Tacrolimus hydrate (FK506): therapeutic effects and selection of responders in the treatment of myasthenia gravis

Clinical Neurology and Neurosurgery 106 (2003) 5–8

Tacrolimus hydrate (FK506): therapeutic effects and selection of responders in the treatment of myasthenia gravis Nobuo Wakata a,∗ , Toyokazu Saito b , Sachiko Tanaka c , Toshihiko Hirano c , Kitaro Oka c a

Fourth Department of Internal Medicine, Toho University School of Medicine, 2-17-6 Oohashi, Meguro-ku, Tokyo 153-8515, Japan b Department of Neurology, Kitasato University, Kitasato, Japan c Department of Clinical Pharmacology, Tokyo College of Pharmacy, Tokyo, Japan Received 17 December 2002; received in revised form 11 April 2003; accepted 17 April 2003

Abstract Tacrolimus hydrate (FK506) reduces myasthenic symptoms due to its immunosuppressive properties. We studied the therapeutic effects of FK506 and noted improvement in 7 of 13 myasthenic patients on the clinical muscle test (myasthenia gravis, MG score). Two other patients with relapsing ocular symptoms improved. We also examined patient sensitivity to FK506, but could not predict such sensitivity before FK506 treatment in the present study. © 2003 Elsevier B.V. All rights reserved. Keywords: Myasthenia gravis; Tacrolimus hydrate; Immunosuppressant; Sensitivity test

1. Introduction It is widely accepted that an autoimmune mechanism is responsible for myasthenia gravis (MG) and that the anti-acetylcholine receptor (AChR) antibody binds to post-synaptic receptor sites. Alternate-day prednisolone administration and extended thymectomy have remarkably improved the prognosis for MG; however, some MG patients are refractory to current immunosuppressive therapy. Tacrolimus hydrate (FK506) is a macrolide molecule of the same immunosuppressant class as cyclosporine, and is isolated from streptomyces tsukubanesis [1]. It has a potent immunosuppressive property brought about by selective inhibition of helper T cell activation, which might lead to a reduction in myasthenic symptoms [2,3]. FK506 has been used to prevent organ rejection in kidney transplantation and in atopic dermatitis because of its immunosuppressive effect; it also has a neuro-protective effect in ischemic injury in peripheral nerves [4] and brain [5]. In Japan, FK506 has been used for MG patients who do not respond to high-dose prednisolone and extended thymectomy.

∗ Corresponding author. Tel.: +81-3-3468-1251; fax: +81-3-3468-5082. E-mail address: [email protected] (N. Wakata).

0303-8467/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0303-8467(03)00046-5

We discuss the therapeutic effects of FK506 in patients with MG and a method for identifying potential FK506 responders.

2. Patients and methods In order to determine FK506 responder criteria, 38 myasthenic patients were examined. They included 14 type I, 12 type IIa and 12 type IIb patients by Osserman classification (before FK506 treatment). They were diagnosed on the basis of typical history and signs, positive responses to an edrophoneum chloride test, positive serum anti-AChR antibody titer and decrement of muscle fiber potential on repetitive nerve stimulation. To evaluate therapeutic potency, FK506 was examined using peripheral blood mononuclear cells (PBMCs) from patients with MG. The drug concentration that inhibited 50% of mitogen-stimulated PBMC proliferation in vitro (IC50 ; in ng/ml) was determined in each patient using a previously described method [6,7]. The results were compared with 26 age-matched normal controls. Maximum sensitivity level is expressed as mean ± 2 S.D. of normal control IC50 . The efficacy of FK506 was evaluated in 13 patients with a predetermined sensitivity for FK506. FK506 was administered to longstanding MG patients, except for case 5, who

