Dose-dependent pharmacokinetics of rapamycin-28-N,N-dimethylglycinate in the mouse

Subcutaneous Anti-inflammatory Therapies to Prevent Burn Progression in a Swine Model of Contact Burn Injury

INTRODUCTION

If left untreated, burn injuries can deepen or progress in depth within the first 72 hours after injury as a result of increased wound inflammation, subsequently worsening healing outcomes. This can be especially detrimental to warfighters who are constrained to resource-limited environments with delayed evacuation times to higher roles of care and more effective treatment. Preventing this burn progression at the point of injury has the potential to improve healing outcomes but requires a field-deployable therapy and delivery system. Subcutaneous therapies known to treat inflammation delivered local to the wound site may prove to be one such avenue for success.

MATERIALS AND METHODS

Seven Yorkshire-cross swine received partial-thickness burn injuries using a previously established contact burn model. Each animal received one of the seven therapies: (1) saline, (2) heparin, (3) ibuprofen, (4) erythropoietin, (5) resolvin, (6) rapamycin, and (7) placental extract, all of which are either currently employed or are experimental in field use and indicated to treat inflammation. Treatments were delivered subcutaneously on the day of injury and 24 hours post-injury to simulate a prolonged field care scenario, before potential evacuation. Animals and wound development were observed for 28 days before euthanasia. Throughout the course of the study, wounds were observed macroscopically via non-invasive imaging. Histological analyses provided the critical metric of burn progression. Treatment success criteria were designated as the ability to prevent burn progression past 80% of the dermal depth in two of the three treated wounds, a clinically relevant metric of burn progression.

RESULTS

It was determined that the applied model successfully created reproducible partial-thickness burn injuries in this porcine study. No significant differences with regard to lateral wound size or the rate of lateral wound closure were observed in any treatments. Several treatments including resolvin, rapamycin, ibuprofen, and erythropoietin successfully reduced burn progression to less than 80% of the dermal depth in two of the three wounds, 24 hours after injury.

CONCLUSIONS

This report employs an established model of porcine contact burn injury in order to test the ability of local subcutaneous delivery of therapeutics to prevent burn progression at the point of injury, via what is believed to be the inhibition of inflammation. Several treatments successfully prevented burn progression to a full-thickness injury, potentially improving wound healing outcomes in a simulated battlefield scenario. Subcutaneously administered therapies combating burn-induced inflammation at the point of injury may serve as a field-deployable treatment modality to improve warfighter recovery and return to duty.

Occurrence of Total and Proteinase K-Resistant Alpha-Synuclein in Glioblastoma Cells Depends on mTOR Activity

Simple Summary

The accumulation of alpha-synuclein (α-syn) is considered a pathological hallmark of the neurodegenerative disorders known as synucleinopathies. The clearance of α-syn depends on autophagy activity, which is inhibited by the mechanistic target of rapamycin (mTOR). Thus, it is likely that α-syn accumulation may occur whenever mTOR is overactive and autophagy is suppressed. In fact, the lack of effective autophagy increases the amount of α-syn and may produce protein aggregation. Therefore, in the present study, we questioned whether cells from glioblastoma multiforme (GBM), a lethal brain neoplasm, wherein mTOR is upregulated and autophagy is suppressed, may overexpress α-syn. In fact, a large quantity of α-syn is measured in GBM cells compared with astrocytes, which includes proteinase K-resistant α-syn. Rapamycin, while inhibiting mTOR activity, significantly reduces the amount of α-syn and allocates α-syn within autophagy-like vacuoles.

