Recommendations for Cell-Free DNA Assay Validations: A Joint Consensus Recommendation of the Association for Molecular Pathology and College of American Pathologists.

Diagnosing, selecting therapy for, and monitoring cancer in patients using a minimally invasive blood test represents a significant advance in precision medicine. Wide variability exists in how circulating tumor DNA (ctDNA) assays are developed, validated, and reported in the literature, which hinders clinical adoption and may negatively impact patient care. Standardization is needed for factors affecting ctDNA assay performance and reporting, including pre-analytical variables, analytical considerations, and elements of laboratory assay reporting. The Association for Molecular Pathology Clinical Practice Committee's Liquid Biopsy Working Group (LBxWG), including organizational representation from the American Society of Clinical Oncology and the College of American Pathologists, has undertaken a full-text data extraction of 1228 ctDNA publications that describe assays performed in patients with lymphoma and solid tumor malignancies. With an emphasis on clinical assay validation, the LBxWG has developed a set of 13 best practice consensus recommendations for validating, reporting, and publishing clinical ctDNA assays. Recommendations include reporting key pre-analytical considerations and assay performance metrics; this analysis demonstrates these elements are inconsistently included in publications. The LBxWG recommendations are intended to assist clinical laboratories with validating and reporting ctDNA assays and to ensure high-quality data are included in publications. It is expected that these recommendations will need to be updated as the body of literature continues to mature.

Assessments of Somatic Variant Classification Using the Association for Molecular Pathology/American Society of Clinical Oncology/College of American Pathologists Guidelines: A Report from the Association for Molecular Pathology.

To assess the clinical implementation of the 2017 Standards and Guidelines for the Interpretation and Reporting of Sequence Variants in Cancer: A Joint Consensus Recommendation of the Association for Molecular Pathology, American Society of Clinical Oncology, and College of American Pathologists, identify content that may result in classification inconsistencies, and evaluate implementation barriers, an Association for Molecular Pathology Working Group conducted variant interpretation challenges and a guideline implementation survey. A total of 134 participants participated in the variant interpretation challenges, consisting of 11 variants in four cancer cases. Results demonstrate 86% (range, 54% to 94%) of the respondents correctly classified clinically significant variants, variants of uncertain significance, and benign/likely benign variants; however, only 59% (range, 39% to 84%) of responses agreed with the working group's consensus intended responses regarding both tiers and categories of clinical significance. In the implementation survey, 71% (157/220) of respondents have implemented the 2017 guidelines for variant classification and reporting either with or without modifications. Collectively, this study demonstrates that, although they may not yet be optimized, the 2017 guideline recommendations are being adopted for standardized somatic variant classification. The working group identified significant areas for future guideline improvement, including the need for a more granular and comprehensive classification system and education resources to meet the growing needs of both laboratory professionals and medical oncologists.

Enhancement of Radiotherapy with Human Mesenchymal Stem Cells Containing Gold Nanoparticles.

Radiotherapy is a common approach for the treatment of a wide variety of cancer types. Available data indicate that nanoparticles can enhance the effect of radiotherapy. We report the use of human mesenchymal stem cells to selectively deliver gold nanoparticles (GNPs) to MDA-MB-231 breast tumor xenografts in mice for the purpose of enhancing the effect of radiation therapy. Targeted delivery of GNPs to the tumor site, followed by irradiation of the tumor, enabled control of tumor growth. The results indicate that tumor-selective GNP delivery by human mesenchymal stem cells may represent a viable way to enhance the effectiveness of radiotherapy.

Clinical Significance of DNA Variants in Chronic Myeloid Neoplasms: A Report of the Association for Molecular Pathology.

