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Cancer has long been a grievous disease complicated by innumerable players aggravating its cure. Many clinical studies demonstrated the prognostic relevance of the tumor suppressor protein p53 for many human tumor types. Overexpression of mutated p53 with reduced or abolished function is often connected to resistance to standard medications, including cisplatin, alkylating agents (temozolomide), anthracyclines, (doxorubicin), antimetabolites (gemcitabine), antiestrogenes (tamoxifen) and EGFR-inhibitors (cetuximab). Such mutations in the TP53 gene are often accompanied by changes in the conformation of the p53 protein. Small molecules that restore the wild-type conformation of p53 and, consequently, rebuild its proper function have been identified. These promising agents include PRIMA-1, MIRA-1, and several derivatives of the thiosemicarbazone family. In addition to mutations in p53 itself, p53 activity may be also be impaired due to alterations in p53s regulating proteins such as MDM2. MDM2 functions as primary cellular p53 inhibitor and deregulation of the MDM2/p53-balance has serious consequences. MDM2 alterations often result in its overexpression and therefore promote inhibition of p53 activity. To deal with this problem, a judicious approach is to employ MDM2 inhibitors. Several promising MDM2 inhibitors have been described such as nutlins, benzodiazepinediones or spiro-oxindoles as well as novel compound classes such as xanthone derivatives and trisubstituted aminothiophenes. Furthermore, even naturally derived inhibitor compounds such as a-mangostin, gambogic acid and siladenoserinols have been discovered. In this review, we discuss in detail such small molecules that play a pertinent role in affecting the p53-MDM2 signaling axis and analyze their potential as cancer chemotherapeutics.

Background .The pharmacology, toxicology and pharmacokinetics of bioactive preparations derived from natural sources has become a flourishing field of research. However, researching complex extracts and natural products faces numerous challenges. More broadly in recent years the critique of pharmacological research, and specifically its design, the methods used and reporting has intensified.. Aims: This consensus document provides a perspective on what constitutes best practice in pharmacological research on bioactive preparations derived from natural sources, providing a perspective of what the leading specialist journals in the field consider as the core characteristics of good research. Approach ('Methods'). The editors in chief of seven journals developed this best practice statement in an iterative process. A first draft of the guidelines (prepared by MH) was then discussed and amended by the other authors. Outcomes. Core to this contribution is a table which provides detailed advice including simple points like a use of appropriate controls and the full taxonomic validity of the material under investigation (see also below), to the relevance of the model for the question being researched (e.g. can specific in silico or in vitro models really say s.th. about the species antiinflammatory activity?). Therefore, obviously, researchers must pay detailed attention to reporting and discussing such studies. This information must be discussed critically (as much as it is possible based on the published papers) in terms of their scientific quality and validity. While these points are obvious, as editors we are aware that they are often not properly implemented. Conclusion. We call for an approach which incorporates a careful design, meticulous execution and a detailed reporting of studies focusing on the pharmacology / bioactivity of bioactive preparations. Clearly testable research questions must be developed and investigated experimentally. As the founder of pharmacology Claude Bernard put it already in 1865: '…. either the experimenter's hypothesis will be disproved or it will be proved by experiment. When experiment disproves its preconceived ideas, the experimenter must discard or modify it.'

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