Structural Basis for Induction of Peripheral Neuropathy by Microtubule-Targeting Cancer Drugs

Bystander Effects, Pharmacokinetics, and Linker-Payload Stability of EGFR-Targeting Antibody-Drug Conjugates Losatuxizumab Vedotin and Depatux-M in Glioblastoma Models

PURPOSE

Antibody-drug conjugates (ADC) are targeted therapies with robust efficacy in solid cancers, and there is intense interest in using EGFR-specific ADCs to target EGFR-amplified glioblastoma (GBM). Given GBM's molecular heterogeneity, the bystander activity of ADCs may be important for determining treatment efficacy. In this study, the activity and toxicity of two EGFR-targeted ADCs with similar auristatin toxins, Losatuxizumab vedotin (ABBV-221) and Depatuxizumab mafodotin (Depatux-M), were compared in GBM patient-derived xenografts (PDX) and normal murine brain following direct infusion by convection-enhanced delivery (CED).

EXPERIMENTAL DESIGN

EGFRviii-amplified and non-amplified GBM PDXs were used to determine in vitro cytotoxicity, in vivo efficacy, and bystander activities of ABBV-221 and Depatux-M. Nontumor-bearing mice were used to evaluate the pharmacokinetics (PK) and toxicity of ADCs using LC-MS/MS and immunohistochemistry.

RESULTS

CED improved intracranial efficacy of Depatux-M and ABBV-221 in three EGFRviii-amplified GBM PDX models (Median survival: 125 to >300 days vs. 20-49 days with isotype control AB095). Both ADCs had comparable in vitro and in vivo efficacy. However, neuronal toxicity and CD68+ microglia/macrophage infiltration were significantly higher in brains infused with ABBV-221 with the cell-permeable monomethyl auristatin E (MMAE), compared with Depatux-M with the cell-impermeant monomethyl auristatin F. CED infusion of ABBV-221 into the brain or incubation of ABBV-221 with normal brain homogenate resulted in a significant release of MMAE, consistent with linker instability in the brain microenvironment.

CONCLUSIONS

EGFR-targeting ADCs are promising therapeutic options for GBM when delivered intratumorally by CED. However, the linker and payload for the ADC must be carefully considered to maximize the therapeutic window.

Local production of reactive oxygen species drives vincristine-induced axon degeneration

Neurological side effects arising from chemotherapy, such as severe pain and cognitive impairment, are a major concern for cancer patients. These major side effects can lead to reduction or termination of chemotherapy medication in patients, negatively impacting their prognoses. With cancer survival rates improving dramatically, addressing side effects of cancer treatment has become pressing. Here, we use iPSC-derived human neurons to investigate the molecular mechanisms that lead to neurotoxicity induced by vincristine, a common chemotherapeutic used to treat solid tumors. Our results uncover a novel mechanism by which vincristine causes a local increase in mitochondrial proteins that produce reactive oxygen species (ROS) in the axon. Vincristine triggers a cascade of axon pathology, causing mitochondrial dysfunction that leads to elevated axonal ROS levels and SARM1-dependent axon degeneration. Importantly, we show that the neurotoxic effect of increased axonal ROS can be mitigated by the small molecule mitochondrial division inhibitor 1 (mdivi-1) and antioxidants glutathione and mitoquinone, identifying a novel therapeutic avenue to treat the neurological effects of chemotherapy.

Abnormal intraepidermal nerve fiber density in disease: A scoping review

Background

Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.

Methods

We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).

Results

We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 73 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6% and -34.7%, respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.

Interpretation

Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.

Spatial and temporal dynamics of ATP synthase from mitochondria toward the cell surface

Ectopic ATP synthase complex (eATP synthase), located on cancer cell surface, has been reported to possess catalytic activity that facilitates the generation of ATP in the extracellular environment to establish a suitable microenvironment and to be a potential target for cancer therapy. However, the mechanism of intracellular ATP synthase complex transport remains unclear. Using a combination of spatial proteomics, interaction proteomics, and transcriptomics analyses, we find ATP synthase complex is first assembled in the mitochondria and subsequently delivered to the cell surface along the microtubule via the interplay of dynamin-related protein 1 (DRP1) and kinesin family member 5B (KIF5B). We further demonstrate that the mitochondrial membrane fuses to the plasma membrane in turn to anchor ATP syntheses on the cell surface using super-resolution imaging and real-time fusion assay in live cells. Our results provide a blueprint of eATP synthase trafficking and contribute to the understanding of the dynamics of tumor progression.

