Positron emission tomography/computed tomography and radioimmunotherapy of prostate cancer

Fatty Acid Metabolism Reprogramming in Advanced Prostate Cancer

Prostate cancer (PCa) is a carcinoma in which fatty acids are abundant. Fatty acid metabolism is rewired during PCa development. Although PCa can be treated with hormone therapy, after prolonged treatment, castration-resistant prostate cancer can develop and can lead to increased mortality. Changes to fatty acid metabolism occur systemically and locally in prostate cancer patients, and understanding these changes may lead to individualized treatments, especially in advanced, castration-resistant prostate cancers. The fatty acid metabolic changes are not merely reflective of oncogenic activity, but in many cases, these represent a critical factor in cancer initiation and development. In this review, we analyzed the literature regarding systemic changes to fatty acid metabolism in PCa patients and how these changes relate to obesity, diet, circulating metabolites, and peri-prostatic adipose tissue. We also analyzed cellular fatty acid metabolism in prostate cancer, including fatty acid uptake, de novo lipogenesis, fatty acid elongation, and oxidation. This review broadens our view of fatty acid switches in PCa and presents potential candidates for PCa treatment and diagnosis.

Novel Monoclonal Antibodies Recognizing Human Prostate-Specific Membrane Antigen (PSMA) as Research and Theranostic Tools

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a validated target for the imaging and therapy of prostate cancer. Here, we report the detailed characterization of four novel murine monoclonal antibodies (mAbs) recognizing human PSMA as well as PSMA orthologs from different species.

METHODS

Performance of purified mAbs was assayed using a comprehensive panel of in vitro experimental setups including Western blotting, immunofluorescence, immunohistochemistry, ELISA, flow cytometry, and surface-plasmon resonance. Furthermore, a mouse xenograft model of prostate cancer was used to compare the suitability of the mAbs for in vivo applications.

RESULTS

All mAbs demonstrate high specificity for PSMA as documented by the lack of cross-reactivity to unrelated human proteins. The 3F11 and 1A11 mAbs bind linear epitopes spanning residues 226-243 and 271-288 of human PSMA, respectively. 3F11 is also suitable for the detection of PSMA orthologs from mouse, pig, dog, and rat in experimental setups where the denatured form of PSMA is used. 5D3 and 5B1 mAbs recognize distinct surface-exposed conformational epitopes and are useful for targeting PSMA in its native conformation. Most importantly, using a mouse xenograft model of prostate cancer we show that both the intact 5D3 and its Fab fragment are suitable for in vivo imaging.

CONCLUSIONS

With apparent affinities of 0.14 and 1.2 nM as determined by ELISA and flow cytometry, respectively, 5D3 has approximately 10-fold higher affinity for PSMA than the clinically validated mAb J591 and, therefore, is a prime candidate for the development of next-generation theranostics to target PSMA. Prostate 77:749-764, 2017. © 2017 Wiley Periodicals, Inc.

Targeting the de novo biosynthesis of thymidylate for the development of a PET probe for pancreatic cancer imaging

The development of cancer-specific probes for imaging by positron emission tomography (PET) is gaining impetus in cancer research and clinical oncology. One of the hallmarks of most cancer cells is incessant DNA replication, which requires the continuous synthesis of nucleotides. Thymidylate synthase (TSase) is unique in this context because it is the only enzyme in humans that is responsible for the de novo biosynthesis of the DNA building block 2'-deoxy-thymidylate (dTMP). TSase catalyzes the reductive methylation of 2'-deoxy-uridylate (dUMP) to dTMP using (R)-N(5),N(10)-methylene-5,6,7,8-tetrahydrofolate (MTHF) as a cofactor. Not surprisingly, several human cancers overexpress TSase, which makes it a common target for chemotherapy (e.g., 5-fluorouracil). We envisioned that [(11)C]-MTHF might be a PET probe that could specifically label cancerous cells. Using stable radiotracer [(14)C]-MTHF, we had initially found increased uptake by breast and colon cancer cell lines. In the current study, we examined the uptake of this radiotracer in human pancreatic cancer cell lines MIAPaCa-2 and PANC-1 and found predominant radiolabeling of cancerous versus normal pancreatic cells. Furthermore, uptake of the radiotracer is dependent on the intracellular level of the folate pool, cell cycle phase, expression of folate receptors on the cell membrane, and cotreatment with the common chemotherapeutic drug methotrexate (MTX, which blocks the biosynthesis of endogenous MTHF). These results point toward [(11)C]-MTHF being used as PET probe with broad specificity and being able to control its signal through MTX co-administration.

