Dali Yin, R. Mark Richardson, Massimo S. Fiandaca, John Bringas, John Forsayeth, Mitchel S. Berger and Krystof S. Bankiewicz
The purpose of this study was to optimize stereotactic coordinates for delivery of therapeutic agents into the thalamus and brainstem, using convection-enhanced delivery (CED) to avoid leakage into surrounding anatomical structures while maximizing CED of therapeutics within the target volume.
The authors recently published targeting data for the nonhuman primate putamen in which they defined infusion parameters, referred to as “red,” “blue,” and “green” zones, that describe cannula placements resulting in poor, suboptimal, and optimal volumes of distribution, respectively. In the present study, the authors retrospectively analyzed 22 MR images with gadoteridol as a contrast reagent, which were obtained during CED infusions into the thalamus (14 cases) and brainstem (8 cases) of nonhuman primates.
Excellent distribution of gadoteridol within the thalamus was obtained in 8 cases and these were used to define an optimal target locus (or green zone). Good distribution in the thalamus, with variable leakage into adjacent anatomical structures, was noted in 6 cases, defining a blue zone. Quantitative containment (99.7 ± 0.2%) of gadoteridol within the thalamus was obtained when the cannula was placed in the green zone, and less containment (85.4 ± 3.8%) was achieved with cannula placement in the blue zone. Similarly, a green zone was also defined in the brainstem, and quantitative containment of infused gadoteridol within the brainstem was 99.4 ± 0.6% when the cannula was placed in the green zone. These results were used to determine a set of 3D stereotactic coordinates that define an optimal site for infusions intended to cover the thalamus and brainstem of nonhuman primates.
The present study provides quantitative analysis of cannula placement and infusate distribution using real-time MR imaging and defines an optimal zone for infusion in the nonhuman primate thalamus and brainstem. Cannula placement recommendations developed from such translational nonhuman primate studies have significant implications for the design of anticipated clinical trials featuring CED therapy into the thalamus and brainstem for CNS diseases.
Vanja Varenika, Peter Dickinson, John Bringas, Richard LeCouteur, Robert Higgins, John Park, Massimo Fiandaca, Mitchel Berger, John Sampson and Krystof Bankiewicz
The authors have shown that convection-enhanced delivery (CED) of gadoteridol-loaded liposomes (GDLs) into different regions of normal monkey brain results in predictable, widespread distribution of this tracking agent as detected by real-time MR imaging. They also have found that this tracking technique allows monitoring of the distribution of similar nanosized agents such as therapeutic liposomes and viral vectors. A limitation of this procedure is the unexpected leakage of liposomes out of targeted parenchyma or malignancies into sulci and ventricles. The aim of the present study was to evaluate the efficacy of CED after the onset of these types of leakage.
The authors documented this phenomenon in a study of 5 nonhuman primates and 7 canines, comprising 54 CED infusion sessions. Approximately 20% of these infusions resulted in leakage into cerebral ventricles or sulci. All of the infusions and leakage events were monitored with real-time MR imaging. The authors created volume-distributed versus volume-infused graphs for each infusion session. These graphs revealed the rate of distribution of GDL over the course of each infusion and allowed the authors to evaluate the progress of CED before and after leakage.
The distribution of therapeutics within the target structure ceased to increase or resulted in significant attenuation after the onset of leakage.
An analysis of the cases in this study revealed that leakage undermines the efficacy of CED. These findings reiterate the importance of real-time MR imaging visualization during CED to ensure an accurate, robust distribution of therapeutic agents.
Michal T. Krauze, Ryuta Saito, Charles Noble, Matyas Tamas, John Bringas, John W. Park, Mitchel S. Berger and Krystof Bankiewicz
Object. Clinical application of the convection-enhanced delivery (CED) technique is currently limited by low infusion speed and reflux of the delivered agent. The authors developed and evaluated a new step-design cannula to overcome present limitations and to introduce a rapid, reflux-free CED method for future clinical trials.
Methods. The CED of 0.4% trypan blue dye was performed in agarose gel to test cannula needles for distribution and reflux. Infusion rates ranging from 0.5 to 50 µl/minute were used. Agarose gel findings were translated into a study in rats and then in cynomolgus monkeys (Macaca fascicularis) by using trypan blue and liposomes to confirm the efficacy of the reflux-free step-design cannula in vivo.
Results of agarose gel studies showed reflux-free infusion with high flow rates using the step-design cannula. Data from the study in rats confirmed the agarose gel findings and also revealed increasing tissue damage at a flow rate above 5-µl/minute. Robust reflux-free delivery and distribution of liposomes was achieved using the step-design cannula in brains in both rats and nonhuman primates.
Conclusions. The authors developed a new step-design cannula for CED that effectively prevents reflux in vivo and maximizes the distribution of agents delivered in the brain. Data in the present study show reflux-free infusion with a constant volume of distribution in the rat brain over a broad range of flow rates. Reflux-free delivery of liposomes into nonhuman primate brain was also established using the cannula. This step-design cannula may allow reflux-free distribution and shorten the duration of infusion in future clinical applications of CED in humans.
Ryuta Saito, John Bringas, Hanna Mirek, Mitchel S. Berger and Krys S. Bankiewicz
Object. Chemotherapy is suspected of having an effect on the generation of phenotypical heterogeneity and the development of drug resistance in tumors. Recurrent gliomas feature drug resistance as well as greater invasive growth than original tumors. The authors investigated phenotypical changes in invasion observed in 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)—resistant sublines of the 9L rat gliosarcoma.
Methods. Two established BCNU-resistant sublines, derived from 9L gliosarcoma cells by treating these cells with BCNU in vivo or in vitro, were used in the study. An in vitro examination confirmed the resistance of the cells to BCNU treatment. The cells were implanted into the striatum of Fisher 344 rats, and histological examinations were performed to compare the growth patterns of the resultant tumors. A new brain tumor model was established by implanting 9L-2 cells in Fisher 344 rats.
The 9L-2 and BTRC-19 cells displayed a distinct increase in BCNU resistance compared with the 9L cells. Both BCNU-resistant sublines developed a tumor mass with invasive margins, which is not the case with 9L tumor models. The newly developed 9L-2 tumor model demonstrated 100% tumor uptake with consistent growth patterns.
Conclusions. Cells that acquire drug resistance also demonstrated invasive growth. Because the 9L-2 and BTRC-19 cells were derived from 9L cells that had been treated with BCNU in vivo and in vitro, this change in phenotype was likely caused by the drug treatment, which may have implications for chemotherapy of gliomas. The tumor model that developed from the 9L-2 cells can be used as a model of a recurrent glioma, which features drug resistance and invasive growth.