Abstract

Alpha-synuclein (α-syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which α-syn aggregates are considered a pathological hallmark. The clearance of α-syn strongly depends on autophagy, which can be stimulated by inhibiting the mechanistic target of rapamycin (mTOR). Thus, the overexpression of mTOR and severe autophagy suppression may produce α-syn accumulation, including the proteinase K-resistant protein isoform. Glioblastoma multiforme (GBM) is a lethal brain tumor that features mTOR overexpression and severe autophagy inhibition. Cell pathology in GBM is reminiscent of a fast, progressive degenerative disorder. Therefore, the present work questions whether, as is analogous to neurons during degenerative disorders, an overexpression of α-syn occurs within GBM cells. A high amount of α-syn was documented in GBM cells via real-time PCR (RT-PCR), Western blotting, immunohistochemistry, immuno-fluorescence, and ultrastructural stoichiometry, compared with the amount of β- and γ-synucleins and compared with the amount of α-syn counted within astrocytes. The present study indicates that (i) α-syn is overexpressed in GBM cells, (ii) α-syn expression includes a proteinase-K resistant isoform, (iii) α-syn is dispersed from autophagy-like vacuoles to the cytosol, (iv) α-syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the α-syn-related GBM-like phenotype is mitigated by silencing the SNCA gene.

Rapamycin Ameliorates Defects in Mitochondrial Fission and Mitophagy in Glioblastoma Cells

Glioblastoma (GBM) cells feature mitochondrial alterations, which are documented and quantified in the present study, by using ultrastructural morphometry. Mitochondrial impairment, which roughly occurs in half of the organelles, is shown to be related to mTOR overexpression and autophagy suppression. The novelty of the present study consists of detailing an mTOR-dependent mitophagy occlusion, along with suppression of mitochondrial fission. These phenomena contribute to explain the increase in altered mitochondria reported here. Administration of the mTOR inhibitor rapamycin rescues mitochondrial alterations. In detail, rapamycin induces the expression of genes promoting mitophagy (PINK1, PARKIN, ULK1, AMBRA1) and mitochondrial fission (FIS1, DRP1). This occurs along with over-expression of VPS34, an early gene placed upstream in the autophagy pathway. The topographic stoichiometry of proteins coded by these genes within mitochondria indicates that, a remarkable polarization of proteins involved in fission and mitophagy within mitochondria including LC3 takes place. Co-localization of these proteins within mitochondria, persists for weeks following rapamycin, which produces long-lasting mitochondrial plasticity. Thus, rapamycin restores mitochondrial status in GBM cells. These findings add novel evidence about mitochondria and GBM, while fostering a novel therapeutic approach to restore healthy mitochondria through mTOR inhibition.

The mTORC1 inhibitor rapamycin and the mTORC1/2 inhibitor AZD2014 impair the consolidation and persistence of contextual fear memory

RATIONALE

The mechanistic target of rapamycin (mTOR) kinase mediates various long-lasting forms of synaptic and behavioural plasticity. However, there is little information concerning the temporal pattern of mTOR activation and susceptibility to pharmacological intervention during consolidation of contextual fear memory. Moreover, the contribution of both mTOR complex 1 and 2 together or the mTOR complex 1 downstream effector p70S6K (S6K1) to consolidation of contextual fear memory is unknown.

OBJECTIVE

Here, we tested whether different timepoints of vulnerability to rapamycin, a first generation mTOR complex 1 inhibitor, exist for contextual fear memory consolidation and persistence. We also sought to characterize the effects of dually inhibiting mTORC1/2 as well as S6K1 on fear memory formation and persistence.

METHODS

Rapamycin was injected systemically to mice immediately, 3 h, or 12 h after contextual fear conditioning, and retention was measured at different timepoints thereafter. To determine the effects of a single injection of the dual mTROC1/2 inhibitor AZD2014 after learning on memory consolidation and persistence, a dose-response experiment was carried out. Memory formation and persistence was also assessed in response to the S6K1 inhibitor PF-4708671.

RESULTS

A single systemic injection of rapamycin immediately or 3 h, but not 12 h, after learning impaired the formation and persistence of contextual fear memory. AZD2014 was found, with limitations, to dose-dependently attenuate memory consolidation and persistence at the highest dose tested (50 mg/kg). In contrast, PF-4708671 had no effect on consolidation or persistence.