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had experienced considerable fluctuation of MG symptoms. All patients received extended thymectomy before prednisolone administration except case 1, who declined the procedure. Three patients had a non-invasive thymoma. Thymoma was discovered before onset of MG in case 4. Prednisolone 20 or 30 mg every other day was begun and gradually increased to 80 or 100 mg in every patient except case 9. These maximum dosages were maintained for more than 4 weeks and gradually decreased. Prednisolone was administered before, and during, FK506 treatment, except in case 9. Cases 2, 3, 6 and 10 had been given azathioprine, but the treatment was ineffective. Cases 7, 8, 10 and 13 showed type IIb by Osserman classification and experienced complete remissions at high doses of prednisolone treatment; however, ocular symptoms reappeared after decreasing prednisolone [8]. FK506 was administered 3 mg per daily after evening meal for 16 weeks. Clinical evaluation was based on duration of MG, duration from thymectomy to FK506 treatment, thymus pathology, the use of prednisolone, change in serum anti-AChR antibody and MG score [9]. Significant improvement was defined up to 3 points using MG score. Statistical analysis was performed using the Student t-test and two-ways analysis of variance (ANOVA).

3. Results Low sensitivity to FK506, exceeding mean ± 2 S.D. of normal control IC50 (0.36), was noted in nine patients. Among them, four patients had very low sensitivity because of high IC50 levels (Fig. 1). Sensitivity to FK506 was simi-

lar in thymectomized and unthymectomized patients and in prednisolone-treated and -untreated patients. The therapeutic effect of FK506 is summarized in Table 1. Three patients had a low sensitivity to FK506, and ten patients were normally sensitive. Anti-AChR antibody decreased in seven patients. MG score improved by at least 3 points in seven patients: four of these subjects had decreased anti-AChR antibody, two were unchanged, and one was elevated after 16 weeks. In case 2, a low sensitivity case, the prednisolone dose was decreased by 5 mg. In the other patients, prednisolone dose was unchanged. Clinical improvement started 2–16 weeks (mean 4.4 weeks) after FK506 administration. Four patients had predominantly ocular symptoms (relapsing ocular symptoms: cases 7, 8, 10 and 12); these patients were difficult to evaluate by MG score. Case 10 reported fewer falls due to an improvement in ptosis. Case 12 experienced ptosis and diplopia recurrence after only a 1 mg decrease of prednisolone. Subsequent FK506 administration improved these symptoms. Change in MG score for each patient is shown in Fig. 2. There were significant differences in total MG score before and after FK506 treatment (8 and 16 weeks: P < 0.05). Regarding muscle strength, significant improvements were noted in lower extremities (MG score at 4, 8 and 16 weeks compared with before FK506 treatment: P < 0.05), in grip strength (8 weeks: P < 0.05), in ptosis (16 weeks: P < 0.05) and in swallowing (8 and 16 weeks: P < 0.05) (Fig. 3). There was no significant difference between low-sensitive and normal-sensitive patients in total MG score. No significant side effects were seen except in case 8, a borderline diabetic patient, who suffered hyperglycemia. In case 8, blood FK506 concentration level was 5 ng/ml at 2 and 4 weeks after administration; however, it increased to 11 ng/ml at 8 weeks. At that time, the blood sugar level was 588 mg/ml and HbA1c was 10.5%. Subsequently FK506 was withdrawn. After 16 weeks, serum FK506 concentration levels decreased to 6 ng/ml without medication, with concomitant normal blood sugar levels.

4. Discussion

Fig. 1. Individual PBMC sensitivity to FK506 in MG patients and healthy subjects; 䊊, indicates MG patient; and 䊉, indicates healthy control. Line 0.36 indicates mean ± 2 S.D. of healthy controls.

At the beginning of this study, we attempted to identify potential the FK506 responders. We then administered FK506 to both low- and normal-sensitivity patients and compared the efficacy in these two groups. Though the number of FK506-treated patients was limited, FK506 was effective in seven generalized MG subjects and in another two subjects with ocular symptoms. FK506 appears to work by decreasing anti-AChR antibody, because in four of seven generalized MG patients whose MG symptoms improved, a decreased anti-AChR antibody titer was noted. In other FK506 responders, who did not show reduced anti-AChR antibody, case 4 decreased to 36, case 11 decreased to 2100 and case 13 decreased to 18 nmol/l within 2–3 months after the 16 weeks trial (FK506 continued). Clinical improve-

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Table 1 Patient clinical data Case

Age/sex

Osserman classification

Duration

Thymec.

