Molecular imaging of prostate cancer with PET

Zirconium-containing nanoscale coordination polymers for positron emission tomography and fluorescence-guided cargo delivery to triple-negative breast tumors

Nanoscale coordination polymer (NCP) is a class of hybrid materials formed by self-assembly of metal ions and organic ligands through coordination. The applications of NCP in biomedicine are quite extensive due to the diversity choice of metal ions and organic ligands. Here we designed Zr-P1 NCP based on Zr4+ selected as metal ion nodes and tetrakis(4-carboxyphenyl) ethylene as bridging ligands. Zr-P1 NCP was modified with functionalized pyrene derived polyethylene glycol (Py-PAA-PEG-Mal) on the surface and further conjugated with cRGD for active targeting of integrin αvβ3 overexpressed in triple-negative breast cancer. Doxorubicin was loaded on Zr-P1 NCP with encapsulation efficiency up to 22 % for the treatment of triple negative breast cancer. 89Zr-P1 NCP can be used for in vivo tumor imaging due to the fluorescence properties resulting from the enhanced aggregation-induced Emission (AIE) behavior of P1 ligands and its positron emission tomography (PET) capability. Cellular evaluation indicated that the functionalized Zr-P1@PEG-RGD presented a good function for tumor cell targeting imaging and doxorubicin could be targeted to triple negative breast cancer when it was loaded onto Zr-P1@PEG-RGD, which corroborated with the in vivo results. In summary, 89Zr-P1@PEG-RGD can serve as a biocompatible nanoplatform for fluorescence and PET image-guided cargo delivery. STATEMENT OF SIGNIFICANCE: Nanoscale coordination polymer (NCP) is a class of hybrid materials formed by self-assembly of metal ions and organic ligands through coordination. The diversity of available metals and ligand structures upon NCP synthesis plays an advantage in establishing multimodal imaging platforms. Here we designed 89Zr-P1@PEG-RGD NCP based on Zr4+ selected as metal ion nodes and tetrakis(4-carboxyphenyl) ethylene as bridging ligands. 89Zr-P1@PEG-RGD nanomaterials have positron emission tomography (PET) capability due to the incorporation of zirconium-89, which can be used for in vivo tumor imaging with high sensitivity. The chemotherapeutic drug DOX was loaded on Zr-P1 NCP for the treatment of triple-negative breast cancer, and dual modality imaging can provide visual guidance for drug delivery.

Examining the Relationship and Prognostic Significance of Cell-Free DNA Levels and the PSMA-Positive Tumor Volume in Men with Prostate Cancer: A Retrospective-Prospective [68Ga]Ga-PSMA-11 PET/CT Study

Functional imaging with prostate-specific membrane antigen (PSMA) ligands has emerged as the standard imaging method for prostate cancer (PCA). In parallel, the analysis of blood-derived, cell-free DNA (cfDNA) has been shown to be a promising quantitative biomarker of PCA aggressiveness and patient outcome. This study aimed to evaluate the relationship and prognostic value of cfDNA concentrations and the PSMA-positive tumor volume (PSMA-TV) in men with PCA undergoing [68Ga]Ga-PSMA-11 PET/CT imaging. Methods: We recruited 148 men with histologically proven PCA (mean age, 70.7 ± 7.7 y) who underwent [68Ga]Ga-PSMA-11 PET/CT (184.9 ± 18.9 MBq) and blood sampling between March 2019 and August 2021. Among these, 74 (50.0%) had hormone-sensitive PCA and 74 (50.0%) had castration-resistant PCA (CRPC). All patients provided written informed consent before blood sample collection and imaging. The cfDNA was extracted and quantified, and PSMA-expressing tumor lesions were delineated to extract the PSMA-TVs. The Spearman coefficient assessed correlations between PSMA-TV and cfDNA concentrations and cfDNA's relation with clinical parameters. The Kruskal-Wallis test examined the mean cfDNA concentration differences based on PSMA-TV quartiles for significantly correlated patient groups. Log-rank and multivariate Cox regression analyses evaluated the prognostic significance of high and low cfDNA and PSMA-TV levels for overall survival. Results: Weak positive correlations were found between cfDNA concentration and PSMA-TV in the overall group (r = 0.16, P = 0.049) and the CRPC group (r = 0.31, P = 0.007) but not in hormone-sensitive PCA patients (r = -0.024, P = 0.837). In the CRPC cohort, cfDNA concentrations significantly differed between PSMA-TV quartiles 4 and 1 (P = 0.002) and between quartiles 4 and 2 (P = 0.016). Survival outcomes were associated with PSMA-TV (P < 0.0001, P = 0.004) but not cfDNA (P = 0.174, P = 0.12), as per the log-rank and Cox regression analysis. Conclusion: These findings suggest that cfDNA might serve as a biomarker of advanced, aggressive CRPC but does not reliably reflect total tumor burden or prognosis. In comparison, [68Ga]Ga-PSMA-11 PET/CT provides a highly granular and prognostic assessment of tumor burden across the spectrum of PCA disease progression.

Functional Diversity in Radiolabeled Nanoceramics and Related Biomaterials for the Multimodal Imaging of Tumors

Nanotechnology advances have the potential to assist toward the earlier detection of diseases, giving increased accuracy for diagnosis and helping to personalize treatments, especially in the case of noncommunicative diseases (NCDs) such as cancer. The main advantage of nanoparticles, the scaffolds underpinning nanomedicine, is their potential to present multifunctionality: synthetic nanoplatforms for nanomedicines can be tailored to support a range of biomedical imaging modalities of relevance for clinical practice, such as, for example, optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). A single nanoparticle has the potential to incorporate myriads of contrast agent units or imaging tracers, encapsulate, and/or be conjugated to different combinations of imaging tags, thus providing the means for multimodality diagnostic methods. These arrangements have been shown to provide significant improvements to the signal-to-noise ratios that may be obtained by molecular imaging techniques, for example, in PET diagnostic imaging with nanomaterials versus the cases when molecular species are involved as radiotracers. We surveyed some of the main discoveries in the simultaneous incorporation of nanoparticulate materials and imaging agents within highly kinetically stable radio-nanomaterials as potential tracers with (pre)clinical potential. Diversity in function and new developments toward synthesis, radiolabeling, and microscopy investigations are explored, and preclinical applications in molecular imaging are highlighted. The emphasis is on the biocompatible materials at the forefront of the main preclinical developments, e.g., nanoceramics and liposome-based constructs, which have driven the evolution of diagnostic radio-nanomedicines over the past decade.

