Potential for improved therapeutic index of FK506 in liposomal formulation demonstrated in a mouse cardiac allograft model

Evaluation of immunosuppression protocols for MHC-matched allogeneic iPS cell-based transplantation using a mouse skin transplantation model

BACKGROUND

Off-the-shelf major histocompatibility complex (MHC)-matched iPS cells (iPSC) can potentially initiate host immune responses because of the existence of numerous minor antigens. To suppress allo-immune responses, combination of immunosuppressants is usually used, but its efficacy to the allogeneic iPSC-based transplantation has not been precisely evaluated.

METHODS

Three transplantation models were used in this study; MHC-matched, minor antigen-mismatched mouse skin or iPSC-graft transplantation, and fully allogeneic human iPSC-derived liver organoid transplantation in immune-humanized mice. The recipients were treated with triple drugs combination (TDC; tacrolimus, methylprednisolone, and mycophenolate mofetil) or co-stimulatory molecule blockade (CB) therapy with some modifications. Graft survival as well as anti-donor T and B cell responses was analyzed.

RESULTS

In the mouse skin transplantation model, immunological rejection caused by the minor antigen-mismatch ranged from mild to severe according to the donor-recipient combination. The TDC treatment could apparently control the mild skin graft rejection when combined with a transient T cell depletion, but unexpected anti-donor T or B cell response was observed. On the other hand, CB therapy, particularly when combined with rapamycin treatment, was capable of attenuating both mild and severe skin graft rejection and allowing them to survive long-term without any unfavorable anti-donor immune responses. The efficacy of the CB therapy was confirmed in both mouse and human iPSC-derived graft transplantation.

CONCLUSIONS

The findings suggest that the CB-based treatment seems suitable to well manage the MHC-matched allogeneic iPSC-based transplantation. The TDC-based treatment may be also used to suppress the rejection, but screening of its severity prior to the transplantation seems to be needed.

Macrophage-to-Myofibroblast Transition Contributes to Interstitial Fibrosis in Chronic Renal Allograft Injury

Interstitial fibrosis is an important contributor to graft loss in chronic renal allograft injury. Inflammatory macrophages are associated with fibrosis in renal allografts, but how these cells contribute to this damaging response is not clearly understood. Here, we investigated the role of macrophage-to-myofibroblast transition in interstitial fibrosis in human and experimental chronic renal allograft injury. In biopsy specimens from patients with active chronic allograft rejection, we identified cells undergoing macrophage-to-myofibroblast transition by the coexpression of macrophage (CD68) and myofibroblast (α-smooth muscle actin [α-SMA]) markers. CD68⁺/α-SMA⁺ cells accounted for approximately 50% of the myofibroblast population, and the number of these cells correlated with allograft function and the severity of interstitial fibrosis. Similarly, in C57BL/6J mice with a BALB/c renal allograft, cells coexpressing macrophage markers (CD68 or F4/80) and α-SMA composed a significant population in the interstitium of allografts undergoing chronic rejection. Fate-mapping in Lyz2-Cre/Rosa26-Tomato mice showed that approximately half of α-SMA⁺ myofibroblasts in renal allografts originated from recipient bone marrow-derived macrophages. Knockout of Smad3 protected against interstitial fibrosis in renal allografts and substantially reduced the number of macrophage-to-myofibroblast transition cells. Furthermore, the majority of macrophage-to-myofibroblast transition cells in human and experimental renal allograft rejection coexpressed the M2-type macrophage marker CD206, and this expression was considerably reduced in Smad3-knockout recipients. In conclusion, our studies indicate that macrophage-to-myofibroblast transition contributes to interstitial fibrosis in chronic renal allograft injury. Moreover, the transition of bone marrow-derived M2-type macrophages to myofibroblasts in the renal allograft is regulated via a Smad3-dependent mechanism.

