The SR-B1 Receptor as a Potential Target for Treating Glioblastoma.

PURPOSE: The goal of these studies was to provide proof of concept for a novel targeted therapy for Glioblastoma Multiforme (GBM). Methods. These studies involve the evaluation of reconstituted high density lipoprotein (rHDL) nanoparticles (NPs) as delivery agents for the drug, mammalian Target of Rapamycin (mTOR) inhibitor Everolimus (EVR) to GBM cells. Cytotoxicity studies and assessment of downstream effects, including apoptosis, migration, and cell cycle events, were probed, in relation to the expression of scavenger receptor B type 1 (SR-B1) by GBM cells. RESULTS: Findings from cytotoxicity studies indicate that the rHDL/EVR formulation was 185 times more potent than free EVR against high SR-B1 expressing cell line (LN 229). Cell cycle analysis revealed that rHDL/EVR treated LN229 cells had a 5.8 times higher apoptotic cell population than those treated with EVR. The sensitivity of GBM cells to EVR treatment was strongly correlated with SR-B1 expression. CONCLUSIONS: These studies present strong proof of concept regarding the efficacy of delivering EVR and likely other agents, via a biocompatible transport system, targeted to the SR-B1 receptor that is upregulated in most cancers, including GBM. Targeting the SR-B1 receptor could thus lead to effective personalized therapy of GBM.

Scavenger receptor class B type 1 regulates neuroblastoma cell proliferation, migration and invasion.

Neuroblastoma (NB) is an extra cranial pediatric embryonal tumor most prevalent in children less than 1 year of age. NB accounts for 7% of all pediatric cancers but accounts for 15% of all childhood cancer deaths. Scavenger receptor class B type 1 (SR-B1), a mediator of cellular cholesterol uptake, is overexpressed in and have been linked to the aggressiveness of many cancers. Nevertheless, no studies have so far investigated the relationship between SR-B1 and NB. Elucidation of receptors that promote NB may pave the way for discovery of new therapeutic targets. Here we show that inhibition of SR-B1 reduced cell survival, migration and invasion, and cholesterol content in NB cell lines. Additionally analysis of SR-B1 levels in NB patient biopsies using the R2: Genomics Analysis and Visualization Platform showed that high SR-B1 expression correlated with decreased overall and event-free survival.

Targeting the SR-B1 Receptor as a Gateway for Cancer Therapy and Imaging.

Malignant tumors display remarkable heterogeneity to the extent that even at the same tissue site different types of cells with varying genetic background may be found. In contrast, a relatively consistent marker the scavenger receptor type B1 (SR-B1) has been found to be consistently overexpressed by most tumor cells. Scavenger Receptor Class B Type I (SR-BI) is a high density lipoprotein (HDL) receptor that facilitates the uptake of cholesterol esters from circulating lipoproteins. Additional findings suggest a critical role for SR-BI in cholesterol metabolism, signaling, motility, and proliferation of cancer cells and thus a potential major impact in carcinogenesis and metastasis. Recent findings indicate that the level of SR-BI expression correlate with aggressiveness and poor survival in breast and prostate cancer. Moreover, genomic data show that depending on the type of cancer, high or low SR-BI expression may promote poor survival. This review discusses the importance of SR-BI as a diagnostic as well as prognostic indicator of cancer to help elucidate the contributions of this protein to cancer development, progression, and survival. In addition, the SR-B1 receptor has been shown to serve as a potential gateway for the delivery of therapeutic agents when reconstituted high density lipoprotein nanoparticles are used for their transport to cancer cells and tumors. Opportunities for the development of new technologies, particularly in the areas of cancer therapy and tumor imaging are discussed.

Emerging therapeutics for targeting Akt in cancer.