Nano-Theranostics for the Sensing, Imaging and Therapy of Prostate Cancers

We highlight hereby recent developments in the emerging field of theranostics, which encompasses the combination of therapeutics and diagnostics in a single entity aimed for an early-stage diagnosis, image-guided therapy as well as evaluation of therapeutic outcomes of relevance to prostate cancer (PCa). Prostate cancer is one of the most common malignancies in men and a frequent cause of male cancer death. As such, this overview is concerned with recent developments in imaging and sensing of relevance to prostate cancer diagnosis and therapeutic monitoring. A major advantage for the effective treatment of PCa is an early diagnosis that would provide information for an appropriate treatment. Several imaging techniques are being developed to diagnose and monitor different stages of cancer in general, and patient stratification is particularly relevant for PCa. Hybrid imaging techniques applicable for diagnosis combine complementary structural and morphological information to enhance resolution and sensitivity of imaging. The focus of this review is to sum up some of the most recent advances in the nanotechnological approaches to the sensing and treatment of prostate cancer (PCa). Targeted imaging using nanoparticles, radiotracers and biomarkers could result to a more specialised and personalised diagnosis and treatment of PCa. A myriad of reports has been published literature proposing methods to detect and treat PCa using nanoparticles but the number of techniques approved for clinical use is relatively small. Another facet of this report is on reviewing aspects of the role of functional nanoparticles in multimodality imaging therapy considering recent developments in simultaneous PET-MRI (Positron Emission Tomography-Magnetic Resonance Imaging) coupled with optical imaging in vitro and in vivo, whilst highlighting feasible case studies that hold promise for the next generation of dual modality medical imaging of PCa. It is envisaged that progress in the field of imaging and sensing domains, taken together, could benefit from the biomedical implementation of new synthetic platforms such as metal complexes and functional materials supported on organic molecular species, which can be conjugated to targeting biomolecules and encompass adaptable and versatile molecular architectures. Furthermore, we include hereby an overview of aspects of biosensing methods aimed to tackle PCa: prostate biomarkers such as Prostate Specific Antigen (PSA) have been incorporated into synthetic platforms and explored in the context of sensing and imaging applications in preclinical investigations for the early detection of PCa. Finally, some of the societal concerns around nanotechnology being used for the detection of PCa are considered and addressed together with the concerns about the toxicity of nanoparticles–these were aspects of recent lively debates that currently hamper the clinical advancements of nano-theranostics. The publications survey conducted for this review includes, to the best of our knowledge, some of the most recent relevant literature examples from the state-of-the-art. Highlighting these advances would be of interest to the biomedical research community aiming to advance the application of theranostics particularly in PCa diagnosis and treatment, but also to those interested in the development of new probes and methodologies for the simultaneous imaging and therapy monitoring employed for PCa targeting.

Propionic Acid-Based PET Imaging of Prostate Cancer

PURPOSE

This study aimed to evaluate the potential value of 2-[18F]fluoropropionic acid ([18F]FPA) for PET imaging of prostate cancer (PCa) and to explore the relationship between [18F]FPA accumulation and fatty acid synthase (FASN) levels in PCa models. The results of the first [18F]FPA PET study of a PCa patient are reported.

PROCEDURES

The LNCaP, PC-3 cell lines with high FASN expression, and DU145 cell lines with low FASN expression were selected for cell culture. A PET imaging comparison of [18F]FDG and [18F]FPA was performed in LNCaP, PC-3, and DU145 tumors. Additionally, in vivo inhibition experiments in those models were conducted with orlistat. In a human PET study, a patient with PCa before surgery was examined with [18F]FPA PET and [18F]FDG PET.

RESULTS

The uptake of [18F]FPA in the LNCaP and PC-3 tumors was higher than that of [18F]FDG (P<0.05 and P<0.05), but was lower in DU145 tumors (P<0.05). The accumulation (% ID/g) of [18F]FPA in the LNCaP, PC-3, and DU145 tumors decreased by 27.6, 40.5, and 11.7 %, respectively, after treatment with orlistat. The [18F]FPA showed higher radioactive uptake than [18F]FDG in the first PCa patient.

CONCLUSIONS

The [18F]FPA uptake in PCa models may be varies with fatty acid synthase activity and could be reduced after administration of a single FASN inhibitor, albeit the activity that is not measured directly. The [18F]FPA seems to be a potential broad-spectrum PET imaging agent and may serve as a valuable tool in the diagnosis of PCa in humans.

Reaction of [18F]Fluoride at Heteroatoms and Metals for Imaging of Peptides and Proteins by Positron Emission Tomography

The ability to radiolabel proteins with [18F]fluoride enables the use of positron emission tomography (PET) for the early detection, staging and diagnosis of disease. The direct fluorination of native proteins through C-F bond formation is, however, a difficult task. The aqueous environments required by proteins severely hampers fluorination yields while the dry, organic solvents that promote nucleophilic fluorination can denature proteins. To circumvent these issues, indirect fluorination methods making use of prosthetic groups that are first fluorinated and then conjugated to a protein have become commonplace. But, when it comes to the radiofluorination of proteins, these indirect methods are not always suited to the short half-life of the fluorine-18 radionuclide (110 min). This review explores radiofluorination through bond formation with fluoride at boron, metal complexes, silicon, phosphorus and sulfur. The potential for these techniques to be used for the direct, aqueous radiolabeling of proteins with [18F]fluoride is discussed.

A retrospective study assessing the accuracy of [18F]-fluorocholine PET/CT for primary staging of lymph node metastases in intermediate and high-risk prostate cancer patients undergoing robotic-assisted laparoscopic prostatectomy with extended lymph node dissection

BACKGROUND

Previous studies have investigated [18F]-fluorocholine (FCH) positron emission tomography with computed tomography (PET/CT) in primary staging of men with intermediate or high-risk prostate cancer and have generally shown high specificity and poor sensitivity. FCH PET/CT is not recommended for the primary staging of metastases in the European guidelines for prostate cancer. However, it has been an option in the Swedish recommendations. Our aim was to assess PET/CT for primary staging of lymph node metastases before robotic-assisted laparoscopic prostatectomy (RALP) with extended pelvic lymph node dissection (ePLND) in patients with intermediate or high-risk prostate cancer.

METHOD

We identified all men with prostate cancer undergoing FCH PET/CT for initial staging followed by RALP and ePLND at Skåne University Hospital between 2015 and 2018. The result from PET/CT scan was compared with pathology report as the reference method for calculation of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).

RESULTS

In total, 252 patients were included in the final analysis. Among 85 patients with a suspicion of regional lymph node metastases on FCH PET/CT only 31 had pathology-proven metastases. The sensitivity was 43% (95% CI 0.32-0.55) and the specificity 70% (95% CI 0.63-0.76) for PET/CT to predict lymph node metastases. PPV was 36% and NPV was 75%. Risk group analyses showed similar results.

CONCLUSION

Our study emphasizes the poor performance of FCH PET/CT to predict lymph node metastasis in intermediate and high-risk prostate cancer. The method should be replaced with newer radiopharmaceuticals, such as prostate-specific membrane antigen ligands.

Clinical Evaluation of (4S)-4-(3-[18F]Fluoropropyl)-L-glutamate (18F-FSPG) for PET/CT Imaging in Patients with Newly Diagnosed and Recurrent Prostate Cancer

PURPOSE

(4S)-4-(3-[¹⁸F]Fluoropropyl)-L-glutamic acid (¹⁸F-FSPG) is a radiopharmaceutical for PET imaging of system x_C ^- activity, which can be upregulated in prostate cancer. We present data on the first evaluation of patients with newly diagnosed or recurrent prostate cancer with this radiopharmaceutical.

EXPERIMENTAL DESIGN

Ten patients with primary and 10 patients with recurrent prostate cancer were enrolled in this prospective multicenter study. After injection of 300 MBq of ¹⁸F-FSPG, three whole-body PET/CT scans were obtained. Visual analysis was compared with step-section histopathology when available as well as other imaging studies and clinical outcomes. Metabolic parameters were measured semiquantitatively. Expression levels of xCT and CD44 were evaluated by IHC for patients with available tissue samples.

RESULTS

¹⁸F-FSPG PET showed high tumor-to-background ratios with a relatively high tumor detection rate on a per-patient (89%) and per-lobe (87%) basis. The sensitivity was slightly higher with imaging at 105 minutes in comparison with 60 minutes. The maximum standardized uptake values (SUV_max) for cancer was significantly higher than both normal (P < 0.005) and benign pathology (P = 0.011), while there was no significant difference between normal and benign pathology (P = 0.120). In the setting of recurrence, agreement with standard imaging was demonstrated in 7 of 9 patients (78%) and 13 of 18 lesions (72%), and revealed true local recurrence in a discordant case. ¹⁸F-FSPG accumulation showed moderate correlation with CD44 expression.

CONCLUSIONS

¹⁸F-FSPG is a promising tumor imaging agent for PET that seems to have favorable biodistribution and high cancer detection rate in patients with prostate cancer. Further studies are warranted to determine the diagnostic value for both initial staging and recurrence, and how it compares with other investigational radiotracers and conventional imaging modalities.

