H2S Donors and Their Use in Medicinal Chemistry

Hydrogen sulfide (H2S) is a ubiquitous gaseous signaling molecule that has an important role in many physiological and pathological processes in mammalian tissues, with the same importance as two others endogenous gasotransmitters such as NO (nitric oxide) and CO (carbon monoxide). Endogenous H2S is involved in a broad gamut of processes in mammalian tissues including inflammation, vascular tone, hypertension, gastric mucosal integrity, neuromodulation, and defense mechanisms against viral infections as well as SARS-CoV-2 infection. These results suggest that the modulation of H2S levels has a potential therapeutic value. Consequently, synthetic H2S-releasing agents represent not only important research tools, but also potent therapeutic agents. This review has been designed in order to summarize the currently available H2S donors; furthermore, herein we discuss their preparation, the H2S-releasing mechanisms, and their -biological applications.

Experimental research into the potential therapeutic effect of GYY4137 on Ovariectomy-induced osteoporosis

BACKGROUND

Evidence has shown that endogenous H2S plays an important role in the physiological and pathophysiological processes of many organs. The study aimed to explore whether exogenous H2S has a potential therapeutic effect on a rat ovariectomy-induced model of osteoporosis.

METHODS

The OVX osteoporosis model was established in female Sprague-Dawley rats by full bilateral ovariectomy. The rats were randomly divided into four groups, with the two experimental groups receiving an intraperitoneal injection of GYY4137 or sodium alendronate. The level of H2S in the plasma was determined and common laboratory indicators to diagnose osteoporosis, such as alkaline phosphatase (ALP) activity and the levels of osteocalcin (OCN), calcitonin, parathyroid hormone and leptin were measured. The bone mineral density (BMD) of the 4th and 5th lumbar vertebrae was measured using dual-energy X-ray absorptiometry. The maximum stress of femoral fracture was obtained through a three-point bending test of the femur.

RESULTS

The OVX osteoporosis model was successfully established. GYY4137 was injected to increase the level of H2S in the plasma in one group, designated OVX-GYY during the observation period (p < 0.05). At 12 weeks, the BMD value of the fourth lumbar vertebra in the OVX-GYY group had increased (p < 0.05). The BMD femur value in the OVX-vehicle group had decreased (p < 0.05). Bilateral ovariectomy leads to biochemical disorders related to bone metabolism and hormone levels in rat plasma (all p < 0.05). Ovariectomy also reduced blood calcium, blood phosphate and calcitonin, and increased parathyroid hormone and leptin. The opposite results were obtained for the groups with alendronate sodium or GYY4137 treatment (all p < 0.05).

CONCLUSIONS

Through the slow release of H2S, GYY4137 did an excellent job of simulating endogenous neuroendocrine gaseous signaling molecules. Exogenous H2S had a regulatory effect on osteoporosis in ovariectomized rats, showing potential value for the treatment of human postmenopausal osteoporosis.

Effectiveness of a long-lasting piperonyl butoxide-treated insecticidal net and indoor residual spray interventions, separately and together, against malaria transmitted by pyrethroid-resistant mosquitoes: a cluster, randomised controlled, two-by-two factorial design trial

BACKGROUND

Progress in malaria control is under threat by wide-scale insecticide resistance in malaria vectors. Two recent vector control products have been developed: a long-lasting insecticidal net that incorporates a synergist piperonyl butoxide (PBO) and a long-lasting indoor residual spraying formulation of the insecticide pirimiphos-methyl. We evaluated the effectiveness of PBO long-lasting insecticidal nets versus standard long-lasting insecticidal nets as single interventions and in combination with the indoor residual spraying of pirimiphos-methyl.

METHODS

We did a four-group cluster randomised controlled trial using a two-by-two factorial design of 48 clusters derived from 40 villages in Muleba (Kagera, Tanzania). We randomly assigned these clusters using restricted randomisation to four groups: standard long-lasting insecticidal nets, PBO long-lasting insecticidal nets, standard long-lasting insecticidal nets plus indoor residual spraying, or PBO long-lasting insecticidal nets plus indoor residual spraying. Both standard and PBO nets were distributed in 2015. Indoor residual spraying was applied only once in 2015. We masked the inhabitants of each cluster to the type of nets received, as well as field staff who took blood samples. Neither the investigators nor the participants were masked to indoor residual spraying. The primary outcome was the prevalence of malaria infection in children aged 6 months to 14 years assessed by cross-sectional surveys at 4, 9, 16, and 21 months after intervention. The endpoint for assessment of indoor residual spraying was 9 months and PBO long-lasting insecticidal nets was 21 months. This trial is registered with ClinicalTrials.gov, number NCT02288637.

FINDINGS

7184 (68·0%) of 10 560 households were selected for post-intervention survey, and 15 469 (89·0%) of 17 377 eligible children from the four surveys were included in the intention-to-treat analysis. Of the 878 households visited in the two indoor residual spraying groups, 827 (94%) had been sprayed. Reported use of long-lasting insecticidal nets, across all groups, was 15 341 (77·3%) of 19 852 residents after 1 year, decreasing to 12 503 (59·2%) of 21 105 in the second year. Malaria infection prevalence after 9 months was lower in the two groups that received PBO long-lasting insecticidal nets than in the two groups that received standard long-lasting insecticidal nets (531 [29%] of 1852 children vs 767 [42%] of 1809; odds ratio [OR] 0·37, 95% CI 0·21-0·65; p=0·0011). At the same timepoint, malaria prevalence in the two groups that received indoor residual spraying was lower than in groups that did not receive indoor residual spraying (508 [28%] of 1846 children vs 790 [44%] of 1815; OR 0·33, 95% CI 0·19-0·55; p<0·0001) and there was evidence of an interaction between PBO long-lasting insecticidal nets and indoor residual spraying (OR 2·43, 95% CI 1·19-4·97; p=0·0158), indicating redundancy when combined. The PBO long-lasting insecticidal net effect was sustained after 21 months with a lower malaria prevalence than the standard long-lasting insecticidal net (865 [45%] of 1930 children vs 1255 [62%] of 2034; OR 0·40, 0·20-0·81; p=0·0122).

INTERPRETATION

The PBO long-lasting insecticidal net and non-pyrethroid indoor residual spraying interventions showed improved control of malaria transmission compared with standard long-lasting insecticidal nets where pyrethroid resistance is prevalent and either intervention could be deployed to good effect. As a result, WHO has since recommended to increase coverage of PBO long-lasting insecticidal nets. Combining indoor residual spraying with pirimiphos-methyl and PBO long-lasting insecticidal nets provided no additional benefit compared with PBO long-lasting insecticidal nets alone or standard long-lasting insecticidal nets plus indoor residual spraying.

FUNDING

UK Department for International Development, Medical Research Council, and Wellcome Trust.

