Clinical Pharmacology for Kebilidi
Mechanism Of Action
KEBILIDI is a recombinant adeno-associated virus serotype 2 (rAAV2) based gene therapy designed to deliver a copy of the DDC gene which encodes the AADC enzyme. Intraputaminal infusion of KEBILIDI results in AADC enzyme expression and subsequent production of dopamine in the putamen.
Pharmacodynamics
Homovanillic Acid In Cerebrospinal Fluid
In Study 1, homovanillic acid (HVA), a downstream metabolite of dopamine, in cerebrospinal fluid (CSF) was measured at baseline, Week 8, and Week 48 using a high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). In all patients of Study 1, an increase in CSF HVA levels from baseline was observed at Week 8 and Week 48 (Table 4).
Table 4: HVA Levels in CSF (Study 1)
| Timepoint |
Observed Values (nmol/L) |
Change from Baseline (nmol/L) |
Percent Change from Baseline (%) |
| Baseline |
| N |
13 |
- |
- |
| Median (Min, Max) |
3.34 (1.00, 93.73) |
- |
- |
| Week 8 |
| N |
12 |
12 |
12 |
| Median (Min, Max) |
35.09 (15.09, 150.48) |
26.62 (12.49, 56.75) |
534.7 (57.4, 2810.0) |
| Week 48 |
| N |
9 |
9 |
9 |
| Median (Min, Max) |
29.16 (14.21, 125.84) |
24.7 (13.21, 58.02) |
773.1 (33.9, 3991.0) |
Note: Lower limit of quantification (LLOQ) was 2 nmol/L, and values reported as <LLOQ were imputed as 0.5*LLOQ.
Abbreviations: CSF=cerebrospinal fluid; HVA=homovanillic acid; N=number of subjects; Max=maximum; Min=minimum |
18F-DOPA Uptake In The Putamen
18F-DOPA is a positron-emitting fluorine-labeled substrate of the AADC enzyme. Following administration of 18F-DOPA, its uptake into the putamen assessed by positron emission tomography (PET) imaging reflects AADC enzyme activity of dopaminergic neurons in the putamen. In Study 1, 18F-DOPA uptake in the putamen was assessed at baseline and followed up at Week 8 in 12 out 13 patients and at Week 48 in 10 out 13 patients indicating increased AADC 18F-DOPA uptake in all assessed patients. The median (range) percent increase from baseline was 259% (65% to 620%) at Week 8 and 271% (25% to 760%) at Week 48.
Pharmacokinetics
Biodistribution (Within The Body) And Vector Shedding (Excretion/Secretion)
KEBILIDI vector DNA levels in various tissues and secretions were determined using a validated quantitative polymerase chain reaction (qPCR) assay.
Nonclinical Data
Biodistribution of eladocagene exuparvovec-tneq was evaluated in rats at Days 7, 30, 90, and 180 after single-dose intraputaminal infusion at dose levels up to 7.5×109 vg/animal (21-fold higher than the recommended human dose based on relative brain weight). At Day 7, vector DNA was observed in the putamen, cerebellum, cerebrum, and spinal cord. Vector DNA levels declined from Day 7 to Day 90, with DNA levels primarily sustained in the putamen at Day 180.
Clinical Data
Following administration of KEBILIDI at a total dose for each patient of 1.8×1011 vg in Study 1, biodistribution and viral shedding in CSF, blood, and urine were evaluated in 13 patients. CSF was collected at Weeks 8 and 48, and blood and urine were collected from Day 3 up to Week 48. Five (38%) patients showed detectable vector DNA levels in blood at Day 3 ranging from 4.0×103 to 6.5×103 copies/mL, which became below the limit of detection (<3.1×103 copies/mL) by Week 3. No vector was detected in CSF or urine.
Immunogenicity
The observed incidence of anti-AAV2 antibodies is highly dependent on the sensitivity and specificity of the assay. Differences in assay methods preclude meaningful comparisons of the incidence of anti-AAV2 antibodies in the studies described below with the incidence of anti-AAV2 antibodies in other studies.
There is no clinical experience with KEBILIDI in patients with pre-existing anti-AAV2 neutralizing antibody at titers >1:1200.
In Study 1, anti-AAV2 total binding antibodies and anti-AAV2 neutralizing antibodies were assessed from Day 3 up to Week 48 following administration of KEBILIDI. In all patients  (N=13), titers of total binding antibody and neutralizing antibody increased from Week 3 and remained elevated, as measured at Week 48 (N=9). The highest titers in each patient ranged from 1:800 to 1:204,800 for total binding antibodies and from 1:80 to 1:10,240 for neutralizing antibody. Because of the small sample size of Study 1, there is insufficient data to determine the effect of anti-AAV2 antibody on the pharmacokinetics, pharmacodynamics, safety, or effectiveness.
Clinical Studies
The efficacy of KEBILIDI was evaluated in one open-label, single arm study (Study 1;
NCT04903288). The study enrolled pediatric patients with genetically confirmed, severe AADC deficiency who had achieved skull maturity assessed with neuroimaging. The main efficacy outcome measure was gross motor milestone achievement evaluated at week 48 and assessed using the Peabody Developmental Motor Scale, Second Edition (PDMS-2). Patients treated with KEBILIDI were compared to an external untreated natural history cohort of 43 pediatric patients with severe AADC deficiency who had at least one motor milestone assessment after 2 years of age.
A total of 13 patients received a single total dose of 1.8×1011 vg of KEBILIDI given as four intraputaminal infusions in a single stereotactic neurosurgical procedure. The demographic characteristics of the population were as follows: the median age was 2.8 years (1.3 to 10.8 years), 7 patients (54%) were female, 10 patients (77%) were Asian, 2 patients (15%) were White, and 1 patient was of “other” race. Twelve of the 13 patients had the severe phenotype of AADC deficiency, defined as having no motor milestone achievement at baseline and no clinical response to standard of care therapies. The one remaining patient had a “variant” of the severe disease phenotype, with the ability to sit with assistance but with lack of head control.
Gross motor milestone achievement at Week 48 was assessed in 12 of the 13 patients treated in Study 1 (one patient dropped out of the study prior to Week 48).
Eight (67%) of the 12 treated patients achieved a new gross motor milestone at week 48: 3 patients achieved full head control, 2 patients achieved sitting with or without assistance, 2 patients achieved walking backwards and the patient with the “variant” severe phenotype was able to sit unassisted. The two patients who achieved walking backwards at week 48 were treated before 2 years of age. The four patients who were unable to achieve new gross motor milestones at week 48 were treated between the ages of 2.8 and 10.8 years. In comparison, none of the 43 untreated patients with the severe phenotype had documented motor milestone achievement at last assessment at a median age of 7.2 years (range 2 to 19 years).