CONCLUSION

Our results indicate the need to further understand the role of mTORC1/2 kinase activity in the molecular mechanisms underlying memory processing and also demonstrate that the effects of mTORC1 inhibition at different timepoints well after learning on memory consolidation and persistence.

Amino Acids in the Development of Prodrugs

Although drugs currently used for the various types of diseases (e.g., antiparasitic, antiviral, antibacterial, etc.) are effective, they present several undesirable pharmacological and pharmaceutical properties. Most of the drugs have low bioavailability, lack of sensitivity, and do not target only the damaged cells, thus also affecting normal cells. Moreover, there is the risk of developing resistance against drugs upon chronic treatment. Consequently, their potential clinical applications might be limited and therefore, it is mandatory to find strategies that improve those properties of therapeutic agents. The development of prodrugs using amino acids as moieties has resulted in improvements in several properties, namely increased bioavailability, decreased toxicity of the parent drug, accurate delivery to target tissues or organs, and prevention of fast metabolism. Herein, we provide an overview of models currently in use of prodrug design with amino acids. Furthermore, we review the challenges related to the permeability of poorly absorbed drugs and transport and deliver on target organs.

Immunosuppression for in vivo research: state-of-the-art protocols and experimental approaches

Almost every experimental treatment strategy using non-autologous cell, tissue or organ transplantation is tested in small and large animal models before clinical translation. Because these strategies require immunosuppression in most cases, immunosuppressive protocols are a key element in transplantation experiments. However, standard immunosuppressive protocols are often applied without detailed knowledge regarding their efficacy within the particular experimental setting and in the chosen model species. Optimization of such protocols is pertinent to the translation of experimental results to human patients and thus warrants further investigation. This review summarizes current knowledge regarding immunosuppressive drug classes as well as their dosages and application regimens with consideration of species-specific drug metabolization and side effects. It also summarizes contemporary knowledge of novel immunomodulatory strategies, such as the use of mesenchymal stem cells or antibodies. Thus, this review is intended to serve as a state-of-the-art compendium for researchers to refine applied experimental immunosuppression and immunomodulation strategies to enhance the predictive value of preclinical transplantation studies.

Amino acids as promoieties in prodrug design and development

Prodrugs are biologically inactive agents that upon biotransformation in vivo result in active drug molecules. Since prodrugs might alter the tissue distribution, efficacy and the toxicity of the parent drug, prodrug design should be considered at the early stages of preclinical development. In this regard, natural and synthetic amino acids offer wide structural diversity and physicochemical properties. This review covers the use of amino acid prodrugs to improve poor solubility, poor permeability, sustained release, intravenous delivery, drug targeting, and metabolic stability of the parent drug. In addition, practical considerations and challenges associated with the development of amino acid prodrugs are also covered.

Systemic rapamycin alone may not be a treatment option for malignant glioma: evidence from an in vivo study

The mammalian target of rapamycin (mTOR) plays a central role in regulating the proliferation of cancer cells, and mTOR-specific inhibitors such as rapamycin analogs are considered as a promising therapy for malignant glioma. In this study, we investigated the possibility of using mTOR inhibitors to treat gliomas. We used a molecular marker, phosphorylation of S6 protein, to monitor biological effects of mTOR inhibitors within xenografts. Phosphorylation was decreased more in U87MG glioma after treatment with high doses of rapamycin or its analog, torisel (10 mg/kg or 25 mg/kg), but only slightly after a low dose of rapamycin (3 mg/kg). This effect correlated with enhanced survival of rats after weekly peritoneal injections of both drugs at the highest two doses but not at the low dose. High doses of both drugs caused weight loss in rats. Clinical trial data indicates that low doses of Torisel (<3 mg/kg) were not efficacious in recurrent GBM. It is concluded that systemic administration of rapamycin analogues may not be a treatment option for patients with malignant glioma due to the intolerability of high doses that might otherwise be effective. The present study underscores the need for better pre-clinical evaluation of drugs with respect to therapeutic window.