A multivalent approach of imaging probe design to overcome an endogenous anion binding competition for noninvasive assessment of prostate specific membrane antigen

2[(3-Amino-3-carboxypropyl)(hydroxy)(phosphinyl)methyl]pentane-1,5-dioic acid) (GPI) is a highly potent inhibitor of prostate specific membrane antigen (PSMA) with a rapid in vivo clearance profile from nontarget organs including kidneys, but its use for imaging of PSMA is impeded by an endogenous anion (serum phosphate) competition, which compromises its specific binding to the antigen. Multipresentation of a targeting molecule on a single entity has been recognized as a practical way for imaging sensitivity enhancement. Herein, we demonstrate a multivalent approach based on a (64)Cu-specific bifunctional chelator scaffold to overcome the endogenous phosphate competition thus enabling the utility of GPI conjugates for in vivo detection of PSMA and imaging quantification. Both monomeric (H2CBT1G) and dimeric (H2CBT2G) conjugates were synthesized and labeled with (64)Cu for in vitro and in vivo evaluations. A 4-fold enhancement of PSMA binding affinity was observed for H2CBT2G as compared to H2CBT1G from the PSMA competitive binding assays performed on LNCaP cells. In vivo PET imaging studies were conducted on mouse xenograft models established with a PSMA(+) cell line, LNCaP, and PSMA(-) PC3 and H2009 cell lines. (64)Cu-CBT2G showed significantly higher LNCaP tumor uptake than (64)Cu-CBT1G at 1, 4, and 24 h postinjection (p.i.) (p < 0.05). In addition, tumor uptake of (64)Cu-CBT2G remained steady out to 24 h p.i. (1.46 ± 0.54, 1.12 ± 0.56, and 1.00 ± 0.50% ID/g at 1, 4, and 24 h p.i., respectively), while (64)Cu-CBT1G showed a great decrease from 1 to 4 h p.i. The PSMA imaging specificity of both H2CBT1G and H2CBT2G was demonstrated by their low uptake in PSMA(-) tumors (PC3 and H2009) and further confirmed by a significant signal reduction in PSMA(+) LNCaP tumors in the blockade study. In addition, the LNCaP tumor uptake (% ID/g) of (64)Cu-CBT2G was found to be in a positive linear correlation with the tumor size (R(2) = 0.92, 0.94, and 0.93 for 1 h, 4 h, and 24 h p.i.). This may render the probe with potential application in the management of patients with prostate cancer.

Image guided biodistribution and pharmacokinetic studies of theranostics

Image guided technique is playing an increasingly important role in the investigation of the biodistribution and pharmacokinetics of drugs or drug delivery systems in various diseases, especially cancers. Besides anatomical imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI), molecular imaging strategy including optical imaging, positron emission tomography (PET) and single-photon emission computed tomography (SPECT) will facilitate the localization and quantization of radioisotope or optical probe labeled nanoparticle delivery systems in the category of theranostics. The quantitative measurement of the bio-distribution and pharmacokinetics of theranostics in the fields of new drug/probe development, diagnosis and treatment process monitoring as well as tracking the brain-blood-barrier (BBB) breaking through by high sensitive imaging method, and the applications of the representative imaging modalities are summarized in this review.

Molecular imaging of prostate cancer: PET radiotracers

OBJECTIVE

Recent advances in the fundamental understanding of the complex biology of prostate cancer have provided an increasing number of potential targets for imaging and treatment. The imaging evaluation of prostate cancer needs to be tailored to the various phases of this remarkably heterogeneous disease.

