Tumour microenvironment heterogeneity affects the perceived spatial concordance between the intratumoural patterns of cell proliferation and 18F-fluorothymidine uptake.

BACKGROUND AND PURPOSE: PET imaging with (18)F-fluorothymidine ((18)F-FLT) can potentially be used to identify tumour subvolumes for selective dose escalation in radiation therapy. The purpose of this study is to analyse the co-localization of intratumoural patterns of cell proliferation with (18)F-FLT tracer uptake. MATERIALS AND METHODS: Mice bearing FaDu or SQ20B xenograft tumours were injected with (18)F-FLT, and bromodeoxyuridine (proliferation marker). Ex vivo images of the spatial pattern of intratumoural (18)F-FLT uptake and that of bromodeoxyuridine DNA incorporation were obtained from thin tumour tissue sections. These images were segmented by thresholding and Relative Operating Characteristic (ROC) curves and Dice similarity indices were evaluated. RESULTS: The thresholds at which maximum overlap occurred between FLT-segmented areas and areas of active cell proliferation were significantly different for the two xenograft tumour models, whereas the median Dice values were not. However, ROC analysis indicated that segmented FLT images were more specific at detecting the proliferation pattern in FaDu tumours than in SQ20B tumours. CONCLUSION: Highly dispersed patterns of cell proliferation observed in certain tumours can affect the perceived spatial concordance between the spatial pattern of (18)F-FLT uptake and that of cell proliferation even when high-resolution ex vivo autoradiography imaging is used for (18)F-FLT imaging.

Comprehensive approach to coregistration of autoradiography and microscopy images acquired from a set of sequential tissue sections.

UNLABELLED: Histopathologic validation of a PET tracer requires assessment of colocalization of the tracer with its intended biologic target. Using thin tissue section autoradiography, it is possible to visualize the spatial distribution of the PET tracer uptake and compare it with the distribution of the intended biologic target (as visualized with immunohistochemistry). The purpose of this study was to develop and evaluate an objective methodology for deformable coregistration of autoradiography and microscopy images acquired from a set of sequential tissue sections. METHODS: Tumor-bearing animals were injected with 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT), (14)C-FDG, and other markers of tumor microenvironment including Hoechst 33342 (blood-flow surrogate). After sacrifice, tumors were excised, frozen, and sectioned. Multiple stacks of sequential 8 µm sections were collected from each tumor. From each stack, the middle (reference) sections were used to obtain images of (18)F-FLT and (14)C-FDG uptake distributions using dual-tracer autoradiography. Sections adjacent to the reference were used to acquire all histopathologic data (e.g., images of cell proliferation, hematoxylin and eosin). Hoechst images were acquired from all sections. To correct for deformations and misalignments induced by tissue processing and image acquisition, the Hoechst image of each nonreference section was deformably registered to the reference Hoechst image. This transformation was then applied to all images acquired from the same tissue section. In this way, all microscopy images were registered to the reference Hoechst image. The Hoechst-to-autoradiography image registration was done using rigid point-set registration based on external markers visible in both images. RESULTS: The mean error of Hoechst to (18)F-FLT autoradiography registration (both images acquired from the same section) was 30.8 ± 20.1 µm. The error of Hoechst-based deformable registration of histopathologic images (acquired from sequential tissue sections) was 23.1 ± 17.9 µm. Total error of registration of autoradiography images to the histopathologic images acquired from adjacent sections was evaluated at 44.9 µm. This coregistration precision supersedes current rigid registration methods with reported errors of 100-200 µm. CONCLUSION: Deformable registration of autoradiography and histopathology images acquired from sequential sections is feasible and accurate when performed using corresponding Hoechst images.

Human dosimetry and preliminary tumor distribution of 18F-fluoropaclitaxel in healthy volunteers and newly diagnosed breast cancer patients using PET/CT.

