A pilot study in the swine model of lethal cyanide intoxication indicates efficacy of a platinum-methionine complex countermeasure

Abstract

Cyanide presents a chemical security threat because of its wide availability, due to industrial uses, and significant toxicity. Platinum-thioether complexes are a recent addition to candidate antidotes, showing efficacy in mouse models of hydrogen cyanide inhalation and reversing toxicity measures in rabbits. This pilot study evaluated the effectiveness of a platinum-methionine complex (Met2Pt), a potent lead candidate, in a lethal swine model, which provides a solid foundation for future research. Potassium cyanide (0.2 mg/kg/min; IV) was infused into anesthetized swine until 6 min post-apnea. Met2Pt (2.9 mg Pt/kg in 3 mL) or 100 mM phosphate buffer vehicle (3 mL) were then administered intravenously (IV) or intramuscularly (IM). Vital signs, metabolites, and pharmacokinetics were monitored for > 90 min. IV Met2Pt was highly efficacious compared to all other treatments, rescuing all swine in the group and reversing cyanide-derangements in lactate concentration (Welch One-Way ANOVA, p < 10^− 4), blood oxygenation (p = 0.002), etc. IM Met2Pt did not significantly improve survival due to lower systemic availability (7%). The results of this pilot study indicate that Met2Pt is efficacious via the IV route, while IM availability of Met2Pt is a limiting factor.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-55739-8.

Introduction

As both a potent poison and a widely used industrial reagent, cyanide presents a dual-use threat and an occupational and military safety concern^1,2. Cyanide can cause rapid death in exposed individuals^3,4. The mining industry uses cyanide for metal leaching, and it is a chemical precursor for herbicides, nitrile polymers, and dyes⁵. Industrial cyanide production exceeds 1.1 million tons each year, posing a potential for large-scale disasters, as seen previously with the Baia Mare cyanide spill and the Ok Tedi environmental disaster^5–8. Inhalation of cyanide-enriched smoke and other poisonous gases arising from burning plastic and polyurethanes are associated with high morbidity and mortality, with an example of mass casualties of 230 people in a nightclub fire in Brazil in 2013^9–11. The wide availability of cyanide adds the risk of exploitation for malicious use, as evidenced in an attempted terrorist attack in Tokyo, Japan, involving cyanide gas generation in a train station¹².

Currently, approved cyanide antidotes are unsuitable for use in large-scale incidents like industrial disasters, fires, or terrorist attacks. The rapid action of cyanide poisoning requires immediate on-site administration. Thiosulfate, nitrite, and dicobalt edetate are efficacious for treating cyanide poisoning but require diagnosis of cyanide poisoning before administration due to toxicity concerns^13–16. Hydroxocobalamin, the latest approved antidote, has reduced risks and does not require the extra time burden of a definitive diagnosis^17–20. Unfortunately, all current antidotes, including hydroxocobalamin, are administered by intravenous infusion and require trained personnel in a clinical setting. In the case of a larger-scale catastrophe, it becomes logistically impossible to transport hundreds of victims to a hospital before casualties occur^21–23. An unmet medical need is a cyanide countermeasure that minimally trained individuals can rapidly deliver in field settings^23–25.

There are examples of candidate cyanide antidotes that can be delivered by a single bolus, intramuscular (IM) injection, to enable treatment in the field^26–32. Autoinjectors for IM administration are ideal for large-scale catastrophes if formulations and doses meet the maximum volume requirements. Sulfur-based agents, tetrathionate, and dimethyl trisulfide (DMTS) act by converting toxic cyanide into the less harmful product, thiocyanate^28–31. IM administration of sodium tetrathionate rescued 100% of lethal CN-exposed swine compared to saline injections (17% survival in the same model)²⁹. DMTS delivered in oily and aqueous formulations rescued 83.3% and 90% survival in the same swine CN model, respectively^30,31. Glyoxylate, a metabolic rescue agent and cyanohydrin-forming scavenger, also rescued 83% of swine compared to saline injections (12% survival)³². Cobinamide, a biosynthetic precursor of vitamin B12, has also shown efficacy in treating cyanide poisoning in swine when administered intravenously³³. Cobinamide derivatives, nitrocobinamide and cobinamide sulfite, are deliverable via the IM route and have shown efficacy in a rabbit model^27,34.

