A double-blind, randomized, placebo-controlled, cross-over, single center, pharmacodynamic trial to collect data for quantitative modeling of HPA axis modulation with desmopressin and CRH in healthy volunteers

Arginine vasopressin (AVP) together with Corticotrophin-Releasing Hormone (CRH)
is one of the main regulators of the activity of the
hypothalamus-pituitary-adrenal (HPA) axis. Hyperactivity of the HPA axis is one
of the key biological abnormalities described in major depressive disorder
(Barden et al, 1995), occurring in 30-50% of depressed
subjects, especially in subjects with melancholic depression. Many subjects
appear to respond poorly to standard antidepressant treatment (Dinan et al,
1994). AVP and CRH act synergistically in bringing about adrenocorticotrophic
(ACTH) release from the anterior pituitary, which releases cortisol from the
adrenal gland. By itself AVP is only a weak stimulus for ACTH secretion, but it
markedly potentates the stimulatory effects of CRH. In depression, sustained
hypercortisolemia is seen which is difficult to understand as the pituitary CRH
receptors are expected to undergo significant adaptive downregulation. It has
therefore been suggested that AVP might play a role in this HPA over-activity
(Von Bardeleben et al, 1988). Upon chronic stress in rats, paraventricular
hypothalamic neurons appear to shift from secretion of CRH to co-secretion of
AVP (Ma et al, 1998). Dinan et al. have observed that the reduced response to
CRH in depression was associated with an enhanced response to a combination of
CRH and desmopressin (dDAVP), -a synthetic analogue of vasopressin-, suggesting
that HPA axis regulation in depression shifts from primary regulation by CRH to
regulation towards a predominant AVP regulation (Dinan et al, 1999, Dinan et
al, 2004). Within the anterior pituitary, the *vasopressin 3* (V3) receptor
(also referred to as V1b receptor) is the binding site for AVP. Thus, V3
receptor antagonists may normalize the HPA regulation and reduce the HPA
disturbances observed in a proportion of depressed patients and provide
therapeutic benefit to these patients. In addition, over activity in the AVP/V3
system may not be specific for (melancholic) depression, but it may also be
encountered in other CNS disorders like anxiety, post traumatic stress disorder
and others.

Currently, Organon is investigating several potential V3 receptor antagonists
in preclinical development. In order to exploit optimally the clinical
potential of this novel concept of V3 antagonism, it is the intention to look
in advance for the potentially most responsive target population by exploring
V3 receptor responsivity. The aim is to identify these patient populations
using an objective biomarker for which a challenge test may be a suitable tool.
On basis of the current literature, the use of the synthetic vasopressin
analogue dDAVP, -possibly in combination with CRH-, as a challenge,and the
elevation of ACTH and cortisol as readout parameters seems the most promising.

Definition and validation (by means of cross-validation techniques) of such
challenge tests as objective parameter is to be done in a *negative* population
(i.e. normal HPA axis function - healthy volunteers) and a *positive*
population (i.e. hyperactive HPA axis function with enhanced vasopressinergic
responsivity - melancholic depressed patients (Dinan et al, 1999; Dinan et al,
2004). The optimal biomarker/challenge test is that test which best separates
melancholic depressive patients from healthy volunteers.

To develop and test adaptation of experimental paradigms, first studies in
healthy volunteers will be performed. In Organon 291002 *Part I*, ACTH and
cortisol responses upon a stepwise and bolus injection of dDAVP were studied as
well as the safety aspects linked to dDAVP injection. From the data of this
trial combined with the data from literature
(Dinan et al. 1999, 2004), it became clear that a challenge test based on dDAVP
alone may not have enough discriminatory potential to discriminate populations
with a hyperactive HPA axis function with enhanced vasopressinergic
responsivity fromthose with a normal HPA axis. CRH could be used to optimize a
challenge test as AVP and CRH display synergistic effects on the HPA axis.

Optimization may be achieved in two ways.
(1) AVP and CRH act synergistically in bringing about ACTH release from the
anterior pituitary, which releases cortisol from the adrenal gland.
Theoretically, a lack of CRH may prevent dDAVP to exert its full effect.
Therefore, a small amount of CRH added simultaneously to dDAVP may lower the
variability seen in ACTH/cortisol responses induced upon dDAVP only challenge.
By lowering the variability, the discriminatory potential may increase. A
potential downside of this approach may be that the mean ACTH/cortisol
concentration increases relatively more in healthy volunteers compared to
populations with a disturbed HPA axis. Another possible downside from this
approach may be that the variability in response of healthy volunteers who
already are sensitive to dDAVP alone might increase. This depends on the
unknown individual concentration-response curve to endogenous and exogenous CRH
and its intersubject variability.

(2) Instead of having a single challenge test simultaneously combining dDAVP
with a small amount of CRH, a potential discriminative test may also consist of
subsequent challenge tests of dDAVP and a (high) amount of CRH given at
different time-points. The ACTH/cortisol responses induced upon both challenges
can be used to categorize target populations on their HPA-axis status (e.g.
using a *ratio*, or a decision-tree approach). The downside of this approach
may be an increased
complexity in the logistics of the challenge test. The current protocol will
provide data to explore both hypotheses.

Primary objectives:
1) Describe the PD effects on plasma ACTH and serum cortisol upon 100 µg hCRH
injection with or without a preceding injection of 10 µg dDAVP 2 hours earlier
and study the PK-PD relationship (*Block B*). In particular, the outcome will
be used to determine the optimal (bolus) dose of hCRH to be used in a possible
future challenge test consisting of dDAVP followed by hCRH (*Block A*).
2) Describe the pharmacodynamic (PD) effects on plasma ACTH and serum cortisol
of dDAVP given together with different concentrations of hCRH and study the
PKPD relationship. In particular, the outcome will be used to investigate
whether
addition of a small amount of hCRH can reduce the variability in ACTH/cortisol
responses found after a challenge with 10 µg dDAVP. In addition, it will be
investigated how mean (maximum) ACTH/cortisol responses following a challenge
with 10 µg dDAVP will change upon addition of small amounts of hCRH (*Block B*).
3) Describe the pharmacokinetics (PK) of dDAVP and hCRH.

Secondary objectives:
1) evaluate the safety of dDAVP and hCRH injections
2) to bank DNA, extracted from blood samples, for future association studies of
genotype with the pharmacokinetic, pharmacodynamic and safety characteristics
obtained in this trial
3) to obtain results of questionnaires on mood, anxiety state and personality
structure for future analysis of these psychological characteristics in
relation to HPA axis sensitivity.

This trial will be a double-blind, randomized, placebo-controlled, cross-over,
single center, pharmacodynamic trial to collect data for quantitative modeling
of HPA axis modulation with desmopressin only, desmopressin with small amounts
of CRH and CRH only.

The experiment makes use of known drugs which have been use extensively and
with minimal risks involved. The burden for participants consists of blood
sampling and fluid restriction. Blood sampling will remain within the limiets
set ny the blood bank and constitutes a minimal burden.