Hydrogen Sulfide Induces Keap1 S-sulfhydration and Suppresses Diabetes-Accelerated Atherosclerosis via Nrf2 Activation

Hydrogen sulfide (H2S) has been shown to have powerful antioxidative and anti-inflammatory properties that can regulate multiple cardiovascular functions. However, its precise role in diabetes-accelerated atherosclerosis remains unclear. We report here that H2S reduced aortic atherosclerotic plaque formation with reduction in superoxide (O2 (-)) generation and the adhesion molecules in streptozotocin (STZ)-induced LDLr(-/-) mice but not in LDLr(-/-)Nrf2(-/-) mice. In vitro, H2S inhibited foam cell formation, decreased O2 (-) generation, and increased nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation and consequently heme oxygenase 1 (HO-1) expression upregulation in high glucose (HG) plus oxidized LDL (ox-LDL)-treated primary peritoneal macrophages from wild-type but not Nrf2(-/-) mice. H2S also decreased O2 (-) and adhesion molecule levels and increased Nrf2 nuclear translocation and HO-1 expression, which were suppressed by Nrf2 knockdown in HG/ox-LDL-treated endothelial cells. H2S increased S-sulfhydration of Keap1, induced Nrf2 dissociation from Keap1, enhanced Nrf2 nuclear translocation, and inhibited O2 (-) generation, which were abrogated after Keap1 mutated at Cys151, but not Cys273, in endothelial cells. Collectively, H2S attenuates diabetes-accelerated atherosclerosis, which may be related to inhibition of oxidative stress via Keap1 sulfhydrylation at Cys151 to activate Nrf2 signaling. This may provide a novel therapeutic target to prevent atherosclerosis in the context of diabetes.

GYY4137 ameliorates intestinal barrier injury in a mouse model of endotoxemia

Intestinal barrier injury has been reported to play a vital role in the pathogenesis of endotoxemia. This study aimed to investigate the protective effect of GYY4137, a newly synthesized H₂S donor, on the intestinal barrier function in the context of endotoxemia both in vitro and in vivo. Caco-2 (a widely used human colon cancer cell line in the study of intestinal epithelial barrier function) monolayers incubated with lipopolysaccharide (LPS) or TNF-α/IFN-γ and a mouse model of endotoxemia were used in this study. The results suggested that GYY4137 significantly attenuated LPS or TNF-α/IFN-γ induced increased Caco-2 monolayer permeability. The decreased expression of TJ (tight junction) proteins induced by LPS and the altered localization of TJs induced by TNF-α/IFN-γ was significantly inhibited by GYY4137; similar results were obtained in vivo. Besides, GYY4137 promoted the clinical score and histological score of mice with endotoxemia. Increased level of TNF-α/IFN-γ in the plasma and increased apoptosis in colon epithelial cells was also attenuated by GYY4137 in mice with endotoxemia. This study indicates that GYY4137 preserves the intestinal barrier function in the context of endotoxemia via multipathways and throws light on the development of potential therapeutic approaches for endotoxemia.

Incremental impact upon malaria transmission of supplementing pyrethroid-impregnated long-lasting insecticidal nets with indoor residual spraying using pyrethroids or the organophosphate, pirimiphos methyl

BACKGROUND

Long-lasting, insecticidal nets (LLINs) and indoor residual spraying (IRS) are the most widely accepted and applied malaria vector control methods. However, evidence that incremental impact is achieved when they are combined remains limited and inconsistent.

METHODS

Fourteen population clusters of approximately 1000 residents each in Zambia's Luangwa and Nyimba districts, which had high pre-existing usage rates (81.7 %) of pyrethroid-impregnated LLINs were quasi-randomly assigned to receive IRS with either of two pyrethroids, namely deltamethrin [Wetable granules (WG)] and lambdacyhalothrin [capsule suspension (CS)], with an emulsifiable concentrate (EC) or CS formulation of the organophosphate pirimiphos methyl (PM), or with no supplementary vector control measure. Diagnostic positivity of patients tested for malaria by community health workers in these clusters was surveyed longitudinally over pre- and post-treatment periods spanning 29 months, over which the treatments were allocated and re-allocated in advance of three sequential rainy seasons.

RESULTS

Supplementation of LLINs with PM CS offered the greatest initial level of protection against malaria in the first 3 months of application (incremental protective efficacy (IPE) [95 % confidence interval (CI)] = 0.63 [CI 0.57, 0.69], P < 0.001), followed by lambdacyhalothrin (IPE [95 % CI] = 0.31 [0.10, 0.47], P = 0.006) and PM EC (IPE, 0.23 [CI 0.15, 0.31], P < 0.001) and then by deltamethrin (IPE [95 % CI] = 0.19 [-0.01, 0.35], P = 0.064). Neither pyrethroid formulation provided protection beyond 3 months after spraying, but the protection provided by both PM formulations persisted undiminished for longer periods: 6 months for CS and 12 months for EC. The CS formulation of PM provided greater protection than the combined pyrethroid IRS formulations throughout its effective life IPE [95 % CI] = 0.79 [0.75, 0.83] over 6 months. The EC formulation of PM provided incremental protection for the first 3 months (IPE [95 % CI] = 0.23 [0.15, 0.31]) that was approximately equivalent to the two pyrethroid formulations (lambdacyhalothrin, IPE [95 % CI] = 0.31 [0.10, 0.47] and deltamethrin, IPE [95 % CI] = 0.19 [-0.01, 0.35]) but the additional protection provided by the former, apparently lasted an entire year.

CONCLUSION

Where universal coverage targets for LLIN utilization has been achieved, supplementing LLINs with IRS using pyrethroids may reduce malaria transmission below levels achieved by LLIN use alone, even in settings where pyrethroid resistance occurs in the vector population. However, far greater reduction of transmission can be achieved under such conditions by supplementing LLINs with IRS using non-pyrethroid insecticide classes, such as organophosphates, so this is a viable approach to mitigating and managing pyrethroid resistance.

Phosphinodithioate and Phosphoramidodithioate Hydrogen Sulfide Donors

Hydrogen sulfide is rapidly emerging as a key physiological mediator and potential therapeutic tool in numerous areas such as acute and chronic inflammation, neurodegenerative and cardiovascular disease, diabetes, obesity and cancer. However, the vast majority of the published studies have employed crude sulfide salts such as sodium hydrosulfide (NaSH) and sodium sulfide (Na2S) as H2S "donors" to generate H2S. Although these salts are cheap, readily available and easy to use, H2S generated from them occurs as an instantaneous and pH-dependent dissociation, whereas endogenous H2S synthesis from the enzymes cystathionine γ-lyase, cystathionine-β-synthase and 3-mercaptopyruvate sulfurtransferase is a slow and sustained process. Furthermore, sulfide salts are frequently used at concentrations (e.g. 100 μM to 10 mM) far in excess of the levels of H2S reported in vivo (nM to low μM). For the therapeutic potential of H2S is to be properly harnessed, pharmacological agents which generate H2S in a physiological manner and deliver physiologically relevant concentrations are needed. The phosphorodithioate GYY4137 has been proposed as "slow-release" H2S donors and has shown promising efficacy in cellular and animal model diseases such as hypertension, sepsis, atherosclerosis, neonatal lung injury and cancer. However, H2S generation from GYY4137 is inefficient necessitating its use at high concentrations/doses. However, structural modification of the phosphorodithioate core has led to compounds (e.g. AP67 and AP105) with accelerated rates of H2S generation and enhanced biological activity. In this review, the therapeutic potential and limitations of GYY4137 and related phosphorodithioate derivatives are discussed.

