Monitoring therapeutic efficacy of sunitinib using [(18)F]FDG and [(18)F]FMISO PET in an immunocompetent model of luminal B (HER2-positive)-type mammary carcinoma

Obesity is a risk factor for intrahepatic cholangiocarcinoma progression associated with alterations of metabolic activity and immune status

Body mass index (BMI) is well known to be associated with poor prognosis in several cancers. The relationship between BMI and the long-term outcomes of patients with intrahepatic cholangiocarcinoma (ICC) is incompletely understood. This study investigated the relationships of BMI with clinicopathological characteristics and patient outcomes, focusing on metabolic activity and immune status. The relationship between BMI and the maximum standardized uptake value (SUVmax) on fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) was analyzed. In addition, immunohistochemistry was performed for programmed cell death-ligand 1 (PD-L1), cluster of differentiation 8 (CD8), and forkhead box protein P3 (Foxp3). Seventy-four patients with ICC were classified into normal weight (BMI < 25.0 kg/m², n = 48) and obesity groups (BMI ≥ 25.0 kg/m², n = 26), respectively. Serum carbohydrate antigen 19–9 levels were higher in the obesity group than in the normal weight group. Tumor size and the intrahepatic metastasis rate were significantly larger in the obesity group. Patients in the obesity group had significantly worse prognoses than those in the normal weight group. Moreover, BMI displayed a positive correlation with SUVmax on ¹⁸F-FDG PET/CT (n = 46, r = 0.5152). Patients with high ¹⁸F-FDG uptake had a significantly higher rate of PD-L1 expression, lower CD8 + tumor-infiltrating lymphocyte (TIL) counts, and higher Foxp3 + TIL counts. The elevated BMI might predict the outcomes of patients with ICC. Obesity might be associated with ICC progression, possibly through alterations in metabolic activity and the immune status.

A preclinical PET dual-tracer imaging protocol for ER and HER2 phenotyping in breast cancer xenografts

BACKGROUND

Nuclear medicine is on the constant search of precision radiopharmaceutical approaches to improve patient management. Although discordant expression of the estrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER2) in breast cancer is a known dilemma for appropriate patient management, traditional tumor sampling is often difficult or impractical. While 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG)-positron emission tomography (PET) is an option to detect subclinical metastases, it does not provide phenotype information. Radiolabeled antibodies are able to specifically target expressed cell surface receptors. However, their long circulating half-lives (days) require labeling with long-lived isotopes, such as 89Zr, in order to allow sufficient time for tracer clearance from the blood compartment and to accumulate adequately in target tumors and, thus, generate high-quality PET images. The aim of this study was to develop a dual-tracer PET imaging approach consisting of a fast-clearing small molecule and a slow-clearing antibody. This approach was evaluated in a model consisting of mice harboring separate breast cancer xenografts with either an ER+/HER2- or ER-/HER2+ phenotype, comparable to human metastatic disease with intertumor heterogeneity. Lastly, the aim of our study was to determine the feasibility of specifically identifying these two important phenotypes in an acceptable time window.

METHODS

Female nude mice were subcutaneously implanted on opposite shoulders with the ER+/HER2- and ER-/HER2+ MCF-7 and JIMT-1 tumor cell lines, respectively. A second model was developed consisting of mice implanted orthotopically with either MCF-7 or JIMT-1 cells. Pharmacokinetic analysis, serial PET imaging, and biodistribution were first performed for [89Zr]Zr-DFO-trastuzumab (89Zr-T) up to 8 days post-injection (p.i.) in JIMT-1 bearing mice. Region-of-interest (ROI) and biodistribution-derived uptake (% injected-activity/gram of tissue [%IA/g]) values and tumor-to-background ratios were obtained. Results were compared in order to validate ROI and identify early time points that provided high contrast tumor images. For the dual-tracer approach, cohorts of tumor-bearing mice were then subjected to sequential tracer PET imaging. On day 1, mice were administered 4-fluoro-11β-methoxy-16α-[18F]-fluoroestradiol (4FMFES) which targets ER and imaged 45 min p.i. This was immediately followed by the injection of 89Zr-T. Mice were then imaged on day 3 or day 7. ROI analysis was performed, and uptake was calculated in tumors and selected healthy organs for all radiotracers. Quality of tumor targeting for all tracers was evaluated by tumor contrast visualization, tumor and normal tissue uptake, and tumor-to-background ratios.

