Synthetic lethality in DNA repair network: A novel avenue in targeted cancer therapy and combination therapeutics

Targeted Therapies in Type II Endometrial Cancers: Too Little, but Not Too Late

Type II endometrial carcinomas (ECs) are responsible for most endometrial cancer-related deaths due to their aggressive nature, late stage detection and high tolerance for standard therapies. However, there are no targeted therapies for type II ECs, and they are still treated the same way as the clinically indolent and easily treatable type I ECs. Therefore, type II ECs are in need of new treatment options. More recently, molecular analysis of endometrial cancer revealed phosphorylation-dependent oncogenic signalling in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways to be most frequently altered in type II ECs. Consequently, clinical trials tested pharmacologic kinase inhibitors targeting these pathways, although mostly with rather disappointing results. In this review, we highlight the most common genetic alterations in type II ECs. Additionally, we reason why most clinical trials for ECs using targeted kinase inhibitors had unsatisfying results and what should be changed in future clinical trial setups. Furthermore, we argue that, besides kinases, phosphatases should no longer be ignored in clinical trials, particularly in type II ECs, where the tumour suppressive phosphatase protein phosphatase type 2A (PP2A) is frequently mutated. Lastly, we discuss the therapeutic potential of targeting PP2A for (re)activation, possibly in combination with pharmacologic kinase inhibitors.

Cancer Risks Linked to the Bad Luck Hypothesis and Epigenomic Mutational Signatures

Exposure to pathogen infection, and occupational and environmental agents, contributes to induction of most types of cancer through different mechanisms. Cancer is defined and characterized by accumulation of mutations and epimutations that lead to changes in the cellular genome and epigenome. According to a recent Bad Luck Hypothesis, random error mutations during DNA replication in a small population of stem cells may be implicated in two-thirds of variation of cancer risk in 25 organs and tissues. What determines stem cell vulnerability and risk of malignancy across the spectrum of organs, such as the brain, bone marrow, skeletal muscles, skin, and liver? Have stem cells pooled in particular tissues or organs evolved some critical ability to deal with DNA damage in the presence of extrinsic environmental factors? This paper describes how the complex replication and repair DNA systems control mutational events. In addition, recent advances on cancer epigenomic signatures and epigenetic mechanisms are discussed, which will guide future investigation of the origin of cancer initiating cells in tissue and organs in a clinical setting.

Pigments from Filamentous Ascomycetes for Combination Therapy

Filamentous ascomycetes (Neurospora and Monascus) have been studied for a long time because of their production of secondary metabolites such as microbial pigments. The ascomycetes represent an interesting group of compounds with high potential for medicinal applications. Many recent studies have shown their efficacy in the treatment of serious pathological states such as oncological diseases, neurodegenerative diseases and hyperlipidaemia. Nevertheless, the clinical usability of ascomycetes is still limited. However, this problem can be solved by the use of these compounds with combinations of other therapeutic agents. This strategy can suppress their side effects and improve their therapeutic efficacy. Moreover, their co-application can significantly enhance conventional therapies that are used. This review summarizes and discusses the general principles of this approach, introduced and supported by numerous examples. In addition, the prediction of the future potential application of this methodology is included.

Immunological Approaches Towards Cancer and Inflammation: A Cross Talk

The inflammation is the protective response of the body against various harmful stimuli; however, the aberrant and inappropriate activation tends to become harmful. The acute inflammatory response tends to resolved once the offending agent is subside but this acute response becomes chronic in nature when the body is unable to successfully neutralized the noxious stimuli. This chronic inflammatory microenvironment is associated with the release of various pro-inflammatory and oncogenic mediators such as nitric oxide (NO), cytokines [IL-1β, IL-2, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)], growth factor, and chemokines. These mediators make the inflammatory microenvironment more vulnerable toward tumorigenesis. The pro-inflammatory mediators released during the chronic inflammation tends to induce several molecular signaling cascades such as nuclear factor kappa B, MAPKinase, nuclear factor erythroid 2-related factor 2, phosphoinositide-3-kinase, Janus kinases/STAT, Wnt/B-catenin, and cyclic AMP response element binding protein. The immune system and its components have a pleiotropic effect on inflammation and cancer progression. Immune components such as T cells, natural killer cells, macrophages, and neutrophils either inhibit or enhance tumor initiation depending on the type of tumor and immune cells involved. Tumor-associated macrophages and tumor-associated neutrophils are pro-tumorigenic cells highly prevalent in inflammation-mediated tumors. Similarly, presence of T regulatory (Treg) cells in an inflammatory and tumor setting suppresses the immune system, thus paving the way for oncogenesis. However, Treg cells also inhibit autoimmune inflammation. By contrast, cytotoxic T cells and T helper cells confer antitumor immunity and are associated with better prognosis in patients with cancer. Cytotoxic T cells inflict a direct cytotoxic effect on cells expressing oncogenic markers. Currently, several anti-inflammatory and antitumor therapies are under trials in which these immune cells are exploited. Adoptive cell transfer composed of tumor-infiltrating lymphocytes has been tried for the treatment of tumors after their ex vivo expansion. Mediators released by cells in a tumorigenic and inflammatory microenvironment cross talk with nearby cells, either promoting or inhibiting inflammation and cancer. Recently, several cytokine-based therapies are either being developed or are under trial to treat such types of manifestations. Monoclonal antibodies directed against TNF-α, VEGF, and IL-6 has shown promising results to ameliorate inflammation and cancer, while direct administration of IL-2 has been shown to cause tumor regression.