The slow-releasing hydrogen sulfide donor, GYY4137, exhibits novel anti-cancer effects in vitro and in vivo

The slow-releasing hydrogen sulfide (H₂S) donor, GYY4137, caused concentration-dependent killing of seven different human cancer cell lines (HeLa, HCT-116, Hep G2, HL-60, MCF-7, MV4-11 and U2OS) but did not affect survival of normal human lung fibroblasts (IMR90, WI-38) as determined by trypan blue exclusion. Sodium hydrosulfide (NaHS) was less potent and not active in all cell lines. A structural analogue of GYY4137 (ZYJ1122) lacking sulfur and thence not able to release H₂S was inactive. Similar results were obtained using a clonogenic assay. Incubation of GYY4137 (400 µM) in culture medium led to the generation of low (<20 µM) concentrations of H₂S sustained over 7 days. In contrast, incubation of NaHS (400 µM) in the same way led to much higher (up to 400 µM) concentrations of H₂S which persisted for only 1 hour. Mechanistic studies revealed that GYY4137 (400 µM) incubated for 5 days with MCF-7 but not IMR90 cells caused the generation of cleaved PARP and cleaved caspase 9, indicative of a pro-apoptotic effect. GYY4137 (but not ZYJ1122) also caused partial G₂/M arrest of these cells. Mice xenograft studies using HL-60 and MV4-11 cells showed that GYY4137 (100–300 mg/kg/day for 14 days) significantly reduced tumor growth. We conclude that GYY4137 exhibits anti-cancer activity by releasing H₂S over a period of days. We also propose that a combination of apoptosis and cell cycle arrest contributes to this effect and that H₂S donors should be investigated further as potential anti-cancer agents.

Efficacy of imidacloprid, imidacloprid/permethrin and phoxim for flea control in the Mustelidae (ferrets, mink)

Farmed mink (Mustela vison), a close relative of the domestic ferret (Mustela putorius furo), naturally infested with the squirrel flea (Ceratophyllus sciurorum) were included in a study to investigate three compounds for flea control. The test products were imidacloprid in a 10% (w/v) solution, an imidacloprid 10% (w/v)/permethrin 50% (w/v) solution, and phoxim; all three are well-known compounds for the control of different ectoparasites in a wide range of animals. Two groups of mink received 0.1 ml per animal of the imidacloprid or the imidacloprid/permethrin combination at days 0 and 28, respectively. Two groups of mink were sprayed with 25 ml of a 0.1% phoxim solution at day 0 and either 1x25 ml or 2x25 ml, respectively, of a 0.05% phoxim solution at day 28. One group of mink served as an untreated control. At assessment on day 56 the efficacy was 91.9% in the imidacloprid group, 89.3% in the imidacloprid/permethrin group, 92.2% in the phoxim 1x25-ml group and 99.3% in the phoxim 2x25 ml group, respectively. In the untreated control group an average of 757 fleas per mink nesting material was recorded.

Natural infestation of the chewing lice (Werneckiella equi) on horses and treatment with imidacloprid and phoxim

Infestation with the chewing louse (Werneckiella (Damalinia) equi) can be found on horses world-wide. Louse infestations, including clinical signs of louse-derived dermatitis, are known from Icelandic horses. A clinical field investigation was conducted in Iceland using horses with natural louse infestations to evaluate the efficacy of imidacloprid in a 10% solution in comparison with phoxim in a 0.05% solution. A total of 27 horses received a single imidacloprid treatment using 16 ml of the 10% solution along the mane and on the dorso-lateral trunk. A further 43 horses were treated twice, 14 days apart, with phoxim, using 2 x 50 ml solution applied along the mane and the dorso-lateral trunk. At the final evaluation on day 28, complete control of the lice was obtained for the imidacloprid treated horses and only a single moribund louse was found on two horses treated with phoxim.

Therapeutic potential of antisense nucleic acid molecules

Elucidation of many disease-related signal transduction and gene expression pathways has provided unparalleled opportunities for the development of targeted therapeutics. The types of molecules in development are increasingly varied and include small-molecule enzyme inhibitors, humanized antibodies to cell surface receptors, and antisense nucleic acids for silencing the expression of specific genes. This Perspective reviews the basis for various antisense strategies for modulating gene expression, including RNA interference, and discusses the prospects for their clinical use.

Comparative efficacy of several insecticides for control of cattle lice (Mallophaga: Trichodectidae and Anoplura: Haematopinidae)

Several insecticides were applied to cattle at various rates, mixtures, application methods and numbers of treatments and evaluated for control of cattle lice. The insecticides included permethrin at various rates as a pour-on with and without the synergist piperonyl butoxide (PBO), and also at various rates as a spray with and without PBO. Pirimiphos-methyl was evaluated as a pour-on at various rates and with one or two applications. Lambda cyhalothrin in microencapsulated formulation was compared to a non-microencapsulated formulation. Rabon(R) was applied as a pour-on at two rates and at one or two treatments for each rate. Dimilin(R) was applied as a pour-on at two rates and mixed with permethrin and applied at two rates. Five endectocides, Eprinex(R), Ivomec(R), Dectomax(R), Cydectin(R) and Phoenectin(R) were all applied at the same rate. The cattle utilized in this research were all infested with a mixture of lice species. The species included: Bovicola (Damalinia) bovis (L.), Haematopinus eurysternus (Nitzsch), Linognthus vituli (L.) and Solenoptes capillatus (Enderlein). Most of the cattle were infested with at least two species and some had three or all four species present. All of the treatments except permethrin 1.0%+5% PBO, at a rate of 3ml/45.4kgwt. provided acceptable lice control with one application. Data indicated that applying the insecticides in early January should provide enough control to render the need for a second treatment unnecessary.

Antisense oligonucleotide-induced inhibition of adrenocorticotropic hormone release from cultured human corticotrophs

OBJECT

Available therapies for Cushing's disease are often inadequate or involve the risk of significant morbidity. Accordingly, the need arises for the development of novel treatments, especially for cases caused by corticotroph hyperplasia, a condition difficult to treat using standard therapies. In this study, the authors investigated the use of phosphorothioate antisense oligonucleotides as a potential treatment for Cushing's disease.

METHODS

Corticotrophs, obtained from a patient with Cushing's disease in whom pathological findings showed multifocal areas of corticotroph adenoma and hyperplasia, were grown in tissue culture. By assessing cell viability and using immunoradiometric assay techniques, it was determined that these cells grew autonomously and secreted adrenocorticotropic hormone (ACTH) in vitro. A fully phosphorothioated antisense oligonucleotide was constructed to be complementary to the first 25 bp of the region coding for ACTH in exon 3 of the proopiomelanocortin precursor. After incubation of the corticotrophs with liposome-coated phosphorothioate antisense oligonucleotides, a greater than 90% decrease in ACTH release was noted on Days 3 and 6, compared with nonsense-treated controls (p < 0.05).

