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6-Diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist with robust anticancer efficacy; however, its therapeutic potential was hampered by its biodistribution and toxicity to normal tissues, specifically gastrointestinal (GI) tissues. To circumvent DON’s toxicity, we synthesized a series of tumor-targeted DON prodrugs designed to circulate inert in plasma and preferentially activate over DON in tumor. Our best prodrug 6 (isopropyl 2-(6-acetamido-2-(adamantane-1-carboxamido)hexanamido)-6-diazo-5-oxohexanoate) showed stability in plasma, liver, and intestinal homogenates yet was readily cleaved to DON in P493B lymphoma cells, exhibiting a 55-fold enhanced tumor cell-to-plasma ratio versus that of DON and resulting in a dose-dependent inhibition of cell proliferation. Using carboxylesterase 1 knockout mice that were shown to mimic human prodrug metabolism, systemic administration of 6 delivered 11-fold higher DON exposure to tumor (target tissue; AUC(0–t) = 5.1 nmol h/g) versus GI tissues (toxicity tissue; AUC(0–t) = 0.45 nmol h/g). In summary, these studies describe the discovery of a glutamine antagonist prodrug that provides selective tumor exposure.

Prescription opioids such as oxycodone are highly effective analgesics for clinical pain management, but their misuse and abuse have led to the current opioid epidemic in the United States. In order to ameliorate this public health crisis, the development of effective pharmacotherapies for the prevention and treatment of opioid abuse and addiction is essential and urgently required. In this study, we evaluated—in laboratory rats—the potential utility of VK4-116, a novel and highly selective dopamine D3 receptor (D3R) antagonist, for the prevention and treatment of prescription opioid use disorders. Pretreatment with VK4-116 (5–25 mg/kg, i.p.) dose-dependently inhibited the acquisition and maintenance of oxycodone self-administration. VK4-116 also lowered the break-point (BP) for oxycodone self-administration under a progressive-ratio schedule of reinforcement, shifted the oxycodone dose–response curve downward, and inhibited oxycodone extinction responding and reinstatement of oxycodone-seeking behavior. In addition, VK4-116 pretreatment dose-dependently enhanced the antinociceptive effects of oxycodone and reduced naloxone-precipitated conditioned place aversion in rats chronically treated with oxycodone. In contrast, VK4-116 had little effect on oral sucrose self-administration. Taken together, these findings indicate a central role for D3Rs in opioid reward and support further development of VK4-116 as an effective agent for mitigating the development of opioid addiction, reducing the severity of withdrawal and preventing relapse.

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in preclinical models of psychostimulant abuse. In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine, but did not exhibit psychostimulant behaviors itself. While further development of 3b is ongoing, diastereomeric separation, as well as improvements in potency and pharmacokinetics were desirable for discovering pipeline drug candidates. Thus, a series of bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines, where the piperazine-2-propanol scaffold was modified, were designed, synthesized and evaluated for binding affinities at DAT, as well as the serotonin transporter and sigma(1) receptors. Within the series, 14a showed improved DAT affinity (K(i)=23 nM) over 3b (K(i)=230 nM), moderate metabolic stability in human liver microsomes, and a hERG/DAT affinity ratio = 28. While 14a increased locomotor activity relative to vehicle, it was significantly lower than activity produced by cocaine. These results support further investigation of 14a as a potential treatment for psychostimulant use disorders.

Dopamine D(3) receptors (D(3)R) play a critical role in neuropsychiatric conditions including substance use disorders (SUD). Recently, we reported a series of N-(3-hydroxy-4-(4-phenylpiperazin-1yl)butyl)-1H-indole-2-carboxamide analogues as high affinity and selective D(3)R lead molecules for the treatment of opioid use disorders (OUD). Further optimization led to a series of analogues that replaced the 3-OH with a 3-F in the linker between the primary pharmacophore (PP) and secondary pharmacophore (SP). Among the 3-F-compounds, 9b demonstrated the highest D(3)R binding affinity (K(i) = 0.756 nM) and was 327-fold selective for D(3)R over D(2)R. In addition, modification of the PP or SP with a 3,4-(methylenedioxy)phenyl group was also examined. Further, an enantioselective synthesis as well as chiral HPLC methods were developed to give enantiopure R- and S-enantiomers of the four lead compounds. Off-target binding affinities, functional efficacies, and metabolic profiles revealed critical structural components for D(3)R selectivity as well as drug-like features required for development as pharmacotherapeutics.

