Sotrastaurin, a novel small molecule inhibiting protein kinase C: first clinical results in renal-transplant recipients

Long-Term Outcome after Early Mammalian Target of Rapamycin Inhibitor-Based Immunosuppression in Kidney Transplant Recipients

Background: The use of mammalian target of rapamycin inhibitors (mTORis) in kidney transplantation increases the risk of donor-specific human leukocyte antigen (HLA) antibody formation and rejection. Here, we investigated the long-term consequences of early mTORi treatment compared to calcineurin inhibitor (CNI) treatment. Methods: In this retrospective single-center analysis, key outcome parameters were compared between patients participating in randomized controlled immunosuppression trials between 1998 and 2011, with complete follow-up until 2018. The outcomes of eligible patients on a CNI-based regimen (n = 384) were compared with those of patients randomized to a CNI-free mTORi-based regimen (n = 81) and 76 patients randomized to a combination of CNI and mTORi treatments. All data were analyzed according to the intention-to-treat (ITT) principle. Results: Deviation from randomized immunosuppression for clinical reasons occurred significantly more often and much earlier in both mTORi-containing regimens than in the CNI treatment. Overall patient survival, graft survival, and death-censored graft survival did not differ between the treatment groups. Donor-specific HLA antibody formation and BPARs were significantly more common in both mTORi regimens than in the CNI-based immunosuppression. Conclusions: The tolerability and efficacy of the mTORi treatment in kidney graft recipients are inferior to those of CNI-based immunosuppression, while the long-term patient and graft survival rates were similar.

Protein Kinase C Inhibitors Reduce SARS-CoV-2 Replication in Cultured Cells

Infection by severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has posed a severe threat to global public health. The current study revealed that several inhibitors of protein kinases C (PKCs) possess protective activity against SARS-CoV-2 infection. Four pan-PKC inhibitors, Go 6983, bisindolylmaleimide I, enzastaurin, and sotrastaurin, reduced the replication of a SARS-CoV-2 replicon in both BHK-21 and Huh7 cells. A PKCδ-specific inhibitor, rottlerin, was also effective in reducing viral infection. The PKC inhibitors acted at an early step of SARS-CoV-2 infection. Finally, PKC inhibitors blocked the replication of wild-type SARS-CoV-2 in ACE2-expressing A549 cells. Our work highlights the importance of the PKC signaling pathway in infection by SARS-CoV-2 and provides evidence that PKC-specific inhibitors are potential therapeutic agents against SARS-CoV-2. IMPORTANCE There is an urgent need for effective therapeutic drugs to control the pandemic caused by severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2). We found that several inhibitors of protein kinases C (PKCs) dramatically decrease the replication of SARS-CoV-2 in cultured cells. These PKC inhibitors interfere with an early step of viral infection. Therefore, the rapid and prominent antiviral effect of PKC inhibitors underscores that they are promising antiviral agents and suggests that PKCs are important host factors involved in infection by SARS-CoV-2.

Protein kinase C theta (Prkcq) affects nerve degeneration and regeneration through the c-fos and c-jun pathways in injured rat sciatic nerves

BACKGROUND

Previous finding using DNA microarray and bioinformatics analysis, we have reported some key factors which regulated gene expression and signaling pathways in injured sciatic nerve during Wallerian Degeneration (WD). This research is focused on protein kinase C theta (Prkcq) participates in the regulation of the WD process.

METHODS

In this study, we explored the molecular mechanism by which Prkcq in Schwann cells (SCs) affects nerve degeneration and regeneration in vivo and in vitro after rat sciatic nerve injury.

RESULTS

Study of the cross-sectional model showed that Prkcq expression decreased significantly during sciatic nerve repair. Functional analysis showed that upregulation and downregulation of Prkcq could affect the proliferation, migration and apoptosis of Schwann cells and lead to the expression of related factors through the activation of the β-catenin, c-fos, and p-c-jun/c-jun pathways.

CONCLUSION

The study provides insights into the role of Prkcq in early WD during peripheral nerve degeneration and/or regeneration.

Key driver genes as potential therapeutic targets in renal allograft rejection

Acute rejection (AR) in renal transplantation is an established risk factor for reduced allograft survival. Molecules with regulatory control among immune pathways of AR that are inadequately suppressed, despite standard-of-care immunosuppression, could serve as important targets for therapeutic manipulation to prevent rejection. Here, an integrative, network-based computational strategy incorporating gene expression and genotype data of human renal allograft biopsy tissue was applied, to identify the master regulators - the key driver genes (KDGs) - within dysregulated AR pathways. A 982-meta-gene signature with differential expression in AR versus non-AR was identified from a meta-analysis of microarray data from 735 human kidney allograft biopsy samples across 7 data sets. Fourteen KDGs were derived from this signature. Interrogation of 2 publicly available databases identified compounds with predicted efficacy against individual KDGs or a key driver-based gene set, respectively, which could be repurposed for AR prevention. Minocycline, a tetracycline antibiotic, was chosen for experimental validation in a murine cardiac allograft model of AR. Minocycline attenuated the inflammatory profile of AR compared with controls and when coadministered with immunosuppression prolonged graft survival. This study demonstrates that a network-based strategy, using expression and genotype data to predict KDGs, assists target prioritization for therapeutics in renal allograft rejection.

