sirolimus and Psoriasis

The dysregulated phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway has been implicated in various immune-mediated inflammatory and hyperproliferative dermatoses such as acne, atopic dermatitis, alopecia, psoriasis, wounds, and vitiligo, and is associated with poor treatment outcomes. Improved comprehension of the consequences of the dysregulated PI3K/Akt/mTOR pathway in patients with inflammatory dermatoses has resulted in the development of novel therapeutic approaches. Nonetheless, more studies are necessary to validate the regulatory role of this pathway and to create more effective preventive and treatment methods for a wide range of inflammatory skin diseases. Several studies have revealed that certain natural products and synthetic compounds can obstruct the expression/activity of PI3K/Akt/mTOR, underscoring their potential in managing common and persistent skin inflammatory disorders. This review summarizes recent advances in understanding the role of the activated PI3K/Akt/mTOR pathway and associated components in immune-mediated inflammatory dermatoses and discusses the potential of bioactive natural products, synthetic scaffolds, and biologic agents in their prevention and treatment. However, further research is necessary to validate the regulatory role of this pathway and develop more effective therapies for inflammatory skin disorders.

Topics: Biological Products; Dermatitis; Humans; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Psoriasis; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The field of pediatric dermatology treatment has been rich in new developments. Several recent therapeutic advances in pediatric dermatology have been made. This review will focus on critical approach to the new treatments for several entities encountered in pediatric dermatology. The use of biologics and small molecules in children with atopic dermatitis and psoriasis, exciting advances in the use of propranolol and other beta-blockers for the treatment of infantile hemangiomas, the use of sirolimus for vascular anomalies will be discussed.

Topics: Adrenergic beta-Antagonists; Biological Products; Child; Dermatitis, Atopic; Hemangioma; Humans; Phosphodiesterase 4 Inhibitors; Psoriasis; Sirolimus; Skin Diseases

Systemic mammalian target of rapamycin (mTOR) inhibitors are currently used in many dermatologic indications. Their topical use is recent and poorly codified.. To provide an overview of the topical use of mTOR inhibitors in dermatologic conditions and evaluate their efficacy and safety.. A literature search was performed in January 2017. Reports of all studies investigating the use of topical mTOR inhibitors in any dermatology diseases were included. The exclusion criteria were systemic use and mucosal administration.. We included 40 studies with a total of 262 patients. In all, 11 dermatologic conditions were found, the most frequent being angiofibromas linked to tuberous sclerosis complex (157 patients). Topical mTOR inhibitors were significantly more efficient than placebo for angiofibromas (relative risk, 2.52; 95% confidence interval, 1.27-5.00; I. High heterogeneity in most studies.. This systematic review supports the efficacy of topical sirolimus for angiofibromas linked to tuberous sclerosis complex, with only local side effects reported. Other indications require further research.

Topics: Administration, Cutaneous; Angiofibroma; Antibiotics, Antineoplastic; Humans; Port-Wine Stain; Psoriasis; Sirolimus; Skin Neoplasms; TOR Serine-Threonine Kinases; Tuberous Sclerosis

Psoriasis is an immune-mediated disease with a chronic relapsing course, and the particularly severe forms that are refractory to traditional therapies are often difficult to manage. Everolimus (Certican; Novartis, Basel, Switzerland) is a new rapamycin-derived macrolide that is used in the prophylaxis of rejection in heart and kidney transplant patients. The mechanism underlying its immunosuppressant and antiproliferative activity is different from, but complementary to, that of calcineurin inhibitors such as ciclosporin. We describe a woman with severe psoriasis treated with everolimus combined with subtherapeutic doses of ciclosporin.

Topics: Cyclosporine; Drug Synergism; Drug Therapy, Combination; Everolimus; Female; Humans; Immunosuppressive Agents; Middle Aged; Psoriasis; Sirolimus; Treatment Outcome

Discovered in fungi in the remote Easter Island, sirolimus (rapamycin) shows potential beyond its obvious antiproliferative and immunosuppressant activity. Studies have demonstrated that sirolimus acts as a vascular endothelial growth factor inhibitor, providing prospective therapeutic benefits and possible prevention of tuberous sclerosis and Kaposi's sarcoma. Its ability to decrease keratinocyte proliferation may help patients with psoriasis. In those with tuberous sclerosis complex, it may prevent the development of hamartomas and reduce or eliminate them once grown by blocking the mammalian target of rapamycin, a critical regulatory kinase. A great advantage for this drug is in the decreased risk of malignancies, including Kaposi's sarcoma, associated with its use compared with other immunosuppressants, namely calcineurin inhibitors. This review will focus on the pharmacology and potential uses of sirolimus.

