Sirolimus (rapamycin) in clinical transplantation

Exploiting immunometabolism and T cell function for solid organ transplantation

Cellular metabolism is central to T cell function and proliferation, with most of the research to date focusing on cancer and autoimmunity. Cellular metabolism is associated with a host of physiological phenomena, from epigenetic changes, to cellular function and fate. For the purpose of this review, we will discuss the metabolism of T cells relating to their differentiation and function. We will cover a variety of metabolic processes, ranging from glycolysis to amino acid metabolism. Understanding how T cell metabolism informs T cell function may be useful to understand alloimmune responses and design novel therapies to improve graft outcome.

An overview of rapamycin: from discovery to future perspectives

Rapamycin is an immunosuppressive metabolite produced from several actinomycete species. Besides its immunosuppressive activity, rapamycin and its analogs have additional therapeutic potentials, including antifungal, antitumor, neuroprotective/neuroregenerative, and lifespan extension activities. The core structure of rapamycin is derived from (4R,5R)-4,5-dihydrocyclohex-1-ene-carboxylic acid that is extended by polyketide synthase. The resulting linear polyketide chain is cyclized by incorporating pipecolate and further decorated by post-PKS modification enzymes. Herein, we review the discovery and biological activities of rapamycin as well as its mechanism of action, mechanistic target, biosynthesis, and regulation. In addition, we introduce the many efforts directed at enhancing the production of rapamycin and generating diverse analogs and also explore future perspectives in rapamycin research. This review will also emphasize the remarkable pilot studies on the biosynthesis and production improvement of rapamycin by Dr. Demain, one of the world's distinguished scientists in industrial microbiology and biotechnology.

Targeting AMPK for the Alleviation of Pathological Pain

Chronic pain is a major clinical problem that is poorly treated with available therapeutics. Adenosine monophosphate-activated protein kinase (AMPK) has recently emerged as a novel target for the treatment of pain with the exciting potential for disease modification. AMPK activators inhibit signaling pathways that are known to promote changes in the function and phenotype of peripheral nociceptive neurons and promote chronic pain. AMPK activators also reduce the excitability of these cells suggesting that AMPK activators may be efficacious for the treatment of chronic pain disorders, like neuropathic pain, where changes in the excitability of nociceptors is thought to be an underlying cause. In agreement with this, AMPK activators have now been shown to alleviate pain in a broad variety of preclinical pain models indicating that this mechanism might be engaged for the treatment of many types of pain in the clinic. A key feature of the effect of AMPK activators in these models is that they can lead to a long-lasting reversal of pain hypersensitivity even long after treatment cessation, indicative of disease modification. Here, we review the evidence supporting AMPK as a novel pain target pointing out opportunities for further discovery that are likely to have an impact on drug discovery efforts centered around potent and specific allosteric activators of AMPK for chronic pain treatment.

mTORC1 inhibition induces pain via IRS-1-dependent feedback activation of ERK

Mammalian target of rapamycin complex 1 (mTORC1) inhibitors are extensively used as immunosuppressants to prevent transplant rejection and in treatment of certain cancers. In patients, chronic treatment with rapamycin or its analogues (rapalogues) has been reported to lead to sensory hypersensitivity and pain conditions via an unknown mechanism. Here, we show that pharmacological or genetic inhibition of mTORC1 activates the extracellular signal-regulated kinase (ERK) pathway in sensory neurons via suppression of S6K1 to insulin receptor substrate 1 negative feedback loop. As a result, increased ERK activity induces sensory neuron sensitization, mechanical hypersensitivity, and spontaneous pain. The clinically available adenosine monophosphate-activated protein kinase activator, metformin, which is an antidiabetic drug, prevents rapamycin-induced ERK activation and the development of mechanical hypersensitivity and spontaneous pain. Taken together, our findings demonstrate that activation of the ERK pathway in sensory neurons as a consequence of mTORC1 inhibition leads to the development of pain. Importantly, this effect is abolished by co-treatment with metformin, thus providing a potential treatment option for rapalogue-evoked pain. Our findings highlight the physiological relevance of feedback signaling through mTORC1 inhibition and have important implications for development of pain therapeutics that target the mTOR pathway.

Biosynthesis of rapamycin and its regulation: past achievements and recent progress

Rapamycin and its analogs are clinically important macrolide compounds produced by Streptomyces hygroscopicus. They exhibit antifungal, immunosuppressive, antitumor, neuroprotective and antiaging activities. The core macrolactone ring of rapamycin is biosynthesized by hybrid type I modular polyketide synthase (PKS)/nonribosomal peptide synthetase systems primed with 4,5-dihydrocyclohex-1-ene-carboxylic acid. The linear polyketide chain is condensed with pipecolate by peptide synthetase, followed by cyclization to form the macrolide ring and modified by a series of post-PKS tailoring steps. The aim of this review was to outline past and recent advances in the biosynthesis and regulation of rapamycin, with an emphasis on the distinguished contributions of Professor Demain to the study of rapamycin. In addition, this article describes the biological activities as well as mechanism of action of rapamycin and its derivatives. Recent attempts to improve the productivity of rapamycin and generate diverse rapamycin analogs through mutasynthesis and mutagenesis are also introduced, along with some future perspectives.

