"Lethal Mutations" a Misnomer or the Start of a Scientific Revolution?

The aim of this paper is to review the history surrounding the discovery of lethal mutations, later described as delayed reproductive death. Lethal mutations were suggested very early on, to be due to a generalised instability in a cell population and are considered now to be one of the first demonstrations of "radiation-induced genomic instability" which led later to the establishment of the field of "non-targeted effects." The phenomenon was first described by Seymour et al. in 1986 and was confirmed by Trott's group in Europe and by Little and colleagues in the United States before being extended by Mendonca et al. in 1989, who showed conclusively that the distinguishing feature of lethal mutation occurrence was that it happened suddenly after about 9-10 population doublings in progeny which had survived the original dose of ionizing radiation. However, many authors then suggested that in fact, lethal mutations were implicit in the original experiments by Puck and Marcus in 1956 and were described in the extensive work by Sinclair in 1964, who followed clonal progeny for up to a year after irradiation and described "small colony formation" as a persistent consequence of ionizing radiation exposure. In this paper, we examine the history from 1956 to the present using the period from 1986-1989 as an anchor point to reach into the past and to go forward through the evolution of the field of low dose radiobiology where non-targeted effects predominate.

Isolated Clones of a Human Colorectal Carcinoma Cell Line Display Variation in Radiosensitivity Following Gamma Irradiation.

Objective: To determine whether the width of the shoulder and the size of the bystander effect are correlated using clonal lineages derived from a cultured cell line. Methods: HCT 116 (p53 wildtype) cells were grown at cloning density and individual viable colonies were picked off and grown to establish a series of cell lines from both unirradiated and irradiated progenitors. These cell lines were then irradiated to generate full survival curves. Highly variant clones were then tested to determine the level of the bystander effect using a medium transfer protocol. Results: The multi-target model gave the best fit in these experiments and size of the shoulder n is assessed in terms of radiosensitivity. The parent cell line has an n value of 1.1 while the most variant clones have n values of 0.88 (Clone G) and 5.5 (Clone A). Clonal lines subject to irradiation prior to isolation differed in bystander signal strength in comparison to clonal lines which were not initially irradiated (P = .055). Conclusions: Based on these experiments we suggest there may be a link between shoulder size of a mammalian cell line and the strength of a bystander effect produced in vitro. This may have implications for radiotherapy related to out-of-field effects.

Dissecting the Genetic and Non-Genetic Heterogeneity of Acute Myeloid Leukemia Using Next-Generation Sequencing and In Vivo Models.

Acute myeloid leukemia (AML) is an extremely aggressive and heterogeneous disorder that results from the transformation of hematopoietic stem cells. Although our understanding of the molecular pathology of AML has greatly improved in the last few decades, the overall and relapse free survival rates among AML patients remain quite poor. This is largely due to evolution of the disease and selection of the fittest, treatment-resistant leukemic clones. There is increasing evidence that most AMLs possess a highly complex clonal architecture and individual leukemias are comprised of genetically, phenotypically and epigenetically distinct clones, which are continually evolving. Advances in sequencing technologies as well as studies using murine AML models have provided further insights into the heterogeneity of leukemias. We will review recent advances in the field of genetic and non-genetic heterogeneity in AML.

N-acetylcysteine (NAC) ameliorates Epstein-Barr virus latent membrane protein 1 induced chronic inflammation.

Chronic inflammation results when the immune system responds to trauma, injury or infection and the response is not resolved. It can lead to tissue damage and dysfunction and in some cases predispose to cancer. Some viruses (including Epstein-Barr virus (EBV)) can induce inflammation, which may persist even after the infection has been controlled or cleared. The damage caused by inflammation, can itself act to perpetuate the inflammatory response. The latent membrane protein 1 (LMP1) of EBV is a pro-inflammatory factor and in the skin of transgenic mice causes a phenotype of hyperplasia with chronic inflammation of increasing severity, which can progress to pre-malignant and malignant lesions. LMP1 signalling leads to persistent deregulated expression of multiple proteins throughout the mouse life span, including TGFα S100A9 and chitinase-like proteins. Additionally, as the inflammation increases, numerous chemokines and cytokines are produced which promulgate the inflammation. Deposition of IgM, IgG, IgA and IgE and complement activation form part of this process and through genetic deletion of CD40, we show that this contributes to the more tissue-destructive aspects of the phenotype. Treatment of the mice with N-acetylcysteine (NAC), an antioxidant which feeds into the body's natural redox regulatory system through glutathione synthesis, resulted in a significantly reduced leukocyte infiltrate in the inflamed tissue, amelioration of the pathological features and delay in the inflammatory signature measured by in vivo imaging. Reducing the degree of inflammation achieved through NAC treatment, had the knock on effect of reducing leukocyte recruitment to the inflamed site, thereby slowing the progression of the pathology. These data support the idea that NAC could be considered as a treatment to alleviate chronic inflammatory pathologies, including post-viral disease. Additionally, the model described can be used to effectively monitor and accurately measure therapies for chronic inflammation.