Targeted Therapy for Acute Autoimmune Myocarditis with Nano-Sized Liposomal FK506 in Rats

Immunosuppressive agents are used for the treatment of immune-mediated myocarditis; however, the need to develop a more effective therapeutic approach remains. Nano-sized liposomes may accumulate in and selectively deliver drugs to an inflammatory lesion with enhanced vascular permeability. The aims of this study were to investigate the distribution of liposomal FK506, an immunosuppressive drug encapsulated within liposomes, and the drug’s effects on cardiac function in a rat experimental autoimmune myocarditis (EAM) model. We prepared polyethylene glycol-modified liposomal FK506 (mean diameter: 109.5 ± 4.4 nm). We induced EAM by immunization with porcine myosin and assessed the tissue distribution of the nano-sized beads and liposomal FK506 in this model. After liposomal or free FK506 was administered on days 14 and 17 after immunization, the cytokine expression in the rat hearts along with the histological findings and hemodynamic parameters were determined on day 21. Ex vivo fluorescent imaging revealed that intravenously administered fluorescent-labeled nano-sized beads had accumulated in myocarditic but not normal hearts on day 14 after immunization and thereafter. Compared to the administration of free FK506, FK506 levels were increased in both the plasma and hearts of EAM rats when liposomal FK506 was administered. The administration of liposomal FK506 markedly suppressed the expression of cytokines, such as interferon-γ and tumor necrosis factor-α, and reduced inflammation and fibrosis in the myocardium on day 21 compared to free FK506. The administration of liposomal FK506 also markedly ameliorated cardiac dysfunction on day 21 compared to free FK506. Nano-sized liposomes may be a promising drug delivery system for targeting myocarditic hearts with cardioprotective agents.

Treatment of cerebral ischemia-reperfusion injury with PEGylated liposomes encapsulating FK506

FK506 (Tacrolimus) has the potential to decrease cerebral ischemia-reperfusion injury. However, the clinical trial of FK506 as a neuroprotectant failed due to adverse side effects. This present study aimed to conduct the selective delivery of FK506 to damaged regions, while at the same time reducing the dosage of FK506, by using a liposomal drug delivery system. First, the cytoprotective effect of polyethylene glycol-modified liposomes encapsulating FK506 (FK506-liposomes) on neuron-like pheochromocytoma PC12 cells was examined. FK506-liposomes protected these cells from H2O2-induced toxicity in a dose-dependent manner. Next, we investigated the usefulness of FK506-liposomes in transient middle cerebral artery occlusion (t-MCAO) rats. FK506-liposomes accumulated in the brain parenchyma by passing through the disrupted blood-brain barrier at an early stage after reperfusion had been initiated. Histological analysis showed that FK506-liposomes strongly suppressed neutrophil invasion and apoptotic cell death, events that lead to a poor stroke outcome. Corresponding to these results, a single injection of FK506-liposomes at a low dosage significantly reduced cerebral cell death and ameliorated motor function deficits in t-MCAO rats. These results suggest that liposomalization of FK506 could reduce the administration dose by enhancing the therapeutic efficacy; hence, FK506-liposomes should be a promising neuroprotectant after cerebral stroke.

Effects of cyclosporine, tacrolimus and rapamycin on renal calcium transport and vitamin D metabolism

BACKGROUND

Abnormalities in mineral metabolism are common complications of organ transplantation. The role of immunosuppressive agents in alteration of mineral metabolism is not clear.

METHODS

We conducted an animal study to investigate the effects of cyclosporine A (CsA), tacrolimus, and sirolimus on renal calcium, magnesium and vitamin D metabolism.

RESULTS

CsA and tacrolimus induced a 2- to 3-fold and 1.6- to 1.8-fold increase in urinary calcium and magnesium excretion, respectively, while rapamycin had no effects on calcium, but doubled the urinary magnesium excretion. CsA and tacrolimus, but not rapamycin, elevated serum 1,25(OH)(2) vitamin D without affecting the parathyroid hormone level. CsA and tacrolimus reduced mRNA abundance in TRPV5 (CsA: 64 ± 3% of control; tacrolimus: 50 ± 3%) calbindin-D28k (CsA: 62 ± 4%; tacrolimus: 43 ± 3%), and vitamin D receptor (CsA: 52 ± 3%; tacrolimus: 58 ± 2%, all p < 0.05). Rapamycin did not affect gene expression in any of studied proteins. The immunofluorescence staining study demonstrated a 50% reduction of TRPV5 and calbindin-D28k by CsA and tacrolimus.

