The currently fielded pre-hospital therapeutic regimen for the treatment of organophosphorus (OP) poisoning in the United States (U.S.) is the administration of atropine in combination with an oxime antidote (2-PAM Cl) to reactivate inhibited acetylcholinesterase (AChE). Depending on clinical symptoms, an anticonvulsant, e.g., diazepam, may also be administered. Unfortunately, 2-PAM Cl does not offer sufficient protection across the range of OP threat agents, and there is some question as to whether it is the most effective oxime compound available. The objective of the present study is to identify an oxime antidote, under standardized and comparable conditions, that offers protection at the FDA approved human equivalent dose (HED) of 2-PAM Cl against tabun (GA), sarin (GB), soman (GD), cyclosarin (GF), and VX, and the pesticides paraoxon, chlorpyrifos oxon, and phorate oxon. Male Hartley guinea pigs were subcutaneously challenged with a lethal level of OP and treated at approximately 1 min post challenge with atropine followed by equimolar oxime therapy (2-PAM Cl, HI-6 DMS, obidoxime Cl2, TMB-4, MMB4-DMS, HLö-7 DMS, MINA, and RS194B) or therapeutic-index (TI) level therapy (HI-6 DMS, MMB4-DMS, MINA, and RS194B). Clinical signs of toxicity were observed for 24 hours post challenge and blood cholinesterase [AChE and butyrylcholinesterase (BChE)] activity was analyzed utilizing a modified Ellman’s method. When the oxime is standardized against the HED of 2-PAM Cl for guinea pigs, the evidence from clinical observations, lethality, quality of life (QOL) scores, and cholinesterase reactivation rates across all OPs indicated that MMB4 DMS and HLö-7 DMS were the two most consistently efficacious oximes.

Given the rapid onset of symptoms from intoxication by organophosphate (OP) compounds, a quick-acting, efficacious therapeutic regimen is needed. A primary component of anti-OP therapy is an oxime reactivator to rescue OP-inhibited acetylcholinesterases. Male guinea pigs, clipped of hair, received neat applications of either VR, VX, parathion, or phorate oxon (PHO) at the 85th percentile lethal dose, and, beginning with presentation of toxicosis, received the human equivalent dose therapy by intramuscular injection with two additional follow-on treatments at 3-hr intervals. Each therapy consisted of atropine free base at 0.4 mg/kg followed by one of eight candidate oximes. Lethality rates were obtained at 24 hr after VR, VX and PHO challenges, and at 48 hr after challenge with parathion. Lethality rates among symptomatic, oxime-treated groups were compared with that of positive control (OP-challenged and atropine-only treated) guinea pigs composited across the test days. Significant (p ≤ 0.05) protective therapy was afforded by 1,1-methylene bis(4(hydroxyimino- methyl)pyridinium) dimethanesulfonate (MMB4 DMS) against challenges of VR (p ≤ 0.001) and VX (p ≤ 0.05). Lethal effects of VX were also significantly (p ≤ 0.05) mitigated by treatments with oxo-[[1-[[4-(oxoazaniumylmethylidene)pyridin-1-yl] methoxymethyl]pyridin-4-ylidene]methyl]azanium dichloride (obidoxime Cl2) and 1-(((4-(aminocarbonyl) pyridinio)methoxy)methyl)-2,4-bis((hydroxyimino)methyl)pyridinium dimethanesulfonate (HLö-7 DMS). Against parathion, significant protective therapy was afforded by obidoxime dichloride (p ≤ 0.001) and 1,1′-propane-1,3-diylbis{4-[(E)-(hydroxyimino)methyl]pyridinium} dibromide (TMB-4, p ≤ 0.01). None of the oximes evaluated was therapeutically effective against PHO. Across the spectrum of OP chemicals tested, the oximes that offered the highest level of therapy were MMB4 DMS and obidoxime dichloride.

Introduction While exposure to sulfur mustard (SM) is commonly associated with the production of vesicating dermal, ocular, and respiratory injuries, systemic damage to bone marrow and lymphatic tissue can decrease critical immune cell populations leading to higher susceptibility to life-threatening infection and septicemia. There are currently no approved medical countermeasures for SM-induced myelosuppression. An intravenous SM challenge model was developed in adult rats as a preliminary proof-of-principle platform to evaluate the efficacy of candidate immunostimulants. Materials and Methods Adult male and female Sprague Dawley rats were exposed to SM through tail vein injection. Toxicity progression was monitored through clinical observations, body weights, body temperatures, hematology, serum clinical chemistry, and flow cytometry of blood and bone marrow samples. Results Following SM exposure, overt toxicity progression was characterized by weight loss, changes in body temperature, and manifestation of toxic clinical signs (diarrhea, lethargy, hunched posture, rough hair coat, respiratory distress, and death). Drastic alterations in complete blood cell profiles included an early-onset lymphopenia followed by a delayed-onset neutropenia and thrombocytopenia. Only transient changes in serum clinical chemistry parameters were observed. Flow cytometry analysis of circulating blood revealed that B-cells were more predominantly affected by SM exposure than T-cells. Challenge with SM resulted in loss of hematopoietic and mesenchymal stem cell populations in the bone marrow. Conclusions The small animal model developed in this study replicates many key aspects of human SM exposures and should serve as a relevant, rapid, and cost-effective platform to screen candidate medical countermeasures for SM-induced hematologic toxicity.

Organophosphorus (OP) compounds, including pesticides and chemical warfare nerve agents (CWNA), are threats to the general population as possible weapons of terrorism or by accidental exposure whether through inadvertent release from manufacturing facilities or during transport. To mitigate the toxicities posed by these threats, a therapeutic regimen that is quick-acting and efficacious against a broad spectrum of OPs is highly desired. The work described herein sought to assess the protective ratio (PR), median effective doses (ED), and therapeutic index (TI = oxime 24-h LD/oxime ED) of MMB4 DMS, HLö-7 DMS, and 2-PAM Cl against the OPs sarin (GB), VX, and phorate-oxon (PHO). All OPs are representative of the broader classes of G and V chemical warfare nerve agents and persistent pesticides. MMB4 DMS and HLö-7 DMS were previously identified as comparative efficacy leads warranting further evaluations. 2-PAM Cl is the U.S. FDA-approved standard-of-care oxime therapy for OP intoxication. Briefly, PRs were determined in male guinea pigs by varying the subcutaneously (SC) delivered OP dose followed then by therapy with fixed levels of the oxime and atropine (0.4 mg/kg; administered intramuscularly [IM]). EDs were determined using a similar approach except the OP dose was held constant at twice the median lethal dose (2 × LD) while the oxime treatment levels were varied. The ED information was then used to calculate the TI for each OP/oxime combination. Both MMB4 DMS and HLö-7 DMS provided significant protection, i.e., higher PR against GB, VX, and PHO when compared to atropine controls, but significance was not readily demonstrated across the board when compared against 2-PAM Cl. The ED values of MMB4 DMS was consistently lower than that of the other oximes against all three OPs. Furthermore, based on those EDs, the TI trend of the various oximes against both GB and VX was MMB4 DMS > HLö-7 DMS > 2-PAM Cl, while against PHO, MMB4 DMS > 2-PAM Cl > HLö-7 DMS.