Inducing autophagy by rapamycin before, but not after, the formation of plaques and tangles ameliorates cognitive deficits

Previous studies have shown that inducing autophagy ameliorates early cognitive deficits associated with the build-up of soluble amyloid-β (Aβ). However, the effects of inducing autophagy on plaques and tangles are yet to be determined. While soluble Aβ and tau represent toxic species in Alzheimer's disease (AD) pathogenesis, there is well documented evidence that plaques and tangles also are detrimental to normal brain function. Thus, it is critical to assess the effects of inducing autophagy in an animal model with established plaques and tangles. Here we show that rapamycin, when given prophylactically to 2-month-old 3xTg-AD mice throughout their life, induces autophagy and significantly reduces plaques, tangles and cognitive deficits. In contrast, inducing autophagy in 15-month-old 3xTg-AD mice, which have established plaques and tangles, has no effects on AD-like pathology and cognitive deficits. In conclusion, we show that autophagy induction via rapamycin may represent a valid therapeutic strategy in AD when administered early in the disease progression.

The effect of mTOR inhibition alone or combined with MEK inhibitors on brain metastasis: an in vivo analysis in triple-negative breast cancer models

mTOR inhibitor rapamycin and its analogs are lipophilic, demonstrate blood-brain barrier penetration, and have shown promising antitumor effects in several types of refractory tumors. We thus try to explore the therapeutic effects of mTOR inhibitors on brain metastasis models. We examined the effects of different dose of mTOR inhibitors (rapamycin, Temsirolimus-CCI-779) on cell invasion in two brain metastatic breast cancer cell lines (MDA-MB231-BR and CN34-BrM2). Antibody microarray and immunoblotting were applied to detect signaling pathways underlying the dose differential drug effects. The in vivo effects of single drug (CCI-779), and drug combination of CCI-779 with SL327 (a brain penetrant MEK inhibitor) to eliminate the unfavorable activation of MAPK pathway were evaluated in MDA-MB231-BR brain metastases xenograft mice. The two mTOR inhibitors, rapamycin and CCI-779, inhibited the invasion of brain metastatic cells only at a moderate concentration level, which was lost at higher concentrations secondary to activation of the MAPK signaling pathway. Pharmacological inhibition of ERK1/2 by PD98059 and SL327 restored the anti-invasion effects of mTOR inhibition in vitro. In vivo, a significant decrease was noted in the average number of micro and large metastatic lesions as well as the whole brain GFP expression in the CCI-779 1 mg/kg/day treated group compared with that in the vehicle group (P < 0.05). However, 10 mg/kg CCI-779 treatment did not show significant anti-metastasis effect on the animal model. High-dose CCI-779 eliciting the ERK MAPK activation in the brain metastatic lesion was corroborated. Combined with the brain penetrant MEK inhibitor SL327, high-dose CCI-779 significantly reduces the brain metastasis, and the combination treatment prohibited perivascular invasion of tumor cells and inhibits tumor angiogenesis in vivo. This study provides evidence on the potential value of CCI-779 as well as CCI-779 + SL327 in prohibiting breast cancer brain metastasis.

Prodrug strategies to overcome poor water solubility

Drug design in recent years has attempted to explore new chemical spaces resulting in more complex, larger molecular weight molecules, often with limited water solubility. To deliver molecules with these properties, pharmaceutical scientists have explored many different techniques. An older but time-tested strategy is the design of bioreversible, more water-soluble derivatives of the problematic molecule, or prodrugs. This review explores the use of prodrugs to effect improved oral and parenteral delivery of poorly water-soluble problematic drugs, using both marketed as well as investigational prodrugs as examples. Prodrug interventions should be considered early in the drug discovery paradigm rather than as a technique of last resort. Their importance is supported by the increasing percentage of approved new drug entities that are, in fact, prodrugs.

