The optogenetic promise for oncology: Episode I

Optogenetics: A new tool for cancer investigation and treatment

Despite the progress made in the diagnosis and treatment of cancer, it has remained the second cause of death in industrial countries. Cancer is a complex multifaceted disease with unique genomic and proteomic hallmarks. Optogenetics is a biological approach, in which the light-sensitive protein modules in combination with effector proteins that trigger reversibly fundamental cell functions without producing a long-term effect. The technology was first used to address some key issues in neurology. Later on, it was also used for other diseases such as cancer. In the case of cancer, there exist several signaling pathways with key proteins that are involved in the initiation and/or progression of cancer. Such aberrantly expressed proteins and the related signaling pathways need to be carefully investigated in terms of cancer diagnosis and treatment, which can be managed with optogenetic tools. Notably, optogenetics systems offer some advantages compared to the traditional methods, including spatial-temporal control of protein or gene expression, cost-effective and fewer off-target side effects, and reversibility potential. Such noticeable features make this technology a unique drug-free approach for diagnosis and treatment of cancer. It can be used to control tumor cells, which is a favorable technique to investigate the heterogeneous and complex features of cancerous cells. Remarkably, optogenetics approaches can provide us with outstanding tool to extend our understanding of how cells perceive, respond, and behave in meeting with complex signals, particularly in terms of cancer evasion from the anticancer immune system functions.

Clinical Potential of Nerve Input to Tumors: A Bioelectricity Perspective

We support the notion that the neural connections of the tumor microenvironment (TME) and the associated 'bioelectricity' play significant role in the pathophysiology of cancer. In several cancers, the nerve input promotes the cancer process. While straightforward surgical denervation of tumors, therefore, could improve prognosis, resulting side effects of such a procedure would be unpredictable and irreversible. On the other hand, tumor innervation can be manipulated effectively for therapeutic purposes by alternative novel approaches broadly termed "electroceuticals." In this perspective, we evaluate the clinical potential of targeting the TME first through manipulation of the nerve input itself and second by application of electric fields directly to the tumor. The former encompasses several different biophysical and biochemical approaches. These include implantable devices, nanoparticles, and electroactive polymers, as well as optogenetics and chemogenetics. As regard bioelectrical manipulation of the tumor itself, the "tumor-treating field" technique, applied to gliomas commonly in combination with chemotherapy, is evaluated. Also, as electroceuticals, drugs acting on ion channels and neurotransmitter receptors are highlighted for completeness. It is concluded, first, that electroceuticals comprise a broad range of biomedical tools. Second, such electroceuticals present significant clinical potential for exploiting the neural component of the TME as a strategy against cancer. Finally, the inherent bioelectric characteristics of tumors themselves are also amenable to complementary approaches. Collectively, these represent an evolving, dynamic field and further progress and applications can be expected to follow both conceptually and technically.

Optogenetics: the new molecular approach to control functions of neural cells in epilepsy, depression and tumors of the central nervous system

The optogenetic tools have been described as valuable techniques to study neural activity through light stimulation, as well as potential neuromodulator approaches in the management of several central nervous system (CNS) diseases. Since the first bacteriorhodopsin protein described as a single-component light-activated regulator of transmembrane ion flow description, in 1980's, the focus has been on channel proteins for neurobiology; however, the advances in engineering techniques showed involvement changes in cellular biological behavior in several types of proteins involved in cell cytoskeleton regulation, motility and gene expression. Although the use of this technology has been published in many papers, a question still remains regarding real results and potential clinical applicability in CNS diseases, as well as the publications scarcity that systematically analyses the published results. Lastly, the aim of this review is to discuss the experimental results, molecular mechanisms and potential clinical applications of optogenetic tools in epilepsy and depression treatment, as well as its applicability in the treatment of CNS tumors.

Optogenetic toolkit for precise control of calcium signaling

Calcium acts as a second messenger to regulate a myriad of cell functions, ranging from short-term muscle contraction and cell motility to long-term changes in gene expression and metabolism. To study the impact of Ca2+-modulated 'ON' and 'OFF' reactions in mammalian cells, pharmacological tools and 'caged' compounds are commonly used under various experimental conditions. The use of these reagents for precise control of Ca2+ signals, nonetheless, is impeded by lack of reversibility and specificity. The recently developed optogenetic tools, particularly those built upon engineered Ca2+ release-activated Ca2+ (CRAC) channels, provide exciting opportunities to remotely and non-invasively modulate Ca2+ signaling due to their superior spatiotemporal resolution and rapid reversibility. In this review, we briefly summarize the latest advances in the development of optogenetic tools (collectively termed as 'genetically encoded Ca2+ actuators', or GECAs) that are tailored for the interrogation of Ca2+ signaling, as well as their applications in remote neuromodulation and optogenetic immunomodulation. Our goal is to provide a general guide to choosing appropriate GECAs for optical control of Ca2+ signaling in cellulo, and in parallel, to stimulate further thoughts on evolving non-opsin-based optogenetics into a fully fledged technology for the study of Ca2+-dependent activities in vivo.