RELIEF OF PROFOUND FEEDBACK INHIBITION OF MITOGENIC SIGNALING BY RAF INHIBITORS ATTENUATES THEIR ACTIVITY IN BRAFV600E MELANOMAS

BRAFV600E drives tumors by dysregulating ERK signaling. Here we show that, in these tumors, high levels of ERK-dependent negative feedback potently suppress liganddependent mitogenic signaling and Ras function. BRAFV600E activation is Rasindependent and signals as a RAF-inhibitor sensitive monomer. RAF inhibitors potently inhibit RAF monomers and ERK signaling, causing relief of ERK-dependent feedback, reactivation of ligand-dependent signal transduction, increased Ras-GTP and generation of RAF inhibitor-resistant RAF dimers. This results in a rebound in ERK activity and culminates in a new steady state, wherein ERK signaling is elevated compared to its initial nadir after RAF inhibition. In this state, ERK signaling is RAF inhibitor resistant, and MEK inhibitor sensitive, and combined inhibition results in enhancement of ERKpathway inhibition and antitumor activity

Multimodal silica nanoparticles are effective cancer-targeted probes in a model of human melanoma

Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine–glycine–aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin–expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting

Direct Reversal of Glucocorticoid Resistance by AKT Inhibition in Acute Lymphoblastic Leukemia

SummaryGlucocorticoid resistance is a major driver of therapeutic failure in T cell acute lymphoblastic leukemia (T-ALL). Here, we identify the AKT1 kinase as a major negative regulator of the NR3C1 glucocorticoid receptor protein activity driving glucocorticoid resistance in T-ALL. Mechanistically, AKT1 impairs glucocorticoid-induced gene expression by direct phosphorylation of NR3C1 at position S134 and blocking glucocorticoid-induced NR3C1 translocation to the nucleus. Moreover, we demonstrate that loss of PTEN and consequent AKT1 activation can effectively block glucocorticoid-induced apoptosis and induce resistance to glucocorticoid therapy. Conversely, pharmacologic inhibition of AKT with MK2206 effectively restores glucocorticoid-induced NR3C1 translocation to the nucleus, increases the response of T-ALL cells to glucocorticoid therapy, and effectively reverses glucocorticoid resistance in vitro and in vivo