Novel Immunosuppressive Drugs

Janus Kinase 3 Inhibition: Tofacitinib

Janus kinases (JAKs) are cytoplasmic tyrosine kinases that participate in the signaling of a broad range of cell surface receptors, particularly members of the cytokine receptor common gamma (cγ) chain family. There are four mammalian JAKs: JAK 1, 2, 3, and tyrosine kinase 2. Activation of JAK by ligand-receptor interaction results in signaling via the phosphorylation of cytokine receptors and the creation of docking sites for signaling proteins known as signal transducers and activators of transcription (STATs). JAKs catalyze STAT phosphorylation, which facilitates STAT dimerization, transport to the nucleus, and ultimately regulation of gene expression and transcription.

Unlike the ubiquitous expression of other JAK subtypes, JAK 3 has a restricted tissue distribution and is found primarily on hematopoietic cells and uniquely associates with the cγ chain. The importance of this pathway can be demonstrated by the fact that mice and humans with genetic absence or mutation in either the cγ subunit or JAK 3 express defects in lymphoid development that give rise to a severe combined immunodeficiency syndrome phenotype.

CP-690,550, or tofacitinib, is a synthetic orally available JAK 3. The results of a phase IIa 6-month pilot study comparing two doses of tofacitinib (15 mg and 30 mg twice daily) to tacrolimus in de novo kidney allograft recipients has been published. Tacrolimus dosing was adjusted to achieve a 12-hour trough of 7 to 14 ng/mL during the first 3 months and 5 to 12 ng/mL for months 4 through 12. All subjects received IL)-2 receptor antagonist induction, mycophenolate mofetil (MMF), and corticosteroids. At 12 months, compared with tacrolimus, subjects enrolled in the high–tofacitinib dose group (T-30) experienced a significantly higher rate of BK virus nephropathy (20%) and cytomegalovirus (CMV) disease (21.1%). In comparison, the 12-month rate of BK virus nephropathy and CMV disease in tacrolimus-treated patients was 0%. Consequently the study protocol was amended after enrollment was complete such that subjects receiving T-30 underwent MMF discontinuation and a more rapid steroid taper. Possibly as a result of these changes, the 6-month incidence of biopsy-proven acute rejection (BPAR) was 5.3%, 21.1%, and 4.8% for low-dose tofacitinib (T-15), T-30, and tacrolimus, respectively.

The cardiometabolic data for tofacitinib were mixed. The 6-month estimated glomerular filtration rate (eGFR) was similar across the three groups; however, the 12-month extension study eGFR was 83.6, 77.6, and 73.3 mL/min for T-15, T-30, and tacrolimus, respectively. By month 12 there was no difference between the three groups in regard to hemoglobin concentration or in the incidence of new-onset diabetes mellitus after transplantation (NODAT). Levels of total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol, and triglycerides were increased in the T-15 and T-30 groups by up to 34% and 44%, respectively, compared with the tacrolimus group through month 12. By 12 months, the mean systolic blood pressures in all groups were reduced from pretransplant baseline. The mean ± SD decrease from baseline in systolic blood pressure for tacrolimus (−17.1 ± 30.5 mm Hg) was larger than that from both T-15 (−11.6 ± 30.6 mm Hg) and T-30 (−11. 2 ± 20.0 mm Hg).

Given the encouraging results with the T-15 regimen, a phase IIb trial was undertaken to evaluate the effectiveness of two different dosing strategies of tofacitinib compared with a cyclosporine-based regimen. Patients were randomized 1:1:1 to one of two tofacitinib regimens or cyclosporine. Group 1, the more intensive (MI) tofacitinib group, received T-15 for months 1 to 6 then tofacitinib 10 mg twice daily (T-10) for months 7 to 12. Group 3, the less intensive (LI) tofacitinib group, received T-15 for months 1 to 3 followed by T-10 for months 4 to 12. Group 3 received the active comparator cyclosporine. All three groups also received mycophenolic acid (MPA) and steroids as well as basiliximab (an IL-2 receptor antagonist) induction. The primary efficacy end point was the incidence of first clinical BPAR at month 6, defined as a BPAR episode with an increase in serum creatinine of 0.3 mg/dL or more and 20% or more from the prerejection baseline. The other primary end point was measured GFR at month 12.

In total 331 patients were randomized, and 322 patients received study treatment (106 in MI, 107 in LI, and 109 in cyclosporine). The primary efficacy end point of 6-month incidence of clinical BPAR met noninferiority criteria for both MI and LI when compared with cyclosporine (11.4% and 7.1% vs. 9.0%). There was also a similar incidence rate of total BPAR at 6 and 12 months with MI and LI being noninferior to cyclosporine ( Table 95-2 ). In addition, the 12-month mean measured GFR (mGFR) was significantly better for both tofacitinib groups compared with cyclosporine: 64.6 mL/min, 64.7 mL/min, and 53.9 mL/min for MI, LI, and cyclosporine, respectively ( P < .05 MI/LI vs. cyclosporine).

From a cardiometabolic standpoint, the incidence of NODAT at 12 months was lower in both tofacitinib groups compared with cyclosporine: 9.9%, 9.3%, and 20.8% for MI, LI, and cyclosporine, respectively. At month 12 total serum and LDL cholesterol levels were similar in the MI (195 mg/dL and 111 mg/dL, respectively) and cyclosporine-treated patients (194 mg/dL and 108 mg/dL, respectively). At month 12 the total serum and LDL cholesterol levels were higher in the LI group (209 mg/dL and 115 mg/dL, respectively) compared with cyclosporine; however, lipid-lowering agents were used less frequently in the LI group. Lastly, more patients treated with cyclosporine had stage 1 or greater hypertension at month 12 compared with MI or LI (MI, 35.6%; LI, 33.9%; cyclosporine, 41.6%).