Imaging Biochemical Recurrence After Prostatectomy: Where Are We Headed?

OBJECTIVE. In this article, we discuss the evolving roles of imaging modalities in patients presenting with biochemical recurrence after prostatectomy. CONCLUSION. Multiple imaging modalities are currently available to evaluate patients with prostate cancer presenting with biochemical recurrence after prostatectomy. Multiparametric MRI (mpMRI) focuses on the postsurgical bed as well as regional lymph nodes and bones. PET/CT studies using ¹⁸F-fluciclovine, ¹¹C-choline, and prostate-specific membrane antigen (PSMA) ligands are useful in detecting locoregional and distant metastasis. Multiparametric MRI is preferred for patients with low risk of metastasis for localizing recurrence in prostate bed as well as pelvic lymph node and bone recurrence. Moreover, mpMRI aids in guiding biopsy and additional salvage treatments. For patients with high risk of metastatic disease, both mpMRI and whole-body PET/CT may be performed. PET/MRI using ⁶⁸Ga-PSMA has potential to enable a one-stop shop for local recurrence and metastatic disease evaluation, and clinical trials of PET/MRI are ongoing.

Prostate Cancer Recurrence in Kidney Transplant Recipient 15 Years After Radical Prostatectomy: A Case Report

Incidence of malignant tumors in kidney transplant recipients is higher than nontransplanted population due to many factors, such as immunosuppression therapy and complex donor-recipient interaction. Genitourinary malignancies have been reported as the second most common malignancy in kidney transplant recipients. In this regard, prostate cancer is the most common neoplasm. Herein, we describe a rare case of prostate cancer recurrence after 15 years in a patient who underwent kidney transplant after radical prostatectomy.

Preclinical evaluation of a 64Cu-labeled disintegrin for PET imaging of prostate cancer

A novel recombinant disintegrin, vicrostatin (VCN), displays high binding affinity to a broad range of human integrins in substantial competitive biological advantage over other integrin-based antagonists. In this study, we synthesized a new ⁶⁴Cu-labeled VCN probe and evaluated its imaging properties for prostate cancer in PC-3 tumor-bearing mice. Macrocyclic chelating agent 1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-eicosine (DiAmSar) was conjugated with PEG unit and followed by coupling with VCN. The precursor was then radiolabeled with positron emitter ⁶⁴Cu (t_1/2 = 12.7 h) in ammonium acetate buffer to provide ⁶⁴Cu-Sar-PEG-VCN, which was subsequently subjected to in vitro studies, small animal PET, and biodistribution studies. The PC-3 tumor-targeting efficacy of ⁶⁴Cu-Sar-PEG-VCN was compared to a cyclic RGD peptide-based PET probe (⁶⁴Cu-Sar-RGD). ⁶⁴Cu labeling was achieved in 75% decay-corrected yield with radiochemical purity of  > 98%. The specific activity of ⁶⁴Cu-Sar-PEG-VCN was estimated to be 37 MBq/nmol. MicroPET imaging results showed that ⁶⁴Cu-Sar-PEG-VCN has preferential tumor uptake and good tumor retention in PC-3 tumor xenografts. As compared to ⁶⁴Cu-Sar-RGD, ⁶⁴Cu-Sar-PEG-VCN produces higher tumor-to-muscle (T/M) imaging contrast ratios at 2 h (4.66 ± 0.34 vs. 2.88 ± 0.46) and 24 h (4.98 ± 0.80 vs. 3.22 ± 0.30) post-injection (pi) and similar tumor-to-liver ratios at 2 h (0.43 ± 0.09 vs. 0.37 ± 0.04) and 24 h (0.57 ± 0.13 vs. 0.52 ± 0.07) pi. The biodistribution results were consistent with the quantitative analysis of microPET imaging, demonstrating good T/M ratio (2.73 ± 0.36) of ⁶⁴Cu-Sar-PEG-VCN at 48 h pi in PC-3 tumor xenografts. For both microPET and biodistribution studies at 48 h pi, the PC-3 tumor uptake of ⁶⁴Cu-Sar-PEG-VCN is lower than that of ⁶⁴Cu-Sar-RGD. ⁶⁴Cu-Sar-PEG-VCN has the potential for in vivo imaging of prostate cancer with PET, which may provide a unique non-invasive method to quantitatively localize and characterize prostate cancer.

The Utility of [18F]DASA-23 for Molecular Imaging of Prostate Cancer with Positron Emission Tomography

PURPOSE

There is a strong, unmet need for superior positron emission tomography (PET) imaging agents that are able to measure biochemical processes specific to prostate cancer. Pyruvate kinase M2 (PKM2) catalyzes the concluding step in glycolysis and is a key regulator of tumor growth and metabolism. Elevation of PKM2 expression was detected in Gleason 8-10 tumors compared to Gleason 6-7 carcinomas, indicating that PKM2 may potentially be a marker of aggressive prostate cancer. We have recently reported the development of a PKM2-specific radiopharmaceutical [18F]DASA-23 and herein describe its evaluation in cell culture and preclinical models of prostate cancer.

PROCEDURE

The cellular uptake of [18F]DASA-23 was evaluated in a panel of prostate cancer cell lines and compared to that of [18F]FDG. The specificity of [18F]DASA-23 to measure PKM2 levels in cell culture was additionally confirmed through the use of PKM2-specific siRNA. PET imaging studies were then completed utilizing subcutaneous prostate cancer xenografts using either PC3 or DU145 cells in mice.

RESULTS

[18F]DASA-23 uptake values over 60-min incubation period in PC3, LnCAP, and DU145 respectively were 23.4 ± 4.5, 18.0 ± 2.1, and 53.1 ± 4.6 % tracer/mg protein. Transient reduction in PKM2 protein expression with siRNA resulted in a 50.1 % reduction in radiotracer uptake in DU145 cells. Small animal PET imaging revealed 0.86 ± 0.13 and 1.6 ± 0.2 % ID/g at 30 min post injection of radioactivity in DU145 and PC3 subcutaneous tumor bearing mice respectively.

CONCLUSION

Herein, we evaluated a F-18-labeled PKM2-specific radiotracer, [18F]DASA-23, for the molecular imaging of prostate cancer with PET. [18F]DASA-23 revealed rapid and extensive uptake levels in cellular uptake studies of prostate cancer cells; however, there was only modest tumor uptake when evaluated in mouse subcutaneous tumor models.

Pitfalls in Gallium-68 PSMA PET/CT Interpretation-A Pictorial Review

The novel Gallium-68 prostate-specific membrane antigen (PSMA)-bis [2-hydroxy-5-(carboxyethyl)benzyl] ethylenediamine-diacetic acid positron emission tomography (PET) tracer is increasingly used in the evaluation of prostate cancer, particularly in the detection of recurrent disease. However, PSMA is expressed in nonprostatic tissues, as well as in other pathologic conditions. Here we illustrate such interpretive pitfalls with relevant images that one may encounter while reporting PSMA PET/CT. This study aims to show variation in physiological distribution of PSMA activity and uptake in various benign and neoplastic disorders that may be misinterpreted as prostatic metastatic disease. These pitfalls are illustrated to enhance awareness, aiding a more accurate interpretation of the study. Retrospective database of all (68)Ga PSMA PET/CT was created and reviewed. In total, 1115 PSMA PET/CT studies performed between February 27, 2015, and May 31, 2017, were reviewed. Any unusual uptake of PSMA was documented, described, and followed up. All cases were then subdivided into the following 4 categories: physiological uptake, benign pathological uptake, nonprostatic neoplastic uptake, and miscellaneous uptake. A variety of nonprostatic tissues and lesions, including accessory salivary gland, celiac ganglion, gall bladder, Paget's bone disease, reactive lymph nodes, non–small cell lung cancer, renal cell cancer, and neuroendocrine tumor, were found to show PSMA uptake. PSMA uptake is not prostate-specific and can be taken up physiologically and pathologically in nonprostatic tissue. It is important for reporting physicians to recognize these findings and instigate appropriate investigations when required while avoiding unnecessary procedures in physiological variation.

