Recent Patents on Anti-Cancer Drug Discovery - Volume 8, Issue 1, 2013

Both increases in the basal cytosolic calcium concentration ([Ca2+]cyt) and [Ca2+]cyt transients play a major role in cell cycle progression, cell proliferation and division. Calcium influx and release from endoplasmic reticulum are the major routes involved in the variations in [Ca2+]cyt and past studies have clearly shown that calcium influx controls cell growth and proliferation in several cell types. Furthermore, various studies in the past thirty years have demonstrated that calcium channel expression levels, as well as cell specific expression, were determinant in these physiological processes. Cell proliferation is directly linked to cell cycle progression, and again, it became evident that calcium channel expression interferes here. It is also clear that calcium influx and cell proliferation relationship can be uncoupled in transformed and cancer cells, resulting in an external calcium-independent proliferation. Other divalent cations such as iron and zinc involved in cell proliferation permeating some calcium channels may interfere in this cellular process. This patent review is focused on transient receptor potential and ORAI channels, and, as calcium influx regulates several other transduction pathways, we assume that specific signalization complexes are needed to trigger activation of proliferation and cell division in mammalian cells.

Calcium channels significantly contribute to many cellular processes, including such critical ones as proliferation, differentiation, and apoptosis. In prostate cancer, the influence of calcium channels has been known for over 30 years, with the first observations that calcium channel blockers affect the progression of cancer towards more aggressive phase. Later research identified additional classes of channel proteins having an important regulatory role and affecting malignant transformation. This review discusses the accumulated scientific knowledge focused on calcium channel involvement in regulation of cell fate in prostate tissues as well as recent developments in patents targeted at prostate cancer treatments and involving calcium channel modulators.

Blood vessels and endothelial cells (ECs) are highly versatile in order to accomplish local tissutal needs in the physiological and pathological conditions. Tumor vasculature, in particular, exhibits special morphological and functional features, partly due to the peculiarity of tumor-derived ECs (TECs). This is of great importance for the discovery of selective molecular targets potentially suitable to interfere with tumor growth and spread. In normal ECs, proangiogenic calcium signaling is mediated by different calcium channels, mainly TRPs and Orai, that could play a pivotal role in physiological angiogenesis. They are regulated through multiple mechanisms, involving their interaction with bioactive lipids (arachidonic acid and its metabolites), nitrosylation, sulfhydration, phosphorylation, cytoskeleton-mediated membrane trafficking, and calcium stores depletion. On the other hand, proangiogenic calcium events in TECs have been investigated only recently and their characterization is still preliminary. ECs obtained from human breast and renal carcinomas (B-TECs and R-TECs respectively) display altered calcium signals, which are associated with modified expression and function of TRP channels. Here, we review the state of the art in the field of calcium signaling and tumor vascularization, the related recent literature and patents. Finally, we provide some suggestions for future developments.

In the nervous system, the neuronal nicotinic acetylcholine receptors (nAChRs) mediate fast excitatory postsynaptic potentials as well as slower paracrine actions of ACh. They are also widely expressed in non-nervous tissue, including the neoplastic, which is intriguing as smoking is an established risk factor for cancer. Moreover, recent evidence attributes to the gene cluster coding for the α3/α5/β4 nAChR subunits a role in both development of lung cancer and nicotine addiction. Many cellular effects of nicotine and the tobacco-derived carcinogenic N-nitrosamines are probably caused by nAChR activation, which regulates cell proliferation, migration, apoptosis and neoangiogenesis. Nonetheless, the precise nAChR roles in tumors are difficult to determine because cancer cells express a wide variety of nicotinic subunits, whose function is unclear. Patented compounds which selectively target nAChRs subtypes are increasingly available and will hopefully allow better understanding of the physiology of these channels in specific cell types, as well as suggest novel diagnostic and therapeutic approaches. At the present state, however, thorough functional studies of these compounds are still limited and whether they act as agonists, antagonists or partial agonists is often unclear. Such a blurred distinction between activators and inhibitors makes detailed studies in expression systems sorely needed for both physiological understanding and outlining the possible side-effects.

