Recent clinical trials and optical control as a potential strategy to develop microtubule-targeting drugs in colorectal cancer management

Colorectal cancer(CRC)has remained the second and the third leading cause of cancer-related death worldwide and in the United States,respectively.Although significant improvement in overall survival has been achieved,death in adult populations under the age of 55 appears to have increased in the past decades.Although new classes of therapeutic strategies such as immunotherapy have emerged,their application is very limited in CRC so far.Microtubule(MT)inhibitors such as taxanes,are not generally successful in CRC.There may be some way to make MT inhibitors work effectively in CRC.One potential advantage that we can take to treat CRC may be the combination of optical techniques coupled to an endoscope or other fiber optics-based devices.A combination of optical devices and photo-activatable drugs may allow us to locally target advanced CRC cells with highly potent MT-targeting drugs.In this Editorial review,we would like to discuss the potential of optogenetic approaches in CRC management.

Boosting ferroptosis and microtubule inhibition for antitumor therapy via a carrier-free supermolecule nanoreactor

Traditional microtubule inhibitors fail to significantly enhance+e effect of colorectal cancer;hence,new and efficient strategies are necessary.In+is study,a supramolecular nanoreactor(DOC@TA-Fe^(3+))based on tannic acid(TA),iron ion(Fe^(3+)),and docetaxel(DOC)wi+microtubule inhibition,reactive oxygen species(ROS)generation,and gluta+ione peroxidase 4(GPX4)inhibition,is prepared for ferroptosis/apoptosis treatment.After internalization by CT26 cells,+e DOC@TA-Fe^(3+)nanoreactor escapes from+e lysosomes to release payloads.+e subsequent Fe^(3+)/Fe^(2+)conversion mediated by TA reducibility can trigger+e Fenton reaction to enhance+e ROS concentration.Additionally,Fe^(3+)can consume gluta+ione to repress+e activity of GPX4 to induce ferroptosis.Meanwhile,+e released DOC controls microtubule dynamics to activate+e apoptosis pa+way.+e superior in vivo antitumor efficacy of DOC@TA-Fe^(3+)nanoreactor in terms of tumor grow+inhibition and improved survival is verified in CT26 tumor-bearing mouse model.+erefore,+e nanoreactor can act as an effective apoptosis and ferroptosis inducer for application in colorectal cancer+erapy.

Fidgetin interacting with microtubule end binding protein EB3 affects axonal regrowth in spinal cord injury

Fidgetin,a microtubule-severing enzyme,regulates neurite outgrowth,axonal regeneration,and cell migration by trimming off the labile domain of microtubule polymers.Because maintenance of the microtubule labile domain is essential for axon initiation,elongation,and navigation,it is of interest to determine whether augmenting the microtubule labile domain via depletion of fidgetin serves as a therapeutic approach to promote axonal regrowth in spinal cord injury.In this study,we constructed rat models of spinal cord injury and sciatic nerve injury.Compared with spinal cord injury,we found that expression level of tyrosinated microtubules in the labile portion of microtubules continuously increased,whereas fidgetin decreased after peripheral nerve injury.Depletion of fidgetin enhanced axon regeneration after spinal cord injury,whereas expression level of end binding protein 3(EB3)markedly increased.Next,we performed RNA interference to knockdown EB3 or fidgetin.We found that deletion of EB3 did not change fidgetin expression.Conversely,deletion of fidgetin markedly increased expression of tyrosinated microtubules and EB3.Deletion of fidgetin increased the amount of EB3 at the end of neurites and thereby increased the level of tyrosinated microtubules.Finally,we deleted EB3 and overexpressed fidgetin.We found that fidgetin trimmed tyrosinated tubulins by interacting with EB3.When fidgetin was deleted,the labile portion of microtubules was elongated,and as a result the length of axons and number of axon branches were increased.These findings suggest that fidgetin can be used as a novel therapeutic target to promote axonal regeneration after spinal cord injury.Furthermore,they reveal an innovative mechanism by which fidgetin preferentially severs labile microtubules.