CONCLUSION

The suppression of VDR by calcineurin inhibitors is probably the underlying mechanism of renal calcium wasting. In spite of an increased 1,25(OH)(2) vitamin D level, the kidney is not able to reserve calcium, suggesting a role of vitamin D resistance that may be related to bone loss.

Polyoxyl 60 hydrogenated castor oil free nanosomal formulation of immunosuppressant Tacrolimus: pharmacokinetics, safety, and tolerability in rodents and humans

OBJECTIVE

Develop Nanosomal formulation of Tacrolimus to provide safer alternative treatment for organ transplantation patients. Investigate safety, tolerability and pharmacokinetics of Nanosomal Tacrolimus formulation versus marketed Tacrolimus containing polyoxyl 60 hydrogenated castor oil (HCO-60) that causes side effects.

METHODS

Nanosomal Tacrolimus was prepared in an aqueous system. The particle size was measured by Particle Sizing Systems and structure morphology was determined by freeze-fracture electron microscopy. Investigational safety studies were conducted in mice and rats. Safety and pharmacokinetics of Nanosomal Tacrolimus were also evaluated in healthy human subjects.

RESULTS

The morphology of Nanosomal Tacrolimus showed a homogeneous population of nanosized particles with mean particle size of less than 100 nm. A 14 day consecutive administration of Nanosomal Tacrolimus up to 5 and 10mg/kg dose in rats and mice respectively, resulted in no mortality. Nanosomal Tacrolimus in human studies showed that it is safe and the pharmacokinetics profile is similar to the marketed HCO-60 based Tacrolimus. No significant change in peripheral blood lymphocyte percentage was noted in either mice or healthy human male subjects.

CONCLUSIONS

Nanosomal Tacrolimus is well characterized product which provides a new treatment option. It contains no alcohol or surfactants like HCO-60. Thus, Nanosomal Tacrolimus presents a new and improved therapeutic approach for organ transplant patients compared to the marketed HCO-60 based Tacrolimus product.

Biodegradable microsphere-loaded tacrolimus enhanced the effect on mice islet allograft and reduced the adverse effect on insulin secretion

The adverse effects of tacrolimus have limited the use of this potent immunosuppressive drug in clinical transplantation. To improve the therapeutic effects, we developed a new type of tacrolimus with biodegradable microsphere technology and examined the immunosuppressive effects on allogeneic islet transplantation and the side-effects on insulin secretion in vivo. With a single subcutaneous injection, mouse blood concentrations of tacrolimus (M-FK) carried in biodegradable microspheres remained flat for 2 weeks (only 10 h for conventional tacrolimus). A single subcutaneous administration of 20 mg/kg of M-FK significantly prolonged the survival of islet allografts (MST = 28 days) compared with the control group (MST = 10 days). Series administration of 10 mg/kg of M-FK at 7-day intervals markedly prolonged the survival of islet grafts, and resulted in 60% allograft acceptance. In mice with syngeneic islet transplantations, a single administration of 30 mg/kg of tacrolimus inhibited insulin secretion, whereas a single administration of an equal dosage of M-FK did not. The results suggested that M-FK enhanced the immunosuppressive effects on islet allograft rejection more effectively with reduced side-effects on insulin secretion.

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

Liposomal tacrolimus lotion as a novel topical agent for treatment of immune-mediated skin disorders: experimental studies in a murine model

BACKGROUND

Systemic but not topical tacrolimus (TAC) is effective against psoriasis. Mechanical methods that enhance skin penetration by TAC increase its topical antipsoriatic effect. Liposomal delivery of TAC would increase its penetration of skin, allow for slow release and diminish its toxicity.