CONCLUSIONS

Antisense oligonucleotides may prove to be a useful adjunct in treating Cushing's disease by targeting one of its fundamental problems, ACTH hypersecretion.

The in vitro response of sheep scab mites to pyrethroid insecticides

The response of sheep scab mites to pyrethroid insecticides and organophosphate compounds was studied in vitro with the objective of finding a simple test for detecting insecticide resistance in scab mites. Psoroptes cuniculi from rabbits or P. ovis from sheep were enclosed in small 'tea bags' made from heat sealable paper prior to dipping in insecticide. Mites failed to die 24 h after a 1 min dip in working concentrations of insecticidal sheep dips. With flumethrin a variety of different conditions were tested but most failed to improve the efficacy of flumethrin. It is suggested with freshly collected mites pyrethroids may be taken up by ingestion.

The efficacy of simplified eradication strategies against sarcoptic mange mite infections in swine herds monitored by an ELISA

Eradication programmes directed against Sarcoptes scabiei var. suis, performed without any disinfection of the environment, were compared to an eradication programme including a simultaneous environmental disinfection. The performance of such programmes would be facilitated considerably if environmental disinfection could be avoided. The trial was conducted in four conventional piglet-producing herds designated A-D. All herds suffered from a subclinical but persistent infection with the sarcoptic mite. Herd A was treated with two injections of ivermectin and simultaneously disinfection of the environment was done. In the other herds, the animals were treated twice (B and C) or three times (D) with acaricides (ivermectin or phoxim) at intervals of 7-12 days without any simultaneous disinfection of the buildings or environment. The results were monitored by attempts to demonstrate the mite by skin scrapings, and by monitoring the levels of serum antibodies to Sarcoptes scabiei by an ELISA. Samples were taken from all adults and from 20% of the piglets aged 10-12 weeks, before initiating the control programmes, every third month during the first year and a final sampling 18 months after the treatments. After treatment, the levels of antibodies continuously decreased. Presumably dead S. scabiei were demonstrated in one sow from two of the herds 3 months after initiating acaricidal treatments. S. scabiei was not demonstrated later, nor from skin scrapings of the piglets. The results obtained demonstrate that it is possible to eradicate sarcoptic mange mites in swine herds with the use of simplified eradication programmes. The success of such programmes may efficiently be monitored by measuring the levels of serum antibodies to S. scabiei.

[Psoroptic scab control in sheep herds--experiences in use of medications]

Due to an uncontrolled trade in sheep, the importance of sheep scab has increased recently. Alone in Thuringia six outbreaks occurred in 1993. Now psoroptic mange is endemic in Germany. Mutual infections between sheep and cattle seem to be extremely rare in the field. Outbreaks of sheep scab entails heavy economic losses. Therefore, control has to be successful and to aim at eradication. The survivability of the psoroptic mites aside from the host until 48 days has to be considered. Eradication can be achieved, as proved by own field trials for a period of 10 months only either by two repeated dipping using Phoxim or HCH drugs or by subcutaneous Ivermectin injections (0.2 mg/kg bodyweight) seven days apart. The success of treatment has to be checked carefully.

Organophosphate polyneuropathy and neuropathy target esterase: studies with methamidophos and its resolved optical isomers

Methamidophos (O,S-dimethyl phosphorothioamidate) causes polyneuropathy in man and hens. However, experiments in the hen show that lower doses of methamidophos either protect from or promote the neuropathy caused by certain organophosphates. The initiation of neuropathy as well as protection from neuropathy are thought to be related to neuropathy target esterase (NTE), whereas promotion is likely to be due to interactions with another unknown target. Methamidophos is a racemate and we report studies with its resolved optical isomers, aimed at elucidating which isomer is responsible for the described effects. The time-course of acetylcholinesterase (AChE) and NTE activity in nervous tissues of hens after inhibition by single doses of either isomer showed that after D-(+) methamidophos (25 mg/kg PO) peak inhibition of both enzymes was achieved within 24 h (80-90%). However, after L-(-) methamidophos (15 mg/kg PO), peak inhibition (80-90%) was obtained within 24 h for AChE, whereas similar NTE inhibition (120 mg/kg PO) was observed only 4 days after dosing. The minimal neuropathic doses of D-(+) and L-(-) methamidophos were 60 and 120 mg/kg PO, respectively, and correlated with > 80% NTE inhibition in nervous tissues. OPIDP initiation by either isomer was slightly promoted by phenylmethanesulfonyl fluoride (120 mg/kg SC). D-(+) Methamidophos (25 mg/kg PO) partially protected from dibutyl dichlorovinyl-phosphate (DBDCVP) neuropathy (up to 0.8 mg/kg SC). This effect correlated with about 70% NTE inhibition. L-(-) Methamidophos (15 or 60 mg/kg PO) did not protect from DBDCVP neuropathy (0.2-0.8 mg/kg SC).

Radioprotection by WR-151327 against the late normal tissue damage in mouse hind legs from gamma ray radiation

PURPOSE

To evaluate the protective effect of WR-151327 on late radiation-induced damage to normal tissues in mice.

METHODS AND MATERIALS

The right hind legs of mice with or without WR-151327 administration (400 mg/kg) were irradiated with 137Cs gamma rays. Leg contracture and skin shrinkage assays were performed at 380 days after irradiation. The mice were killed on day 400 postirradiation and histological sections of the legs were made. The thickness of the dermis, epidermis, and skin (dermis plus epidermis) was measured. The muscular area of the legs and the posterior knee angle between the femur and tibia were also measured. The left hind legs were similarly assessed as nonirradiated controls. Group means and standard deviations were calculated and dose-response curves were drawn for every endpoint. Then, the dose modifying factor (DMF) for each endpoint and the correlations among endpoints were determined.

RESULTS

Late damage assayed by leg contracture and skin shrinkage progressed with increasing radiation dose. However, it was reduced by drug treatment. The significant effect was indicated for skin shrinkage by a DMF of 1.8 at 35%. The DMF for leg contracture was 1.3 at 6 mm. In the irradiated legs, epidermal hyperplasia and dermal fibrosis in the skin, muscular atrophy, and extension disturbance of the knee joint were observed. These changes progressed with increasing radiation dose. Skin damage assayed by the present endpoints was also reduced by drug treatment by DMFs of 1.4 to 1.7. However, DMFs for damage to the muscle and knee were not determined because no isoeffect was observed. There were good correlations between leg contracture or skin shrinkage and the other endpoints in both untreated and drug-treated mice.

CONCLUSIONS

WR-151327 has the potential to protect against radiation-induced late normal tissue damage.

