High-grade gliomas are extremely difficult to treat because they are invasive and therefore are not curable by surgical resection; the toxicity of currently chemo- and radiation therapies limits the doses that can be used. Neural stem cells (NSCs) have inherent tumor-tropic properties that enable their use as delivery vehicles that can target enzyme/prodrug therapy selectively to tumors. We have used a cytosine deaminase (CD)-expressing clonal human NSC line, HB1.F3.CD, to home to gliomas in mice and locally convert the tumor-localized prodrug 5-fluorocytosine to the active chemotherapeutic 5-fluorouracil. In vitro studies confirmed that the NSCs have normal karyotype, tumor tropism, and CD expression, indicating that these cells are genetically and functionally stable. In vivo biodistribution studies demonstrated that these NSCs retained tumor tropism, even in mice pre-treated with radiation or dexamethasone to mimic clinically relevant adjuvant therapies. We evaluated safety and toxicity after intracerebral administration of the NSCs in non-tumor bearing, and in orthotopic glioma-bearing, immunocompetent and immunodeficient mice. We detected no difference in toxicity associated with conversion of 5-fluorocytosine to 5-fluorouracil, no NSCs outside the brain, and no histological evidence of pathology or tumorigenesis attributable to the NSCs. The average tumor volume in mice that received HB1.F3.CD NSCs and 5-fluorocytosine was approximately one-third that of the average volume in control mice. On the basis of these results, we conclude that combination therapy with HB1.F3.CD NSCs and 5-fluorocytosine is safe, non-toxic and effective in mice. These data have led to approval of a first-inhuman study of an allogeneic NSC-mediated enzyme/prodrug targeted cancer therapy in patients with recurrent high-grade glioma.

Although chimeric antigen receptor (CAR) T cells have demonstrated signs of antitumor activity against glioblastoma (GBM), tumor heterogeneity remains a critical challenge. To achieve broader and more effective GBM targeting, we developed a peptide-bearing CAR exploiting the GBM-binding potential of chlorotoxin (CLTX). We find that CLTX peptide binds a great proportion of tumors and constituent tumor cells. CAR T cells using CLTX as the targeting domain (CLTX-CAR T cells) mediate potent anti-GBM activity and efficiently target tumors lacking expression of other GBM-associated antigens. Treatment with CLTX-CAR T cells resulted in tumor regression in orthotopic xenograft GBM tumor models. CLTX-CAR T cells do not exhibit observable off-target effector activity against normal cells or after adoptive transfer into mice. Effective targeting by CLTX-CAR T cells requires cell surface expression of matrix metalloproteinase–2. Our results pioneer a peptide toxin in CAR design, expanding the repertoire of tumor-selective CAR T cells with the potential to reduce antigen escape.

Human neural stem cells (NSC) are inherently tumor tropic, making them attractive drug delivery vehicles. Toward this goal, we retrovirally transduced an immortalized, clonal NSC line to stably express cytosine deaminase (HB1.F3.CD.C21; CD-NSCs), which converts the prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU). Recurrent high-grade glioma patients underwent intracranial administration of CD-NSCs during tumor resection or biopsy. Four days later, patients began taking oral 5-FC every 6 hours for 7 days. Study treatment was given only once. A standard 3 + 3 dose escalation schema was used to increase doses of CD-NSCs from 1 × 10 to 5 × 10 and 5-FC from 75 to 150 mg/kg/day. Intracerebral microdialysis was performed to measure brain levels of 5-FC and 5-FU. Serial blood samples were obtained to assess systemic drug concentrations as well as to perform immunologic correlative studies. Fifteen patients underwent study treatment. We saw no dose-limiting toxicity (DLT) due to the CD-NSCs. There was 1 DLT (grade 3 transaminitis) possibly related to 5-FC. We did not see development of anti-CD-NSC antibodies and did not detect CD-NSCs or replication-competent retrovirus in the systemic circulation. Intracerebral microdialysis revealed that CD-NSCs produced 5-FU locally in the brain in a 5-FC dose-dependent manner. Autopsy data indicate that CD-NSCs migrated to distant tumor sites and were nontumorigenic. Collectively, our results from this first-in-human study demonstrate initial safety and proof of concept regarding the ability of NSCs to target brain tumors and locally produce chemotherapy. .

