Identifying molecular targets mediating the anticancer activity of histone deacetylase inhibitors: a work in progress

The anticancer properties of histone deacetylase inhibitors have been known for some time. However, it is only recently that the functional identities of the intracellular targets mediating the anticancer properties have started to be revealed. These targets appear to play significant roles in cell cycle control, apoptosis and differentiation. Importantly, the modulation of these activities is likely to be mediated by alterations in the acetylation status of both histone and non-histone targets. Identification of these targets, and the specific histone deacetylase enzymes that modulate them, is an important step in designing rational-based therapies for the treatment of cancer. In this review we discuss the state of progress in identifying the molecular pathways/events mediating the anticancer activity of histone deacetylase inhibitors.     

Stromal inhibition of megakaryocytic differentiation is associated with blockade of sustained Rap1 activation

Coculture with stromal cells tends to maintain normal hematopoietic progenitors and their leukemic counterparts in an undifferentiated, proliferative state. An example of this effect is seen with megakaryocytic differentiation, wherein stromal contact renders many cell types refractory to potent induction stimuli. This inhibitory effect of stroma on megakaryocytic differentiation correlates with a blockade within hematopoietic cells of protein kinase C-epsilon (PKC-epsilon) up-regulation and of extracellular signal-regulated kinase/mitogen-activated protein (ERK/MAP) kinase activation, both of which have been implicated in promoting megakaryocytic differentiation. In this study K562DeltaRafER.5 cells, expressing an estradiol-responsive mutant of the protein kinase Raf-1, were used to determine the relevance and stage of ERK/MAPK pathway blockade by stromal contact. Activation of DeltaRafER by estradiol overrode stromal blockade of megakaryocytic differentiation, implicating the proximal stage of the ERK/MAPK pathway as a relevant control point. Because stromal contact blocked delayed but not early ERK activation, the small guanosine triphosphatase (GTPase) Rap1 was considered as a candidate inhibitory target. Activation assays confirmed that Rap1 underwent sustained activation as a result of megakaryocytic induction, as previously described. As with ERK activation, stromal contact selectively blocked delayed but not early Rap1 activation, having no effect on Ras activation. Enforced expression of either wild-type Rap1 or the GTPase (GAP) resistant mutant Rap1 V12 failed to override stromal inhibition, suggesting that the inhibitory mechanism does not involve GAP up-regulation but rather may target upstream guanine nucleotide exchange factor (GEF) complexes. Accordingly, coimmunoprecipitation demonstrated stromally induced alterations in a protein complex associated with c-Cbl, a scaffolding factor for Rap1-GEF complexes.     

Fibroblast growth factor receptor-1 and neonatal compensatory lung growth after exposure to 95% oxygen

Neonatal rats exposed to 95% oxygen (O2) for 7 days from birth had inhibited lung growth, DNA synthesis, and secondary septation. These parameters were rapidly restored by a period of recovery in air. Northern and Western blot analysis and immunohistochemistry were used to screen for the fibroblast growth factor receptor-1 (FGF-R1) and its high affinity ligand, basic fibroblast growth factor (bFGF), which could have a role in this recovery process. Expression of bFGF in the lung was significantly reduced at the end of the 7-day exposure to 95% O2 and was increased after 3 days of recovery in air. Expression of FGF-R1 was not affected by exposure to 95% O2 or recovery in air. We hypothesized that the increase in bFGF after removal from 95% O2, acting through the FGF-R1, would be critical for compensatory growth. Intraperitoneal injection of soluble truncated FGF-R1 at the onset of the recovery phase arrested compensatory lung DNA synthesis and secondary septation seen in control animals after 3 days of recovery, confirming a role for FGF-R1 in this model of compensatory neonatal lung growth.     

Suberoylanilide hydroxamic acid (SAHA) overcomes multidrug resistance and induces cell death in P-glycoprotein-expressing cells

Multidrug resistance (MDR) mediated by the ATP-dependent efflux protein P-glycoprotein (P-gp) is a major obstacle to the successful treatment of many cancers. In addition to effluxing toxins, P-gp has been shown to protect tumor cells against caspase-dependent apoptosis mediated by Fas and tumor necrosis factor receptor (TNFR) ligation, serum starvation and ultraviolet (UV) irradiation. However, P-gp does not protect against caspase-independent cell death mediated by granzyme B or pore-forming proteins (perforin, pneumolysin and activated complement). We examined the effects of the chemotherapeutic hybrid polar compound suberoylanilide hydroxamic acid (SAHA) on P-gp-expressing MDR human tumor cell lines. In the CEM T-cell line, SAHA, a histone deacetylase inhibitor, induced equivalent death in P-gp-positive cells compared with P-gp-negative cells. Cell death was marked by the caspase-independent release of cytochrome c, reactive oxygen species (ROS) production and Bid cleavage that was not affected by P-gp expression. However, consistent with our previous findings, SAHA-induced caspase activation was inhibited in P-gp-expressing cells. These data provide evidence that P-gp inhibits caspase activation after chemotherapeutic drug treatment and demonstrates that SAHA may be of value for the treatment of P-gp-expressing MDR cancers.     