Methamphetamine (METH) is a highly addictive drug, but no pharmacological treatment is yet available for METH use disorders. Similar to METH, the wake-promoting drug (R)- modafinil (R-MOD) binds to the dopamine transporter (DAT). Unlike METH, R-MOD is not a substrate for transport by DAT and has low abuse potential. We tested the hypothesis that the atypical DAT inhibitor R-MOD and compounds that are derived from Modafinil would decrease METH intake by reducing the actions of METH at the DAT. We tested the effects of systemic injections of R-MOD and four novel Modafinil-derived ligands with increased DAT affinity (JJC8-016, JJC8-088, JJC8-089, and JJC8-091) on intravenous (i.v.) METH self-administration in rats that were allowed short access (ShA; 1 h) or long access (LgA; 6 h) to the drug. ShA rats exhibited stable METH intake over sessions, whereas LgA rats exhibited an escalation of drug intake. R-MOD decreased METH self-administration in ShA and LgA rats (in the 1(st) hour only). JJC8-091, and JJC8-016 decreased METH self-administration in both ShA and LgA rats. JJC8- 089 decreased METH self-administration in LgA rats only, whereas JJC8-088 had no effect on METH self-administration in either ShA or LgA rats. These findings support the potential of atypical DAT inhibitors for the treatment of METH use disorders and suggest several novel compounds as candidate drugs.

Insulin delivery to the brain has emerged as an important therapeutic target for cognitive disorders associated with abnormal brain energy metabolism. Although insulin is transported across the blood–brain barrier, peripheral routes of administration are problematic due to systemic effects of insulin on blood glucose. Intranasal (IN) administration is being investigated as an alternative route. We conducted a head-to-head comparison of subcutaneous (SC) and IN insulin, assessing plasma and brain pharmacokinetics and blood glucose levels in the mouse. SC insulin (2.4 IU) achieved therapeutically relevant concentrations in the brain (AUCbrain = 2537 h·μIU/mL) but dramatically increased plasma insulin (AUCplasma = 520 351 h·*μIU/mL), resulting in severe hypoglycemia and in some cases death. IN administration of the same dose resulted in similar insulin levels in the brain (AUCbrain = 3442 h·μIU/mL) but substantially lower plasma concentrations (AUCplasma = 354 h·μIU/mL), amounting to a ~ 2000-fold increase in the AUCbrain:plasma ratio relative to SC. IN dosing also had no significant effect on blood glucose. When administered daily for 9 days, IN insulin increased brain glucose and energy metabolite concentrations (e.g., adenosine triphosphate and phosphocreatine) without causing overt toxicity, suggesting that IN insulin may be a safe therapeutic option for cognitively impaired patients.

Here we evaluate the potential for local administration of a small molecule FOLH1/GCPII inhibitor 2-phosphonomethyl pentanedioic acid (2-PMPA) as a novel treatment for inflammatory bowel disease (IBD). We found that FOLH1/GCPII enzyme activity was increased in the colorectal tissues of mice with TNBS-induced colitis, and confirmed that 2-PMPA inhibited FOLH1/GCPII enzyme activity ex vivo. In order to maximize local enema delivery of 2-PMPA, we studied the effect of vehicle tonicity on the absorption of 2-PMPA in the colon. Local administration of 2-PMPA in a hypotonic enema vehicle resulted in increased colorectal tissue absorption at 30 min compared to 2-PMPA administered in an isotonic enema vehicle. Furthermore, local delivery of 2-PMPA in hypotonic enema vehicle resulted in prolonged drug concentrations for at least 24 h with minimal systemic exposure. Finally, daily treatment with the hypotonic 2-PMPA enema ameliorated macroscopic and microscopic symptoms of IBD in the TNBS-induced colitis mouse model, indicating the potential of FOLH1/GCPII inhibitors for the local treatment of IBD.

