Activation of the p75 neurotrophin receptor through conformational rearrangement of disulphide-linked receptor dimers

Ligand-mediated dimerization has emerged as a universal mechanism of growth factor receptor activation. Neurotrophins interact with dimers of the p75 neurotrophin receptor (p75(NTR)), but the mechanism of receptor activation has remained elusive. Here, we show that p75(NTR) forms disulphide-linked dimers independently of neurotrophin binding through the highly conserved Cys(257) in its transmembrane domain. Mutation of Cys(257) abolished neurotrophin-dependent receptor activity but did not affect downstream signaling by the p75(NTR)/NgR/Lingo-1 complex in response to MAG, indicating the existence of distinct, ligand-specific activation mechanisms for p75(NTR). FRET experiments revealed a close association of p75(NTR) intracellular domains that was transiently disrupted by conformational changes induced upon NGF binding. Although mutation of Cys(257) did not alter the oligomeric state of p75(NTR), the mutant receptor was no longer able to propagate conformational changes to the cytoplasmic domain upon ligand binding. We propose that neurotrophins activate p75(NTR) by a mechanism involving rearrangement of disulphide-linked receptor subunits

Selenoether oxytocin analogues have analgesic properties in a mouse model of chronic abdominal pain

Poor oral availability and susceptibility to reduction and protease degradation is a major hurdle in peptide drug development. However, drugable receptors in the gut present an attractive niche for peptide therapeutics. Here we demonstrate, in a mouse model of chronic abdominal pain, that oxytocin receptors are significantly upregulated in nociceptors innervating the colon. Correspondingly, we develop chemical strategies to engineer non-reducible and therefore more stable oxytocin analogues. Chemoselective selenide macrocyclization yields stabilized analogues equipotent to native oxytocin. Ultra-high-field nuclear magnetic resonance structural analysis of native oxytocin and the seleno-oxytocin derivatives reveals that oxytocin has a pre-organized structure in solution, in marked contrast to earlier X-ray crystallography studies. Finally, we show that these seleno-oxytocin analogues potently inhibit colonic nociceptors both in vitro and in vivo in mice with chronic visceral hypersensitivity. Our findings have potentially important implications for clinical use of oxytocin analogues and disulphide-rich peptides in general

Tivantinib (ARQ197) in hepatocellular carcinoma

Here we review the development of tivantinib, a selective oral inhibitor of c-MET. The initially identified dose and schedule for clinical use was 360 mg twice daily. Biological considerations and early results suggested its activity against hepatocellular carcinoma after progression on sorafenib. The results of randomized Phase II study in this setting have already been reported; while in the overall population, the risk of progression was reduced by 36% (HR: 0.64; 90% CI: 0.43-0.94; p = 0.04), in the pre-defined MET-high population median overall survival (7.2 vs 3.8 months; p = 0.01), median time to progression (2.7 vs 1.4 months; p = 0.03) as well as disease control rate (50 vs 20%), were increased by tivantinib. During study conduction, tivantinib dose was amended to 240 mg twice daily, due to a high incidence of neutropenia, without losing clinical efficacy. Presently, a global Phase III trial is being conducted

Ligand-independent signaling by disulfide-crosslinked dimers of the p75 neurotrophin receptor

Dimerization is recognized as a crucial step in the activation of many plasma membrane receptors. However, a growing number of receptors pre-exist as dimers in the absence of ligand, indicating that, although necessary, dimerization is not always sufficient for signaling. The p75 neurotrophin receptor (p75NTR) forms disulfide-linked dimers at the cell surface independently of ligand binding through Cys257 in its transmembrane domain. Here, we show that crosslinking of p75NTR dimers by cysteine-scanning mutagenesis results in constitutive, ligand-independent activity in several pathways that are normally engaged upon neurotrophin stimulation of native receptors. The activity profiles of different disulfide-crosslinked p75NTR mutants were similar but not identical, suggesting that different configurations of p75NTR dimers might be endowed with different functions. Interestingly, crosslinked p75NTR mutants did not mimic the effects of the myelin inhibitors Nogo or MAG, suggesting the existence of ligand-specific activation mechanisms. Together, these results support a conformational model of p75NTR activation by neurotrophins, and reveal a genetic approach to generate gain-of-function receptor variants with distinct functional profiles

