Clinical and investigational use of proteasome inhibitors for transplant rejection

Review of bortezomib treatment of antibody-mediated rejection in renal transplantation

SIGNIFICANCE

Development of donor-specific antibodies (DSA) after kidney transplantation is associated with reduced allograft survival. A few strategies have been tested in controlled clinical trials for the treatment of antibody-mediated rejection (AMR), and no therapies are approved by regulatory authorities. Thus development of antihumoral therapies that provide prompt elimination of DSA and improve allograft survival is an important goal.

RECENT ADVANCES

Proteasome inhibitor (PI)-based regimens provide a promising new approach for treating AMR. To date, experiences have been limited to off-label bortezomib use in AMR. Key findings with PI-based therapy are that they provide effective primary and rescue therapy for AMR by prompt reduction in immunodominant DSA and improvements in histologic and renal function. Early and late AMR differ immunologically and in response to PI therapy. Bortezomib-related toxicities in renal transplant recipients are similar to those observed in the multiple myeloma population.

CRITICAL ISSUES

Although preliminary evidence with PI therapy for AMR is encouraging, the evidence is limited. Larger, prospective, randomized controlled trials with long-term follow up are needed. Advancement in endpoints of clinical trial designs and rigorous clinical trials with more standardized adjunct therapies are also required to explore the risks and benefits of AMR treatment modalities.

FUTURE DIRECTIONS

In the next few years, new PIs are likely to be introduced and new approaches would be developed for achieving synergy with PIs. The ultimate goal will be to develop a regimen that delivers reliable, rapid, complete, and durable elimination of DSA with an acceptable safety profile.

Bortezomib for refractory autoimmunity in pediatrics

Therapy of refractory autoimmunity remains challenging. In this study, we evaluated the therapeutic effect of bortezomib, a proteasome inhibitor, by targeting plasma cells in 7 patients (median age, 9.9 years). Four doses of bortezomib were administered at a dose of 1.3 mg/m(2) intravenously (n = 6) or subcutaneously (n = 1) every 72 hours. Bortezomib was administered at a median of 120 days from laboratory confirmation of autoantibodies. All patients had failed 2 or more standard therapies. Rituximab was administered on the first day if B cells were present, and all patients received plasmapheresis 2 hours before bortezomib administration. Six patients experienced resolution of cytopenias. Two of 6 patients experienced recurrence of cytopenias after initial response. Adverse effects include nausea (n = 1), thrombocytopenia (n = 2), Clostridium difficile colitis (n = 1)), febrile neutropenia (n = 1), and cellulitis at the subcutaneous injection site (n = 1). Our experience suggests that bortezomib may be beneficial in the treatment of refractory autoimmunity in children.

Use of bortezomib as anti-humoral therapy in kidney transplantation

This study aimed to investigate the effect of bortezomib in the desensitization and treatment of acute antibody mediated rejection (AAMR) in kidney transplantation. Nine patients who received bortezomib therapy for desensitization (DSZ group, n = 3) or treatment of AAMR (AAMR group, n = 6) were included in this study. In the DSZ group, 2 patients required DSZ owing to positive cross match and 1 owing to ABO mismatch with high baseline anti-ABO antibody titer (1:1,024). Bortezomib was used at 1, 3, 8, and 11 days from the start of the treatment. In the AAMR group, 3 patients showed full recovery of allograft function after bortezomib use and decrease in donor specific anti-HLA antibody (HLA-DSA). However, 3 patients did not respond to bortezomib and experienced allograft failure. In the DSZ group, negative conversion of T-CDC (complement-dependent cytotoxicity) was achieved, and HLA-DSA was decreased to lower than a weak level (median fluorescence intensity [MFI] < 5,000) in 2 patients. In the case of ABO mismatch kidney transplantation, the anti-A/B antibody titer decreased to below the target (≤ 1:16) after bortezomib therapy. Therefore, bortezomib could be an alternative therapeutic option for desensitization and treatment of AAMR that is unresponsive to conventional therapies.

Management of antibody-mediated rejection in transplantation

Despite intensive traditional immunosuppressive therapy, rates of graft loss have approximated 15% to 20% at 1 year following antibody-mediated rejection (AMR) in solid organ transplant recipients. Therefore, the development of antihumoral therapies that provide prompt elimination of donor-specific anti-HLA antibodies and improve allograft survival is an important goal. Traditional treatment modalities for AMR deplete B-cell populations but not the cell at the source of antibody production, the mature plasma cell. Plasma cell-targeted therapies using proteasome inhibition is a novel approach to treating AMR. This review discusses current and emerging treatment modalities used for AMR.

