Everolimus in Combination with Mycophenolate Mofetil as Pre- and Post-Transplantation Immunosuppression after Nonmyeloablative Hematopoietic Stem Cell Transplantation in Canine Littermates

Genetic Basis of Hypertrophic Cardiomyopathy in Cats

Hypertrophic cardiomyopathy (HCM) is a common cardiovascular condition in cats, affecting yth males and females of all ages. Some breeds, such as Ragdolls and Maine Coons, can develop HCM at a young age. The disease has a wide range of progression and severity, characterized by various pathological changes in the heart, including arteritis, fibrous tissue deposition, and myocardial cell hypertrophy. Left ventricular hypertrophy, which can restrict blood flow, is a common feature of HCM. The disease may persist into old age and eventually lead to heart failure and increased diastolic pressure. The basis of HCM in cats is thought to be genetic, although the exact mechanisms are not fully understood. Mutations in sarcomeric proteins, in particular myosin-binding protein C (MYBPC3), have been identified in cats with HCM. Two specific mutations, MYBPC3 [R818W] and MYBPC3 [A31P], have been classified as 'pathogenic'. Other variants in genes such as MYBPC3, TNNT2, ALMS1, and MYH7 are also associated with HCM. However, there are cases where cats without known genetic mutations still develop HCM, suggesting the presence of unknown genetic factors contributing to the disease. This work aims to summarise the new knowledge of HCM in cats and the alterations in cardiac tissue as a result of genetic variants.

Noncompartmental pharmacokinetics of three intravenous mycophenolate mofetil concentrations in healthy Standardbred mares

BACKGROUND

Mycophenolate mofetil (MMF) is the prodrug of mycophenolic acid (MPA) which acts as an immunosuppressive agent. During the biotransformation of MMF to MPA, additional metabolites including MPA phenol glucuronide (MPAG), MPA acyl glucuronide (AcMPAG) and MPA phenol glucoside (MPG) are formed.

OBJECTIVE

To define the noncompartmental pharmacokinetic (PK) parameters of three single doses of intravenous (i.v.) MMF and its downstream metabolites in healthy horses.

ANIMALS

Six healthy Standardbred mares.

MATERIALS AND METHODS

Generic MMF (Par Pharmaceuticals; Chestnut Ridge, NY, USA) was reconstituted and administered as a single i.v. bolus at 1.0 mg/kg, 5.0 mg/kg and 10.0 mg/kg with an eight day washout between treatments. Blood samples were collected immediately before MMF administration and over 24 h. A liquid chromatography-tandem mass spectrometry assay was developed following FDA guidance to determine plasma MMF, MPA, MPAG, AcMPAG and MPG concentrations. Plasma concentrations were analysed independently, followed by calculation of geometric mean and coefficient of variation.

RESULTS

Noncompartmental PK parameters were determined for MMF and all metabolites at all doses. MMF was rapidly converted to MPA in all horses. Each incremental dose of MMF resulted in increases in C_max and AUC_inf _obs for MPA and the three additional metabolites. Within the 10-fold dose range, the increase in C_max and AUC_inf _obs for MMF and its metabolites was nonlinear.

CONCLUSIONS AND CLINICAL RELEVANCE

Horses biotransform MMF into MPA, MPAG, AcMPAG and MPG via the glucuronidation and glucosidation clearance pathways. Equine reference PK profiles for MPA and the metabolites, MPAG, AcMPAG and MPG were established.