UNLABELLED: (18)F-fluoropaclitaxel is a radiolabeled form of paclitaxel, a widely used chemotherapy agent. Preclinical data suggest that (18)F-fluoropaclitaxel may be a reasonable surrogate for measuring the uptake of paclitaxel. As a substrate of P-glycoprotein, a drug efflux pump associated with multidrug resistance, (18)F-fluoropaclitaxel may also be useful in identifying multidrug resistance and predicting tumor response for drugs other than paclitaxel. METHODS: After informed consent was obtained, 3 healthy volunteers and 3 patients with untreated breast cancer (neoadjuvant chemotherapy candidates, tumor size > 2 cm) received an intravenous infusion of (18)F-fluoropaclitaxel and then underwent PET/CT. Healthy volunteers underwent serial whole-body imaging over an approximately 3-h interval, and organ (18)F residence times were determined from the time-activity curves uncorrected for decay to determine dosimetry. Radiation dose estimates were calculated using OLINDA/EXM software. For breast cancer patients, dynamic imaging of the primary tumor was performed for 60 min, followed by static whole-body scans at 1 and 2 h after injection. RESULTS: Dosimetry calculations showed that the gallbladder received the highest dose (229.50 µGy/MBq [0.849 rad/mCi]), followed by the small and large intestines (161.26 µGy/MBq [0.597 rad/mCi] and 184.59 µGy/MBq [0.683 rad/mCi]). The resultant effective dose was 28.79 µGy/MBq (0.107 rem/mCi). At approximately 1 h after injection, an average of 42% of the decay-corrected activity was in the gastrointestinal system, with a mean of 0.01% in the tumor. All 3 breast cancer patients showed retention of (18)F-fluoropaclitaxel and ultimately demonstrated a complete pathologic response (no invasive cancer in the breast or axillary nodes) to chemotherapy that included a taxane (either paclitaxel or docetaxel) at surgical resection. The tumor-to-background ratio increased with time to a maximum of 7.7 at 20 min. CONCLUSION: This study demonstrates the feasibility of using (18)F-fluoropaclitaxel PET/CT tumor imaging and provides radiation dosimetry measurements in humans. Although further study is needed, it is hoped that the measured intratumoral (18)F-fluoropaclitaxel distribution can serve as a surrogate for paclitaxel, and potentially other chemotherapeutic agent retention, in solid tumors.

Conjugation of functionalized gadolinium metallofullerenes with IL-13 peptides for targeting and imaging glial tumors.

BACKGROUND: Glioblastoma multiforme is the most common and most lethal primary brain tumor in humans, with median survival of approximately 1 year. Owing to the ability of glioma cells to aggressively infiltrate normal brain tissue and survive exposure to current adjuvant therapies, there is a great need for specific targeted nanoplatforms capable of delivering both therapeutic and imaging agents directly to invasive tumor cells. METHOD: Gadolinium-containing endohedral fullerenes, highly efficient contrast agents for MRI, were functionalized and conjugated with a tumor-specific peptide and assessed for their ability to bind to glioma cells in vitro. RESULTS: We report the successful conjugation of the carboxyl functionalized metallofullerene Gd(3)N@C(80)(OH)(-26)(CH(2)CH(2)COOH)(-16) to IL-13 peptides and the successful targeting ability towards brain tumor cells that overexpress the IL-13 receptor (IL-13Rα2). CONCLUSION: These studies demonstrate that IL-13 peptide-conjugated gadolinium metallofullerenes could serve as a platform to deliver imaging and therapeutic agents to tumor cells.

Encapsulation of a radiolabeled cluster inside a fullerene cage, (177)Lu(x)Lu((3-x))N@C(80): an interleukin-13-conjugated radiolabeled metallofullerene platform.