Discovery of Selective, Orally Bioavailable Pyrazolopyridine Inhibitors of Protein Kinase Cθ (PKCθ) That Ameliorate Symptoms of Experimental Autoimmune Encephalomyelitis

PKCθ plays an important role in T cell biology and is a validated target for a number of disease states. A series of potent and selective PKCθ inhibitors were designed and synthesized starting from a HTS hit compound. Cell activity, while initially a challenge to achieve, was built into the series by transforming the nitrile unit of the scaffold into a primary amine, the latter predicted to form a new hydrogen bond to Asp508 near the entrance of the ATP binding site of PKCθ. Significant improvements in physiochemical parameters were observed on introduction of an oxetane group proximal to a primary amine leading to compound 22, which demonstrated a reduction of symptoms in a mouse model of multiple sclerosis.

High frequency of valganciclovir underdosing for cytomegalovirus prophylaxis after renal transplantation

Background

The correct valganciclovir dose for cytomegalovirus (CMV) prophylaxis depends on renal function estimated by the Cockcroft–Gault (CG) estimated creatinine clearance (CG-CrCl) formula. Patients with delayed or rapidly changing graft function after transplantation (tx) will need dose adjustments.

Methods

We performed a retrospective investigation of valganciclovir dosing in renal transplant patients receiving CMV prophylaxis between August 2003 and August 2011, and analysed valganciclovir dosing, CG-CrCl, CMV viraemia (CMV-PCR <750 copies/mL), leucopenia (<3500/µL) and neutropenia (<1500/µL) in the first year post-transplant. On Days 30 and 60 post-transplant, dosing pattern in relation to estimated creatinine clearance was analysed regarding CMV viraemia, leucopenia and neutropenia.

Results

Six hundred and thirty-five patients received valganciclovir prophylaxis that lasted 129 ± 68 days with a mean dose of 248 ± 152 mg/day of whom 112/635 (17.7%) developed CMV viraemia, 166/635 (26.1%) leucopenia and 48/635 (7.6%) neutropenia. CMV resistance within 1 year post-transplant was detected in three patients. Only 137/609 (22.6%) patients received the recommended dose, while n = 426 (70.3%) were underdosed and n = 43 (7.1%) were overdosed at Day 30 post-tx. Risk factors for CMV viraemia were donor positive D (+)/receptor negative R (−) status and short prophylaxis duration, but not low valganciclovir dose. Risk factors for developing leucopenia were D+/R− status and low renal function. No significant differences in dosing frequency were observed in patients developing neutropenia or not (P = 0.584).

Conclusion

Most patients do not receive the recommended valganciclovir dose. Despite obvious underdosing in a large proportion of patients, effective prophylaxis was maintained and it was not associated as a risk factor for CMV viraemia or leucopenia.

Chelerythrine ameliorates acute cardiac allograft rejection in mice

The improvement in graft survival over the past decade has been mainly due to calcineurin inhibitors, which interfere with the calcium-mediated pathway. Recently, other pathways such as those mediated by protein kinase C (PKC) are coming into view. The purpose of this study was to assess the immunosuppressive properties of chelerythrine, a specific PKC inhibitor, in preventing acute rejection in murine heterotopic heart transplantation. Mice were randomly divided into control and chelerythrine treated group. The control group received PBS while the chelerythrine treated group was given intraperitoneal injection doses (1, 5, 10mg/kg) of chelerythrine from day 0 to day 14 after heart transplantation. Six days after transplantation, cardiac allografts were harvested for further tests. The mean survival time (MST) of the cardiac allograft in untreated animals was 8days while graft MSTs observed in chelerythrine treated group was 13 and 23days at 5 and 10mg/kg treatment doses, respectively (P<0.05). Histologic assessment of the allograft in chelerythrine group showed a significant decline in histologic rejection score, as well as CD4+ and CD8+ T cell infiltration and ICAM-1+ endothelial cell activation. Down-regulation of Th1/Th2 cytokine expression was observed in chelerythrine treatment group. Meanwhile, chelerythrine was also found to inhibit the dephosphorylation of phosphorylated nuclear factor of activated T cells (NFAT) protein 1 and 4.

PKC-Theta in Regulatory and Effector T-cell Functions

One of the major goals in immunology research is to understand the regulatory mechanisms that underpin the rapid switch on/off of robust and efficient effector (Teffs) or regulatory (Tregs) T-cell responses. Understanding the molecular mechanisms underlying the regulation of such responses is critical for the development of effective therapies. T-cell activation involves the engagement of T-cell receptor and co-stimulatory signals, but the subsequent recruitment of serine/threonine-specific protein Kinase C-theta (PKC-θ) to the immunological synapse (IS) is instrumental for the formation of signaling complexes, which ultimately lead to a transcriptional network in T cells. Recent studies demonstrated that major differences between Teffs and Tregs occurred at the IS where its formation induces altered signaling pathways in Tregs. These pathways are characterized by reduced recruitment of PKC-θ, suggesting that PKC-θ inhibits Tregs suppressive function in a negative feedback loop. As the balance of Teffs and Tregs has been shown to be central in several diseases, it was not surprising that some studies revealed that PKC-θ plays a major role in the regulation of this balance. This review will examine recent knowledge on the role of PKC-θ in T-cell transcriptional responses and how this protein can impact on the function of both Tregs and Teffs.