CONCLUSION

In this article, I review the current state of affairs on a range of PET radiotracers for potential use in the imaging evaluation of men with prostate cancer.

[18F]fluoromethylcholine (FCH) positron emission tomography/computed tomography (PET/CT) for lymph node staging of prostate cancer: a prospective study of 210 patients

Study Type--Diagnostic (exploratory cohort) Level of Evidence 2a. What's known on the subject? and What does the study add? Staging of patients with prostate cancer is the cornerstone of treatment. However, after curative intended therapy a high portion of patients relapse with local and/or distant recurrence. Therefore, one may question whether surgical lymph node dissection (LND) is sufficiently reliable for staging of these patients. Several imaging methods for primary LN staging of patients with prostate cancer have been tested. Acceptable detection rates have not been achieved by CT or MRI or for that matter with PET/CT using the most common tracer fluoromethylcholine (FCH). Other more recent metabolic tracers like acetate and choline seem to be more sensitive for assessment of LNs in both primary staging and re-staging. However, previous studies were small. Therefore, we assessed the value of [(18) F]FCH PET/CT for primary LN staging in a prospective study of a larger sample and with a 'blinded' review. After a study period of 3 years and >200 included patients, we concluded that [(18) F]FCH PET/CT did not reach an optimal detection rate compared with LND, and, therefore, it cannot replace this procedure. However, we did detect several bone metastases with [(18) F]FCH PET/CT that the normal bone scans had missed, and this might be worth pursuing.

OBJECTIVES

• To assess the value of [(18) F]fluoromethylcholine (FCH) positron emission tomography/computed tomography (PET/CT) for lymph node (LN) staging of prostate cancer. • To evaluate if FCH PET/CT can replace LN dissection (LND) for LN staging of prostate cancer, as about one-third of patients with prostate cancer who receive intended curative therapy will have recurrence, one reason being undetected LN involvement.

PATIENTS AND METHODS

• From January 2008 to December 2010, 210 intermediate- or high-risk patients had a FCH PET/CT scan before regional LND. • After dissection, the result of histological examination of the LNs (gold standard) was compared with the result of FCH PET/CT obtained by 'blinded review'. • Sensitivity, specificity, positive (PPV), and negative predictive values (NPV) of FCH PET/CT were measured for detection of LNe metastases.

RESULTS

• Of the 210 patients, 76 (36.2%) were in the intermediate-risk group and 134 (63.8%) were in the high-risk group. A medium (range) of 5 (1-28) LNs were removed per patient. • Histological examination of removed LNs showed metastases in 41 patients. Sensitivity, specificity, PPV, and NPV of FCH PET/CT for patient-based LN staging were 73.2%, 87.6%, 58.8% and 93.1%, respectively. • Corresponding values for LN-based analyses were 56.2%, 94.0%, 40.2%, and 96.8%, respectively. • The mean diameter of the true positive LN metastases was significantly larger than that of the false negative LNs (10.3 vs 4.6 mm; P < 0.001). • In addition, FCH PET/CT detected a high focal bone uptake, consistent with bone metastases, in 18 patients, 12 of which had histologically benign LNs.

CONCLUSIONS

• Due to a relatively low sensitivity and a correspondingly rather low PPV, FCH PET/CT is not ideal for primary LN staging in patients with prostate cancer. • However, FCH PET/CT does convey important additional information otherwise not recognised, especially for bone metastases.