Is implicit learning spared in amnesia? Rule abstraction and item familiarity in artificial grammar learning

We examined implicit learning of an artificial grammar in amnesic and control participants. The "biconditional" grammar used to generate study and test strings allows two potential sources of judgements in artificial grammar learning to be unconfounded: participants could either learn the abstract biconditional rules or could learn about the distributional statistics of the surface elements (e.g. bigrams) composing the study items. Test strings varied these two sources orthogonally. We found no evidence of abstract rule learning either in the control or amnesic groups. In contrast, both groups learned about the surface elements and tended to call test strings "grammatical" when they were composed of familiar bigrams. However, this sensitivity to bigram familiarity was significantly reduced in the amnesic compared to the control group. The results challenge the claim that implicit learning is intact in amnesia.     

Local injection of pertussis toxin attenuates morphine withdrawal excitation of rat supraoptic nucleus neurones

Morphine inhibits oxytocin neurones via G(i/o)-protein-linked mu-opioid receptors. Following chronic morphine administration oxytocin cells develop dependence, shown by withdrawal excitation after administration of the opioid antagonist, naloxone. Here, inactivation of G(i/o)-proteins by pre-treatment of morphine-dependent rats with pertussis toxin injected into the left supraoptic nucleus reduced withdrawal-induced Fos protein expression within the injected nucleus by 41+/-10% compared to the contralateral nucleus, indicating that functional G(i/o)-proteins are essential for the development and/or expression of morphine dependence by oxytocin cells in the supraoptic nucleus. In another group of rats, pertussis toxin did not alter the responses to either systemic cholecystokinin administration or systemic hypertonic saline administration, indicating that pertussis toxin does not prevent oxytocin cells from responding to stimuli that are not mediated by G(i/o)-proteins. Finally, pertussis toxin reduced acute morphine inhibition of systemic hypertonic saline-induced Fos protein expression in the supraoptic nucleus, confirming that pertussis toxin effectively inactivates G(i/o)-proteins in the supraoptic nucleus. Thus, the expression of morphine withdrawal excitation by supraoptic nucleus oxytocin cells requires the functional integrity of G(i/o)-proteins within the nucleus.     

Obstetric risk factors for postnatal depression in urban and rural community samples

OBJECTIVE: The objective of this study was to examine obstetric risk factors for postnatal depression in an urban and rural community sample, with concurrent consideration of personality, psychiatric history and recent life events. METHODS: This was a prospective study with women planning to give birth in one of the four participating hospitals recruited antenatally. Obstetric information was obtained from the New South Wales Midwives Data Collection, completed shortly after delivery. Personality, psychiatric history and life-events information were obtained from a questionnaire, administered within 1 week postpartum. Depression status was assessed at 8 weeks postpartum using the Edinburgh Postnatal Depression Scale. RESULTS: Complete data were obtained from 490 women. Several non-obstetric risk factors for the development of postnatal depression at 8 weeks postpartum were reported including: sociodemographic (up to technical college level education, rented housing, receiving a pension/benefit), personality (those who described themselves as either nervy, shy/selfconscious, obsessional, angry or a worrier), psychiatric history (familial history of mental illness, personal history of depression or anxiety or a history of depression in the participant's mother) and recent life-events (major health problem, arguments with partner and friends/relatives). None of the obstetric variables were significantly associated with increased risk for postnatal depression, but several showed marginally significant increases (multiparous women, antepartum haemorrhage, forceps and caesarean section deliveries). CONCLUSIONS: The results emphasize the importance of psychosocial risk factors for postnatal depression and suggest that most obstetric factors during pregnancy and birth do not significantly increase risk for this depression. Early identification of potential risk for postnatal depression should include assessment of sociodemography, personality, psychiatric history and recent life events, as well as past and present obstetric factors.     

A randomized, controlled trial of a brief interventional package for schizophrenic out-patients

OBJECTIVE: To evaluate the impact on outcome of a simple educational intervention in schizophrenic patients at risk of relapse. Method: At discharge, 114 schizophrenic patients with at least one previous episode were assigned randomly to a simple educational intervention which had no resource implications, or standard care. RESULTS: The intervention failed to improve outcome. While insight and treatment attitudes improved, suicidal ideation increased. Systematic management of treatment-emergent adverse effects offered no benefits, although incapacitation from extrapyramidal side-effects at discharge predicted relapse. CONCLUSION: There are limits to which psychoeducational interventions can be simplified without loss of effectiveness in terms of relapse prevention in schizophrenia. Enhanced insight may be associated with increased suicidal ideation.