Protein kinase C in the immune system: from signalling to chromatin regulation

Protein kinase C (PKC) form a key family of enzymes involved in signalling pathways that specifically phosphorylates substrates at serine/threonine residues. Phosphorylation by PKC is important in regulating a variety of cellular events such as cell proliferation and the regulation of gene expression. In the immune system, PKCs are involved in regulating signal transduction pathways important for both innate and adaptive immunity, ultimately resulting in the expression of key immune genes. PKCs act as mediators during immune cell signalling through the immunological synapse. PKCs are traditionally known to be cytoplasmic signal transducers and are well embedded in the signalling pathways of cells to mediate the cells' response to a stimulus from the plasma membrane to the nucleus. PKCs are also found to transduce signals within the nucleus, a process that is distinct from the cytoplasmic signalling pathway. There is now growing evidence suggesting that PKC can directly regulate gene expression programmes through a non-traditional role as nuclear kinases. In this review, we will focus on the role of PKCs as key cytoplasmic signal transducers in immune cell signalling, as well as its role in nuclear signal transduction. We will also highlight recent evidence for its newly discovered regulatory role in the nucleus as a chromatin-associated kinase.

PKCθ-regulated signalling in health and disease

Protein kinase Cθ (PKCθ) is a key enzyme in T-lymphocytes where it plays an important role in signal transduction downstream of the activated T-cell receptor (TCR) and the CD28 co-stimulatory receptor. Antigenic stimulation of T-cells triggers PKCθ translocation to the centre of the immunological synapse (IS) at the contact site between antigen-specific T-cells and antigen-presenting cells (APCs). The IS-residing PKCθ phosphorylates and activates effector molecules that transduce signals into distinct subcellular compartments and activate the transcription factors, nuclear factor κB (NF-κB), nuclear factor of activated T-cells (NFAT) and activating protein 1 (AP-1), which are essential for the induction of T-cell-mediated responses. Besides its major biological role in T-cells, PKCθ is expressed in several additional cell types and is involved in a variety of distinct physiological and pathological phenomena. For example, PKCθ is expressed at high levels in platelets where it regulates signal transduction from distinct surface receptors, and is required for optimal platelet activation and aggregation, as well as haemostasis. In addition, PKCθ is involved in physiological processes regulating insulin resistance and susceptibility to obesity, and is expressed at high levels in gastrointestinal stromal tumours (GISTs), although the functional importance of PKCθ in these processes and cell types is not fully clear. The present article briefly reviews selected topics relevant to the biological roles of PKCθ in health and disease.

Targeting protein kinase C in sarcoma

Protein kinase C (PKC) is a family of serine/threonine tyrosine kinases that regulate many cellular processes including division, proliferation, survival, anoikis and polarity. PKC is abundant in many human cancers and aberrant PKC signalling has been demonstrated in cancer models. On this basis, PKC has become an attractive target for small molecule inhibition within oncology drug development programmes. Sarcoma is a heterogeneous group of mesenchymal malignancies. Due to their relative insensitivity to conventional chemotherapies and the increasing recognition of the driving molecular events of sarcomagenesis, sarcoma provides an excellent platform to test novel therapeutics. In this review we provide a structure-function overview of the PKC family, the rationale for targeting these kinases in sarcoma and the state of play with regard to PKC inhibition in the clinic.

Beyond calcineurin inhibitors: emerging agents in kidney transplantation

PURPOSE OF REVIEW

Despite their effectiveness, calcineurin inhibitors (CNIs) represent a major obstacle in the improvement of long-term graft survival in transplantation. The identification of new agents to implement CNI-free regimens is the focus of current transplant research. The purpose of this review is to summarize the novel immunosuppressive agents, including details about their mechanisms of action, stages of development, potential benefits and challenges.

RECENT FINDINGS

Targeting costimulation with belatacept is now an option for controlling the alloimmune response and has proved to be more effective in preserving long-term allograft function than CNIs despite an increased rate of acute rejection in some studies. mTOR inhibitors are also promising with their remarkable antineoplastic properties, though frequent side-effects may limit their broader use. Other agents under development include JAK inhibitors, CD40 blockade and leukocyte adhesion blockers, with unique potential benefits and side-effects in transplantation.

SUMMARY

Novel immunosuppressive agents are now available for use in CNI-free regimens in solid organ transplantation. Timing of initiation as well as long-term efficacy and safety are questions that remain to be answered in future clinical trials.

Protein kinase C inhibitors for immune disorders

Protein kinase C (PKC) proteins are a group of well-conserved, intracellular signaling enzymes expressed in all cells and tissues, including immune cells. Much of the molecular insight into PKC immunobiology has been gleaned from studies using PKC gene (Prkc) knockout mice and the analysis of different disease models in these animals. More-recent studies have revealed that PKCs also have crucial roles in the pathogenesis of human immune disorders. Therefore, strategies to modulate the functions of PKC enzymes could have a major impact on the treatment and therapies of autoimmune diseases and other immune disorders.

