Medical Needs and Therapeutic Options for Melanoma Patients Resistant to Anti-PD-1-Directed Immune Checkpoint Inhibition.

Available 4- and 5-year updates for progression-free and for overall survival demonstrate a lasting clinical benefit for melanoma patients receiving anti-PD-directed immune checkpoint inhibitor therapy. However, at least one-half of the patients either do not respond to therapy or relapse early or late following the initial response to therapy. Little is known about the reasons for primary and/or secondary resistance to immunotherapy and the patterns of relapse. This review, prepared by an interdisciplinary expert panel, describes the assessment of the response and classification of resistance to PD-1 therapy, briefly summarizes the potential mechanisms of resistance, and analyzes the medical needs of and therapeutic options for melanoma patients resistant to immune checkpoint inhibitors. We appraised clinical data from trials in the metastatic, adjuvant and neo-adjuvant settings to tabulate frequencies of resistance. For these three settings, the role of predictive biomarkers for resistance is critically discussed, as well as are multimodal therapeutic options or novel immunotherapeutic approaches which may help patients overcome resistance to immune checkpoint therapy. The lack of suitable biomarkers and the currently modest outcomes of novel therapeutic regimens for overcoming resistance, most of them with a PD-1 backbone, support our recommendation to include as many patients as possible in novel or ongoing clinical trials.

Melanoma brain metastases - Interdisciplinary management recommendations 2020.

Melanoma brain metastases (MBM) are common and associated with a particularly poor prognosis; they directly cause death in 60-70% of melanoma patients. In the past, systemic treatments have shown response rates around 5%, whole brain radiation as standard of care has achieved a median overall survival of approximately three months. Recently, the combination of immune checkpoint inhibitors and combinations of MAP-kinase inhibitors both have shown very promising response rates of up to 55% and 58%, respectively, and improved survival. However, current clinical evidence is based on multi-cohort studies only, as prospectively randomized trials have been carried out rarely in MBM, independently whether investigating systemic therapy, radiotherapy or surgical techniques. Here, an interdisciplinary expert team reviewed the outcome of prospectively conducted clinical studies in MBM, identified evidence gaps and provided recommendations for the diagnosis, treatment, outcome evaluation and monitoring of MBM patients. The recommendations refer to four distinct scenarios: patients (i) with 'brain-only' disease, (ii) with oligometastatic asymptomatic intra- and extracranial disease, (iii) with multiple asymptomatic metastases, and (iv) with multiple symptomatic MBM or leptomeningeal disease. Changes in current management recommendations comprise the use of immunotherapy - preferably combined anti-CTLA-4/PD-1-immunotherapy - in asymptomatic MBM minus/plus stereotactic radiosurgery which remains the mainstay of local brain therapy being safe and effective. Adjuvant whole-brain radiotherapy provides no clinical benefit in oligometastatic MBM. Among the systemic therapies, combined MAPK-kinase inhibition provides, in BRAFV600-mutated patients with rapidly progressing or/and symptomatic MBM, an alternative to combined immunotherapy.

Unexpected suppression of neuronal G protein-activated, inwardly rectifying K+ current by common phospholipase C inhibitor.

Stabilization of the binding of phosphatidylinositol bisphosphate (PIP(2)) to G protein-coupled inward rectifier K+ (GIRK) channels is essential for their activation, whereas hydrolysis of PIP(2) by phospholipase C (PLC) inhibits channel activity. Apparently inconsistent with this mechanism, we found that the commonly used PLC inhibitor, U73122 (1 microM), produced a significant reduction in the amplitude of baclofen (20 microM)-evoked GIRK currents in whole-cell recordings from acutely isolated rat neocortical pyramidal cells. Also, U73122 reduced the percentage of baclofen-responsive neurons from 100% (n=40) to 56% (n=25). Since NCDC (100 microM), a PLC inhibitor of another molecular class, displayed no effect on GIRK current amplitude or responsiveness (100%, n=6), inhibition of PLC is unlikely to account for the effects of U73122 in our preparation. Lending further support to this notion, the structurally closely related compound, U73343, which does not inhibit PLC, proved to be even more efficient in suppressing GIRK current as compared to U73122. In neurons, in which GIRK channels were irreversibly activated by GTPgammaS (n=10), the depressant action of U71322 was fully preserved. These findings hint at a direct interaction of U73122 with the GIRK channel or a closely associated protein. Caution is therefore warranted when employing this compound to examine the role of PLC and PIP(2) in the regulation of GIRK channel activity.

Short-term desensitization of G-protein-activated, inwardly rectifying K+ (GIRK) currents in pyramidal neurons of rat neocortex.

Whole cell recordings from acutely isolated rat neocortical pyramidal cells were performed to study the kinetics and the mechanisms of short-term desensitization of G-protein-activated, inwardly rectifying K+ (GIRK) currents during prolonged application (5 min) of baclofen, adenosine, or serotonin. Most commonly, desensitization of GIRK currents was characterized by a biphasic time course with average time constants for fast and slow desensitization in the range of 8 and 120 s, respectively. The time constants were independent of the agonist used to evoke the current. The biphasic time course was preserved in perforated-patch recordings, indicating that neither component of desensitization is attributable to cell dialysis. Desensitization of GIRK currents displayed a strong heterologous component in that application of a second agonist substantially reduced the responsiveness to a test agonist. Fast desensitization, but not slow desensitization, was lost in cells loaded with GDP, suggesting that the hydrolysis cycle of G proteins might underlie the initial, rapid current decline. Hydrolysis of phosphatidylinositol biphosphate is an unlikely candidate underlying short-term desensitization, because both components of desensitization were preserved in the presence of the phospholipase C inhibitor U73122. We conclude that short-term desensitization does neither result from receptor downregulation nor from altered channel gating but might involve modifications of the G-protein-dependent pathway that serves to translate receptor activation into channel opening.

Agonist-specific maturation of GIRK current responses in acutely isolated pyramidal neurons of rat neocortex.

We performed whole-cell recordings from acutely isolated pyramidal cell somata of rat neocortex to measure and compare G protein-activated, inwardly rectifying K+ (GIRK) currents induced by adenosine, serotonin and baclofen at different postnatal stages (postnatal days 3-19). In about two thirds of neurons, baclofen-induced GIRK currents were already detected at postnatal days 3 and 4 (P3-P4) and almost all neurons between P5 and P19 were responsive. This robust response suggests that postsynaptic effects of baclofen occur much earlier than previously thought. Sensitivity to adenosine was around 70% during the first two postnatal weeks. Given the late maturation of functional synaptic inhibition in neocortex, we propose that phasic and/or tonic activation of GIRK current by baclofen and adenosine might serve as a mechanism to control neuronal excitability during early postnatal development. In marked contrast to the pronounced early sensitivity to baclofen and adenosine, only 20% of the neurons displayed a GIRK current response to serotonin during the first postnatal week. After that, about half of the neurons tested positive for serotonin. GIRK current densities for baclofen and adenosine attained a maximum at the end of the second postnatal week, whereas the serotonin-induced current showed a linear increase during the second and third week of life. Set in relationship with previous data on the postnatal expression of receptor protein and GIRK channel mRNA, our findings suggest that the maturation of GIRK current responses is determined predominantly by the different postnatal patterns of receptor expression.