Photopharmacology of Antimitotic Agents

Dual-target inhibitors of colchicine binding site for cancer treatment

Colchicine binding site inhibitors (CBSIs) have attracted much attention due to their antitumor efficacies and the advantages of inhibiting angiogenesis and overcoming multidrug resistance. However, no CBSI has been currently approved for cancer treatment due to the insufficient efficacies, serious toxicities and poor pharmacokinetic properties. Design of dual-target inhibitors is becoming a potential strategy for cancer treatment to improve anticancer efficacy, decrease adverse events and overcome drug resistance. Therefore, we reviewed dual-target inhibitors of colchicine binding site (CBS), summarized the design strategies and the biological activities of these dual-target inhibitors, expecting to provide inspiration for developing novel dual inhibitors based on CBS.

Synthesis and Study of Building Blocks with Dibenzo[b,f]oxepine: Potential Microtubule Inhibitors

The synthesis of biphenylmethoxydibenzo[b,f]oxepine or photoswitchable fluorinated dibenzo[b,f]oxepine derivatives with one or three azo bonds, potential microtubule inhibitors, is described. Our studies provide a concise method for constructing derivatives containing the dibenzo[b,f]oxepine skeleton. An analysis of products was run using experimental and theoretical methods. Next, we evaluated the E/Z isomerization of azo-dibenzo[b,f]oxepine derivatives, which could be photochemically controlled using visible-wavelength light.

Photopharmacology of Protease Inhibitors: Current Status and Perspectives

Proteases are involved in many essential biological processes. Dysregulation of their activity underlies a wide variety of human diseases. Photopharmacology, as applied on various classes of proteins, has the potential to assist protease research by enabling spatiotemporal control of protease activity. Moreover, it may be used to decrease side-effects of protease-targeting drugs. In this review, we discuss the current status of the chemical design of photoactivatable proteases inhibitors and their biological application. Additionally, we give insight into future possibilities for further development of this field of research.

Reversible Influence of Hemipiperazine Photochromism on the Early Development of Zebrafish Embryo

This study explores the potential of controlling organismal development with light by using reversible photomodulation of activity in bioactive compounds. Specifically, our research focuses on plinabulin 1, an inhibitor of tubulin dynamics that contains a photochromic motif called hemipiperazine. The two isomeric forms, Z-1 and E-1, can partially interconvert with light, yet show remarkable thermal stability in darkness. The Z-isomer exhibits higher cytotoxicity due to stronger binding to α-tubulin's colchicine site. The less toxic E-1 form, considered a "pro-drug", can be isolated in vitro and stored. Upon activation by blue or cyan light, it predominantly generates the more toxic Z-1 form. Here we demonstrate that 1 can effectively photomodulate epiboly, a critical microtubule-dependent cell movement during gastrulation in zebrafish embryos. This research highlights the potential of photomodulation for precise and reversible control of cellular activities and organismal development.

Microtubule stabilising peptides: new paradigm towards management of neuronal disorders

Neuronal cells made of soma, axon, and dendrites are highly compartmentalized and possess a specialized transport system that can convey long-distance electrical signals for the cross-talk. The transport system is made up of microtubule (MT) polymers and MT-binding proteins. MTs play vital and diverse roles in various cellular processes. Therefore, defects and dysregulation of MTs and their binding proteins lead to many neurological disorders as exemplified by Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, and many others. MT-stabilising agents (MSAs) altering the MT-associated protein connections have shown great potential for several neurodegenerative disorders. Peptides are an important class of molecules with high specificity, biocompatibility and are devoid of side effects. In the past, peptides have been explored in various neuronal disorders as therapeutics. Davunetide, a MT-stabilising octapeptide, has entered into phase II clinical trials for schizophrenia. Numerous examples of peptides emerging as MSAs reflect the emergence of a new paradigm for peptides which can be explored further as drug candidates for neuronal disorders. Although small molecule-based MSAs have been reviewed in the past, there is no systematic review in recent years focusing on peptides as MSAs apart from davunetide in 2013. Therefore, a systematic updated review on MT stabilising peptides may shed light on many hidden aspects and enable researchers to develop new therapies for diseases related to the CNS. In this review we have summarised the recent examples of peptides as MSAs.

Dibenzo[b,f]oxepine Molecules Used in Biological Systems and Medicine

In this short review, including 113 references, issues related to dibenzo[b,f]oxepine derivatives are presented. Dibenzo[b,f]oxepine scaffold is an important framework in medicinal chemistry, and its derivatives occur in several medicinally relevant plants. At the same time, the structure, production, and therapeutic effects of dibenzo[b,f]oxepines have not been extensively discussed thus far and are presented in this review. This manuscript addresses the following issues: extracting dibenzo[b,f]oxepines from plants and its significance in medicine, the biosynthesis of dibenzo[b,f]oxepines, the active synthetic dibenzo[b,f]oxepine derivatives, the potential of dibenzo[b,f]oxepines as microtubule inhibitors, and perspective for applications of dibenzo[b,f]oxepine derivatives. In conclusion, this review describes studies on various structural features and pharmacological actions of dibenzo[b,f]oxepine derivatives.