Novel immunosuppressive agents in kidney transplantation

Excellent outcomes have been achieved in the field of renal transplantation. A significant reduction in acute rejection has been attained at many renal transplant centers using contemporary immunosuppressive, consisting of an induction agent, a calcineurin inhibitor, an antiproliferative agent plus or minus a corticosteroid. Despite improvements with these regimens, chronic allograft injury and adverse events still persist. The perfect immunosuppressive regimen would limit or eliminate calcineurin inhibitors and/or corticosteroid toxicity while providing enhanced allograft outcomes. Potential improvements to the calcineurin inhibitor class include a prolonged release tacrolimus formulation and voclosporin, a cyclosporine analog. Belatacept has shown promise as an agent to replace calcineurin inhibitors. A novel, fully-human anti-CD40 monoclonal antibody, ASKP1240, is currently enrolling patients in phase 2 trials with calcineurin minimization and avoidance regimens. Another future goal of transplant immunosuppression is effective and safe treatment of allograft rejection. Novel treatments for antibody mediated rejection include bortezomib and eculizumab. Several investigational agents are no longer being pursed in transplantation including the induction agents, efalizumab and alefacept, and maintenance agents, sotrastaurin and tofacitinib. The purpose of this review is to consolidate the published evidence of the effectiveness and safety of investigational immunosuppressive agents in renal transplant recipients.

Association of BK viremia with human leukocyte antigen mismatches and acute rejection, but not with type of calcineurin inhibitor

INTRODUCTION

BK viremia and polyomavirus-associated nephropathy (PVN) represent a significant problem after kidney transplantation. Both are associated with intensified immunosuppression, but other risk factors and the impact of a screening program on outcome are incompletely understood.

METHODS

Here, we report on the short- and long-term outcome of a cohort of patients, who were transplanted in 2006/2007 and included in a newly introduced systematic 3-monthly screening for BK viremia at the University Hospital Zurich. In patients testing positive for BK viremia, screening frequency was intensified and immunosuppression reduced. Patients with suspected PVN underwent transplant biopsy.

RESULTS

Among 152 included patients, 49 (32%) tested positive for BK viremia, but only 8 developed biopsy-proven PVN. BK viremia had a significant impact on estimated glomerular filtration rate and proteinuria in the first 2 years. Acute rejection episodes and the number of human leukocyte antigen (HLA) mismatches were the strongest independent predictors of BK viremia in a multiple logistic model. In contrast, no particular immunosuppressive agent or regimen was associated with enhanced risk.

CONCLUSION

Taken together, systematic BK viremia screening led to detection of a high percentage of viremic patients. With adjustment of immunosuppression, an excellent outcome was achieved. The independent association of HLA mismatches with BK viremia suggests impaired polyomavirus immunosurveillance in highly mismatched allografts.

Pharmacologic inhibition of PKCα and PKCθ prevents GVHD while preserving GVL activity in mice

Allogeneic hematopoietic cell transplantation (HCT) is the most effective therapy for hematopoietic malignancies through T-cell-mediated graft-vs-leukemia (GVL) effects but often leads to severe graft-vs-host disease (GVHD). Given that protein kinase Cθ (PKCθ), in cooperation with PKCα, is essential for T-cell signaling and function, we have evaluated PKCθ and PKCα as potential therapeutic targets in allogeneic HCT using genetic and pharmacologic approaches. We found that the ability of PKCα(-/-)/θ(-/-) donor T cells to induce GVHD was further reduced compared with PKCθ(-/-) T cells in relation with the relevance of both isoforms to allogeneic donor T-cell proliferation, cytokine production, and migration to GVHD target organs. Treatment with a specific inhibitor for both PKCθ and PKCα impaired donor T-cell proliferation, migration, and chemokine/cytokine production and significantly decreased GVHD in myeloablative preclinical murine models of allogeneic HCT. Moreover, pharmacologic inhibition of PKCθ and PKCα spared T-cell cytotoxic function and GVL effects. Our findings indicate that PKCα and θ contribute to T-cell activation with overlapping functions essential for GVHD induction while less critical to the GVL effect. Thus, targeting PKCα and PKCθ signaling with pharmacologic inhibitors presents a therapeutic option for GVHD prevention while largely preserving the GVL activity in patients receiving HCT.

Report of the second joint meeting of ESOT and AST: current pipelines in biotech and pharma

Following the first joint meeting organized by the European (ESOT) and American (AST) Societies of Transplantation in 2010, a second joint meeting was held in Nice, France, on October 12-14, 2012 at the Palais de la Mediterannee. Co-chairs of the scientific advisory committee were Dr. Flavio Vincenti (AST) and Dr. Teun Van Gelder (ESOT). The goal was to discuss the key unmet needs in solid organ transplantation with the opportunity to interrelate current basic research efforts with clinical translation. Thus, the topic of this second meeting "Transformational therapies and diagnostics in transplantation" was devised and a summary of this meeting follows.

Efficacy of sotrastaurin plus tacrolimus after de novo kidney transplantation: randomized, phase II trial results

Sotrastaurin, a novel immunosuppressant, blocks early T cell activation through protein kinase C inhibition. Efficacy and safety of sotrastaurin with tacrolimus were assessed in a dose-ranging non-inferiority study in renal transplant recipients. A total of 298 patients were randomized 1:1:1:1 to receive sotrastaurin 100 (n = 77; discontinued in December 2011) or 200 mg (n = 73) b.i.d. plus standard tacrolimus (sTAC; 5-12 ng/mL), sotrastaurin 300 mg (n = 75) b.i.d. plus reduced tacrolimus (rTAC; 2-5 ng/mL) or enteric-coated mycophenolic acid (MPA) plus sTAC (n = 73); all patients received basiliximab and corticosteroids. Composite efficacy failure (treated biopsy-proven acute rejection ≥ grade IA, graft loss, death or loss to follow up) rates at Month 12 were 18.8%, 12.4%, 10.9% and 14.0% for the sotrastaurin 100, 200 and 300 mg, and MPA groups, respectively. The median estimated glomerular filtration rates were 55.7, 53.3, 64.9 and 59.2 mL/min, respectively. Mean heart rates were faster with higher sotrastaurin doses and discontinuations due to adverse events and gastrointestinal adverse events were more common. Fewer patients in the sotrastaurin groups experienced leukopenia than in the MPA group (1.3-5.5% vs. 16.5%). Sotrastaurin 200 and 300 mg had comparable efficacy to MPA in prevention of rejection with no significant difference in renal function between the groups.