Kinesin-microtubule interaction reveals the mechanism of kinesin-1 for discriminating the binding site on microtubule

Microtubule catalyzes the mechanochemical cycle of kinesin,a kind of molecular motor,through its crucial roles in kinesin's gating,ATPase and force-generation process.These functions of microtubule are realized through the kinesin-microtubule interaction.The binding site of kinesin on the microtubule surface is fixed.For most of the kinesin-family members,the binding site on microtubule is in the groove betweenα-tubulin andβ-tubulin in a protofilament.The mechanism of kinesin searching for the appropriate binding site on microtubule is still unclear.Using the molecular dynamics simulation method,we investigate the interactions between kinesin-1 and the different binding positions on microtubule.The key non-bonded interactions between the motor domain and tubulins in kinesin's different nucleotide-binding states are listed.The differences of the amino-acid sequences betweenα-andβ-tubulins make kinesin-1 binding to theα–βgroove much more favorable than to theβ–αgroove.From these results,a two-step mechanism of kinesin-1 to discriminate the correct binding site on microtubule is proposed.Most of the kinesin-family members have the conserved motor domain and bind to the same site on microtubule,the mechanism may also be shared by other family members of kinesin.

Ideal type 1 is caused by a point mutation in the a-tubulin gene that affects microtubule arrangement in soybean

Plant architecture is a target of crop improvement.The soybean mutant ideal type 1(it1)displays a pleiotropic phenotype characterized by compact plant architecture,reduced plant height,shortened petioles,wrinkled leaves,and indented seeds.Genetic analysis revealed that the pleiotropic phenotype was controlled by an incomplete dominant gene.We characterized the cellular phenotypes of it1 and positionally cloned the it1 locus.Detailed morphogenetic analysis of the it1 mutant revealed an excess of xylem cells and expanded phloem,and polygonal pavement cells.Positional cloning showed that the phenotype was caused by a G-to-A mutation in the second exon of the a-tubulin gene(Glyma.05G157300).The mutation altered microtubule arrangement in pavement cells,changing their morphology.Overexpression of Gmit1 resulted in an it1-like phenotype and polygonal pavement cells and microtubules of overexpressors were parallel or slightly inclined.Five suppressor mutants able to suppress the phenotype of it1 were obtained by EMS mutagenesis in the it1 background.All these mutants carried an additional mutation in the it1 gene.These results suggest that the pleiotropic phenotype of it1 is caused by the mutation in the atubulin gene.

Dissipation and amplification management in an electrical model of microtubules: Hybrid behavior network

The control of dissipation and amplification of solitary waves in an electrical model of a microtubule is demonstrated.This model consists of a shunt nonlinear resistance–capacitance(J(V)–C(V)) circuit and a series resistance–inductance(R–L) circuit. Through linear dispersion analysis, two features of the network are found, that is, low bandpass and bandpass filter characteristics. The effects of the conductance’s parameter λ on the linear dispersion curve are also analyzed. It appears that an increase of λ induces a decrease(an increase) of the width of the bandpass filter for positive(negative) values of λ. By applying the reductive perturbation method, we derive the equation governing the dynamics of the modulated waves in the system. This equation is the well-known nonlinear Schr?dinger equation extended by a linear term proportional to a hybrid parameter σ, i.e., a dissipation or amplification coefficient. Based on this parameter, we successfully demonstrate the hybrid behavior(dissipation and amplification) of the system. The exact and approximate solitary wave solutions of the obtained equation are derived, and the effects of the coefficient σ on the characteristic parameters of these waves are investigated. Using the analytical solutions found, we show numerically that the waves that are propagated throughout the system can be dissipated, amplified, or remain stable depending on the network parameters. These results are not only in agreement with the analytical predictions, but also with the existing experimental results in the literature.

Study on regulating mechanisms of oxocrebanine obtained from Stephania hainanensis H.S.Lo et Y.Tsoong on microtubule sites and tubulin in human breast cancer MCF-7 cells

Objective:To determine the destructive ability of oxocrebanine,an anti-breast cancer active compound obtained from Stephania hainanensis H.S.Lo et Y.Tsoong,on microtubule network,and investigate the effect of oxocrebanine on microtubule network homeostasis at both molecular and cellular levels.Methods:the EBI site competition method and molecular docking method were used to determine the occupation of the microtubule site of oxocrebanine.Western Blot was used to detect the effect of oxocrebanine on microtubule-associated proteins including STAT3,PAK1,CAMK4,and PKA.Results:The results of EBI site competition assay showed that the binding of EBI toβ-Tubulin covalent fusions produced adducts that appeared in regions of lower molecular weight thanβ-tubulin(ctrl 2).Molecular docking results showed that oxocrebanine could occupy the colchicine site of microtubule proteins.As revealed by Western Blot,the expression of STAT3 protein was decreased after MCF-7 cells have been treated with low,medium,and high concentration of oxocrebanine or the positive drug taxol for 48 h(P<0.01).The expression levels of PAK1 and Camk4 proteins aslo showed significant reductions(P<0.05,or P<0.01).Oxocrebanine also decreased the PKA protein in MCF-7 cells compared to the control group(P<0.01).Conclusions:Oxocrebanine,a ligand that binds at the colchicine site of tubulin,perturbs tubulin polymerization and causes mitosis in MCF-7 cells,thus leading to MCF-7 cell death.Oxocrebanine may promote microtubule dynamics through stathmin by inhibiting the expression levels of STAT3,PAK1,Camk4,and PKA proteins in MCF-7 cells.Oxocrebanine interfers with spindle formation,and ultimately causes mitotic catastrophe in MCF-7 cells.

