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

Abstract

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.

Fig. 1.

Convection-enhanced delivery equipment used in the canine model system. (A) Schematic representation of indwelling guide pedestal system. (B) MRI compatible head frame utilizing ear bars and a dental bite plate. (C) Fused silica infusion cannulae with a reflux resistant step design are directed into the tumor site through the stereotactically placed guide pedestals. (D) Guide pedestals contain multiple ports to allow modification of targeting coordinates within the tumor. (E) Simultaneous infusion of liposomal infusate through 3 infusion cannulae. (F) Guide pedestals are secured in situ using rapid curing urethane dimethacrylate.

Fig. 2.

Patient tumor volumes following intratumoral CED of liposomal CPT-11. CED infusions are represented by asterisks, with total percentage of tumor coverage for each infusion. Patient 1 is shown with associated MR imaging. MR images (T1 weighted) correlate to therapeutic or monitoring time points represented graphically. Real-time monitoring of infusions defined appropriate targeting and volume of distribution critical for objective assessment of therapeutic efficacy. (A) Initial MR imaging and tumor volume. (B) Initial single cannula infusion resulting in 13% Vd within the tumor and subsequent minimal effect on tumor growth. (C) Rapid tumor growth was followed by a second infusion, resulting in 25% Vd within the tumor and a subsequent decrease in tumor volume (D). (E) Third infusion, using two cannulae, resulted in 55% Vd within the tumor. A dramatic decrease in tumor volume was seen (F) followed by static disease before the animal was euthanized for disease unrelated to the primary tumor. Reflux of infusate (E, upper panel) and leakage into ventricles and the subarachnoid space (E, lower panel) were clearly visible on imaging, and dictated eventual infusion termination to minimize potential toxicity. In this apparently chemosensitive tumor, increasing real-time defined volume of distribution was associated with increasing response based on tumor volume.

Fig. 3.

MR images from a Boxer with a grade III astrocytoma. (A) Initial diagnostic MRI; the temporal/pyriform lobe tumor is most easily seen on T2-weighted images. (B and C) T1-weighted real-time images during two separate infusions (2 weeks apart) showing poor Vd within the tumor because of leakage into the subarachnoid space and lateral ventricle. Documented poor Vd was associated with minimal effect of tumor volume (D). Repositioning of guide pedestals to target different sites within the tumor resulted in improved Vd (>50%) using 3 infusion cannulae (E, F, G, T1-weighted images). (H) T2-weighted image 2 months following the successful infusion; improved Vd is associated with a decrease in tumor volume with associated decreased mass effect (an area of malacia is present within the tumor and the ipsilateral sulci and lateral ventricle are more prominent).

Fig. 4.

MR images from a Boston Terrier with a grade III oliogdendroglioma. Two infusion procedures (CED 1,2) achieved 28% and 62% Vd, respectively, within the tumor, resulting in an 88% total reduction in tumor volume 5 months following initial treatment. Decreased tumor volume, decreased mass effect, and presumed necrosis (n) of the tumor is seen on posttreatment MR images. Real-time imaging of the first CED procedure identified poor coverage of the medial aspect of the mass (arrow head). An infusion cannula was specifically targeted to this area in the second procedure resulting in good medial coverage (arrows). Suboptimal placement of this cannula superficially within the tumor eventually resulted in leakage into the internal capsule (double arrow heads). Real-time imaging allowed detection and termination of the infusion to limit potential toxicity. Tr, transverse plane image; Sag, sagittal plane image; Dor, dorsal plane image.

Fig. 5.

Necropsy data from Patient 1. Real-time imaging of infusions and availability of necropsy in all clinical cases allowed histopathological data to be correlated with areas of infused and noninfused tumor and normal brain. (A) T1-weighted real-time imaging of the final CED showing poor infusion of tumor tissue medially (arrow). (B) Gross pathological specimen at the same level as the MRI (scale bar = 1 cm). (C) Whole brain section (hematoxylin and eosin) showing distinct areas consisting of infused tumor with malacia (M), infused tumor with modified tumor (I), and noninfused tumor (T) (scale bar = 500 µm). (D) Magnified view of infusion area (hematoxylin and eosin, scale bar = 500 µm). Modification of tumor phenotype was seen in areas of tumor that were infused (G, hematoxylin and eosin) compared with noninfused tumor (E, hematoxylin and eosin). Infused tumor was less cellular with a more homogenous cellular phenotype. MIB-1 index in infused tumor (H) was <1% compared with 15% in noninfused tumor (E) (E, F, G, H, sacle bar = 60 µm).

Fig. 6.

Adverse effects associated with nanoliposomal CPT-11/gadoteridol infusions. (Patient 3, A–F; Patient 8, G–K.) (A) Preinfusion T2W MR image. (B and C) CED using 3 cannulae resulted in intratumoral delivery rostrally; however, reflux of infusate from the caudal cannula resulted in delivery into the internal capsule instead of the target site (arrowhead). (D and E) T2W MR images 8 weeks postinfusion; T2 hyperintensity is present predominantly affecting white matter, resulting in ventricular compression and effacement of sulci. (F) T2W MR image 6 weeks later following corticosteroid treatment with resolution of the majority of the white matter hyperintensity. (G) Preinfusion T2W MR image. First (H) and second (I) infusions (T1W MR images). The first infusion achieved good intratumoral Vd, whereas the second was restricted to the ventral aspect of the tumor. Both infusions were eventually limited by ventricular leakage (arrowhead). (J) Four weeks postinfusion, clinical deterioration was associated with T2 hyperintensity predominantly associated with white matter and also increased tumor volume. (K) Four weeks following corticosteroid treatment and rapid resolution of clinical signs, T2 hyperintensity and associated mass effect has resolved, and tumor volume is decreased.