Topics: Animals; Humans; Immunosuppressive Agents; Psoriasis; Sarcoma, Kaposi; Sirolimus; Skin Neoplasms

Although superpotent topical corticosteroids are the first-line treatment for oral erosive lichen planus (OELP), topical rapamycin was found efficient in a previous case series.. To compare the efficacy and safety of topical rapamycin and betamethasone dipropionate ointment for OELP in a randomized, double-blind trial.. During a 4-year period, 76 patients were randomized and 75 received treatment (rapamycin, n = 39; betamethasone, n = 36). At 3 months, 39.4% of patients with betamethasone and 27.3% with rapamycin showed clinical remission (odds ratio 0.68, 95% CI [0.24; 1.89]; P = 0.46). Rates of remission after 1 and 2 months, reduction in pain and impact on food intake after 3 months, were higher with betamethasone than rapamycin. Recurrence of oral erosions was similar between groups. Adverse events occurred in 43.6% of patients with rapamycin (mostly burning sensation, impaired taste) and 27.8% with betamethasone (mostly oral candidiasis).. Although the study was limited by insufficient recruitment, we did not find any superiority of topical rapamycin over betamethasone dipropionate ointment for OELP. Given the rapid remission and pain improvement in the betamethasone group, it appears that superpotent topical corticosteroids should remain the first-line treatment for OELP.

Topics: Administration, Topical; Betamethasone; Double-Blind Method; Humans; Lichen Planus, Oral; Neoplasm Recurrence, Local; Ointments; Psoriasis; Sirolimus; Treatment Outcome

Systemically administered sirolimus has demonstrated efficacy in psoriasis in a multicentre European study.. To determine the efficacy and safety of topically applied sirolimus in treating psoriasis.. In vitro studies were followed by a pilot study designed to determine if sirolimus penetrates human skin, and by a randomized, double-blind, left-right comparative, dose-ranging study consisting of treatment with 2.2% sirolimus for 6 weeks and 8% sirolimus for an additional 6 weeks in 24 patients with stable, chronic plaque psoriasis. The primary outcome measure was clinical score. Secondary measures were ultrasound plaque thickness, plaque erythema, and computerized image analysis of immunohistochemical stains for immunocytes and proliferating cells. Pharmacokinetics and blood chemistry monitoring for safety were also performed.. A significant reduction in the clinical score (P = 0.03) (mean score 9.1 following sirolimus vs. 11.2 in control) was achieved with topical sirolimus. Measurements of plaque thickness and erythema did not show significant improvement with treatment. Computerized image analysis of biopsies showed a significant reduction in CD4+ cells (P = 0.0054) and proliferating cells (stained by Ki-67) in the epidermis (P = 0.0153) with sirolimus treatment compared with control.. Topically applied sirolimus penetrates normal skin and may have some antipsoriatic and immunosuppressive activity.

Topics: Administration, Topical; Adult; Aged; Double-Blind Method; Drug Administration Schedule; Female; Humans; Immunohistochemistry; Immunosuppressive Agents; Male; Middle Aged; Pilot Projects; Psoriasis; Sirolimus; Skin; Treatment Outcome

The identification of a highly potent immunosuppressive/antiproliferative agent with an acceptable toxicity profile has long been a goal for the management of severe plaque psoriasis.. To investigate the efficacy and safety of sirolimus (Rapamune) for severe psoriasis when given alone or in association with cyclosporin.. In a randomized, double-blind, eight parallel group, pilot study in 24 out-patient centres in seven European countries, 150 patients, 18 years and older, with severe chronic plaque psoriasis were given sirolimus 0.5, 1.5 and 3.0 mg m(-2) daily for 8 weeks, either alone or in association with a subtherapeutic dose of cyclosporin (1.25 mg kg(-1) daily). Cyclosporin 5 mg kg(-1) daily was the positive control and cyclosporin 1.25 mg kg(-1) daily the negative control. The primary efficacy variable was the mean percentage reduction in Psoriasis Area and Severity Index (PASI). Safety assessments included monitoring of adverse events, clinical laboratory parameters and sirolimus/cyclosporin blood concentrations.. The greatest mean percentage decreases in PASI were seen with cyclosporin 5.0 mg kg(-1) daily (70.5%) and with sirolimus 3.0 mg m(-2) daily + cyclosporin 1.25 mg kg(-1) daily (63.7%). Both groups demonstrated significantly better results than cyclosporin 1.25 mg kg(-1) daily (mean decrease 33.4%). Serum creatinine levels were significantly lower for groups with sirolimus alone and sirolimus plus reduced-dose cyclosporin when compared with cyclosporin 5.0 mg kg(-1) daily. Adverse events associated with sirolimus included thrombocytopenia (5%), hyperlipidaemia (9%), aphthous stomatitis (9%) and acne (13%), whereas adverse events associated with cyclosporin included hot flushes (12%), hyperlipidaemia (9%) and increased serum creatinine (9%).. The concomitant administration of sirolimus with a subtherapeutic dose of cyclosporin in severe psoriasis may permit a reduction in their respective toxicities, notably cyclosporin-induced nephrotoxicity.