RESULTS

89Zr-T provided sufficiently high tumor and low background uptake values that furnished high contrast tumor images by 48 h p.i. For the dual-tracer approach, 4FMFES provided tumor uptake values that were significantly increased in MCF-7 tumors. When 89Zr-T-PET was combined with 18F-4FMFES-PET, the entire dual-tracer sequential-imaging procedure provided specific high-quality contrast images of ER+/HER2- MCF-7 and ER-/HER2+ JIMT-1 tumors for 4FMFES and 89Zr-T, respectively, as short as 72 h from start to finish.

CONCLUSIONS

This protocol can provide high contrast images of tumors expressing ER or HER2 within 3 days from injection of 4FMFES to final scan of 89Zr-T and, hence, provides a basis for future dual-tracer combinations that include antibodies.

Sodium bicarbonate nanoparticles modulate the tumor pH and enhance the cellular uptake of doxorubicin

Acidic pH in the tumor microenvironment is associated with cancer metabolism and creates a physiological barrier that prevents from drugs to penetrate cells. Specifically, ionizable weak-base drugs, such as doxorubicin, freely permeate membranes in their uncharged form, however, in the acidic tumor microenvironment these drugs become charged and their cellular permeability is retarded. In this study, 100-nm liposomes loaded with sodium bicarbonate were used as adjuvants to elevate the tumor pH. Combined treatment of triple-negative breast cancer cells (4T1) with doxorubicin and sodium-bicarbonate enhanced drug uptake and increased its anti-cancer activity. In vivo, mice bearing orthotropic 4T1 breast cancer tumors were administered either liposomal or free bicarbonate intravenously. 3.7 ± 0.3% of the injected liposomal dose was detected in the tumor after twenty-four hours, compared to 0.17% ± 0.04% in the group injected free non-liposomal bicarbonate, a 21-fold increase. Analyzing nanoparticle biodistribution within the tumor tissue revealed that 93% of the PEGylated liposomes accumulated in the extracellular matrix, while 7% were detected intracellularly. Mice administered bicarbonate-loaded liposomes reached an intra-tumor pH value of 7.38 ± 0.04. Treating tumors with liposomal bicarbonate combined with a sub-therapeutic dose of doxorubicin achieved an improved therapeutic outcome, compared to mice treated with doxorubicin or bicarbonate alone. Interestingly, analysis of the tumor microenvironment demonstrated an increase in immune cell' population (T-cell, B-cell and macrophages) in tumors treated with liposomal bicarbonate. This study demonstrates that targeting metabolic adjuvants with nanoparticles to the tumor microenvironment can enhance anticancer drug activity and improve treatment.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

Targeting of the breast cancer microenvironment with a potent and linkable oxindole based antiangiogenic small molecule

The clinical efficacy of antiangiogenic small molecules (e.g., sunitinib) in breast carcinoma has largely failed with substantial off-target toxicity. We rationally designed and evaluated preclinically a novel sunitinib analogue, SAP, with favourable pharmacological properties and the ability to be readily conjugated to a targeting peptide or antibody for active tumour targeting.

SAP was evaluated in silico and in vitro in order to verify target engagement (e.g., VEGFR2). Pharmacokinetic and biodistribution parameters were determined in mice using LC-MS/MS. SAP efficacy was tested in two breast cancer xenograft and two syngeneic animal models and pharmacodynamic evaluation was accomplished using phosphokinase assays and immunohistochemistry. Cardiac and blood toxicity of SAP were also monitored.

SAP retained the antiangiogenic and cytotoxic properties of the parental molecule with an increased blood exposure and tumor accumulation compared to sunitinib. SAP proved efficacious in all animal models. Tumors from SAP treated animals had significantly decreased Ki-67 and CD31 markers and reduced levels of phosphorylated AKT, ERK and S6 compared to vehicle treated animals. In mice dosed with SAP there was negligible hematotoxicity, while cardiac function measurements showed a reduction in the percentage left ventricular fractional shortening compared to vehicle treated animals.

In conclusion, SAP is a novel rationally designed conjugatable small antiangiogenic molecule, efficacious in preclinical models of breast cancer.

Quantitative [18F]FMISO PET Imaging Shows Reduction of Hypoxia Following Trastuzumab in a Murine Model of HER2+ Breast Cancer

PURPOSE

Evaluation of [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO)-positron emission tomography (PET) imaging as a metric for evaluating early response to trastuzumab therapy with histological validation in a murine model of HER2+ breast cancer.

PROCEDURES

Mice with BT474, HER2+ tumors, were imaged with [¹⁸F]FMISO-PET during trastuzumab therapy. Pimonidazole staining was used to confirm hypoxia from imaging.

