Synthesis and growth regulatory activity of a prototype member of a new family of aminothiol radioprotectors

Significant Reduction of Total-Body Irradiation-Induced Death in Mice Treated with PrC-210 24 Hours Postirradiation

The search for radiation countermeasures that can serve as: i. a pre-exposure agent to protect against subsequent irradiation, and/or ii. a post-exposure agent to mitigate the development of Acute Radiation Syndrome after radiation exposure, remains a prominent goal of the U.S. Government. This study was undertaken to determine whether PrC-210, when administered once, 24 h postirradiation, would provide a survival benefit and would mitigate Acute Radiation Syndrome in mice that had received an otherwise 95-100% lethal radiation dose. Our results show that a single intraperitoneal dose of PrC-210 (0.3-0.4 MTD, 151-201 ug/gm body weight) administered 24 h postirradiation, conferred: i. a 45% survival advantage (P = 0.002) in outbred ICR mice and a 25% survival advantage (P = 0.037) in inbred C57Bl/6 mice, ii. a significant increase in body weight in surviving mice (P = 0.012), iii. a discernible protection of intestinal structure by MRI imaging of live mice, iv. visibly denser jejunal villi and surface epithelium and v. visible bone marrow population in PrC-210-treated mice versus saline controls. The ability of PrC-210 to suppress 100% of radiation-induced death when administered minutes before irradiation, or roughly half of this effect (45%) when administered 24 h postirradiation is noteworthy. Determining the multiple paths by which PrC-210 protection is conferred is a process; the results in this report showing protection of two of the major systems central to Acute Radiation Syndrome damage, is a good first step. This was the first study of PrC-210 administered postirradiation; it conferred substantial survival benefit and suppression of Acute Radiation Syndrome. This outcome supports the continued development of PrC-210 to protect humans exposed to ionizing radiation.

Design, Synthesis, and Biological Evaluation of a Novel Aminothiol Compound as Potential Radioprotector

The risk of radiation damage has increased with the rapid development of nuclear technology and radiotherapy. Hence, research on radioprotective agents is of utmost importance. In the present study, a novel aminothiol compound 12, containing a linear alkylamino backbone and three terminal thiols, was synthesized. Owing to the appropriate capped groups in the chains, it has an improved permeability and oral bioavailability compared to other radioprotective agents. Oral administration of compound 12 improved the survival of mice that received lethal doses of γ-irradiation. Experimental results demonstrated that compound 12 not only mitigated total body irradiation-induced hematopoietic injury by increasing the frequencies of hematopoietic stem and progenitor cells but also prevented abdominal irradiation-induced intestinal injury by increasing the survival of Lgr5⁺ intestinal cells, lysozyme⁺ Paneth cells, and Ki67⁺ cells. In addition, compound 12 decreased oxidative stress by upregulating the expression of Nrf2 and NQO1 and downregulating the expression of NOX1. Further, compound 12 inhibited γ-irradiation-induced DNA damage and alleviated G2/M phase arrest. Moreover, compound 12 decreased the levels of p53 and Bax and increased the level of Bcl-2, demonstrating that it may suppress radiation-induced apoptosis via the p53 pathway. These results indicate that compound 12 has the possibility of preventing radiation injury and can be a potential radioprotector for clinical applications.

Suppression of Inflammation-Associated Kidney Damage Post-Transplant Using the New PrC-210 Free Radical Scavenger in Rats

Allograft kidney transplantation, which triggers host cellular- and antibody-mediated rejection of the kidney, is a major contributor to kidney damage during transplant. Here, we asked whether PrC-210 would suppress damage seen in allograft kidney transplant. Brown Norway (BN) rat kidneys were perfused in situ (UW Solution) with or without added 30 mM PrC-210, and then immediately transplanted into Lewis (LEW) rats. 20 h later, the transplanted BN kidneys and LEW rat plasma were analyzed. Kidney histology, and kidney/serum levels of several inflammation-associated cytokines, were measured to assess mismatch-related kidney pathology, and PrC-210 protective efficacy. Twenty hours after the allograft transplants: (i) significant histologic kidney tubule damage and mononuclear inflammatory cell infiltration were seen in allograft kidneys; (ii) kidney function metrics (creatinine and BUN) were significantly elevated; (iii) significant changes in key cytokines, i.e., TIMP-1, TNF-alpha and MIP-3A/CCL20, and kidney activated caspase levels were seen. In PrC-210-treated kidneys and recipient rats, (i) kidney histologic damage (Banff Scores) and mononuclear infiltration were reduced to untreated background levels; (ii) creatinine and BUN were significantly reduced; and (iii) activated caspase and cytokine changes were significantly reduced, some to background. In conclusion, the results suggest that PrC-210 could provide broadly applicable organ protection for many allograft transplantation conditions; it could protect transplanted kidneys during and after all stages of the transplantation process-from organ donation, through transportation, re-implantation and the post-operative inflammation-to minimize acute and chronic rejection.

