Dynamic (18) F-FDG PET for Assessment of Tumor Physiology in Two Breast Carcinoma Xenografts

Parametric imaging in salivary gland scintigraphy

Salivary gland scintigraphy (SGS) is an imaging technique to evaluate functional aspects of the salivary glands. First described in 1965, visual analyses of summed images and of time-activity curves generated through regions of interest (ROI) are still the main evaluation tools used in clinical practice. An alternative to ROI-based analysis is the use of parametric images, which are images generated through pixel-by-pixel calculation of parameters from the original frames. In this article, we would like to present some parametric images for SGS studies and how to create and use them. Two images, vascular flow and uptake velocity, were created using the intercept and slope of a linear model of the frames from after the first to fifth minute of acquisition. And two others, excretion fraction and absolute excretion, by subtraction and division methods of the frames before and after sialogogue stimulation. These images allow the visualization of the spatial distribution and heterogeneity of these quantitative parameters, favoring different forms of analysis and helping with image segmentation. After more than a year of using these images in daily routine, our general impression is that they have been very helpful. This article, however, still represents only our early experiences with this technique, and clinical studies are yet needed to better evaluate this method.

GlucoCEST MRI for the Evaluation Response to Chemotherapeutic and Metabolic Treatments in a Murine Triple-Negative Breast Cancer: A Comparison with[18F]F-FDG-PET

PURPOSE

Triple-negative breast cancer (TNBC) patients have usually poor outcome after chemotherapy and early prediction of therapeutic response would be helpful. [¹⁸F]F-FDG-PET/CT acquisitions are often carried out to monitor variation in metabolic activity associated with response to the therapy, despite moderate accuracy and radiation exposure limit its application. The glucoCEST technique relies on the use of unlabelled D-glucose to assess glucose uptake with conventional MRI scanners and is currently under active investigations at clinical level. This work aims at validating the potential of MRI-glucoCEST in monitoring the therapeutic responses in a TNBC tumor murine model.

PROCEDURES

Breast tumor (4T1)-bearing mice were treated with doxorubicin or dichloroacetate for 1 week. PET/CT with [¹⁸F]F-FDG and MRI-glucoCEST were performed at baseline and after 3 cycles of treatment. Metabolic changes measured with [¹⁸F]F-FDG-PET and glucoCEST were compared and evaluated with changes in tumor volumes.

RESULTS

Doxorubicin-treated mice showed a significant decrease in tumor growth when compared to the control group. GlucoCEST imaging provided metabolic response after three cycles of treatment. Conversely, no variations were detected in [¹⁸F]F-FDG uptake. Dichloroacetate-treated mice did not show any decrease either in tumor volume or in tumor metabolic activity as assessed by both glucoCEST and [¹⁸F]F-FDG-PET.

CONCLUSIONS

Metabolic changes during doxorubicin treatment can be predicted by glucoCEST imaging that appears more sensitive than [¹⁸F]F-FDG-PET in reporting on therapeutic response. These findings support the view that glucoCEST may be a sensitive technique for monitoring metabolic response, but future studies are needed to explore the accuracy of this approach in other tumor types and treatments.

Influx rate of 18F-fluoroaminosuberic acid reflects cystine/glutamate antiporter expression in tumour xenografts

PURPOSE

¹⁸F-fluoroaminosuberic acid (¹⁸F-FASu) is a recently developed amino acid tracer for positron emission tomography (PET) of oxidative stress that may offer improved tumour assessment over the conventional tracer ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Our aim was to evaluate and relate dynamic ¹⁸F-FASu and ¹⁸F-FDG uptake with pharmacokinetic modelling to transporter protein expression levels in a panel of diverse tumour xenograft lines.