Dual-Modality ImmunoPET/Fluorescence Imaging of Prostate Cancer with an Anti-PSCA Cys-Minibody

Inadequate diagnostic methods for prostate cancer lead to over- and undertreatment, and the inability to intraoperatively visualize positive margins may limit the success of surgical resection. Prostate cancer visualization could be improved by combining the complementary modalities of immuno-positron emission tomography (immunoPET) for preoperative disease detection, and fluorescence imaging-guided surgery (FIGS) for real-time intraoperative tumor margin identification. Here, we report on the evaluation of dual-labeled humanized anti-prostate stem cell antigen (PSCA) cys-minibody (A11 cMb) for immunoPET/fluorescence imaging in subcutaneous and orthotopic prostate cancer models.

Methods: A11 cMb was site-specifically conjugated with the near-infrared fluorophore Cy5.5 and radiolabeled with ¹²⁴I or ⁸⁹Zr. ¹²⁴I-A11 cMb-Cy5.5 was used for successive immunoPET/fluorescence imaging of prostate cancer xenografts expressing high or moderate levels of PSCA (22Rv1-PSCA and PC3-PSCA). ⁸⁹Zr-A11 cMb-Cy5.5 dual-modality imaging was evaluated in an orthotopic model. Ex vivo biodistribution at 24 h was used to confirm the uptake values, and tumors were visualized by post-mortem fluorescence imaging.

Results: A11 cMb-Cy5.5 retained low nanomolar affinity for PSCA-positive cells. Conjugation conditions were established (dye-to-protein ratio of 0.7:1) that did not affect the biodistribution, pharmacokinetics, or clearance of A11 cMb. ImmunoPET using dual-labeled ¹²⁴I-A11 cMb-Cy5.5 showed specific targeting to both 22Rv1-PSCA and PC3-PSCA s.c. xenografts in nude mice. Ex vivo biodistribution confirmed specific uptake to PSCA-expressing tumors with 22Rv1-PSCA:22Rv1 and PC3-PSCA:PC3 ratios of 13:1 and 5.6:1, respectively. Consistent with the immunoPET, fluorescence imaging showed a strong signal from both 22Rv1-PSCA and PC3-PSCA tumors compared with non-PSCA expressing tumors. In an orthotopic model, ⁸⁹Zr-A11 cMb-Cy5.5 immunoPET was able to detect intraprostatically implanted 22Rv1-PSCA cells. Importantly, fluorescence imaging clearly distinguished the prostate tumor from surrounding seminal vesicles.

Conclusion: Dual-labeled A11 cMb specifically visualized PSCA-positive tumor by successive immunoPET/fluorescence, which can potentially be translated for preoperative whole-body prostate cancer detection and intraoperative surgical guidance in patients.

Metabolic Volumetric Parameters in 11C-Choline PET/MR Are Superior PET Imaging Biomarkers for Primary High-Risk Prostate Cancer

Purpose

Positron emission tomography/magnetic resonance imaging (PET/MRI) can facilitate the use of noninvasive imaging biomarkers in clinical prostate cancer staging. Although multiparametric MRI is a widely used technique, the clinical value of simultaneous PET imaging remains unclear. This study aimed at investigating this issue.

Methods

Between January 2015 and December 2016, 31 high-risk prostate cancer patients underwent ¹¹C-choline PET/MRI for staging purposes. Clinical characteristics and imaging parameters, including the standardized uptake value (SUV) and metabolic volumetric parameters from PET imaging; apparent diffusion coefficient (ADC) values from diffusion-weighted imaging; and volume transfer rate constant (Ktrans), reflux rate constant (Kep), and initial area under curve (iAUC) in 60 seconds from dynamic contrast-enhanced (DCE) MRI were analyzed.

Results

¹¹C-Choline PET imaging parameters were significantly correlated with prostate-specific antigen (PSA) levels, and metabolic volumetric parameters, including metabolic tumor volume (MTV) and uptake volume product (UVP), showed significant correlations with other MRI parameters. In our cohort analysis, the PET/MRI parameters UVP/minimal ADC value (ADC_min) and kurtosis of Kep (Kep_kur)/ADC_min were significant predictors for progression-free survival (PFS) (HR = 1.01, 95% CI: 1.00-1.02, p=0.031 and HR = 1.09, 95% CI: 1.02-1.16, p=0.009, respectively) in multivariate Cox regression analysis. High UVP/ADC_min and Kep_kur/ADC_min values were significantly associated with shorter PFS.

Conclusions

Metabolic volumetric parameters such as MTV and UVP can be routinely used as PET imaging biomarkers to add prognostic value and show better correlations in combination with MR imaging parameters in high-risk prostate cancer patients undergoing ¹¹C-choline PET/MRI.

PET imaging for assessing tumor response to therapy

Positron emission tomography (PET) is a radioisotope imaging technique capable of quantifying the regional distribution of molecular imaging probes targeted to biochemical pathways and processes allowing direct measurement of biochemical changes induced by cancer therapy, including the activity of targeted growth pathways and cellular populations. In this manuscript, we review the underlying principles of PET imaging, choices for PET radiopharmaceuticals, methods for tumor analysis and PET applications for cancer therapy response assessment including potential future directions.

One-year experience with 68Ga-PSMA PET/CT: applications and results in biochemical recurrence of prostate cancer

Objective

To show the initial (first-year) experience with ⁶⁸Ga-PSMA PET/CT at a clinic in Brazil.

Materials and Methods

Over a one-year period, 96 examinations with ⁶⁸Ga-PSMA PET/CT (85 related to prostate cancer and 11 related to kidney cancer) were performed in 90 patients.

Results

In the prostate and kidney cancer patients alike, the main clinical indication for ⁶⁸Ga-PSMA PET/CT was suspicion of recurrence during follow-up (in 65.8% and 63.0% of the cases, respectively). Among the prostate cancer patients, 38.5% of those with a prostate specific antigen (PSA) < 0.5 ng/mL tested positive for recurrence on ⁶⁸Ga-PSMA PET/CT, compared with 71.0% of those with a PSA of 0.5-0.99, 85.7% of those with a PSA of 1.0-1.99, and 92.6% of those with a PSA > 1.99.

Conclusion

Although ⁶⁸Ga-PSMA PET/CT is a technique that has only recently been applied in clinical settings, despite its high cost, ⁶⁸Ga-PSMA PET/CT shows great promise as a tool in the clinical management of patients with kidney and prostate cancer, especially in those with prostate cancer whose PSA levels are elevated even after treatment.

Construction and Evaluation of the Tumor-Targeting, Cell-Penetrating Multifunctional Molecular Probe iCREKA

A novel tumor stroma targeting and membrane-penetrating cyclic peptide, named iCREKA, was designed and labeled by fluorescein isothiocyanate (FITC) and positron emitter ¹⁸F to build the tumor-targeting tracers. The FITC-iCREKA was proved to have significantly higher cellular uptake in the glioma U87 cells in the presence of activated MMP-2 than that in absence of activated MMP-2 by cells fluorescence test in vitro. The tumor tissue fluorescence microscope imaging demonstrated that FITC-iCREKA accumulated in the walls of the blood vessels and the surrounding stroma in the glioma tumor at 1 h after intravenous injection. While at 3 h after injection, FITC-iCREKA was found to be uptaken in the tumor cells. However, the control FITC-CREKA can only be found in the tumor stroma, not in the tumor cells, no matter at 1 h or 3 h after injection. The whole-animal fluorescence imaging showed that the glioma tumor could be visualized clearly with high fluorescence signal. The microPET/CT imaging further demonstrated that 18F-iCREKA could target U87MG tumor in vivo from 30 min to 2 h after injection. The present study indicated the iCREKA had the capacity of tumor stroma targeting and the membrane-penetrating. It was potential to be developed as the fluorescent and PET tracers for tumor imaging.