In the evolving landscape of IM-deliverable cyanide antidotes, platinum(II) complexes have the potential to be more efficacious per molar equivalent. One platinum(II) atom reacts with four equivalents of cyanide to form the considerably less toxic byproduct, tetracyanoplatinate³⁵. By comparison, sulfur agents neutralize one cyanide equivalent per sulfur atom, hydroxocobalamin reacts with one cyanide equivalent, while cobinamide reacts with two equivalents per cobalt center^35–39. Platinum agents that rescue animals from cyanide toxicity were discovered using a zebrafish model³⁶. The initial screen identified known chemotherapy drugs, cisplatin, and oxaliplatin and prompted the targeted assessment of commercially available platinum complexes. Notably, it was discovered that agents that exhibited cyanide antidotal activity required activation with dimethyl sulfoxide (DMSO), also when used in rabbit³⁶ and swine models of cyanide toxicity⁴⁰. The known reactivity of platinum complexes with DMSO inspired the design of methyl sulfide-containing bidentate ligands to enhance reactivity with cyanide³⁵. A promising candidate bis(L-methionine-((S, N))platinum(II) dichloride (Met₂Pt) showed improved performance over previously tested platinum complexes in zebrafish. In addition, Met₂Pt demonstrated efficacy in mouse and rabbit models using IM administration³⁵.

The goal of this pilot study was to assess the efficacy of IV and IM-administered Met₂Pt compared to a vehicle control based on survival and clinical outcomes in swine after acute systemic cyanide poisoning⁴¹. A well- established cyanide swine model was used. The experimental agent Met₂Pt could rescue swine when given via the IV route. Better performance was achieved with IV administration than with IM indicative of a direct correlation to systemic availability. The overall results of this study provide preliminary evidence for Met₂Pt efficacy, especially by IV administration; however, not all endpoints reached significance in this pilot-powered study. Several observations are made that inform what consideration will be required for fully powered studies in the swine model of cyanide intoxication.

Materials and methods

The Supplementary Information provides procedures for metabolomics, compound preparation, compound formulation, and plasma Pt analysis.

Swine cyanide model

This treatment protocol is pictorialized in Fig. 1a. Female Yorkshire swine (Sus domesticus, 45–55 kg) (Oak Hill Genetics) were anesthetized with intramuscular ketamine (10–20 mg/kg) and nosecone isoflurane and intubated with an 8.0 mm cuffed endotracheal tube, after which peripheral venous access was obtained. Sedation was maintained with 1–3% isoflurane using the Drager Apollo anesthesia machine. If needed, pressure support ventilation was provided to maintain an end-tidal CO₂ of 35–45 mmHg, with a driving pressure of 5–8 cm H₂O, a peak expiratory pressure of 5 cm H₂O, and a FiO₂ of 0.4. Before central line placement, a 7.5 ml/kg bolus of 0.9% saline was given. The external jugular vein and femoral artery were visualized using the M9 ultrasound system (Mindray), and central venous and arterial access was obtained. A Drager Infinity Delta Monitor was used to record pulse oximetry, body temperature, invasive blood pressure, and ECG throughout the experiment. Invasive hemodynamic variables were measured via pulmonary artery catheterization using an 8- French Swan Ganz CCOmbo catheter and the Edwards Vigilance II monitor. Arterial blood was obtained at baseline, at 30 s post-apnea, and at the indicated times and analyzed with a handheld blood analyzer (iSTAT, Abbott); parameters measured included paO₂, paCO₂, lactate, and pH.

Potassium cyanide (Sigma Aldrich) diluted in saline was delivered via continuous infusion into the right jugular vein (0.2 mg/kg/min; total KCN dose was ~ 2 mg/kg) until 6 min after occurrence of apnea (defined as ≤ 6 breaths per minute for 20 s as determined by capnography). At this point, treatments were administered. Animals were treated with IV Met₂Pt (given as a 3 mL injection via jugular vein over 1 min), IM Met₂Pt (3 mL into the gluteal muscle), IV 100 mM phosphate buffer vehicle (pH 7), or IM phosphate vehicle. Animals from platinum or vehicle groups were run simultaneously and periodically throughout the year to ensure negligible cohort-to-cohort variation. However, the IV Pt/vehicle and IM Pt/vehicle groups were run at different times. Met₂Pt was given as a total fixed dose of 135 mg Pt formulated in a phosphate vehicle. All Met₂Pt formulations were normalized using total platinum concentration as measured by UV-visible spectroscopy after titration with cyanide. Following the treatment, animals were observed continuously for 90 min or until death (defined as a mean arterial pressure of less than 30 mmHg for 10 min, sustained apnea for 30 min, or pulse oximetry ≤ 70% for 30 consecutive minutes as confirmed by arterial blood oxygenation of ≤ 50 mmHg). The efficacy of each antidote treatment was evaluated by assessing the primary outcome, survival at 90 min post-treatment, in addition to secondary outcomes (clinical, laboratory, and metabolic parameters). At the end of the study, all animals were euthanized with an intravenous administration of 100 mg/kg sodium pentobarbital. All swine in these studies were anesthetized in accordance with IACUC-recommended procedures to prevent unnecessary distress and suffering. All methods were carried out in accordance with the regulations and guidelines of the Animal Welfare Act and the American Association for Accreditation of Laboratory Animal Care. The University of Colorado IACUC committee approved all experimental protocols.

