Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1     Pharmacodynamic properties

Pharmacotherapeutic group: Immunostimulants, Other immunostimulants, ATC code: L03AX15 
Mechanism of action

Mifamurtide (muramyl tripeptide phosphatidyl ethanolamine, MTP-PE) is a fully synthetic derivative of muramyl dipeptide (MDP), the smallest naturally-occurring immune stimulatory component of cell walls from Mycobacterium sp. It has similar immunostimulatory effects as natural MDP. MEPACT is a liposomal formulation specifically designed for in vivo targeting to macrophages by intravenous infusion.

MTP-PE is a specific ligand of NOD2, a receptor found primarily on monocytes, dendritic cells and macrophages. MTP-PE is a potent activator of monocytes and macrophages. Activation of human macrophages by mifamurtide is associated with production of cytokines, including tumour necrosis factor (TNF-α), interleukin-1 (IL-1β), IL-6, IL-8, and IL-12 and adhesion molecules, including lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule- 1 (ICAM-1). In vitro-treated human monocytes killed allogeneic and autologous tumour cells (including melanoma, ovarian, colon, and renal carcinoma), but had no toxicity towards normal cells.

In vivo administration of mifamurtide resulted in the inhibition of tumour growth in mouse and rat models of lung metastasis, skin and liver cancer, and fibrosarcoma. Significant enhancement of disease-free survival was also demonstrated in the treatment of dog osteosarcoma and hemangiosarcoma with mifamurtide as adjuvant therapy. The exact mechanism by which mifamurtide activation of monocytes and macrophages leads to anti-tumour activity in animals and humans is not yet known.

Clinical safety and efficacy

The safety of liposomal mifamurtide has been assessed in more than 700 patients with various kinds and stages of cancer and in 21 healthy adult subjects (see section 4.8).

In a randomised phase III study of 678 patients (age range from 1.4 to 30.6 years) with newly-diagnosed resectable high-grade osteosarcoma, the addition of adjuvant mifamurtide to chemotherapy (either doxorubicin cisplatin and methotrexate with or without ifosfamide), significantly increased the 6-year overall survival and resulted in a relative reduction in the risk of death by 28% (p = 0.0313, hazard ratio (HR) = 0.72 [95% confidence interval (CI): 0.53, 0.97]).

Paediatric population

Based on the prevalence of the disease, children and young adults were studied in the pivotal trial.
However, no specific subset analyses for efficacy are available in patients < 18 years of age and ≥ 18 years of age.

Pharmacokinetic Properties

5.2     Pharmacokinetic properties

The pharmacokinetics of mifamurtide have been characterised in healthy adult subjects following a 4 mg intravenous infusion and in paediatric and adult patients with osteosarcoma following a 2 mg/m2 intravenous infusion.

In 21 healthy adult subjects mifamurtide was cleared rapidly from serum (minutes) with a half-life of 2.05 ± 0.40 hours, resulting in a very low serum concentration of total (liposomal and free) mifamurtide. The mean area under the curve (AUC) was 17.0 ± 4.86 h x nM and Cmax (maximum concentration) was 15.7 ± 3.72 nM.
In 28 osteosarcoma patients aged 6 to 39 years serum total (liposomal and free) mifamurtide concentrations declined rapidly with a mean half-life of 2.04 ± 0.456 hours. BSA-normalised clearance and half-life were similar across the age range and consistent with that determined in healthy adult subjects, supporting the recommended dose of 2 mg/m2.

In a separate study in 14 patients, mean serum concentration-time curves of total and free mifamurtide that were assessed after the first infusion of mifamurtide and after a last infusion 11 or 12 weeks later, were almost superimposable and the mean AUC values of the free mifamurtide after the first and last infusion were similar. These data indicate that neither total nor free mifamurtide accumulated during the treatment period.

At 6 hours after injection of radiolabelled liposomes containing 1 mg mifamurtide, radioactivity was found in liver, spleen, nasopharynx, thyroid, and, to a lesser extent, in lung. The liposomes were phagocytosed by cells of the reticuloendothelial system. In 2 of 4 patients with lung metastases, radioactivity was associated with lung metastases.

Metabolism of liposomal MTP-PE has not been studied in humans.

After injection of radiolabelled liposomes containing mifamurtide, mean half-life of radiolabelled material was biphasic with an α-phase of about 15 minutes and a terminal half-life of approximately 18 hours.

Special populations

Renal impairment
The pharmacokinetics of a single 4 mg dose of mifamurtide following a 1 hour intravenous infusion were evaluated in adult volunteers with mild (n=9) or moderate (n=8) renal impairment and in age- ,sex-, and weight-matched healthy adults with normal renal function (n=16). There was no effect of mild (50 mL/min ≤ creatinine clearance [CLcr] ≤ 80 mL/min) or moderate (30 mL/min ≤ CLcr < 50 mL/min) renal insufficiency on the clearance of total MTP-PE, when compared with that observed in healthy adult subjects with normal renal function (CLcr > 80 mL/min). Additionally, the systemic exposures AUC from zero to infinity (AUCinf of free (non-liposome associated) MTP-PE in mild or moderate renal insufficiency were similar to those observed in healthy adult subjects with normal renal function.

Hepatic impairment
The pharmacokinetics of a single 4 mg dose of mifamurtide following a 1 hour intravenous infusion were evaluated in adult volunteers with mild (Child-Pugh class A; n=9) or moderate (Child-Pugh class B; n=8) hepatic impairment and in age-, sex- and weight-matched healthy adults with normal hepatic function (n=19). There was no effect of mild hepatic impairment on the systemic exposure (AUCinf) of total MTP-PE. Moderate hepatic impairment resulted in a small increase in AUCinf of total MTP-PE, with the geometric least square mean ratio (expressed as %) for moderate hepatic impairment in reference to the matched normal hepatic function group being 119% (90% confidence interval [CI]: 94.1%-151%). Pharmacokinetic variability was higher in the moderate hepatic impairment group (co-efficient of variation in systemic exposure [AUCinf] was 50% versus < 30% in the other hepatic function groups).

Mean half-lives of total and free MTP-PE in mild hepatic impairment were 2.02 hours and 1.99 hours, respectively, and were comparable to those in subjects with normal hepatic function (2.15 hours and 2.26 hours, respectively). Mean half-lives of total and free MTP-PE in moderate hepatic impairment were 3.21 hours and 3.15 hours, respectively. Additionally, the geometric mean plasma AUCinf of free (non-liposome associated) MTP-PE in mild and moderate hepatic impairment were 47% higher than the corresponding values in the matched normal hepatic function groups. These changes were not considered to be clinically meaningful as the maximum tolerated dose (4-6 mg/m2) of mifamurtide is 2-3 times the recommended dose (2 mg/m2).