PET Imaging of Innate Immune Activation Using 11C Radiotracers Targeting GPR84

Chronic innate immune activation is a key hallmark of many neurological diseases and is known to result in the upregulation of GPR84 in myeloid cells (macrophages, microglia, and monocytes). As such, GPR84 can potentially serve as a sensor of proinflammatory innate immune responses. To assess the utility of GPR84 as an imaging biomarker, we synthesized 11C-MGX-10S and 11C-MGX-11Svia carbon-11 alkylation for use as positron emission tomography (PET) tracers targeting this receptor. In vitro experiments demonstrated significantly higher binding of both radiotracers to hGPR84-HEK293 cells than that of parental control HEK293 cells. Co-incubation with the GPR84 antagonist GLPG1205 reduced the binding of both radiotracers by >90%, demonstrating their high specificity for GPR84 in vitro. In vivo assessment of each radiotracer via PET imaging of healthy mice illustrated the superior brain uptake and pharmacokinetics of 11C-MGX-10S compared to 11C-MGX-11S. Subsequent use of 11C-MGX-10S to image a well-established mouse model of systemic and neuro-inflammation revealed a high PET signal in affected tissues, including the brain, liver, lung, and spleen. In vivo specificity of 11C-MGX-10S for GPR84 was confirmed by the administration of GLPG1205 followed by radiotracer injection. When compared with 11C-DPA-713-an existing radiotracer used to image innate immune activation in clinical research studies-11C-MGX-10S has multiple advantages, including its higher binding signal in inflamed tissues in the CNS and periphery and low background signal in healthy saline-treated subjects. The pronounced uptake of 11C-MGX-10S during inflammation, its high specificity for GPR84, and suitable pharmacokinetics strongly support further investigation of 11C-MGX-10S for imaging GPR84-positive myeloid cells associated with innate immune activation in animal models of inflammatory diseases and human neuropathology.

Tracking adoptive T cell immunotherapy using magnetic particle imaging

Adoptive cellular therapy (ACT) is a potent strategy to boost the immune response against cancer. ACT is effective against blood cancers but faces challenges in treating solid tumors. A critical step for the success of ACT immunotherapy is to achieve efficient trafficking and persistence of T cells to solid tumors. Non-invasive tracking of the accumulation of adoptively transferred T cells to tumors would greatly accelerate development of more effective ACT strategies. We demonstrate the use of magnetic particle imaging (MPI) to non-invasively track ACT T cells in vivo in a mouse model of brain cancer. Magnetic labeling did not impair primary tumor-specific T cells in vitro, and MPI allowed the detection of labeled T cells in the brain after intravenous or intracerebroventricular administration. These results support the use of MPI to track adoptively transferred T cells and accelerate the development of ACT treatments for brain tumors and other cancers.

Emerging Biomedical Applications Based on the Response of Magnetic Nanoparticles to Time-Varying Magnetic Fields

Magnetic nanoparticles are of interest for biomedical applications because of their biocompatibility, tunable surface chemistry, and actuation using applied magnetic fields. Magnetic nanoparticles respond to time-varying magnetic fields via physical particle rotation or internal dipole reorientation, which can result in signal generation or conversion of magnetic energy to heat. This dynamic magnetization response enables their use as tracers in magnetic particle imaging (MPI), an emerging biomedical imaging modality in which signal is quantitative of tracer mass and there is no tissue background signal or signal attenuation. Conversion of magnetic energy to heat motivates use in nanoscale thermal cancer therapy, magnetic actuation of drug release, and rapid rewarming of cryopreserved organs. This review introduces basic concepts of magnetic nanoparticle response to time-varying magnetic fields and presents recent advances in the field, with an emphasis on MPI and conversion of magnetic energy to heat.

Long circulating tracer tailored for magnetic particle imaging

Superparamagnetic iron oxide nanoparticle (SPION) tracers possessing long blood circulation time and tailored for magnetic particle imaging (MPI) performance are crucial for the development of this emerging molecular imaging modality. Here, single-core SPION MPI tracers coated with covalently bonded polyethyelene glycol (PEG) brushes were obtained using a semi-batch thermal decomposition synthesis with controlled addition of molecular oxygen, followed by an optimized PEG-silane ligand exchange procedure. The physical and magnetic properties, MPI performance, and blood circulation time of these newly synthesized tracers were compared to those of two commercially available SPIONs that were not tailored for MPI but are used for MPI: ferucarbotran and PEG-coated Synomag^®-D. The new tailored tracer has MPI sensitivity that is ~3-times better than the commercial tracer ferucarbotran and much longer circulation half-life than both commercial tracers (t_1/2=6.99 h for the new tracer, vs t_1/2=0.59 h for ferucarbotran, and t_1/2=0.62 h for PEG-coated Synomag^®-D).