Survival of irradiated mice treated with WR-151327, synthetic trehalose dicorynomycolate, or ofloxacin

Spaceflight personnel need treatment options that would enhance survival from radiation and would not disrupt task performance. Doses of prophylactic or therapeutic agents known to induce significant short-term (30-day) survival with minimal behavioral (locomotor) changes were used for 180-day survival studies. In protection studies, groups of mice were treated with the phosphorothioate WR-151327 (200 mg/kg, 25% of the LD(10)) or the immunomodulator, synthetic trehalose dicorynomycolate (S-TDCM; 8 mg/kg), before lethal irradiation with reactor-generated fission neutrons and gamma-rays (n/gamma=1) or 60Co gamma-rays. In therapy studies, groups of mice received either S-TDCM, the antimicrobial ofloxacin, or S-TDCM plus ofloxacin after irradiation. For WR-151327 treated-mice, survival at 180 days for n/gamma=1 and gamma-irradiated mice was 90% and 92%, respectively; for S-TDCM (protection), 57% and 78%, respectively; for S-TDCM (therapy), 20% and 25%, respectively; for ofloxacin, 38% and 5%, respectively; for S-TDCM combined with ofloxacin, 30% and 30%, respectively; and for saline, 8% and 5%, respectively. Ofloxacin or combined ofloxacin and S-TDCM increased survival from the gram-negative bacterial sepsis that predominated in n/gamma=1 irradiated mice. The efficacies of the treatments depended on radiation quality, treatment agent and its mode of use, and microflora of the host.

Pathological evaluation of WR-151327 administered orally in irradiated and non-irradiated male mice

Studies were made on the radioprotective and toxic effects of orally administered WR-151327 in male CD2F1 mice. The lowest dose of orally administered drug permitting probit analysis of data was 450 mg per kg. The calculated radioprotective dose reduction factors (DRF) at 450 mg per kg and 900 mg per kg of body weight (BW) WR-151327 were 1.2 and 1.3, respectfully. Pathological examination at 8, 30 or 90 days post administration of 100, 450, or 900 mg per kg of the drug demonstrated that the major target organ for orally dosed mice was the testes. There was a decrease in the number of cells in the germinal cell layers of testes from animals administered 450 mg per kg WR-151327 or 10 Gy whole body irradiation after eight days. Moreover, there was a dramatic reduction in the germinal cells in mice seminiferous tubules treated with a combination of 450 mg per kg WR-151327 plus 10 Gy radiation after eight days.

Protection by WR-2721 and WR-151327 against late effects of gamma rays and neutrons

Two thiophosphoroate compounds WR-2721 and WR-151327 were assessed for their ability to modify the deleterious effects (life shortening and carcinogenesis) of fission-spectrum neutrons (kerma-weighted mean energy of 0.85 MeV) or gamma rays on B6CF1 hybrid mice. Male and female mice, 200 of each sex per experimental group, were irradiated individually at 110 days of age. Radioprotectors (400 mg/kg of WR-2721 or 580 mg/kg of WR-151327) were administered intraperitoneally 30 min prior to irradiation. Neutron doses were 10 cGy or 40 cGy and gamma ray doses were 206 cGy or 417 cGy. Animals were housed five to a cage; cage locations in the holding rooms were randomized by computer. Animals were checked daily and all deceased animals were necropsied. WR-2721 afforded protection against both neutron- and gamma-ray-induced carcinogenesis and subsequent life shortening. Cumulative survival curves for unirradiated mice of either sex were unaffectecd by protectors. WR-2721 protected irradiated groups against life shortening by approximately 10 cGy of neutrons or 100 cGy of gamma rays. WR-151327 was as effective as WR-2721 against neutron irradiation.

Protection by WR-151327 against late-effect damage from fission-spectrum neutrons

The mutagenic and carcinogenic properties of fission-spectrum neutrons (KERMA-weighted mean energy of 0.85 MeV) from Argonne National Laboratory's JANUS reactor are substantially greater than those of low-LET radiation sources such as X-ray and 60Co photons. However, in contrast to the vast amount of work focused on chemical protection against damage induced by low-LET radiation, studies on the prevention of carcinogenic damage induced by fission neutrons have been limited. We have investigated the protective properties of the thiophosphorate compound S-3-(3-methylaminopropylamino)propylphosphorothioic acid (WR-151327) against carcinogenesis and life shortening in the B6CF1 hybrid mouse strain. Male and female mice, 200 of each sex per experimental group, were irradiated individually at 110 days of age. WR-151327 was administered intraperitoneally at a dose of 580 mg/kg 30 min prior to irradiation with a dose of 10 cGy. Animals were housed five to a cage; cage locations in holding rooms were controlled by computer and randomized. Mice were checked daily and all deceased animals were necropsied. A neutron dose of 10 cGy significantly altered the patterns of death of male and female animals compared to corresponding unirradiated control groups (logrank P values of 0.01 and 0.07, respectively). This was evidenced by a shortening of the life span due to tumor induction in the irradiated groups. WR-151327, when administered 30 min prior to irradiation, effectively protected both male and female animals from these effects. The life curves of irradiated male and female animals and those of corresponding unirradiated control groups were not significantly different (logrank P values of 0.63 and 0.25, respectively).

Antitumor organometallics. I. Activity of some diphenyltin(IV) and diphenylantimony(III) derivatives on in vitro and in vivo Ehrlich ascites tumor

Diphenyltin(IV) and diphenylantimony(III) derivatives of dithiophosphorus ligands, i.e. Ph2Sn(S2PPh2)2 (1), Ph2Sn[S2P(OPr)2]2 (2), Ph2SbS2PPh2 (3) and Ph2SbS2P(OPri)2 (4), have been tested in vitro and in vivo against Ehrlich ascites tumor. All four compounds were almost equally effective in vitro, exhibiting inhibitory effects on cell proliferation, viability and protein synthesis, and exacerbated respiration and Ca-ATPase activity. In mice bearing Ehrlich ascites tumor cells, all four compounds inhibited the tumor growth, the organometallic phosphorodithioates being more active than phosphinodithioate analogues, and the organoantimony derivatives more active than organotins. Compound 4 (5 mg/kg/day, i.p., on days 1,3 and 5) produced an increase in life span of 83% and a cure rate of 30% in mice bearing this tumor.

The first organoantimony(III) compounds possessing antitumor properties: diphenylantimony(III) derivatives of dithiophosphorus ligands

Two organoantimony (III) derivatives, i.e., diphenylantimony diphenyl-dithiophosphinate, Ph2SbS2PPh2, and diphenylantimony diizopropyldithiophosphate, Ph2SbS2P(OPri)2, were shown to exhibit antitumor properties. Both compounds produced strong tumor inhibition effects in mice bearing Ehrlich ascites tumor. Moreover, the dithiophosphate (15 mg/kg, i.p., in days 1, 3 and 5) produced a cure rate of 30%.

