Aryl-7-deazapurine nucleosides possess interesting cytotoxic and antiparasitic activities. This review summarizes synthetic approaches to introduction of aryl group to the nucleobase of 7-deazapurine nucleosides. Biological activities of 7-deazapurine nucleosides, their mode of action and structure-activity relationships are discussed. The most promising compounds with cytotoxic activities against cancer cells are 6-hetaryl-7-deazapurine ribonucleosides substituted with a 5-membered heterocycle and 7‑hetaryl-7-deazaadenosines with the same substituents. A new complex mode of action was described for 7‑(2‑thienyl)-7-deazaadenosine (AB61). Significant antitrypanosomal activities both in vitro and in vivo were discovered among 7-phenyl-7-deazaadenine nucleosides. 6‑Hetaryl-7-deazapurine ribonucleosides with bulky heterocyclic substituents in position 6 strongly and selectively inhibit mycobacterial adenosine kinase. Due to their diverse application possibilities and relatively easy synthesis, aryl-7-deazapurine nucleosides represent a source of interesting new compounds for further research by medicinal chemists.
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G-quadruplexes belong to noncanonical secondary structures of the nucleic acids commonly referred to as non-B DNA. In recent years there is growing evidence about the existence of G-quadruplex structures in vivo and their important regulatory roles in biological processes. This mini-review brings up the latest results on the transcriptional regulation by G-quadruplexes. On one hand G-quadruplexes might inhibit general expression potential of the genes as a part of a basal transcription activity, which is not specific to any genes or pathways. On the other hand, G-quadruplexes might dynamically monitor the activity of a gene together with other secondary structures localized predominantly in regulatory regions such as promoters, transcription start sites and transcription termination sites. Last but not least, it has been shown that G-quadruplexes serve as sensors of oxidative stress and subsequently modulate the transcription. The inhibitory or stimulatory effect of the G-quadruplexes on a gene transcription depends on its position on the template or coding strand.
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Tumor markers known also as cancer or oncological markers are substances produced either by tumor or normal cells as a response to the presence of cancer . The markers are used for the detection, diagnosis, prognosis and control of treatment. There is no absolutely specific or universal cancer marker; therefore different markers for different cancer types are used in clinical practice. A problematic feature of cancer markers is their falsely positive results under physiological and non-cancer conditions.
