In vitro evaluation of sunitinib loaded bioresorbable microspheres for potential application in arterial chemoembolization.

Drug-loadable bioresorbable microspheres (BRMS) are designed for treating hypervascular tumors through chemoembolization, thereby reducing systemic side effects via controllable local delivery. The present study investigated the degradation and loading capability of bioresorbable microspheres with an anti-angiogenic agent, sunitinib, and then evaluated the release profiles in different media (PBS, 10µg/mL and 4mg/mL lysozyme solutions), and tested catheter deliverability as well as potential antiangiogenic effects of the loaded microspheres. The dry weight of the BRMS showed a consistent decrease over the period of incubation in a 10µg/mL lysozyme solution with 61.3% mass remaining on day 21. Sunitinib was loaded efficiently onto the microspheres, with smaller sizes exhibiting a slightly faster loading and release rate. At 2h, the loading percentages were 99.28%, 97.95%, and 94.39% for 100-300, 300-500, and 500-700µm microspheres, respectively. At 8h, the percentage of drug released were 78.4±5.8%, 71.7±0.3%, and 67.0±2.9% for 100-300, 300-500, and 500-700µm microspheres under static medium conditions, respectively. Under replacing-medium conditions, the presence of 10µg/mL lysozyme slightly delayed the drug release while 4mg/mL lysozyme significantly facilitated the drug release from the microspheres as compared with PBS solution. Confocal imaging revealed an even distribution of sunitinib throughout the microspheres. Drug loaded microspheres were delivered through microcatheters smoothly without any clogging. Sunitinib retained its efficacy at reducing the viability of human endothelial cells after elution from the microspheres. Thus, these bioresorbable microspheres are promising for arterial chemoembolization.

Active efflux of Dasatinib from the brain limits efficacy against murine glioblastoma: broad implications for the clinical use of molecularly targeted agents.

The importance of the blood-brain barrier in preventing effective pharmacotherapy of glioblastoma has been controversial. The controversy stems from the fact that vascular endothelial cell tight junctions are disrupted in the tumor, allowing some systemic drug delivery. P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) efflux drugs from brain capillary endothelial cells into the blood. We tested the hypothesis that although the tight junctions are "leaky" in the core of glioblastomas, active efflux limits drug delivery to tumor-infiltrated normal brain and consequently, treatment efficacy. Malignant gliomas were induced by oncogene transfer into wild-type (WT) mice or mice deficient for Pgp and BCRP (knockout, KO). Glioma-bearing mice were orally dosed with dasatinib, a kinase inhibitor and dual BCRP/PgP substrate that is being currently tested in clinical trials. KO mice treated with dasatinib survived for twice as long as WT mice. Microdissection of the tumor core, invasive rim, and normal brain revealed 2- to 3-fold enhancement in dasatinib brain concentrations in KO mice relative to WT. Analysis of signaling showed that poor drug delivery correlated with the lack of inhibition of a dasatinib target, especially in normal brain. A majority of human glioma xenograft lines tested expressed BCRP or PgP and were sensitized to dasatinib by a dual BCRP/Pgp inhibitor, illustrating a second barrier to drug delivery intrinsic to the tumor itself. These data show that active efflux is a relevant obstacle to treating glioblastoma and provide a plausible mechanistic basis for the clinical failure of numerous drugs that are BCRP/Pgp substrates.

Human Flt3L generates dendritic cells from canine peripheral blood precursors: implications for a dog glioma clinical trial.

BACKGROUND: Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and carries a dismal prognosis. We have developed a conditional cytotoxic/immunotherapeutic approach using adenoviral vectors (Ads) encoding the immunostimulatory cytokine, human soluble fms-like tyrosine kinase 3 ligand (hsFlt3L) and the conditional cytotoxic molecule, i.e., Herpes Simplex Type 1- thymide kinase (TK). This therapy triggers an anti-tumor immune response that leads to tumor regression and anti-tumor immunological memory in intracranial rodent cancer models. We aim to test the efficacy of this immunotherapy in dogs bearing spontaneous GBM. In view of the controversy regarding the effect of human cytokines on dog immune cells, and considering that the efficacy of this treatment depends on hsFlt3L-stimulated dendritic cells (DCs), in the present work we tested the ability of Ad-encoded hsFlt3L to generate DCs from dog peripheral blood and compared its effects with canine IL-4 and GM-CSF. METHODOLOGY/PRINCIPAL FINDINGS: Our results demonstrate that hsFlT3L expressed form an Ad vector, generated DCs from peripheral blood cultures with very similar morphological and phenotypic characteristics to canine IL-4 and GM-CSF-cultured DCs. These include phagocytic activity and expression of CD11c, MHCII, CD80 and CD14. Maturation of DCs cultured under both conditions resulted in increased secretion of IL-6, TNF-alpha and IFN-gamma. Importantly, hsFlt3L-derived antigen presenting cells showed allostimulatory potential highlighting their ability to present antigen to T cells and elicit their proliferation. CONCLUSIONS/SIGNIFICANCE: These results demonstrate that hsFlt3L induces the proliferation of canine DCs and support its use in upcoming clinical trials for canine GBM. Our data further support the translation of hsFlt3L to be used for dendritic cells' vaccination and gene therapeutic approaches from rodent models to canine patients and its future implementation in human clinical trials.