Statistical approach and multiple hypothesis testing

All treatment groups were treated as separate categorical variables for clinical measurements and compared using a Welch One-Way ANOVA. Survival amongst treatment groups was compared using Log-Rank Mantel-Cox and Gehan–Breslow–Wilcoxon tests. Survival trends were assessed using the Log-Rank test-for-trend. Survival at 90 min was compared using Fisher’s exact test or the chi-squared test, as noted. Statistical analysis across treatment groups with metabolite measurements made by liquid chromatography-tandem mass spectrometry (LC-MSMS) used the difference between metabolite values at clinical apnea (occurring before treatment) and 15 min post-treatment, with error propagation of standard deviations to correct for pretreatment changes. These differences were compared across treatment groups using a Welch’s One-Way ANOVA. All statistical tests were performed using GraphPad Prism 9.5. In this pilot study, results were often interpreted post-hoc and thus must be further validated in follow-up studies.

Results

Baseline characteristics of study subjects

Animals from platinum and vehicle groups were run on the same day throughout the year to ensure negligible cohort-to-cohort variation. However, the IV Pt/vehicle and IM Pt/vehicle groups were conducted at different times. Physiological parameters and clinical pathology markers were similar between all vehicle and Met₂Pt groups at baseline (Table S1). The four groups showed no significant differences in weight, blood lactate levels, blood pH, pulse rates, systolic blood pressure (SBP), mean arterial pressure (MAP), or respiratory rates. However, the pulse oximetry assessment revealed a statistically significant decrease in oxygen saturation in the swine group treated intravenously with a phosphate-buffered vehicle, but this was clinically insignificant. In a previous study, the group’s baseline blood oxygenation was not significantly different from that of a control swine group from a similar model³². A t-test with Welch’s correction showed that these two swine groups did not achieve significance (p = 0.07; 90 ± 1.5% vs. 92 ± 3.0%). Based on these observations, this group was at the lower end of the distribution but within the range of baseline blood oxygenation values for swine. Nevertheless, this may be a potential confounder in the study.

Each treatment group was dosed with cyanide until apnea occurred before administration of the control vehicles or Met₂Pt formulations, as per the treatment protocol (Fig. 1a). As expected, all swine experienced respiratory depression leading to apnea and decreased blood oxygenation. No statistical significance was observed in the measured physiological parameters between all four groups (Table S2). Notably, the cyanide doses required to induce apnea were similar across all four groups; treatment effects were assessed over a 90-min period, starting 6 min after apnea.

Fig. 1.

(a) Swine treatment protocol involves infusion with potassium cyanide until 6 min. post apnea, at which time antidote is given; blood is serially sampled over 90 min, at the end of which survival is determined; (b) Kaplan–Meier survival curve comparing treatment with IV phosphate vehicle (blue solid line, n = 6), IV Met₂Pt (red solid line, n = 6), IM vehicle (green dashed line, n = 9), and IM Met₂Pt (purple dashed line, n = 9).

Survival after lethal cyanide exposure

The Met₂Pt doses were based on measured platinum concentrations and delivered in 3 mL volume by either IV bolus or IM injection into the gluteal muscle, with each pig receiving 135 mg Pt formulated in 100 mM sodium phosphate buffer (pH 7.4). Vehicle treatments used 3 mL volume injections of 100 mM phosphate buffer (pH 7.4). The Met₂Pt dose corresponds to an average of 2.9 mg Pt/kg. This dose is 2x greater than the allometrically scaled efficacious dose in the mouse model using IM administration³⁵.