To address the clinical relevance of small DNA variants in chronic myeloid neoplasms (CMNs), an Association for Molecular Pathology Working Group comprehensively reviewed published literature, summarized key findings that support clinical utility, and defined critical gene inclusions for high-throughput sequencing testing panels. This review highlights the biological complexity of CMNs [including myelodysplastic syndromes, myeloproliferative neoplasms, entities with overlapping features (myelodysplastic syndromes/myeloproliferative neoplasms), and systemic mastocytosis], the genetic heterogeneity within diagnostic categories, and similarities between apparently disparate diagnostic entities. The founding variant's hematopoietic differentiation compartment, specific genes and variants present, order of variant appearance, individual subclone dynamics, and therapeutic intervention all contribute to the clinicopathologic features of CMNs. Selection and efficacy of targeted therapies are increasingly based on DNA variant profiles present at various time points; therefore, high-throughput sequencing remains critical for patient management. The following genes are a minimum recommended list to provide relevant clinical information for the management of most CMNs: ASXL1, BCOR, BCORL1, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, IDH1, IDH2, JAK2, KIT, KRAS, MPL, NF1, NPM1, NRAS, PHF6, PPM1D, PTPN11, RAD21, RUNX1, SETBP1, SF3B1, SMC3, SRSF2, STAG2, TET2, TP53, U2AF1, and ZRSR2. This list is not comprehensive for all myeloid neoplasms and will evolve as insights into effects of combinations of relevant biomarkers on specific clinicopathologic characteristics of CMNs accumulate.

Standards and Guidelines for Validating Next-Generation Sequencing Bioinformatics Pipelines: A Joint Recommendation of the Association for Molecular Pathology and the College of American Pathologists.

Bioinformatics pipelines are an integral component of next-generation sequencing (NGS). Processing raw sequence data to detect genomic alterations has significant impact on disease management and patient care. Because of the lack of published guidance, there is currently a high degree of variability in how members of the global molecular genetics and pathology community establish and validate bioinformatics pipelines. Improperly developed, validated, and/or monitored pipelines may generate inaccurate results that may have negative consequences for patient care. To address this unmet need, the Association of Molecular Pathology, with organizational representation from the College of American Pathologists and the American Medical Informatics Association, has developed a set of 17 best practice consensus recommendations for the validation of clinical NGS bioinformatics pipelines. Recommendations include practical guidance for laboratories regarding NGS bioinformatics pipeline design, development, and operation, with additional emphasis on the role of a properly trained and qualified molecular professional to achieve optimal NGS testing quality.

Low-Level Endogenous PSMA Expression in Nonprostatic Tumor Xenografts Is Sufficient for In Vivo Tumor Targeting and Imaging.

Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and within the neovasculature of other solid tumors. The nonprostatic expression of PSMA has been reported exclusively within the neovasculature endothelial cells of nonprostatic cancers; however, there are few reports on PSMA expression in epithelial cells. Herein, we describe PSMA expression in nonprostatic epithelial cells and characterize the potential of PSMA-binding agents to noninvasively detect that expression. Methods: PSMA expression data were extracted from publicly available genomic databases. Genomic data were experimentally validated for PSMA expression-by quantitative reverse transcription polymerase chain reaction, flow cytometry, and Western blotting-in several nonprostatic cell lines and xenografts of melanoma and small cell lung cancer (SCLC) origin. The feasibility of PSMA detection in those tumor models was further established using PSMA-based nuclear and optical imaging agents and by biodistribution, blocking, and ex vivo molecular characterization studies. Results: We discovered that a small percentage of nonprostatic cancer cell lines and tumors express PSMA. Importantly, PSMA expression was sufficiently high to image established melanoma and SCLC xenografts using PSMA-based nuclear and optical imaging agents. Conclusion: These results indicate that PSMA expression in nonprostatic tumors may not be limited to the endothelium but may also include solid tumor tissue of nonprostatic cancers including melanoma and SCLC. Our observations indicate broader applicability of PSMA-targeted imaging and therapeutics.

A PSMA-targeted theranostic agent for photodynamic therapy.