Topics: Adolescent; Adult; Aged; Cyclosporine; Dermatologic Agents; Dose-Response Relationship, Drug; Double-Blind Method; Drug Administration Schedule; Drug Therapy, Combination; Female; Humans; Immunosuppressive Agents; Male; Middle Aged; Pilot Projects; Psoriasis; Severity of Illness Index; Sirolimus; Treatment Outcome

Recently, the mTOR signaling has emerged as an important player in the pathogenesis of psoriasis. We previously found that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced psoriatic skin inflammation was related to the inhibition of autophagy in keratinocytes. However, the effects and detailed molecular mechanisms of the mTOR inhibitor rapamycin and TCDD on psoriasis in vivo remain to be elucidated. In this study, we aimed to evaluate the effects of rapamycin and TCDD on skin lesions in imiquimod (IMQ)-induced psoriasis using a mouse model. TCDD aggravated skin inflammation in an IMQ-induced psoriatic mouse model. Furthermore, TCDD increased the expression of aryl hydrocarbon receptor (AHR), CYP1A1, proinflammatory cytokines, oxidative stress markers (NADPH oxidase (Nox) 2, Nox4), and phosphorylated P65NF-ĸB, whereas the expression of autophagy-related factors and the antioxidant marker nuclear factor-erythroid 2-related factor 2 (NRF2) decreased. Rapamycin reduced the aggravated skin inflammation induced by TCDD and restored TCDD-induced autophagy suppression and the increase of AHR expression, oxidative stress, and inflammatory response in the skin lesions of a psoriatic mouse model. In conclusion, we demonstrated that rapamycin alleviates TCDD-induced aggravated dermatitis in mice with imiquimod-induced psoriasis-like dermatitis through AHR and autophagy modulation.

Topics: Animals; Autophagy; Cell Differentiation; Cells, Cultured; Cytochrome P-450 CYP1A1; Dermatitis; Gene Expression Regulation; Humans; Imiquimod; Inflammation; Keratinocytes; Mice; NADPH Oxidase 4; NF-E2-Related Factor 2; Polychlorinated Dibenzodioxins; Psoriasis; Receptors, Aryl Hydrocarbon; Sirolimus

Psoriasis is a chronic inflammatory disease, affecting more than millions of people in the world. Recently, the mTOR inhibitor rapamycin (RAPA) was reported to be involved in the pathogenesis of psoriasis. However, the underlying mechanism remains unclear. Haematoxylin and eosin staining was used to examine the effects of RAPA on inflammatory level of lesional tissues from patients with psoriasis and animal models. Quantitative real-time PCR, immunohistochemistry and western blot assay were performed to assess the effects of RAPA on tropomyosins (TPMs) expression in patients with psoriasis, cell models and animal models. Phalloidin staining was used to assess the RAPA effects on cell skeleton. The effects of RAPA on cell proliferation and cell cycle were detected by CCK-8 assay, EdU staining and flow cytometry. Methylation status of TPMs was analysed by methylation-specific PCR. The expression of TPM1 and TPM2 was significantly downregulated, while their methylation level was obviously higher in the lesional tissues, cell models and animal models of psoriasis. After treated with RAPA, the expression and methylation levels of TPMs were all restored in the cell models and animal models of psoriasis. RAPA inhibited cell proliferation and decreased the ratio of S phase cell in Hacat or human epidermal keratinocytes cell models of psoriasis. Finally, the activated ERK1/2 and mTOR pathways in the cell model and animal model of psoriasis were suppressed by the treatment of RAPA. RAPA could be used as an effective agent for the treatment of psoriasis by decreasing the methylation level of TPM1 and TPM2 via inhibiting the ERK1/2 and mTOR signalling pathways.