Protection against chemical-induced lung injury by inhibition of pulmonary cytochrome P-450

Protection afforded by trialkyl phosphorothionates against the lung injury caused by trialkyl phosphorothiolates probably results from the inhibition by the P = S moiety of the thionates, of one or more pulmonary cytochrome P-450 isozymes. The aromatic hydrocarbons p-xylene and pseudocumene also protect against this injury and inhibit some P-450 isozymes, but by a different mechanism. OOS-Trimethylphosphorothionate and p-xylene were compared as protective agents against the effect of OOS-trimethylphosphorothiolate and two other lung toxins ipomeanol and 1-nitronaphthalene that are known to be activated by cytochrome P-450. The effects of these protective compounds, in vivo, on pulmonary cytochrome P-450 activity were also determined. Both compounds inhibited pentoxyresorufin O-deethylase activity, but not ethoxyresorufin O-deethylase. The phosphorothionate was most effective against lung injury caused by the phosphorothiolates and 1-nitronaphthalene, whereas p-xylene was much more effective against ipomeanol. beta-Naphthoflavone, which induces pulmonary ethoxyresorufin O-deethylase activity, did not protect against phosphorothiolate or 1-nitronaphthalene injury, and it was only marginally effective in decreasing the toxicity of ipomeanol.

WR-2721 reduces bone loss after hindlimb tenotomy in rats

WR-2721 is a thiophosphate analog of cysteamine that produces hypocalcemia in vivo. Previous studies suggest that WR-2721 produces hypocalcemia by independent inhibitory effects on parathyroid hormone (PTH) secretion, osteoclastic bone resorption, and tubular reabsorption of calcium. We sought to determine if WR-2721 would decrease bone loss in an animal model of disuse osteoporosis produced by unilateral knee tenotomy in the rat. Tenotomy significantly increased osteoclast number in tibias on the side of the procedure compared with tibias on the opposite side which had not undergone the procedure at 3 and 14 days. Femoral weight of tenotomized limbs were also reduced significantly compared with the contralateral limb at 3 and 14 days. WR-2721 treatment (240 mg/kg daily) prevented 26% of the loss of femoral dry weight and 29% of the loss of femoral ashed weight produced 14 days after tenotomy. In addition, WR-2721 treated (240 mg/kg daily) animals had fewer osteoclasts in tenotomized tibias than control animals at 3 days (6.6 +/- 0.7/mm versus 10.3 +/- 0.9/mm, p less than 0.02) and at 14 days (5.8 +/- 0.3/mm versus 8.7 +/- 0.4/mm, p less than 0.02). These data suggest that WR-2721 decreases bone loss in this model by decreasing osteoclastic bone resorption.

Protection by WR-3689 against gamma-ray-induced intestinal damage: comparative effect on clonogenic cell survival, mouse survival, and DNA damage

The aminophosphorothioate WR-3689 was characterized for its ability to protect mouse jejunal cells in vivo from single doses of X or gamma radiation. First, the effect of the drug on the survival of jejunal stem cells was examined using a clonogenic end point, the crypt microcolony assay. When WR-3689 was administered 30 min prior to whole-body irradiation, the number of surviving crypt cells was markedly increased at all doses of the drug, although protection began to level out at doses larger than 600 mg/kg. Protection was maximal when the drug was given 30 min before whole-body irradiation and declined rapidly with both shorter and longer intervals. Protection factors (PFs) were obtained by measuring survival curves for clonogenic crypt cells as a function of radiation dose; WR-3689 given 30 min before whole-body irradiation protected jejunum in the microcolony assay with a PF of 1.26 +/- 0.02, 1.50 +/- 0.10, and 1.65 +/- 0.10 at doses of 200, 400, and 800 mg/kg, respectively. Next, the effect of WR-3689 on the survival of jejunal stem cells was determined by assaying the survival of mice given X-ray doses to the whole abdomen in the range leading to death from the gastrointestinal syndrome. The PFs based on the LD50 values for 11-day survival were 1.31 +/- 0.05 (200 mg/kg) and 1.48 +/- 0.05 (400 mg/kg). Crypt-cell survival and animal survival were thus modified to a similar extent by this agent. Finally, the effect of WR-3689 on the induction of DNA single-strand breaks (SSBs) in jejunal cells was measured using an adaptation of the alkaline elution methodology. In mice treated with WR-3689 (400 or 800 mg/kg) 30 min prior to whole-body irradiation with 10 Gy there was no significant reduction in the number of DNA SSBs induced either in samples of the jejunum or in the cycling crypt cells, providing further evidence that there is no simple relationship between the modification of DNA SSBs and the survival of jejunal stem cells.

N-acyl dehydroalanines protect from radiation toxicity and inhibit radiation carcinogenesis in mice

N-Acyl dehydroalanines have shown free radical scavenging activity. They react with and scavenge mainly oxygen-derived free radicals such as the superoxide anion (O2-.) and the hydroxyl radical (HO.). Ortho-methoxyphenylacetyl dehydroalanine (AD-20) protects total-body irradiated mice against the toxicity induced by X-rays when delivered as a single dose of 700 rads in a short period of time. This degree of protection was of the same order of magnitude as that obtained with the aminothiol S-2-(3-aminopropylamino)-ethylphosphorothioic acid (WR-2721). The radioprotection of AD-20 is extended to all other doses of X-rays tested (from 600 to 800 rads). Furthermore, AD-20 inhibits the development of thymic lymphomas in C57Bl/Ka mice undergoing a leukaemogenic course of irradiation (4 x 175 rads applied at weekly intervals). We postulate that AD-20 may act as a radioprotector and anticarcinogenic agent, most probably by inactivating the oxygen-derived free radicals formed during water radiolysis.

Purging of small cell lung cancer cells from human bone marrow using ethiofos (WR-2721) and light-activated merocyanine 540 phototreatment

One limitation of autologous bone marrow transplantation for patients with cancer has been the presence of tumor cells in the bone marrow. Methods to eliminate tumor cells while preserving hematopoietic stem cells have been sought. The present study was performed to analyze the in vitro effectiveness of light-activated merocyanine 540 phototreatment (LAMP) and an aminothiol (ethiofos) as a marrow-purging regimen for small cell lung cancer (SCLC). Two human SCLC cell lines (ATCC HTB-119 and HTB-120) were treated with LAMP and exposed to light for varying periods of time up to 120 min. LAMP reduced SCLC cell proliferation and colony formation in a light exposure-dependent manner; colony formation was not totally inhibited until light exposure of 120 min was used. At this light exposure interval, multipotential hematopoietic progenitors, colony-forming units-granulocyte, erythroid, macrophage, megakaryocyte (CFU-GEMM), were substantially reduced. In an attempt to diminish hematopoietic toxicity, SCLC cells were incubated with ethiofos (formerly WR-2721) for 1 hour before LAMP. SCLC colony formation was eliminated at light exposure intervals (90 min or less) which had no inhibitory effect on CFU-GEMM. Ethiofos did not protect CFU-GEMM from LAMP inhibition at 120 min. Ethiofos alone had no effect on the SCLC or hematopoietic cells. When normal bone marrow was contaminated with 1 or 5% SCLC cells, ethiofos plus 60 min of LAMP eliminated SCLC cells but had no effect on CFU-GEMM. The results suggest that ethiofos sensitized SCLC cells to LAMP; thus ethiofos-enhanced LAMP may be an effective method for removing metastatic SCLC cells from bone marrow used for autologous marrow transplantation after high dose chemotherapy.