Vertebral and femoral bone mineral density and bone strength in prostate cancer patients assessed in phantomless PET/CT examinations

PURPOSE

Bone fracture risk assessed ancillary to positron emission tomography with computed tomography co-registration (PET/CT) could provide substantial clinical value to oncology patients with elevated fracture risk without introducing additional radiation dose. The purpose of our study was to investigate the feasibility of obtaining valid measurements of bone mineral density (BMD) and finite element analysis-derived bone strength of the hip and spine using PET/CT examinations of prostate cancer patients by comparing against values obtained using routine multidetector-row computed tomography (MDCT) scans-as validated in previous studies-as a reference standard.

MATERIALS AND METHODS

Men with prostate cancer (n=82, 71.6±8.3 years) underwent Fluorine-18 NaF PET/CT and routine MDCT within three months. Femoral neck and total hip areal BMD, vertebral trabecular BMD and femur and vertebral strength based on finite element analysis were assessed in 63 paired PET/CT and MDCT examinations using phantomless calibration and Biomechanical-CT analysis. Men with osteoporosis or fragile bone strength identified at either the hip or spine (vertebral trabecular BMD ≤80mg/cm³, femoral neck or total hip T-score ≤-2.5, vertebral strength ≤6500N and femoral strength ≤3500N, respectively) were considered to be at high risk of fracture. PET/CT- versus MDCT-based BMD and strength measurements were compared using paired t-tests, linear regression and by generating Bland-Altman plots. Agreement in fracture-risk classification was assessed in a contingency table.

RESULTS

All measurements from PET/CT versus MDCT were strongly correlated (R²=0.93-0.97; P<0.0001 for all). Mean differences for total hip areal BMD (0.001g/cm², 1.1%), femoral strength (-60N, 1.3%), vertebral trabecular BMD (2mg/cm³, 2.6%) and vertebral strength (150N; 1.7%) measurements were not statistically significant (P>0.05 for all), whereas the mean difference in femoral neck areal BMD measurements was small but significant (-0.018g/cm²; -2.5%; P=0.007). The agreement between PET/CT and MDCT for fracture-risk classification was 97% (0.89 kappa for repeatability).

CONCLUSION

Ancillary analyses of BMD, bone strength, and fracture risk agreed well between PET/CT and MDCT, suggesting that PET/CT can be used opportunistically to comprehensively assess bone integrity. In subjects with high fracture risk such as cancer patients this may serve as an additional clinical tool to guide therapy planning and prevention of fractures.

Ultra-small superparamagnetic iron oxides for metastatic lymph node detection: back on the block

In the past 15 years, encouraging clinical results for the detection of small lymph node metastases was obtained by the use of Combidex‐enhanced MRI (CEM, also known as magnetic resonance lymphography). Withdrawal of the European Medicines Agency approval application by the manufacturer made it impossible for patients to benefit from this agent; a loss, especially for men with prostate cancer. Current conventional imaging techniques are not as accurate as CEM is, thus a surgical diagnostic exploration (extended lymph node dissection) is still the preferred technique to evaluate the lymph nodes, resulting in peri‐ and postoperative complications. In 2013, the Radboud University Medical Center (Radboudumc) obtained all licenses and documentation for the production process of Combidex (ferumoxtran‐10), and manufactured the contrast agent under supervision of the Department of Pharmacy. Since 2014, 310 men with prostate cancer have been examined with CEM in the Radboudumc. Within this cohort, seven minor possibly contrast‐related adverse effects were observed after administration of Combidex. As the contrast agent is now back again in the Netherlands, this review highlights the working mechanism, previous results, observed side effects since the reintroduction, and the future perspectives for Combidex. WIREs Nanomed Nanobiotechnol 2018, 10:e1471. doi: 10.1002/wnan.1471

This article is categorized under: 1

Diagnostic Tools > In Vivo Nanodiagnostics and Imaging

2

Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease

Metabolic Imaging of Prostate Cancer Reveals Intrapatient Intermetastasis Response Heterogeneity to Systemic Therapy

Although intrapatient heterogeneity of prostate cancer (PCa) has recently been characterized via genomic and transcriptomic studies, the heterogeneity of systemic treatment responses has yet to be reported or imaged. Our objective was to evaluate the intrapatient intermetastasis response to systemic treatment among patients with metastatic PCa. We evaluated the metabolic response for each individual metastatic lesion (n=165) in 15 patients with metastatic PCa who underwent ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography before and at least 3 mo after initiation of a systemic therapy that did not change in that period. Intermetastasis heterogeneity was defined as opposite metabolic responses for at least two metastases from the same compartment (bone or soft tissue) between the two time points. We found intrapatient intermetastasis response heterogeneity in 40% of the cases in our retrospective series. Our results suggest that systemic therapies can induce heterogeneous responses among individual metastases in patients with PCa, supporting the polyclonal evolution of PCa in advanced disease. Molecular imaging may thus be useful in identifying clinical resistance early after therapy initiation and could also allow targeted biopsy of resistant clones for molecular analysis.

PATIENT SUMMARY

Systemic therapies can lead to heterogeneous responses in individual metastases of prostate cancer in a patient. Molecular imaging may be useful for identifying heterogeneity and could allow targeted biopsy for molecular analysis or therapy.

Gallium-68 Prostate-Specific Membrane Antigen PET Imaging

The role of gallium-68 (⁶⁸Ga) prostate-specific membrane antigen (PSMA) PET imaging is evolving and finding its place in the imaging armamentarium for prostate cancer (PCa). Despite the progress of conventional imaging strategies, significant limitations remain, including identification of small-volume disease and assessment of bone. Clinical studies have demonstrated that ⁶⁸Ga-PSMA is a promising tracer for detection of PCa metastases, even in patients with low prostate-specific antigen. To provide an accurate interpretation of ⁶⁸Ga-PSMA PET/computed tomography, nuclear medicine specialists and radiologists should be familiar with physiologic ⁶⁸Ga-PSMA uptake, common variants, patterns of locoregional and distant spread of PCa, and inherent pitfalls.

Androgen deprivation leads to increased carbohydrate metabolism and hexokinase 2-mediated survival in Pten/Tp53-deficient prostate cancer

Prostate cancer is characterized by a dependence upon androgen receptor (AR) signaling, and androgen deprivation therapy (ADT) is the accepted treatment for progressive prostate cancer. Although ADT is usually initially effective, acquired resistance termed castrate-resistant prostate cancer (CRPC) develops. PTEN and TP53 are two of the most commonly deleted or mutated genes in prostate cancer, the compound loss of which is enriched in CRPC. To interrogate the metabolic alterations associated with survival following ADT, we used an orthotopic model of Pten/Tp53 null prostate cancer. Metabolite profiles and associated regulators were compared in tumors from androgen-intact mice and in tumors surviving castration. AR inhibition led to changes in the levels of glycolysis and tricarboxylic acid (TCA) cycle pathway intermediates. As anticipated for inhibitory reciprocal feedback between AR and PI3K/AKT signaling pathways, pAKT levels were increased in androgen-deprived tumors. Elevated mitochondrial hexokinase 2 (HK2) levels and enzyme activities also were observed in androgen-deprived tumors, consistent with pAKT-dependent HK2 protein induction and mitochondrial association. Competitive inhibition of HK2-mitochondrial binding in prostate cancer cells led to decreased viability. These data argue for AKT-associated HK2-mediated metabolic reprogramming and mitochondrial association in PI3K-driven prostate cancer as one survival mechanism downstream of AR inhibition.