Mechanisms of action of rapamycin in gliomas

Rapamycin has previously been shown to be efficacious against intracerebral glioma xenografts and to act in a cytostatic manner against gliomas. However, very little is known about the mechanism of action of rapamycin. The purpose of our study was to further investigate the in vitro and in vivo mechanisms of action of rapamycin, to elucidate molecular end points that may be applicable for investigation in a clinical trial, and to examine potential mechanisms of treatment failure. In the phosphatase and tensin homolog deleted from chromosome 10 (PTEN)-null glioma cell lines U-87 and D-54, but not the oligodendroglioma cell line HOG (PTEN null), doses of rapamycin at the IC50 resulted in accumulation of cells in G1, with a corresponding decrease in the fraction of cells traversing the S phase as early as 24 h after dosing. All glioma cell lines tested had markedly diminished production of vascular endothelial growth factor (VEGF) when cultured with rapamycin, even at doses below the IC50. After 48 h of exposure to rapamycin, the glioma cell lines (but not HOG cells) showed downregulation of the membrane type-1 matrix metalloproteinase (MMP) invasion molecule. In U-87 cells, MMP-2 was downregulated, and in D-54 cells, both MMP-2 and MMP-9 were downregulated after treatment with rapamycin. Treatment of established subcutaneous U-87 xenografts in vivo resulted in marked tumor regression (P < 0.05). Immunohistochemical studies of subcutaneous U-87 tumors demonstrated diminished production of VEGF in mice treated with rapamycin. Gelatin zymography showed marked reduction of MMP-2 in the mice with subcutaneous U-87 xenografts that were treated with rapamycin as compared with controls treated with phosphatebuffered saline. In contrast, treatment of established intracerebral U-87 xenografts did not result in increased median survival despite inhibition of the Akt pathway within the tumors. Also, in contrast with our findings for subcutaneous tumors, immunohistochemistry and quantitative Western blot analysis results for intracerebral U-87 xenografts indicated that there is not significant VEGF production, which suggests possible deferential regulation of the hypoxia-inducible factor 1alpha in the intracerebral compartment. These findings demonstrate that the complex operational mechanisms of rapamycin against gliomas include cytostasis, anti-VEGF, and anti-invasion activity, but these are dependent on the in vivo location of the tumor and have implications for the design of a clinical trial.

Inhibition of mTOR induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease

Huntington disease is one of nine inherited neurodegenerative disorders caused by a polyglutamine tract expansion. Expanded polyglutamine proteins accumulate abnormally in intracellular aggregates. Here we show that mammalian target of rapamycin (mTOR) is sequestered in polyglutamine aggregates in cell models, transgenic mice and human brains. Sequestration of mTOR impairs its kinase activity and induces autophagy, a key clearance pathway for mutant huntingtin fragments. This protects against polyglutamine toxicity, as the specific mTOR inhibitor rapamycin attenuates huntingtin accumulation and cell death in cell models of Huntington disease, and inhibition of autophagy has the converse effects. Furthermore, rapamycin protects against neurodegeneration in a fly model of Huntington disease, and the rapamycin analog CCI-779 improved performance on four different behavioral tasks and decreased aggregate formation in a mouse model of Huntington disease. Our data provide proof-of-principle for the potential of inducing autophagy to treat Huntington disease.

Distribution of sirolimus in rat tissue

OBJECTIVES

To examine the distribution of sirolimus (SRL, rapamycin), an immunosuppressive macrolide antibiotic, in the tissues of adult male Wistar-Furth rats following continuous intravenous infusion (CIVI) and repeated daily peroral gavage (PO).