Prescription opioid abuse is a global crisis. New treatment strategies for pain and opioid use disorders are urgently required. We evaluated the effects of R-VK4-40, a highly selective dopamine (DA) D3 receptor (D3R) antagonist, on the rewarding and analgesic effects of oxycodone, the most commonly abused prescription opioid, in rats and mice. Systemic administration of R-VK4-40 dose-dependently inhibited oxycodone self-administration and shifted oxycodone dose-response curves downward in rats. Pretreatment with R-VK4-40 also dose-dependently lowered break-points for oxycodone under a progressive-ratio schedule. To determine whether a DA-dependent mechanism underlies the impact of D3 antagonism in reducing opioid reward, we used optogenetic approaches to examine intracranial self-stimulation (ICSS) maintained by optical activation of ventral tegmental area (VTA) DA neurons in DAT-Cre mice. Photoactivation of VTA DA in non-drug treated mice produced robust ICSS behavior. Lower doses of oxycodone enhanced, while higher doses inhibited, optical ICSS. Pretreatment with R-VK4-40 blocked oxycodone-enhanced brain-stimulation reward. By itself, R-VK4-40 produced a modest dose-dependent reduction in optical ICSS. Pretreatment with R-VK4-40 did not compromise the antinociceptive effects of oxycodone in rats, and R-VK4-40 alone produced mild antinociceptive effects without altering open-field locomotion or rotarod locomotor performance. Together, these findings suggest R-VK4-40 may permit a lower dose of prescription opioids for pain management, potentially mitigating tolerance and dependence, while diminishing reward potency. Hence, development of R-VK4-40 as a therapy for the treatment of opioid use disorders and/or pain is currently underway. This article is part of the Special Issue entitled 'New Vistas in Opioid Pharmacology'.

Chemotherapy-Induced Peripheral Neurotoxicity (CIPN) is often dose-limiting and impacts life quality and survival of cancer patients. Ghrelin agonists have neuroprotectant effects and may have a role in treating or preventing CIPN. We evaluated the CNS-penetrant ghrelin agonist HM01 in three experimental models of CIPN at doses of 3–30 mg/kg p.o. daily monitoring orexigenic properties, nerve conduction, mechanical allodynia, and intra-epidermal nerve fiber density (IENFD). In a cisplatin-based study, rats were dosed daily for 3 days (0.5 mg/kg i.p.) + HM01. Cisplatin treatment induced mechanical hypersensitivity which was significantly reduced by HM01. In a second study, oxaliplatin was administered to mice (6 mg/kg i.p. 3 times/week for 4 weeks) resulting in significant digital nerve conduction velocity (NCV) deficits and reduction of IENFD. Concurrent HM01 dose dependently prevented the decline in NCV and attenuated the reduction in IENFD. Pharmacokinetic studies showed HM01 accumulation in the dorsal root ganglia and sciatic nerves which reached concentrations > 10 fold that of plasma. In a third model, HM01 was tested in preventive and therapeutic paradigms in a bortezomib-based rat model (0.2 mg/kg i.v., 3 times/week for 8 weeks). In the preventive setting, HM01 blocked bortezomib-induced hyperalgesia and IENFD reduction at all doses tested. In the therapeutic setting, significant effect was observed, but only at the highest dose. Altogether, the robust peripheral nervous system penetration of HM01 and its ability to improve multiple oxaliplatin-, cisplatin-, and bortezomib-induced neurotoxicities suggest that HM01 may be a useful neuroprotective adjuvant for CIPN.

Mebendazole (MBZ) was developed as a broad-spectrum anthelmintic but has recently shown efficacy as an anticancer agent. The use of MBZ for cancer, however, is challenging due to its poor solubility leading to poor bioavailability. Herein, we developed a prodrug approach with various N-linked promoieties including acyloxymethyl, aminoacyloxymethyl, and substituted phosphonooxymethyl in attempt to improve these characteristics. Compound 12, containing an (((((isopropoxycarbonyl)oxy)methoxy)phosphoryl)oxy)methyl promoiety, showed a >10 000-fold improvement in aqueous solubility. When evaluated in mice, 12 displayed a 2.2-fold higher plasma AUC0–t and a 1.7-fold improvement in brain AUC0–t with a calculated oral bioavailability of 52%, as compared to 24% for MBZ-polymorph C (MBZ-C), the most bioavailable polymorph. In dogs, 12 showed a 3.8-fold higher plasma AUC0–t with oral bioavailability of 41% compared to 11% for MBZ-C. In summary, we have identified a prodrug of MBZ with better physicochemical propertie...