Prostate-specific membrane antigen (PSMA) is over-expressed in the epithelium of prostate cancer and in the neovasculature of many non-prostate solid tumors. PSMA has been increasingly used as a target for cancer imaging and therapy. Here we describe a low-molecular-weight theranostic photosensitizer, YC-9, for PSMA-targeted optical imaging and photodynamic therapy (PDT). YC-9 was synthesized by conjugating IRDye700DX N-hydroxysuccinimide (NHS) ester with a PSMA targeting Lys-Glu urea through a lysine-suberate linker in suitable yield. Optical imaging in vivo demonstrated PSMA-specific tumor uptake of YC-9 with rapid clearance from non-target tissues. PSMA-specific cell kill was demonstrated with YC-9in vitro through PDT in PSMA+ PC3-PIP and PSMA- PC3-flu cells. In vivo PDT in mice bearing PSMA+ PC3-PIP tumors at 4h post-injection of YC-9 (A total of four PDT sessions were performed, 48h apart) resulted in significant tumor growth delay, while tumors in control groups continued to grow. PDT with YC-9 significantly increased the median survival of the PSMA+ PC3-PIP tumor mice (56.5days) compared to control groups [23.5-30.0days, including untreated, light alone, YC-9 alone (without light) and non-targeted IRDye700DX PDT treatment groups], without noticeable toxicity at the doses used. This study proves in principle that YC-9 is a promising therapeutic agent for targeted PDT of PSMA-expressing tissues, such as prostate tumors, and may also be useful against non-prostate tumors by virtue of neovascular PSMA expression.

111In- and IRDye800CW-Labeled PLA-PEG Nanoparticle for Imaging Prostate-Specific Membrane Antigen-Expressing Tissues.

Targeted delivery of drug-encapsulated nanoparticles is a promising new approach to safe and effective therapeutics for cancer. Here we investigate the pharmacokinetics and biodistribution of a prostate-specific membrane antigen (PSMA)-targeted nanoparticle based on a poly(lactic acid)-polyethylene glycol copolymer by utilizing single photon emission computed tomography (SPECT) and fluorescence imaging of a low-molecular-weight, PSMA-targeting moiety attached to the surface and oriented toward the outside environment. Tissue biodistribution of the radioactive, PSMA-targeted nanoparticles in mice containing PSMA(+) PC3 PIP and PSMA(-) PC3 flu (control) tumors demonstrated similar accumulation compared to the untargeted particles within all tissues except for the tumor and liver by 96 h postinjection. For PSMA(+) PC3 PIP tumor, the targeted nanoparticle demonstrated retention of 6.58% injected dose (ID)/g at 48 h and remained nearly at that level out to 96 h, whereas the untargeted nanoparticle showed a 48 h retention of 8.17% ID/g followed by a significant clearance to 2.37% ID/g at 96 h (P < 0.02). On the other hand, for control tumor, both targeted and untargeted particles displayed similar 48 h retentions and rates of clearance over 96 h. Ex vivo microscopic analysis with near-infrared versions of the nanoparticles indicated retention within PSMA(+) tumor epithelial cells as well as tumor-associated macrophages for targeted particles and primarily macrophage-associated uptake for the untargeted particles. Retention in control tumor was primarily associated with tumor vasculature and macrophages. The data demonstrate the utility of radioimaging to assess nanoparticle biodistribution and suggest that active targeting has a modest positive effect on tumor localization of PSMA-targeted PLA-PEG nanoparticles that have been derivatized for imaging.

[(18)F]Fluoroethyl Triazole Substituted PSMA Inhibitor Exhibiting Rapid Normal Organ Clearance.

