Discovery of pyrrolo[2,1-f][1,2,4]triazine-based inhibitors of adaptor protein 2-associated kinase 1 for the treatment of pain

Adaptor protein 2-associated kinase 1 (AAK1) is a member of the Ark1/Prk1 family of serine/threonine kinases and plays a role in modulating receptor endocytosis. AAK1 was identified as a potential therapeutic target for the treatment of neuropathic pain when it was shown that AAK1 knock out (KO) mice had a normal response to the acute pain phase of the mouse formalin model, but a reduced response to the persistent pain phase. Herein we report our early work investigating a series of pyrrolo[2,1-f][1,2,4]triazines as part of our efforts to recapitulate this KO phenotype with a potent, small molecule inhibitor of AAK1. The synthesis, structure-activity relationships (SAR), and in vivo evaluation of these AAK1 inhibitors is described.

Graphical Abstract

Abstract 593: Anti-tumor immunity and efficacy of combination treatment of M6223 and bintrafusp alfa versus the combination of M6223 and anti-PD-L1 in preclinical tumor models

Background: T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT) is an inhibitory receptor expressed on lymphocytes and has recently emerged as a target in cancer immunotherapy. M6223 is a fully human antagonistic anti-TIGIT antibody in immunoglobulin (Ig) G1 format with Fc-mediated effector function. Preclinical studies demonstrated that M6223 could induce an anti-tumor immune response by complementary mechanisms including but not limited to direct blockade of the TIGIT pathway, stimulation of CD226 dimerization/activation, and depletion of TIGIT+ immune subsets by Fc-mediated effector function. M6223 showed dose-dependent anti-tumor efficacy in multiple preclinical tumor models. Bintrafusp alfa, a first-in-class bifunctional fusion protein composed of the extracellular domain of the human transforming growth factor β receptor II (TGF-βRII or TGF-β "trap") fused via a flexible linker to the C-terminus of each heavy chain of an IgG1 antibody blocking programmed death ligand 1 (anti-PD-L1), was designed to target two key immunosuppressive pathways in the tumor microenvironment.

Methods: To attenuate the tumor immunosuppressive microenvironment, the anti-tumor immunity and efficacy of combining M6223 with bintrafusp alfa was investigated in syngeneic models in humanized mice with huTIGIT knock-in sequences.

Results: M6223 combined with bintrafusp alfa significantly enhanced anti-tumor efficacy and extended survival compared with either monotherapies or the combination of M6223 with anti-PD-L1. M6223 combined with bintrafusp alfa stimulated higher CD8+ T cells and natural killer cells infiltration, proliferation and cytotoxicity in tumor microenvironment in comparison to the combination of M6223 with anti-PD-L1. The ratio of CD8+ T cells to regulatory T cells and the ratio of CD226 to TIGIT were significantly increased, indicating the conversion of the tumor microenvironment from an immuno-suppressive phenotype to a more immune-permissive phenotype. With the combination therapy, bintrafusp alfa was the main driver promoting CD8+ T cell proliferation, infiltration, and cytotoxicity. Alternatively, adding M6223 to bintrafusp alfa may decrease the risk of immune resistance caused by elevated TIGIT expression triggered by bintrafusp alfa treatment.

Conclusion: These complementary mechanisms of M6223 and bintrafusp alfa orchestrate antitumor activity in preclinical tumor models. Currently, M6223 and bintrafusp alfa combination is being investigated in a Phase I clinical trial (NCT04457778) in patients with metastatic or locally advanced solid unresectable tumors.

Citation Format: Chunxiao Xu, Sireesha Yalavarthi, Clotilde Bourin, Christie Kelton, Joern-Peter Halle, Jacques Moisan. Anti-tumor immunity and efficacy of combination treatment of M6223 and bintrafusp alfa versus the combination of M6223 and anti-PD-L1 in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 593.