Comparative cost-effectiveness of focal and total salvage 125I brachytherapy for recurrent prostate cancer after primary radiotherapy

PURPOSE

Focal salvage (FS) iodine 125 (125I) brachytherapy could be an effective treatment for locally radiorecurrent prostate cancer (PCa). Toxicity is often reduced compared to total salvage (TS) while cancer control can be maintained, which could increase cost-effectiveness. The current study estimates the incremental cost per quality-adjusted life year (QALY) of FS compared to TS.

MATERIAL AND METHODS

A decision analytic Markov model was developed, which compares costs and QALYs associated with FS and TS. A 3-year time horizon was adopted with six month cycles, with a hospital perspective on costs. Probabilities for genitourinary (GU) and gastrointestinal (GI) toxicity and their impact on health-related quality of life (SF-36) were derived from clinical studies in the University Medical Center Utrecht (UMCU). Probabilistic sensitivity analysis, using 10,000 Monte Carlo simulations, was performed to quantify the joint decision uncertainty up to the recommended maximum willingness-to-pay threshold of €80,000/QALY.

RESULTS

Focal salvage dominates TS as it results in less severe toxicity and lower treatment costs. Decision uncertainty is small, with a 97-100% probability for FS to be cost-effective compared to TS (€0-€80,000/QALY). Half of the difference in costs between FS and TS was explained by higher treatment costs of TS, the other half by higher incidence of severe toxicity. One-way sensitivity analyses show that model outcomes are most sensitive to utilities and probabilities for severe toxicity.

CONCLUSIONS

Focal salvage 125I brachytherapy dominates TS, as it has lower treatment costs and leads to less toxicity in our center. Larger comparative studies with longer follow-up are necessary to assess the exact influence on (biochemical disease free) survival and toxicity.

Precision Nanomedicine Using Dual PET and MR Temperature Imaging-Guided Photothermal Therapy

Imaging-based techniques have enabled the direct integration of noninvasive imaging with minimally invasive interventions such as photothermal therapy (PTT) to improve the precision of treatment.

METHODS

We investigated the feasibility of PTT for ovarian cancer under the guidance of PET and MR temperature imaging using copper sulfide nanoparticles (CuS NPs). The tumor distribution of the CuS NPs after systemic administration was assessed using highly sensitive, quantifiable PET imaging. Two wavelengths of near-infrared (NIR) lasers-808 and 980 nm-were tested for PTT using noninvasive MR temperature imaging real-time monitoring.

RESULTS

The in vivo studies revealed that the 980-nm NIR laser had better photothermal effects than the 808-nm NIR laser. These results were in accord with the histologic findings. In vivo PTT using CuS NPs combined with 980-nm laser irradiation achieved significant tumor ablation compared with no treatment control in both subcutaneous (P = 0.007) and orthotopic (P < 0.001) models of ovarian cancer with regard to the percentage of necrotic damage.

CONCLUSION

Our results indicate that real-time monitoring of the accuracy of PTT is a promising approach for future clinical translation of this emerging thermal ablation technique.

PET-CT in the UK: current status and future directions

Combined positron-emission tomography and computed tomography (PET-CT) has taken the oncological world by storm since being introduced into the clinical domain in the early 21(st) century and is firmly established in the management pathway of many different tumour types. Non-oncological applications of PET-CT represent a smaller but steadily growing area of interest. PET-CT continues to be the focus of a large number of research studies and keeping up-to-date with the literature is important but represents a challenge. Consequently guidelines recommending PET-CT usage need to be revised regularly to encompass new developments. The purpose of this article is twofold: first, it provides a detailed review of the evidence-base underpinning the major uses of PET-CT in clinical practice, which may be of value to a wide-range of individuals, including those directly involved with PET-CT and to a much larger group with limited exposure, but for whom a précis of the current state-of-play may help inform other radiology and multidisciplinary team (MDT) work; the second purpose is as a companion to revised guidelines on evidence-based indications for PET-CT in the UK (being published concurrently) providing a detailed commentary on new indications with a summary of emerging data supporting these additional clinical uses of the technique.

A Review of Imaging Methods for Prostate Cancer Detection

Imaging is playing an increasingly important role in the detection of prostate cancer (PCa). This review summarizes the key imaging modalities-multiparametric ultrasound (US), multiparametric magnetic resonance imaging (MRI), MRI-US fusion imaging, and positron emission tomography (PET) imaging-used in the diagnosis and localization of PCa. Emphasis is laid on the biological and functional characteristics of tumors that rationalize the use of a specific imaging technique. Changes to anatomical architecture of tissue can be detected by anatomical grayscale US and T2-weighted MRI. Tumors are known to progress through angiogenesis-a fact exploited by Doppler and contrast-enhanced US and dynamic contrast-enhanced MRI. The increased cellular density of tumors is targeted by elastography and diffusion-weighted MRI. PET imaging employs several different radionuclides to target the metabolic and cellular activities during tumor growth. Results from studies using these various imaging techniques are discussed and compared.

PET/MRI: Emerging Clinical Applications in Oncology

Positron emission tomography (PET), commonly performed in conjunction with computed tomography (CT), has revolutionized oncologic imaging. PET/CT has become the standard of care for the initial staging and assessment of treatment response for many different malignancies. Despite this success, PET/CT is often supplemented by magnetic resonance imaging (MRI), which offers superior soft-tissue contrast and a means of assessing cellular density with diffusion-weighted imaging. Consequently, PET/MRI, the newest clinical hybrid imaging modality, has the potential to provide added value over PET/CT or MRI alone. The purpose of this article is to provide a comprehensive review of the current body of literature pertaining to the clinical performance of PET/MRI, with the aim of summarizing current evidence and identifying gaps in knowledge to direct clinical expansion and future research. Multiple example cases are also provided to illustrate the central findings of these publications.

Novel Imaging of Prostate Cancer with MRI, MRI/US, and PET

Imaging of prostate cancer presents many challenges to the imaging community. There has been much progress in this space in large part due to MRI and PET radiopharmaceuticals. Though MRI has been focused on the evaluation of local disease and PET on the detection of metastatic disease, these two areas do converge and will be complementary especially with the growth of new PET/MRI technologies. In this review article, we review novel MRI, MRI/US, and PET radiopharmaceuticals which will offer insight into the future direction of imaging in prostate cancer.

Current Status of Hybrid PET/MRI in Oncologic Imaging

OBJECTIVE

This review article explores recent advancements in PET/MRI for clinical oncologic imaging.

CONCLUSION

Radiologists should understand the technical considerations that have made PET/MRI feasible within clinical workflows, the role of PET tracers for imaging various molecular targets in oncology, and advantages of hybrid PET/MRI compared with PET/CT. To facilitate this understanding, we discuss clinical examples (including gliomas, breast cancer, bone metastases, prostate cancer, bladder cancer, gynecologic malignancy, and lymphoma) as well as future directions, challenges, and areas for continued technical optimization for PET/MRI.

Pretargeted immunoPET of prostate cancer with an anti-TROP-2 x anti-HSG bispecific antibody in mice with PC3 xenografts

PURPOSE

Pretargeting with bispecific antibodies and radiolabeled hapten-peptides could be used to specifically target tumors with high target-to-background ratios. TF12 is a trivalent bispecific antibody that consists of two anti-TROP-2 Fab fragments and one anti-HSG (histamine-succinyl-glycine) Fab fragment. The TROP-2 antigen is expressed in many epithelial cancers, including prostate cancer (PC), and therefore, this bispecific antibody can be used for pretargeting of PC. In this study, the potential for pretargeted radioimmunoPET with TF12 and the (68)Ga-labeled di-HSG peptide IMP288 in mice with human PC xenografts was investigated using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) as a reference.