Abnormal Intraepidermal Nerve Fiber Density in Disease: A Scoping Review

Background

Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.

Methods

We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).

Results

We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 74 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6 % and - 34.7% respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.

Interpretation

Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.

Anti-Inflammatory Properties of KLS-13019: a Novel GPR55 Antagonist for Dorsal Root Ganglion and Hippocampal Cultures

KLS-13019, a novel devised cannabinoid-like compound, was explored for anti-inflammatory actions in dorsal root ganglion cultures relevant to chemotherapy-induced peripheral neuropathy (CIPN). Time course studies with 3 µM paclitaxel indicated > 1.9-fold increases in immunoreactive (IR) area for cell body GPR55 after 30 min as determined by high content imaging. To test for reversibility of paclitaxel-induced increases in GPR55, cultures were treated for 8 h with paclitaxel alone and then a dose response to KLS-13019 added for another 16 h. This "reversal" paradigm indicated established increases in cell body GPR55 IR areas were decreased back to control levels. Because GPR55 had previously reported inflammatory actions, IL-1β and NLRP3 (inflammasome-3 marker) were also measured in the "reversal" paradigm. Significant increases in all inflammatory markers were produced after 8 h of paclitaxel treatment alone that were reversed to control levels with KLS-13019 treatment. Accompanying studies using alamar blue indicated that decreased cellular viability produced by paclitaxel treatment was reverted back to control levels by KLS-13019. Similar studies conducted with lysophosphatidylinositol (GPR55 agonist) in DRG or hippocampal cultures demonstrated significant increases in neuritic GPR55, NLRP3 and IL-1β areas that were reversed to control levels with KLS-13019 treatment. Studies with a human GPR55-β-arrestin assay in Discover X cells indicated that KLS-13019 was an antagonist without agonist activity. These studies indicated that KLS-13019 has anti-inflammatory properties mediated through GPR55 antagonist actions. Together with previous studies, KLS-13019 is a potent neuroprotective, anti-inflammatory cannabinoid with therapeutic potential for high efficacy treatment of neuropathic pain.

Building a Network of Adverse Outcome Pathways (AOPs) Incorporating the Tau-Driven AOP Toward Memory Loss (AOP429)

The adverse outcome pathway (AOP) concept was first proposed as a tool for chemical hazard assessment facilitating the regulatory decision-making in toxicology and was more recently recommended during the BioMed21 workshops as a tool for the characterization of crucial endpoints in the human disease development. This AOP framework represents mechanistically based approaches using existing data, more realistic and relevant to human biological systems. In principle, AOPs are described by molecular initiating events (MIEs) which induce key events (KEs) leading to adverse outcomes (AOs). In addition to the individual AOPs, the network of AOPs has been also suggested to beneficially support the understanding and prediction of adverse effects in risk assessment. The AOP-based networks can capture the complexity of biological systems described by different AOPs, in which multiple AOs diverge from a single MIE or multiple MIEs trigger a cascade of KEs that converge to a single AO. Here, an AOP network incorporating a recently proposed tau-driven AOP toward memory loss (AOP429) related to sporadic (late-onset) Alzheimer’s disease is constructed. This proposed AOP network is an attempt to extract useful information for better comprehending the interactions among existing mechanistic data linked to memory loss as an early phase of sporadic Alzheimer’s disease pathology.

PI3K/AKT Signaling Tips the Balance of Cytoskeletal Forces for Cancer Progression

The PI3K/AKT signaling pathway plays essential roles in multiple cellular processes, which include cell growth, survival, metabolism, and motility. In response to internal and external stimuli, the PI3K/AKT signaling pathway co-opts other signaling pathways, cellular components, and cytoskeletal proteins to reshape individual cells. The cytoskeletal network comprises three main components, which are namely the microfilaments, microtubules, and intermediate filaments. Collectively, they are essential for many fundamental structures and cellular processes. In cancer, aberrant activation of the PI3K/AKT signaling cascade and alteration of cytoskeletal structures have been observed to be highly prevalent, and eventually contribute to many cancer hallmarks. Due to their critical roles in tumor progression, pharmacological agents targeting PI3K/AKT, along with cytoskeletal components, have been developed for better intervention strategies against cancer. In our review, we first discuss existing evidence in-depth and then build on recent advances to propose new directions for therapeutic intervention.

