Influence of patient and tumor characteristics on therapy persistence with letrozole in postmenopausal women with advanced breast cancer: results of the prospective observational EvAluate-TM study

Background: Treatment of postmenopausal, hormone receptor-positive metastatic breast cancer (MBC) patients varies despite clear therapy guidelines, favoring endocrine treatment (ET). Aim of this study was to analyze persistence of palliative aromatase inhibitor (AI) monotherapy in MBC patients. Methods: EvAluate-TM is a prospective, multicenter, noninterventional study to evaluate treatment with letrozole in postmenopausal women with hormone receptor–positive breast cancer. To assess therapy persistence, defined as the time from therapy start to the end of the therapy (TTEOT), two pre-specified study visits took place after 6 and 12 months. Competing risk survival analyses were performed to identify patient and tumor characteristics that predict TTEOT. Results: Out of 200 patients, 66 patients terminated treatment prematurely, 26 (13%) of them due to causes other than disease progression. Persistence rate for reasons other than progression at 12 months was 77.7%. Persistence was lower in patients who reported any adverse event (AE) in the first 30 days of ET (89.5% with no AE and 56% with AE). Furthermore, patients had a lower persistence if they reported compliance problems in the past before letrozole treatment. Conclusions: Despite suffering from a life-threatening disease, AEs of an AI will result in a relevant number of treatment terminations that are not related to progression. Some subgroups of patients have very low persistence rates. Especially with regard to novel endocrine combination therapies, these data imply that some groups of patients will need special attention to guide them through the therapy process. Trial registration Clinical Trials Number: CFEM345DDE1

Quantitative Measurement of cAMP Concentration Using an Exchange Protein Directly Activated by a cAMP-Based FRET-Sensor

Förster resonance energy transfer (FRET)-based biosensors for the quantitative analysis of intracellular signaling, including sensors for monitoring cyclic adenosine monophosphate (cAMP), are of increasing interest. The measurement of the donor/acceptor emission ratio in tandem biosensors excited at the donor excitation wavelength is a commonly used technique. A general problem, however, is that this ratio varies not only with the changes in cAMP concentration but also with the changes of the ionic environment or other factors affecting the folding probability of the fluorophores. Here, we use a spectral FRET analysis on the basis of two excitation wavelengths to obtain a reliable measure of the absolute cAMP concentrations with high temporal and spatial resolution by using an “exchange protein directly activated by cAMP”. In this approach, FRET analysis is simplified and does not require additional calibration routines. The change in FRET efficiency (E) of the biosensor caused by [cAMP] changes was determined as ΔE = 15%, whereas E varies between 35% at low and 20% at high [cAMP], allowing quantitative measurement of cAMP concentration in the range from 150 nM to 15 μM. The method described is also suitable for other FRET-based biosensors with a 1:1 donor/acceptor stoichiometry. As a proof of principle, we measured the specially resolved cAMP concentration within living cells and determined the dynamic changes of cAMP levels after stimulation of the Gs-coupled serotonin receptor subtype 7 (5-HT7)

Serotonin targets inhibitory synapses to induce modulation of network functions

The cellular effects of serotonin (5-HT), a neuromodulator with widespread influences in the central nervous system, have been investigated. Despite detailed knowledge about the molecular biology of cellular signalling, it is not possible to anticipate the responses of neuronal networks to a global action of 5-HT. Heterogeneous expression of various subtypes of serotonin receptors (5-HTR) in a variety of neurons differently equipped with cell-specific transmitter receptors and ion channel assemblies can provoke diverse cellular reactions resulting in various forms of network adjustment and, hence, motor behaviour

5-HT7 receptor is coupled to G alpha subunits of heterotrimeric G12-protein to regulate gene transcription and neuronal morphology.

The neurotransmitter serotonin (5-HT) plays an important role in the regulation of multiple events in the CNS. We demonstrated recently a coupling between the 5-HT4 receptor and the heterotrimeric G13-protein resulting in RhoA-dependent neurite retraction and cell rounding (Ponimaskin et al., 2002). In the present study, we identified G12 as an additional G-protein that can be activated by another member of serotonin receptors, the 5-HT7 receptor. Expression of 5-HT7 receptor induced constitutive and agonist-dependent activation of a serum response element-mediated gene transcription through G12-mediated activation of small GTPases. In NIH3T3 cells, activation of the 5-HT7 receptor induced filopodia formation via a Cdc42-mediated pathway correlating with RhoA-dependent cell rounding. In mouse hippocampal neurons, activation of the endogenous 5-HT7 receptors significantly increased neurite length, whereas stimulation of 5-HT4 receptors led to a decrease in the length and number of neurites. These data demonstrate distinct roles for 5-HT7R/G12 and 5-HT4R/G13 signaling pathways in neurite outgrowth and retraction, suggesting that serotonin plays a prominent role in regulating the neuronal cytoarchitecture in addition to its classical role as neurotransmitter