Novel positron emission tomography tracer distinguishes normal from cancerous cells

Development of tumor-specific probes for imaging by positron emission tomography has broad implications in clinical oncology, such as diagnosis, staging, and monitoring therapeutic responses in patients, as well as in biomedical research. Thymidylate synthase (TSase)-based de novo biosynthesis of DNA is an important target for drug development. Increased DNA replication in proliferating cancerous cells requires TSase activity, which catalyzes the reductive methylation of dUMP to dTMP using (R)-N(5),N(10)-methylene-5,6,7,8-tetrahydrofolate (MTHF) as a cofactor. In principle, radiolabeled MTHF can be used as a substrate for this reaction to identify rapidly dividing cells. In this proof-of-principle study, actively growing (log phase) breast cancer (MCF7, MDA-MB-231, and hTERT-HME1), normal breast (human mammary epithelial and MCF10A), colon cancer (HT-29), and normal colon (FHC) cells were incubated with [(14)C]MTHF in culture medium from 30 min to 2 h, and uptake of radiotracer was measured. Cancerous cell lines incorporated significantly more radioactivity than their normal counterparts. The uptake of radioactively labeled MTHF depended upon a combination of cell doubling time, folate receptor status, S phase percentage, and TSase expression in the cells. These findings suggest that the recently synthesized [(11)C]MTHF may serve as a new positron emission tomography tracer for cancer imaging.

Development of polymeric microbubbles targeted to prostate-specific membrane antigen as prototype of novel ultrasound contrast agents

Ultrasound-targeted microbubbles (MBs) offer new opportunities to enhance the capabilities of diagnostic ultrasound (US) imaging to specific pathological tissue. Herein, we report on the design and development of a novel prototype of US contrast agent based on polymeric MBs targeted to prostate-specific membrane antigen (PSMA) for use in the diagnosis of prostate cancer (PCa). First, a set of air-filled MBs by a variety of biocompatible polymers were prepared and characterized in terms of morphology and echogenic properties after exposure to US. MBs derived from poly(D,L-lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG) copolymer resulted as the most effective in terms of reflectivity. Such polymer was therefore preconjugated with a urea-based PSMA inhibitor molecular probe (DCL), and the obtained MBs were investigated in vitro for their targeting efficacy toward PSMA positive PCa (LNCaP) cells. Fluorescence microscopy proved a specific and efficient adhesion of targeted MBs to LNCaP cells. To our knowledge, this work reports the first model of polymeric MBs appropriately engineered to target PSMA, which might be further optimized and used for PCa diagnosis and potential carriers for selective drug delivery.

Automated production of [11C]acetate and [11C]palmitate using a modified GE Tracerlab FX(C-Pro)

As researchers explore new applications for positron emission tomography radiopharmaceuticals, the demand for effective and readily available radiopharmaceuticals continues to increase. The syntheses of two such radiopharmaceuticals, [(11)C]acetate and [(11)C]palmitate, can be automated on the GE Tracerlab FX(C-Pro) by utilizing Grignard reactions. Radiochemical purities of the [(11)C]acetate and the [(11)C]palmitate products were high (>98% and >99.9%, respectively) with average non-corrected yields of 18% (n = 3) and 10% (n = 5), respectively. These data comprise the validation trials for site qualification of clinical production of both radiopharmaceuticals.

PET/CT Imaging and Radioimmunotherapy of Prostate Cancer

Prostate cancer is a common cancer in men and continues to be a major health problem. Imaging plays an important role in the clinical management of patients with prostate cancer. An important goal for prostate cancer imaging is more accurate disease characterization through the synthesis of anatomic, functional, and molecular imaging information. Positron emission tomography (PET)/computed tomography (CT) in oncology is emerging as an important imaging tool. The most common radiotracer for PET/CT in oncology, (18)F-fluorodeoxyglucose (FDG), is not very useful in the imaging of prostate cancer. However, in recent years other PET tracers have improved the accuracy of PET/CT imaging of prostate cancer. Among these, choline labeled with (18)F or (11)C, (11)C-acetate, and (18)F-fluoride has demonstrated promising results, and other new radiopharmaceuticals are under development and evaluation in preclinical and clinical studies. Large prospective clinical PET/CT trials are needed to establish the role of PET/CT in prostate cancer patients. Because there are only limited available therapeutic options for patients with advanced metastatic prostate cancer, there is an urgent need for the development of more effective treatment modalities that could improve outcome. Prostate cancer represents an attractive target for radioimmunotherapy (RIT) for several reasons, including pattern of metastatic spread (lymph nodes and bone marrow, sites with good access to circulating antibodies) and small volume disease (ideal for antigen access and antibody delivery). Furthermore, prostate cancer is also radiation sensitive. Prostate-specific membrane antigen is expressed by virtually all prostate cancers, and represents an attractive target for RIT. Antiprostate-specific membrane antigen RIT demonstrates antitumor activity and is well tolerated. Clinical trials are underway to further improve upon treatment efficacy and patient selection. This review focuses on the recent advances of clinical PET/CT imaging and RIT of prostate cancer.