Met₂Pt and phosphate promoted different degrees of survival in the lethal CN swine model (Fig. 1b)⁴¹. The most efficacious treatment in this study, resulting in 100% survival, was IV Met₂Pt, while IM dosing achieved 45% survival. In contrast, the phosphate buffer (100 mM) effect resulted in 50% survival with IV dosing and 22% with IM dosing. When all four curves were compared, none achieved 95% confidence by Log-Rank Mantel-Cox test (p = 0.0765) or the Gehan–Breslow–Wilcoxon test (p = 0.0994). Nevertheless, a log-rank test for trend was significant (p = 0.0152) in the order IM vehicle < IM Met₂Pt < IV vehicle < IV Met₂Pt. Lastly, when the IV vehicle was excluded from the comparison, significance was achieved in both the Log-Rank Mantel–Cox test (p = 0.0244) and the Gehan–Breslow–Wilcoxon test (p = 0.0328). These comparisons are consistent with the IV Met₂Pt being superior to dosing IM Met₂Pt and IM vehicle alone. While a log-rank test did not show a difference between IV Met2Pt and IV vehicle (p = 0.0554), a 2 × 2 chi-square test comparing survival at 90 min. was significant (p = 0.0455). The result is consistent with a limitation of the study, which requires a larger sample size to measure this difference truly.

Met₂Pt improves clinical parameters following cyanide exposure

Statistically significant differences in some, but not all, clinical parameters measured were observed among the four treatment groups at death or at the end of the study (Table S3). IV Met₂Pt demonstrates the best recoveries after cyanide poisoning by reducing lactate levels (W = 9.04, p < 10^− 4), maintaining blood pH (W = 3.74, p = 0.04) at physiological levels, and increasing blood oxygenation (W = 9.02, p = 0.002). Time-based monitoring reveals similar trends in these parameters (Fig. 2; note n decreased at later timepoints due to death, denoted by the black dashed line). Although the four groups were not statistically different (W = 1.925, p = 0.2950), times to rebreathing trended towards shorter in both platinum treatment groups compared to vehicle treatments (Fig. 2d). The results of these clinical trends (respiratory rate, time to rebreathing, blood oxygenation, pH, and lactate) suggest that platinum agents may be promoting recovery via faster rebreathing after cyanide exposure than the phosphate buffer vehicle alone. However, this pilot study appears to be underpowered to detect these differences due to variability in the control group.

Fig. 2.

Time courses of clinical parameters for (a) lactate, (b) pH, and (c) pulse oximetry, and (d) an end-of-study plot of rebreathing times in surviving animals. Time points after 15 min (black dashed line) reflect survival bias; the groups in panels (a–c) are IV vehicle (blue squares, n = 6 at 0 min.), IV Met2Pt (red circles, n = 6 at 0 min.), IM vehicle (green triangles, n = 9 at 0 min.), and IM Met2Pt (purple upside down triangles, n = 9 at 0 min.). (d) Summarizes the range of time-to-rebreathing values for surviving animals in each study group. BL denotes baseline, and AP denotes apnea.

Met₂Pt improves tricarboxylic acid metabolite profile

Previous metabolite profiling studies of plasma from cyanide-poisoned animals indicate elevations in fumaric acid, lactic acid, and succinic acid^32,40. The plasma levels of these metabolites reverse upon treatment with cyanide-rescue agents such as glyoxylate. Metabolite profiles of plasma samples collected at various time points in the swine model reveal the tricarboxylic acid intermediates that increase along with lactic acid in response to cyanide exposure, as expected (Figs. S1 and S2: note that sample size n decreased at the later time points due to death). To account for survivor bias and increase power, we pooled end-of-study and time-of-death data points (Tables S4, S5). There was a trend toward restoration of metabolite levels in the IV Met2Pt group compared to the IV controls; none of the findings reached FDR-adjusted significance (Table S4): fumaric acid 2.5 ± 1.1 vs. 12.7 ± 10.1, succinic acid 1.8 ± 0.6 vs. 13.4 ± 12.4, and lactic acid 4.1 ± 1.5 vs. 10.4 ± 6.2. These trends were not present in the IM Met2Pt group, consistent with the absence of a survival effect (Table S5).

The levels of fumaric and lactic acids during rebreathing phases were evaluated for changes, since this clinical parameter showed a trend toward improvement (Fig. 3d). To assess treatment-related effects independently of those occurring prior to treatment, the arithmetic difference in fold-changes for each treatment group between the time of apnea and 15 min post-treatment, was calculated with error propagation of the standard deviations (Fig. 3b,d, and Fig. S3). The timepoint of 15 min is short enough to avoid survival bias and long enough for maximal treatment effects to occur. As assessed by Welch’s ANOVA test, fumaric acid and lactic acid achieved significance in differentiating IM from IV groups but did not distinguish IM control from IM Met2Pt, or IV control from IV Met2Pt (Fig. 3b,d). This unexpected lack of statistical differences between vehicle and treatment arms is unexplained and warrants further consideration in experimental study design. The limitations of the current study indicate the need for a larger cohort size to power the analysis.