Discovery and Optimization of Biaryl Alkyl Ethers as a Novel Class of Highly Selective, CNS-Penetrable, and Orally Active Adaptor Protein-2-Associated Kinase 1 (AAK1) Inhibitors for the Potential Treatment of Neuropathic Pain

Recent mouse knockout studies identified adapter protein-2-associated kinase 1 (AAK1) as a viable target for treating neuropathic pain. BMS-986176/LX-9211 (4), as a highly selective, CNS-penetrable, and potent AAK1 inhibitor, has advanced into phase II human trials. On exploring the structure-activity relationship (SAR) around this biaryl alkyl ether chemotype, several additional compounds were found to be highly selective and potent AAK1 inhibitors with good druglike properties. Among these, compounds 43 and 58 showed very good efficacy in two neuropathic pain rat models and had excellent CNS penetration and spinal cord target engagement. Both compounds also exhibited favorable physicochemical and oral pharmacokinetic (PK) properties. Compound 58, a central pyridine isomer of BMS-986176/LX-9211 (4), was 4-fold more potent than 4 in vitro and showed lower plasma exposure needed to achieve similar efficacy compared to 4 in the CCI rat model. However, both 43 and 58 showed an inferior preclinical toxicity profile compared to 4.

Discovery of (S)-1-((2',6-Bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (BMS-986176/LX-9211): A Highly Selective, CNS Penetrable, and Orally Active Adaptor Protein-2 Associated Kinase 1 Inhibitor in Clinical Trials for the Treatment of Neuropathic Pain

Recent mouse knockout studies identified adapter protein-2 associated kinase 1 (AAK1) as a viable target for treating neuropathic pain. Potent small-molecule inhibitors of AAK1 have been identified and show efficacy in various rodent pain models. (S)-1-((2',6-Bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (BMS-986176/LX-9211) (34) was identified as a highly selective, CNS penetrant, potent AAK1 inhibitor from a novel class of bi(hetero)aryl ethers. BMS-986176/LX9211 (34) showed excellent efficacy in two rodent neuropathic pain models and excellent central nervous system (CNS) penetration and target engagement at the spinal cord with an average brain to plasma ratio of 20 in rat. The compound exhibited favorable physicochemical and pharmacokinetic properties, had an acceptable preclinical toxicity profile, and was chosen for clinical trials. BMS-986176/LX9211 (34) completed phase I trials with good human pharmacokinetics and minimum adverse events and is currently in phase II clinical trials for diabetic peripheral neuropathic pain (ClinicalTrials.gov identifier: NCT04455633) and postherpetic neuralgia (ClinicalTrials.gov identifier: NCT04662281).

Abstract P077: Composition of CD4 T cell subsets and impact on tumor growth control across mouse syngeneic tumor models

CD4 T cells include multiple sublineages orchestrating a broad range of effector activities during the initiation, promotion, and progression of carcinogenesis. Although regulatory T cells (Tregs) are well-characterized to promote tumor progression, the impact of effector CD4+ T cell subsets (Teff) in anti-tumor immunity is less well known. Further, the relative contribution of Teff and Treg cell subsets in different syngeneic tumor models has not been characterized. We observed that CD4 depletion had significantly different impact of tumor growth across different syngeneic tumor models: no effect on MC38 tumor growth; enhanced tumor growth in CT26.KSA tumor model; while almost complete tumor regression in the EMT-6 tumor model. We hypothesized that each tumor model has a vastly different composition in the CD4 T cell compartment. To test this, we characterized expression of activation and CD4 T cell differentiation markers as well as cytokine production from CD4 TILs in each of the syngeneic tumor models. We found that while effector CD4 TILs (FoxP3−CD4+) from MC38 and CT26.KSA tumors expressed high levels activation and differentiation markers, Teff from EMT-6 tumors expressed very low levels of T cell activation and differentiation markers, suggesting the Teff in EMT-6 tumors are largely dysfunctional. Ex vivo restimulation of tumor samples with anti-CD3/anti-CD28 promoted IFNγ production in CD4 TILs from MC38 and CT26.KSA tumor models, but not from EMT-6 tumor models, further supporting that Teff from MC38 and CT26.KSA tumors remain highly active, while CD4 TILs from EMT-6 tumors are dysfunctional. When looking at the Treg compartment, the frequency of Tregs in CT26.KSA tumors was reduced compared to MC38 and EMT-6 tumors. Further, Tregs in MC38 and EMT-6 tumors expressed very high levels of CD69, a marker of highly immunosuppressive Tregs, while Tregs in CT26.KSA tumors expressed lower levels of CD69, suggesting that these Tregs may be less immunosuppressive. In summary, the CD4 T cell compartment is vastly different across CT26.KSA, MC38 and EMT-6 syngeneic tumor models, resulting in very different impact of tumor growth control.