Polycysteine as a new type of radio-protector ameliorated tissue injury through inhibiting ferroptosis in mice

Amifostine has been the only small molecule radio-protector approved by FDA for decades; however, the serious adverse effects limit its clinical use. To address the toxicity issues and maintain the good potency, a series of modified small polycysteine peptides had been prepared. Among them, compound 5 exhibited the highest radio-protective efficacy, the same as amifostine, but much better safety profile. To confirm the correlation between the radiation-protective efficacy and the DNA binding capability, each of the enantiomers of the polycysteine peptides had been prepared. As a result, the L-configuration compounds had obviously higher efficacy than the corresponding D-configuration enantiomers; among them, compound 5 showed the highest DNA binding capability and radiation-protective efficacy. To our knowledge, this is the first study that has proved their correlations using direct comparison. Further exploration of the mechanism revealed that the ionizing radiation (IR) triggered ferroptosis inhibition by compound 5 could be one of the pathways for the protection effect, which was different from amifostine. In summary, the preliminary result showed that compound 5, a polycysteine as a new type of radio-protector, had been developed with good efficacy and safety profile. Further study of the compound for potential use is ongoing.

Significant Improvement in Rat Kidney Cold Storage Using UW Organ Preservation Solution Supplemented With the Immediate-Acting PrC-210 Free Radical Scavenger

Ischemia-reperfusion injury, including injury from warm- and cold-ischemia (CI) organ storage, remains a significant problem for all solid organ transplants. Suppressing CI damage would reduce delayed graft function and increase the donor organ pool size. PrC-210 has demonstrated superior prevention of damage in several preclinical studies as an immediate-acting free-radical scavenger. Here, we describe its profound efficacy in suppressing CI injury in a rat kidney model.

Impact of the PrC-210 Radioprotector Molecule on Cancer Deaths in p53-Deficient Mice

Radiation-induced cancer is an ongoing and significant problem, with sources that include clinics worldwide in which 3.1 billion radiology exams are performed each year, as well as a variety of other scenarios such as space travel and nuclear cleanup. These radiation exposures are typically anticipated, and the exposure is typically well below 1 Gy. When radiation-induced (actually ROS-induced) DNA mutation is prevented, then so too are downstream radiation-induced cancers. Currently, there is no protection available against the effects of such <1 Gy radiation exposures. In this study, we address whether the new PrC-210 ROS-scavenger is effective in protecting p53-deficient (p53^-/-) mice against X-ray-induced accelerated tumor mortality; this is the most sensitive radiation tumorigenesis model currently known. Six-day-old p53^-/- pups received a single intraperitoneal PrC-210 dose [0.5 maximum tolerated dose (MTD)] or vehicle, and 25 min later, pups received 4.0 Gy X-ray irradiation. At 5 min postirradiation, blood was collected to quantify white blood cell c-H2AX foci. Over the next 250 days, tumor-associated deaths were recorded. Findings revealed that when administered 25 min before 4 Gy X-ray irradiation, PrC-210 reduced DNA damage (c-H2AX foci) by 40%, and in a notable coincidence, caused a 40% shift in tumor latency/incidence, and the 0.5 MTD PrC210 dose had no discernible toxicities in these p53^-/- mice. Essentially, the moles of PrC-210 thiol within a single 0.5 MTD PrC-210 dose suppressed the moles of ROS generated by 40% of the 4 Gy X-ray dose administered to p53^-/- pups, and in doing so, eliminated the lifetime leukemia/lymphoma risk normally residing "downstream" of that 40% of the 4 Gy dose. In conclusion: 1. PrC-210 is readily tolerated by the 6-day-old p53^-/- mice, with no discernible lifetime toxicities; 2. PrC-210 does not cause the nausea, emesis or hypotension that preclude clinical use of earlier aminothiols; and 3. PrC-210 significantly increased survival after 4 Gy irradiation in the p53^-/- mouse model.