Patho.

PSL (mg)

FK506 (IC50 )

Anti-AChR 0/16 ws

MG score 0/16 ws

Low sensitivity to FK506 1 (H.K) 57/F IIb 2 (Y.K) 24/F IIa 3 (H.I) 43/F IIb

33.1 y 10/10 y 29.5/14 y

− + +

Hyper. Hyper.

15 35 30

42.98 0.55 0.65

92/9.9 180/140 3.9/5.8

15/12 8/4 9/9

2 ws 8 ws

Normal sensitivity to FK506 4 (T.Y) 65/M IIa 5 (T.S) 43/M IIb 6 (K.S) 54/F IIa 7 (T.T) 56/F I 8 (M.T) 61/M I 9 (H.K) 51/M IIb 10 (Y.M) 67/F IIa 11 (M.C) 49/F IIb 12 (A.M) 63/F I 13 (Y. A) 49/F IIb

12.3/14 y 0.7/0.4 y 33/14 y 7.8/5 y 15/5 y 3.5/3 y 30/25 y 21.6/21 y 2.4/2 y 5.8/5.2 y

+ + + + + + + + + +

Thymoma Thymoma Hyper. Hyper. Hyper. Thymoma Hyper. Hyper. Hyper. Hyper.

± 20 27.5 18 30 − ± 22.5 16 5

0.15 0.1 0.03 0.01 0.02 0.01 0.08 0.03 0.05 0.01

48/49 24/11 540/460 9.7/5.6 0.5/0.2 9.8/7.6 34/34 2300/2400 < 0.2/ < 0.2 20/20

13/3 6/0 4/4 1/1 0/0 11/5 6/5 6/2 0/0 14/3

2 ws 16 ws

Improvement

Others

PSL 5 mg↓

(HG) 2 2 4 2 2

ws ws ws ws ws

Fall down↓ Improve

M, male; F, female; y, year; duration, onset to treatment/thymectomy to treatment; thymec., thymectomy; patho., pathology; PSL, prednisolone (alternate-day dosage at the time of this study); ±, PSL was discontinued; improvement, clinical improvement started after FK506 administered; ws, weeks; anti-AChR, anti-acetylcholine receptor antibody titer (normal < 0.02 nmol/1); hyper., hyperplasia; HG, hyperglycemia.

ments started within 2–16 weeks. Other studies have found that patients improved within a few days after FK506 administration [10], probably due to the direct effect of FK506 on the neuro-muscular junction, as with prednisolone. We could not determine what symptoms were most effectively treated with FK506, though muscle strength in the lower extremities, grip strength, ptosis and swallowing all significantly improved. We administered FK506 in combination with prednisolone, however, some authors have reported good results with FK506 mono-therapy [11], suggesting that FK506 is useful both in combination with prednisolone and alone. Moreover, the relationship between serum FK506 concentration levels and MG symptoms should be examined in the future. Hyperglycemia is a well-known side effect of FK506, linked to serum FK506 concentration levels. Serum FK506

concentration levels should be monitored for 1–3 months after beginning FK506 administration, and paid attention to over 10 ng/ml of serum FK506 concentration levels. The present study was undertaken to predict the effects of FK506 before administration. We administered FK506 both to low-sensitivity and normal-sensitivity patients, but FK506 efficacy was similar. The MG score in two patients improved by at least 3 points in low-sensitivity patients. In addition, we measured FK506 sensitivity twice in three patients, two of them treated by FK506, and sensitivity had improved at the second measurement. This finding suggests that it is not possible to predict the therapeutic effect of FK506 at this time. Because, the number of FK506 treated patients was limited and even initially low sensitivity patients, FK506 administration can lead to improvement in sensitivity.

Fig. 2. MG scores in each patient. There are significant differences in total MG score before and after FK506 treatment (8, 16 ws; P < 0.05); ws, weeks.

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Fig. 3. MG scores in each muscle (mean of 13 patients). Significant differences are seen in lower limb strength (4, 8, 16 ws), in grip strength (8 ws), in ptosis (16 ws) and in swallowing (8, 16 ws) (P < 0.05); ws, weeks.

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