Sotrastaurin in calcineurin inhibitor-free regimen using everolimus in de novo kidney transplant recipients

Sotrastaurin, a novel selective protein-kinase-C inhibitor, inhibits early T cell activation via a calcineurin-independent pathway. Efficacy and safety of sotrastaurin in a calcineurin inhibitor-free regimen were evaluated in this two-stage Phase II study of de novo kidney transplant recipients. Stage 1 randomized 131 patients (2:1) to sotrastaurin 300 mg or cyclosporine A (CsA). Stage 2 randomized 180 patients (1:1:1) to sotrastaurin 300 or 200 mg or CsA. All patients received basiliximab, everolimus (EVR) and prednisone. Primary endpoint was composite efficacy failure rate of treated biopsy-proven acute rejection, graft loss, death or lost to follow-up. Main safety assessment was estimated glomerular filtration rate (eGFR) by MDRD-4 at Month 12. Composite efficacy failure rates at 12 months were higher in sotrastaurin arms (Stage 1: 16.5% and 10.9% for sotrastaurin 300 mg and CsA; Stage 2: 27.2%, 34.5% and 19.4% for sotrastaurin 200 mg, 300 mg and CsA). eGFR was significantly better in sotrastaurin groups versus CsA at most time points, except at 12 months. Gastrointestinal and cardiac adverse events were more frequent with sotrastaurin. Higher treatment discontinuation, deaths and graft losses occurred with sotrastaurin 300 mg. Sotrastaurin combined with EVR showed higher efficacy failure rates and some improvement in renal allograft function compared to a CsA-based therapy.

Is it time to give up with calcineurin inhibitors in kidney transplantation?

Calcineurin inhibitors (CNIs) represent today a cornerstone for the maintenance immunosuppressive treatment in solid organ transplantation. Nevertheless, several attempts have been made either to minimize their dosage or to avoid CNIs at all because these drugs have the severe side effect of chronic nephrotoxicity. This issue represents a frontier for renal transplantation. The principal problem is to understanding whether the poor outcome over the long-term may be ascribed to CNIs nephrotoxicity or to the inability of these drugs to control the acute and chronic rejection B cells mediated. The authors analyze extensively all the international trials attempting to withdraw, minimize or avoid the use of CNIs. Few trials undertaken in low risk patients with an early conversion from CNIs to proliferation signal inhibitors were successful, but the vast majority of trials failed to improve CNIs side effects. To date the use of a new drug, a co-stimulation blocker, seems promising in avoiding CNIs with similar efficacy, better glomerular filtration rate and an improved metabolic profile. Moreover the use of this drug is not associated with the development of donor-specific anti-human leukocyte antigen antibodies. This point has a particular relevance, because the failure of CNIs to realize good outcomes in renal transplantation has recently ascribed to their inability to control the acute and chronic rejections B-cell mediated. This paper analyzes all the recent studies that have been done on this issue that represents the real frontier that should be overcome to realize better results over the long-term after transplantation.

Cervical cancer screening in immunocompromised women

Human papillomavirus (HPV) is a sexually transmitted virus that is associated with increased risk of anogenital cancers in immunosuppressed hosts. The behavior of HPV infection is controlled by the systemic immune system response as well as the local tissue immune system to the HPV virus. Individuals with a depressed immune system, either by viral infection (such as human immunodeficiency virus) or by chronic immunosuppressive agents (such as transplant recipients or patients with autoimmune disease) are at an increased risk of HPV-associated malignancies. This article addresses the data and limitations in developing evidence-driven guidelines for cervical cancer screening in immunocompromised women.

Protein kinase C, an elusive therapeutic target?

Protein kinase C (PKC) has been a tantalizing target for drug discovery ever since it was first identified as the receptor for the tumour promoter phorbol ester in 1982. Although initial therapeutic efforts focused on cancer, additional indications--including diabetic complications, heart failure, myocardial infarction, pain and bipolar disorder--were targeted as researchers developed a better understanding of the roles of eight conventional and novel PKC isozymes in health and disease. Unfortunately, both academic and pharmaceutical efforts have yet to result in the approval of a single new drug that specifically targets PKC. Why does PKC remain an elusive drug target? This Review provides a short account of some of the efforts, challenges and opportunities in developing PKC modulators to address unmet clinical needs.

Immunomodulating options for liver transplant patients

Much has changed since the early years of liver transplantation. Improvements in post-transplant survival are largely due to more selective and less toxic immunosuppression regimens and advances in operative and perioperative care. This has allowed liver transplantation to become an extremely successful treatment option for patients with endstage liver disease. Beginning with cyclosporine, a cyclic endecapeptide of fungal origin and the first of the calcineurin inhibitors to find widespread use, immunosuppressive regimens have evolved to include additional calcineurin inhibitors, steroids, mTOR inhibitors, antimetabolites and antibodies, mostly targeting T-cell activation. This review will present currently available immunosuppressive agents used in the perioperative period of liver transplantation, as well as maintenance treatments, tailoring therapeutic strategies for specific populations, and advances in immune monitoring and tolerance.

