A 2-Part, Randomized, Double-blind, Double-Dummy, Placebo- and Active Comparator-controlled, Repeat Dose Study to Establish Proof-of-Concept of GRX-917 in Experimentally Induced Panic and to Further Characterize its Repeated Dose Pharmacokinetics and Pharmacodynamics in Healthy Subjects

The pharmacological treatment of anxiety disorders and anxiety-related states
is limited by important shortcomings. Currently available first-line treatments
such as Selective serotonin reuptake inhibitors (SSRIs) and Serotonin and
Norepinephrine Reuptake Inhibitors (SNRIs) are characterized by slow onset of
action and/or (partial) ineffectiveness in up to 50% of patients, and although
benzodiazepines (BZDs) as second line treatment are effective, their use is
limited by side effects such as sedation, memory deficits, risk of falling, and
liability for dependence and abuse. Altogether, there is a need for novel
anxiolytic compounds with superior efficacy and improved side effect profiles
compared to currently available drugs.

Etifoxine hydrochloride (etifoxine; Stresam®) is an anxiolytic drug approved in
France in 1979 and has demonstrated efficacy comparable to BZDs such as
lorazepam, alprazolam, and clonazepam. It primarily potentiates
neurosteroidogenesis via targets distinct from those engaged by BZDs, and
demonstrates a side effect profile superior to BZDs. Moreover, etifoxine
demonstrates therapeutic uses in anxiety-related states, depression, and
epilepsy.

GRX-917 is a novel, deuterated form of etifoxine hydrochloride that potentiates
neurosteroidogenesis. The major circulating metabolite of GRX-917 M4
(N-desethyl metabolite) does not contribute to the anxiolytic activity.

In early phase CNS drug trials, challenge paradigms are often applied to
demonstrate pharmacodynamic effects in healthy human subjects. Particularly, in
anxiolytic drug development, challenges that experimentally induce anxiety
and/or fear are especially relevant to novel mechanisms-of-action such as
neurosteroidogenesis, since anxiolytic effects are not expected under basal,
non-challenged circumstances in healthy volunteers. This approach can increase
confidence moving forward towards larger proof-of-concept and/or therapeutic
trials in anxiety patient populations. Although various pharmacological and
behavioural challenges have been used to this effect in the past, outcomes have
been largely inconsistent due to inadequate validation and/or methodological
variability across research groups. Acute intrapulmonary administration of
carbon dioxide (CO2) has however consistently demonstrated the provocation of a
panic reaction in sensitive healthy volunteers that phenomenologically and
physiologically resembles panic attacks in patients with anxiety disorders. In
addition, it has been shown to be sensitive to pharmacological manipulation by
a range of drugs used to treat anxiety disorders and emerging new treatments
with novel mechanisms of action. CO2 inhalation in humans therefore displays
adequate face-validity as a panic challenge in experimental drug research for
proof-of-anxiolysis of novel compounds such as GRX-917.

Part 1:
Primary Objective
- To investigate whether repeated dose GRX-917 reduces panic symptoms elicited
by an experimental 35% CO2 -induced fear challenge administered in healthy
CO2-sensitive subjects.

Secondary Objectives
- To investigate whether repeated dose GRX-917 reduces subjective fear elicited
by an experimental 35% CO2 -induced fear challenge in healthy CO2-sensitive
subjects
- To investigate if repeated doses of GRX-917 modulate the cardiovascular
response elicited by an experimental 35% CO2 -induced fear challenge in healthy
CO2-sensitive subjects
- To further characterize the plasma pharmacokinetics (PK) of repeated doses of
GRX-917 and its major metabolite, M4, in healthy CO2-sensitive subjects
- To evaluate the pharmacodynamic (PD) effects of GRX-917 following single and
multiple oral doses using NeuroCart assessment in healthy CO2-sensitive subjects
- To further investigate the safety and tolerability of multiple dose GRX-917
in healthy CO2-sensitive subjects

