Patient-derived xenograft (PDX) models have recently emerged as a highly desirable platform in oncology and are expected to substantially broaden the way in vivo studies are designed and executed and to reshape drug discovery programs. However, acquisition of patient-derived samples, and propagation, annotation and distribution of PDXs are complex processes that require a high degree of coordination among clinic, surgery and laboratory personnel, and are fraught with challenges that are administrative, procedural and technical. Here, we examine in detail the major aspects of this complex process and relate our experience in establishing a PDX Core Laboratory within a large academic institution.

In acute myeloid leukemia (AML), chemotherapy resistance remains prevalent and poorly understood. Using functional proteomics of patient AML specimens, we identified MEF2C S222 phosphorylation as a specific marker of primary chemoresistance. We found that knock-in mutant mice engineered to block MEF2C phosphorylation exhibited normal hematopoiesis, but were resistant to leukemogenesis induced by MEF2C phosphorylation was required for leukemia stem cell maintenance and induced by MARK kinases in cells. Treatment with the selective MARK/SIK inhibitor MRT199665 caused apoptosis and conferred chemosensitivity in MEF2C-activated human AML cell lines and primary patient specimens, but not those lacking MEF2C phosphorylation. These findings identify kinase-dependent dysregulation of transcription factor control as a determinant of therapy response in AML, with immediate potential for improved diagnosis and therapy for this disease. Functional proteomics identifies phosphorylation of MEF2C in the majority of primary chemotherapy-resistant AML. Kinase-dependent dysregulation of this transcription factor confers susceptibility to MARK/SIK kinase inhibition in preclinical models, substantiating its clinical investigation for improved diagnosis and therapy of AML. .

The C-X-C chemokine receptor type 4 (CXCR4, CD184) pathway is a key regulator of cancer metastasis. Existing therapeutics that block CXCR4 signaling are dependent on single molecule-receptor interactions or silencing CXCR4 expression. CXCR4 localizes in lipid rafts and forms dimers therefore CXCR4 targeting and signaling may depend on ligand density. Herein, we report liposomes presenting a CXCR4 binding peptide (DV1) as a three-dimensional molecular array, ranging from 9k to 74k molecules μm−2, target triple negative breast cancer (TNBC). TNBC cells exhibit a maxima in binding and uptake of DV1-functionalized liposomes (L-DV1) in vitro at a specific density, which yields a significant reduction in cell migration. This density inhibits metastasis from a primary tumor for 27 days, resulting from peptide density dependent gene regulation. We show that complementing cell membrane receptor expression may be a strategy for targeting cells and regulating signaling.

Atomic force microscopy (AFM) is a powerful tool to detect in vitro antibody-antigen interactions. To date, however, AFM-measured antibody-antigen interactions have yet to be exploited to predict in vivo tumor specificity of antibody-directed nanomedicines. In this study, we have utilized AFM to directly measure the biomechanical interaction between live triple negative breast cancer (TNBC) cells and an antibody against ICAM1, a recently identified TNBC target. For the first time, we provide proof-of-principle evidence that in vitro TNBC cell-ICAM1 antibody binding force measured by AFM on live cells more precisely correlates with in vivo tumor accumulation and therapeutic efficacy of ICAM1 antibody-directed liposomes than ICAM1 gene and surface protein overexpression levels. These studies demonstrate that live cell-antibody binding force measurements may be used as a novel in vitro metric for predicting the in vivo tumor recognition of antibody-directed nanomedicines.

<p>Extended methods, supplementary figures and supplementary tables.</p>