Citation Format: Chunxiao Xu, Lindsay Webb, Sireesha Yalavarthi, Clotilde Bourin, Jacques Moisan. Composition of CD4 T cell subsets and impact on tumor growth control across mouse syngeneic tumor models [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P077.

757 M9657, a novel tumor-targeted conditional anti-CD137 agonist displays MSLN-dependent anti-tumor immunity

Background

The costimulatory receptor CD137 (also known as 4-1BB and TNFRSF9) plays an important role in sustaining effective cytotoxic T cell immune responses and its agonism has been investigated as a cancer immunotherapy. In clinical trials, the systemic administration of the 1st generation CD137 agonist monotherapies, utomilumab and urelumab, were suspended due to either low anti-tumor efficacy or hepatotoxicity mediated by recognized epitope on CD137 and FcγR ligand-dependent clustering.

Methods

M9657, a bispecific antibody was engineered a tetravalent bispecific antibody (mAb2) format with the Fab portion binding to the tumor antigen Mesothelin (MSLN) and a modified CH2-CH3 domain as Fc antigen binding (Fcab) portion binding to CD137. M9657 has a human IgG1 backbone with LALA mutations to abrogate the binding to Fcγ receptor. The biological characteristics and activities of M9657 were investigated in a series of in vitro assays and the in vivo efficacy was investigated in syngeneic tumor models with FS122m, a murine-reactive surrogate with the same protein structure of M9657.

Results

M9657 binds efficiently to both human and Cynomolgus CD137 as well as MSLN. In the cellular functional assay, M9657 displayed MSLN- and TCR/CD3 interaction (signal 1)-dependent cytokine release and tumor cell cytotoxicity associated with Bcl-XL activation and immune memory formation. FS122m demonstrated potent MSLN- and dose- dependent in vivo anti-tumor efficacy (figure 1). Comparing with 3H3, a Urelumab surrogate Ab, FS122m displayed an improved therapeutic window with significantly lower for on-target /off-tumor toxicity.

Conclusions

Taken together, M9657 exhibits a promising developability profile as a tumor-targeted immune agonist with potent anti-cancer activity, but without systemic immune activation.

Ethics Approval

All animal experiments were performed in accordance with EMD Serono Research & Development Institute (protocol 17-008, 20-005) and Wuxi AppTec Animal Care and Use Committee (IACUC) guidelines.

Abstract 757 Figure 1

FS122m displayed dose-dependent anti-tumor efficacy

326 The anti-TIGIT antibody M6223 induces significant anti-tumor efficacy and immune response via multiple mechanisms of action

Background

M6223 is a fully human antagonistic anti-T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) antibody in IgG1 format with Fc-mediated effector function.

Methods

The ability of M6223 to block the interaction of TIGIT with its ligands, CD155 and CD112, and the interaction of TIGIT with CD226 was determined by a flow cytometry-based binding assay. The anti-tumor efficacy, immune profile, and effector function of M6223 were investigated in syngeneic tumor models in huTIGIT knock-in mice. M6223 was either formatted with an effector competent mouse IgG2c constant region (M6223-muIgG2c) or formatted with effector null mouse IgG1-D256A constant region (M6223-muIgG1) as two versions of chimeric antibodies for the in vivo studies.

Results

M6223 dose-dependently blocked the binding of TIGIT to its ligands, including CD155 and CD112, thereby inhibiting a TIGIT-mediated immunosuppressive pathway. In addition, M6223 interrupted the interaction of TIGIT with the costimulatory receptor CD226. By blocking the interactions, the chimeric protein M6223-muIgG2c showed anti-tumor efficacy in multiple tumor models, including an MC38 tumor model (figure 1), and generated tumor antigen-specific long-term protective immunity in immunocompetent huTIGIT knock-in mice. M6223 monotherapy dose-dependently elevated the ratio of CD8+ cytotoxic T cells to regulatory T cells and the ratio of CD226 to TIGIT expression in immune cells in the tumor microenvironment. We also found that M6223 selectively depleted suppressive and exhausted TIGIT+ immune cell subsets and the anti-tumor activity of effector null M6223-muIgG1 was significantly lost (p<0.0001), suggesting that Fc-mediated effector function contributes to M6223 anti-tumor activity. Antibody depletion studies demonstrated that CD8+ T cells and natural killer cells contributed to the anti-tumor activity of M6223 in a complementary manner.

Abstract 326 Figure 1

M6223-muIgG2c displayed dose-dependent anti-tumor efficacy. M6223-muIgG2c displayed dose-dependent anti-tumor efficacy in an MC38 tumor model in hTIGIT knock-in mice.