Significant reduction of ischemia-reperfusion cell death in mouse myocardial infarcts using the immediate-acting PrC-210 ROS-scavenger

Managing myocardial infarction (MI) to reduce cardiac cell death relies primarily on timely reperfusion of the affected coronary site, but reperfusion itself induces cell death through a toxic, ROS-mediated process. In this study, we determined whether the PrC-210 aminothiol ROS-scavenger could prevent ROS-induced damage in post-MI hearts. In a series of both in vitro and in vivo experiments, we show that: (a) in vitro, PrC-210 was the most potent and effective ROS-scavenger when functionally compared to eight of the most commonly studied antioxidants in the MI literature, (b) in vitro PrC-210 ROS-scavenging efficacy was both immediate (seconds) and long-lasting (hours), which would make it effective in both (1) real-time (seconds), as post-MI or cardiac surgery hearts are reperfused with PrC-210-containing blood, and (2) long-term (hours), as hearts are bathed with systemic PrC-210 after MI or surgery, (c) systemic PrC-210 caused a significant 36% reduction of mouse cardiac muscle death following a 45-minute cardiac IR insult; in a striking coincidence, the PrC-210 36% reduction in cardiac muscle death equals the 36% of the MI-induced cardiac cell death estimated 6 years ago by Ovize and colleagues to result from "reperfusion injury," (d) hearts in PrC-210-treated mice performed better than controls after heart attacks when functionally analyzed using echocardiography, and (e) the PrC-210 ROS-scavenging mechanism of action was corroborated by its ability to prevent >85% of the direct, H2O2-induced killing of neonate cardiomyocytes in cell culture. PrC-210 does not cause the nausea, emesis, nor hypotension that preclude clinical use of the WR-1065/amifostine aminothiol. PrC-210 is a highly effective ROS-scavenger that significantly reduces IR injury-associated cardiac cell death.

Significant Reduction of Murine Renal Ischemia-Reperfusion Cell Death Using the Immediate-Acting PrC-210 Reactive Oxygen Species Scavenger

Background.

Ischemia-reperfusion (IR) injury remains a significant problem for all solid organ transplants; thus, an important unmet need in transplantation is the prevention of IR injury. PrC-210 has demonstrated superior prevention of reactive oxygen species damage in several preclinical studies as a free radical scavenger. Here, we describe its profound efficacy in suppressing IR injury in a murine model of kidney IR injury.

Methods.

C57/B6 mice underwent laparotomy with the left renal pedicle occluded for 30 minutes to induce IR injury. Right nephrectomy was performed at the time of surgery. Mice received a single systemic dose of the PrC-210, PrC-211, or PrC-252 aminothiols 20 minutes before IR injury. Twenty-four hours following IR injury, blood and kidney tissue were collected for analysis. Kidney caspase-3 level (a marker of cell death), direct histological analysis of kidneys, and serum blood urea nitrogen (BUN) were measured in animals to assess reactive oxygen species scavenger protective efficacies.

Results.

A single systemic PrC-210 dose 20 minutes before IR injury resulted in significant reductions in (1) IR-induced kidney caspase level (P < 0.0001); caspase was reduced to levels not significantly different than control caspase levels seen in unperturbed kidneys, (2) IR-induced renal tubular injury scores (P < 0.0001); brush border loss and tubular dilation were markedly reduced, and (3) serum BUN compared with control IR injury kidneys (P < 0.0001). The ranked protective efficacies of PrC-210 > PrC-211 >> PrC-252 paralleled previous radioprotection studies of the molecules.

Conclusions.

A single PrC-210 dose, minutes before the IR insult, profoundly reduced caspase, renal tubular injury, and serum BUN in mice exposed to standard kidney IR injury. These findings support further development of the PrC-210 molecule to suppress or prevent IR injury in organ transplant and other IR injury settings.

