Canine model of convection-enhanced delivery of liposomes containing CPT-11 monitored with real-time magnetic resonance imaging: laboratory investigation.

OBJECT: Many factors relating to the safety and efficacy of convection-enhanced delivery (CED) into intracranial tumors are poorly understood. To investigate these factors further and establish a more clinically relevant large animal model, with the potential to investigate CED in large, spontaneous tumors, the authors developed a magnetic resonance (MR) imaging-compatible system for CED of liposomal nanoparticles into the canine brain, incorporating real-time MR imaging. Additionally any possible toxicity of liposomes containing Gd and the chemotherapeutic agent irinotecan (CPT-11) was assessed following direct intraparenchymal delivery. METHODS: Four healthy laboratory dogs were infused with liposomes containing Gd, rhodamine, or CPT-11. Convection-enhanced delivery was monitored in real time by sequential MR imaging, and the volumes of distribution were calculated from MR images and histological sections. Assessment of any toxicity was based on clinical and histopathological evaluation. Convection-enhanced delivery resulted in robust volumes of distribution in both gray and white matter, and real-time MR imaging allowed accurate calculation of volumes and pathways of distribution. RESULTS: Infusion variability was greatest in the gray matter, and was associated with leakage into ventricular or subarachnoid spaces. Complications were minimal and included mild transient proprioceptive deficits, focal hemorrhage in 1 dog, and focal, mild perivascular, nonsuppurative encephalitis in 1 dog. CONCLUSIONS: Convection-enhanced delivery of liposomal Gd/CPT-11 is associated with minimal adverse effects in a large animal model, and further assessment for use in clinical patients is warranted. Future studies investigating real-time monitored CED in spontaneous gliomas in canines are feasible and will provide a unique, clinically relevant large animal translational model for testing this and other therapeutic strategies.

Canine spontaneous glioma: a translational model system for convection-enhanced delivery.

Canine spontaneous intracranial tumors bear striking similarities to their human tumor counterparts and have the potential to provide a large animal model system for more realistic validation of novel therapies typically developed in small rodent models. We used spontaneously occurring canine gliomas to investigate the use of convection-enhanced delivery (CED) of liposomal nanoparticles, containing topoisomerase inhibitor CPT-11. To facilitate visualization of intratumoral infusions by real-time magnetic resonance imaging (MRI), we included identically formulated liposomes loaded with Gadoteridol. Real-time MRI defined distribution of infusate within both tumor and normal brain tissues. The most important limiting factor for volume of distribution within tumor tissue was the leakage of infusate into ventricular or subarachnoid spaces. Decreased tumor volume, tumor necrosis, and modulation of tumor phenotype correlated with volume of distribution of infusate (Vd), infusion location, and leakage as determined by real-time MRI and histopathology. This study demonstrates the potential for canine spontaneous gliomas as a model system for the validation and development of novel therapeutic strategies for human brain tumors. Data obtained from infusions monitored in real time in a large, spontaneous tumor may provide information, allowing more accurate prediction and optimization of infusion parameters. Variability in Vd between tumors strongly suggests that real-time imaging should be an essential component of CED therapeutic trials to allow minimization of inappropriate infusions and accurate assessment of clinical outcomes.

Growth inhibition of an orthotopic glioblastoma in immunocompetent mice by cationic lipid-DNA complexes.

The effect of a cationic liposome non-coding plasmid DNA complex on the growth of an intracerebral glioblastoma in an immunocompetent syngeneic mouse strain was evaluated. Previous studies of extraneural tumors in mice have demonstrated that such complexes containing plasmid DNA are capable of stimulating a potent Th-1 cytokine immune-mediated response with a dramatic inhibition of tumor growth. A DOTIM-cholesterol cationic liposome complexed to non-coding plasmid DNA (EV-CLDC) was administered intravenously (i.v.) at weekly intervals to 6-week-old male mice of the B6D2F1 strain at either 3, 10 or 17 days post-inoculation (DPI) of 4C8 glioblastoma cells. Tumor growth was monitored by volumetric image analysis obtained from sequential weekly magnetic resonance imaging studies of the brain. Experiments were terminated between 30 to 38 DPI. Terminal tumor volumes calculated from histological sections directly correlated with tumor volumes from corresponding MR images. The EV-CLDC administered at 3 DPI resulted in a statistically significant (P<0.0001) sustained inhibition of tumor growth compared with tumors in mice administered only individual components of the EV-CLDC. The EV-CLDC similarly inhibited growth of longer established glioblastomas. Histopathologic evaluation of terminal tumors did not find any hemorrhage, edema or necrosis in either the EV-CLDC-treated or control tumors. The results indicate that an i.v.-administered EV-CLDC can significantly inhibit the growth of a brain tumor in immunocompetent syngeneic mice.