Connecting neurodevelopment to neurodegeneration:a spotlight on the role of kinesin superfamily protein 2A(KIF2A)

Microtubules play a central role in cytoskeletal changes during neuronal development and maintenance.Microtubule dynamics is essential to polarity and shape transitions underlying neural cell division,differentiation,motility,and maturation.Kinesin superfamily protein 2A is a member of human kinesin 13 gene family of proteins that depolymerize and destabilize microtubules.In dividing cells,kinesin superfamily protein 2A is involved in mitotic progression,spindle assembly,and chromosome segregation.In postmitotic neurons,it is required for axon/dendrite specification and extension,neuronal migration,connectivity,and survival.Humans with kinesin superfamily protein 2A mutations suffer from a variety of malformations of cortical development,epilepsy,autism spectrum disorder,and neurodegeneration.In this review,we discuss how kinesin superfamily protein 2A regulates neuronal development and function,and how its deregulation causes neurodevelopmental and neurological disorders.

How do neurons age?A focused review on the aging of the microtubular cytoskeleton

Aging is the leading risk factor for Alzheimer’s disease and other neurodegenerative diseases. We now understand that a breakdown in the neuronal cytoskeleton, mainly underpinned by protein modifications leading to the destabilization of microtubules, is central to the pathogenesis of Alzheimer’s disease. This is accompanied by morphological defects across the somatodendritic compartment, axon, and synapse. However, knowledge of what occurs to the microtubule cytoskeleton and morphology of the neuron during physiological aging is comparatively poor. Several recent studies have suggested that there is an age-related increase in the phosphorylation of the key microtubule stabilizing protein tau, a modification, which is known to destabilize the cytoskeleton in Alzheimer’s disease. This indicates that the cytoskeleton and potentially other neuronal structures reliant on the cytoskeleton become functionally compromised during normal physiological aging. The current literature shows age-related reductions in synaptic spine density and shifts in synaptic spine conformation which might explain age-related synaptic functional deficits. However, knowledge of what occurs to the microtubular and actin cytoskeleton, with increasing age is extremely limited. When considering the somatodendritic compartment, a regression in dendrites and loss of dendritic length and volume is reported whilst a reduction in soma volume/size is often seen. However, research into cytoskeletal change is limited to a handful of studies demonstrating reductions in and mislocalizations of microtubule-associated proteins with just one study directly exploring the integrity of the microtubules. In the axon, an increase in axonal diameter and age-related appearance of swellings is reported but like the dendrites, just one study investigates the microtubules directly with others reporting loss or mislocalization of microtubule-associated proteins. Though these are the general trends reported, there are clear disparities between model organisms and brain regions that are worthy of further investigation. Additionally, longitudinal studies of neuronal/cytoskeletal aging should also investigate whether these age-related changes contribute not just to vulnerability to disease but also to the decline in nervous system function and behavioral output that all organisms experience. This will highlight the utility, if any, of cytoskeletal fortification for the promotion of healthy neuronal aging and potential protection against age-related neurodegenerative disease. This review seeks to summarize what is currently known about the physiological aging of the neuron and microtubular cytoskeleton in the hope of uncovering mechanisms underpinning age-related risk to disease.