Signal turn-on probe for nucleic acid detection based on (19)F nuclear magnetic resonance

To image gene expression in vivo, we designed and synthesized a novel signal turn-on probe for (19)F nuclear magnetic resonance (MR) imaging based on paramagnetic relaxation enhancement. The stem-loop structured oligodeoxyribonucleotide (ODN) having a molecular beacon sequence for point mutated K-ras mRNA was doubly labeled with bis(trifluoromethyl)benzene moiety and Gd-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid chelate moiety at the each termini of the ODN probe, respectively. We found that the (19)F MR signal of the bis(trifluoromethyl)benzene moiety tethered at the 5' termini of the probe turned on by the addition of complementary ODN. The probe has the potential to image gene expressions in vivo.

The pre-requisite of a second-generation glioma PET biomarker

Since the introduction of FDG into the field of molecular imaging with positron emission tomography (PET) more than three decades ago, FDG has been the tracer of choice for oncology PET imaging. Despite the relative disadvantages of FDG and the relative benefits of its challengers, FDG remains the most commonly used glioma tracer nowadays. The present article surveys the expectations of the field and gives a concise summary of recent developments; including the issues pertaining to the continued search for an optimal second-generation PET biomarker for glioma.

MINI-ABSTRACT

The present article gives a concise summary of recent developments; including the issues pertaining to the continued search for an optimal PET biomarker for glioma.

'Image and treat': an individualized approach to urological tumors

PURPOSE OF REVIEW

The current treatment options for advanced urologic cancers demonstrate limited efficacy. To obtain optimal clinical results, there is a need for new, individualized, therapeutic strategies, which have only recently been applied to these malignancies. Nuclear medicine plays an important role in establishing imaging biomarkers necessary for personalized medicine. This review focuses on the current status of the 'image and treat' approach combining molecular imaging with targeted radionuclide therapy of urological malignancies

RECENT FINDINGS

Tumor-specific targets in uro-oncology are showing promising results for development of personalized therapy using positron emission tomography/computed tomography (PET/CT) molecular imaging and radioimmunotherapy. The antibody cG250, which binds to carbonic anhydrase IX, is being evaluated as a radiolabeled imaging and therapeutic agent in clear-cell renal cell carcinoma. I-cG250 PET/CT has demonstrated excellent targeting of clear-cell renal cell carcinoma. Prostate-specific membrane antigen is a promising target for both PET/CT and radioimmunotherapy of prostate cancer. HER2 may be another potential target in bladder and prostate cancer.

SUMMARY

Tumor-specific targets and biomarkers are being studied for PET/CT and radioimmunotherapy. This may lead to development of new therapeutic strategies. However, considerable investment in new research will be required for personalized medicine to be routinely used in uro-oncology.

Role and cost effectiveness of PET/CT in management of patients with cancer

PET/CT is a relatively new imaging technology, whose undoubted advantages are valuable in clinical oncology as well as in all fields of diagnosis, staging, and treatment. The hardware combination of anatomy and function has been the true evolution in imaging. PET using 18F-fluorodeoxyglucose (FDG) is increasingly used for the staging of solid malignancies, including colon, lung, etc., but anatomic information is limited. Integrated PET/CT enables optimal anatomic delineation of PET findings and identification of FDG-negative lesions on computed tomography (CT) images and might improve preoperative staging. However, controversy still exists in relation to the application of PET/CT in clinical practice, mainly because of its high cost. It is evident that apart from additional costs, potential savings also are associated with PET/CT as a result of avoiding additional imaging examinations or invasive procedures and by helping clinicians make the optimum treatment decisions. The authors review the literature on the role of PET/CT in management of various tumors and discuss the medicoeconomic usefulness.