Gingival status of Brazilian renal transplant recipients under sirolimus-based regimens

BACKGROUND

Although the prevalence of gingival overgrowth (GO) in calcineurin-inhibitor (CNI) immunosuppressive regimens has been well documented, to the best of our knowledge data from sirolimus (SIR) regimens have not been described. We sought to investigate the gingival status of renal transplant recipients under SIR-based regimens with regard to the prevalence and potential risk variables associated with GO.

METHODS

A cross-sectional study was conducted at a public hospital in Belo Horizonte, MG, Brazil. Of 886 transplant recipients, an eligible sample of 144 subjects was selected. Medical, pharmacologic, and periodontal variables were recorded for each subject. GO was assessed through visual inspection and was evaluated in relation to variables of interest by univariate and multivariate analyses.

RESULTS

Although not clinically significant, 20.8% of the samples had GO, with a mean GO score of 5.0% +/- 3.98% (range, 0% to 19%) and mean GO score per papilla of 0.378 +/- 0.361 (range, 0.1 to 1.9); the percentage of papilla affected by GO was 14.35% +/- 9.86% (range, 5% to 45%). The multivariate final model, excluding periodontal variables, showed that the concomitant use of calcium channel blockers (P = 0.033) and the interaction between time since transplant and previous CNI use (P <0.001) were associated with GO. Adding periodontal variables to the model improved its accuracy and retained papillary bleeding index as being strongly associated with GO (P <0.001).

CONCLUSIONS

GO was observed in a considerable number of subjects under SIR-based immunosuppressive regimens, although the relationship was not clinically significant. Findings point to the importance of cooperation between medical and dental health care personnel in the maintenance of renal transplant recipients under SIR-based immunosuppressive regimens.

Reversal of tacrolimus-related hypertrophic cardiomyopathy after conversion to rapamycin in a pediatric liver transplant recipient

Tacrolimus (Tac)-related hypertrophic cardiomyopathy (HCM) has been reported to be an unusual but serious complication affecting pediatric patients after solid organ transplantation. Herein, we present a case of young liver transplant recipient with Tac-induced HCM, treated by discontinuation of Tac followed by conversion to rapamycin (Rap). Our case report points out the potential but rather low risk of HCM during Tac immunosuppression in pediatric liver transplants and demonstrates that replacement of calcineurin inhibitors with mammalian target of Rap (mTOR) inhibitors may be an efficacious therapeutic tool to effect regression of established cardiac hypertrophy.

Rapamycin at subimmunosuppressive levels inhibits mesangial cell proliferation and extracellular matrix production

In view of its proven antiproliferative effects, rapamycin offers potential in the treatment of mesangioproliferative disease. Previous data have shown an effect of rapamycin on mesangial cell proliferation at high doses and have not explored the mechanism of action. Therefore, we explored the effects and mechanism of action of low levels of rapamycin on mesangial cell proliferation. Primary cultures of mouse mesangial cells were grown in medium containing serum with differing concentrations of rapamycin. A rapamycin concentration of 0.1 ng/ml caused a decrease in cell number and DNA synthesis with no effect on apoptosis. Type IV collagen protein production was inhibited at 0.01 ng/ml rapamycin, although gene expression was unaffected. P70S6K phosphorylation was inhibited in parallel with the effects on cell number and DNA synthesis in a dose-dependent manner, but no effect was seen at 0.01 ng/ml rapamycin. These data show an effect on mesangial cell proliferation and p70S6 kinase phosphorylation of 0.1 ng/ml rapamycin and an effect on collagen IV production of 0.01 ng/ml rapamycin. We suggest that further in vivo studies should explore the potential for low-dose rapamycin in the treatment of mesangioproliferative glomerulonephritis.

Immunosuppression in pediatric solid organ transplantation: opportunities, risks, and management

The pediatric transplant community stands at a time of unprecedented choice of immunosuppressive agents - and with a legacy of morbidity from those agents used in the previous two decades. This review considers the clinical utility and side-effect profiles of immunosuppressants used widely in current practice (e.g., glucocorticoids, azathioprine, ciclosporin, tacrolimus, mycophenolate, and sirolimus) and those agents which are in increasing use or in evaluation (e.g., IL-2 receptor antibodies, everolimus, FTY720, LEA29Y, and deoxyspergualin). Further consideration is given to the wider drug interactions likely during the use of new immunosuppressant regimens and to our growing awareness of the influences of genetic heterogeneity on drug efficacy and handling. Finally, we consider the new demands being placed on the use of drug monitoring to regulate dosage of this new repertoire of immunosuppressants.