Topics: Animals; Cell Proliferation; Cytoskeleton; Down-Regulation; Female; Gene Expression; HEK293 Cells; Humans; Imiquimod; Immunosuppressive Agents; Keratinocytes; Male; MAP Kinase Signaling System; Methylation; Mice; Psoriasis; S Phase Cell Cycle Checkpoints; Sirolimus; TOR Serine-Threonine Kinases; Tropomyosin

The mTOR (mechanistic target of rapamycin) inhibitor rapamycin has long been known for its immune suppressive properties, but it has shown limited therapeutic success when given systemically to patients with psoriasis. Recent data have shown that the mTOR pathway is hyperactivated in lesional psoriatic skin, which probably contributes to the disease by interfering with maturation of keratinocytes. This study investigated the effect of topical rapamycin treatment in an imiquimod-induced psoriatic mouse model. The disease was less severe if the mice had received rapamycin treatment. Immunohistological analysis revealed that rapamycin not only prevented the activation of mTOR signalling (P-mTOR and P-S6 levels), but almost normalized the expression of epidermal differentiation markers. In addition, the influx of innate immune cells into the draining lymph nodes was partially reduced by rapamycin treatment. These data emphasize the role of mTOR signalling in the pathogenesis of psoriasis, and support the investigation of topical mTOR inhibition as a novel anti-psoriatic strategy.

Topics: Administration, Topical; Aminoquinolines; Animals; Caspase 14; Dendritic Cells; Disease Models, Animal; Imiquimod; Immunosuppressive Agents; Keratin-10; Keratin-14; Ki-67 Antigen; Langerhans Cells; Lymph Nodes; Macrophages; Membrane Proteins; Mice, Inbred BALB C; Neovascularization, Physiologic; Protein Precursors; Psoriasis; Sirolimus; Skin; TOR Serine-Threonine Kinases

Interleukin 22 (IL-22), a relatively new cytokine has been found to induce significant proliferation of human keratinocytes and fibroblast like synoviocytes (FLS) and thus plays an important role in the pathogenesis of autoimmune diseases like psoriasis and rheumatoid arthritis (RA) which are characterized by hyperproliferation of keratinocytes and FLS respectively. PI3K/Akt/mTOR signaling cascade plays crucial role in cell growth and survival. Therefore our objective was to see the regulatory role of PI3K/Akt/mTOR signaling cascade in IL-22 induced proliferation of keratinocytes and FLS.. Normal human epidermal keratinocytes (NHEK) and FLS were isolated from skin of healthy volunteer's undergone plastic surgery and synovial tissue of psoriatic arthritis (PsA) and RA patients respectively. IL-22 induced proliferation of NHEK and FLS was measured by MTT assay. Phosphorylation of Akt/mTOR was determined by western blot assay and further confirmed by real time polymerase chain reaction (RT-PCR).. We observed that IL-22 induced significant proliferation of NHEK and FLS which was effectively inhibited by dual kinase (PI3K/mTOR) inhibitor, NVP-BEZ235 and specific mTOR inhibitor, Rapamycin. In NHEK and FLS, IL-22 significantly induced phosphorylation of Akt and mTOR which was effectively blocked by Rapamycin and NVP-BEZ235. Further we did RT-PCR in NHEK and found that IL-22 significantly upregulated AKT1 and MTOR gene.. These results show that IL-22 induced proliferation of NHEK and FLS is dependent on PI3K/Akt/mTOR signaling pathway. This novel observation provides the scope to develop new therapeutics targeting PI3K/Akt/mTOR signaling pathway in autoimmune diseases like psoriasis and rheumatoid arthritis.

Topics: Arthritis; Arthritis, Rheumatoid; Blotting, Western; Cell Proliferation; Cells, Cultured; Fibroblasts; Humans; Imidazoles; Interleukin-22; Interleukins; Keratinocytes; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proto-Oncogene Proteins c-akt; Psoriasis; Quinolines; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Sirolimus; Synovial Membrane; TOR Serine-Threonine Kinases