Conclusions

Given that TIGIT blockade can inhibit an immunosuppressive pathway as well as remove the suppression on a costimulatory pathway, M6223 has the potential to induce an anti-tumor immune response by three complementary mechanisms: direct blockade of the TIGIT pathway, stimulation of CD226 dimerization/activation, and depletion of TIGIT+ immune subsets by Fc-mediated effector function. Our data demonstrate that these complementary mechanisms orchestrate the anti-tumor activity of M6223. A Phase I, first-in-human clinical trial (NCT04457778) is underway to determine the safety, tolerability, maximum tolerated dose and recommended dose for expansion of M6223 as a single agent (Part 1A) and in combination with bintrafusp alfa (Part 1B) in patients with metastatic or locally advanced solid unresectable tumors.

Ethics Approval

All animal experiments were performed in accordance with EMD Serono Research & Development Institute, Inc., Billerica, MA, USA, an affiliate of Merck KGaA (protocol 17-008, 20-005) and Wuxi AppTec Animal Care and Use Committee (IACUC) guidelines.

Abstract PO062: Isolation of tumor-infiltrating lymphocytes for higher sensitivity gene expression profiling

Gene expression profiling is a powerful approach to address the mechanism of action (MOA) of cancer immunotherapy-driven reprogramming of tumor-infiltrating lymphocytes (TILs) in the tumor microenvironment. However, TILs, particularly T and NK cells, are a very rare population within the tumor. Gene expression profiling using Nanostring or RNAseq is often not sensitive enough to detect expression changes in rare populations, and it is difficult to separate gene expression profiles between different cell subsets. Although single-cell RNAseq can distinguish gene expression profiles between different cell subsets, it is very costly and would require many cells to be sequenced before obtaining the rare cell type of interest. Classically, fluorescence-activated cell sorting (FACS) has been used to isolate rare populations, but this method is a long process that can affect cell phenotype and results in dramatic cell loss. Thus, we developed a protocol for rapid and reproducible magnetic bead-based isolation of tumor-infiltrating lymphocytes (TILs) for higher sensitivity MOA studies. CD8 and CD4 TILs were isolated from both MC38 and CT26.KSA tumor models with high purity and sufficient yield for further Nanostring gene expression analysis. As expected, CD8 and CD4 T cell gene expression profiles were dramatically enriched in the isolated TILs compared to the whole tumor. Thus, our protocol for isolating TILs from mouse tumors can be applied broadly to multiple tumor types and provides sufficient yield to perform downstream high-sensitivity gene expression profiling.

Citation Format: Lindsay M. Webb, Bartholomew Naughton, Sireesha Yalavarthi, Clotilde Bourin, Jacques Moisan, Chunxiao Xu. Isolation of tumor-infiltrating lymphocytes for higher sensitivity gene expression profiling [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO062.

Discovery of Indole- and Indazole-acylsulfonamides as Potent and Selective NaV1.7 Inhibitors for the Treatment of Pain

3-Aryl-indole and 3-aryl-indazole derivatives were identified as potent and selective Na_v1.7 inhibitors. Compound 29 was shown to be efficacious in the mouse formalin assay and also reduced complete Freund's adjuvant (CFA)-induced thermal hyperalgesia and chronic constriction injury (CCI) induced cold allodynia and models of inflammatory and neuropathic pain, respectively, following intraperitoneal (IP) doses of 30 mg/kg. The observed efficacy could be correlated with the mouse dorsal root ganglion exposure and Na_V1.7 potency associated with 29.

Development of New Benzenesulfonamides As Potent and Selective Nav1.7 Inhibitors for the Treatment of Pain

By taking advantage of certain features in piperidine 4, we developed a novel series of cyclohexylamine- and piperidine-based benzenesulfonamides as potent and selective Nav1.7 inhibitors. However, compound 24, one of the early analogs, failed to reduce phase 2 flinching in the mouse formalin test even at a dose of 100 mpk PO due to insufficient dorsal root ganglion (DRG) exposure attributed to poor membrane permeability. Two analogs with improved membrane permeability showed much increased DRG concentrations at doses of 30 mpk PO, but, confoundingly, only one of these was effective in the formalin test. More data are needed to understand the disconnect between efficacy and exposure relationships.

