Addendum: The antibody aducanumab reduces Aß plaques in Alzheimer's disease.

This corrects the article DOI: 10.1038/nature21361.

Pharmacological SARM1 inhibition protects axon structure and function in paclitaxel-induced peripheral neuropathy.

Axonal degeneration is an early and ongoing event that causes disability and disease progression in many neurodegenerative disorders of the peripheral and central nervous systems. Chemotherapy-induced peripheral neuropathy (CIPN) is a major cause of morbidity and the main cause of dose reductions and discontinuations in cancer treatment. Preclinical evidence indicates that activation of the Wallerian-like degeneration pathway driven by sterile alpha and TIR motif containing 1 (SARM1) is responsible for axonopathy in CIPN. SARM1 is the central driver of an evolutionarily conserved programme of axonal degeneration downstream of chemical, inflammatory, mechanical or metabolic insults to the axon. SARM1 contains an intrinsic NADase enzymatic activity essential for its pro-degenerative functions, making it a compelling therapeutic target to treat neurodegeneration characterized by axonopathies of the peripheral and central nervous systems. Small molecule SARM1 inhibitors have the potential to prevent axonal degeneration in peripheral and central axonopathies and to provide a transformational disease-modifying treatment for these disorders. Using a biochemical assay for SARM1 NADase we identified a novel series of potent and selective irreversible isothiazole inhibitors of SARM1 enzymatic activity that protected rodent and human axons in vitro. In sciatic nerve axotomy, we observed that these irreversible SARM1 inhibitors decreased a rise in nerve cADPR and plasma neurofilament light chain released from injured sciatic nerves in vivo. In a mouse paclitaxel model of CIPN we determined that Sarm1 knockout mice prevented loss of axonal function, assessed by sensory nerve action potential amplitudes of the tail nerve, in a gene-dosage-dependent manner. In that CIPN model, the irreversible SARM1 inhibitors prevented loss of intraepidermal nerve fibres induced by paclitaxel and provided partial protection of axonal function assessed by sensory nerve action potential amplitude and mechanical allodynia.

The antibody aducanumab reduces Aß plaques in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by deposition of amyloid-ß (Aß) plaques and neurofibrillary tangles in the brain, accompanied by synaptic dysfunction and neurodegeneration. Antibody-based immunotherapy against Aß to trigger its clearance or mitigate its neurotoxicity has so far been unsuccessful. Here we report the generation of aducanumab, a human monoclonal antibody that selectively targets aggregated Aß. In a transgenic mouse model of AD, aducanumab is shown to enter the brain, bind parenchymal Aß, and reduce soluble and insoluble Aß in a dose-dependent manner. In patients with prodromal or mild AD, one year of monthly intravenous infusions of aducanumab reduces brain Aß in a dose- and time-dependent manner. This is accompanied by a slowing of clinical decline measured by Clinical Dementia Rating-Sum of Boxes and Mini Mental State Examination scores. The main safety and tolerability findings are amyloid-related imaging abnormalities. These results justify further development of aducanumab for the treatment of AD. Should the slowing of clinical decline be confirmed in ongoing phase 3 clinical trials, it would provide compelling support for the amyloid hypothesis.

Studies to Assess the Utility of Serum Neurofilament Light Chain as a Biomarker in Chemotherapy-Induced Peripheral Neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most common and disabling dose-limiting toxicities of chemotherapy. We report here the results of two separate non-interventional studies (49 patients), which evaluated blood neurofilament light chain (NfL) as a biomarker of CIPN in breast cancer patients treated with paclitaxel. All patients underwent a standard treatment protocol that was established independently of the present studies. NfL was measured in serum using an ultrasensitive single-molecule array and compared with the self-administered European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-CIPN twenty-item scale (CIPN20) and Total Neuropathy Score clinical version (TNSc), a clinician-reported measure of neuropathy progression. The TNSc increased with cumulative dose compared with baseline, and the NfL concentrations were also strongly associated with the cumulative dose of chemotherapy. The analysis showed a correlation between TNSc and NfL. Both TNSc and NfL showed weak to moderate associations with CIPN20 subscores, with a better association for the CIPN20 sensory compared with motor and autonomic subscores. Data from the two studies provide evidence that serum NfL has the potential to be used as a biomarker to monitor and mitigate CIPN. However, studies with additional patients planned in the ongoing clinical trial will determine the universal application of NfL as a biomarker in CIPN.