Reduction of X-ray-induced DNA damage in normal human cells treated with the PrC-210 radioprotector

The aim of our study was to determine the protective efficacy of the PrC-210 aminothiol radioprotector against X-ray-induced DNA damage in normal human cells and to establish dose- and time-effect models for future PrC-210 use in humans. The PrC-210 structure has a branched structure which enables scavenging of reactive oxygen species (ROS) away from DNA. Normal human blood lymphocytes, fibroblasts and naked genomic DNA were exposed to PrC-210 seconds to hours prior to irradiation. Biological (γ-H2AX foci), chemical (8-oxo-deoxyguanosine) and physical (genomic DNA electrophoretic migration) DNA damage endpoints were scored to determine the ability of PrC-210 to suppress radiation-induced DNA damage. X-ray-induced γ-H2AX foci in blood lymphocytes were reduced by 80% after irradiation with 10, 50 and 100 mGy, and DNA double-strand breaks in fibroblasts were reduced by 60% after irradiation with 20 Gy. Additionally, we observed a reduction of 8-oxo-deoxyguanosine (an ROS-mediated, DNA damage marker) in human genomic DNA to background in a PrC-210 dose-dependent manner. PrC-210 also eliminated radiation-induced cell death in colony formation assays after irradiation with 1 Gy. The protective efficacy of PrC-210 in each of these assay systems supports its development as a radioprotector for humans in multiple radiation exposure settings.

Summary: A new strategy is decribed, using a new radioprotector (PrC-210) to significantly reduce radiation-induced DNA damage.

Significant Suppression of CT Radiation-Induced DNA Damage in Normal Human Cells by the PrC-210 Radioprotector

While computed tomography (CT) is now commonly used and considered to be clinically valuable, significant DNA double-strand breaks (γ-H2AX foci) in white blood cells from adult and pediatric CT patients have been frequently reported. In this study to determine whether γ-H2AX foci and X-ray-induced naked DNA damage are suppressed by administration of the PrC-210 radioprotector, human blood samples were irradiated in a CT scanner at 50-150 mGy with or without PrC-210, and γ-H2AX foci were scored. X-ray-induced naked DNA damage was also studied, and the DNA protective efficacy of PrC-210 was compared against 12 other common "antioxidants." PrC-210 reduced CT radiation-induced γ-H2AX foci in white blood cells to near background ( P < 0.0001) at radiation doses of 50-150 mGy. PrC-210 was most effective among the 13 "antioxidants" in reducing naked DNA X-ray damage, and its addition at 30 s before an ^•OH pulse reduced to background the ^•OH insult that otherwise induced >95% DNA damage. A systemic PrC-210 dose known to confer 100% survival in irradiated mice had no discernible effect on micro-CT image signal-to-noise ratio and CT image integrity. PrC-210 suppressed DNA damage to background or near background in each of these assay systems, thus supporting its development as a radioprotector for humans in multiple radiation exposure settings.

A new strategy to prevent chemotherapy and radiotherapy-induced alopecia using topically applied vasoconstrictor

In a new strategy, we sought to determine whether topically applied vasoconstrictor, with its accompanying transient skin hypoxia and exclusion of systemic drug, would prevent or suppress radiotherapy or chemotherapy-induced alopecia. Topical vasoconstrictor was applied to 1-cm(2) skin patches on the backs of 10-day-old rats and minutes later they received either 7.1 gray (Gy) whole-body radiation or systemic N-nitroso-N-methylurea (MNU) or Cytoxan. The degree of alopecia was scored 10 days later by visual assessment (% coat retention) and hair follicle histologic analysis. Topical application of epinephrine or norepinephrine in an alcohol:water delivery vehicle induced clear skin blanch, and in a dose-dependent manner, topical epinephrine or norepinephrine (20-1,000 mM) applied before 7.1 Gy irradiation conferred 95% of coat retention in the treated skin patches versus 0% coat retention in vehicle controls, or in skin outside the treated patches. By histology, small numbers of dystrophic hair follicles were observed in hairless skin versus the normal density of anagen follicles in the immediately adjacent, drug-protected skin patches at day 20; protected coats were retained into adulthood. Topical epinephrine or norepinephrine before systemic MNU (30 ug/gm body weight) conferred up to 95% of coat retention in treated skin patches versus 0% coat retention elsewhere. Epinephrine-conferred % coat retention dropped to 16% in rats that received systemic Cytoxan, a drug whose plasma half-life is at least 8- to 10-fold longer than MNU. A general strategy is discussed for the use of topical epinephrine or norepinephrine in the clinic to provide an inexpensive and convenient strategy to prevent cancer therapy-induced alopecia.