Investigation of the effects of mTOR inhibitors rapamycin and everolimus in combination with carboplatin on canine malignant melanoma cells

Background

Malignant melanoma in dogs is considered to be largely resistant to conventional chemotherapy, although responses to carboplatin have been documented. Invasion and early metastasis are common features of certain melanoma subtypes that contribute to tumour progression despite aggressive local and systemic therapy. Upregulation of the PI3K/AKT/mTOR pathway has been observed in canine malignant melanoma and may represent a potential target for therapy. Rapamycin (sirolimus) and everolimus are commercially available small molecule inhibitors that target mTOR and therefore may have anticancer activity in canine melanoma. It was hypothesized that there is synergism between rapamycin or everolimus and platinum chemotherapy, and that combination drug treatment would inhibit target/downstream proteins involved in cell viability/proliferation and increase cell death in canine melanoma cells. It was further hypothesized that rapamycin or everolimus would impact metabolism by reducing glycolysis in these cells. Four canine melanoma cell lines were treated in vitro with rapamycin and everolimus as sole treatment or combined with carboplatin. Cell viability, apoptosis, target modulation, and glycolytic metabolism were evaluated by crystal violet colourimetric assay, Annexin V/PI flow cytometry, western blotting, and Seahorse bioanalyzer, respectively.

Results

When combined with carboplatin chemotherapy, rapamycin or everolimus treatment was overall synergistic in reducing cell viability. Carboplatin-induced apoptosis was noted at 72 h after treatment compared to the vehicle control. Levels of phosphorylated mTOR were reduced by rapamycin and everolimus in all four cell lines, but activation of the downstream protein p70S6K was not consistently reduced by treatment in two of the cell lines. Both mTOR inhibitors decreased the extracellular acidification rate of canine melanoma cells, indicating reduced cancer cell glycolytic activity.

Conclusions

Inhibition of mTOR by rapalogs, such as rapamycin and everolimus combined with carboplatin chemotherapy may have activity in canine melanoma. Future mechanistic investigation is warranted, including in vivo assessment of this combination therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03089-0.

Single-dose pharmacokinetics of mycophenolic acid following administration of immediate-release mycophenolate mofetil in healthy Beagle dogs

Mycophenolic acid (MPA) is an immunomodulating agent commonly used in human medicine for the treatment of immune-mediated diseases. There is growing evidence that the immunomodulating properties of mycophenolate mofetil (MMF), a prodrug of MPA, are therapeutically beneficial for the treatment of immune-mediated diseases in dogs. A narrow therapeutic index and high inter-and intra-patient pharmacokinetic (PK) variability complicate the use of MMF. A better characterization of MPA pharmacokinetics is needed to help establish dosing regimens and standardized treatment protocols for canine patients. The purpose of this study was to evaluate the pharmacokinetics of MPA in dogs. MMF oral suspension (10 mg/kg) was administered to five healthy beagle dogs. Serial blood samples were collected from 0 to 18 hours after administration. The simultaneous quantification of MPA, and its metabolites MPA-7-O-glucuronide (MPAG), and acyl glucuronide (AcMPAG) was determined by liquid chromatography (LC)-mass spectrometry (MS)/MS. MPA peak concentrations were achieved rapidly (median Tmax of 0.5 h). Concentrations fell through 3 hours post-dose and then plateaued around 20% of Cmax. The mean elimination half-life was rapid (5.8 hours) and notable variability was observed in all PK parameters. The PK profiles for the MPAG and AcMPAG metabolites followed a similar pattern as MPA concentration. Future repeat-dose studies will be needed to evaluate steady-state PK parameters and to define therapeutic MPA dose levels.

Mycophenolic acid in patients with immune-mediated inflammatory diseases: From humans to dogs

Mycophenolic acid (MPA), a noncompetitive, selective and reversible inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH), is an immunosuppressive agent that has a long history in medicine. Mechanistically, the inhibition of IMPDH leads to the selective and eventual arrest of T- and B-lymphocyte proliferation. Mycophenolate mofetil (MMF), the first MPA-based product to receive marketing approval over two decades ago, was originally indicated for the prophylaxis of organ rejection in human transplant patients. Given its broad immunosuppressive properties and ability to selectively inhibit lymphocyte division and effector functions, the clinical utility of MPA was subsequently explored in a host of autoimmune diseases. Human clinical studies have shown MPA to be safe and effective and support its off-label administration for immune-mediated diseases such as lupus, myasthenia gravis and atopic dermatitis. MMF became generically available in the United States in 2008, and its clinical utility is increasingly being explored as a treatment option for dogs with immune-mediated diseases. This review summarizes the available literature for MPA pharmacokinetics and pharmacodynamics, and the current status of MPA as a treatment for client-owned dogs diagnosed with immune-mediated diseases.

