CLINICAL PHARMACOLOGY
Mechanism Of Action
ALA occurs endogenously as a metabolite that is formed in the mitochondria from succinyl-CoA and
glycine. Exogenous administration of ALA leads to accumulation of the ALA metabolite PpIX in tumor
cells. The reason for the accumulation of PpIX in neoplastic brain tissue is not known.
During glioma surgery, Gleolan is used with an operating microscope adapted with a blue emitting light
source (power density 40-80 mW/cm2) and filters for excitation light of wavelength 375 to 440 nm, and
observation at wavelengths of 620 to 710 nm. This allows tumor tissue to be visualized as red
fluorescence. Tissue lacking sufficient PpIX concentrations appears blue.
Pharmacodynamics
The effect of the timing of the Gleolan dosing on fluorescence intensity in brain tissue is unknown. The
relationship between systemic ALA plasma concentrations at the time of visualization and fluorescence
intensity in brain is also unknown. The dose of 20 mg / kg provided stronger ALA-induced
fluorescence in glioma tissue by both visual and spectrophotometric assessment compared to lower
doses tested.
Cardiac Electrophysiology
Administration of the approved recommended dose of Gleolan did not prolong the QT interval to any
clinically relevant extent.
Pharmacokinetics
In 12 healthy subjects, the mean half-life of ALA following the recommended dose of Gleolan solution
was 0.9 ± 1.2 hours (mean ± std dev) with a range of 0.8 to 1.3 hours. Maximum concentrations of the
PpIX metabolite (T for PpIX) occurred with a median of 4 hours and a range of 1.2 to 7.8 hours.
The elimination half-life of PpIX was 3.6 ± 1.8 hours (mean ± std dev) with a range of 1.2 to 7.8 hours.
Absorption
In 12 healthy subjects, the absolute bioavailability of ALA following the recommended dose of Gleolan
solution was 100.0% ± 1.1 with a range of 78.5% to 131.2%. Maximum ALA plasma concentrations
were reached with a median of 0.8 hour (range 0.5 – 1.0 hour).
Distribution
In in vitro experiments using ALA concentrations up to approximately 25% of the maximal concentration
that occurs in plasma following the recommended dose of Gleolan solution, the mean protein binding of
ALA was 12%.
Elimination
Metabolism
Exogenous ALA is metabolized to PpIX, but the fraction of administered ALA that is metabolized to
PpIX is unknown. The average plasma AUC of PpIX is less than 6% of that of ALA.
Excretion
In 12 healthy subjects, excretion of parent ALA in urine in the 12 hours following administration of the
recommended dose of Gleolan solution was 34 ± 8% (mean ± std dev) with a range of 27% to 57%.
Specific Populations
The effect of renal or hepatic impairment on the pharmacokinetics of ALA following Gleolan
administration is unknown.
Drug Interaction Studies
In vitro studies suggest that phenytoin and other anti-convulsants may decrease cellular PpIX
accumulation following Gleolan dosing.
ALA is not an inhibitor of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, or 3A.
Clinical Studies
The efficacy of 20 mg / kg ALA HCl was evaluated in 3 clinical studies (Study 1-3) involving patients,
ages 18 to 75 years old, who had a preoperative MRI compatible with high-grade glioma (WHO Grade
III or IV) and were undergoing surgical resection.
Study 1 was an open-label study of 33 patients with newly diagnosed high-grade glioma and Study 2 was
an open-label study of 36 patients with recurrent high-grade glioma. In Studies 1 and 2, after initial
debulking was carried out under white light, biopsies were obtained under fluorescent light from
fluorescent and nonfluorescent sites. Presence of fluorescence (positive/negative) was compared to
tumor status (true/false) using histopathology as the reference standard. True positives and false
positives among fluorescent biopsies and true negatives and false negatives among nonfluorescent
biopsies are provided in Table 1.
Study 3 was a randomized, multicenter study in 415 patients with a preoperative diagnosis of high-grade
glioma by MRI. Patients were randomized in 1:1 ratio to ALA fluorescence arm or to white light control
arm. Biopsies were obtained from tumor-core, tumor-margin and regions just distant to the tumor
margins. In 349 patients high grade glioma was confirmed by a blinded central read and histopathology.
The remaining patients were diagnosed with metastatic disease, abscess, low-grade glioma or other
conditions.
In patients with confirmed high-grade glioma randomized to the ALA fluorescence arm, presence of
fluorescence at a biopsy level was compared to tumor status using histopathology as the reference
standard (Table 1). In 4 patients with low-grade glioma (WHO Grade I or II) who received ALA HCl, 9
out of 10 biopsies were false negative.
The extent of resection among patients with confirmed high-grade glioma in the ALA fluorescence arm
was compared to that among patient in the control arm, with the "completeness" of resection being
determined by a central blinded read of early post-surgical MRI. Percentage of patients who had
"completeness" of resection was 64% in the ALA arm and 38% in the control arm, with the difference
of 26% [95% CI: (16%, 36%)].
Table 1. Presence of Fluorescence Compared to Histopathology (biopsy
level)
|
Study 1
(N=297)* |
Study 2
(N=370)* |
Study 3
(N=479)* |
Number of Fluorescent
Biopsies |
185 |
354 |
319 |
True Positive |
178 |
342 |
312 |
False Positive |
7 |
12 |
7 |
Number of Nonfluorescent
Biopsies |
112 |
16 |
160 |
True Negative |
27 |
3 |
30 |
False Negative |
85 |
13 |
130 |
* N is Number of total (fluorescent and non-fluorescent) biopsies |