Clinical and preclinical features of eribulin-related peripheral neuropathy

Different microtubule-targeting agents (MTAs) possess distinct modes of action and their clinical use in cancer treatment is often limited by chemotherapy-induced peripheral neurotoxicity (CIPN). Eribulin is a member of the halichondrin class of antineoplastic drugs, which is correlated with a high antimitotic activity against metastatic breast cancer and liposarcoma. Current clinical evidence suggests that eribulin treatment, unlike some of the other MTAs, is associated with a relatively low incidence of severe peripheral neuropathy. This suggests that different MTAs possess unique mechanisms of neuropathologic induction. Animal models reliably reproduced eribulin-related neuropathy providing newer insights in CIPN pathogenesis, and they are highly suitable for in vivo functional, symptomatic and morphological characterizations of eribulin-related CIPN. The purpose of this review is to discuss the most recent literature on eribulin with a focus on both clinical and preclinical data, to explain the molecular events responsible for its favorable neurotoxic profile.

Toxicity in Peripheral Nerves: An Overview

Introduction to a collection. This article is intended to introduce a collection of papers on toxic neuropathies. Toxic neuropathies can be caused by a variety of substances and by different mechanisms. Toxic agents are numerous and can be distinguished between drugs, recreational agents, heavy metals, industrial agents, pesticides, warfare agents, biologic substances and venoms. Toxic agents reach the nervous system by ingestion, transcutaneously, via the mucous membranes, parenterally and by aerosols. The most frequent types are cumulative toxicities. Other types are acute or delayed toxicities. Pathogenetic mechanisms range from a specific toxic substance profile causing axonal or demyelinating lesions, towards ion channel interferences, immune-mediated mechanisms and a number of different molecular pathways. In addition, demyelination, focal lesions and small fiber damage may occur. Clinically, neurotoxicity presents most frequently as axonal symmetric neuropathies. In this work, we present a panoramic view of toxic neuropathy, in terms of symptoms, causes, mechanisms and classification.

Mini-Review: Mitochondrial dysfunction and chemotherapy-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) is a somatosensory axonopathy in cancer patients receiving any of a variety of widely-use antitumor agents. CIPN can lead to long-lasting neuropathic pain that limits the dose or length of otherwise life-saving cancer therapy. Accumulating evidence over the last two decades indicates that many chemotherapeutic agents cause mitochondrial injury in the peripheral sensory nerves by disrupting mitochondrial structure and bioenergetics, increasing nitro-oxidative stress and altering mitochondrial transport, fission, fusion and mitophagy. The accumulation of abnormal and dysfunctional mitochondria in sensory neurons are linked to axonal growth defects resulting in the loss of intraepidermal nerve fibers in the hands and feet, increased spontaneous discharge and the sensitization of peripheral sensory neurons that provoke and promote changes in the central nervous system that establish a chronic neuropathic pain state. This has led to the propose mitotoxicity theory of CIPN. Strategies that improve mitochondrial function have shown success in preventing and reversing CIPN in pre-clinical animal models and have begun to show some progress toward translation to the clinic. In this review, we will review the evidence for, the causes and effects of and current strategies to target mitochondrial dysfunction in CIPN.

Microtubule and tubulin binding and regulation of microtubule dynamics by the antibody drug conjugate (ADC) payload, monomethyl auristatin E (MMAE): Mechanistic insights into MMAE ADC peripheral neuropathy

Monomethyl auristatin E (MMAE) is a potent anti-cancer microtubule-targeting agent (MTA) used as a payload in three approved MMAE-containing antibody drug conjugates (ADCs) and multiple ADCs in clinical development to treat different types of cancers. Unfortunately, MMAE-ADCs can induce peripheral neuropathy, a frequent adverse event leading to treatment dose reduction or discontinuation and subsequent clinical termination of many MMAE-ADCs. MMAE-ADC-induced peripheral neuropathy is attributed to non-specific uptake of the ADC in peripheral nerves and release of MMAE, disrupting microtubules (MTs) and causing neurodegeneration. However, molecular mechanisms underlying MMAE and MMAE-ADC effects on MTs remain unclear. Here, we characterized MMAE-tubulin/MT interactions in reconstituted in vitro soluble tubulin or MT systems and evaluated MMAE and vcMMAE-ADCs in cultured human MCF7 cells. MMAE bound to soluble tubulin heterodimers with a maximum stoichiometry of ~1:1, bound abundantly along the length of pre-assembled MTs and with high affinity at MT ends, introduced structural defects, suppressed MT dynamics, and reduced the kinetics and extent of MT assembly while promoting tubulin ring formation. In cells, MMAE and MMAE-ADC (via nonspecific uptake) suppressed proliferation, mitosis and MT dynamics, and disrupted the MT network. Comparing MMAE action to other MTAs supports the hypothesis that peripheral neuropathy severity is determined by the precise mechanism(s) of each individual drug-MT interaction (location of binding, affinity, effects on morphology and dynamics). This work demonstrates that MMAE binds extensively to tubulin and MTs and causes severe MT dysregulation, providing convincing evidence that MMAE-mediated inhibition of MT-dependent axonal transport leads to severe peripheral neuropathy.