The ultimate goal of cancer therapeutic research is to develop effective, targeted therapeutics that exploit the vulnerabilities of cancer cells. The three isoforms of Akt, also known as protein kinase B (PKB), are important mediators of various pathways that transmit mitogenic signals from the cell's exterior to the effector proteins of the cell's interior. Due to Akt\\\\\\\'s importance in cell functions such as growth, proliferation and cell survival, many cancer cells rely on this pathway to aid in their survival. This dependence can lead to chemoresistance and selection of more adapted populations of cancer cells. Thus, it is important to understand the functional significance of isoform specificity and its relation to chemoresistance. In this review, we have summarized recent studies on Akt isoform specific regulation as well as each isoform's role in chemoresistance, emphasizing their potential as targets for cancer therapy. We have also condensed ongoing clinical studies involving various types of Akt inhibitors while highlighting the type of study, rationale and co-therapies involved in identifying Akt isoforms as promising therapeutic targets.

Role of helicase-like transcription factor (hltf) in the G2/m transition and apoptosis in brain.

HLTF participates in transcription, chromatin remodeling, DNA damage repair, and tumor suppression. Aside from being expressed in mouse brain during embryonic and postnatal development, little is known about Hltf's functional importance. Splice variant quantification of wild-type neonatal (6-8 hour postpartum) brain gave a ratio of 5:1 for Hltf isoform 1 (exons 1-25) to isoform 2 (exons 1-21 with exon 21 extended via a partial intron retention event). Western analysis showed a close correlation between mRNA and protein expression. Complete loss of Hltf caused encephalomalacia with increased apoptosis, and reduced viability. Sixty-four percent of Hltf null mice died, 48% within 12-24 hours of birth. An RNA-Seq snapshot of the neonatal brain transcriptome showed 341 of 20,000 transcripts were altered (p < 0.05) - 95 up regulated and 246 down regulated. MetaCore™ enrichment pathway analysis revealed Hltf regulates cell cycle, cell adhesion, and TGF-beta receptor signaling. Hltf's most important role is in the G2/M transition of the cell cycle (p  =  4.672e-7) with an emphasis on transcript availability of major components in chromosome cohesion and condensation. Hltf null brains have reduced transcript levels for Rad21/Scc1, histone H3.3, Cap-E/Smc2, Cap-G/G2, and Aurora B kinase. The loss of Hltf in its yeast Rad5-like role in DNA damage repair is accompanied by down regulation of Cflar, a critical inhibitor of TNFRSF6-mediated apoptosis, and increased (p<0.0001) active caspase-3, an indicator of intrinsic triggering of apoptosis in null brains. Hltf also regulates Smad7/Bambi/Tgf-beta/Bmp5/Wnt10b signaling in brain. ChIP confirmed Hltf binding to consensus sequences in predicted (promoter Scgb3a1 gene) and previously unidentified (P-element on chromosome 7) targets. This study is the first to provide a comprehensive view of Hltf targets in brain. Moreover, it reveals how silencing Hltf disrupts cell cycle progression, and attenuates DNA damage repair.

Prolactin-induced Jak2 phosphorylation of RUSH: a key element in Jak/RUSH signaling.

Jak2/Stat-mediated prolactin signaling culminates in Stat5a-DNA-binding. However, not all Jak2-dependent genes have Stat5 sites. Western analysis with inhibitors showed Jak2 is a proximal intermediate in prolactin-induced RUSH phosphorylation. Transfection assays with HRE-H9 cells showed the RUSH-binding site mediated the ability of prolactin to augment progesterone-dependent transcription of the RUSH gene. Jak2 inhibitors or targeted RUSH-site mutation blocked the prolactin effect. RUSH co-immunoprecipitated with phospho-Jak2 from nuclear extracts. Jak2 inhibitors abolished the nuclear pool of phospho-RUSH not the nuclear content of RUSH in HRE-H9 cells. Nucleolar-affiliated partners, e.g. nucleolin, were identified by microLC/MS/MS analysis of nuclear proteins that co-immunoprecipitated with RUSH/GST-RING. RUSH did not exclusively co-localize with fibrillarin to the nucleolus. MG-132 (proteasomal inhibitor) failed to block Tyrene CR4-mediated decrease in phospho-RUSH, and did not promote RUSH accumulation in the nucleolus. These studies authenticate prolactin-dependent Jak2 phosphorylation of RUSH, and provide functional implications on the RUSH network of nuclear interactions.