METHODS

Four different tumour xenograft lines were implanted in female athymic nude mice: MAS98.12 and HBCx3 (breast), TPMX (osteosarcoma) and A549 (lung). Dynamic PET over 60 min was performed on a small animal unit. The time-activity curves (TACs) for ¹⁸F-FASu and ¹⁸F-FDG in individual tumours were used to extract early (SUV_E; 2 min p.i.) and late (SUV_L; 55 min p.i.) standardised uptake values. Pharmacokinetic two-tissue compartment models were applied to the TACs to estimate rate constants K₁-k₄ and blood volume fraction v_B. Relative levels of cystine/glutamate antiporter subunit xCT were assessed by western blotting, and expression of GLUT1 and CD31 by immunohistochemistry.

RESULTS

¹⁸F-FASu showed higher SUV_E, whilst ¹⁸F-FDG exhibited higher SUV_L. Influx rate K₁ for ¹⁸F-FASu was significantly correlated with xCT levels (p = 0.001) and was significantly higher than K₁ for ¹⁸F-FDG (p < 0.001). K₁ for ¹⁸F-FDG was significantly correlated with GLUT1 levels (p = 0.002). v_B estimated from ¹⁸F-FASu and ¹⁸F-FDG TACs was highly consistent and significantly correlated (r = 0.85, p < 0.001). Two qualitatively different ¹⁸F-FASu uptake profiles were identified: type α with low xCT expression and low K₁ (A549 and HBCx3), and type β with high xCT expression and high K₁ (MAS98.12 and TPMX).

CONCLUSION

The influx rate of ¹⁸F-FASu reflects xCT activity in tumour xenografts. Dynamic PET with pharmacokinetic modelling is needed to fully appraise ¹⁸F-FASu distribution routes.

Roles of GLUT-1 and HK-II expression in the biological behavior of head and neck cancer

The Warburg effect plays an important role in the proliferation and invasion of malignant tumors. Glucose transporter 1 and hexokinase II are two key energy transporters involved in mediating the Warburg effect. This review will analyze the mechanisms of these two markers in their effects on the biological behavior of head and neck cancer.

Cabazitaxel-loaded Poly(2-ethylbutyl cyanoacrylate) nanoparticles improve treatment efficacy in a patient derived breast cancer xenograft

The effect of poly(2-ethyl-butyl cyanoacrylate) nanoparticles containing the cytotoxic drug cabazitaxel was studied in three breast cancer cell lines and one basal-like patient-derived xenograft model grown in the mammary fat pad of immunodeficient mice. Nanoparticle-encapsulated cabazitaxel had a much better efficacy than similar concentrations of free drug in the basal-like patient-derived xenograft and resulted in complete remission of 6 out of 8 tumors, whereas free drug gave complete remission only with 2 out of 9 tumors. To investigate the different efficacies obtained with nanoparticle-encapsulated versus free cabazitaxel, mass spectrometry quantification of cabazitaxel was performed in mice plasma and selected tissue samples. Nanoparticle-encapsulated drug had a longer circulation time in blood. There was approximately a three times higher drug concentration in tumor tissue 24 h after injection, and two times higher 96 h after injection of nanoparticles with drug compared to the free drug. The tissue biodistribution obtained after 24 h using mass spectrometry analyses correlates well with biodistribution data obtained using IVIS® Spectrum in vivo imaging of nanoparticles labeled with the fluorescent substance NR668, indicating that these data also are representative for the nanoparticle distribution. Furthermore, immunohistochemistry was used to estimate infiltration of macrophages into the tumor tissue following injection of nanoparticle-encapsulated and free cabazitaxel. The higher infiltration of anti-tumorigenic versus pro-tumorigenic macrophages in tumors treated with the nanoparticles might also contribute to the improved effect obtained with the nanoparticle-encapsulated drug. Tumor infiltration of pro-tumorigenic macrophages was four times lower when using nanoparticles containing cabazitaxel than when using particles without drug, and we speculate that the very good therapeutic efficacy obtained with our cabazitaxel-containing particles may be due to their ability to reduce the level of pro-tumorigenic macrophages in the tumor. In summary, encapsulation of cabazitaxel in poly(2-ethyl-butyl cyanoacrylate) nanoparticles seems promising for treatment of breast cancer.

