Search

Type II topoisomerases transiently cleave duplex DNA as part of a strand passage mechanism that helps control chromosomal organization and superstructure. Aberrant DNA cleavage can result in genomic instability, and how topoisomerase activity is controlled to prevent unwanted breaks is poorly understood. Using a genetic screen, we identified mutations in the beta isoform of human topoisomerase II (hTOP2β) that render the enzyme hypersensitive to the chemotherapeutic agent etoposide. Several of these variants were unexpectedly found to display hypercleavage behavior in vitro and to be capable of inducing cell lethality in a DNA repair–deficient background; surprisingly, a subset of these mutations were also observed in TOP2B sequences from cancer genome databases. Using molecular dynamics simulations and computational network analyses, we found that many of the mutations obtained from the screen map to interfacial points between structurally coupled elements, and that dynamical modeling could be used to identify other damage-inducing TOP2B alleles present in cancer genome databases. This work establishes that there is an innate link between DNA cleavage predisposition and sensitivity to topoisomerase II poisons, and that certain sequence variants of human type II topoisomerases found in cancer cells can act as DNA-damaging agents. Our findings underscore the potential for hTOP2β to function as a clastogen capable of generating DNA damage that may promote or support cellular transformation.

PURPOSE: Novel targeted therapeutics have transformed the care of subsets of patients with cancer. In pediatric malignancies, however, with simple tumor genomes and infrequent targetable mutations, there have been few new FDA-approved targeted drugs. The cyclin-dependent kinase (CDK)4/6 pathway recently emerged as a dependency in Ewing sarcoma. Given the heightened efficacy of this class with targeted drug combinations in other cancers, as well as the propensity of resistance to emerge with single agents, we aimed to identify genes mediating resistance to CDK4/6 inhibitors and biologically relevant combinations for use with CDK4/6 inhibitors in Ewing. EXPERIMENTAL DESIGN: We performed a genome-scale open reading frame (ORF) screen in 2 Ewing cell lines sensitive to CDK4/6 inhibitors to identify genes conferring resistance. Concurrently, we established resistance to a CDK4/6 inhibitor in a Ewing cell line. RESULTS: The ORF screen revealed IGF1R as a gene whose overexpression promoted drug escape. We also found elevated levels of phospho-IGF1R in our resistant Ewing cell line, supporting the relevance of IGF1R signaling to acquired resistance. In a small-molecule screen, an IGF1R inhibitor scored as synergistic with CDK4/6 inhibitor treatment. The combination of CDK4/6 inhibitors and IGF1R inhibitors was synergistic in vitro and active in mouse models. Mechanistically, this combination more profoundly repressed cell cycle and PI3K/mTOR signaling than either single drug perturbation. CONCLUSIONS: Taken together, these results suggest that IGF1R inhibitors activation is an escape mechanism to CDK4/6 inhibitors in Ewing sarcoma and that dual targeting of CDK4/6 inhibitors and IGF1R inhibitors provides a candidate synergistic combination for clinical application in this disease.

Copyright © 2018 American Chemical Society. Natural products and their derivatives continue to be wellsprings of nascent therapeutic potential. However, many laboratories have limited resources for biological evaluation, leaving their previously isolated or synthesized compounds largely or completely untested. To address this issue, the Canvass library of natural products was assembled, in collaboration with academic and industry researchers, for quantitative high-throughput screening (qHTS) across a diverse set of cell-based and biochemical assays. Characterization of the library in terms of physicochemical properties, structural diversity, and similarity to compounds in publicly available libraries indicates that the Canvass library contains many structural elements in common with approved drugs. The assay data generated were analyzed using a variety of quality control metrics, and the resultant assay profiles were explored using statistical methods, such as clustering and compound promiscuity analyses. Individual compounds were then sorted by structural class and activity profiles. Differential behavior based on these classifications, as well as noteworthy activities, are outlined herein. One such highlight is the activity of (-)-2(S)-cathafoline, which was found to stabilize calcium levels in the endoplasmic reticulum. The workflow described here illustrates a pilot effort to broadly survey the biological potential of natural products by utilizing the power of automation and high-throughput screening. ©

This corrects the article DOI: 10.1038/nrd.2018.14.