Part 2:
Primary Objective
- To explore whether repeated doses of GRX-917 up to 27 days is associated with
auto-induction of its metabolism in healthy subjects
- To characterize the CSF PK of GRX-917 and its major metabolite M4 following
repeated doses up to 27 days

Secondary Objectives
- To further characterize the plasma PK of GRX-917 and its major metabolite M4
following repeated doses up to 27 days
- To further explore the safety and tolerability of GRX-917 repeated doses up
to 27 days
- To evaluate the pharmacodynamic (PD) effects of GRX-917 following multiple
oral doses using NeuroCart assessment in healthy subjects

Part 1 (Proof-of-Concept)
Randomized, Double-blind, Double-Dummy, Placebo- and Active
Comparator-controlled study investigating the potential panicolytic effects of
GRX-917 following repeated dosing using an experimental CO2 inhalation
challenge in healthy volunteers.
The 35% CO2 double-breath inhalation challenge test will be used to provoke
subjective fear and its related physical symptoms.

Part 2 (Plasma and CSF pharmacokinetics and pharmacodynamics)
Open-label, repeated dose administration of 27 days (10 days total in-house
dosing and 17 days total outpatient dosing).

GRX-917
Alprazolam

GRX-917
GRX-917 is not expected to provide any clinical benefit to healthy subjects.
The trial is designed primarily to generate preliminary efficacy, safety,
tolerability, and pharmacokinetic (PK) data which will inform further clinical
development for the treatment of amongst others anxiety disorders.
There are no important identified risks for GRX-917, however, preclinical
testing with GRX-917 has demonstrated the potential for prolongation of the QT
interval. More detailed information about the known and expected benefits and
risks and reasonably expected AEs of GRX-917 are found in the Investigator*s
Brochure.
The study design has been used previously in many studies and is accepted by
scientists and regulatory authorities. All study drug administrations for part
1 will be done in the clinic under medical supervision. Thus, the subjects can
be closely monitored for any adverse signs during the different treatments.
Therefore, providing the protocol is adhered to, careful observation and
medical management will minimize any associated risk in this study. For part 2,
the first two dosing will be done under medical supervision. Subsequently, the
subject leaves the Clinical Research Unit if the IMP is well tolerated by the
subjects. The subjects then continue the outpatient dosing at his own home.

Alprazolam
The BZD alprazolam is a non-selective GABAA PAM and is indicated for the
short-term treatment of moderate or severe anxiety states and anxiety
associated with depression. As the subjective anxiogenic effects elicited by
the 35% CO2 double breath inhalation challenge were previously shown to be
decreased by alprazolam 1 mg BID (Salvadore et al, 2019, and Cerevel 2022), it
will be used as active comparator to facilitate the interpretation of the PD
effects of GRX-917. Administration of alprazolam over a period of 8 days is not
expected to induce dependence in the selected trial population.

CO2 inhalation
The acute inhalation of 35% CO2 has been developed and validated as a reliable
challenge model to induce an acute panic reaction that adequately resembles
panic attacks phenomenologically. Both CO2 and O2 are harmless physiological
substances that are inhaled according to a standardized challenge protocol that
has been developed by Maastricht University. Numerous trials in several hundred
healthy volunteers and patients suffering from panic disorder, social anxiety
disorder, post-traumatic stress disorder, and major depressive disorder have
been conducted according to this protocol over the past 30 years. In the
majority of these trials, a mixture of 35% CO2/65% O2 had been administered as
either single or double vital capacity inhalation. To the best of CHDR*s
knowledge in all performed trials, neither acute nor chronic related AEs have
been reported and no related SAEs have occurred. Evidence from prospective
trials point out that healthy volunteers who underwent 35% CO2 inhalation were
not at greater risk to develop panic disorder in the years following the
challenge. To ensure subject safety for the current trial, absolute and
relative contra-indications are harmonized with previous protocols and are
incorporated into the inclusion and exclusion criteria of the protocol.

CSF sampling
The procedure of continuous CSF sampling by indwelling CSF catheters has been
demonstrated to be safe and well tolerated in previous studies performed by
CHDR. Side effects were generally mild, with headache, back pain and catheter
site pain most frequently reported.