The multifunctional cytokine tumor necrosis factor-alpha (TNF-alpha) is known to play an important role in inflammatory and immunological responses in human skin. Although it has been documented that reactive oxygen species (ROS) are involved in TNF-alpha-induced signaling pathways associated with certain inflammatory diseases, their role in TNF-alpha signaling cascades has not been examined in primary human keratinocytes used as a model of inflammatory skin disease and psoriasis. Employing a series of in vitro and in cellulo approaches, we have demonstrated that in primary human keratinocytes (i) TNF-alpha rapidly induces ROS generation, IkappaB degradation, NF-kappaB p65 nuclear translocation, and ultimately production of inflammatory cytokines; (ii) TNF-alpha-induced cytokine production is mediated both by the mammalian target of rapamycin signaling pathway via NF-kappaB activation and by ROS; (iii) TNF-alpha-dependent NF-kappaB activation (that is, IkappaB degradation and NF-kappaB p65 nuclear translocation) is not mediated by ROS; and (iv) a cell-penetrating derivative of the antioxidant enzyme, catalase, as well as taurine and N-acetyl-cysteine attenuate the TNF-alpha-induced production of cytokines. These latter results suggest that catalase and perhaps other antioxidants should be considered as part of a more specific and effective therapy for the treatment of inflammatory skin diseases, including psoriasis.

Topics: Acetylcysteine; Antioxidants; Catalase; Cells, Cultured; Free Radical Scavengers; Humans; Hydrogen Peroxide; I-kappa B Proteins; Interleukin-6; Interleukin-8; Keratinocytes; Male; Protein Kinases; Psoriasis; Reactive Oxygen Species; Signal Transduction; Sirolimus; Skin Diseases; Taurine; TOR Serine-Threonine Kinases; Transcription Factor RelA; Tumor Necrosis Factor-alpha

This case report describes the successful treatment of severe plaque psoriasis with etanercept in a patient who underwent a liver transplant. It also addresses the concerns that arise in the treatment of chronic inflammatory dermatologic disease accompanied by multiple organ disorders.

Topics: Anti-Inflammatory Agents, Non-Steroidal; Diabetes Mellitus, Type 1; Etanercept; Graft Rejection; Humans; Immunocompromised Host; Immunoglobulin G; Immunosuppressive Agents; Liver Transplantation; Male; Middle Aged; Psoriasis; Receptors, Tumor Necrosis Factor; Renal Insufficiency; Sirolimus; Tacrolimus

The immunosuppressive macrolides are a novel class of antiinflammatory substances, which could supplant glucocorticosteroids for the topical treatment of some chronic inflammatory skin diseases. Cyclosporine A (CyA), well known from transplantation medicine for years, is licensed in Germany for oral treatment of psoriasis and atopic dermatitis but is not suitable for topical therapy. Tacrolimus (FK506) penetrates the inflamed epidermis and is regarded as the key immunosuppressive macrolide. Clinical trials have demonstrated the efficacy of FK506 ointment for atopic dermatitis, many case reports have been published regarding other inflammatory skin diseases. The ascomycin derivative ASM 981 has many of the properties of FK506 but less data is available at present. Sirolimus (Rapamycin) is structurally related to FK506 but has other biological effects since its molecular actions involve different biochemical pathways. A review of the biochemical and cellular properties, mode of action, therapeutic efficacy and unwanted side effects, as well as data from clinical trials and status of licensing, is given for the respective drugs.

Topics: Administration, Topical; Clinical Trials as Topic; Cyclosporine; Dermatitis, Atopic; Humans; Immunosuppressive Agents; Psoriasis; Sirolimus; Tacrolimus

Sirolimus (formerly rapamycin) is an immunosuppressive agent that interferes with T-cell activation. After 2 individuals with psoriasis developed a capillary leak syndrome following treatment with oral sirolimus lesional skin cells and activated peripheral blood cells were analyzed for induction of apoptosis.. A keratome skin specimen from 1 patient with sirolimus-induced capillary leak syndrome had a 2.3-fold increase in percentage of apoptotic cells (to 48%) compared with an unaffected sirolimus-treated patient with psoriasis (21%). Activated peripheral blood T cells from patients with psoriasis tended to exhibit greater spontaneous or dexamethasone-induced apoptosis than did normal T cells, particularly in the presence of sirolimus.. Severe adverse effects of sirolimus include fever, anemia, and capillary leak syndrome. These symptoms may be the result of drug-induced apoptosis of lesional leukocytes, especially activated T lymphocytes, and possibly release of inflammatory mediators. Because patients with severe psoriasis may develop capillary leak from various systemic therapies, clinical monitoring is advisable for patients with inflammatory diseases who are treated with immune modulators.