PROCEDURES

The potential of pretargeted immunoPET with TF12 and the (68)Ga-labeled di-HSG hapten-peptide, IMP288, was studied in mice with subcutaneous PC3 tumors using [(18)F]FDG as a reference. Furthermore, the use of this pretargeting system for imaging PC lesions was evaluated in mice with intraperitoneally growing tumors with [(18)F]FDG as a reference.

RESULTS

[(68)Ga]lMP288 showed rapid accumulation in the TF12 pretargeted subcutaneous tumor (7.2 ± 1.1 % ID/g) with low uptake in the kidneys (1.8 ± 0.5 % ID/g) and high tumor-to-blood ratios (17.4 ± 11.2) at 1 h p.i. Accumulation of [(18)F]FDG in the s.c. tumors was significantly lower (3.4 ± 0.9 % ID/g, P = 0.008), with lower tumor-to-blood ratios (3.0 ± 1.9, P = 0.011). ImmunoPET/CT images clearly visualized both subcutaneous and intraperitoneal tumors as small as 5 mm(3) with low blood levels and kidney uptake as early as 1 h p.i.

CONCLUSION

Pretargeted immunoPET with TF12 in combination with a (68)Ga-labeled hapten-peptide is an efficient system for rapid, sensitive, and specific imaging of prostate cancer.

Positron Emission Tomography in Prostate Cancer: Summary of Systematic Reviews and Meta-Analysis

Prostate cancer is a prevalent public health problem worldwide. Over the past decade, there has been tremendous research activity in the potential use of positron emission tomography with a number of radiotracers targeted to various biological aspects of this complex tumor. Systematic reviews and meta-analyses are important contributions to the relevant literature that summarize the evidence while reducing the effect of various sources of bias in the published data. The accumulation of relevant data in this clinical setting has recently provided the opportunity for systematic reviews. In this brief article, I summarize the published systematic reviews and meta-analyses of positron emission tomography in prostate cancer. Most robust evidence suggests a probable role for first-line use of positron emission tomography with radiolabeled choline in restating patients with biochemical relapse of prostate cancer with the diagnostic performance that seems to be positively associated with the serum prostate-specific antigen level and velocity. Future systematic reviews will be needed for other emerging radiotracers such as those based on the prostate-specific membrane antigen and gastrin-releasing peptide receptor.

Accumulation of trans-1-amino-3-[(18)F]fluorocyclobutanecarboxylic acid in prostate cancer due to androgen-induced expression of amino acid transporters

PURPOSE

Androgens play a crucial role in prostate cancer progression, and trans-1-amino-3-[(18)F]fluorocyclobutanecarboxylic acid (anti-[(18) F]FACBC) are used for visualization of prostate cancer. We examined the effect of androgen on the expression of amino acid transporters related to anti-[(18)F]FACBC transport and uptake of trans-1-amino-3-fluoro-[1-(14)C]cyclobutanecarboxylic acid (anti-[(14)C]FACBC).

PROCEDURES

Expression of amino acid transporters and uptake of anti-[(14)C]FACBC in androgen receptor (AR)-positive LNCaP and AR-negative DU145 human prostate cancer cells cultured with/without 5α-dihydrotestosterone (DHT) and the effect of bicalutamide, an AR antagonist, on DHT-associated changes were investigated.

RESULTS

DHT stimulated the expression of amino acid transporters ASCT2, SNAT5, 4F2 heavy chain, and LAT3 in LNCaP but not in DU145 cells. Anti-[(14)C]FACBC uptake was enhanced, in a DHT-dependent manner, in LNCaP cells only.

CONCLUSIONS

DHT enhanced the expression of ASCT2, the transporter responsible for anti-[(18)F]FACBC uptake, thereby increasing anti-[(14)C]FACBC uptake in AR-positive LNCaP cells. Androgen-mediated induction may contribute to the distinct anti-[(18)F]FACBC accumulation pattern in prostate cancer.

¹⁸F-DCFBC PET/CT for PSMA-Based Detection and Characterization of Primary Prostate Cancer

We previously demonstrated the ability to detect metastatic prostate cancer using N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-4-(18)F-fluorobenzyl-L-cysteine ((18)F-DCFBC), a low-molecular-weight radiotracer that targets the prostate-specific membrane antigen (PSMA). PSMA has been shown to be associated with higher Gleason grade and more aggressive disease. An imaging biomarker able to detect clinically significant high-grade primary prostate cancer reliably would address an unmet clinical need by allowing for risk-adapted patient management.

METHODS

We enrolled 13 patients with primary prostate cancer who were imaged with (18)F-DCFBC PET before scheduled prostatectomy, with 12 of these patients also undergoing pelvic prostate MR imaging. Prostate (18)F-DCFBC PET was correlated with MR imaging and histologic and immunohistochemical analysis on a prostate-segment (12 regions) and dominant-lesion basis. There were no incidental extraprostatic findings on PET suggestive of metastatic disease.

RESULTS

MR imaging was more sensitive than (18)F-DCFBC PET for detection of primary prostate cancer on a per-segment (sensitivities of up to 0.17 and 0.39 for PET and MR imaging, respectively) and per-dominant-lesion analysis (sensitivities of 0.46 and 0.92 for PET and MR imaging, respectively). However, (18)F-DCFBC PET was more specific than MR imaging by per-segment analysis (specificities of 0.96 and 0.89 for PET and MR imaging for corresponding sensitivity, respectively) and specific for detection of high-grade lesions (Gleason 8 and 9) greater than 1.0 mL in size (4/4 of these patients positive by PET). (18)F-DCFBC uptake in tumors was positively correlated with Gleason score (ρ = 0.64; PSMA expression, ρ = 0.47; and prostate-specific antigen, ρ = 0.52). There was significantly lower (18)F-DCFBC uptake in benign prostatic hypertrophy than primary tumors (median maximum standardized uptake value, 2.2 vs. 3.5; P = 0.004).

CONCLUSION

Although the sensitivity of (18)F-DCFBC for primary prostate cancer was less than MR imaging, (18)F-DCFBC PET was able to detect the more clinically significant high-grade and larger-volume tumors (Gleason score 8 and 9) with higher specificity than MR imaging. In particular, there was relatively low (18)F-DCFBC PET uptake in benign prostatic hypertrophy lesions, compared with cancer in the prostate, which may allow for more specific detection of primary prostate cancer by (18)F-DCFBC PET. This study demonstrates the utility of PSMA-based PET, which may be used in conjunction with MR imaging to identify clinically significant prostate cancer.

New developments in the imaging of metastatic prostate cancer

PURPOSE OF REVIEW

In the last 10 years, metastatic castration-resistant prostate cancer (mCRPC) treatment has completely changed. Several new agents have been shown to increase mCRPC patients' overall survival. The importance to define castration-resistant prostate cancer as metastatic and to enable earlier detection of cancer progression set a renewed role for prostate cancer (PCa) imaging.

RECENT FINDINGS

Recently published data on molecular imaging of metastatic PCa have focused on diagnostic accuracy, clinical impact and prognostic value of newer techniques using PET and MRI.

SUMMARY

Molecular imaging techniques are more sensitive and accurate than conventional imaging for the early detection of lymph node and bone metastases. New capabilities offered by PET imaging, MRI lymphography and whole-body MRI are consolidating the role of imaging in metastatic PCa management. These techniques are particularly useful for detecting metastasis, a driver for treatment initiation, especially in patients under androgen-deprivation therapy. Moreover, there is an increasing body of evidence supporting the use of metabolic PET and computed tomography as a prognostic biomarker able to predict survival in patients with metastatic PCa.