A new setup for localized implantation and live-characterization of keV energy multiply charged ions at the nanoscale

An innovative experimental setup, PELIICAEN, allowing the modification of materials and the study of the effects induced by multiply charged ion beams at the nanoscale is presented. This ultra-high vacuum (below 5 × 10^-10 mbar) apparatus is equipped with a focused ion beam column using multiply charged ions and a scanning electron microscope developed by Orsay Physics, as well as a scanning probe microscope. The dual beam approach coupled to the scanning probe microscope achieves nanometer scale in situ topological analysis of the surface modifications induced by the ion beams. Preliminary results using the different on-line characterization techniques to study the formation of nano-hillocks on silicon and mica substrates are presented to illustrate the performances of the setup.

Inhibition of AAK1 Kinase as a Novel Therapeutic Approach to Treat Neuropathic Pain

To identify novel targets for neuropathic pain, 3097 mouse knockout lines were tested in acute and persistent pain behavior assays. One of the lines from this screen, which contained a null allele of the adapter protein-2 associated kinase 1 (AAK1) gene, had a normal response in acute pain assays (hot plate, phase I formalin), but a markedly reduced response to persistent pain in phase II formalin. AAK1 knockout mice also failed to develop tactile allodynia following the Chung procedure of spinal nerve ligation (SNL). Based on these findings, potent, small-molecule inhibitors of AAK1 were identified. Studies in mice showed that one such inhibitor, LP-935509, caused a reduced pain response in phase II formalin and reversed fully established pain behavior following the SNL procedure. Further studies showed that the inhibitor also reduced evoked pain responses in the rat chronic constriction injury (CCI) model and the rat streptozotocin model of diabetic peripheral neuropathy. Using a nonbrain-penetrant AAK1 inhibitor and local administration of an AAK1 inhibitor, the relevant pool of AAK1 for antineuropathic action was found to be in the spinal cord. Consistent with these results, AAK1 inhibitors dose-dependently reduced the increased spontaneous neural activity in the spinal cord caused by CCI and blocked the development of windup induced by repeated electrical stimulation of the paw. The mechanism of AAK1 antinociception was further investigated with inhibitors of α2 adrenergic and opioid receptors. These studies showed that α2 adrenergic receptor inhibitors, but not opioid receptor inhibitors, not only prevented AAK1 inhibitor antineuropathic action in behavioral assays, but also blocked the AAK1 inhibitor-induced reduction in spinal neural activity in the rat CCI model. Hence, AAK1 inhibitors are a novel therapeutic approach to neuropathic pain with activity in animal models that is mechanistically linked (behaviorally and electrophysiologically) to α2 adrenergic signaling, a pathway known to be antinociceptive in humans.

Tau overexpression impacts a neuroinflammation gene expression network perturbed in Alzheimer's disease

Filamentous inclusions of the microtubule-associated protein, tau, define a variety of neurodegenerative diseases known as tauopathies, including Alzheimer's disease (AD). To better understand the role of tau-mediated effects on pathophysiology and global central nervous system function, we extensively characterized gene expression, pathology and behavior of the rTg4510 mouse model, which overexpresses a mutant form of human tau that causes Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). We found that the most predominantly altered gene expression pathways in rTg4510 mice were in inflammatory processes. These results closely matched the causal immune function and microglial gene-regulatory network recently identified in AD. We identified additional gene expression changes by laser microdissecting specific regions of the hippocampus, which highlighted alterations in neuronal network activity. Expression of inflammatory genes and markers of neuronal activity changed as a function of age in rTg4510 mice and coincided with behavioral deficits. Inflammatory changes were tau-dependent, as they were reversed by suppression of the tau transgene. Our results suggest that the alterations in microglial phenotypes that appear to contribute to the pathogenesis of Alzheimer's disease may be driven by tau dysfunction, in addition to the direct effects of beta-amyloid.

Discovery of (S,E)-3-(2-fluorophenyl)-N-(1-(3-(pyridin-3-yloxy)phenyl)ethyl)-acrylamide as a potent and efficacious KCNQ2 (Kv7.2) opener for the treatment of neuropathic pain

Acrylamide (S)-6, a potent and efficacious KCNQ2 (Kv7.2) opener, demonstrated significant activity in two models of neuropathic pain and in the formalin test, suggesting that KCNQ2 openers may be useful in the treatment of neuropathic pain including diabetic neuropathy.