Radioprotective efficacy and toxicity of a new family of aminothiol analogs

PURPOSE

A family of 17 new nucleophilic-polyamine and aminothiol structures was designed and synthesized to identify new topical or systemic radioprotectors with acceptable mammalian toxicity profiles. design elements included: (i) Length and charge of the DNA-interacting, alkylamine backbone, (ii) nucleophilicity of the reactive oxygen species (ROS)-scavenging group, and (iii) non-toxic drug concentration achievable in animal tissues.

MATERIALS AND METHODS

Mouse maximum tolerated doses (MTD) were determined by increasing intraperitoneal (IP) doses. To assess radioprotective efficacy, mice received IP 0.5 MTD doses prior to an LD95 radiation dose (8.63 Gy), and survival was monitored. Topically applied aminothiol was also scored for prevention of radiation-induced dermatitis (17.3 Gy to skin).

RESULTS

The most radioprotective aminothiols had 4-6 carbons and 1-2 amines, and unlike amifostine and its analogs, displayed a terminal thiol from an alkyl side chain that projected the thiol away from the DNA major groove into the environment surrounding the DNA. The five carbon, single thiol, alkylamine, PrC-210, conferred 100% survival to an otherwise 100% lethal dose of whole-body radiation and achieved 100% prevention of Grade 2-3 radiation dermatitis. By mass spectrometry analysis, the one aminothiol that was tested formed mixed disulfides with cysteine and glutathione.

CONCLUSIONS

Multiple, highly radioprotective, aminothiol structures, with acceptable systemic toxicities, were identified.

ROS-scavenger and radioprotective efficacy of the new PrC-210 aminothiol

To identify new aminothiol radioprotectors that are active when applied topically and have fewer side effects when administered systemically, a new family of aminothiol radioprotectors was designed and synthesized. Three key elements in the aminothiol design were, (1) small size for efficient transmembrane diffusion, (2) positive charged amines in alkyl backbone for strong ionic interaction with DNA backbone, and (3) a perpendicular, alkyl side-chain with a terminal thiol that is projected away from the DNA backbone to enable reactive oxygen species scavenging around DNA. Several in vitro assays were used to characterize the prototype aminothiol, PrC-210, for efficacy: protection against reactive oxygen species-induced plasmid DNA nicking, mass spectrometry to detect aminothiol-reactive oxygen species by-products, S. typhimurium mutagenesis, human cell growth inhibition, Western blot for p21 expression, and FACS analysis. Additionally, two in vivo assays were used to assess radioprotective efficacy; a Sprague-Dawley rat dorsal skin radiodermatitis assay was developed to screen for aminothiol efficacy when topically applied, and ICR mouse survival was scored after systemic PrC-210 administration and whole-body radiation. PrC-210 efficiently scavenged reactive oxygen species and completely protected supercoiled plasmid DNA against reactive oxygen species-induced damage. Neither PrC-210 nor its analog PrC-211 were bacterial mutagens. In cell culture, PrC-210 application to diploid human fibroblasts showed: (1) inhibition of cell growth with an IC(70) of 4.1 mM, (2) induced levels of p21 expression, and (3) a G(1)/S-cell cycle block that was reversed after washout of PrC-210-containing medium. In rodents, PrC-210 was an effective radioprotector showing: (1) complete prevention of Grade 2-3 radiodermatitis when applied topically (370 mM in ethanol:propylene glycol:water solution) prior to skin irradiation, (2) complete prevention of Grade 2-3 radiodermatitis when administered by i.p. injection (200 μg/g of body weight) before skin irradiation, (3) 100% survival of mice from an otherwise 100% lethal dose of whole-body radiation (8.75 Gy) when administered by i.p. injection (252 μg/g of body weight = 0.5 × maximum tolerated dose) before irradiation, and (4) a dose reduction factor of 1.6, the same as amifostine. These data suggest that the PrC-210 aminothiol is a plausible candidate for drug development as a human pre-exposure radioprotector.