Comparative Analysis of Chemotherapy-Induced Peripheral Neuropathy in Bioengineered Sensory Nerve Tissue Distinguishes Mechanistic Differences in Early-Stage Vincristine-, Cisplatin-, and Paclitaxel-Induced Nerve Damage

Chemotherapy-induced peripheral neuropathy (CIPN) is a well-known, potentially permanent side effect of widely used antineoplastic agents. The mechanisms of neuropathic progression are poorly understood, and the need to test efficacy of novel interventions to treat CIPN continues to grow. Bioengineered microphysiological nerve tissue ("nerve on a chip") has been suggested as an in vitro platform for modeling the structure and physiology of in situ peripheral nerve tissue. Here, we find that length-dependent nerve conduction and histopathologic changes induced by cisplatin, paclitaxel, or vincristine in rat dorsal root ganglion-derived microphysiological sensory nerve tissue recapitulate published descriptions of clinical electrophysiological changes and neuropathologic biopsy findings in test animals and human patients with CIPN. We additionally confirm the postulated link between vincristine-induced axoplasmic transport failure and functional impairment of nerve conduction, the postulated paclitaxel-induced somal toxicity, and identify a potential central role of gliotoxicity in cisplatin-induced sensory neuropathy. Microphysiological CIPN combines the tight experimental control afforded by in vitro experimentation with clinically relevant functional and structural outputs that conventionally require in vivo models. Microphysiological nerve tissue provides a low-cost, high-throughput alternative to conventional nonclinical models for efficiently and effectively investigating lesions, mechanisms, and treatments of CIPN. Neural microphysiological systems are capable of modeling complex neurological disease at the tissue level offering unique advantages over conventional methodology for both testing and generating hypotheses in neurological disease modeling. Impact Statement Recapitulation of distinct hallmarks of clinical CIPN in microphysiological sensory nerve validates a novel peripheral neurotoxicity model with unique advantages over conventional model systems.

Vincristine- and bortezomib-induced neuropathies - from bedside to bench and back

Vincristine and bortezomib are effective chemotherapeutics widely used to treat hematological cancers. Vincristine blocks tubulin polymerization, whereas bortezomib is a proteasome inhibitor. Despite different mechanisms of action, the main non-hematological side effect of both is peripheral neuropathy that can last long after treatment has ended and cause permanent disability. Many different cellular and animal models of various aspects of vincristine and bortezomib-induced neuropathies have been generated to investigate underlying molecular mechanisms and serve as platforms to develop new therapeutics. These models revealed that bortezomib induces several transcriptional programs in dorsal root ganglia that result in the activation of different neuroinflammatory pathways and secondary central sensitization. In contrast, vincristine has direct toxic effects on the axon, which are accompanied by changes similar to those observed after nerve cut. Axon degeneration following both vincristine and bortezomib is mediated by a phylogenetically ancient, genetically encoded axon destruction program that leads to the activation of the Toll-like receptor adaptor SARM1 (sterile alpha and TIR motif containing protein 1) and local decrease of nicotinamide dinucleotide (NAD+). Here, I describe current in vitro and in vivo models of vincristine- and bortezomib induced neuropathies, present discoveries resulting from these models in the context of clinical findings and discuss how increased understanding of molecular mechanisms underlying different aspects of neuropathies can be translated to effective treatments to prevent, attenuate or reverse vincristine- and bortezomib-induced neuropathies. Such treatments could improve the quality of life of patients both during and after cancer therapy and, accordingly, have enormous societal impact.