Multiple actions of systemic artemin in experimental neuropathy.

The clinical management of neuropathic pain is particularly challenging. Current therapies for neuropathic pain modulate nerve impulse propagation or synaptic transmission; these therapies are of limited benefit and have undesirable side effects. Injuries to peripheral nerves result in a host of pathophysiological changes associated with the sustained expression of abnormal pain. Here we show that systemic, intermittent administration of artemin produces dose- and time-related reversal of nerve injury-induced pain behavior, together with partial to complete normalization of multiple morphological and neurochemical features of the injury state. These effects of artemin were sustained for at least 28 days. Higher doses of artemin than those completely reversing experimental neuropathic pain did not elicit sensory or motor abnormalities. Our results indicate that the behavioral symptoms of neuropathic pain states can be treated successfully, and that partial to complete reversal of associated morphological and neurochemical changes is achievable with artemin.

Small Molecule SARM1 Inhibitors Recapitulate the SARM1-/- Phenotype and Allow Recovery of a Metastable Pool of Axons Fated to Degenerate.

Axonal degeneration is responsible for disease progression and accumulation of disability in many neurodegenerative conditions. The axonal degenerative process can generate a metastable pool of damaged axons that remain structurally and functionally viable but fated to degenerate in the absence of external intervention. SARM1, an NADase that depletes axonal energy stores upon activation, is the central driver of an evolutionarily conserved program of axonal degeneration. We identify a potent and selective small molecule isoquinoline inhibitor of SARM1 NADase that recapitulates the SARM1-/- phenotype and protects axons from degeneration induced by axotomy or mitochondrial dysfunction. SARM1 inhibition post-mitochondrial injury with rotenone allows recovery and rescues axons that already entered the metastable state. We conclude that SARM1 inhibition with small molecules has the potential to treat axonopathies of the central and peripheral nervous systems by preventing axonal degeneration and by allowing functional recovery of a metastable pool of damaged, but viable, axons.

Axons Matter: The Promise of Treating Neurodegenerative Disorders by Targeting SARM1-Mediated Axonal Degeneration.

Attempts to develop neuroprotective treatments for neurodegenerative disorders have not yet been clinically successful. Axonal degeneration has been recognized as a predominant driver of disability and disease progression in central nervous system (CNS) diseases such as amyotrophic lateral sclerosis (ALS), multiple sclerosis, and Parkinson's disease, peripheral nervous system (PNS) disorders such as chemotherapy-induced, diabetic, and inherited neuropathies, and ocular disorders, such as glaucoma. In recent years, sterile alpha and TIR motif containing 1 (SARM1) has emerged as the first compelling axonal-specific target for therapeutic intervention. In this review, we discuss the role of axonal degeneration in neurodegenerative disorders, with a focus on SARM1 and the discovery of its intrinsic enzymatic function. Establishment of neurofilament light chain (NfL) as a reliable biomarker of axonal damage, and the availability of an ultrasensitive method for measuring NfL in plasma or serum, provide translational tools to make development of axonal protective, SARM1 inhibitors a viable approach to treat multiple neurodegenerative disorders.

cADPR is a gene dosage-sensitive biomarker of SARM1 activity in healthy, compromised, and degenerating axons.