K+ Channels form the largest family among ion channels. Besides regulating many physiological functions, K+ channels, being aberrantly expressed in different types of tumors, affect several hallmarks of cancer. In cancer cells, K+ channel activity regulates cell proliferation, resistance to apoptotic cell death, tumor angiogenesis, invasiveness and metastatic spread. Moreover, being expressed in cells of the tumor microenvironment, K+ channels can also modulate the immune/inflammatory response which contributes to drive cancer establishment and progression. After almost 30 years of studies, some K+ channels are emerging as novel cancer biomarkers, to be employed to stratify patients for either prognostic or predictive purposes. Moreover, it is not remote the time in which it will be possible to target specific K+ channels in cancer for therapeutic purposes. One hindrance for applying a K+ channel-based therapy to cancer is the fact that K+ channel blockers can cause side effects, which often overlap with, but can mask, benefits. We here show some strategies to overcome harmful side effects caused by blocking K+ channels. Once taken into account these strategies, K+ channels may represent suitable and easily accessible cancer biomarkers and targets for therapy. The relevant patents related to K+ channels and cancer are discussed.

A range of experimental and clinical data suggests strongly (i) that metastatic progression in carcinomas is accompanied (maybe even preceded) by upregulation of functional voltage-gated sodium channels (VGSCs) and (ii) that VGSC activity enhances cancer cell invasiveness. First, this review outlines the available in vitro and in vivo evidence for the VGSC expression and its proposed pathophysiological role. Second, we question the mechanism(s) whereby VGSC activity can induce such a cancer-promoting effect. We advance the hypothesis that it is the hypoxia-sensitive persistent component of the VGSC current (INaP) that is central to the phenomenon. Indeed, blockers of INaP are very effective in suppressing cancer cell invasiveness in vitro. Based upon these data, UK and international patent applications have been filed which describe the use of INaP blockers, like ranolazine (“Ranexa”) and riluzole (“Rilutex”), as anti-metastatic agents. Importantly, since these drugs are already in clinical use, against conditions like cardiac angina and amyotrophic lateral scelerosis, there are no issues of dosage, unacceptable side effects or long-term use. Thus, INaP blockers have the potential to turn cancer into a chronic condition.

Cancer cells and tissues, regardless of their origin and genetic background, have an aberrant regulation of hydrogen ion dynamics leading to a reversal of the intracellular to extracellular pH gradient (ΔpHi to ΔpHe) in cancer cells and tissue as compared to normal tissue. This perturbation in pH dynamics rises very early in carcinogenesis and is one of the most common patho-physiological hallmarks of tumors. Recently, there has been a very large increase in our knowledge of the importance and roles of pHi and pHe in developing and driving a series of tumor hallmarks. This reversed proton gradient is driven by a series of proton export mechanisms that underlie the initiation and progression of the neoplastic process. In this context, one of the primary and best studied regulators of both pHi and pHe in tumors is the Na+/H+ exchanger isoform 1 (NHE1). The NHE1 is an integral membrane transport protein involved in regulating pH and in tumor cells is a major contributor to the production and maintenance of their reversed proton gradient. It is activated during oncogene- dependent transformation resulting in cytosolic alkalinization which then drives subsequent hallmark behaviors including growth factor- and substrate-independent growth, and glycolytic metabolism. It is further activated by various growth factors, hormone, the metabolic microenvironment (low serum, acidic pHe and hypoxia) or by ECM receptor activation. This review will present the recent progress in understanding the role the NHE1 in determining tumor progression and invadopodia- guided invasion/metastasis and recent patents for NHE1 inhibitors and novel therapeutic protocols for anti-NHE1 pharmacological approaches. These may represent a real possibility to open up new avenues for wide-spread and efficient treatments against cancer.