Prostate-specific membrane antigen (PSMA) is overexpressed in the epithelium of prostate cancer and nonprostate solid tumor neovasculature. PSMA is increasingly utilized as a target for cancer imaging and therapy. Here, we report the synthesis and in vivo biodistribution of a low-molecular-weight PSMA-based imaging agent, 2-[3-(1-carboxy-5-{3-[1-(2-[(18)F]fluoroethyl)-1H-1,2,3-triazol-yl]propanamido}pentyl)ureido]pentanedioic acid ([(18)F]YC-88), containing an [(18)F]fluoroethyl triazole moiety. [(18)F]YC-88 was synthesized from 2-[(18)F]fluoroethyl azide and the corresponding alkyne precursor in two steps using either a one- or two-pot procedure. Biodistribution and positron emission tomography (PET) imaging were performed in immunocompromised mice using isogenic PSMA(+) PC3 PIP and PSMA(-) PC3 flu xenografts. YC-88 exhibited high affinity for PSMA as evidenced by a Ki value of 12.9 nM. The non-decay corrected radiochemical yields of [(18)F]YC-88 averaged 14 ± 1% (n = 5). Specific radioactivities ranged from 320 to 2,460 Ci/mmol (12-91 GBq/µmol) with an average of 940 Ci/mmol (35 GBq/µmol, n = 5). In an immunocompromised mouse model, [(18)F]YC-88 clearly delineated PSMA(+) PC3 PIP prostate tumor xenografts on imaging with PET. At 1 h postinjection, 47.58 ± 5.19% injected dose per gram of tissue (% ID/g) was evident within the PSMA(+) PC3 PIP tumor, with a ratio of 170:1 of uptake within PSMA(+) PC3 PIP to PSMA(-) PC3 flu tumor placed in the opposite flank. The tumor-to-kidney ratio at 2 h postinjection was 4:1. At or after 30 min postinjection, minimal nontarget tissue uptake of [(18)F]YC-88 was observed. Compared to [(18)F]DCFPyL, which is currently in clinical trials, the uptake of [(18)F]YC-88 within the kidney, liver, and spleen was significantly lower at all time-points studied. At 30 min and 1 h postinjection, salivary gland uptake of [(18)F]YC-88 was significantly less than that of [(18)F]DCFPyL. [(18)F]YC-88 is a new PSMA-targeted PET agent synthesized utilizing click chemistry that demonstrates high PSMA(+) tumor uptake in a xenograft model. Because of its low uptake in the kidney, rapid clearance from nontarget organs, and relatively simple one-pot, two-step radiosynthesis, [(18)F]YC-88 is a viable new PET radiotracer for imaging PSMA-expressing lesions.

Preclinical Comparative Study of (68)Ga-Labeled DOTA, NOTA, and HBED-CC Chelated Radiotracers for Targeting PSMA.

(68)Ga-labeled, low-molecular-weight imaging agents that target the prostate-specific membrane antigen (PSMA) are increasingly used clinically to detect prostate and other cancers with positron emission tomography (PET). The goal of this study was to compare the pharmacokinetics of three PSMA-targeted radiotracers: (68)Ga-1, using DOTA-monoamide as the chelating agent; (68)Ga-2, containing the macrocyclic chelating agent p-SCN-Bn-NOTA; and (68)Ga-DKFZ-PSMA-11, currently in clinical trials, which uses the acyclic chelating agent, HBED-CC. The PSMA-targeting scaffold for all three agents utilized a similar Glu-urea-Lys-linker construct. Each radiotracer enabled visualization of PSMA+ PC3 PIP tumor, kidney, and urinary bladder as early as 15 min post-injection using small animal PET/computed tomography (PET/CT). (68)Ga-2 demonstrated the fastest rate of clearance from all tissues in this series and displayed higher uptake in PSMA+ PC3 PIP tumor compared to (68)Ga-1 at 1 h post-injection. There was no significant difference in PSMA+ PC3 PIP tumor uptake for the three agents at 2 and 3 h post-injection. (68)Ga-DKFZ-PSMA-11 demonstrated the highest uptake and retention in normal tissues, including kidney, blood, spleen, and salivary glands and PSMA-negative PC3 flu tumors up to 3 h post-injection. In this preclinical evaluation (68)Ga-2 had the most advantageous characteristics for PSMA-targeted PET imaging.

Targeted Imaging of the Atypical Chemokine Receptor 3 (ACKR3/CXCR7) in Human Cancer Xenografts.

