Recent Approaches to the Identification of Novel Microtubule-Targeting Agents

Abstract

Microtubules are key components of the eukaryotic cytoskeleton with essential roles in cell division, intercellular transport, cell morphology, motility, and signal transduction. They are composed of protofilaments of heterodimers of α-tubulin and β-tubulin organized as rigid hollow cylinders that can assemble into large and dynamic intracellular structures. Consistent with their involvement in core cellular processes, affecting microtubule assembly results in cytotoxicity and cell death. For these reasons, microtubules are among the most important targets for the therapeutic treatment of several diseases, including cancer. The vast literature related to microtubule stabilizers and destabilizers has been reviewed extensively in recent years. Here we summarize recent experimental and computational approaches for the identification of novel tubulin modulators and delivery strategies. These include orphan small molecules, PROTACs as well as light-sensitive compounds that can be activated with high spatio-temporal accuracy and that represent promising tools for precision-targeted chemotherapy.

Quantification of Engagement of Microtubules by Small Molecules in Living Cells by Flow Cytometry

“…The allosteric microtubule destabilizers , colchicine, vinblastine, and maytansine were investigated with PB-GABA-Taxol using previously optimized cellular binding conditions (Figure ). Potent allosteric binding affinities were observed for colchicine ( K b = 80 ± 12 nM, α = 0.08), vinblastine ( K b = 7 ± 2 nM, α = 0.18), and maytansine ( K b = 3 ± 1 nM, α = 0.21).…”

“…This class of compounds includes FDA-approved microtubule stabilizers such as taxanes and epothilones and microtubule destabilizers such as colchicine, vinblastine, and maytansinoids, which are delivered as antibody–drug conjugates (Figure ). The mechanism of action of taxane drugs involves the engagement of a 3.5 Å hydrophobic cleft of the protein β-tubulin when it heterodimerizes with α-tubulin to form tubular protein assemblies. , Binding of taxanes to polymerized microtubules is favored, and this binding induces conformational changes to microtubules that lower the critical concentration required for their assembly of these structures. − In contrast, destabilizers such as vinblastine weaken microtubule lattices, whereas colchicine inhibits the growth of microtubules by preventing conformational changes of dimers of α- and β-tubulin required for their polymerization . Although microtubule-targeting drugs are effective first- and second-line therapies for numerous cancers, novel agents that bind microtubules are of substantial interest due to the emergence of drug resistance, the lack of efficacy for some cancers, and the complexity associated with the syntheses of some of these compounds. − Furthermore, dose-limiting side effects such as peripheral neuropathy associated with taxanes, epothilones, and their delivery vehicles continues to drive the discovery of novel agents with greater bioavailability and improved therapeutic windows. − Resistance to these drugs can be mediated by several mechanisms, including the overexpression of drug efflux transporters such as p -glycoprotein (MDR1), mutations in β-tubulin, and the expression of antiapoptotic proteins such as survivin. − …”

Donor–Acceptor Stenhouse Adduct Displaying Reversible Photoswitching in Water and Neuronal Activity

“…30 These properties are appealing for photopharmacology, which aims at controlling drug action on demand at selected locations using light, to enable precise responses and reduce unwanted side effects of treatments, or to manipulate specific cell types and neural circuits for investigational purposes. 31,32 Many photoswitchable bioactive molecules have been reported that offer high pharmacological specificity and potency for a diversity of targets, including ion channels, 33−36 G protein-coupled receptors, 37−39 protein−protein interactions, 40,41 and enzymes. 42−45 Most are based on aryl azo compounds, 46−48 which are difficult to isomerize using orange−red light without introducing substituents that often perturb the pharmacological properties of the original compound.…”

“…The hurdles to operate DASAs in aqueous solutions are most aggravating since they are native red/NIR-absorbing, negative photochromic compounds that would afford low scattering and deep penetration in tissue without incurring phototoxicity in biological applications . These properties are appealing for photopharmacology, which aims at controlling drug action on demand at selected locations using light, to enable precise responses and reduce unwanted side effects of treatments, or to manipulate specific cell types and neural circuits for investigational purposes. , Many photoswitchable bioactive molecules have been reported that offer high pharmacological specificity and potency for a diversity of targets, including ion channels, − G protein-coupled receptors, − protein–protein interactions, , and enzymes. − Most are based on aryl azo compounds, − which are difficult to isomerize using orange–red light without introducing substituents that often perturb the pharmacological properties of the original compound. − Photoswitching with continuous NIR light has been achieved in diazocines and using two-photon (2P) excitation of simple azobenzenes ,, in neurons, but the latter requires pulsed lasers and precision optics. , Thus, developing compounds that can be directly photoswitched in vivo with continuous-wave red or NIR light using portable devices (e.g., LEDs) remains an unmet need in basic and applied photopharmacology. They would enable noninvasive drug-based phototherapies and facilitate their translation to the clinic.…”

Design, Synthesis, In Vitro Biological Activity Evaluation and Stabilized Nanostructured Lipid Carrier Formulation of Newly Synthesized Schiff Bases-Based TMP Moieties

“…Microtubules are among the most important molecular targets for cancer chemotherapeutic treatment [1][2][3]. The formation of microtubules is a dynamic process that involves the assembly and disassembly of α and β-tubulin subunits [4][5][6].…”