Ohlfest, John R.

2546 Background: We recently reported that tumor cell vaccines cultured in 5% oxygen (O2) had enhanced the immunogenicity relative to those grown in standard atmospheric O2. In order to develop an “off-the-shelf” source of whole cell antigen we screened a panel of primary glioblastoma (GBM) cell lines, leading to identification of (GBM6) as an ideal candidate. GBM6 was extensively characterized and shown to express glioma-associated antigens (IL13Ra2, Sox2, Epha2, etc.). A Phase I clinical trial was initiated to evaluate the safety and feasibility of a vaccine consisting of dendritic cells (DC) pulsed with apoptotic bodies from GBM6 grown in 5% O2. Methods: Patients ranging from 3 to 71 years with recurrent GBM (n=6) or ependymoma (n=1) were enrolled. Monocytes were collected via apheresis, matured into DC and pulsed with apoptotic bodies derived from GBM6. The first three patients received escalating doses of DC (5x106, 10x106, and 15x106), the remainder received 15 x 106 DC. Pulsed dendritic cellswere injectedsubcutaneously into the supra-scapular region. Imiquimod cream was applied at the injection site just prior to vaccination and 24 hours later. The vaccine schedule dictated administration every 2 weeks for 8 weeks (total of 5 doses) then monthly to progression or a total of 52 weeks. Prior to each vaccination, patients met eligibility parameters and had no progression on MRI. Patients were imaged monthly and blood was drawn to evaluate toxicity and immune response. Results: No vaccine-related toxicity has been reported. Time to progression ranges from 6.5 weeks for the patient treated at the first dose level to 35 weeks for one patient receiving 15 x 106 DC. The latter patient experienced a partial response at 20 weeks. Two patients have stable disease at 18.5 and 28 weeks, respectively. One patient was not evaluable. Flow cytometric analysis demonstrated expansion of central memory T cells amidst declining effector memory cells following vaccination in three patients at a dose of 15x106 DC. Conclusions: Apoptotic body-pulsed DC vaccination was well tolerated and preliminarily demonstrated clinical activity but a minimum of 15x106 DC was required for a modulation of central memory T cells.

Abstract 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. Mol Cancer Ther; 11(10); 2183–92. ©2012 AACR.

Abstract With recent approval of the first dendritic cell (DC) vaccine for patient use, many other DC vaccine approaches are now being tested in clinical trials. Many of these DC vaccines employ tumor cell lysates (TL) generated from cells cultured in atmospheric oxygen (∼20% O2) that greatly exceeds levels found in tumors in situ. In this study, we tested the hypothesis that TLs generated from tumor cells cultured under physiologic oxygen (∼5% O2) would be more effective as a source for DC antigens. Gene expression patterns in primary glioma cultures established at 5% O2 more closely paralleled patient tumors in situ and known immunogenic antigens were more highly expressed. DCs treated with TLs generated from primary tumor cells maintained in 5% O2 took up and presented antigens to CD8 T cells more efficiently. Moreover, CD8 T cells primed in this manner exhibited superior tumoricidal activity against target cells cultured in either atmospheric 20% O2 or physiologic 5% O2. Together, these results establish a simple method to greatly improve the effectiveness of DC vaccines in stimulating the production of tumoricidal T cells, with broad implications for many of the DC-based cancer vaccines being developed for clinical application. Cancer Res; 71(21); 6583–9. ©2011 AACR.