The safety profile trended in favor of cyclosporine-treated patients. Specifically, serious infections were significantly more common in MI-treated patients compared with cyclosporine-treated patients (44.5% versus 32.8%; P < .001) and were numerically higher in LI-treated patients (37%; P = not significant [NS]). CMV disease occurred in 19.5%, 13.3%, and 4.5% of MI-, LI-, and cyclosporine-treated patients, respectively ( P < .05 MI/LI versus cyclosporine), whereas BK virus infection occurred in 14.2%, 17.8%, and 5.5% of MI-, LI-, and cyclosporine-treated patients, respectively. There was also a non–statistically significant trend toward higher rates of BK nephropathy in tofacitinib-treated patients (MI and LI, 2.6% and 3.9%, respectively) compared with cyclosporine-treated patients (1.1%).

The incidence of malignancies was higher in MI-versus cyclosporine-treated patients (5.7% versus 0.9%) but was similar to cyclosporine when compared with LI-treated patients (0.9%). Posttransplantation lymphoproliferative disorder (PTLD) was also more common in tofacitinib-treated patients. No cases of PTLD occurred in cyclosporine-treated patients compared with two and one cases in the MI- and LI-treated patients, respectively. In addition, two more cases of PTLD occurred after month 12 in the MI-treated group. Among the five patients who developed PTLD, four were Epstein-Barr virus (EBV) seropositive at the time of transplantation, suggesting that unlike those in the belatacept trials, EBV seronegativity did not increase the risk of PTLD. Additionally, all five cases of PTLD were associated with above-median tofacitinib time-weighted average concentration at 2 hours postdose.

Although tofacitinib is a promising alternative to a CNI-based regimen, the optimal therapeutic window has yet to be determined. It should be noted that tofacitinib has been studied extensively and has been approved for the treatment of rheumatoid arthritis by the FDA and is being further studied in other autoimmune diseases. Given that tofacitinib is available, it could be used off-label in low-dose form (5 mg twice daily) as an alternative to CNIs in liver transplantation in patients who cannot tolerate any other immunosuppressive drugs.

Protein Kinase C Inhibition: Aeb-071 (Sotrastaurin)

Protein kinase C (PKC) isoforms are an important part of intracellular signaling pathways. Activation of the T-cell receptor (signal 1) plus CD28 (signal 2) results in T-cell activation via PKC signaling and IL-2 production. The PKC family consists of at least 10 isoforms with the isoforms PKC-α, -β, and -θ playing a role in T- or B-cell signaling. PKC-θ is largely restricted to T-lymphocytes and mediates activation of the transcription factors activator protein-1 and nuclear factor (NF) κB, leading to downstream IL-2 production. The importance of this pathway is illustrated by the fact that PKC-θ knockout mice demonstrate impaired T-cell activation.

AEB-071, or sotrastaurin, is an oral low-molecular-weight compound that blocks early T-cell activation by selective inhibition of PKC. Unlike CNIs, sotrastaurin exerts minimal effect on nuclear factor of activated T cells (NFAT) and on cytokine and growth factor–induced cell proliferation. With a mechanism for blocking T-cell activation that is distinct from CNIs, there has been tremendous excitement at the prospect that sotrastaurin may not possess the toxicities usually associated with inhibition of the calcineurin pathway.

Initial phase II trials evaluating the effectiveness of sotrastaurin were disappointing and were stopped early because of an increase in acute rejection in sotrastaurin-treated groups. The complete results of one of the phase II trials have been published. This was a 12-month, open-label, randomized, three-arm, phase II trial in de novo renal transplant recipients. Patients were randomized (1:1:1) to one of two sotrastaurin groups or the control group. Patients in the sotrastaurin groups received sotrastaurin 200 mg twice daily and steroids plus either standard-exposure tacrolimus (SET, n = 76; tacrolimus dose adjusted for a target level of 8 to 15 ng/mL month 1, 6 to 12 ng/mL months 2 to 3) or reduced-exposure tacrolimus (RET, n = 66; tacrolimus dose adjusted for a target level of 5 to 8 ng/mL month 1, 3 to 6 ng/mL months 2 to 3). At 3 months, patients were eligible for conversion to MPA in place of tacrolimus. In nonconverted patients the tacrolimus target level from month 4 onward was 5 to 10 ng/mL. The control group (n = 74) consisted of standard-exposure tacrolimus, MPA, and steroids. During the 3-month preconversion period, both sotrastaurin groups demonstrated comparable efficacy to the control group in regard to the composite end point of BPAR, graft loss, or death. However, after conversion there was a significant increase in the composite end point in sotrastaurin-treated patients compared with the control group, driven primarily by an increase in BPAR. The Kaplan-Meier estimate demonstrated a 4.6%, 40.2%, and 32.4% rate of BPAR by study end in the control, SET, and RET groups, respectively. The incidence of new-onset diabetes in the control group was 14.9% compared with 6.7% and 7.7% in the SET and RET groups, respectively. However, the median eGFR was not significantly different for the two study groups compared with the control group at any time.