SARM1 is the central executioner of pathological axon degeneration, promoting axonal demise in response to axotomy, traumatic brain injury, and neurotoxic chemotherapeutics that induce peripheral neuropathy. SARM1 is an injury-activated NAD+ cleavage enzyme, and this NADase activity is required for the pro-degenerative function of SARM1. At present, SARM1 function is assayed by either analysis of axonal loss, which is far downstream of SARM1 enzymatic activity, or via NAD+ levels, which are regulated by many competing pathways. Here we explored the utility of measuring cADPR, a product of SARM1-dependent cleavage of NAD+, as an in cell and in vivo biomarker of SARM1 enzymatic activity. We find that SARM1 is a major producer of cADPR in cultured dorsal root ganglion (DRG) neurons, sciatic nerve, and brain, demonstrating that SARM1 has basal activity in the absence of injury. Following injury, there is a dramatic SARM1-dependent increase in the levels of axonal cADPR that precedes morphological axon degeneration. In vivo, there is also a rapid and large injury-stimulated increase in cADPR in sciatic and optic nerves. The increase in cADPR after injury is proportional to SARM1 gene dosage, suggesting that SARM1 activity is the prime regulator of cADPR levels. The role of cADPR as an important calcium mobilizing agent prompted exploration of its functional contribution to axon degeneration. We used multiple bacterial and mammalian engineered enzymes to manipulate cADPR levels in neurons but found no changes in the time course of axonal degeneration, suggesting that cADPR is unlikely to be an important contributor to the degenerative mechanism. Using cADPR as a SARM1 biomarker, we find that SARM1 can be partially activated by a diverse array of mitochondrial toxins administered at doses that do not induce axon degeneration. Hence, the subcritical activation of SARM1 induced by mitochondrial dysfunction may contribute to the axonal vulnerability common to many neurodegenerative diseases. Finally, we assay levels of both nerve cADPR and plasma neurofilament light chain (NfL) following nerve injury in vivo, and demonstrate that both biomarkers are excellent readouts of SARM1 activity, with cADPR reporting the early molecular changes in the nerve and NfL reporting subsequent axonal breakdown. The identification and characterization of cADPR as a SARM1 biomarker will help identify neurodegenerative diseases in which SARM1 contributes to axonal loss and expedite target validation studies of SARM1-directed therapeutics.

Therapeutic efficacy of sonic hedgehog protein in experimental diabetic neuropathy.

Hedgehog proteins modulate development and patterning of the embryonic nervous system. As expression of desert hedgehog and the hedgehog receptor, patched-1, persist in the postnatal and adult peripheral nerves, the hedgehog pathway may have a role in maturation and maintenance of the peripheral nervous system in normal and disease states. We measured desert hedgehog expression in the peripheral nerve of maturing diabetic rats and found that diabetes caused a significant reduction in desert hedgehog mRNA. Treating diabetic rats with a sonic hedgehog-IgG fusion protein fully restored motor- and sensory-nerve conduction velocities and maintained the axonal caliber of large myelinated fibers. Diabetes-induced deficits in retrograde transport of nerve growth factor and sciatic-nerve levels of calcitonin gene-related product and neuropeptide Y were also ameliorated by treatment with the sonic hedgehog-IgG fusion protein, as was thermal hypoalgesia in the paw. These studies implicate disruption of normal hedgehog function in the etiology of diabetes-induced peripheral-nerve dysfunction and indicate that delivery of exogenous hedgehog proteins may have therapeutic potential for the treatment of diabetic neuropathy.

Novel diamino derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine as potent and selective adenosine A2a receptor antagonists.

Piperazine derivatives of 2-furanyl[1,2,4]triazolo[1,5-a][1,3,5]triazine have recently been demonstrated to be potent and selective adenosine A(2a) receptor antagonists with oral activity in rodent models of Parkinson's disease. We have replaced the piperazinyl group with a variety of linear, monocyclic, and bicyclic diamines. Of these diamines, (R)-2-(aminomethyl)pyrrolidine is a particularly potent and selective replacement for the piperazinyl group. With this diamine component, we have been able to prepare numerous analogues with low nanomolar affinity toward the A(2a) receptor and good selectivity with respect to the A(1) receptor (>200-fold in some cases). Selected analogues from this series of [1,2,4]triazolo[1,5-a][1,3,5]triazine have now been shown to be orally active in the mouse catalepsy model.

Piperazine derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine as potent and selective adenosine A2a receptor antagonists.

