CRAF gene fusions in pediatric low-grade gliomas define a distinct drug response based on dimerization profiles.

Pediatric low-grade gliomas (PLGGs) are commonly associated with BRAF gene fusions that aberrantly activate the mitogen-activated protein kinase (MAPK) signaling pathway. This has led to PLGG clinical trials utilizing RAF- and MAPK pathway-targeted therapeutics. Whole-genome profiling of PLGGs has also identified rare gene fusions involving another RAF isoform, CRAF/RAF1, in PLGGs and cancers occuring in adults. Whereas BRAF fusions primarily dysregulate MAPK signaling, the CRAF fusions QKI-RAF1 and SRGAP3-RAF1 aberrantly activate both the MAPK and phosphoinositide-3 kinase/mammalian target of rapamycin (PI3K/mTOR) signaling pathways. Although ATP-competitive, first-generation RAF inhibitors (vemurafenib/PLX4720, RAFi) cause paradoxical activation of the MAPK pathway in BRAF-fusion tumors, inhibition can be achieved with 'paradox breaker' RAFi, such as PLX8394. Here we report that, unlike BRAF fusions, CRAF fusions are unresponsive to both generations of RAFi, vemurafenib and PLX8394, highlighting a distinct responsiveness of CRAF fusions to clinically relevant RAFi. Whereas PLX8394 decreased BRAF-fusion dimerization, CRAF-fusion dimerization is unaffected primarily because of robust protein-protein interactions mediated by the N-terminal non-kinase fusion partner, such as QKI. The pan-RAF dimer inhibitor, LY3009120, could suppress CRAF-fusion oncogenicity by inhibiting dimer-mediated signaling. In addition, as CRAF fusions activate both the MAPK and PI3K/mTOR signaling pathways, we identify combinatorial inhibition of the MAPK/mTOR pathway as a potential therapeutic strategy for CRAF-fusion-driven tumors. Overall, we define a mechanistic distinction between PLGG-associated BRAF- and CRAF/RAF1 fusions in response to RAFi, highlighting the importance of molecularly classifying PLGG patients for targeted therapy. Furthermore, our study uncovers an important contribution of the non-kinase fusion partner to oncogenesis and potential therapeutic strategies against PLGG-associated CRAF fusions and possibly pan-cancer CRAF fusions.

Insulin administration reverses the metabolic and electrocardiographic changes in acute myocarditis induced by Indian red scorpion (Buthus tamulus) venom in experimental dogs.

Acute myocarditis was produced by injection of 4 mg/kg Indian red scorpion (Buthus tamulus) venom in dogs. Several rhythm changes, conduction defects, infarction-like pattern and many other ECG abnormalities; hyperglycemia, reduced insulin secretion, rise in free fatty acids along with fall in triglycerides; depletion of glycogen content of atria, ventricles, liver and skeletal muscles was noticed within 20-30 minutes after scorpion envenomation. Ten units of crystalline insulin was given i.v. at this time. All the arrhythmias, conduction defects and other ECG abnormalities disappeared after intervention with insulin. The sinus rhythm persisted for a duration of 120 minutes till the animals were sacrificed. Reduction in free fatty acids along with a rise in triglycerides; glycogenesis in liver, cardiac and skeletal muscles was observed at the time when ECG tracing was normal. It is suggested that catecholamines released during autonomic storm in scorpion poisoning suppress insulin secretion. These in turn result in glycogenolysis; lipolysis resulting in increased free fatty acids and produce arrhythmias. Insulin administration results in glycogenesis; lipogenesis and stops arrhythmias.