UNLABELLED: The atypical chemokine receptor ACKR3 (formerly CXCR7), overexpressed in various cancers compared with normal tissues, plays a pivotal role in adhesion, angiogenesis, tumorigenesis, metastasis, and tumor cell survival. ACKR3 modulates the tumor microenvironment and regulates tumor growth. The therapeutic potential of ACKR3 has also been demonstrated in various murine models of human cancer. Literature findings underscore the importance of ACKR3 in disease progression and suggest it as an important diagnostic marker for noninvasive imaging of ACKR3-overexpressing malignancies. There are currently no reports on direct receptor-specific detection of ACKR3 expression. Here we report the evaluation of a radiolabeled ACKR3-targeted monoclonal antibody (ACKR3-mAb) for the noninvasive in vivo nuclear imaging of ACKR3 expression in human breast, lung, and esophageal squamous cell carcinoma cancer xenografts. METHODS: ACKR3 expression data were extracted from Cancer Cell Line Encyclopedia, The Cancer Genome Atlas, and the Clinical Lung Cancer Genome Project. (89)Zr-ACKR3-mAb was evaluated in vitro and subsequently in vivo by PET and ex vivo biodistribution studies in mice xenografted with breast (MDA-MB-231-ACKR3 [231-ACKR3], MDA-MB-231 [231], MCF7), lung (HCC95), or esophageal (KYSE520) cancer cells. In addition, ACKR3-mAb was radiolabeled with (125)I and evaluated by SPECT imaging and ex vivo biodistribution studies. RESULTS: ACKR3 transcript levels were highest in lung squamous cell carcinoma among the 21 cancer type data extracted from The Cancer Genome Atlas. Also, Clinical Lung Cancer Genome Project data showed that lung squamous cell carcinoma had the highest CXCR7 transcript levels compared with other lung cancer subtypes. The (89)Zr-ACKR3-mAb was produced in 80% ± 5% radiochemical yields with greater than 98% radiochemical purity. In vitro cell uptake of (89)Zr-ACKR3-mAb correlated with gradient levels of cell surface ACKR3 expression observed by flow cytometry. In vivo PET imaging and ex vivo biodistribution studies in mice with breast, lung, and esophageal cancer xenografts consistently showed enhanced (89)Zr-ACKR3-mAb uptake in high-ACKR3-expressing tumors. SPECT imaging of (125)I-ACKR3-mAb showed the versatility of ACKR3-mAb for in vivo monitoring of ACKR3 expression. CONCLUSION: Data from this study suggest ACKR3 to be a viable diagnostic marker and demonstrate the utility of radiolabeled ACKR3-mAb for in vivo visualization of ACKR3-overexpressing malignancies.

A fully human CXCR4 antibody demonstrates diagnostic utility and therapeutic efficacy in solid tumor xenografts.

For physiologically important cancer therapeutic targets, use of non-invasive imaging for therapeutic guidance and monitoring may improve outcomes for treated patients. The CXC chemokine receptor 4 (CXCR4) is overexpressed in many cancers including non-small cell lung cancer (NSCLC) and triple negative breast cancer (TNBC). CXCR4 overexpression contributes to tumor growth, progression and metastasis. There are several CXCR4-targeted therapeutic agents currently in clinical trials. Since CXCR4 is also crucial for normal biological functions, its prolonged inhibition could lead to unwanted toxicities. While CXCR4-targeted imaging agents and inhibitors have been reported and evaluated independently, there are currently no studies demonstrating CXCR4-targeted imaging for therapeutic guidance. Monoclonal antibodies (mAbs) are commonly used for cancer therapy and imaging. Here, an 89Zr-labeled human CXCR4-mAb (89Zr-CXCR4-mAb) was evaluated for detection of CXCR4 expression with positron emission tomography (PET) while its native unmodified analogue was evaluated for therapy in relevant models of NSCLC and TNBC. In vitro and in vivo evaluation of 89Zr-CXCR4-mAb showed enhanced uptake in NSCLC xenografts with a high expression of CXCR4. It also had the ability to detect lymph node metastases in an experimental model of metastatic TNBC. Treatment of high and low CXCR4 expressing NSCLC and TNBC xenografts with CXCR4-mAb demonstrated a therapeutic response correlating with the expression of CXCR4. Considering the key role of CXCR4 in normal biological functions, our results suggest that combination of 89Zr-CXCR4-mAb-PET with non-radiolabeled mAb therapy may provide a precision medicine approach for selecting patients with tumors that are likely to be responsive to this treatment.