The [1,2,4]triazolo[1,5-a]triazine derivative 3, more commonly known in the field of adenosine research as ZM-241385, has previously been demonstrated to be a potent and selective adenosine A2a receptor antagonist, although with limited oral bioavailability. This [1,2,4]triazolo[1,5-a]triazine core structure has now been improved by incorporating various piperazine derivatives. With some preliminary optimization, the A2a binding affinity of some of the best piperazine derivatives is almost as good as that of compound 3. The selectivity level over the adenosine A1 receptor subtype for some of the more active analogues is also fairly high, > 400-fold in some cases. Many compounds within this piperazine series of [1,2,4]triazolo[1,5-a]triazine have now been shown to have good oral bioavailability in the rat, with some as high as 89% (compound 35). More significantly, some piperazines derivatives of [1,2,4]triazolo[1,5-a]triazine also possessed good oral efficacy in rodent models of Parkinson's disease. For instance, compound 34 was orally active in the rat catalepsy model at 3 mg/kg. In the 6-hydroxydopamine-lesioned rat model, this compound was also quite effective, with a minimum effective dose of 3 mg/kg po.

Novel bicyclic piperazine derivatives of triazolotriazine and triazolopyrimidines as highly potent and selective adenosine A2A receptor antagonists.

A series of bicyclic piperazine derivatives of triazolotriazine and triazolopyrimidines was synthesized. Some of these analogues show high affinity and excellent selectivity for adenosine A(2a) receptor versus the adenosine A(1) receptor. Structure-activity-relationship (SAR) studies based on octahydropyrrolo[1,2-a]pyrazine and octahydropyrido[1,2-a]pyrazine with various capping groups are reported. Among these analogues, the most potent and selective A(2a) antagonist 26 h has a K(i) value of 0.2 nM and is 16 500-fold selective with respect to the A(1) receptor. Among a number of compounds tested, compounds 21a and 21c exhibited significantly improved metabolic stability. Compounds 21a, 21c, and 18a showed good oral efficacy in rodent catalepsy models of Parkinson's disease.

Long-acting forms of Sonic hedgehog with improved pharmacokinetic and pharmacodynamic properties are efficacious in a nerve injury model.

The therapeutic effects of the Sonic hedgehog (Shh) have been difficult to evaluate because of its relatively short serum half-life. To address this issue polyethylene glycol modification (PEGylation) was investigated as an approach to improve systemic exposure. Shh was PEGylated by a targeted approach using cysteines that were engineered into the protein by site-directed mutagenesis as the sites of attachment. Sixteen different versions of the protein containing one, two, three, or four sites of attachment were characterized. Two forms were selected for extensive testing in animals, Shh A192C, which provided a single site for PEGylation, and Shh A192C/N91C, which provided two sites. The PEGylated proteins were evaluated for reaction specificity by SDS-PAGE and peptide mapping, in vitro potency, pharmacokinetic and pharmacodynamic properties, and efficacy in a sciatic nerve injury model. Targeted PEGylation was highly selective for the engineered cysteines and had no deleterious effect on Shh function in vitro. Systemic clearance values in rats decreased from 117.4 mL/h/kg for unmodified Shh to 29.4 mL/h/kg for mono-PEGylated Shh A192C that was modified with 20 kDa PEG-maleimide and to 2.5 mL/h/kg for di-PEGylated Shh A192C/N91C modified with 2, 20 kDa PEG vinylsulfone adducts. Serum half-life increased from 1 h for unmodified Shh to 7.0 and 12.6 h for the mono- and di-PEGylated products. These changes in clearance and half-life resulted in higher serum levels of Shh in the PEG-Shh-treated animals. In Ptc-LacZ knock-in mice expressing lacZ under regulation of the Shh receptor Patched, about a 10-fold lower dose of PEG-Shh was needed to induce beta-galactosidase than for the unmodified protein. Therapeutic treatment of mice with PEG-Shh enhanced the regeneration of injured sciatic nerves. These studies demonstrate that targeted PEGylation greatly alters the pharmacokinetic and pharmacodynamic properties of Shh, resulting in a form with improved pharmaceutical properties.

