists of 44 different subunits encoded in the mitochondrial and nuclear genome. Its biosynthesis is a highly complicated and multifaceted process involving at least 14 additional assembly factors. How these subunits assemble into a functional complex I and where the assembly factors come into play is largely unknown. Here, we applied a dynamic complexome profiling approach to elucidate the assembly of human mitochondrial complex I and its further incorporation into respiratory chain supercomplexes. We delineate the stepwise incorporation of all but one subunit into a series of distinct assembly intermediates and their association with known and putative assembly factors, which had not been implicated in this process before. The resulting detailed and comprehensive model of complex I assembly is fully consistent with recent structural data and the remarkable modular architecture of this multiprotein complex.

Stereotactic Body Radiation Therapy Can Be Used Safely to Boost Residual Disease in Locally Advanced Non-Small Cell Lung Cancer: A Prospective Study

PURPOSE To report the results of a prospective, single-institution study evaluating the feasibility of conventional chemoradiation (CRT) followed by stereotactic body radiation therapy (SBRT) as a means of dose escalation for patients with stage II-III non-small cell lung cancer (NSCLC) with residual disease. METHODS AND MATERIALS Patients without metastatic disease and with radiologic evidence of limited residual disease (≤5 cm) within the site of the primary tumor and good or complete nodal responses after standard CRT to a target dose of 60 Gy were considered eligible. The SBRT boost was done to achieve a total combined dose biological equivalent dose >100 Gy to the residual primary tumor, consisting of 10 Gy × 2 fractions (20 Gy total) for peripheral tumors, and 6.5 Gy × 3 fractions (19.5 Gy total) for medial tumors using the Radiation Therapy Oncology Group protocol 0813 definitions. The primary endpoint was the development of grade ≥3 radiation pneumonitis (RP). RESULTS After a median follow-up of 13 months, 4 patients developed acute grade 3 RP, and 1 (2.9%) developed late and persistent grade 3 RP. No patients developed grade 4 or 5 RP. Mean lung dose, V2.5, V5, V10, and V20 values were calculated for the SBRT boost, and none were found to significantly predict for RP. Only advancing age (P=.0147), previous smoking status (P=.0505), and high CRT mean lung dose (P=.0295) were significantly associated with RP development. At the time of analysis, the actuarial local control rate at the primary tumor site was 82.9%, with only 6 patients demonstrating recurrence. CONCLUSIONS Linear accelerator-based SBRT for dose escalation of limited residual NSCLC after definitive CRT was feasible and did not increase the risk for toxicity above that for standard radiation therapy.

Accuracy of self-reported tobacco assessments in a head and neck cancer treatment population.

Prospective analysis was performed of self-reported and biochemically confirmed tobacco use in 50 head and neck cancer patients during treatment. With 93.5% compliance to complete weekly self-report and biochemical confirmatory tests, 29.4% of smokers required biochemical assessment for identification. Accuracy increased by 14.9% with weekly vs. baseline self-reported assessments. Data confirm that head and neck cancer patients misrepresent true tobacco use during treatment.

Reactive oxygen species mediate arsenic induced cell transformation and tumorigenesis through Wnt/β-catenin pathway in human colorectal adenocarcinoma DLD1 cells

Long term exposure to arsenic can increase incidence of human cancers, such as skin, lung, and colon rectum. The mechanism of arsenic induced carcinogenesis is still unclear. It is generally believed that reactive oxygen species (ROS) may play an important role in this process. In the present study, we investigate the possible linkage between ROS, β-catenin and arsenic induced transformation and tumorigenesis in human colorectal adenocarcinoma cell line, DLD1 cells. Our results show that arsenic was able to activate p47(phox) and p67(phox), two key proteins for activation of NADPH oxidase. Arsenic was also able to generate ROS in DLD1 cells. Arsenic increased β-catenin expression level and its promoter activity. ROS played a major role in arsenic-induced β-catenin activation. Treatment of DLD1 cells by arsenic enhanced both transformation and tumorigenesis of these cells. The tumor volumes of arsenic treated group were much larger than those without arsenic treatment. Addition of either superoxide dismutase (SOD) or catalase reduced arsenic induced cell transformation and tumor formation. The results indicate that ROS are involved in arsenic induced cell transformation and tumor formation possible through Wnt/β-catenin pathway in human colorectal adenocarcinoma cell line DLD1 cells.

Low dose fractionated radiation potentiates the effects of taxotere in nude mice xenografts of squamous cell carcinoma of head and neck

This study evaluated the combined effect of Low Dose Fractionated Radiation (LDFRT) and Taxotere (TXT) therapy on the growth of SCCHN (squamous cell carcinoma of head and neck; SQ-20B, a p53 mutant SCCHN cell line) tumors in a nude mouse model to exploit the increased hyper radiation sensitivity (HRS) phenomenon present in G2M cell cycle phase when induced by low doses of radiation that was demonstrated in in-vitro settings. Seventy-eight animals were randomized into one control group and 5 treatment groups (treatments were administered weekly for six weeks). Tumor regression was observed in all the groups, however, tumor regression was not significant in 2 Gy or TXT or 2 Gy plus TXT treated groups when compared to control group. The tumor regression was significant in both the LDFRT group (p