[(18)F]Fluorobenzoyllysinepentanedioic Acid Carbamates: New Scaffolds for Positron Emission Tomography (PET) Imaging of Prostate-Specific Membrane Antigen (PSMA).

Radiolabeled urea-based low-molecular weight inhibitors of the prostate-specific membrane antigen (PSMA) are under intense investigation as imaging and therapeutic agents for prostate and other cancers. In an effort to provide agents with less nontarget organ uptake than the ureas, we synthesized four (18)F-labeled inhibitors of PSMA based on carbamate scaffolds. 4-Bromo-2-[(18)F]fluorobenzoyllysineoxypentanedioic acid (OPA) carbamate [(18)F]23 and 4-iodo-2-[(18)F]fluorobenzoyllysine OPA carbamate [(18)F]24 in particular exhibited high target-selective uptake in PSMA+ PC3 PIP tumor xenografts, with tumor-to-kidney ratios of >1 by 4 h postinjection, an important benchmark. Because of its high tumor uptake (90% injected dose per gram of tissue at 2 h postinjection) and high tumor-to-organ ratios, [(18)F]23 is promising for clinical translation. Prolonged tumor-specific uptake demonstrated by [(18)F]24, which did not reach equilibrium during the 4 h study period, suggests carbamates as alternative scaffolds for mitigating dose to nontarget tissues.

Synthesis and Evaluation of Gd(III) -Based Magnetic Resonance Contrast Agents for Molecular Imaging of Prostate-Specific Membrane Antigen.

Magnetic resonance (MR) imaging is advantageous because it concurrently provides anatomic, functional, and molecular information. MR molecular imaging can combine the high spatial resolution of this established clinical modality with molecular profiling in vivo. However, as a result of the intrinsically low sensitivity of MR imaging, high local concentrations of biological targets are required to generate discernable MR contrast. We hypothesize that the prostate-specific membrane antigen (PSMA), an attractive target for imaging and therapy of prostate cancer, could serve as a suitable biomarker for MR-based molecular imaging. We have synthesized three new high-affinity, low-molecular-weight Gd(III) -based PSMA-targeted contrast agents containing one to three Gd(III)  chelates per molecule. We evaluated the relaxometric properties of these agents in solution, in prostate cancer cells, and in an in vivo experimental model to demonstrate the feasibility of PSMA-based MR molecular imaging.

Auger Radiopharmaceutical Therapy Targeting Prostate-Specific Membrane Antigen.

UNLABELLED: Auger electron emitters such as (125)I have a high linear energy transfer and short range of emission (<10 µm), making them suitable for treating micrometastases while sparing normal tissues. We used a highly specific small molecule targeting the prostate-specific membrane antigen (PSMA) to deliver (125)I to prostate cancer cells. METHODS: The PSMA-targeting Auger emitter 2-[3-[1-carboxy-5-(4-(125)I-iodo-benzoylamino)-pentyl]-ureido]-pentanedioic acid ((125)I-DCIBzL) was synthesized. DNA damage (via phosphorylated H2A histone family member X staining) and clonogenic survival were tested in PSMA-positive (PSMA+) PC3 PIP and PSMA-negative (PSMA-) PC3 flu human prostate cancer cells after treatment with (125)I-DCIBzL. Subcellular drug distribution was assessed with confocal microscopy using a related fluorescent PSMA-targeting compound YC-36. In vivo antitumor efficacy was tested in nude mice bearing PSMA+ PC3 PIP or PSMA- PC3 flu flank xenografts. Animals were administered (intravenously) 111 MBq (3 mCi) of (125)I-DCIBzL, 111 MBq (3 mCi) of (125)I-NaI, an equivalent amount of nonradiolabeled DCIBzL, or saline. RESULTS: After treatment with (125)I-DCIBzL, PSMA+ PC3 PIP cells exhibited increased DNA damage and decreased clonogenic survival when compared with PSMA- PC3 flu cells. Confocal microscopy of YC-36 showed drug distribution in the perinuclear area and plasma membrane. Animals bearing PSMA+ PC3 PIP tumors had significant tumor growth delay after treatment with (125)I-DCIBzL, with only 1 mouse reaching 5 times the initial tumor volume by 60 d after treatment, compared with a median time to 5 times volume of less than 15 d for PSMA- PC3 flu tumors and all other treatment groups (P = 0.002 by log-rank test). CONCLUSION: PSMA-targeted radiopharmaceutical therapy with the Auger emitter (125)I-DCIBzL yielded highly specific antitumor efficacy in vivo, suggesting promise for treatment of prostate cancer micrometastases.

