Current Medicinal Chemistry - Volume 22, Issue 35, 2015

The hedgehog (Hh) pathway is a developmental signaling pathway that is essential to the proper embryonic development of many vertebrate systems. Dysregulation of Hh signaling has been implicated as a causative factor in the development and progression of several forms of human cancer. As such, the development of small molecule inhibitors of Hh signaling as potential anti-cancer chemotherapeutics has been a major area of research interest in both academics and industry over the past ten years. Through these efforts, synthetic small molecules that target multiple components of the Hh pathway have been identified and advanced to preclinical or clinical development. The goal of this review is to provide an update on the current status of several synthetic small molecule Hh pathway inhibitors and explore the potential of several recently disclosed inhibitory scaffolds.

Natural products drug discovery has allowed the identification of many biologically active compounds from plants, microbial species, and marine organisms. A significant number of these compounds are currently used as drugs in therapeutic protocols, while other naturally occurring chemical entities gave suggestions for designing nonnatural-productderived drugs or have been modified in their structure to have semi-synthetic analogues. In the last decade, experimental evidence that correlated the aberrant activation of the Hedgehog (Hh) signaling pathway with many types of cancer, prompted the researchers to check natural compounds for their ability to modulate this signaling cascade. As a result, many compounds from natural sources showed inhibitory activity toward one or more of the Hh signaling pathway components, such as Smoothened (Smo) and the downstream effectors Gli. On the other hand, only a few natural compounds were able to stimulate the same pathway. This review reports a survey of the compounds extracted from natural sources (especially plants) that showed activity in inhibiting the Hh signaling machinery by interfering with its components.

Cell-to-cell signaling molecules such as the Wnt proteins that directly influence the expression of cell-type specific transcriptional programs are essential for tissue generation in metazoans. The mechanisms supporting cellular responses to these molecules represent potential points of intervention for directing cell fate outcomes in therapeutic contexts. Small molecules that modulate Wnt-mediated cellular responses have proven to be powerful probes for Wnt protein function in diverse biological settings including cancer, development, and regeneration. Whereas efforts to develop these chemicals as therapeutic agents have dominated conversation, the unprecedented modes-of-action associated with these molecules and their implications for drug development deserve greater examination. In this review, we will discuss how medicinal chemistry efforts focused on first in class small molecules targeting two Wnt pathway components – the polytopic Porcupine (Porcn) acyltransferase and the cytoplasmic Tankyrase (Tnks) poly-ADP-ribosylases – have contributed to our understanding of the druggable genome and expanded the armamentarium of chemicals that can be used to influence cell fate decision-making.

The Hippo signaling pathway is critical in regulating tissue homeostasis, organ size, and tumorigenesis. YAP and TAZ, two major effectors of the Hippo pathway, function as transcriptional co-activators and promote target gene expression mainly through interaction with TEAD family transcription factors. As oncoproteins, YAP and TAZ are frequently activated or highly expressed in various cancer specimens. Moreover, their activity has been linked to resistance to a few widely used anti-cancer drugs, and YAP activation contributes to cancer relapse. Thus, the Hippo pathway, especially YAP/TAZ-TEAD interaction, represents an attractive target for anti-cancer therapies. Here, we will discuss potential approaches to inhibit YAP/TAZ activity, and also review currently available small molecules targeting the Hippo pathway.

A key barrier to the development of gene therapy remains the lack of safe, efficient and easily controllable vehicles for gene delivery. The fundamental problems associated with the viral vehicles, e.g. lack of specificity and immunogenic potential, have driven the development of non-viral systems of gene delivery. In the last decade, studies on p53 gene replacement therapy have dominated the literature. Although clinical trials of p53 gene therapy have achieved limited success, it remains the only tumor suppressor gene to be evaluated formally in clinical trials for cancer treatment, with increasing focus on delivery using non-viral systems. In this article, we particularly review current investigations on p53 gene delivery using non-viral methods, including both physical and chemical approaches, with an emphasis on the latter. The existing opportunities and challenges for successful p53 cancer gene therapy are also discussed.