Clinical trials of WR-2721 and cis-platinum

WR-2721 is an aminothiol compound; in the animal model it protects against the nephrotoxicity, neurotoxicity, and hematologic toxicity of cis-platinum. We initiated Phase I trials of WR-2721 and cis-platinum to determine toxicity when WR-2721 was given prior to escalating doses of cis-platinum. With mannitol diuresis and WR-2721, transient nephrotoxicity occurred in 9 of 30 (27%) patients treated with cis-platinum 150 mg/m2 and 7% of patients given with cis-platinum 120 mg/m2. Bone marrow suppression was mild and infrequent. Mild to moderate peripheral neuropathies occurred in 26% of patients courses following a mean cumulative cis-platinum dose of 725 mg/m2. Objective partial responses were observed in 53 of 118 (45%) patients with measurable disease. Antitumor responses were observed in 25 of 53 patients with metastatic melanoma, 12 of 22 patients with locally recurrent or metastatic head and neck cancer, and 7 of 13 patients with metastatic breast cancer refractory to conventional chemotherapy. Controlled studies of WR-2721 and cis-platinum will be performed in the Eastern Cooperative Oncology Group in these disease sites to better define the activity of this regimen and its toxicity.

Ultrastructural effects of phosphorothionates and other inhibitors of lung monooxygenases: protection against trialkylphosphorothiolate-induced lung injury

An oral dose (25 mg/kg) of O,O,S-triethylphosphorothiolate (OOSEtO) to rats results in selective injury of type I pneumocytes, degranulation of Clara cells, and pronounced increase in lung weight. A dose (12.5 mg/kg) of the related compound O,O,S-trimethylphosphorothionate (OOSMeS) causes neither injury nor degranulation but, when administered 2 h before OOSEtO (25 mg/kg), protects against all the signs of lung injury that would otherwise result from this dose of the compound. The administration of OOSMeS also results in the formation of large, electron-lucent granules within the apical cytoplasm of the Clara cells. The granules are not birefringent, and histochemical procedures indicate that they do not contain carbohydrate but may consist of lipid accumulated around a proteinaceous core. Similar granules are also observed after administration of p-xylene, pseudocumene, and the pesticide bromophos. These compounds, like OOSMeS, inhibit 7-ethoxycoumarin O-deethylase activity in the lung and are capable of protecting against trialkylphosphorothiolate toxicity. This inhibition of 7-ethoxycoumarin O-deethylase activity suggests loss of pulmonary cytochrome P-450. This loss may account for both the protective action of these compounds and the formation of abnormal granules within Clara cells.

Postirradiation glucan administration enhances the radioprotective effects of WR-2721

Based on murine survival studies, endogenous hemopoietic spleen colony formation (E-CFU), and recovery of bone marrow and splenic granulocyte-macrophage colony-forming cells (GM-CFC), it was demonstrated that the postirradiation administration of glucan, an immunomodulator and hemopoietic stimulant, enhances the radioprotective effects of WR-2721. LD50/30 dose reduction factors for mice treated with WR-2721 (200 mg/kg approximately 30 min before irradiation), glucan (250 mg/kg approximately 1 h after irradiation), or both agents were 1.37, 1.08, and 1.52, respectively. Enhanced survival in mice treated with both agents appeared to be due in part to glucan's ability to accelerate hemopoietic regeneration from stem cells initially protected from radiation-induced lethality by WR-2721. Following a 10-Gy radiation exposure, E-CFU numbers in mice treated with saline, WR-2721, glucan, or both WR-2721 and glucan were 0.05 +/- 0.03, 6.70 +/- 1.05, 0.95 +/- 0.24, and 33.90 +/- 2.96, respectively. Similarly, bone marrow and splenic GM-CFC numbers were greater in mice treated with both WR-2721 and glucan than in mice treated with either agent alone. These results demonstrated at least additive radioprotective effects when mice were given WR-2721 prior to irradiation and glucan following irradiation. These effects appeared to depend on the sequential cell protection mediated by WR-2721 and hemopoietic repopulation mediated by glucan.

Protection of microvasculature in rat brain against late radiation injury by gammaphos

The ability of the radioprotector gammaphos to modify the development of late vascular changes in rat brain after local irradiation with 25 Gy was investigated by means of angiographic method. A protective effect was seen against late vascular abnormalities. It is suggested that a causative relationship exists between vascular abnormalities, brain necrosis, and radiation mortality after irradiation with moderate doses.

Protection of mice against mixed fission neutron-gamma (n: gamma = 1:1) irradiation by WR-2721, 16,16-dimethyl PGE2, and the combination of both agents

The survival of mice after whole-body exposure to a modified fission neutron-gamma field (n: gamma = 1:1) was used to examine radiation protection by WR-2721, 16,16-dimethyl PGE2(DiPGE2), and the combination of both agents. Administration of WR-2721 (453 mg/kg) increased the LD50/30 from 5.24 to 7.17 Gy (DMF = 1.37), whereas pretreatment with DiPGE2 (1.6 mg/kg) increased the LD50/30 to 5.77 Gy (dose modification factor (DMF) = 1.10). The combination of 453 mg/kg WR-2721 and 0.4 mg/kg DiPGE2 resulted in an LD50/30 of 7.33 Gy, yielding a DMF of 1.39. However, no significant difference in protection was obtained with the combination of the two agents compared to that seen with WR-2721 alone.

Protection of mouse bone marrow by WR-2721 after fractionated irradiation

The ability of WR-2721 to protect mouse bone marrow after single or fractionated doses of radiation was assessed using both a clonogenic assay (survival of colony-forming units spleen (CFU) and a functional assay (lethality at 30 days) of stem cell survival. Cell survival curves and dose-response curves for radiation alone and drug with radiation were constructed over the dose range of .5 to 8 Gy and 1.5 to 15 Gy, respectively. The fractionated regimen consisted of four fractions ranging from 0.5 to 1.75 Gy given at 6-hr intervals for a total treatment time of 19.5 hr. WR-2721 was given 30 min before each fraction at a dose of 200 mg/kg. The protection factor was smaller after fractionated doses than after single doses for both assays, 1.3 (95% c.l., 1.0-1.6) vs. 2.3 (95% c.l., 2.0-2.6) for CFU survival and 1.34 vs. 1.8 for lethality at 30 days. No drug cytotoxicity could be demonstrated in the fractionated schedule. These data suggest that protection by WR-2721 is dependent on size of dose and will be less after clinically relevant, small dose fractions. However, some protection does remain even in the low dose range, where proportionally more damage is due to single-hit irreparable events.

[Functional capacity of the kidneys in whole-body irradiated rats protected with gammaphos and merkamine]

In experiments with Wistar rats it was shown that gammaphos promotes the recovery of the kidneys' filtration function at early times after 7.4 Gy gamma-irradiation and inhibits it after 210 days. Merkamine induces haemodynamic and functional disorders in the exposed rat kidneys within the first 30 days after irradiation.