Combining magnetic particle imaging and magnetic fluid hyperthermia for localized and image-guided treatment

Magnetic fluid hyperthermia (MFH) has been widely investigated as a treatment tool for cancer and other diseases. However, focusing traditional MFH to a tumor deep in the body is not feasible because the in vivo wavelength of 300 kHz very low frequency (VLF) excitation fields is longer than 100 m. Recently we demonstrated that millimeter-precision localized heating can be achieved by combining magnetic particle imaging (MPI) with MFH. In principle, real-time MPI imaging can also guide the location and dosing of MFH treatments. Hence, the combination of MPI imaging plus real time localized MPI-MFH could soon permit closed-loop high-resolution hyperthermia treatment. In this review, we will discuss the fundamentals of localized MFH (e.g. physics and biosafety limitations), hardware implementation, MPI real-time guidance, and new research directions on MPI-MFH. We will also discuss how the scale up to human-sized MPI-MFH scanners could proceed.

IMMU-31. QUANTITATIVE EVALUATION OF ROUTES OF ADMINISTRATION OF IMMUNOTHERAPEUTIC T CELLS TO ORTHOTOPIC GLIOMA

SIGNIFICANCE

Adoptive T cell therapy (ACT) has emerged as the most effective treatment against advanced malignant melanoma, eliciting remarkable objective clinical responses in up to 75% of patients with refractory metastatic disease, including within the central nervous system. Immunologic surrogate endpoints correlating with treatment outcome have been identified in these patients, with clinical responses being dependent on the migration of transferred T cells to sites of tumor growth.

OBJECTIVE

We investigated the biodistribution of intravenously or intraventricularly administered T cells in a murine model of glioblastoma at whole body, organ, and cellular levels.

METHODS

gp100-specific T cells were isolated from the spleens of pmel DsRed transgenic C57BL/6 mice and injected intravenously or intraventricularly, after in vitro expansion and activation, in murine KR158B-Luc-gp100 glioma-bearing mice. To determine transferred T cell spatial distribution, the brain, lymph nodes, heart, lungs, spleen, liver, and kidneys of mice were processed for 3D imaging using light-sheet and multiphoton imaging. ACT T cell quantification in various organs was performed ex vivo using flow cytometry, 2D optical imaging (IVIS), and magnetic particle imaging (MPI) after ferucarbotran nanoparticle transfection of T cells. T cell biodistribution was also assessed in vivo using MPI.

RESULTS

Following T cell intravenous injection, the spleen, liver, and lungs accounted for more than 90% of transferred T cells; the proportion of DsRed T cells in the brains was found to be very low, hovering below 1%. In contrast, most ACT T cells persisted in the tumor-bearing brains following intraventricular injections. ACT T cells mostly concentrated at the periphery of tumor masses and in proximity to blood vessels.

CONCLUSIONS

The success of ACT immunotherapy for brain tumors requires optimization of delivery route, dosing regimen, and enhancement of tumor-specific lymphocyte trafficking and effector functions to achieve maximal penetration and persistence at sites of invasive tumor growth.

EXTH-42. QUANTITATIVE BIODISTRIBUTION OF ADOPTIVELY TRANSFERRED T CELLS IN BRAIN TUMOR-BEARING MICE

SIGNIFICANCE

Adoptive T cell therapy (ACT) has emerged as the most effective treatment strategy against advanced malignant melanoma, eliciting remarkable objective clinical responses in up to 75% of patients with refractory metastatic disease, including those with lesions within the central nervous system. Importantly, immunologic surrogate endpoints that correlate with treatment outcome have been identified in these patients, with clinical responses being dependent on the migration of transferred T cells to sites of tumor growth.

OBJECTIVE

We investigated the biodistribution of exogenously administered T cells in a murine model of glioblastoma at whole body, organ, and cellular levels.