A host GPCR signaling network required for the cytolysis of infected cells facilitates release of apicomplexan parasites

Following intracellular replication, the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii cause host cell cytolysis to facilitate parasite release and disease progression. Parasite exit from infected cells requires the interplay of parasite-derived proteins and host actin cytoskeletal changes; however, the host proteins underlying these changes remain obscure. We report the identification of a Gα(q)-coupled host-signaling cascade required for the egress of both P. falciparum and T. gondii. Gα(q)-coupled signaling results in protein kinase C (PKC)-mediated loss of the host cytoskeletal protein adducin and weakening of the cellular cytoskeleton. This cytoskeletal compromise induces catastrophic Ca(2+) influx mediated by the mechanosensitive cation channel TRPC6, which activates host calpain that proteolyzes the host cytoskeleton allowing parasite release. Reinforcing the feasibility of targeting host proteins as an antiparasitic strategy, mammalian PKC inhibitors demonstrated activity in murine models of malaria and toxoplasmosis. Importantly, an orally bioavailable PKC inhibitor prolonged survival in an experimental cerebral malaria model.

The yin and yang of protein kinase C-theta (PKCθ): a novel drug target for selective immunosuppression

Protein kinase C-theta (PKCθ) is a protein kinase C (PKC) family member expressed predominantly in T lymphocytes, and extensive studies addressing its function have been conducted. PKCθ is the only T cell-expressed PKC that localizes selectively to the center of the immunological synapse (IS) following conventional T cell antigen stimulation, and this unique localization is essential for PKCθ-mediated downstream signaling. While playing a minor role in T cell development, early in vitro studies relying, among others, on the use of PKCθ-deficient (Prkcq(-/-)) T cells revealed that PKCθ is required for the activation and proliferation of mature T cells, reflecting its importance in activating the transcription factors nuclear factor kappa B, activator protein-1, and nuclear factor of activated T cells, as well as for the survival of activated T cells. Upon subsequent analysis of in vivo immune responses in Prkcq(-/-) mice, it became clear that PKCθ has a selective role in the immune system: it is required for experimental Th2- and Th17-mediated allergic and autoimmune diseases, respectively, and for alloimmune responses, but is dispensable for protective responses against pathogens and for graft-versus-leukemia responses. Surprisingly, PKCθ was recently found to be excluded from the IS of regulatory T cells and to negatively regulate their suppressive function. These attributes of PKCθ make it an attractive target for catalytic or allosteric inhibitors that are expected to selectively suppress harmful inflammatory and alloimmune responses without interfering with beneficial immunity to infections. Early progress in developing such drugs is being made, but additional studies on the role of PKCθ in the human immune system are urgently needed.

The protein kinase C inhibitor AEB071 (sotrastaurin) modulates migration and superoxide anion production by human neutrophils in vitro

We examined the effect of the protein kinase C-selective inhibitor AEB071 (sotrastaurin) on neutrophil functions in vitro. Pre-incubation with AEB071 at concentrations similar to those reached during in vivo therapy significantly reduced cell capacity to migrate toward three different chemo-attractants and to produce superoxide anions (O₂⁻) in response to phorbol myristate acetate (PMA) or to N-formyl-methionyl-leucyl-phenylalanine (fMLP). AEB071 also significantly inhibited the O₂⁻ overproduction induced by fMLP in neutrophils primed with tumor necrosis factor alpha (TNF-α) or granulocyte/macrophage-colony stimulating factor (GM-CSF). This inhibition was not linked to fMLP-receptor down-regulation since the drug had no effect on either fMLP-receptors or fMLP-induced CD11b membrane expression. When the activity of AEB071 was compared to that of the conventional protein kinase C (PKC) inhibitor Gö6850 (which, like sotrastaurin, inhibits classical and novel PKC isoforms), Gö6976 (an inhibitor of α and α PKC isoforms) and rottlerin (a prevailing δ PKC isoform inhibitor), AEB071 at an equimolar concentration of 3 μM (close to the maximum drug concentration reached in patients treated with AEB071) caused significantly more inhibition on both chemotactic response and superoxide production. These in vitro findings suggest that neutrophils may offer a cellular target for AEB071 activity in vivo.

Phospho-specific flow cytometry for pharmacodynamic monitoring of immunosuppressive therapy in transplantation

Organ transplant recipients frequently suffer from toxicity or from lack of efficacy of immunosuppressive drugs, which can be attributed to individual variations in drug sensitivity. This problem can be resolved by applying pharmacodynamic monitoring that focuses on measuring the biological effects of drugs. Here we discuss the new technique called phospho-specific flow cytometry to monitor the activity of intracellular immune signaling pathways at the single-cell level in whole blood samples. Through this tool the efficacy of immunosuppressive medication can be assessed, novel targets can be identified, and differences in drug sensitivity between cells and patients can be clarified.

