Association of high microvessel αvβ3 and low PTEN with poor outcome in stage 3 neuroblastoma: rationale for using first in class dual PI3K/BRD4 inhibitor, SF1126

// Anat Erdreich-Epstein 1, 2, * , Alok R. Singh 3 , Shweta Joshi 3 , Francisco M. Vega 3, 4 , Pinzheng Guo 1 , Jingying Xu 1 , Susan Groshen 5 , Wei Ye 5 , Melissa Millard 1 , Mihaela Campan 6 , Guillermo Morales 7 , Joseph R. Garlich 7 , Peter W. Laird 6, 8, 10 , Robert C. Seeger 1 , Hiroyuki Shimada 2 and Donald L. Durden 3, 7, 9, * 1 Department of Pediatrics, Children’s Hospital Los Angeles and University of Southern California Keck School of Medicine, Los Angeles, California, USA 2 Department of Pathology, Children’s Hospital Los Angeles and University of Southern California Keck School of Medicine, Los Angeles, California, USA 3 Department of Pediatrics, Moores Cancer Center, University of California San Diego, California, USA 4 Instituto de Biomedicina de Sevilla, IBiS/HUVR/CSIC/Universidad de Sevilla and Department of Medical Physiology and Biophysics, Universidad de Sevilla, Spain 5 Department of Preventive Medicine, Keck School of Medicine, Los Angeles, California, USA 6 Department of Surgery University of Southern California, Keck School of Medicine, Los Angeles, California, USA 7 SignalRx Pharmaceuticals, San Diego, California, USA 8 USC Epigenome Center, University of Southern California, Keck School of Medicine, Los Angeles, California, USA 9 Department of Pediatrics, UCSD School of Medicine and Rady Children’s Hospital San Diego, California, USA 10 Current Address: Van Andel Research Institute, Grand Rapids, Michigan, USA * These authors contributed equally to this the work Correspondence to: Anat Erdreich-Epstein, email: epstein@usc.edu Donald L. Durden, email: ddurden@ucsd.edu Keywords: angiogenesis, integrin α v β 3 , neuroblastoma, PI3-kinase inhibitors, BRD4 Received: March 21, 2016 Accepted: October 26, 2016 Published: November 18, 2016 ABSTRACT Neuroblastoma (NB) is the most common extracranial solid tumor in children. Our previous studies showed that the angiogenic integrin α v β 3 was increased in high-risk metastatic (stage 4) NB compared with localized neuroblastomas. Herein, we show that integrin α v β 3 was expressed on 68% of microvessels in MYCN-amplified stage 3 neuroblastomas, but only on 34% (means) in MYCN-non-amplified tumors ( p < 0.001; n = 54). PTEN, a tumor suppressor involved in α v β 3 signaling, was expressed in neuroblastomas either diffusely, focally or not at all (immunohistochemistry). Integrin α v β 3 was expressed on 60% of tumor microvessels when PTEN was negative or focal, as compared to 32% of microvessels in tumors with diffuse PTEN expression ( p < 0.001). In a MYCN transgenic mouse model, loss of one allele of PTEN promoted tumor growth, illustrating the potential role of PTEN in neuroblastoma pathogenesis. Interestingly, we report the novel dual PI-3K/BRD4 activity of SF1126 (originally developed as an RGD-conjugated pan PI3K inhibitor). SF1126 inhibits BRD4 bromodomain binding to acetylated lysine residues with histone H3 as well as PI3K activity in the MYCN amplified neuroblastoma cell line IMR-32. Moreover, SF1126 suppressed MYCN expression and MYCN associated transcriptional activity in IMR-32 and CHLA136, resulting in overall decrease in neuroblastoma cell viability. Finally, treatment of neuroblastoma tumors with SF1126 inhibited neuroblastoma growth in vivo . These data suggest integrin α v β 3 , MYCN/BRD4 and PTEN/PI3K/AKT signaling as biomarkers and hence therapeutic targets in neuroblastoma and support testing of the RGD integrin α v β 3 -targeted PI-3K/BRD4 inhibitor, SF1126 as a therapeutic strategy in this specific subgroup of high risk neuroblastoma.