Convection enhanced delivery of panobinostat (LBH589)-loaded pluronic nano-micelles prolongs survival in the F98 rat glioma model.

BACKGROUND: The pan-histone deacetylase inhibitor panobinostat is a potential therapy for malignant glioma, but it is water insoluble and does not cross the blood-brain barrier when administered systemically. In this article, we describe the in vitro and in vivo efficacy of a novel water-soluble nano-micellar formulation of panobinostat designed for administration by convection enhanced delivery (CED). MATERIALS AND METHODS: The in vitro efficacy of panobinostat-loaded nano-micelles against rat F98, human U87-MG and M059K glioma cells and against patient-derived glioma stem cells was measured using a cell viability assay. Nano-micelle distribution in rat brain was analyzed following acute CED using rhodamine-labeled nano-micelles, and toxicity was assayed using immunofluorescent microscopy and synaptophysin enzyme-linked immunosorbent assay. We compared the survival of the bioluminescent syngenic F98/Fischer344 rat glioblastoma model treated by acute CED of panobinostat-loaded nano-micelles with that of untreated and vehicle-only-treated controls. RESULTS: Nano-micellar panobinostat is cytotoxic to rat and human glioma cells in vitro in a dose-dependent manner following short-time exposure to drug. Fluorescent rhodamine-labelled nano-micelles distribute with a volume of infusion/volume of distribution (Vi/Vd) ratio of four and five respectively after administration by CED. Administration was not associated with any toxicity when compared to controls. CED of panobinostat-loaded nano-micelles was associated with significantly improved survival when compared to controls (n=8 per group; log-rank test, P<0.001). One hundred percent of treated animals survived the 60-day experimental period and had tumour response on post-mortem histological examination. CONCLUSION: CED of nano-micellar panobinostat represents a potential novel therapeutic option for malignant glioma and warrants translation into the clinic.

The gene expression signature of anagrelide provides an insight into its mechanism of action and uncovers new regulators of megakaryopoiesis.

BACKGROUND: Anagrelide is a cytoreductive agent used to lower platelet counts in essential thrombocythemia. Although the drug has been known to selectively inhibit megakaryopoiesis for many years, the molecular mechanism accounting for this activity is still unclear. OBJECTIVES AND METHODS: To address this issue we have compared the global gene expression profiles of human hematopoietic cells treated ex-vivo with and without anagrelide while growing under megakaryocyte differentiation conditions, using high-density oligonucleotide microarrays. Gene expression data were validated by the quantitative polymerase chain reaction and mined to identify functional subsets and regulatory pathways. RESULTS: We identified 328 annotated genes differentially regulated by anagrelide, including many genes associated with platelet functions and with the control of gene transcription. Prominent among the latter was TRIB3, whose expression increased in the presence of anagrelide. Pathway analysis revealed that anagrelide up-regulated genes that are under the control of the transcription factor ATF4, a known TRIB3 inducer. Notably, immunoblot analysis demonstrated that anagrelide induced the phosphorylation of eIF2α, which is an upstream regulator of ATF4, and increased ATF4 protein levels. Furthermore, salubrinal, an inhibitor of eIF2α dephosphorylation, increased the expression of ATF4-regulated genes and blocked megakaryocyte growth. CONCLUSIONS: These findings link signaling through eIF2α/ATF4 to the anti-megakaryopoietic activity of anagrelide and identify new potential modulators of megakaryopoiesis.