The interaction between KIF21A and KANK1 regulates dendritic morphology and synapse plasticity in neurons

Morphological alterations in dendritic spines have been linked to changes in functional communication between neurons that affect learning and memory.Kinesin-4 KIF21A helps organize the microtubule-actin network at the cell cortex by interacting with KANK1;however,whether KIF21A modulates dendritic structure and function in neurons remains unknown.In this study,we found that KIF21A was distributed in a subset of dendritic spines,and that these KIF21A-positive spines were larger and more structurally plastic than KIF21A-negative spines.Furthermore,the interaction between KIF21A and KANK1 was found to be critical for dendritic spine morphogenesis and synaptic plasticity.Knockdown of either KIF21A or KANK1 inhibited dendritic spine morphogenesis and dendritic branching,and these deficits were fully rescued by coexpressing full-length KIF21A or KANK1,but not by proteins with mutations disrupting direct binding between KIF21A and KANK1 or binding between KANK1 and talin1.Knocking down KIF21A in the hippocampus of rats inhibited the amplitudes of long-term potentiation induced by high-frequency stimulation and negatively impacted the animals’cognitive abilities.Taken together,our findings demonstrate the function of KIF21A in modulating spine morphology and provide insight into its role in synaptic function.

Endogenous biosynthesis of docosahexaenoic acid(DHA)regulates fish oocyte maturation by promoting pregnenolone production

Omega-3 polyunsaturated fatty acids(n-3 PUFAs),particularly docosahexaenoic acid(22:6n-3,DHA),play crucial roles in the reproductive health of vertebrates,including humans.Nevertheless,the underlying mechanism related to this phenomenon remains largely unknown.In this study,we employed two zebrafish genetic models,i.e.,elovl2^(-/-)mutant as an endogenous DHAdeficient model and fat1(omega-3 desaturase encoding gene)transgenic zebrafish as an endogenous DHA-rich model,to investigate the effects of DHA on oocyte maturation and quality.Results show that the elovl2^(-/-)mutants had much lower fecundity and poorer oocyte quality than the wild-type controls,while the fat1 zebrafish had higher fecundity and better oocyte quality than wildtype controls.DHA deficiency in elovl2^(-/-)embryos led to defects in egg activation,poor microtubule stability,and reduced pregnenolone levels.Further study revealed that DHA promoted pregnenolone synthesis by enhancing transcription of cyp11a1,which encodes the cholesterol side-chain cleavage enzyme,thereby stabilizing microtubule assembly during oogenesis.In turn,the hypothalamic-pituitary-gonadal axis was enhanced by DHA.In conclusion,using two unique genetic models,our findings demonstrate that endogenously synthesized DHA promotes oocyte maturation and quality by promoting pregnenolone production via transcriptional regulation of cyp11a1.

Changes in microtubule-associated protein tau during peripheral nerve injury and regeneration

Tau, a primary component of microtubule-associated protein, promotes microtubule assembly and/or disassembly and maintains the stability of the microtubule structure. Although the importance of tau in neurodegenerative diseases has been well demonstrated, wheth- er tau is involved in peripheral nerve regeneration remains unknown. In the current study, we obtained sciatic nerve tissue from adult rats 0, 1, 4, 7, and 14 days after sciatic nerve crush and examined tau mRNA and protein expression levels and the location of tau in the sciatic nerve following peripheral nerve injury. The results from our quantitative reverse transcription polymerase chain reaction analysis showed that compared with the uninjured control sciatic nerve, mRNA expression levels for both tau and tau tubulin kinase 1, a serine/ threonine kinase that regulates tau phosphorylation, were decreased following peripheral nerve injury. Our western blot assay results suggested that the protein expression levels of tau and phosphorylated tau initially decreased 1 day post nerve injury but then gradually increased. The results of our immunohistochemical labeling showed that the location of tau protein was not altered by nerve injury. Thus, these results showed that the expression of tau was changed following sciatic nerve crush, suggesting that tau may be involved in periph- eral nerve repair and regeneration.

Rho-associated protein kinase modulates neurite extension by regulating microtubule remodeling and vinculin distribution

Rho-associated protein kinase is an essential regulator of cytoskeletal dynamics during the process of neurite extension. However, whether Rho kinase regulates microtubule remodeling or the distri- bution of adhesive proteins to mediate neurite outgrowth remains unclear. By specifically modulat- ing Rho kinase activity with pharmacological agents, we studied the morpho-dynamics of neurite outgrowth. We found that lysophosphatidic acid, an activator of Rho kinase, inhibited neurite out- growth, which could be reversed by Y-27632, an inhibitor of Rho kinase. Meanwhile, reorganization of microtubules was noticed during these processes, as indicated by their significant changes in the soma and growth cone. In addition, exposure to lysophosphatidic acid led to a decreased mem- brane distribution of vinculin, a focal adhesion protein in neurons, whereas Y-27632 recruited vin- culin to the membrane. Taken together, our data suggest that Rho kinase regulates rat hippocampal neurite growth and microtubule formation via a mechanism associated with the redistribution of vinculin.