4-Carboxy-α-[3-(hydroxyamino)-3-oxopropyl]-benzenepropanoic acid 1 is a potent hydroxamate-based inhibitor of glutamate carboxypeptidase II. In an attempt to improve its poor oral pharmacokinetics, we synthesized a series of prodrugs by masking its hydrophilic hydroxamate group. Prodrugs were evaluated for oral availability in mice and showed varying degree of plasma exposure to 1. Of these, para-acetoxybenzyl-based, 4-(5-(((4-acetoxybenzyl)oxy)amino)-2-carboxy-5-oxopentyl)benzoic acid, 12, provided 5-fold higher plasma levels of 1 compared to oral administration of 1 itself. Subsequently, para-acetoxybenzyl-based prodrugs with additional ester promoiety(ies) on carboxylate(s) were examined for their ability to deliver 1 to plasma. Isopropyloxycarbonyloxymethyl (POC) ester 30 was the only prodrug that achieved substantial plasma levels of 1. In vitro metabolite identification studies confirmed stability of the ethyl ester of benzoate while the POC group was rapidly hydrolyzed. At oral daily dose-equivalent of 3 mg/kg, 12 exhibited analgesic efficacy comparable to dose of 10 mg/kg of 1 in the rat chronic constrictive injury model of neuropathic pain.

Aberrant excitatory neurotransmission associated with overproduction of glutamate has been implicated in the development of HIV-associated neurocognitive disorders (HAND). The glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON, 14) attenuates glutamate synthesis in HIV-infected microglia/macrophages, offering therapeutic potential for HAND. We show that 14 prevents manifestation of spatial memory deficits in chimeric EcoHIV-infected mice, a model of HAND. 14 is not clinically available, however, because its development was hampered by peripheral toxicities. We describe the synthesis of several substituted N-(pivaloyloxy)alkoxy-carbonyl prodrugs of 14 designed to circulate inert in plasma and be taken up and biotransformed to 14 in the brain. The lead prodrug, isopropyl 6-diazo-5-oxo-2-(((phenyl(pivaloyloxy)methoxy)-carbonyl)amino)hexanoate (13d), was stable in swine and human plasma but liberated 14 in swine brain homogenate. When dosed systemically in swine, 13d provided a 15-fold enhanced CSF-to-plasma ratio and a 9-fold enhanced brain-to-plasma ratio relative to 14, opening a possible clinical path for the treatment of HAND.

2-(Phosphonomethyl)pentanedioic acid (2-PMPA) is a potent and selective inhibitor of glutamate carboxypeptidase-II (GCPII) with efficacy in multiple neurological and psychiatric disease models, but its clinical utility is hampered by low brain penetration due to the inclusion of multiple acidic functionalities. We recently reported an improvement in the brain-to-plasma ratio of 2-PMPA after intranasal (IN) dosing in both rodents and primates. Herein, we describe the synthesis of several 2-PMPA prodrugs with further improved brain delivery of 2-PMPA after IN administration by masking of the γ-carboxylate. When compared to IN 2-PMPA in rats at 1 h post dose, γ-(4-acetoxybenzyl)-2-PMPA (compound 1) resulted in significantly higher 2-PMPA delivery to both plasma (4.1-fold) and brain (11-fold). Subsequent time-dependent evaluation of 1 also showed high brain as well as plasma 2-PMPA exposures with brain-to-plasma ratios of 2.2, 0.48, and 0.26 for olfactory bulb, cortex, and cerebellum, respectively, as well as an improved sciatic nerve to plasma ratio of 0.84. In contrast, IV administration of compound 1 resulted in similar plasma exposure of 2-PMPA versus the IN route (AUCIV: 76 ± 9 h·nmol/mL versus AUCIN: 99 ± 24 h·nmol/mL); but significantly lower nerve and brain tissue exposures with tissue-to-plasma ratios of 0.21, 0.03, 0.04, and 0.04 in nerve, olfactory bulb, cortex, and cerebellum, respectively. In primates, IN administration of 1 more than doubled 2-PMPA concentrations in the cerebrospinal fluid relative to previously reported levels following IN 2-PMPA. The results of these experiments provide a promising strategy for testing GCPII inhibition in neurological and psychiatric disorders.

