The impact of JAK1/2 inhibitor therapy prior to allogeneic hematopoietic cell transplantation (HCT) has not been studied in a large cohort in myelofibrosis (MF). In this retrospective multicenter study, we analyzed outcomes of patients who underwent HCT for MF with prior exposure to JAK1/2 inhibitors. One hundred consecutive patients from participating centers were analyzed, and based on clinical status and response to JAK1/2 inhibitors at the time of HCT, patients were stratified into five groups: (a) clinical improvement (n=23), (b) stable disease (n=31), (c) new cytopenia/increasing blasts/intolerance (n=15), (d) progressive disease: splenomegaly (n=18), and (e) progressive disease: leukemic transformation (LT) (n=13). Overall survival (OS) at two years was 61% (95%CI, 49–71). This was 91% (95% CI, 69–98) for those who experienced clinical improvement, and 32% (95% CI, 8–59) for those who developed LT on JAK1/2 inhibitors. In multivariable analysis, response to JAK1/2 inhibitors (p=0.03), DIPSS score (p=0.003), and donor type (p=0.006) were independent predictors of survival. Among the 66 patients who remained on JAK1/2 inhibitors until stopped for HCT, two patients developed serious adverse events necessitating delaying of HCT, and another 8 patients had symptoms with lesser severity. Adverse events were more common in patients who started tapering or abruptly stopped their regular dose ≥6 days prior to conditioning therapy. We conclude that prior exposure to JAK1/2 inhibitors did not adversely affect post-transplant outcomes. Our data suggest that JAK1/2 inhibitors should be continued near to the start of conditioning therapy. The favorable outcomes of patients who experienced clinical improvement with JAK1/2 inhibitor therapy prior to HCT were particularly encouraging, and need further prospective validation.

Negative regulation of neuronal serotonin (5-HT1A) receptor levels by glucocorticoids in vivo may contribute to depression. Both types I (mineralocorticoid) and II (glucocorticoid) receptors (MR and GR, respectively) participate in corticosteroid-induced transcriptional repression of the 5-HT1A gene; however, the precise mechanism is unclear. A direct repeat 6-base pair glucocorticoid response element (GRE) half-site 5-TGTCCT separated by 6 nucleotides was conserved in human, mouse, and rat 5-HT1A receptor promoters. In SN-48 neuronal cells that express MR, GR, and 5-HT1A receptors, deletion or inactivation of the nGRE (negative GRE) eliminated negative regulation of the rat 5-HT1A or heterologous promoters by corticosteroids, whereas its inclusion conferred corticosteroid-induced inhibition to a heterologous promoter. Bacterially expressed recombinant MR and GR preferentially bound to the nGRE as a heterodimer, as identified in nuclear extracts of MR/GR-transfected COS-7 cells, and with higher affinity than MR or GR homodimers. In SN48 and COS-7 cells, concentration-dependent coactivation of MR and GR was required for maximal inhibitory action by corticosteroids and was abrogated in the L501P-GR mutant lacking DNA binding activity. Corticosteroid-mediated transcriptional inhibition was greater for MR/GR in combination than for MR or GR alone. These data represent the first identification of an nMRE/GRE and indicate that heterodimerization of MR and GR mediates direct corticosteroid-induced transrepression of the 5-HT1A receptor promoter.