Preparation and magnetic properties of Fe_2O_3 microtubules prepared by sol-gel template method

Fe（OH）3 precursor sol was prepared by a sol-gel method. The precursor sol was dipped onto the absorbent cotton, and gel was formed on the absorbent cotton template after the volatilization of moisture. Fe2O3 microtubules were synthesized after the process of self-propagation or calcination. The phase, morphology, and particle diameter of the samples were examined by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and the magnetic properties of the samples were measured using a vibrating sample magnetometer （VSM）. The external diameters of Fe2O3 microtubules ranged between 8 and 13 μm, and the wall thicknesses ranged between 0.5 and 2 μm. The type of the calcination method plays a significant role in developing the Fe2O3 phase and the variation in the magnetic properties in the sol-gel template complexing method. γ-Fe2O3 was synthesized by a self-propagation method. However, α-Fe203 was synthesized after calcination at 400℃ for 2 h. The coercivity of the samples synthesized by calcination at 400℃ for 2 h after self-propagation was found to increase significantly, thereby presenting hard magnetic properties.

Zonula occludin toxin,a microtubule binding protein

AIM To investigate the interaction of Zot withmicrotubule.METHODS Zot affinity column was applied topurify Zot-binding protein（s）from crudeintestinal cell lysates.After incubation at roomtemperature,the column was washed and theproteins bound to the Zot affinity column wereeluted by step gradient with NaCl(0.3 mol·L-1-0.5mol·L-1).The fractions were subjected to6.0%-15.0%（w/v）gradient SDS-PAGE andthen transferred to PVDF membrane for N-terminal sequencing.Purified Zot and tauprotein were blotted by using anti-Zot or anti-tauantibodies.Finally,purified Zot was tested in anin vitro tubulin binding assay.RESULTS Fractions from Zot affinity columnyielded two protein bands with a Mr of 60 kU and45kU respectively.The N-terminal sequence ofthe 60 kU band resulted identical to β-tubulin.Zot also cross-reacts with anti-tau antibodies.Inthe in vitro tubulin binding assay,Zot co-precipitate with Mt,further suggesting that Zotpossesses tubulin-binding properties.CONCLUSION Taken together,these resultssuggest that Zot regulates the permeability ofintestinal tight junctions by binding tointracellular Mt,with the subsequent activationof the intracellular signaling leading to thepermeabilization of intercellular tight junctions.

Role of microtubule dynamics in Wallerian degeneration and nerve regeneration after peripheral nerve injury

Wallerian degeneration,the progressive disintegration of distal axons and myelin that occurs after peripheral nerve injury,is essential for creating a permissive microenvironment for nerve regeneration,and involves cytoskeletal reconstruction.However,it is unclear whether microtubule dynamics play a role in this process.To address this,we treated cultured sciatic nerve explants,an in vitro model of Wallerian degeneration,with the microtubule-targeting agents paclitaxel and nocodazole.We found that paclitaxel-induced microtubule stabilization promoted axon and myelin degeneration and Schwann cell dedifferentiation,whereas nocodazole-induced microtubule destabilization inhibited these processes.Evaluation of an in vivo model of peripheral nerve injury showed that treatment with paclitaxel or nocodazole accelerated or attenuated axonal regeneration,as well as functional recovery of nerve conduction and target muscle and motor behavior,respectively.These results suggest that microtubule dynamics participate in peripheral nerve regeneration after injury by affecting Wallerian degeneration.This study was approved by the Animal Care and Use Committee of Southern Medical University,China(approval No.SMUL2015081) on October 15,2015.

Biological Fingerprinting Analysis of Interaction Between Taxoids in Taxus and Microtubule Protein by Microdialysis Coupled with High-performance Liquid Chromatography/Mass Spectrometry for Screening Antimicrotubule Agents

Some natural products, such as traditional Chinese medicines（TCMs）, contain compounds with anticancer activity and have attracted a great interest in recent years as alternative anticancer therapies. A quick and convenient assay for screening antimicrotubule compounds in which in vitro microdialysis/high-performance liquid chromatography （HPLC） is used to monitor the binding of the compounds extracted from TCM Taxus cuspidata Siebold ＆ Zucc（Taxus） to microtubules is reported. It was observed that the extract of Taxus contains at least five compounds which have affinity interaction with microtubules by biological fingerprinting analysis, and they were identified as the taxoids of taxol, baccatin III, 10-deacetylbaccatin Ⅲ（10-DAB）, cephalomannine and 7-epi-10-deacetyltaxol （7-epi-10-DAT） based on the comparison of their high-performance liquid chromatographic/mass spectrometric and UV spectra with those of the standard samples, both assembly-promoting and disassembly-inhibiting characteristics of those compounds were evaluated. It was observed that baccatin Ⅲ and 10-DAB bound to microtubules and the binding degrees were influenced by GTP. Competitive binding behavior of taxol with other four taxoids to microtubules was also investigated.

