Therapeutic efficacy of RAS inhibitor trametinib using a juvenile myelomonocytic leukemia patient-derived xenograft model.

Juvenile myelomonocytic leukemia (JMML) is an aggressive pediatric leukemia with few effective treatments and poor outcomes even after stem cell transplantation, the only current curative treatment. We developed a JMML patient-derived xenograft (PDX) mouse model and demonstrated the in vivo therapeutic efficacy and confirmed the target of trametinib, a RAS-RAF-MEK-ERK pathway inhibitor, in this model. A PDX model was created through transplantation of patient JMML cells into mice, up to the second generation, and successful engraftment was confirmed using flow cytometry. JMML PDX mice were treated with trametinib versus vehicle control, with a median survival of 194 days in the treatment group versus 124 days in the control group (p = 0.02). Trametinib's target as a RAS pathway inhibitor was verified by showing inhibition of ERK phosphorylation using immunoblot assays. In conclusion, trametinib monotherapy significantly prolongs survival in our JMML PDX model by inhibiting the RAS pathway. Our model can be effectively used for assessment of novel targeted treatments, including potential combination therapies, to improve JMML outcomes.

SARS-CoV-2-Triggered Hemophagocytic Lymphohistiocytosis with Complications of Posterior Reversible Encephalopathy Syndrome.

In this article, we describe a novel case of SARS-CoV-2-associated-hemophagocytic lymphohistiocytosis (HLH) complicated by posterior reversible encephalopathy syndrome (PRES). Initially diagnosed with multisystem inflammatory response in children (MIS-C), the patient received a large corticosteroid dose days before the onset of neurological symptoms. After developing PRES, the patient was treated with antihypertensives, antiepileptics, dexamethasone, and anakinra, leading to neurologic normalization. We propose that given the challenging diagnostic picture of PRES developing in patients with HLH or MIS-C, institutionalized standards for blood pressure management during corticosteroid induction may significantly improve outcomes in patients being treated for hyperinflammatory syndromes who develop neurological symptoms.