Imaging prostate cancer: an update on positron emission tomography and magnetic resonance imaging

Prostate cancer is a common cancer in men and continues to be a major health problem. Imaging plays an essential role in the clinical management of patients. An important goal for prostate cancer imaging is more accurate disease characterization through the synthesis of anatomic, functional, and molecular imaging information. Developments in imaging technologies, specifically magnetic resonance imaging (MRI) and positron emission tomography (PET)/computed tomography (CT), have improved the detection rate of prostate cancer. MRI has improved lesion detection and local staging. Furthermore, MRI allows functional assessment with techniques such as diffusion-weighted MRI, MR spectroscopy, and dynamic contrast-enhanced MRI. The most common PET radiotracer, (18)F-fluorodeoxyglucose, is not very useful in prostate cancer. However, in recent years other PET tracers have improved the accuracy of PET/CT imaging of prostate cancer. Among these, choline (labeled with (18)F or (11)C), (11)C-acetate, and (18)F-fluoride have demonstrated promising results, and other new radiopharmaceuticals are currently under evaluation in preclinical and clinical studies.

Interventional molecular imaging

Recent common interest in molecular imaging among both diagnostic and interventional radiologists has led to the establishment of a concept that could be called interventional molecular imaging. This concept, by combining interventional radiology with molecular imaging, is aiming to fully apply the advantages of both imaging fields. Interventional radiology can extend the capabilities of currently available molecular imaging techniques to (a) reach deep-seated targets, (b) enable a close look at small targets, (c) precisely guide delivery of nontargeted imaging tracers or therapeutic agents, and (d) superselectively enhance the effectiveness of targeted imaging and treatment. Interventional molecular imaging is becoming one of the frameworks for bringing molecular imaging from benches and small-animal laboratories to large-animal suites and, ultimately, to certain clinical applications in humans. (c) RSNA, 2010.

Modalities for imaging of prostate cancer

Prostate cancer is the second most common cause of cancer deaths among males in the United States. Prostate screening by digital rectal examination and prostate-specific antigen has shifted the diagnosis of prostate cancer to lower grade, organ confined disease, adding to overdetection and overtreatment of prostate cancer. The new challenge is in differentiating clinically relevant tumors from ones that may otherwise never have become evident if not for screening. The rapid evolution of imaging modalities and the synthesis of anatomic, functional, and molecular data allow for improved detection and characterization of prostate cancer. However, the appropriate use of imaging is difficult to define, as many controversial studies regarding each of the modalities and their utilities can be found in the literature. Clinical practice patterns have been slow to adopt many of these advances as a result. This review discusses the more established imaging techniques, including Ultrasonography, Magnetic Resonance Imaging, MR Spectroscopy, Computed Tomography, and Positron Emission Tomography. We also review several promising techniques on the horizon, including Dynamic Contrast-Enhanced MRI, Diffuse-Weighted Imaging, Superparamagnetic Nanoparticles, and Radionuclide Scintigraphy.

Prostate specific membrane antigen- a target for imaging and therapy with radionuclides

Prostate cancer continues to represent a major health problem, and yet there is no effective treatment available for advanced metastatic disease. Thus, there is an urgent need for the development of more effective treatment modalities that could improve the outcome. Because prostate specific membrane antigen (PSMA), a transmembrane protein, is expressed by virtually all prostate cancers, and its expression is further increased in poorly differentiated, metastatic, and hormone-refractory carcinomas, it is a very attractive target. Molecules targeting PSMA can be labelled with radionuclides to become both diagnostic and/or therapeutic agents. The use of PSMA binding agents, labelled with diagnostic and therapeutic radio-isotopes, opens up the potential for a new era of personalized management of metastatic prostate cancer.