Drug Repositioning for the Prevention and Treatment of Chemotherapy-Induced Peripheral Neuropathy: A Mechanism- and Screening-Based Strategy

Chemotherapy-induced peripheral neuropathy (CIPN) is a severe adverse effect observed in most patients treated with neurotoxic anti-cancer drugs. Currently, there are no therapeutic options available for the prevention of CIPN. Furthermore, few drugs are recommended for the treatment of existing neuropathies because the mechanisms of CIPN remain unclear. Each chemotherapeutic drug induces neuropathy by distinct mechanisms, and thus we need to understand the characteristics of CIPN specific to individual drugs. Here, we review the known pathogenic mechanisms of oxaliplatin- and paclitaxel-induced CIPN, highlighting recent findings. Cancer chemotherapy is performed in a planned manner; therefore, preventive strategies can be planned for CIPN. Drug repositioning studies, which identify the unexpected actions of already approved drugs, have increased in recent years. We have also focused on drug repositioning studies, especially for prevention, because they should be rapidly translated to patients suffering from CIPN.

Human Induced Pluripotent Stem Cell Derived Sensory Neurons are Sensitive to the Neurotoxic Effects of Paclitaxel

Chemotherapy‐induced peripheral neuropathy (CIPN) is a dose‐limiting adverse event associated with treatment with paclitaxel and other chemotherapeutic agents. The prevention and treatment of CIPN are limited by a lack of understanding of the molecular mechanisms underlying this toxicity. In the current study, a human induced pluripotent stem cell–derived sensory neuron (iPSC‐SN) model was developed for the study of chemotherapy‐induced neurotoxicity. The iPSC‐SNs express proteins characteristic of nociceptor, mechanoreceptor, and proprioceptor sensory neurons and show Ca²⁺ influx in response to capsaicin, α,β‐meATP, and glutamate. The iPSC‐SNs are relatively resistant to the cytotoxic effects of paclitaxel, with half‐maximal inhibitory concentration (IC₅₀) values of 38.1 µM (95% confidence interval (CI) 22.9–70.9 µM) for 48‐hour exposure and 9.3 µM (95% CI 5.7–16.5 µM) for 72‐hour treatment. Paclitaxel causes dose‐dependent and time‐dependent changes in neurite network complexity detected by βIII‐tubulin staining and high content imaging. The IC₅₀ for paclitaxel reduction of neurite area was 1.4 µM (95% CI 0.3–16.9 µM) for 48‐hour exposure and 0.6 µM (95% CI 0.09–9.9 µM) for 72‐hour exposure. Decreased mitochondrial membrane potential, slower movement of mitochondria down the neurites, and changes in glutamate‐induced neuronal excitability were also observed with paclitaxel exposure. The iPSC‐SNs were also sensitive to docetaxel, vincristine, and bortezomib. Collectively, these data support the use of iPSC‐SNs for detailed mechanistic investigations of genes and pathways implicated in chemotherapy‐induced neurotoxicity and the identification of novel therapeutic approaches for its prevention and treatment.

Two Antagonistic Microtubule Targeting Drugs Act Synergistically to Kill Cancer Cells

Paclitaxel is a microtubule stabilizing agent and a successful drug for cancer chemotherapy inducing, however, adverse effects. To reduce the effective dose of paclitaxel, we searched for pharmaceutics which could potentiate its therapeutic effect. We screened a chemical library and selected Carba1, a carbazole, which exerts synergistic cytotoxic effects on tumor cells grown in vitro, when co-administrated with a low dose of paclitaxel. Carba1 targets the colchicine binding-site of tubulin and is a microtubule-destabilizing agent. Catastrophe induction by Carba1 promotes paclitaxel binding to microtubule ends, providing a mechanistic explanation of the observed synergy. The synergistic effect of Carba1 with paclitaxel on tumor cell viability was also observed in vivo in xenografted mice. Thus, a new mechanism favoring paclitaxel binding to dynamic microtubules can be transposed to in vivo mouse cancer treatments, paving the way for new therapeutic strategies combining low doses of microtubule targeting agents with opposite mechanisms of action.