Topics: Apoptosis; Capillary Leak Syndrome; Cell Count; Female; Humans; Immunosuppressive Agents; Lymphocytes; Male; Middle Aged; Psoriasis; Sirolimus

p70 Ribosomal protein S6 kinase is a critical down-stream effector of a mitogen-stimulated signaling pathway that is selectively inhibited by the immunosuppressant rapamycin. The purpose of this study was to quantify S6 kinase expression in psoriatic involved, uninvolved, and normal epidermis and to characterize regulation of S6 kinase activity in cultured normal human keratinocytes. S6 kinase activity was increased 4-fold in psoriatic lesions (1.63 +/- 0.25 pmol per min per mg, n = 6), compared to nonlesional (0.44 +/- 0.12 pmol per min per mg, n = 6, p < 0.01), and normal (0.35 +/- 0.14 pmol per min per mg, n = 7, p < 0.01) epidermis. In contrast, S6 kinase mRNA and protein levels were not significantly different among psoriatic lesional, nonlesional, and normal epidermis. In keratinocytes, S6 kinase activity was stimulated 3-fold by mitogenic epidermal growth factor (EGF) receptor ligands, EGF and transforming growth factor-alpha (TGF-alpha), but not by cytokines interleukin-1alpha, tumor necrosis factor-alpha, interferon-gamma, or transforming growth factor-beta1. TGF-alpha stimulation of S6 kinase activity was inhibited in a concentration-dependent manner by rapamycin (IC50 < 0.2 nM) and the specific EGF receptor antagonist PD153035 (IC50 = 20 nM). Rapamycin also inhibited EGF-stimulated proliferation of keratinocytes (IC50 = 0.2 ng per ml) with a potency similar to that reported for inhibition of T-cell proliferation. We conclude: (i) the mitogenic signaling pathway(s) regulating S6 kinase is activated in psoriatic lesions, thus accounting for increased S6 kinase activity in the absence of increased S6 kinase gene or protein expression; (ii) S6 kinase activation in lesional keratinocytes likely occurs in response to EGF receptor stimulation by TGF-alpha and/or amphiregulin, which are known to be elevated in psoriatic lesions; and (iii) keratinocyte as well as T-cell mitogenic signaling pathways are susceptible to inhibition by rapamycin, suggesting that rapamycin may be of therapeutic benefit in the treatment of psoriasis.

Topics: Adult; Cell Division; Cells, Cultured; Enzyme Activation; Epidermal Growth Factor; ErbB Receptors; Humans; Immunosuppressive Agents; Keratinocytes; Polyenes; Protein Serine-Threonine Kinases; Psoriasis; Ribosomal Protein S6 Kinases; RNA, Messenger; Sirolimus; Skin; Transforming Growth Factor alpha

Because the immunosuppressant rapamycin (sirolimus) blocks T cell proliferation in G1 phase, it has been proposed as a potential treatment for psoriasis, a skin disease characterized by T cell activation and keratinocyte stem cell hyperproliferation. To determine another potentially important mechanism through which rapamycin can act as an antipsoriatic agent, we tested its direct effect on keratinocyte stem cell proliferation in vitro as well as in vivo. In vivo cell cycle quiescent (G0 phase) stem cell keratinocytes in primary culture sequentially express de novo cyclin D1 and proliferating cell nuclear antigen (PCNA), prior to S phase entry, and upregulate beta1 integrin. Rapamycin inhibited the growth of keratinocytes that were leaving quiescence as well as those already in cell cycle without affecting cell viability. Although beta1 integrin(bright) expression was not affected, the number of beta1 integrin(bright) cells entering S/G2/M was significantly lowered by rapamycin. Cells treated with rapamycin exhibited decreased PCNA expression while cyclin D1 expression, which precedes PCNA expression in the cell cycle, was not affected. We found similar effects on stem cell keratinocytes in patients with psoriasis treated systemically with rapamycin. Because PCNA is required for cell cycle progression from G1 to S phase, our data indicate that inhibition of PCNA protein synthesis may be an important regulatory element in the ability of rapamycin to exert a G1 block.

Topics: Cells, Cultured; Cyclin D1; Cyclins; Flow Cytometry; G1 Phase; Humans; Immunosuppressive Agents; Integrins; Keratinocytes; Oncogene Proteins; Polyenes; Proliferating Cell Nuclear Antigen; Psoriasis; Resting Phase, Cell Cycle; S Phase; Sirolimus; Stem Cells; Up-Regulation