A highlight on Sonic hedgehog pathway

Hedgehog (Hh) signaling pathway plays an essential role during vertebrate embryonic development and tumorigenesis. It is already known that Sonic hedgehog (Shh) pathway is important for the evolution of radio and chemo-resistance of several types of tumors. Most of the brain tumors are resistant to chemotherapeutic drugs, consequently, they have a poor prognosis. So, a better knowledge of the Shh pathway opens an opportunity for targeted therapies against brain tumors considering a multi-factorial molecular overview. Therefore, emerging studies are being conducted in order to find new inhibitors for Shh signaling pathway, which could be safely used in clinical trials. Shh can signal through a canonical and non-canonical way, and it also has important points of interaction with other pathways during brain tumorigenesis. So, a better knowledge of Shh signaling pathway opens an avenue of possibilities for the treatment of not only for brain tumors but also for other types of cancers. In this review, we will also highlight some clinical trials that use the Shh pathway as a target for treating brain cancer.

The promising PARP inhibitors in ovarian cancer therapy: From Olaparib to others

Epithelial ovarian cancer (EOC) accounts for 90% of all ovarian cancer. Initially, approaching 80% of EOC patients respond to standard therapeutic strategy, cytoreduction combining with postoperative auxiliary platinum-based chemotherapy. However, relapse is approximately inevitable because of drug-resistance for high-grade serous ovarian cancer (HGSOC). Recently, the nuclear enzyme poly (ADP-ribose) polymerase (PARP) represents a strikingly novel target in EOC treatment. PARP inhibitors, currently mainly including Olaparib, Niraparib, Velaparib, Rucaparib, and Talazoparib, have demonstrated promising activity in EOC treatment. Especially, studies of Olaparib accelerated it to be approved in Europe and USA. Here, this review focuses on the pre-clinical data, current clinical trials, the development of PARP inhibitors in the last decade and their future roles in clinical treatment for EOC patients.

Localization Microscopy Analyses of MRE11 Clusters in 3D-Conserved Cell Nuclei of Different Cell Lines

In radiation biophysics, it is a subject of nowadays research to investigate DNA strand break repair in detail after damage induction by ionizing radiation. It is a subject of debate as to what makes up the cell’s decision to use a certain repair pathway and how the repair machinery recruited in repair foci is spatially and temporarily organized. Single-molecule localization microscopy (SMLM) allows super-resolution analysis by precise localization of single fluorescent molecule tags, resulting in nuclear structure analysis with a spatial resolution in the 10 nm regime. Here, we used SMLM to study MRE11 foci. MRE11 is one of three proteins involved in the MRN-complex (MRE11-RAD50-NBS1 complex), a prominent DNA strand resection and broken end bridging component involved in homologous recombination repair (HRR) and alternative non-homologous end joining (a-NHEJ). We analyzed the spatial arrangements of antibody-labelled MRE11 proteins in the nuclei of a breast cancer and a skin fibroblast cell line along a time-course of repair (up to 48 h) after irradiation with a dose of 2 Gy. Different kinetics for cluster formation and relaxation were determined. Changes in the internal nano-scaled structure of the clusters were quantified and compared between the two cell types. The results indicate a cell type-dependent DNA damage response concerning MRE11 recruitment and cluster formation. The MRE11 data were compared to H2AX phosphorylation detected by γH2AX molecule distribution. These data suggested modulations of MRE11 signal frequencies that were not directly correlated to DNA damage induction. The application of SMLM in radiation biophysics offers new possibilities to investigate spatial foci organization after DNA damaging and during subsequent repair.