OBJECTIVES

To test a liposomal TAC (LTAC) formulation in a murine model.

METHODS

Drug penetration was assessed using radiolabelled LTAC, and the effect of TAC and LTAC on Balb/c skin graft survival and on ovalbumin-induced delayed-type hypersensitivity reactions was tested in C57BL/6 mice.

RESULTS

Radiotracer studies showed that topical application of LTAC achieved nine times the concentration of TAC at a target site than did systemic administration of TAC. Combination of systemic and topical LTAC significantly increased mean +/- SD skin graft survival (14.8 +/- 1.5 days) compared with systemic TAC (8.0 +/- 0.7 days) and control mice (8.4 +/- 1.2 days). LTAC was more effective systemically than TAC in the prevention of delayed-type hypersensitivity reactions. Topical LTAC also prevented this response.

CONCLUSIONS

Topical LTAC was effective in this model of immune-mediated skin disease. Because LTAC achieves higher skin concentrations than systemic TAC it may be an effective delivery system for TAC in the treatment of psoriasis.

Liposomal encapsulation significantly enchances the immunosuppressive effect of tacrolimus in a discordant islet xenotransplant model

BACKGROUND

Encapsulation of tacrolimus (TAC) in a lipid bilayer to form liposome-encapsulated tacrolimus (LTAC) alters the biodistribution profile, half-life, and efficacy in organ allotransplantation models. LTAC has not been applied to either cell transplantation or xenotransplantation.

METHODS

To test the efficacy of LTAC in a discordant islet xenograft model, tilapia (fish) islets were transplanted under the left kidney capsules of streptozotocin-diabetic Balb/c mice. Recipient mice (groups I-VI) were treated with: I, untreated; II, empty liposomes; III, TAC (2 mg/kg/day); IV, TAC (5 mg/kg/day); V, LTAC (2 mg/kg/day); or VI, LTAC (5 mg/kg/day); all treatments were for 35 days or until rejection (i.e., two glucose measurements >200 mg/dl). Graft-bearing kidneys were removed for histology after rejection.

RESULTS

Mean graft survival time (mGST) for control groups I and II were 6.7+/-1.4 (n=6) and 7.5+/-1.3 days (n=4), respectively. Daily TAC treatment at 2 mg/kg/d (III) did not prolong graft function (mGST=7.7+/-1.6; n=6) although 5 mg/kg/day (IV) produced minimal prolongation to 12.8+/-4.8 days (n=12). Treatment with LTAC at 2 mg/kg/day (V) significantly prolonged mGST to 26.6+/-4.9 (n=5); however, all recipients rejected during treatment (i.e.,<35 days). LTAC at 5 mg/kg/day (VI) further prolonged mGST to 39.9+/-11.8 days (n=12) with only one mouse rejecting before day 35. Histologically, at the time of functional rejection, grafts were generally either totally or partially effaced by mononuclear cells, eosinophils, and fibrosis. In groups VI, islet grafts removed from two mice that died while they were normoglycemic and from a mouse terminated while it was normoglycemic at day 36 were viable, well-granulated, and free from cellular infiltration. The group VI grafts examined at rejection (i.e., 1-2 weeks after discontinuing LTAC) were generally totally obliterated and were in two instances associated with nodular aggregates of atypical lymphocytes resembling posttransplant lymphoproliferative disorder.

CONCLUSIONS

LTAC is the most potent immunosuppressive compound we have tested in our discordant fish-to-mouse islet xenograft model; however, toxicity is an issue at high doses.