A comparison of the effectiveness of cysteamine and phosphocysteamine in elevating plasma cysteamine concentration and decreasing leukocyte free cystine in nephropathic cystinosis

Cysteamine (beta-mercaptoethylamine, MEA) is currently used to treat children with nephropathic cystinosis. In this study MEA was compared to phosphocysteamine (MEAP), a phosphorothioester that tastes and smells better than MEA, with respect to its ability to elevate plasma MEA and deplete leukocytes of cystine. Studies were performed in six children with nephropathic cystinosis ranging in age from 2 to 10 yr. After equimolar oral doses of either MEA or MEAP plasma cysteamine was determined at various times for 6 h. MEA was determined by sodium borohydride reduction followed by high-performance liquid chromatography separation and electrochemical detection. Leukocyte cystine was measured before and 1 and 6 h after drug administration. Peak plasma MEA was obtained 30 min to 1 h after a dose and was not significantly different when MEA (48.6 +/- 10.7, mean +/- SD) or MEAP (54.1 +/- 20.2) was given. Significant plasma MEA concentrations were seen as early as 15 min after an oral dose, indicating rapid absorption. Analysis of vomitus indicated that hydrolysis of the phosphate group of MEAP occurs in the stomach. The percent decrease in leukocyte cystine content obtained with MEA administration (61.9%) was not significantly different from the decrease observed when MEAP was administered (65.3%). MEA and MEAP appear to be equally effective in their cystine-depleting properties.

Propetamphos: a comparison of three formulations in preventing blowfly strike in sheep

A trial was conducted in an area where organophosphate resistance to the green blowfly of sheep, Lucilia curpina WIED had been reported. Three formulations containing Propetamphos, namely an oil based pour-on, a grease based smear-on, and an emulsifiable concentrate were applied to 300 sheep in an attempt to compare the protection that this insecticide afforded, in preventing progressive blowfly strike. One hundred sheep were furthermore treated with an insecticide growth regulator, Cyromazine as a treated control group and a further 300 sheep were exposed as an untreated control group in order to monitor the level of blowfly strike in the area. It was found that the grease-based formulation protected the animals for 2 weeks against blowfly strike, both the pour-on and the emulsifiable concentrate formulation for 3 weeks, while the insect growth regulator afforded 4 weeks protection. It was concluded that if organophosphate resistant blowfly were present, the length of protection might be dosage related and that blowfly strike in sheep was almost equally controlled by Cyromazine and Propetamphos.

Opposite effects of WR-2721 and WR-1065 on radiation-induced hypothermia: possible correlation with oxygen uptake

Ionizing radiation induces hypothermia in guinea pigs. While systemic injection of the radioprotectant S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721) did not block hyperthermia induced by exposure to 10 Gy of gamma radiation, central administration did attenuate it. The dephosphorylated metabolite of WR-2721, N-(2-mercaptoethyl)-1,3-diaminopropane (WR-1065), accentuated radiation-induced hypothermia by both routes of administration. In brain homogenates, oxygen uptake was inhibited by WR-2721 but elevated by WR-1065. These results suggest that the antagonism of radiation-induced hypothermia found only after central administration of WR-2721 is due to its direct actions and not to its dephosphorylated metabolite and that this effect may be correlated with the inhibition by WR-2721 of oxygen uptake.

Radioprotection of mouse jejunum by WR-2721 and WR-1065: effects on DNA strand-break induction and rejoining

WR-2721 and its free-thiol metabolite WR-1065 have been characterized for their ability to protect mouse jejunal cells in vivo from the damaging effects of gamma rays with respect to both cytotoxicity and DNA single-strand break (SSB) induction. SSBs were measured both in the whole jejunal epithelium and in the proliferating crypt cells using an adaptation of the alkaline elution methodology. Protection factors (PFs) were also obtained using the microcolony assay for jejunal crypts. In mice treated with WR-1065 (400 mg/kg) 15 or 30 min prior to irradiation, there was a slight but significant reduction in the initial number of SSBs both in the whole jejunum (PF of between 1.17 and 1.22) and in the proliferating crypt cells (PF of between 1.13 and 1.28). At a dose of 200 mg/kg, the PF for SSBs in the proliferating crypt cells was 1.12 +/- 0.07 while that for crypt-cell survival was approximately 2.0. In mice treated with WR-2721 (400 mg/kg) 15 min prior to irradiation, there was little effect on the initial number of SSBs induced both in the whole jejunum (PF of 1.07 +/- 0.11) and in the proliferating crypt cells (PF of 1.04 +/- 0.07). WR-2721 protected jejunum in the microcolony assay with a much greater PF of 1.8. For each drug the PF for SSBs was therefore always much lower than that indicated by the biological end point under identical conditions. Both drugs also retarded the rate of SSB rejoining in each population of cells. These data suggest that mechanisms such as free-radical scavenging by these drugs may contribute to but not completely explain their protective action. Comparison with data obtained previously with cultured CHO cells supports the idea that the action of these drugs at the DNA lesion level may not be dose-modifying, but may also result in a shift in the spectrum of lesions induced by the radiation.

Adjunctive use of ethiofos (WR-2721) with free radical-generating chemotherapeutic agents in mice: new caveats for therapy

The neurotransmitter analogue 6-hydroxydopamine has been proposed as a selective chemotherapeutic agent for peripheral neural crest tumors. It exerts its action through the generation of cytotoxic oxygen free radicals. Unfortunately, it is toxic to normal peripheral neurons as well. Ethiofos (WR-2721) is a free radical scavenger which appears to be preferentially taken up by normal cells relative to some tumor cells. WR-2721 has been assayed as a protector of the normal autonomic nervous system in mice treated with 6-hydroxydopamine. Although WR-2721 has some activity in this regard, its therapeutic window is narrowed by its depletion of glutathione, a phenomenon which has not previously been noted with this drug. These findings raise issues regarding the safety of adjunctive use of WR-2721 with oxygen free radical-generating chemotherapeutic agents.

WR 2721 modification of type II cell and endothelial cell function in mouse lung after single doses of radiation

The ability of WR 2721 to protect endothelial cells and Type II cells in mouse lung after single doses of X rays was studied using specific assays of cell function to assess damage. The whole thorax of mice was exposed to a range of single doses of X rays either alone or 30 minutes after an i.p. injection of 400 mg/kg of WR 2721. Endothelial cell function was assayed by angiotensin converting enzyme (ACE) and Type II cell function by phosphatidylcholine and total protein present in lavage fluid 28 days after radiation. Similar protection factors (PFs) were found for the functional activity of both cell types, 1.2 and 1.24 for ACE and phosphatidylcholine respectively. These values were somewhat less than the PF of 1.37 for lethality from pneumonitis 7 to 9 months after irradiation for this mouse strain. The lack of a clear difference between the PFs for the functional activity of these two cell types suggests that neither the endothelial cell nor the Type II cell can be accepted or excluded as the target cell for radiation pneumonitis in lung.