The serotonergic neurons of the raphe nuclei are the primary site of serotonin synthesis in the brain. They send projections to a wide variety of brain regions, including the hippocampus, cortex, limbic system, and hypothalamus (1). Activation of postsynaptic receptors in the above regions is associated with serotonergic regulation of memory, motivation, emotion, neuroendocrine stress response, etc. (2-4). The activity of serotonergic neurons of the raphe nuclei is regulated in part by presynaptic autoreceptors. The 5-HT1A autoreceptor is located at the cell body and dendrites of raphe serotonergic neurons (5, 6) and mediates negative feedback inhibition of the firing rate through recurrent activation of potassium channels via pertussis toxin-sensitive G proteins (7) to decrease serotonin release. Thus the 5-HT1A receptor plays a major role in controlling serotonergic outflow to the wide variety of brain regions that are innervated by the raphe nuclei.Abnormal regulation of 5-HT1A receptor expression is implicated in depression and anxiety disorders. 5-HT1A receptor knockout mice display increased anxiety-related behaviors (8 -10), suggesting that a loss of the 5-HT1A autoreceptors is correlated with symptoms of anxiety (3). On the other hand, 5-HT1A receptor levels are increased in the midbrain of suicide victims with major depression compared with nondepressed suicides (11). Down-regulation of the 5-HT1A autoreceptor by antidepressants (12, 13) disinhibits action potential firing of the raphe neuron, thereby enhancing serotonergic neurotransmission (14 -17). The prolonged (2-3 week) time course required for antidepressant action suggests an alteration in transcriptional activity of the 5-HT1A receptor.To investigate the mechanisms that regulate cell-specific and basal regulation of the 5-HT1A receptor, we have identified the transcriptional start site and examined the regulation of the transcriptional activity of a 2.719-kb 1 fragment of the rat 5-HT1A receptor gene in several cell lines, including 5-HT1A receptor-positive RN46A raphe and SN48 septal cells (18 -20) and receptor-negative L6 myoblast and C6 glioblastoma cells (21). We identified a region of the rat 5-HT1A receptor gene located upstream of an ubiquitously active promoter region that reduces transcriptional activity. In the present study, we have identified a 14-bp element in the 5Ј-flanking region of the 5-HT1A gene that mediates transcriptional repression in raphe cells, but is dispensable in receptor-negative cells where an adjacent 12-bp element maintains repression of the gene. In contrast to the single repressor-DNA complex present in 5-HT1A receptor-expressing cells that may modulate basal levels of receptor expression, the presence of two protein-DNA complexes in receptor-negative cell lines provides a dual mechanism to repress 5-HT1A receptor expression.

The hypothesis that antianxiety or antidepressant agents (e.g., Serotonin uptake inhibitors (e.g., fluoxetine, paroxetine) and selective 5-HTIA receptor partial agonists (e.g., buspirone, ipsapirone) are effective in the treatment of major depression and generalized anxiety disorder but require several weeks of drug treatment to observe clinical improvement (Blier et al. 1990; Charney et al. 1990). Acting via distinct mechanisms, these compounds share the property of enhancing serotonergic neurotransmission by selectively downregulating 5-HTIA receptors located on the serotonergic cell body (Azmitia 1994). Serotonin 1A receptors act as inhibitory autoreceptors on serotonergic neurons of the raphe nuclei, whereas 5-HTIB receptors act as inhibitory presynaptic receptors at serotonergic nerve terminals. Both of these 5-HT receptors participate in a negative feedback loop to inhibit serotonergic activity (Figure 1). In experimental animals, long-term treatment with antidepressants induces selective loss of 5-HTIA autoreceptors without altering the responsiveness of postsynaptic 5-HTIA receptors (Welner et al. 1989;Blier et al. 1990; Fanelli and McMonagle-Strucko 1992). Uptake blockers may mediate this action due to chronic elevation of 5-HT levels at the synaptic deft, leading to autoreceptor downregulation. Serotonin 1A receptor agonists appear to have a direct action on the autoreceptor to induce its desensitization. Desensitization of the autoreceptor disinhibits the serotonergic neuron, enhancing the rate of action potential h_ring to augment serotonergic neurotransmission. Increase in serotonergic neurotransmission correlates with the antidepressant or antianxiety activity of these therapeutic compounds. Interestingly, chronic enhancement of serotonergic neurotransmission induced by uptake blockers is potentiated by 5-HTIA receptor agonists, suggesting the importance of autoreceptor desensitization in antidepressant action (Hjorth 1993). The cellular mechanisms involved in the longterm regulation of the 5-HTIA receptor remain uncharacterized, although the time course of therapeutic drug action suggests an effect of these compounds on gene transcription of components in the 5-HT1A receptor signaling system: either the receptor (Welner et al. 1989; 0893-133X/96/$15.00 SSDI 0893-133X(94)00044-Z