Microtubule-targeting agents and their impact on cancer treatment

Microtubule-targeting agents (MTAs) constitute a diverse group of chemical compounds that bind to microtubules and affect their properties and function. Disruption of microtubules induces various cellular responses often leading to cell cycle arrest or cell death, the most common effect of MTAs. MTAs have found a plethora of practical applications in weed control, as fungicides and antiparasitics, and particularly in cancer treatment. Here we summarize the current knowledge of MTAs, the mechanisms of action and their role in cancer treatment. We further outline the potential use of MTAs in anti-metastatic therapy based on inhibition of cancer cell migration and invasiveness. The two main problems associated with cancer therapy by MTAs are high systemic toxicity and development of resistance. Toxic side effects of MTAs can be, at least partly, eliminated by conjugation of the drugs with various carriers. Moreover, some of the novel MTAs overcome the resistance mediated by both multidrug resistance transporters as well as overexpression of specific β-tubulin types. In anti-metastatic therapy, MTAs should be combined with other drugs to target all modes of cancer cell invasion.

The impact of anticancer drugs on the ocular surface

Cancer is a global health problem and is one of the leading causes of death worldwide. Pleasingly, the rate of survival has improved and continues in an upward trend mainly due to better diagnosis and treatment modalities. In particular, the development of anticancer drugs including cytotoxic chemotherapy, hormonal agents and targeted therapies have provided the most effective treatment options in combatting cancerous cells. However, the antineoplastic mechanisms of these drugs can also lead to undesirable systemic and ocular side effects resulting from cytotoxicity, inflammation and neurotoxicity. While survival rates are projected to increase with time, the number of patients presenting with these side effects that can substantially impact quality of life will also rise. The current paper reviews the ocular surface and adnexal side effects of anticancer drugs, the appropriate management and possible interactions between drugs for ocular surface pathology treatment and the anticancer drugs.

Pathogenesis of paclitaxel-induced peripheral neuropathy: A current review of in vitro and in vivo findings using rodent and human model systems

Paclitaxel (Brand name Taxol) is widely used in the treatment of common cancers like breast, ovarian and lung cancer. Although highly effective in blocking tumor progression, paclitaxel also causes peripheral neuropathy as a side effect in 60-70% of chemotherapy patients. Recent efforts by numerous labs have aimed at defining the underlying mechanisms of paclitaxel-induced peripheral neuropathy (PIPN). In vitro models using rodent dorsal root ganglion neurons, human induced pluripotent stem cells, and rodent in vivo models have revealed a number of molecular pathways affected by paclitaxel within axons of sensory neurons and within other cell types, such as the immune system and peripheral glia, as well skin. These studies revealed that paclitaxel induces altered calcium signaling, neuropeptide and growth factor release, mitochondrial damage and reactive oxygen species formation, and can activate ion channels that mediate responses to extracellular cues. Recent studies also suggest a role for the matrix-metalloproteinase 13 (MMP-13) in mediating neuropathy. These diverse changes may be secondary to paclitaxel-induced microtubule transport impairment. Human genetic studies, although still limited, also highlight the involvement of cytoskeletal changes in PIPN. Newly identified molecular targets resulting from these studies could provide the basis for the development of therapies with which to either prevent or reverse paclitaxel-induced peripheral neuropathy in chemotherapy patients.

Assessing pathological changes within the nucleus ambiguus of horses with recurrent laryngeal neuropathy: An extreme, length-dependent axonopathy

INTRODUCTION

Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterized by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn). Distal RLn degeneration is marked, but it is unclear whether degeneration extends to include cell bodies (consistent with a neuronopathy).

METHODS

With examiners blinded to RLN severity, brainstem location, and side, we examined correlations between RLN severity (assessed using left distal RLn myelinated axon count) and histopathological features (including chromatolysis and glial responses) in the nucleus ambiguus cell bodies, and myelinated axon count of the right distal RLn of 16 horses.

RESULTS

RLN severity was not associated with RLn cell body number (P > .05), or degeneration. A positive correlation between the left and right distal RLn myelinated axon counts was identified (R² = 0.57, P < .05).

DISCUSSION

We confirm that RLN, a length-dependent distal axonopathy, occurs in the absence of detectable neuronopathy.

Tubulin-VDAC Interaction: Molecular Basis for Mitochondrial Dysfunction in Chemotherapy-Induced Peripheral Neuropathy