Dynamic 2-Deoxy-2-[18F]Fluoro-D-Glucose Positron Emission Tomography for Chemotherapy Response Monitoring of Breast Cancer Xenografts

PURPOSE

Non-invasive response monitoring can potentially be used to guide therapy selection for breast cancer patients. We employed dynamic 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography ([¹⁸F]FDG PET) to evaluate changes in three breast cancer xenograft lines in mice following three chemotherapy regimens.

PROCEDURES

Sixty-six athymic nude mice bearing bilateral breast cancer xenografts (two basal-like and one luminal-like subtype) underwent three 60 min [¹⁸F]FDG PET scans. Scans were performed prior to and 3 and 10 days after treatment with doxorubicin, paclitaxel, or carboplatin. Tumor growth was monitored in parallel. A pharmacokinetic compartmental model was fitted to the tumor uptake curves, providing estimates of transfer rates between the vascular, non-metabolized, and metabolized compartments. Early and late standardized uptake values (SUV_E and SUV_L, respectively); the rate constants k ₁, k ₂, and k ₃, and the intravascular fraction v _B were estimated. Changes in tumor volume were used as a response measure. Multivariate partial least-squares regression (PLSR) was used to assess if PET parameters could model tumor response and to identify PET parameters with the largest impact on response.

RESULTS

Treatment responders had significantly larger perfusion-related parameters (k ₁ and k ₂) and lower metabolism-related parameter (k ₃) than non-responders 10 days after the start of treatment. These findings were further supported by the PLSR analysis, which showed that k ₁ and k ₂ at day 10 and changes in k ₃ explained most of the variability in response to therapy, whereas SUV_L and particularly SUV_E were of lesser importance.

CONCLUSIONS

Overall, rate parameters related to both tumor perfusion and metabolism were associated with tumor response. Conventional metrics of [¹⁸F]FDG uptake such as SUV_E and SUV_L apparently had little relation to tumor response, thus necessitating full dynamic scanning and pharmacokinetic analysis for optimal evaluation of chemotherapy-induced changes in breast cancers.

Positron emission tomography and pharmacokinetics of 2-[18F]-fluoroethyl choline for metabolic studies in breast cancer xenografts

BACKGROUND

Breast carcinomas (BC) can have abnormal choline (Cho) metabolism. Earlier studies indicated that Cho uptake can differ between different subtypes of BC. The purpose of this study was to investigate uptake of 2-[(18)F]-fluoroethyl-choline ([(18)F]FECh) in three different patient-derived breast cancer xenografts (BCXs) using dynamic positron emission tomography (dPET).

MATERIAL AND METHODS

Nine athymic nude mice bearing bilateral MAS98.12 (basal-like), HBCx34 or MAS98.06 (both luminal B) BCXs were subjected to a 90-minute dPET scan following a bolus injection of 10 MBq of [(18)F]FECh. A Patlak Plot analysis and a well-established two-tissue compartment model were fitted to the uptake curves of the whole tumors, providing estimates of transfer rates between the vascular, non-metabolized and metabolized compartments. Patlak slope KP and intercept V, the rate constants k₁, k₂, k₃, the intravascular fraction vb and MR[(18)F]FECh were estimated. Additionally, analyses of terminal blood samples and tumor cell suspension incubated with [(18)F]FECh were performed.

RESULTS

[(18)F]FECh uptake in all BCXs was similar to surrounding normal tissue, thus creating no image contrast. The average liver uptake was 10 times higher than the tumor uptake. The uptake in MAS98.12 was higher than in the other two BCXs during the whole course of the acquisition, and was significantly higher than in HBCx34 at 10-30 minutes after injection. No significant differences were found for k1, MR[(18)F]FECh and intravascular fraction vb. Patlak slope KP, k₂ and k₃ were significantly lower for the MAS98.12 xenograft, in line with in vitro results. KP was correlated with both MR[(18)F]FECh and k₃.

CONCLUSIONS

dPET demonstrated that different subtypes of breast cancer have different uptake of [(18)F]FECh. Differences in rate constants and KP were in line with in vitro uptake in cell suspensions and earlier spectroscopy and gene expression analysis.