Ex vivo binding of the immunosuppressant mycophenolic acid to dog and cat plasma proteins and the effect of co-incubated dexamethasone and prednisolone

Mycophenolic acid (MPA) has been shown to be promising for the treatment of autoimmune diseases in dogs and cats. In humans, MPA is highly bound to plasma proteins (~97%). It has been recommended to monitor free drug plasma concentrations because the free MPA correlates with its immunosuppressive effect. However, it is unknown if MPA is highly bound to plasma proteins in dogs and cats. The objectives of this study were to determine the extent of plasma protein binding of MPA and evaluate the effect of prednisolone and dexamethasone on the extent of protein binding of MPA in dogs and cats. The extent of plasma protein binding of MPA was determined in plasma collected from clinically healthy adult cats (n = 13) and dogs (n = 14) by combining high-throughput dialysis and ultra-high-liquid chromatography. This study reveals that MPA is highly bound to plasma proteins (>90%) in dogs and cats, mean extent of binding of MPA at 15 μg/ml to plasma proteins being 96% (range, 95%-97%) and 92% (range, 90%-93%) for dogs and cats, respectively. In dog plasma, MPA is primarily bound to albumin. In vitro, prednisolone increased the unbound MPA in dogs (p < .01) but not in cats (p = .07) while dexamethasone had no effect on MPA plasma binding in either species (p > .05). Results of this study provide valuable information for designing future pharmacokinetic and pharmacodynamic studies and also therapeutic monitoring programs for dogs and cats.

New perspectives on the use of mTOR inhibitors in allogeneic haematopoietic stem cell transplantation and graft-versus-host disease

Inhibition of the mechanistic target of rapamycin (mTOR) has been exploited largely both in solid tumour oncology and solid organ transplantation. More recently mTOR inhibitors such as sirolimus and everolimus have been introduced to the field of allogeneic haematopoietic stem cell transplantation where their unique combination of immunosuppressive purposes offering reduced nephrotoxicity and potential antimalignant effects reflect a unique drug profile that has led to their widespread use in both prophylaxis and therapy of graft-versus-host disease (GVHD). On the other hand haematological insufficiency, infectious complications as well as vasculopathies, have been frequently reported as limiting toxicities. Here, we review both the retrospective and prospective experience available to date and stress the need for prospective registration trials to reduce off label use and improve patient safety by optimizing dosing and enhancing pharmacovigilance. Furthermore, we speculate on the future role of mTOR inhibitors in allogeneic haematopoietic stem cell transplantation.

Rapamycin: An InhibiTOR of Aging Emerges From the Soil of Easter Island

Rapamycin (sirolimus) is a macrolide immunosuppressant that inhibits the mechanistic target of rapamycin (mTOR) protein kinase and extends lifespan in model organisms including mice. Although rapamycin is an FDA-approved drug for select indications, a diverse set of negative side effects may preclude its wide-scale deployment as an antiaging therapy. mTOR forms two different protein complexes, mTORC1 and mTORC2; the former is acutely sensitive to rapamycin whereas the latter is only chronically sensitive to rapamycin in vivo. Over the past decade, it has become clear that although genetic and pharmacological inhibition of mTORC1 extends lifespan and delays aging, inhibition of mTORC2 has negative effects on mammalian health and longevity and is responsible for many of the negative side effects of rapamycin. In this review, we discuss recent advances in understanding the molecular and physiological effects of rapamycin treatment, and we discuss how the use of alternative rapamycin treatment regimens or rapamycin analogs has the potential to mitigate the deleterious side effects of rapamycin treatment by more specifically targeting mTORC1. Although the side effects of rapamycin are still of significant concern, rapid progress is being made in realizing the revolutionary potential of rapamycin-based therapies for the treatment of diseases of aging.