In this communication, we describe the successful encapsulation of (177)Lu into the endohedral metallofullerene (177)Lu(x)Lu(3-x)N@C(80) (x = 1-3) starting with (177)LuCl(3) in a modified quartz Kraschmer-Huffman electric generator. We demonstrate that the (177)Lu (beta-emitter) in this fullerene cage is not significantly released for a period of up to at least one-half-life (6.7 days). We also demonstrate that this agent can be conjugated with an interleukin-13 peptide that is designed to target an overexpressed receptor in glioblastoma multiforme tumors. This nanoparticle delivery platform provides flexibility for a wide range of radiotherapeutic and radiodiagnostic multimodal applications.

Imaging multidrug resistance with 4-[18F]fluoropaclitaxel.

Multidrug resistance (MDR) is a cause of treatment failure in many cancer patients. MDR refers to a phenotype whereby a tumor is resistant to a large number of natural chemotherapeutic drugs. Having prior knowledge of the presence of such resistance would decrease morbidity from unsuccessful therapy and allow for the selection of individuals who may benefit from the coadministration of MDR-inhibiting drugs. The Tc-99m-labeled single-photon-emitting radiotracers sestamibi and tetrofosmin have shown some predictive value. However, positron-emitting radiotracers, which allow for dynamic quantitative imaging, hold promise for a more accurate and specific identification of MDRtumors.MDR-expressing tumors are resistant to paclitaxel, which is commonly used as a chemotherapeutic agent. 4-[18F]Fluoropaclitaxel (FPAC) is a PET-radiolabeled analogue of paclitaxel. Preclinical studies have shown the uptake of FPAC to be inversely proportional to tumor MDR expression. FPAC PET imaging in normal volunteers shows biodistribution to be similar to that in nonhuman primates. Imaging in a breast cancer patient showed FPAC localization in a primary tumor that responded to chemotherapy, while failure to localize in mediastinal disease corresponded with only partial response.FPAC PET imaging shows promise for the noninvasive pretreatment identification of MDR-expressing tumors. While much additional work is needed, this work represents a step toward image-guided personalized medicine.

Automated synthesis of 18F analogue of paclitaxel (PAC): [18F]Paclitaxel (FPAC).

A positron-emitting paclitaxel (PAC) derivative could allow in vivo measurement of multidrug resistance in tumors and, therefore, predict a potential chemotherapeutic benefit to patients. [18F]Paclitaxel was produced using a 2-reaction vessel automated synthesizer followed by HPLC purification. Optimized reaction conditions resulted in radiochemical yields of 21.2+/-9.6% at end of bombardment, radiochemical purity >99%, and specific activity of 159+/-43 G Bq/micromol. [18F]Paclitaxel activities of 1.33+/-0.729 G Bq (n=7) were obtained in sterile, pyrogen-free solution for IV administration.

Distribution of adoptively transferred, tumor-sensitized lymphocytes in the glioma-bearing rat.

For adoptively transferred lymphocytes to exert anti-tumor effects in vivo, they must traffic or initiate the migration of endogenous immune cells to the site of tumor. Using a rat model, we examined the trafficking of tumor-sensitized lymphocytes to an intracerebral glioma. By labeling the cells with 111Indium oxine (111In) prior to intravenous injection, we were able to quantify the relative number of lymphocytes that traveled to the tumor site. There was no difference in lymphocytic influx between the tumor-bearing and non-tumor-bearing cerebral hemispheres in 3-day rat glioma models. However, in 7-day models, significantly greater numbers of 111In-labeled lymphocytes resided in the tumor-bearing hemisphere at 12 h post-administration. This number increased more than two-fold by 24 h post-adoptive transfer. Using fluorescent-labeled lymphocytes and microscopy, we confirmed that the detection of radioactivity within the brain was truly due to tumor infiltrating 111In-labeled lymphocytes. Adoptively transferred cells were found in perivascular and peritumoral locations. These data demonstrate that tumor-sensitized lymphocytes traffic to an intracerebral target site where they can exert an effect, further supporting adoptive immunotherapy as a treatment for glioma.