Fig. 3.

Time courses (a,c), measured from baseline (BL) to 90 min. for each group, and treatment effects (b,d), with a Welch One-way ANOVA comparison, of fumaric acid and lactic acid measured by LC-MS/MS. The dotted vertical line denotes apnea (AP) and dashed line denotes 15 min. after which, survival bias occurs in the time courses. Treatment effects were assessed after correction for background related inconsistencies by subtracting apnea values (occurring prior to treatment) from 15 min values (after treatments were given but before significant survival bias across groups). The treatments are indicated by common color and number coding (a) across all panels.

Met₂Pt intramuscular absorption is a limitation

The differences in efficacy between the IV and IM treatment groups with Met₂Pt were further evaluated for dose availability. Blood samples from both treatment groups were serially collected at similar time points and analyzed for total platinum content by inductively coupled plasma mass spectrometry (ICP-MS). Indeed, large differences in blood platinum content between IV and IM Met2Pt treatments were observed, with the latter group showing lower Pt concentrations per dose (Fig. 4a; Table S6). Using the ratios of areas under the two pharmacokinetic curves, the fraction of available platinum by IM administration was only 7% of the IV route. These results are consistent with the hypothesis that dose availability contributes to variable responses in survival, physiological parameters, and tricarboxylic acid metabolites in the IM treatment arm of the study. The overall reduction in the efficacy of the IM-administered Met2Pt warrants further attention to formulations to improve the fraction available.

Fig. 4.

(a) Total plasma Pt pharmacokinetics of IV and IM Met₂Pt show poor systemic availability of the latter, (b) ATCA formation from cyanide, (c) ATCA time courses suggest lower levels of cyanide in both IV treatment groups, (d) AUC’s of ATCA in the first 10 min after IM antidote administration suggest that Met₂Pt treated surviving animals had lower blood cyanide levels, immediately after treatment, in support of a scavenger mechanism.

The Met₂Pt pharmacodynamic effect is anticipated to be cyanide chelation, reducing the free systemic cyanide. The plasma samples were evaluated for the formation of 2-aminothiazoline-4-carboxylic acid (ATCA), a surrogate for cyanide, by reaction with blood cystine (Fig. 4b). The ATCA plasma levels are expected to change in response to a cyanide scavenging agent in the treatment animals (Fig. 4c,d)^42,43. In time courses of the total platinum measurements, ATCA levels were observed to be reduced in both IV treatment groups (Fig. 4c). In the IM Met₂Pt treatment group, surviving animals had lower areas under the first 10 min of the plasma ATCA time courses (Fig. 4d). These results are consistent with a cyanide scavenger mechanism for Met₂Pt, which reduces total cyanide levels in the blood available for ATCA formation. As seen in the metabolite profiles, there was insufficient statistical separation between the IV-administered vehicle and Met₂Pt study arms for ATCA levels. The observation that IV-administered vehicle lowering ATCA levels is not fully understood, but the cohort size may contribute to the effect.

Discussion

Platinum-based agents are new candidates under consideration for developing antidotes for cyanide intoxication. Our original observation that DMSO treatment of cisplatin and related platinum agents provided rescue of zebrafish in a cyanide intoxication model motivated the hypothesis that platinum-sulfur ligand bonds could modulate cyanide scavenging efficacy^36,44. Implementing a new approach using S, N-Pt(II) bidentate ligands to create stable complexes opens avenues to overcome the product limitations of DMSO as a ligand^35,45. The agent Met₂Pt is an example of the new series of bidentate Pt(II) complexes, which provides a stable formulation while increasing the reactivity at the platinum center for cyanide addition⁴⁶. Prior efforts demonstrate that Met₂Pt was efficacious in zebrafish, mouse, and rabbit models of cyanide poisoning. The current work presents the results of the large animal swine model of cyanide intoxication using a phosphate buffer formulation of Met₂Pt.