A drug safety evaluation of everolimus in kidney transplantation

INTRODUCTION

Calcineurin inhibitors (CNI) have greatly reduced the rate of acute rejection and improved short-term graft survival after organ transplantation, however, long-term survival has hardly changed since their introduction. CNIs are believed to contribute to graft fibrosis, have side effects that adversely affect cardiovascular risk, and are associated with an increased rate of post-transplant malignancies. Everolimus, a mammalian target of rapamycin (mTOR) inhibitor, is not associated with graft fibrosis, has a superior cardiovascular risk profile to CNI therapy and has shown potential for the prevention and treatment of diverse forms of cancer.

AREAS COVERED

This review summarizes key aspects of everolimus, including its mechanism of action, pharmacokinetics, pharmacodynamics, drug-drug interactions and pivotal clinical studies with a focus on safety and efficacy.

EXPERT OPINION

Everolimus is effective in improving graft function in selected kidney transplant patients. Most adverse events are present for a short time after the introduction of everolimus, and are manageable. Everolimus has the potential to become an important agent in de novo and maintenance immunotherapy in kidney transplant recipients.

Current state of renal transplant immunosuppression: Present and future

For kidney transplant recipients, immunosuppression commonly consists of combination treatment with a calcineurin inhibitor, an antiproliferative agent and a corticosteroid. Many medical centers use a sequential immunosuppression regimen where an induction agent, either an anti-thymocyte globulin or interleukin-2 receptor antibody, is given at the time of transplantation to prevent early acute rejection which is then followed by a triple immunosuppressive maintenance regimen. Very low rejection rates have been achieved at many transplant centers using combinations of these agents in a variety of protocols. Yet, a large number of recipients suffer chronic allograft injury and adverse events associated with drug therapy. Regimens designed to limit or eliminate calcineurin inhibitors and/or corticosteroid use are actively being pursued. An ideal immunosuppressive regimen limits toxicity and prolongs the functional life of the graft. This article contains a critical analysis of clinical data on currently available immunosuppressive strategies and an overview of therapeutic moieties in development.

Effects of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function and activation

Humoral rejection processes may lead to allograft injury and subsequent dysfunction. Today, only one B-cell-specific agent is in clinical use and the effects of standard and new immunosuppressant substances on B-cell activation and function are not fully clarified. The impact of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function was assessed by analysing proliferation, apoptosis, CD80/CD86 expression and immunoglobulin and IL-10 production in primary stimulated B cells. In addition, B-cell co-cultures with pre-activated T cells were performed to evaluate the effect of the different immunosuppressive agents on T-cell-dependent immunoglobulin production. Sotrastaurin did not inhibit B-cell proliferation, CD80/CD86 expression, and IgG production and had only minor effects on IgM levels at the highest concentration administered. In contrast, mycophenolic acid and everolimus had strong effects on all B-cell functions in a dose-dependent manner. All immunosuppressive agents caused decreased immunoglobulin levels in T-cell-dependent B-cell cultures. The data provided here suggest that mycophenolic acid and everolimus, but not sotrastaurin, are potent inhibitors of human B-lymphocyte function and activation.

Calcineurin inhibitors in kidney transplantation: friend or foe?

PURPOSE OF REVIEW

The utilization of calcineurin inhibitors (CNI) in kidney transplantation has dramatically improved short-term outcomes but significant gains in long-term outcomes have proved elusive. Nephrotoxicity is the major problem associated with CNIs and is responsible for the disappointing progress seen in long-term graft survival. In this review, we assess CNI efficacy as well as the latest strategies employed to limit long-term CNI nephrotoxicity.

RECENT FINDINGS

Three CNI sparing strategies - CNI withdrawal, CNI avoidance, and CNI minimization - are evaluated with discussion of key studies such as the Efficacy Limiting Toxicity Elimination-Symphony and Spare-the-Nephron studies. Recent breakthroughs in transplant immunosuppression are discussed such as the BENEFIT and BENEFIT-EXT studies, which have led to the recent US Food and Drug Administratrion approval of belatacept, a novel T-cell costimulation blocker.

SUMMARY

For now, CNIs remain the proven standard of care in modern immunosuppression. However, some novel agents may challenge the role CNIs play in kidney transplantation in the very near future.

The design, synthesis and in vitro immunosuppressive evaluation of novel isobenzofuran derivatives

The synthesis and biological evaluation of a series of novel isobenzofuran-based compounds are described. The compounds were evaluated for their immunosuppressive effects of T-cell proliferation and IMPDH type II inhibitor activity in vitro, as well as their structure-activity relationships were assessed. Several compounds demonstrated highly efficacious immunosuppressive properties, especially compounds 2d, 2e, 2h and 2j, which were superior to MPA, while compounds 2k, 2m, 2n, 4c and 5d exhibited an equipotent inhibitory activity compared to MPA. Generally, it was obviously demonstrated that α,β-unsaturated amides proved more potent than the diamide and urea series. The present study provides a guide for further research on development of safe and effective immunosuppressive agents.

Recent advances in immunosuppressive therapy for prevention of renal allograft rejection

PURPOSE OF REVIEW

Current immunosuppressive therapies are highly successful at regulating acute allograft rejection and inducing long-term transplanted kidney survival; however, currently available medications are associated with generalized immune suppression and drug toxicities, including nephrotoxicity. In recent years, advances in immunosuppression that target specific pathways involved in immune activation have been developed.