Minimal effect of bortezomib in reducing anti-pig antibodies in human leukocyte antigen-sensitized patients: a pilot study

BACKGROUND

Bortezomib, a proteasome inhibitor used to treat multiple myeloma, has been administered (± plasma exchange ± intravenous immunoglobulin [IVIg]) in attempts to reduce antibodies against human leukocyte antigens (HLA) in sensitized patients undergoing organ transplantation. To our knowledge, bortezomib has not been investigated for its effect on natural anti-pig antibodies. If bortezomib could reduce the production of anti-pig antibodies, this would likely be beneficial to the outcome of pig organ grafts in primates.

METHODS

Nine patients received bortezomib either to reduce anti-HLA antibody levels before organ allotransplantation or to treat antibody-mediated rejection. Patients at the Mayo Clinic (Group 1; n = 4) received bortezomib alone, whereas at the UPMC (Group 2; n = 5), this was combined with plasmaphereses ± IVIg in some cases. Anti-pig IgM and IgG levels against wild-type (WT) and α1,3-galactosyltransferase gene knockout (GTKO) pig aortic endothelial cells (flow cytometry-relative mean fluorescence intensity) and anti-Gal IgM and IgG (ELISA-OD480 nm ) were measured pre- and post-bortezomib therapy.

RESULTS

Mean anti-pig IgM levels were 11.2 (WT) and 1.9 (GTKO) pre-bortezomib treatment and 9.4 (WT: P = 0.02) and 1.7 (GTKO: P = 0.33) post-bortezomib treatment, respectively. Mean anti-pig IgG levels were 4.3 (WT) and 1.5 (GTKO) pre-bortezomib treatment and 3.6 (WT: P = 0.21) and 1.4 (GTKO: P = 0.20) post-bortezomib treatment, respectively. Mean anti-Gal IgM and IgG levels were 0.7 and 1.1, respectively, pre-treatment, and 0.6 (P = 0.03) and 1.1 (NS), respectively, post-treatment. When the data were analyzed in Groups 1 and 2 separately, there were no significant differences between the pre- and post-bortezomib levels of anti-pig, anti-non-Gal, or anti-Gal IgM or IgG.

CONCLUSIONS

From this limited study, we conclude that bortezomib might reduce anti-Gal IgM levels in primates, but, in this respect alone, is unlikely to have any significant effect on the outcome of GTKO pig organ transplantation.

Carfilzomib: a novel agent for multiple myeloma

OBJECTIVES

Carfilzomib is a new agent for the treatment of relapsed and refractory multiple myeloma (MM). This article presents a comprehensive overview of the pharmacokinetics, pharmacodynamics, dosing schedule, safety, efficacy, preparation and administration of carfilzomib, and its role in treating MM patients.

KEY FINDINGS

Carfilzomib is a selective proteasome inhibitor that differs structurally and mechanistically from bortezomib. In patients' whole-blood and peripheral-blood mononuclear cells, carfilzomib inhibited proteasomal and immunoproteasomal activity by 70-80%. Approved carfilzomib dosing is based on body surface area, and is given on days 1, 2, 8, 9, 15 and 16 of a 28-day cycle (20 mg/m(2) in cycle 1; 27 mg/m(2) in cycle 2+). Premedication with dexamethasone and adequate hydration are recommended to reduce the risk of adverse events. The median t1/2 of carfilzomib is short (0.29-0.48 h), with no accumulation detected between doses. In clinical studies in relapsed and refractory MM. and in combinations in newly diagnosed MM, single-agent carfilzomib demonstrated significant durable activity, good tolerability and a favourable safety profile, supporting its extended use.

CONCLUSIONS

Carfilzomib represents an important addition to the treatment armamentarium for patients with relapsed and/or refractory MM, and studies are underway evaluating the role of single-agent carfilzomib in additional clinical settings as well as in different combinations.

Antibody-mediated rejection in kidney transplantation: a review

Antibody mediated rejection (AMR) poses a significant and continued challenge for long term graft survival in kidney transplantation. However, in the recent years, there has emerged an increased understanding of the varied manifestations of the antibody mediated processes in kidney transplantation. In this article, we briefly discuss the various histopathological and clinical manifestations of AMRs, along with describing the techniques and methods which have made it easier to define and diagnose these rejections. We also review the emerging issues of C4d negative AMR, its significance in long term allograft survival and provide a brief summary of the current management strategies for managing AMRs in kidney transplantation.