RESULTS

[¹⁸F]FMISO-PET indicated significant decreases in hypoxia beginning on day 3 (P < 0.01) prior to changes in tumor size. These results were confirmed with pimonidazole staining on day 7 (P < 0.01); additionally, there was a significant positive linear correlation between histology and PET imaging (r ²  = 0.85).

CONCLUSIONS

[¹⁸F]FMISO-PET is a clinically relevant modality which provides the opportunity to (1) predict response to HER2+ therapy before changes in tumor size and (2) identify decreases in hypoxia which has the potential to guide subsequent therapy.

18F-Fluoromisonidazole Kinetic Modeling for Characterization of Tumor Perfusion and Hypoxia in Response to Antiangiogenic Therapy

Multiparametric imaging of tumor perfusion and hypoxia with dynamic ¹⁸F-fluoromisonidazole (¹⁸F-FMISO) PET may allow for an improved response assessment to antiangiogenic therapies. Cediranib (AZD2171) is a potent inhibitor of tyrosine kinase activity associated with vascular endothelial growth factor receptors 1, 2, and 3, currently in phase II/III clinical trials. Serial dynamic ¹⁸F-FMISO PET was performed to investigate changes in tumor biomarkers of perfusion and hypoxia after cediranib treatment. Methods: Twenty-one rats bearing HT29 colorectal xenograft tumors were randomized into a vehicle-treated control group (0.5% methylcellulose daily for 2 d [5 rats] or 7 d [4 rats]) and a cediranib-treated test group (3 mg/kg daily for 2 or 7 d; 6 rats in both groups). All rats were imaged before and after treatment, using a 90-min dynamic PET acquisition after administration of 42.1 ± 3.9 MBq of ¹⁸F-FMISO by tail vein injection. Tumor volumes were delineated manually, and the input function was image-derived (abdominal aorta). Kinetic modeling was performed using an irreversible 1-plasma 2-tissue compartmental model to estimate the kinetic rate constants K₁, K₁/k₂, and k₃-surrogates for perfusion, ¹⁸F-FMISO distribution volume, and hypoxia-mediated entrapment, respectively. Tumor-to-blood ratios (TBRs) were calculated on the last dynamic frame (80-90 min). Tumors were assessed ex vivo by digital autoradiography and immunofluorescence for microscopic visualization of perfusion (pimonidazole) and hypoxia (Hoechst 33342). Results: Cediranib treatment resulted in significant reduction of mean voxelwise ¹⁸F-FMISO TBR, K₁, and K₁/k₂ in both the 2-d and the 7-d groups (P < 0.05). The k₃ parameter was increased in both groups but reached significance only in the 2-d group. In the vehicle-treated groups, no significant change in TBR, K₁, K₁/k₂, or k₃ was observed (P > 0.2). Ex vivo tumor analysis confirmed the presence of hypoxic tumor regions that nevertheless exhibited relatively lower ¹⁸F-FMISO uptake. Conclusion:¹⁸F-FMISO kinetic modeling reveals a more detailed response to antiangiogenic treatment than a single static image is able to reveal. The reduced mean K₁ reflects a reduction in tumor vascular perfusion, whereas the increased k₃ reflects a rise in hypoxia-mediated entrapment of the radiotracer. However, if only late static images are analyzed, the observed reduction in ¹⁸F-FMISO uptake after treatment with cediranib may be mistakenly interpreted as a global decrease, rather than an increase, in tumor hypoxia. These findings support the use of ¹⁸F-FMISO kinetic modeling to more accurately characterize the response to treatments that have a direct effect on tumor vascularization and perfusion.

A Comparative Approach of Tumor-Associated Inflammation in Mammary Cancer between Humans and Dogs

Infiltrating cells of the immune system are widely accepted to be generic constituents of tumor microenvironment. It has been well established that the development of mammary cancer, both in humans and in dogs, is associated with alterations in numbers and functions of immune cells at the sites of tumor progression. These tumor infiltrating immune cells seem to exhibit exclusive phenotypic and functional characteristics and mammary cancer cells can take advantage of signaling molecules released by them. Cancer related inflammation has an important role in mammary carcinogenesis, contributing to the acquisition of core hallmark capabilities that allow cancer cells to survive, proliferate, and disseminate. Indeed, recent studies in human breast cancer and in canine mammary tumors have identified a growing list of signaling molecules released by inflammatory cells that serve as effectors of their tumor-promoting actions. These include the COX-2, the tumor EGF, the angiogenic VEGF, other proangiogenic factors, and a large variety of chemokines and cytokines that amplify the inflammatory state. This review describes the intertwined signaling pathways shared by T-lymphocytic/macrophage infiltrates and important tissue biomarkers in both human and dog mammary carcinogenesis.