Tubulin is a well-established target of microtubule-targeting agents (MTAs), a widely used class of chemotherapeutic drugs. Yet, aside from their powerful anti-cancer efficiency, MTAs induce a dose-limiting and debilitating peripheral neurotoxicity. Despite intensive efforts in the development of neuroprotective agents, there are currently no approved therapies to effectively manage chemotherapy-induced peripheral neuropathy (CIPN). Over the last decade, attempts to unravel the pathomechanisms underlying the development of CIPN led to the observation that mitochondrial dysfunctions stand as a common feature associated with axonal degeneration. Concomitantly, mitochondria emerged as crucial players in the anti-cancer efficiency of MTAs. The findings that free dimeric tubulin could be associated with mitochondrial membranes and interact directly with the voltage-dependent anion channels (VDACs) located in the mitochondrial outer membrane strongly suggested the existence of an interplay between both subcellular compartments. The biological relevance of the interaction between tubulin and VDAC came from subsequent in vitro studies, which found dimeric tubulin to be a potent modulator of VDAC and ultimately of mitochondrial membrane permeability to respiratory substrates. Therefore, one of the hypothetic mechanisms of CIPN implies that MTAs, by binding directly to the tubulin associated with VDAC, interferes with mitochondrial function in the peripheral nervous system. We review here the foundations of this hypothesis and discuss them in light of the current knowledge. A focus is set on the molecular mechanisms behind MTA interference with dimeric tubulin and VDAC interaction, the potential relevance of tubulin isotypes and availability as a free dimer in the specific context of MTA-induced CIPN. We further highlight the emerging interest for VDAC and its interacting partners as a promising therapeutic target in neurodegeneration.

Microtubule-Targeting Drugs: More than Antimitotics

Nature has yielded numerous compounds that bind to tubulin/microtubules and disrupt microtubule function. Even with the advent of targeted therapies for cancer, natural products and their derivatives that target microtubules are some of the most effective drugs used in the treatment of solid tumors and hematological malignancies. For decades, these drugs were thought to work solely through their ability to inhibit mitosis. Accumulating evidence demonstrates that their actions are much more complex, in that they also have significant effects on microtubules in nondividing cells that inhibit a diverse range of signaling events important for carcinogenesis. The abilities of these drugs to inhibit oncogenic signaling likely underlies their efficacy, especially in solid tumors. In this review, we describe the role of microtubules in cells, the proliferation paradox of cells in culture as compared to cancers in patients, and evidence that microtubule-targeting drugs inhibit cellular signaling pathways important for tumorigenesis. The potential mechanisms behind differences in the clinical indications and efficacy of these natural-product-derived drugs are also discussed. Microtubules are an important target for structurally diverse natural products, and a fuller understanding of the mechanisms of action of these drugs will promote their optimal use.

Polyester Nanoparticle Encapsulation Mitigates Paclitaxel-Induced Peripheral Neuropathy

Chemotherapy utilizing cytotoxic drugs, such as paclitaxel (PTX), is still a commonly used therapeutic approach to treat both localized and metastasized cancers. Unlike traditional regimens in which PTX is administered at the maximum tolerated dose, alternative regimens like metronomic dosing are beneficial by administering PTX more frequently and in much lower doses exploiting antiangiogenic and immunomodulatory effects. However, PTX-induced peripheral neuropathy and lack of patient compliant dosage forms of PTX are major roadblocks for the successful implementation of metronomic regimens. Because of the success of polyester nanoparticle drug delivery, we explored the potential of nanoparticle-encapsulated paclitaxel (nPTX) in alleviating peripheral neuropathy using a rat model. Rats were injected intraperitoneally with 2 mg/kg body weight of PTX or nPTX on four alternate days, and neuropathic pain and neuronal damage were characterized using behavioral assessments, histology, and immunohistochemistry. The reduction in tactile and nociceptive pressure thresholds was significantly less in nPTX-treated rats than in PTX-treated rats over a 16-day study period. Histological analysis showed that the degree of dorsal root ganglion (DRG) degeneration and reduction in motor neurons in the spinal cord was significantly lower in the nPTX group than the PTX group. Further, immunofluorescence data reveals that nPTX-treated rats had an increased density of a neuronal marker, β-tubulin-III, reduced TUNEL positive cells, and increased high molecular weight neurofilament in the spinal cord, DRG, and sciatic nerves compared with PTX-treated rats. Therefore, this work has important implications in improving risk-benefit profile of PTX, paving the way for metronomic regimens.

Chemotherapy-induced peripheral neuropathy in breast cancer patients treated with eribulin: interim data from a post-marketing observational study

Background

Few studies have examined chemotherapy-induced peripheral neuropathy (CIPN) following the administration of eribulin as first- or second-line therapy in patients with breast cancer. We therefore assessed CIPN incidence by severity and risk factors for CIPN in patients treated with eribulin for HER2-negative inoperable or recurrent breast cancer, regardless of line therapy status.