Stathmin destabilizing microtubule dynamics promotes malignant potential in cancer cells by epithelial-mesenchymal transition

BACKGROUND： Stathmin is a ubiquitous cytosolic regulatory phosphoprotein and is overexpressed in different human malignancies. The main physiological function of stathmin is to interfere with microtubule dynamics by promoting depolymerization of microtubules or by preventing polymerization of tubulin heterodimers. Stathmin plays important roles in regulating many cellular functions as a result of its microtubuledestabilizing activity. Currently, the critical roles of stathmin in cancer cells, as well as in lymphocytes have been valued. This review discusses stathmin and microtubule dynamics in cancer development, and hypothesizes their possible relationship with epithelial-mesenchymal transition（EMT）.DATA SOURCES： A PubMed search using such terms as ＂stathmin＂, ＂microtubule dynamics＂, ＂epithelial-mesenchymal transition＂, ＂EMT＂, ＂malignant potential＂ and ＂cancer＂ was performed to identify relevant studies published in English.More than 100 related articles were reviewed.RESULTS： The literature clearly documented the relationship between stathmin and its microtubule-destabilizing activity of cancer development. However, the particular mechanism is poorly understood. Microtubule disruption is essential for EMT, which is a crucial process during cancer development. As a microtubule-destabilizing protein, stathmin may promote malignant potential in cancer cells by initiating EMT.CONCLUSIONS： We propose that there is a stathminmicrotubule dynamics-EMT（S-M-E） axis during cancer development. By this axis, stathmin together with itsmicrotubule-destabilizing activity contributes to EMT, which stimulates the malignant potential in cancer cells.

Mechanics of Centriole Microtubules

This is a review paper describing recent findings about the physical properties of centriolar microtubules. Microtubules are the principal structures making up the centrioles. The centrioles in turn are the principal agents in cell duplication and division (mitosis). The microtubules are seen to be long hollow cylinders: approximately 400 nm in length, with a 24 nm outside diameter, and a 5 nm wall thickness. Within the centrioles, the microtubules are arranged into nine parallel sets of triplets—thus numbering 27 parallel cylinders per centriole. Each normal eukaryotic (human and animal) cell, not in mitosis, has two perpendicular centrioles connected at their proximal (base) ends. During mitosis, these two become four, resulting in a total of 108 centriolar microtubules. The structure of the microtubules themselves is found to consist of 13 parallel filaments making up the cylinder walls. The filaments are composed of approximately 40 and β-tubulin connected end-to-end with their proximal (base) ends anchored in γ-tubulin. The longitudinal vibrations of the filaments are believed to create an electro-magnetic field within the cell which plays an important role in mitosis.

Inhibition of kinesin-5 improves regeneration of injured axons by a novel microtubule-based mechanism

Microtubules have been identified as a powerful target for augmenting regeneration of injured adult axons in the central nervous system. Drugs that stabilize microtubules have shown some promise, but there are concerns that abnormally stabilizing microtubules may have only limited benefits for regeneration, while at the same time may be detrimental to the normal work that microtubules perform for the axon. Kinesin-5 （also called kifl I or EgS）, a molecular motor protein best known for its crucial role in mitosis, acts as a brake on microtubule movements by other motor proteins in the axon. Drugs that inhibit kinesin-5, originally developed to treat cancer, result in greater mobility of microtubules in the axon and an overall shift in the forces on the microtubule array. As a result, the axon grows faster, retracts less, and more readily enters environments that are inhibitory to axonal regeneration. Thus, drugs that inhibit kinesin-5 offer a novel microtubule-based means to boost axonal regeneration without the concerns that accompany abnormal stabilization of the microtubule array. Even so, inhibiting kinesin-5 is not without its own caveats, such as potential problems with navigation of the regenerating axon to its target, as well as morphological effects on dendrites that could affect learning and memory if the drugs reach the brain.