METHODS

T cells were isolated from the spleens of DsRed transgenic C57BL/6 mice and injected intravenously, after in vitro expansion and activation, in murine KR158B glioma-bearing mice. To determine transferred T cell spatial distribution, brains, lymph nodes, hearts, lungs, spleens, livers, kidneys and stomachs were isolated for active clearing, immunostaining, and 3D imaging using light sheet microscopy, or processed for fluorescent immunohistochemistry and confocal imaging. Transferred T cell quantification in various organs was performed using flow cytometry, 2D optical imaging (IVIS), and magnetic particle imaging (MPI) after ferucarbotran nanoparticle labeling. T cell distribution was also assessed in vivo using IVIS and MPI.

RESULTS

The spleen, liver, and lungs accounted for more than 90% of transferred T cells in the body. The proportion of DsRed T cells in tumor-bearing brains was found to be very low, hovering below 1% (and representing ~15% of total tumor-infiltrating lymphocytes). Transferred T cells mostly concentrated at the periphery of the tumor mass and in proximity to blood vessels.

CONCLUSIONS

The success of ACT immunotherapy for brain tumors likely requires optimization of delivery route, dosing regimen, and modification of tumor-specific lymphocyte trafficking and effector functions in order to achieve maximal penetration and persistence at sites of invasive tumor growth.

IMMU-25. MAGNETIC PARTICLE IMAGING FOR NON-INVASIVE TRACKING OF ADOPTIVE CELL TRANSFER IN CANCER IMMUNOTHERAPY

BACKGROUND

Adoptive cell therapies (ACT) are strategies being explored to boost the immune response against cancer. ACT cancer immunotherapies are effective against metastatic melanoma, leukemia, and lymphoma, but face challenges in treating other solid tumors, such as in the brain. A critical step for the success of ACT in solid cancers is achieving trafficking and persistence of T-cells at tumor sites. Glioblastoma (GBM) is the most common and aggressive cancer of the central nervous system in adults, with a prognosis of 15-18-month average patient survival after diagnosis. Biomedical imaging is often used to track cell therapies. Magnetic Particle Imaging (MPI) is a novel biomedical imaging modality enabling non-invasive visualization of the distribution of biocompatible superparamagnetic iron oxide (SPIO) tracers.

OBJECTIVE

Label T-cells with SPIO to non-invasively track adoptive T cell transfer immunotherapy with MPI in the context of brain cancer.

METHODS

Murine pmel-DsRed T-cells were isolated from the spleen of a transgenic C57BL/6 mouse, and were exposed to different SPIO concentrations ex vivo. Cell viability, phenotype, and cytotoxic function were analyzed to determine if T-cells were affected by the SPIO labeling. Moreover, in vivo experiments were performed in a murine GBM model, and labeled T-cells were injected intravenously and tracked using MPI.

RESULTS

The SPIO-labeling of T-cells did not affected cell viability, phenotype, or cell cytotoxic function at all tested incubation conditions. The internalized SPIO can be quantified and spatially detected using MPI both in vitro and in vivo. In addition, MPI in vivo tracking shows T-cells accumulation in liver and lungs, as well in the spleen and brain, as showed ex vivo.

CONCLUSIONS

SPIO-labeling of T-cells did not affected its cytotoxic function and MPI allows for in vivo tracking of adoptively T-cell transfer. MPI will provide better understanding of ACT dynamics to accelerate development of novel treatments.

Magnetic nanoparticle hyperthermia potentiates paclitaxel activity in sensitive and resistant breast cancer cells

Introduction

Overcoming resistance to antimitotic drugs, such as paclitaxel (PTX), would represent a major advance in breast cancer treatment. PTX induces mitotic block and sensitive cells exit mitosis dying by mitotic catastrophe. Resistant cells remain in block and continue proliferation after drug decay, denoting one of the PTX resistance mechanisms. Mild hyperthermia (HT) triggers mitotic exit of PTX-pretreated cells, overcoming PTX resistance and suggesting HT-forced mitotic exit as a promising strategy to potentiate PTX.

Methods and results

Superparamagnetic iron oxide nanoparticles (SPIONs) were used to deliver mild HT at 42°C in PTX-pretreated breast adenocarcinoma MCF-7 cells sensitive and resistant to PTX. To evaluate mechanism of cell death, cells were classified based on nuclear morphology into interphase, mitotic, micronucleated, and apoptotic. The combined PTX→SPION treatment resulted in an increase in the percentage of micronucleated cells, an indication of forced mitotic exit. Importantly, in PTX-resistant cells, the combination therapy using SPION HT helps to overcome resistance by reducing the number of cells relative to the control.

Conclusion

SPION HT potentiates PTX by significantly reducing cell survival, suggesting potential of combined treatment for future clinical translation.