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p38α mitogen-activated protein kinase is essential to cellular homeostasis. Two principal mechanisms to activate p38α exist. The first relies on dedicated dual-specificity kinases such as mitogen-activated protein kinase kinase (MAP2K) 3 (MKK3) or 6 (MKK6), which activate p38α by phosphorylating Thr180 and Tyr182 within the activation segment. The second is by autophosphorylation of Thr180 and Tyr182 in cis, mediated by p38α binding the scaffold protein TAB1. The second mechanism occurs during myocardial ischemia, where it aggravates myocardial infarction. Based on the crystal structure of the p38α-TAB1 complex we replaced threonine 185 of p38α with glycine (T185G) to prevent an intramolecular hydrogen bond with Asp150 from being formed. This mutation did not interfere with TAB1 binding to p38α. However, it disrupted the consequent long-range effect of this binding event on the distal activation segment, releasing the constraint on Thr180 that oriented its hydroxyl for phosphotransfer. Based on assays performed in vitro and in vivo, the autoactivation of p38α(T185G) was disabled, while its ability to be activated by upstream MAP2Ks and to phosphorylate downstream substrates remained intact. Furthermore, myocardial cells expressing p38α(T185G) were resistant to injury. These findings reveal a mechanism to selectively disable p38α autoactivation and its consequences, which may ultimately circumvent the toxicity associated with strategies that inhibit p38α kinase activity under all circumstances, such as with ATP-competitive inhibitors. [ABSTRACT FROM AUTHOR]

Low affinity α1/α2 containing GABAA receptors are significantly less able to bind [11C]/[3H]Ro15‐4513 following translocation to the endosomal environment. The alterations in [11C]Ro15‐4513 binding observed in vivo following perturbations in endogenous GABA are likely driven by both alterations in receptor binding parameters following agonist induced internalisation and the GABA Shift. [ABSTRACT FROM AUTHOR]

Despite a rise in clinical use of radiopharmaceutical therapies, the biological effects of radionuclides and their relationship with absorbed radiation dose are poorly understood. Here, we set out to define this relationship for Auger electron emitters [99mTc]TcO 4 − and [123I]I− and β−-particle emitter [188Re]ReO 4 −. Studies were carried out using genetically modified cells that permitted direct radionuclide comparisons. Triple-negative MDA-MB-231 breast cancer cells expressing the human sodium iodide symporter (hNIS) and green fluorescent protein (GFP; MDA-MB-231.hNIS-GFP) were used. In vitro radiotoxicity of [99mTc]TcO 4 −, [123I]I−, and [188Re]ReO 4 − was determined using clonogenic assays. Radionuclide uptake, efflux, and subcellular location were used to calculate nuclear absorbed doses using the Medical Internal Radiation Dose (MIRD) formalism. In vivo studies were performed using female NSG mice bearing orthotopic MDA-MB-231.hNIS-GFP tumors and compared with X-ray–treated (12.6-15 Gy) and untreated cohorts. Absorbed dose per unit activity in tumors and sodium iodide symporter–expressing organs was extrapolated to reference human adult models using OLINDA/EXM. [99mTc]TcO 4 − and [123I]I− reduced the survival fraction only in hNIS-expressing cells, whereas [188Re]ReO 4 − reduced survival fraction in hNIS-expressing and parental cells. [123I]I− required 2.4- and 1.5-fold lower decays/cell to achieve 37% survival compared with [99mTc]TcO 4 − and [188Re]ReO 4 −, respectively, after 72 hours of incubation. Additionally, [99mTc]TcO 4 −, [123I]I−, and [188Re]ReO 4 − had superior cell killing effectiveness in vitro compared with X-rays. In vivo, X-ray led to a greater median survival compared with [188Re]ReO 4 − and [123I]I− (54 days vs 45 and 43 days, respectively). Unlike the X-ray cohort, no metastases were visualized in the radionuclide-treated cohorts. Extrapolated human absorbed doses of [188Re]ReO 4 − to a 1 g tumor were 13.8- and 11.2-fold greater than for [123I]I− in female and male models, respectively. This work reports reference dose-effect data using cell and tumor models for [99mTc]TcO 4 −, [123I]I−, and [188Re]ReO 4 − for the first time. We further demonstrate the tumor-controlling effects of [123I]I− and [188Re]ReO 4 − in comparison with external beam radiation therapy. [ABSTRACT FROM AUTHOR]