Oxime carbamate--discovery of a series of novel FAAH inhibitors

A series of novel oxime carbamates have been identified as potent inhibitors of the key regulatory enzyme of the endocannabinoid signaling system, fatty acid amide hydrolase (FAAH). In this Letter, the rationale behind the discovery and the biological evaluations of this novel class of FAAH inhibitors are presented. Both in vitro and in vivo results of selected targets are discussed, along with inhibition kinetics and molecular modeling studies.(1).

Novel inhibitors of fatty acid amide hydrolase

A class of bisarylimidazole derivatives are identified as potent inhibitors of the enzyme fatty acid amide hydrolase (FAAH). Compound 17 (IC(50)=2 nM) dose-dependently (0.1-10mg/kg, iv) potentiates the effects of exogenous anandamide (1 mg/kg, iv) in a rat thermal escape test (Hargreaves test), and shows robust antinociceptive activity in animal models of persistent (formalin test) and neuropathic (Chung model) pain. Compound 17 (20 mg/kg, iv) demonstrates activity in the formalin test that is comparable to morphine (3mg/kg, iv), and is dose-dependently inhibited by the CB1 antagonist SR141716A. In the Chung model, compound 17 shows antineuropathic effects similar to high-dose (100 mg/kg) gabapentin. FAAH inhibition shows potential utility for the clinical treatment of persistent and neuropathic pain.

Soluble Aβ and cognitive function in aged F-344 rats and Tg2576 mice

Recent findings suggest that Alzheimer's dementia may be mediated by soluble beta amyloid (Abeta) more than the deposits of aggregated, insoluble Abeta, and vulnerability to cognitive deficits after scopolamine challenge may help identify AD even in patients that are still pre-symptomatic. The objectives of the present experiments were to determine if vulnerability to cognitive deficits after scopolamine challenge is related to levels of soluble Abeta, and if levels of soluble Abeta are more closely related to cognitive deficits than levels of insoluble Abeta, even in aged, transgenic mice, after they have developed very high levels of insoluble Abeta. Aged F-344 rats and young mice over-expressing the Swedish mutation in the human amyloid precursor protein (APPsw; Tg2576+) had elevated levels of soluble Abeta, and were more vulnerable to scopolamine challenge in the Morris water maze (MWM), relative to young rats and Tg2576- mice; but, among individual animals, higher levels of soluble Abeta were not correlated with vulnerability to scopolamine. On the other hand, in aged Tg2576+ mice, cognitive deficits were related to levels of soluble Abeta, not insoluble Abeta, despite the fact that the levels of insoluble Abeta were thousands of times higher than the levels of soluble Abeta. The results of the present experiments suggest that vulnerability to cognitive deficits after scopolamine challenge is not related to elevated levels of soluble Abeta, but that high levels of soluble Abeta are more closely correlated with cognitive deficits than the amount insoluble Abeta, even after large amounts of aggregated, insoluble Abeta have been deposited.

Adverse effects of gabapentin and lack of anti-allodynic efficacy of amitriptyline in the streptozotocin model of painful diabetic neuropathy

Amitriptyline and gabapentin are the primary treatments for painful diabetic neuropathy (PDN), and it is clear that they produce beneficial effects, but there are questions about these treatments that have not been adequately addressed. For example, although there is a growing consensus that the therapeutic effects of amitriptyline in pain patients are independent of its effects on mood, it is not clear that amitriptyline has specific and direct effects on pain. There is also a fairly broad consensus that gabapentin is safe and well tolerated, but the side-effect profile of gabapentin has not been adequately assessed in pain populations. The rat streptozotocin (STZ) model of PDN was used (a) to assess the effects of amitriptyline on objective, quantitative measures of tactile allodynia, a common type of pain in PDN patients, and (b) to assess the side effects of gabapentin using measures of motor/ambulatory and cognitive function. Amitriptyline did not attenuate STZ-induced mechanical allodynia, even after chronic administration of high doses. Gabapentin produced robust anti-allodynic effects but also produced deficits in tests of motor/ambulatory and cognitive functions. The present experiments suggest that the beneficial effects of amitriptyline in PDN may not be a result of anti-allodynic efficacy and that gabapentin produces robust anti-allodynic effects but may also produce significant motor and cognitive deficits even at or near the lowest effective doses. These findings challenge the consensus opinions about these primary treatments for PDN and suggest that their therapeutic and adverse effects should be explored further in pain patients.