Multi-centre real-world validation of automated treatment planning for breast radiotherapy

Purpose: To present the results of the first multi-centre real-world validation of autoplanning for whole breast irradiation after breast-sparing surgery, encompassing high complexity cases (e.g. with a boost or regional lymph nodes) and a wide range of clinical practices. Methods: The 24 participating centers each included 10 IMRT/VMAT/Tomotherapy patients, previously treated with a manually generated plan (‘manplan’). There were no restrictions regarding case complexity, planning aims, plan evaluation parameters and criteria, fractionation, treatment planning system or treatment machine/technique. In addition to dosimetric comparisons of autoplans with manplans, blinded plan scoring/ranking was conducted by a clinician from the treating center. Autoplanning was performed using a single configuration for all patients in all centres. Deliverability was verified through measurements at delivery units. Results: Target dosimetry showed comparability, while reductions in OAR dose parameters were 21.4 % for heart Dmean, 16.7 % for ipsilateral lung Dmean, and 101.9 %, 45.5 %, and 35.7 % for contralateral breast D0.03cc, D5% and Dmean, respectively (all p &lt; 0.001). Among the 240 patients included, the clinicians preferred the autoplan for 119 patients, with manplans preferred for 96 cases (p = 0.01). Per centre there were on average 5.0 ± 2.9 (1SD) patients with a preferred autoplan (range [0–10]), compared to 4.0 ± 2.7 with a preferred manplan ([0,9]). No differences were observed regarding deliverability. Conclusion: The automation significantly reduced the hands-on planning workload compared to manual planning, while also achieving an overall superiority. However, fine-tuning of the autoplanning configuration prior to clinical implementation may be necessary in some centres to enhance clinicians’ satisfaction with the generated autoplans.</p

Multi-centre real-world validation of automated treatment planning for breast radiotherapy

Purpose: To present the results of the first multi-centre real-world validation of autoplanning for whole breast irradiation after breast-sparing surgery, encompassing high complexity cases (e.g. with a boost or regional lymph nodes) and a wide range of clinical practices. Methods: The 24 participating centers each included 10 IMRT/VMAT/Tomotherapy patients, previously treated with a manually generated plan (‘manplan’). There were no restrictions regarding case complexity, planning aims, plan evaluation parameters and criteria, fractionation, treatment planning system or treatment machine/technique. In addition to dosimetric comparisons of autoplans with manplans, blinded plan scoring/ranking was conducted by a clinician from the treating center. Autoplanning was performed using a single configuration for all patients in all centres. Deliverability was verified through measurements at delivery units. Results: Target dosimetry showed comparability, while reductions in OAR dose parameters were 21.4 % for heart Dmean, 16.7 % for ipsilateral lung Dmean, and 101.9 %, 45.5 %, and 35.7 % for contralateral breast D0.03cc, D5% and Dmean, respectively (all p &lt; 0.001). Among the 240 patients included, the clinicians preferred the autoplan for 119 patients, with manplans preferred for 96 cases (p = 0.01). Per centre there were on average 5.0 ± 2.9 (1SD) patients with a preferred autoplan (range [0–10]), compared to 4.0 ± 2.7 with a preferred manplan ([0,9]). No differences were observed regarding deliverability. Conclusion: The automation significantly reduced the hands-on planning workload compared to manual planning, while also achieving an overall superiority. However, fine-tuning of the autoplanning configuration prior to clinical implementation may be necessary in some centres to enhance clinicians’ satisfaction with the generated autoplans.</p