The synergistic effect of oxygen, light, and photosensitizer (PS) has found applications in medicine for the treatment of cancer through photodynamic therapy (PDT). Induction of apoptosis to cancerous cells will prevent tumor metastasis that spreads cancer cells to the neighboring organs/tissues. Herein, we report the two apoptotic Ru(II)–polypyridyl complexes that are functionalized with pendant amino acid moieties tyrosine (1) and tryptophan (2), respectively. These two water soluble complexes were found to interact strongly (K1a = (1.18 ± 0.28) × 105 M−1 and K2a = (1.57 ± 0.77) × 105 M−1) with CT-DNA. Isothermal titration calorimetry (ITC) studies revealed that these complexes bind to CT-DNA through an entropically driven process. Both the complexes showed photo-induced cytotoxicity and exhibit apoptotic activity under photo-irradiation conditions. The comet assay indicated that these complexes can damage cellular DNA, which is attributed to the significant build-up of 1O2 level even on irradiation with low intensity light (10 J cm−2, λRange 450–480 nm). This photoinduced DNA damage and apoptosis in A549 cells was induced by reactive oxygen species (ROS) and occurred through up-regulation of apoptotic marker caspase-3. Control experiments under dark conditions revealed an insignificant cytotoxicity towards these cells for two photosensitive molecules.\ud \ud

New-onset refractory status epilepticus (NORSE) is a rare but challenging condition occurring in a previously healthy patient, often with no identifiable cause. We describe the electro-clinical features and outcomes in a group of patients with NORSE who all demonstrated a typical magnetic resonance imaging (MRI) sign characterized by bilateral lesions of the claustrum. The group includes 31 patients (12 personal and 19 previously published cases; 17 females; mean age of 25 years). Fever preceded status epilepticus (SE) in 28 patients, by a mean of 6 days. SE was refractory/super-refractory in 74% of the patients, requiring third-line agents and a median of 15 days staying in an intensive care unit. Focal motor and tonic-clonic seizures were observed in 90%, complex partial seizures in 14%, and myoclonic seizures in 14% of the cases. All patients showed T2/FLAIR hyperintense foci in bilateral claustrum, appearing on average 10 days after SE onset. Other limbic (hippocampus, insular) alterations were present in 53% of patients. Within the personal cases,extensive search for known autoantibodies was inconclusive, though 7 of 11 patients had cerebrospinal fluid lymphocytic pleocytosis and 3 cases had oligoclonal bands. Two subjects died during the acute phase, one in the chronic phase (probable sudden unexplained death in epilepsy), and one developed a persistent vegetative state. Among survivors, 80% developed drug-resistant epilepsy. Febrile illness-related SE associated with bilateral claustrum hyperintensity on MRI represents a condition with defined clinical features and a presumed but unidentified autoimmune etiology. A better characterization of de novo SE is mandatory for the search of specific etiologies. © 2017 Meletti, Giovannini, d'Orsi, Toran, Monti, Guha, Kiryttopoulos, Pascarella, Martino, Alexopoulos, Spilioti and Slonkova.

Receiving the same fractional recovery of par at default for bonds of the same issuer and seniority, regardless of remaining maturity, has been labelled in the academic literature as a Recovery of Face Value at Default (RFV).Such a recovery form results from language found in typical bond indentures and is supported by empirical evidence from defaulted bond values.We incorporate RFV into an exogenous boundary structural credit risk model and compare its e ect to more typical recovery forms found in such models.We find that the chosen recovery form can significantly a ect valuation and the sensitivities produced by these models, thus having important implications for empirical studies attempting to validate structural credit risk models.We show that some features of existing structural models are a result of the recovery form assumed in the model and do not necessarily hold under an RFV recovery form.Some of our results complement those found in the literature which examines the endogeneity of the default boundary.We find that some features that may have been solely attributed to modelling the boundary as an optimal decision by the firm can be obtained in an exogenous boundary framework with RFV.This has direct implications for studies which attempt to determine whether endogenous or exogenous models are better supported empirically.We extend our results to incorporate a multifactor default-free term structure model and examine the impact of the recovery form in estimating the cost of debt capital within a structural model framework.