Radiation and Chemical Program Research for Multi-Utility and Repurposed Countermeasures: A US Department of Health and Human Services Agencies Perspective.

Although chemical and radiological agents cause toxicity through different mechanisms, the multiorgan injuries caused by these threats share similarities that convene on the level of basic biological responses. This publication will discuss these areas of convergence and explore "multi-utility" approaches that could be leveraged to address common injury mechanisms underlying actions of chemical and radiological agents in a threat-agnostic manner. In addition, we will provide an overview of the current state of radiological and chemical threat research, discuss the US Government's efforts toward medical preparedness, and identify potential areas for collaboration geared toward enhancing preparedness and response against radiological and chemical threats. We also will discuss previous regulatory experience to provide insight on how to navigate regulatory paths for US Food and Drug Administration (FDA) approval/licensure/clearance for products addressing chemical or radiological/nuclear threats. This publication follows a 2022 trans-agency meeting titled, "Overlapping Science in Radiation and Sulfur Mustard Exposures of Skin and Lung: Consideration of Models, Mechanisms, Organ Systems, and Medical Countermeasures," sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), a part of the National Institutes of Health (NIH). Discussions from this meeting explored the overlapping nature of radiation and chemical injury and spurred increased interest in how preparedness for one threat leads to preparedness for the other. Herein, subject matter experts from the NIAID and the Biomedical Advanced Research and Development Authority (BARDA), a part of the Administration for Strategic Preparedness and Response (ASPR), summarize the knowledge gained from recently funded biomedical research, as well as insights from the 2022 meeting. These topics include identification of common areas for collaboration, potential use of biomarkers of injury to identify injuries caused by both hazards, and common and widely available treatments that could treat damage caused by radiological or chemical threats.

A delayed treatment model for the evaluation of scopolamine for VX nerve agent intoxication.

Most research on medical countermeasures for nerve agent exposure assumes a military scenario, in which (autoinjector) treatment is envisaged to be available immediately. In a civilian setting however, treatment is delayed until arrival of first-aid responders. This may significantly affect treatment efficacy and the requirements for secondary intensive care. The aim of the current study was to develop a guinea pig model to evaluate the efficacy of delayed treatment following nerve agent exposure. We identified a trigger-to-treat based on a progressive stage of the toxidrome following VX exposure, which was associated with the subsiding of clonic movements. This paradigm resulted in treatment consistently being administered between 15 and 25 min post-exposure. Using the model, we investigated the potential for the anticholinergic scopolamine to act as a delayed treatment either as a standalone treatment, or as an adjunct to delayed treatment with Standard of Care (SOC), containing atropine, 2-PAM, and midazolam. The study provides a framework for a small animal model for evaluating the efficacy of treatment administered at a specific stage of the toxidrome, when immediate treatment is absent. As an adjunct, scopolamine treatment did not result in improved survival, but did show a beneficial effect on recovery, in terms of general posture. As a standalone treatment, scopolamine showed a significant, dose-responsive, beneficial effect on survival and recovery. These promising results warrant additional studies to investigate which observed physiological improvements are relevant for the recovery process and residual injury.

Role of G(q) protein in behavioral effects of the hallucinogenic drug 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane.

Extensive evidence suggests that 5-HT2 receptors may play a role in mental disorders including schizophrenia. In addition, several studies indicate that G(q)-coupled 5-HT(2A) receptors are likely targets for the initiation of events leading to the hallucinogenic behavior elicited by lysergic acid diethylamide (LSD), (+/-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and related drugs. However, 5-HT(2A) receptors couple to other G proteins in addition to G(q) protein. To evaluate the role of the G(q) signaling pathway in DOI-induced behaviors, we utilized two behavioral models of 5-HT(2A) receptor activation: induction of head-twitches by DOI, a common response to hallucinogenic drugs in rodents, and DOI elicited anxiolytic-like effects in the elevated plus maze. Experimental subjects were genetically modified mice [Galpha(q)(-/-)] in which the G(q) alpha gene was eliminated. Galpha(q)(-/-) mice exhibited a decrease in DOI-induced head-twitches, when compared to wild-type littermates. In addition, the DOI-induced increase in anxiolytic-like behavior was abolished in Galpha(q)(-/-) mice. These results, combined with our finding that DOI-induced FOS expression in the medial prefrontal cortex was also eliminated in Galpha(q)(-/-) mice, suggests a key role for G(q) protein in hallucinogenic drug effects.

A selective positive allosteric modulator of metabotropic glutamate receptor subtype 2 blocks a hallucinogenic drug model of psychosis.

Recent clinical studies reveal that selective agonists of group II metabotropic glutamate (mGlu) receptors have robust efficacy in treating positive and negative symptoms in patients with schizophrenia. Group II mGlu receptor agonists also modulate the in vivo activity of psychotomimetic drugs and reduce the ability of psychotomimetic hallucinogens to increase glutamatergic transmission. Because increased excitation of the medial prefrontal cortex (mPFC) has been implicated in pathophysiology of schizophrenia, the ability of group II mGlu receptor agonists to reduce hallucinogenic drug action in this region is believed to be directly related to their antipsychotic efficacy. A novel class of ligands, termed positive allosteric modulators, has recently been identified, displaying exceptional mGlu2 receptor selectivity. These compounds do not activate mGlu2 receptors directly but potentiate the ability of glutamate and other agonists to activate this receptor. We now report that the mGlu2 receptor-selective positive allosteric modulator biphenyl-indanone A (BINA) modulates excitatory neurotransmission in the mPFC and attenuates the in vivo actions of the hallucinogenic 5-HT(2A/2C) receptor agonist (-)2,5-dimethoxy-4-bromoamphetamine [(-)DOB]. BINA attenuates serotonin-induced increases in spontaneous excitatory postsynaptic currents in the mPFC, mimicking the effect of the mGlu2/3 receptor agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV). In addition, BINA reduced (-)DOB-induced head twitch behavior and Fos expression in mPFC, effects reversed by pretreatment with the mGlu2/3 receptor antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropan-1-yl) -3 - (xanth-9-yl-)propionic acid (LY341495). These data confirm the relevance of excitatory signaling in the mPFC to the behavioral actions of hallucinogens and further support the targeting of mGlu2 receptors as a novel strategy for treating glutamatergic dysfunction in schizophrenia.

Dynamic changes in prefrontal cortex gene expression following lysergic acid diethylamide administration.

Lysergic acid diethylamide (LSD) is a psychoactive drug that transiently alters human perception, behavior, and mood at extremely low doses. Certain aspects of the behavior elicited by acute doses of LSD closely resemble symptoms of mental disorders such as schizophrenia. Characterizing gene expression profiles after LSD will be important for understanding how it alters behavior, and will lead to novel insights into disorders, such as schizophrenia, whose behavioral symptoms resemble the temporary effects of hallucinogenic drugs. We previously identified a small collection of genes within the rat prefrontal cortex that respond to LSD. Many of the products of these genes are involved in the process of synaptic plasticity. In the current report, we present a detailed analysis of the expression of these genes within the brain using RNase protection analysis. We find that the gene response to LSD is quite dynamic. The expression of some genes increases rapidly and decreases rapidly, while other genes change more gradually. Dose-response studies show two classes of expression; gene expression maximally stimulated at lower doses, versus gene expression that continues to rise at the higher doses. The role of the 5-HT(1A) and 5-HT(2A) receptor in mediating the increases in gene expression was examined in a series of experiments using receptor specific antagonists. Most expression increases were due to activation of the 5-HT(2A) receptor, however expression of two genes had neither a 5-HT(1A) nor a 5-HT(2A) receptor component.