Effect of combined treatment with methylprednisolone and soluble Nogo-66 receptor after rat spinal cord injury.

Methylprednisolone (MP) is a synthetic glucocorticoid used for the treatment of spinal cord injury (SCI). Soluble Nogo-66 receptor (NgR) ectodomain is a novel experimental therapy for SCI that promotes axonal regeneration by blocking the growth inhibitory effects of myelin constituents in the adult central nervous system. To evaluate the potential complementarity of these mechanistically distinct pharmacological reagents we compared their effects alone and in combination after thoracic (T7) dorsal hemisection in the rat. Treatment with an ecto-domain of the rat NgR (27-310) fused to a rat IgG [NgR(310)ecto-Fc] (50 microm intrathecal, 0.25 microL/h for 28 days) or MP alone (30 mg/kg i.v., 0, 4 and 8 h postinjury) improved the rate and extent of functional recovery measured using Basso, Beattie, Bresnahan (BBB) scoring and footprint analysis. The effect of MP treatment on BBB score was apparent the day after SCI whereas the effect of NgR(310)ecto-Fc was not apparent until 2 weeks after SCI. NgR(310)ecto-Fc or MP treatment resulted in increased axonal sprouting and/or regeneration, quantified by counting biotin dextran amine-labeled corticospinal tract axons, and increased the number of axons contacting motor neurons in the ventral horn gray matter caudal to the lesion. Combined treatment with NgR(310)ecto-Fc and MP had a more pronounced effect on recovery of function and axonal growth compared with either treatment alone. The data demonstrate that NgR(310)ecto-Fc and MP act in a temporally and mechanistically distinct manner and suggest that they may have complementary effects.

Synthesis of alkyne derivatives of a novel triazolopyrazine as A(2A) adenosine receptor antagonists.

A novel [1,2,4]triazolo[1,5-a]pyrazine core was synthesized and coupled with terminal acetylenes. The structure-activity relationship of the alkynes from this novel template was studied for their in vitro and in vivo adenosine A(2A) receptor antagonism. Selected compounds from this series were shown to have potent in vitro and in vivo activities against adenosine A(2A) receptor. Compound 12, in particular, was found to be orally active at 3mg/kg in both a mouse catalepsy model and a 6-hydroxydopamine-lesioned rat model.

Synthesis of [1,2,4]triazolo[1,5-a]pyrazines as adenosine A2A receptor antagonists.

Potent and selective antagonists of the adenosine A2A receptor often contain a nitrogen-rich fused-ring heterocyclic core. Replacement of the core with an isomeric ring system has previously been shown to improve target affinity, selectivity, and in vivo activity. This paper describes the preparation, by a novel route, of A2A receptor antagonists containing the [1,2,4]triazolo[1,5-a]pyrazine nucleus, which is isomeric with the [1,2,4]triazolo[1,5-c]pyrimidine core of a series of known A2A antagonists with in vivo activity in animal models of Parkinson's disease.

Triamino derivatives of triazolotriazine and triazolopyrimidine as adenosine A2a receptor antagonists.

Piperazine derivatives of 2-furanyl[1,2,4]triazolo[1,5-a][1,3,5]triazine have recently been shown to be potent and selective adenosine A(2a) receptor antagonists. We now demonstrate that potent and selective A(2a) receptor antagonists could still be obtained when the arylpiperazines are separated from the triazolotriazine core structure by an ethylenediamine spacer. Selected analogs bearing this triazolotriazine or the related triazolopyrimidine core structure have been found to be orally active in a mouse catalepsy model of Parkinson's disease.

Studies on adenosine A2a receptor antagonists: comparison of three core heterocycles.

Piperazine and (R)-2-(aminomethyl)pyrrolidine derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine have recently been shown to be potent and selective adenosine A(2a) receptor antagonists. We have replaced the triazolotriazine core structure with two different heterocyclic cores. One of these, the one deriving from [1,2,4]triazolo[1,5-c]pyrimidine, appears to be particularly effective and selected analogs from this series have been shown to be orally active in a mouse catalepsy model of Parkinson's disease.