Biomarkers in preclinical cancer imaging

In view of the trend towards personalized treatment strategies for (cancer) patients, there is an increasing need to noninvasively determine individual patient characteristics. Such information enables physicians to administer to patients accurate therapy with appropriate timing. For the noninvasive visualization of disease-related features, imaging biomarkers are expected to play a crucial role. Next to the chemical development of imaging probes, this requires preclinical studies in animal tumour models. These studies provide proof-of-concept of imaging biomarkers and help determine the pharmacokinetics and target specificity of relevant imaging probes, features that provide the fundamentals for translation to the clinic. In this review we describe biological processes derived from the “hallmarks of cancer” that may serve as imaging biomarkers for diagnostic, prognostic and treatment response monitoring that are currently being studied in the preclinical setting. A number of these biomarkers are also being used for the initial preclinical assessment of new intervention strategies. Uniquely, noninvasive imaging approaches allow longitudinal assessment of changes in biological processes, providing information on the safety, pharmacokinetic profiles and target specificity of new drugs, and on the antitumour effectiveness of therapeutic interventions. Preclinical biomarker imaging can help guide translation to optimize clinical biomarker imaging and personalize (combination) therapies.

Imaging active urokinase plasminogen activator in prostate cancer

The increased proteolytic activity of membrane-bound and secreted proteases on the surface of cancer cells and in the transformed stroma is a common characteristic of aggressive metastatic prostate cancer. We describe here the development of an active site-specific probe for detecting a secreted peritumoral protease expressed by cancer cells and the surrounding tumor microenvironment. Using a human fragment antigen-binding phage display library, we identified a human antibody termed U33 that selectively inhibited the active form of the protease urokinase plasminogen activator (uPA, PLAU). In the full-length immunoglobulin form, U33 IgG labeled with near-infrared fluorophores or radionuclides allowed us to noninvasively detect active uPA in prostate cancer xenograft models using optical and single-photon emission computed tomography imaging modalities. U33 IgG labeled with (111)In had a remarkable tumor uptake of 43.2% injected dose per gram (%ID/g) 72 hours after tail vein injection of the radiolabeled probe in subcutaneous xenografts. In addition, U33 was able to image active uPA in small soft-tissue and osseous metastatic lesions using a cardiac dissemination prostate cancer model that recapitulated metastatic human cancer. The favorable imaging properties were the direct result of U33 IgG internalization through an uPA receptor-mediated mechanism in which U33 mimicked the function of the endogenous inhibitor of uPA to gain entry into the cancer cell. Overall, our imaging probe targets a prostate cancer-associated protease, through a unique mechanism, allowing for the noninvasive preclinical imaging of prostate cancer lesions.

The Warburg effect: evolving interpretations of an established concept

Metabolic reprogramming and altered bioenergetics have emerged as hallmarks of cancer and an area of active basic and translational cancer research. Drastically upregulated glucose transport and metabolism in most cancers regardless of the oxygen supply, a phenomenon called the Warburg effect, is a major focuses of the research. Warburg speculated that cancer cells, due to defective mitochondrial oxidative phosphorylation (OXPHOS), switch to glycolysis for ATP synthesis, even in the presence of oxygen. Studies in the recent decade indicated that while glycolysis is indeed drastically upregulated in almost all cancer cells, mitochondrial respiration continues to operate normally at rates proportional to oxygen supply. There is no OXPHOS-to-glycolysis switch but rather upregulation of glycolysis. Furthermore, upregulated glycolysis appears to be for synthesis of biomass and reducing equivalents in addition to ATP production. The new finding that a significant amount of glycolytic intermediates is diverted to the pentose phosphate pathway (PPP) for production of NADPH has profound implications in how cancer cells use the Warburg effect to cope with reactive oxygen species (ROS) generation and oxidative stress, opening the door for anticancer interventions taking advantage of this. Recent findings in the Warburg effect and its relationship with ROS and oxidative stress controls will be reviewed. Cancer treatment strategies based on these new findings will be presented and discussed.

A MR-TRUS Registration Method for Ultrasound-Guided Prostate Interventions

In this paper, we report a MR-TRUS prostate registration method that uses a subject-specific prostate strain model to improve MR-targeted, US-guided prostate interventions (e.g., biopsy and radiotherapy). The proposed algorithm combines a subject-specific prostate biomechanical model with a B-spline transformation to register the prostate gland of the MRI to the TRUS images. The prostate biomechanical model was obtained through US elastography and a 3D strain map of the prostate was generated. The B-spline transformation was calculated by minimizing Euclidean distance between the normalized attribute vectors of landmarks on MR and TRUS prostate surfaces. This prostate tissue gradient map was used to constrain the B-spline-based transformation to predict and compensate for the internal prostate-gland deformation. This method was validated with a prostate-phantom experiment and a pilot study of 5 prostate-cancer patients. For the phantom study, the mean target registration error (TRE) was 1.3 mm. MR-TRUS registration was also successfully performed for 5 patients with a mean TRE less than 2 mm. The proposed registration method may provide an accurate and robust means of estimating internal prostate-gland deformation, and could be valuable for prostate-cancer diagnosis and treatment.

Prognostic Utility of PET in Prostate Cancer

Many standard nonimaging-based prediction tools exist for prostate cancer. However, these tools may be limited in individual cases and need updating based on the improved understanding of the underlying complex biology of the disease and the emergence of the novel targeted molecular imaging methods. A new platform of automated predictive tools that combines the independent molecular, imaging, and clinical information can contribute significantly to patient care. Such a platform will also be of interest to regulatory agencies and payers as more emphasis is placed on supporting those interventions that have quantifiable and significant beneficial impact on patient outcome.

Targeting neuropeptide receptors for cancer imaging and therapy: perspectives with bombesin, neurotensin, and neuropeptide-Y receptors

Receptors for some regulatory peptides are highly expressed in tumors. Selective radiolabeled peptides can bind with high affinity and specificity to these receptors and exhibit favorable pharmacologic and pharmacokinetic properties, making them suitable agents for imaging or targeted therapy. The success encountered with radiolabeled somatostatin analogs is probably the first of a long list, as multiple peptide receptors are now recognized as potential targets. This review focuses on 3 neuropeptide receptor systems (bombesin, neurotensin, and neuropeptide-Y) that offer high potential in the field of nuclear oncology. The underlying biology of these peptide/receptor systems, their physiologic and pathologic roles, and their differential distribution in normal and tumoral tissues are described with emphasis on breast, prostate, and lung cancers. Radiolabeled analogs that selectively target these receptors are highlighted.

Inhibitors of glucose transport and glycolysis as novel anticancer therapeutics

Metabolic reprogramming and altered energetics have become an emerging hallmark of cancer and an active area of basic, translational, and clinical cancer research in the recent decade. Development of effective anticancer therapeutics may depend on improved understanding of the altered cancer metabolism compared to that of normal cells. Changes in glucose transport and glycolysis, which are drastically upregulated in most cancers and termed the Warburg effect, are one of major focuses of this new research area. By taking advantage of the new knowledge and understanding of cancer’s mechanisms, numerous therapeutic agents have been developed to target proteins and enzymes involved in glucose transport and metabolism, with promising results in cancer cells, animal tumor models and even clinical trials. It has also been hypothesized that targeting a pathway or a process, such as glucose transport or glucose metabolism, rather than a specific protein or enzyme in a signaling pathway may be more effective. This is based on the observation that cancer somehow can always bypass the inhibition of a target drug by switching to a redundant or compensatory pathway. In addition, cancer cells have higher dependence on glucose. This review will provide background information on glucose transport and metabolism in cancer, and summarize new therapeutic developments in basic and translational research in these areas, with a focus on glucose transporter inhibitors and glycolysis inhibitors. The daunting challenges facing both basic and clinical researchers of the field are also presented and discussed.