First-in-Class Colchicine-Based Visible Light Photoswitchable Microtubule Dynamics Disrupting Agent

Compounds that disrupt microtubule dynamics, such as colchicine, paclitaxel, or Vinca alkaloids, have been broadly used in biological studies and have found application in clinical anticancer medications. However, their main disadvantage is the lack of specificity towards cancerous cells, leading to severe side effects. In this paper, we report the first synthesis of 12 new visible light photoswitchable colchicine-based microtubule inhibitors AzoCols. Among the obtained compounds, two photoswitches showed light-dependent cytotoxicity in cancerous cell lines (HCT116 and MCF-7). The most promising compound displayed a nearly twofold increase in potency. Moreover, dissimilar inhibition of purified tubulin polymerisation in cell-free assay and light-dependent disruption of microtubule organisation visualised by immunofluorescence imaging sheds light on the mechanism of action as microtubule photoswitchable destabilisers. The presented results provide a foundation towards the synthesis and development of a novel class of photoswitchable colchicine-based microtubule polymerisation inhibitors.

A Novel Photopharmacological Tool: Dual-Step Luminescence for Biological Tissue Penetration of Light and the Selective Activation of Photodrugs

Conventional pharmacology lacks spatial and temporal selectivity in terms of drug action. This leads to unwanted side effects, such as damage to healthy cells, as well as other less obvious effects, such as environmental toxicity and the acquisition of resistance to drugs, especially antibiotics, by pathogenic microorganisms. Photopharmacology, based on the selective activation of drugs by light, can contribute to alleviating this serious problem. However, many of these photodrugs are activated by light in the UV-visible spectral range, which does not propagate through biological tissues. In this article, to overcome this problem, we propose a dual-spectral conversion technique, which simultaneously makes use of up-conversion (using rare earth elements) and down-shifting (using organic materials) techniques in order to modify the spectrum of light. Near-infrared light (980 nm), which penetrates tissue fairly well, can provide a "remote control" for drug activation. Once near-IR light is inside the body, it is up-converted to the UV-visible spectral range. Subsequently, this radiation is down-shifted in order to accurately adjust to the excitation wavelengths of light which can selectively activate hypothetical and specific photodrugs. In summary, this article presents, for the first time, a "dual tunable light source" which can penetrate into the human body and deliver light of specific wavelengths; thus, it can overcome one of the main limitations of photopharmacology. It opens up promising possibilities for the moving of photodrugs from the laboratory to the clinic.

Watching the release of a photopharmacological drug from tubulin using time-resolved serial crystallography

The binding and release of ligands from their protein targets is central to fundamental biological processes as well as to drug discovery. Photopharmacology introduces chemical triggers that allow the changing of ligand affinities and thus biological activity by light. Insight into the molecular mechanisms of photopharmacology is largely missing because the relevant transitions during the light-triggered reaction cannot be resolved by conventional structural biology. Using time-resolved serial crystallography at a synchrotron and X-ray free-electron laser, we capture the release of the anti-cancer compound azo-combretastatin A4 and the resulting conformational changes in tubulin. Nine structural snapshots from 1 ns to 100 ms complemented by simulations show how cis-to-trans isomerization of the azobenzene bond leads to a switch in ligand affinity, opening of an exit channel, and collapse of the binding pocket upon ligand release. The resulting global backbone rearrangements are related to the action mechanism of microtubule-destabilizing drugs.

Heterocyclic Hemipiperazines: Water-Compatible Peptide-Derived Photoswitches

Hemipiperazines are a recently discovered class of peptide-derived molecular photoswitches with high biocompatibility and therapeutic potential. Here, for the first time we describe photochromism of heterocyclic hemipiperazines. They demonstrate long thermal lifetimes, and enlarged band separation between photoisomers. Efficient photoisomerization occurs under aqueous conditions, although with a need for organic co-solvent. Bidirectional switching with visible light is observed for an extended aromatic system.

Hemipiperazines as peptide-derived molecular photoswitches with low-nanomolar cytotoxicity

Molecular photoswitches transform light energy into reversible structural changes. Their combination with known pharmacophores often allows for photomodulation of the biological activity. The effort to apply such compounds in photopharmacology as light-activated pro-drugs is, however, hampered by serious activity reduction upon pharmacophore modifications, or limited biostability. Here we report that a potent antimitotic agent plinabulin and its derivatives demonstrate up to 56-fold reversible activity photomodulation. Alternatively, irreversible photoactivation with cyan light can enhance the cytotoxicity up to three orders of magnitude-all without compromising the original activity level, as the original pharmacophore structure is unchanged. This occurs due to the presence of a peptide-derived photoswitchable motif hemipiperazine inside the plinabulin scaffold. Furthermore, we systematically describe photochromism of these thermally stable and biocompatible hemipiperazines, as well as a photoswitchable fluorophore derived from plinabulin. The latter may further expand the applicability of hemipiperazine photochromism towards super-resolution microscopy.

Synthesis and Study of Dibenzo[b, f]oxepine Combined with Fluoroazobenzenes—New Photoswitches for Application in Biological Systems

Dibenzo[b, f]oxepine derivatives are an important scaffold in natural, medicinal chemistry, and these derivatives occur in several medicinally relevant plants. Two dibenzo[b, f]oxepines were selected and connected with appropriate fluorine azobenzenes. In the next step, the geometry of E/Z isomers was analyzed using density functional theory (DFT) calculations. Then the energies of the HOMO and LUMO orbitals were calculated for the E/Z isomers to determine the HOMO-LUMO gap. Next, modeling of the interaction between the obtained isomers of the compounds and the colchicine α and β-tubulin binding site was performed. The investigated isomers interact with the colchicine binding site in tubulin with a part of the dibenzo[b, f]oxepine or in a part of the azo switch, or both at the same time. Based on the UV-VIS spectra, it was found that in the case of compounds with an azo bond in the meta position, the absorption bands n→π* for both geometric isomers and their separation from π→π* are visible. These derivatives therefore have the potential to be used in photopharmacology.