Malignant peripheral nerve sheath tumor (MPNST) is a sarcoma that occurs in ~10% of patients with neurofibromatosis type I (NF1). Incomplete surgical resection at diagnosis leads to a 4-year event-free survival rate of 30 micromolar). JHU395 delivered GA to MPNST cells with >4-fold higher cell-to-plasma ratio compared to native GA and maintained ~2.5-fold higher tumor-to-plasma GA levels in vivo. Mice treated with JHU395 had >40% smaller mean tumor volume compared to controls with no overt toxicity. Quantitiative bioanalysis revealed that JHU395 treated tumors had >60% higher glutamine levels compared to controls 30 minutes after oral dosing. In vivo flux analysis demonstrated that JHU395 preferentially affects tumor glutamine utilization for nucleotide synthesis, while glutamine-derived substrates for the citric acid cycle appear unaffected. In summary, JHU395 inhibits growth of MPNST with inhibition of glutamine utilization in nucleotide synthesis and is well-tolerated. Nervous tissue penetrant glutamine antagonism is a feasible and effective therapeutic approach in preclinical models of MPNST. Future studies will investigate JHU395 in combination with nucleotide synthesis inhibitors in MPNST and investigate JHU395 efficacy in additional sarcoma models including patient-derived samples. Citation Format: Kathryn M. Lemberg, Liang Zhao, Ying Wu, Jesse Alt, Joanna Marie H. Aguilar, Jenny Lam, Alexandra J. Gadiano, Rana Rais, Pavel Majer, Jaishri Blakeley, Barbara S. Slusher. JHU395, a nervous tissue penetrant glutamine antagonist, restricts growth of malignant peripheral nerve sheath tumor with inhibition of nucleotide synthesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3602.

Neurofibromatosis Type I (NF1) is a heritable tumor predisposition syndrome in which up to 10% of patients develop malignant peripheral nerve sheath tumor (MPNST), an aggressive sarcoma. For MPNST that is incompletely resected at diagnosis, traditional cytotoxic chemotherapeutic strategies offer a 5 year event-free survival of less than 40%; thus new therapeutic strategies are desperately needed. Reprogramming of energy metabolism, whereby tumor cells take up more glutamine than healthy cells and direct this substrate to replenish metabolites for proliferation, is a hallmark of several cancers that has not been effectively leveraged for treatment of MPNST. Our group has recently described JHU 395, a nervous system targeted prodrug of the glutamine antagonist 6-diazo-5-oxo-norleucine (DON) which delivers DON preferentially to the brain resulting in less gastrointestinal toxicity, which was the main toxicity of DON in past clinical trials. The primary goals of this study were to evaluate glutamine antagonism and JHU 395 activity in MPNST. Using multiple Schwann and MPNST cell lines we investigated cell proliferation in culture under glutamine deprivation and antagonism. Mass spectrometry (MS)-based metabolomic profiling was used to characterize differences between MPNST cells treated with vehicle versus DON. MS-based bioanalytical methods were also used to investigate DON delivery to tumor cells by JHU 395. We found that growth of MPNST cells in culture is preferentially inhibited by glutamine deprivation and DON treatment when compared to immortalized Schwann cells derived from non-tumored nerve (IC50 of 8-9 micromolar versus >30 micromolar). Targeted metabolomics analyses of DON treated human MPNST cells demonstrated multiple differences in downstream glutamine-dependent metabolites including intermediates in purine synthesis and amino acid synthesis, suggesting that DON acts broadly within the tumor cell to inhibit growth. While DON showed limited partitioning into MPNST cells versus plasma, JHU 395 preferentially delivered DON into MPNST with over 5-fold higher cell-to-plasma ratio. Prodrug pharmacokinetic studies in mouse demonstrated that oral administration of the prodrug safely delivered DON at micromolar concentrations to peripheral nerve. In conclusion, compared to healthy Schwann cells, MPNST cells have unique vulnerability to antagonizing glutamine utilization. The nervous system directed prodrug JHU 395 enhances DON delivery to MPNST and represents a novel potential therapeutic approach for these aggressive tumors. Based on these results we have initiated efficacy studies of JHU 395 in the murine NPcis (NF1+/-;p53+/-) model of MPNST. Citation Format: Kathryn Lemberg, Ying Wu, Jesse Alt, Liang Zhao, Alexandra J. Gadiano, Chabely Rodriguez, Rana Rais, Pavel Majer, Jaishri Blakeley, Barbara Slusher. Novel prodrugs of the glutamine antagonist 6-diazo-5-oxo-norleucine (DON) as treatment for malignant peripheral nerve sheath tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3524.