Hypoxia is a critical aspect of the microenvironment in glioma and generally signifies unfavorable clinical outcome. Effective targeting of hypoxic areas in gliomas remains a significant therapeutic challenge. New therapeutic platforms using neural stem cells (NSC) for tumor-targeted drug delivery show promise in treatment of cancers that are refractory to traditional therapies. However, the molecular mechanisms of NSC targeting to hypoxic tumor areas are not well understood. Therefore, we investigated the role of hypoxia in directed migration of NSCs to glioma and identified the specific signaling molecules involved. Our data showed that hypoxia caused increased migration of human HB1.F3 NSCs to U251 human glioma-conditioned medium in vitro. In HB1.F3 NSCs, hypoxia led to up-regulation of CXCR4, urokinase-type plasminogen activator receptor (uPAR), vascular endothelial growth factor receptor 2 (VEGFR2), and c-Met receptors. Function-inhibiting antibodies to these receptors inhibited the migration of HB1.F3 cells to glioma-conditioned medium. Small interfering RNA knockdown of hypoxia-inducible factor-1A in glioma cells blocked the hypoxia-induced migration of NSCs, which was due to decreased expression of stromal cell -derived factor-1 (SDF-1), uPA, and VEGF in glioma cells. Our in vivo data provided direct evidence that NSCs preferentially distributed to hypoxic areas inside intracranial glioma xenografts, as detected by pimonidazole hypoxia probe, as well as to the tumor edge, and that both areas displayed high SDF-1 expression. These observations indicate that hypoxia is a key factor in determining NSC tropism to glioma and that SDF-1/CXCR4, uPA/uPAR, VEGF/VEGFR2, and hepatocyte growth factor/c-Met signaling pathways mediate increased NSC-to-glioma tropism under hypoxia. These results have significant implications for development of stem cell -mediated tumor-selective gene therapies.

Treatment options of glioblastoma multiforme are limited due to the blood-brain barrier (BBB). In this study, we investigated the utility of intranasal (IN) delivery as a means of transporting stem cell-based antiglioma therapeutics. We hypothesized that mesenchymal stem cells (MSCs) delivered via nasal application could impart therapeutic efficacy when expressing TNF-related apoptosis-inducing ligand (TRAIL) in a model of human glioma. ¹¹¹In-oxine, histology and magnetic resonance imaging (MRI) were utilized to track MSCs within the brain and associated tumor. We demonstrate that MSCs can penetrate the brain from nasal cavity and infiltrate intracranial glioma xenografts in a mouse model. Furthermore, irradiation of tumor-bearing mice tripled the penetration of (¹¹¹In)-oxine-labeled MSCs in the brain with a fivefold increase in cerebellum. Significant increase in CXCL12 expression was observed in irradiated xenograft tissue, implicating a CXCL12-dependent mechanism of MSCs migration towards irradiated glioma xenografts. Finally, MSCs expressing TRAIL improved the median survival of irradiated mice bearing intracranial U87 glioma xenografts in comparison with nonirradiated and irradiated control mice. Cumulatively, our data suggest that IN delivery of stem cell-based therapeutics is a feasible and highly efficacious treatment modality, allowing for repeated application of modified stem cells to target malignant glioma.

Chimeric antigen receptor (CAR) T-cell therapy has shown promise in the treatment of haematological cancers and is currently being investigated for solid tumours, including high-grade glioma brain tumours. There is a desperate need to quantitatively study the factors that contribute to the efficacy of CAR T-cell therapy in solid tumours. In this work, we use a mathematical model of predator–prey dynamics to explore the kinetics of CAR T-cell killing in glioma: the Chimeric Antigen Receptor T-cell treatment Response in GliOma (CARRGO) model. The model includes rates of cancer cell proliferation, CAR T-cell killing, proliferation, exhaustion, and persistence. We use patient-derived and engineered cancer cell lines with an in vitro real-time cell analyser to parametrize the CARRGO model. We observe that CAR T-cell dose correlates inversely with the killing rate and correlates directly with the net rate of proliferation and exhaustion. This suggests that at a lower dose of CAR T-cells, individual T-cells kill more cancer cells but become more exhausted when compared with higher doses. Furthermore, the exhaustion rate was observed to increase significantly with tumour growth rate and was dependent on level of antigen expression. The CARRGO model highlights nonlinear dynamics involved in CAR T-cell therapy and provides novel insights into the kinetics of CAR T-cell killing. The model suggests that CAR T-cell treatment may be tailored to individual tumour characteristics including tumour growth rate and antigen level to maximize therapeutic benefit.

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Numerous stem cell-based therapies are currently under clinical investigation, including the use of neural stem cells (NSCs) as delivery vehicles to target therapeutic agents to invasive brain tumors. The ability to monitor the time course, migration, and distribution of stem cells following transplantation into patients would provide critical information for optimizing treatment regimens. No effective cell-tracking methodology has yet garnered clinical acceptance. A highly promising noninvasive method for monitoring NSCs and potentially other cell types in vivo involves preloading them with ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) to enable cell tracking using magnetic resonance imaging (MRI). We report here the preclinical studies that led to U.S. Food and Drug Administration approval for first-in-human investigational use of ferumoxytol to label NSCs prior to transplantation into brain tumor patients, followed by surveillance serial MRI. A combination of heparin, protamine sulfate, and ferumoxytol (HPF) was used to label the NSCs. HPF labeling did not affect cell viability, growth kinetics, or tumor tropism in vitro, and it enabled MRI visualization of NSC distribution within orthotopic glioma xenografts. MRI revealed dynamic in vivo NSC distribution at multiple time points following intracerebral or intravenous injection into glioma-bearing mice that correlated with histological analysis. Preclinical safety/toxicity studies of intracerebrally administered HPF-labeled NSCs in mice were also performed, and they showed no significant clinical or behavioral changes, no neuronal or systemic toxicities, and no abnormal accumulation of iron in the liver or spleen. These studies support the clinical use of ferumoxytol labeling of cells for post-transplant MRI visualization and tracking.