Methods

This multicenter, prospective, post-marketing observational study enrolled patients from September 2014 in Japan and followed them for 2 years. For this interim analysis, the data cut-off point was in November 2017. CIPN severity was assessed based on the Japanese version of the Common Terminology Criteria for Adverse Events, version 4.0.

Results

Among 634 patients included in the safety analysis, 374 patients did not have existing CIPN at baseline. CIPN was observed in 105 patients (28.1%), including 67 (17.9%), 34 (9.1%), and 4 (1.1%) patients with grade 1, 2, and 3 severity, respectively. Of the 105 patients, 85.7% patients continued, 7.6% reduced, interrupted or postponed, and 6.7% discontinued eribulin. The median time (min‒max) from baseline to CIPN onset was 60 (3‒337) days. Multivariate logistic regression identified a significant association between CIPN and hemoglobin level at baseline, starting dose of eribulin, and history of radiotherapy.

Conclusions

Our findings indicate that, with respect to CIPN, eribulin is well-tolerated, as approximately one-quarter of patients developed CIPN, most cases were grade 1 or 2, and the majority of patients continued eribulin after CIPN onset.

Electronic supplementary material

The online version of this article (10.1007/s12282-018-0919-8) contains supplementary material, which is available to authorized users.

General Approach to Peripheral Nerve Disorders

PURPOSE OF REVIEW

This article provides a conceptual framework for the evaluation of patients with suspected polyneuropathy to enhance the clinician's ability to localize and confirm peripheral nervous system pathology and, when possible, identify an etiologic diagnosis through use of rational clinical and judicious testing strategies.

RECENT FINDINGS

Although these strategies are largely time-honored, recent insights pertaining to the pathophysiology of certain immune-mediated neuropathies and to evolving genetic testing strategies may modify the way that select causes of neuropathy are conceptualized, evaluated, and managed.

SUMMARY

The strategies suggested in this article are intended to facilitate accurate bedside diagnosis in patients with suspected polyneuropathy and allow efficient and judicious use of supplementary testing and application of rational treatment when indicated.

Microtubule-Targeting Agents Eribulin and Paclitaxel Differentially Affect Neuronal Cell Bodies in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of anticancer treatment with microtubule-targeted agents (MTAs). The frequency of severe CIPN, which can be dose limiting and even life threatening, varies widely among different MTAs. For example, paclitaxel induces a higher frequency of severe CIPN than does eribulin. Different MTAs also possess distinct mechanisms of microtubule-targeted action. Recently, we demonstrated that paclitaxel and eribulin differentially affect sciatic nerve axons, with paclitaxel inducing more pronounced neurodegenerative effects and eribulin inducing greater microtubule stabilizing biochemical effects. Here, we complement and extend these axonal studies by assessing the effects of paclitaxel and eribulin in the cell bodies of sciatic nerve axons, housed in the dorsal root ganglia (DRG). Importantly, the microtubule network in cell bodies is known to be significantly more dynamic than in axons. Paclitaxel induced activating transcription factor 3 expression, a marker of neuronal stress/injury. Paclitaxel also increased expression levels of acetylated tubulin and end binding protein 1, markers of microtubule stability and growth, respectively. These effects are hypothesized to be detrimental to the dynamic microtubule network within the cell bodies. In contrast, eribulin had no significant effect on any of these parameters in the cell bodies. Taken together, DRG cell bodies and their axons, two distinct neuronal cell compartments, contain functionally distinct microtubule networks that exhibit unique biochemical responses to different MTA treatments. We hypothesize that these distinct mechanistic actions may underlie the variability seen in the initiation, progression, persistence, and recovery from CIPN.

Efficacy of eribulin in breast cancer: a short report on the emerging new data

Eribulin is a novel microtubule-targeting agent that is approved for the treatment of patients with locally advanced or metastatic breast cancer who have previously received treatment with an anthracycline and a taxane in either the adjuvant or metastatic setting. Eribulin induces mitotic catastrophe leading to cell death but has other important antitumor effects, including reversal of epithelial–mesenchymal transition and remodeling of the tumor vasculature. Eribulin was licensed for the treatment of advanced breast cancer based on results from two large randomized Phase III clinical trials. Current clinical trials of eribulin for breast cancer are evaluating response to treatment earlier in the patient pathway and in combination with other therapeutic agents. This review provides a short overview of emerging new data on the mode of action of eribulin in breast cancer.