Met₂Pt is efficacious in rescuing pigs from the effects of lethal cyanide intoxication with IV administration. Clinical parameters, including time to rebreathe, pulse oximetry, and lactic acid, all indicate immediate restoration of respiratory function. In addition, there was a trend toward amelioration of metabolic derangements that occur secondary to severe cyanide poisoning. Using the same doses for IM administration results in 10-fold lower circulating platinum levels, but it did not significantly improve survival. In this study, Met₂Pt dosing used ~ 2.9 mg Pt/kg, double the allometrically scaled dose from mice, was required to achieve rescue³⁵. The higher-than-scaled dose requirement reflects the poor systemic availability from the IM administration in swine. However, this dose demonstrates improvement over earlier efforts with a Pt(II)-based rescue agent, hexachloroplatinate-DMSO (HCP-DMSO), tested in the lower-dose cyanide (80% lethal) model, which required 7 mg Pt/kg⁴⁰. Met₂Pt was similar to HCP-DMSO in reducing fumarate, lactate, and lactic acid levels.

A previous observation is that Met₂Pt promotes acute kidney injury in the rat model, with intraperitoneal administration at doses five-fold higher than the allometrically scaled effective dose from the mouse model⁴⁵. The dose used in this study is well below this threshold, and no obvious signs of toxicity were observed during these studies. The effects of Met₂Pt in the swine model are consistent with a scavenger mechanism, where cyanide addition reactions yield tetracyanoplatinate anion (Pt(CN)₄⁻). These results are consistent with the prior observations in vivo using a Pt(IV) agent⁴⁰. In cyanide-intoxicated pigs treated with IV Met₂Pt, the amounts of ATCA in the blood decreased, consistent with a lowering of free cyanide to react with blood cystine. Across several related platinum agents, such as Met₂Pt, the ability to scavenge four molar equivalents of cyanide to produce Pt(CN)₄⁻ is consistently observed in vitro^35,36,45. The same mechanism is likely at play in vivo but awaits additional studies to establish if this is the only pathway for rescue from cyanide intoxication.

As a pilot study, the results provide useful insights for further study design. There are anticipated limitations of the study cohort size which will need to be addressed in future work. Sufficient cohort sizes may lead to statistical significance in the multiple measures that this study could not robustly demonstrate. For instance, based on the survival effects observed in this pilot, a sample size of 11 swine per group is required for a future study to measure the difference between IV Met₂Pt and IV phosphate with 80% statistical power. There are several potential confounders identified in this pilot study that warrant efforts to reconcile moving forward. A potential study limitation is that different batches of Met₂Pt may exhibit different osmolalities (details of the formulations are provided in the supplementary information). Additional potential confounders include animal baseline oxygen (in the IV control group). Finally, the general effects of vehicle controls in this swine model may require further evaluation; this was largely unanticipated based upon prior studies.

Although the observation of a lack of separation for vehicle and Met2Pt treated animals may result from the lack of statistical power, the unexpected observation that 100 mM phosphate buffer vehicle used for formulation, in particular with the IV administration to swine demonstrated 50% survival (3 of 6 animals) and a reversal of some markers of cyanide intoxication may deserve further evaluation. Survival in the IV control group was higher than expected based on the a priori power calculation. Survival in IV phosphate treated animals appears much higher when compared with that in animals previously treated with saline^32,47–50. It is possible that formulation vehicles, like 100 mM phosphate buffer, may not simply be bystanders as would be expected of saline. Validation in other animal models is warranted to determine if these findings are artefactual. If indeed true, we postulate that succinyl thiokinase may convert injected phosphate to form high-energy triphosphates that support endogenous cyanide detoxification mechanisms⁵¹.

Conclusion

Met₂Pt appears efficacious in rescuing swine from acute, lethal cyanide intoxication. The limitation of the current Met₂Pt formulation is poor systemic availability by IM administration, where future studies will seek to develop analogs with better fraction availability. When compared to IM delivery, IV Met₂Pt is far more potent, rescuing all treated swine, improving clinical parameters, and reversing metabolic derangements. Consistent with previous studies, the current observations suggest that the agent has a scavenger mechanism of action, though indirect markers (i.e. ATCA) were used and further investigation is warranted.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

V.S., T.H-H., A.K.N., S.Z., N.F., B.A.L., M.M.B., A.S.A., designed and performed experiments and interpreted data. V.S., C.A.M., R.P., G.T.K., V.S.B., V.J.D. designed and supervised experiments and interpreted data. All authors contributed to writing and editing the manuscript.

Funding

National Institutes of Health (U54NS112107 to C.A.M. and R.P.); Department of Education Graduate Assistance in Areas of National Need (P200A150136 to M.M.B.); The Purdue Center for Cancer Research, National Institutes of Health (P30 CA023168).

Data availability

The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Declarations

Competing interests

The authors declare no competing interests.