RECENT FINDINGS

In particular, promising medications are currently under evaluation that target ischemia-reperfusion injury as well as the cellular and humoral branches of the adaptive immune response. Targets of T-cell-mediated activation include antibodies and fusion proteins interfering with LFA-1/ICAM-1, CD2/LFA-3, CD40/CD154, and CD28/B7.1 and B7.2 interactions. Intracellular targets involved in T- and B-cell activation pathways are being evaluated, including protein kinase C inhibitors, Janus-associated kinase (JAK) inhibitors, and proteasome inhibitors. Several new medications demonstrate promise in inhibiting donor-directed humoral immunity by targeting B-cell-activating factor (BAFF) and complement activation pathways.

SUMMARY

The present review evaluates the recent clinical advances in immunosuppressive therapies for kidney transplantation. Publications regarding advances in immunosuppressive therapies over the past year were evaluated in the context of the specific immune pathways involved in allograft rejection.

Sotrastaurin, a protein kinase C inhibitor, ameliorates ischemia and reperfusion injury in rat orthotopic liver transplantation

Sotraustaurin (STN), a small molecule, targeted protein kinase C (PKC) inhibitor that prevents T-lymphocyte activation via a calcineurin-independent pathway, is currently being tested in Phase II renal and liver transplantation clinical trials. We have documented the key role of activated T cells in the inflammation cascade leading to liver ischemia/reperfusion injury (IRI). This study explores putative cytoprotective functions of STN in a clinically relevant rat model of hepatic cold ischemia followed by orthotopic liver transplantation (OLT). Livers from Sprague-Dawley rats were stored for 30 h at 4°C in UW solution, and then transplanted to syngeneic recipients. STN treatment of liver donors/recipients or recipients only prolonged OLT survival to >90% (vs. 40% in controls), decreased hepatocellular damage and improved histological features of IRI. STN treatment decreased activation of T cells, and diminished macrophage/neutrophil accumulation in OLTs. These beneficial effects were accompanied by diminished apoptosis, NF-κB/ERK signaling, depressed proapoptotic cleaved caspase-3, yet upregulated antiapoptotic Bcl-2/Bcl-xl and hepatic cell proliferation. In vitro, STN decreased PKCθ/IκBα activation and IL-2/IFN-γ production in ConA-stimulated spleen T cells, and diminished TNF-α/IL-1β in macrophage-T cell cocultures. This study documents positive effects of STN on liver IRI in OLT rat model that may translate as an additional benefit of STN in clinical liver transplantation.

Future prospects in immunosuppression for liver transplantation

1. Our increasing understanding of signaling pathways and cellular interactions in transplant immunobiology and the availability of novel immunosuppressive agents have facilitated targeted strategies. 2. The driving forces behind the development of new immunosuppressive regimens are the long-term complications of current immunosuppressive regimens (particularly renal dysfunction and metabolic disturbances). 3. By regulatory mandate, the requirement for the primary endpoint to be a composite of death, graft loss, and rejection remains intact; however, current and future clinical trials could incorporate key secondary endpoints that address renal and metabolic derangements.

Targets of new immunosuppressants in renal transplantation

Although current immunosuppression is highly effective in avoiding acute rejection, it is associated with nephrotoxicity, cardiovascular morbidity, infection, and cancer. Thus, new drugs dealing with new mechanisms, as well as minimizing comorbidities, are warranted in renal transplantation. Few novel drugs are currently under investigation in Phase I, II, or III clinical trials. Belatacept is a humanized antibody that inhibits T-cell co-stimulation and has shown encouraging results in Phase II and III trials. Moreover, two new small molecules are under clinical development: AEB071 or sotrastaurin (a protein kinase C inhibitor) and CP-690550 or tasocitinib (a Janus kinase inhibitor). Refinement in selecting the best combinations for the new and current immunosuppressive agents is probably the main challenge for the next few years.

Sotrastaurin, a novel small molecule inhibiting protein-kinase C: randomized phase II study in renal transplant recipients

Sotrastaurin, a selective protein-kinase-C inhibitor, blocks early T-cell activation through a calcineurin-independent mechanism. In this study, de novo renal transplant recipients with immediate graft function were randomized 1:2 to tacrolimus (control, n = 44) or sotrastaurin (300 mg b.i.d.; n = 81). All patients received basiliximab, mycophenolic acid (MPA) and steroids. The primary endpoint was the composite of treated biopsy-proven acute rejection (BPAR), graft loss, death or lost to follow-up at month 3. The main safety assessment was estimated glomerular filtration rate (eGFR); modification of diet in renal disease (MDRD) at month 3. Composite efficacy failure at month 3 was higher for the sotrastaurin versus control regimen (25.7% vs. 4.5%, p = 0.001), driven by higher BPAR rates (23.6% vs. 4.5%, p = 0.003), which led to early study termination. Median (± standard deviation [SD]) eGFR was higher for sotrastaurin versus control at all timepoints from day 7 (month 3: 59.0 ± 22.3 vs. 49.5 ± 17.7 mL/min/1.73 m(2) , p = 0.006). The most common adverse events were gastrointestinal disorders (control: 63.6%; sotrastaurin: 88.9%) which led to study-medication discontinuation in two sotrastaurin patients. This study demonstrated a lower degree of efficacy but better renal function with the calcineurin-inhibitor-free regimen of sotrastaurin+MPA versus the tacrolimus-based control. Ongoing studies are evaluating alternative sotrastaurin regimens.