Liposomal tacrolimus administered systemically and within the donor cell suspension improves xenograft survival in hemiparkinsonian rats

The most widely used immunosuppressant in neural transplantation is cyclosporine- A (CsA). However, CsA has significant toxic effects when administered systemically. Tacrolimus (FK506), is a more potent immunosuppressant than CsA and can be prepared in lipid micelles (LTAC). This liposomal preparation allows for the administration of tacrolimus to the site of transplantation, possibly reducing the systemic side effects of immunosuppression. In this study we investigated the ability of LTAC to promote graft survival in hemiparkinsonian rats implanted with fetal mouse xenografts when LTAC is administered systemically to the host, when added to the donor cell suspension, or in combination. Rats with unilateral 6-hydroxydopamine lesions were transplanted with 800,000 fetal mouse ventral mesencephalic (VM) cells and were randomly divided into four groups. Group 1 was not immunosuppressed; Group 2 received daily systemic injections of LTAC; Group 3 received LTAC within the cell suspensions of mouse VM cells; and Group 4 received LTAC in the cell suspensions along with daily systemic administration of LTAC. Transplanted rats were assessed for rotational behavior 3 and 6 weeks posttransplantation. Cell survival was assessed using tyrosine hydroxylase (TH) immunohistochemistry. A significant reduction in rotational scores was observed only in the group of animals receiving the combination of LTAC-treated donor cells and systemic LTAC administration. This functional improvement correlated with a significantly greater survival of TH-immunoreactive cells in this group of animals. The other groups had poor cell survival and no significant functional improvement. We conclude that a combination of systemic immunosuppression and treatment of the cell suspension with LTAC may be a superior strategy to optimize xenograft survival. This strategy may have important implications for clinical neural transplantation.

Tacrolimus: a further update of its pharmacology and therapeutic use in the management of organ transplantation

Tacrolimus (FK-506) is an immunosuppressant agent that acts by a variety of different mechanisms which include inhibition of calcineurin. It is used as a therapeutic alternative to cyclosporin, and therefore represents a cornerstone of immunosuppressive therapy in organ transplant recipients. Tacrolimus is now well established for primary immunosuppression in liver and kidney transplantation, and experience with its use in other types of solid organ transplantation, including heart, lung, pancreas and intestinal, as well as its use for the prevention of graft-versus-host disease in allogeneic bone marrow transplantation (BMT), is rapidly accumulating. Large randomised nonblind multicentre studies conducted in the US and Europe in both liver and kidney transplantation showed similar patient and graft survival rates between treatment groups (although rates were numerically higher with tacrolimus- versus cyclosporin-based immunosuppression in adults with liver transplants), and a consistent statistically significant advantage for tacrolimus with respect to acute rejection rate. Chronic rejection rates were also significantly lower with tacrolimus in a large randomised liver transplantation trial, and a trend towards a lower rate of chronic rejection was noted with tacrolimus in a large multicentre renal transplantation study. In general, a similar trend in overall efficacy has been demonstrated in a number of additional clinical trials comparing tacrolimus- with cyclosporin-based immunosuppression in various types of transplantation. One notable exception is in BMT, where a large randomised trial showed significantly better 2-year patient survival with cyclosporin over tacrolimus, which was primarily attributed to patients with advanced haematological malignancies at the time of (matched sibling donor) BMT. These survival results in BMT require further elucidation. Tacrolimus has also demonstrated efficacy in various types of transplantation as rescue therapy in patients who experience persistent acute rejection (or significant adverse effect's) with cyclosporin-based therapy, whereas cyclosporin has not demonstrated a similar capacity to reverse refractory acute rejection. A corticosteroid-sparing effect has been demonstrated in several studies with tacrolimus, which may be a particularly useful consideration in children receiving transplants. The differences in the tolerability profiles of tacrolimus and cyclosporin may well be an influential factor in selecting the optimal treatment for patients undergoing organ transplantation. Although both drugs have a similar degree of nephrotoxicity, cyclosporin has a higher incidence of significant hypertension, hypercholesterolaemia, hirsutism and gingival hyperplasia, while tacrolimus has a higher incidence of diabetes mellitus, some types of neurotoxicity (e.g. tremor, paraesthesia), diarrhoea and alopecia.

CONCLUSION

Tacrolimus is an important therapeutic option for the optimal individualisation of immunosuppressive therapy in transplant recipients.