Immunotherapy of brain tumors

Pilot Preclinical and Clinical Evaluation of (4S)-4-(3-[18F]Fluoropropyl)-L-Glutamate (18F-FSPG) for PET/CT Imaging of Intracranial Malignancies

Purpose

(S)-4-(3-[¹⁸F]Fluoropropyl)-L-glutamic acid (18F-FSPG) is a novel radiopharmaceutical for Positron Emission Tomography (PET) imaging. It is a glutamate analogue that can be used to measure x_C^- transporter activity. This study was performed to assess the feasibility of 18F-FSPG for imaging orthotopic brain tumors in small animals and the translation of this approach in human subjects with intracranial malignancies.

Experimental Design

For the small animal study, GS9L glioblastoma cells were implanted into brains of Fischer rats and studied with 18F-FSPG, the 18F-labeled glucose derivative 18F-FDG and with the 18F-labeled amino acid derivative 18F-FET. For the human study, five subjects with either primary or metastatic brain cancer were recruited (mean age 50.4 years). After injection of 300 MBq of 18F-FSPG, 3 whole-body PET/Computed Tomography (CT) scans were obtained and safety parameters were measured. The three subjects with brain metastases also had an 18F-FDG PET/CT scan. Quantitative and qualitative comparison of the scans was performed to assess kinetics, biodistribution, and relative efficacy of the tracers.

Results

In the small animals, the orthotopic brain tumors were visualized well with 18F-FSPG. The high tumor uptake of 18F-FSPG in the GS9L model and the absence of background signal led to good tumor visualization with high contrast (tumor/brain ratio: 32.7). 18F-FDG and 18F-FET showed T/B ratios of 1.7 and 2.8, respectively. In the human pilot study, 18F-FSPG was well tolerated and there was similar distribution in all patients. All malignant lesions were positive with 18F-FSPG except for one low-grade primary brain tumor. In the 18F-FSPG-PET-positive tumors a similar T/B ratio was observed as in the animal model.

Conclusions

18F-FSPG is a novel PET radiopharmaceutical that demonstrates good uptake in both small animal and human studies of intracranial malignancies. Future studies on larger numbers of subjects and a wider array of brain tumors are planned.

Trial Registration

ClinicalTrials.gov NCT01186601

Glioma-derived extracellular vesicles selectively suppress immune responses

BACKGROUND

Glioma-related immunosuppression is well documented; however, the mechanisms of suppression are not fully understood. Here we explore a role for glioma extracellular vesicles (EVs) as a means of immune modulation.

METHODS

Healthy donor peripheral blood mononuclear cells (PBMCs) were incubated with mitogenic stimuli and various concentrations of glioma-derived EVs. Intracellular signaling and cytokine output were determined by protein microarrays, and phenotypic changes were assessed by flow cytometry. Recall antigen testing, mixed lymphocyte reactions, and migration assays analyzed PBMC functional capacity.

RESULTS

Protein microarray data revealed induction of an immunosuppressive phenotype and cytokine output at high tumor-vesicle concentrations but an activated phenotype at low concentrations. T cell activation antigen expression confirmed differential activation profiles. Functional analyses revealed decreased migratory capacity of PBMCs after incubation with EVs; however, recall antigen and mixed lymphocyte tests indicated that activation capacity is still retained in EV-treated cells.

CONCLUSION

The differential effects of high and low EV concentrations dictate modulatory effects on PBMCs. These data provide a role for EVs at high concentrations for inducing selective tolerance of an immune response in a tumor setting. This suggests that lymphocytes in patients' circulation are not irreparably impaired, as previously thought, but can be rescued to augment antitumor responses.

Glioblastoma: from molecular pathology to targeted treatment

Glioblastoma (GBM) is one of the most lethal human cancers. Genomic analyses are defining the molecular architecture of GBM, uncovering relevant subsets of patients whose disease may require different treatments. Many pharmacological targets have been revealed, promising to transform patient care through targeted therapies. However, for most patients, clinical responses to targeted inhibitors are either not apparent or not durable. In this review, we address the challenge of developing more effective, molecularly guided approaches for the treatment of GBM patients. We summarize the current state of knowledge regarding molecular classifiers and examine their benefit for stratifying patients for treatment. We survey the molecular landscape of the disease, discussing the challenges raised by acquired drug resistance. Furthermore, we analyze the biochemical features of GBM, suggesting a next generation of drug targets, and we examine the contribution of tumor heterogeneity and its implications. We conclude with an analysis of the experimental approaches and their potential benefit to patients.