DESIGN AND METHODS

Animals received 14-day courses of SRL by either CIVI (0.04-0.4 mg/kg/day) or PO (0.4-1.6 mg/kg/day) administration. Samples of whole blood and homogenates of five solid organs (heart, kidney, liver, lung and spleen), and portions of intestinal, muscle and testicular tissues were prepared on day 13 of CIVI treatment or 24 hours after administration of the 14th PO dose. SRL concentrations were determined by high performance liquid chromatography with reference to calibration curves produced from SRL-spiked whole blood or tissue homogenates prepared from drug-free animals.

RESULTS

Following PO but not CIVI administration, SRL concentrations in whole blood and all tissues increased linearly in relation to dose. SRL was extensively distributed among most tissues tested (tissue partitions coefficients of > 40 were observed in some cases). Comparatively, SRL whole blood concentrations were low. The ratio between the SRL whole blood concentrations after PO versus after CIVI administration (at like doses of 0.4 mg/kg/day) was 0.04. Therefore, we inferred that the oral bioavailability of SRL was low.

CONCLUSIONS

The linear relationships between PO dose and SRL concentrations in whole blood and tissues may be attributed to the low oral bioavailability of SRL, which is indicated by the low levels of SRL observed in whole blood and tissues after PO administration. The nonlinear relationships between CIVI dose and SRL concentrations in whole blood and tissues may result because although whole blood depots may be saturated with SRL, the tissues continue to absorb SRL as the dose of SRL increases. Thus, because a high percentage of SRL is widely distributed into tissues stores, caution must be used when administering this drug in humans.

Effects of the pharmacokinetic interaction between orally administered sirolimus and cyclosporine on the synergistic prolongation of heart allograft survival in rats

Oral administration, but not continuous intravenous infusion, of sirolimus (SRL) in combination with cyclosporine (CsA) produces a pharmacokinetic interaction, namely increases in the whole blood trough concentrations of SRL ([SRL(WB)]) and CsA ([CsA(WB)]). The effects of this pharmacokinetic interaction on the synergism between SRL and CsA was examined in Wistar Furth (RT1u) recipients of Buffalo (RT1b) heart allografts. A 14-day course of oral SRL produced dose-dependent prolongation of heart allografts: in untreated controls, 0.5 mg/kg SRL per day extended the mean survival time (MST) from 6.4+/-0.5 days to 12.3+/-3.8 days (P<0.05); SRL at 1.0 mg/kg per day prolonged the MST to 18.0+/-5.5 days (P<0.01); at 2.0 mg/kg SRL per day, MST was extended to 52.5+/-13.2 days (P<0.01); and 4.0 mg/kg SRL per day prolonged MST to 90.0+/-41.1 days (P<0.01). Comparison of the in vivo effects after oral versus continuous intravenous SRL administration suggested that the oral bioavailability of SRL is less than 10%. Combinations of oral SRL and CsA synergistically prolonged heart allograft survival, as documented by combination index values of 0.01-0.64 (combination index <1 indicates synergistic interaction). In rats treated with dual drug combinations, CsA increased the bioavailability of SRL by two- to elevenfold, and SRL increased the bioavailability of CsA by two- to threefold, thereby significantly decreasing the oral effective dose (ED) values for each drug. The ED50 for SRL alone is 2.4 mg/kg per day, which produces an average [SRL(WB)] of 13.2 ng/ml. The ED50 for CsA alone is 8.0 mg/kg per day, which produces an average [CsA(WB)] of 1642 ng/ml. However, when the two drugs are combined, the ED50 effect is achieved with only 0.34 mg/kg SRL per day ([SRL(WB)]=1.1 ng/ml) and 2.1 mg/kg CsA per day ([CsA(WB)] =326 ng/ml). Individually, 0.34 mg/kg SRL per day produces an ED9 with an average [SRL(WB)] of 0.6 ng/ml, and 2.1 mg/kg CsA per day produces an ED22 with an average [CsA(WB)] of 174 ng/ml. Thus, the pharmacokinetic interaction between oral SRL and CsA contributes to the in vivo synergism between the two drugs.