Evaluation of a PSMA-targeted BNF nanoparticle construct.

Early detection enables improved prognosis for prostate cancer (PCa). A promising target for imaging and therapy of PCa is the prostate-specific membrane antigen (PSMA), which exhibits both expression within the epithelium of PCa cells, and becomes internalized upon ligand binding. Here we report the synthesis of a PSMA-targeted bionized nanoferrite (BNF) nanoparticle and its biological evaluation in an experimental model of PCa. The BNF nanoparticle formulation exhibits properties conducive to targeted imaging such as stealth, prolonged circulation time and enhanced clearance from non-target sites. Optical imaging of the targeted BNF in vivo indicates preferential accumulation in PSMA+ tumors 4 h post-injection, suggesting target specificity. On the other hand, non-targeted nanoparticles exhibit lower uptake with similar accumulation in both PSMA+ and PSMA- tumors indicating tumor access without preferential accumulation. Imaging with single photon emission computed tomography (SPECT) and biodistribution studies of a modified construct indicate highest tumor accumulation at 48 h post-injection [4.3 ± 0.4 percentage injected dose per gram of tissue (%ID g(-1))], with tumor/blood and tumor/muscle ratios of 7.5 ± 2.4 and 11.6 ± 1.2 %ID g(-1), respectively. Ex vivo fluorescence microscopy, Prussian blue staining, immunohistochemistry and biodistribution studies confirm enhanced nanoparticle uptake in PSMA+ tumors compared to those not expressing PSMA. The BNF nano-formulation described is promising for PSMA-targeted imaging applications in vivo.

Preclinical evaluation of 86Y-labeled inhibitors of prostate-specific membrane antigen for dosimetry estimates.

UNLABELLED: (86)Y (half-life = 14.74 h, 33% ß(+)) is within an emerging class of positron-emitting isotopes with relatively long physical half-lives that enables extended imaging of biologic processes. We report the synthesis and evaluation of 3 low-molecular-weight compounds labeled with (86)Y for imaging the prostate-specific membrane antigen (PSMA) using PET. Impetus for the study derives from the need to perform dosimetry estimates for the corresponding (90)Y-labeled radiotherapeutics. METHODS: Multistep syntheses were used in preparing (86)Y- 4: - 6: PSMA inhibition constants were evaluated by competitive binding assay. In vivo characterization using tumor-bearing male mice was performed by PET/CT for (86)Y- 4: - 6: and by biodistribution studies of (86)Y- 4: and (86)Y- 6: out to 24 h after injection. Quantitative whole-body PET scans were recorded to measure the kinetics for 14 organs in a male baboon using (86)Y- 6 RESULTS: Compounds (86)Y- 4: - 6: were obtained in high radiochemical yield and purity, with specific radioactivities of more than 83.92 GBq/µmol. PET imaging and biodistribution studies using PSMA-positive PC-3 PIP and PSMA-negative PC-3 flu tumor-bearing mice revealed that (86)Y- 4-6: had high site-specific uptake in PSMA-positive PC-3 PIP tumor starting at 20 min after injection and remained high at 24 h. Compound (86)Y- 6: demonstrated the highest tumor uptake and retention, with 32.17 ± 7.99 and 15.79 ± 6.44 percentage injected dose per gram (%ID/g) at 5 and 24 h, respectively. Low activity concentrations were associated with blood and normal organs, except for the kidneys, a PSMA-expressing tissue. PET imaging in baboons reveals that all organs have a 2-phase (rapid and slow) clearance, with the highest uptake (8 %ID/g) in the kidneys at 25 min. The individual absolute uptake kinetics were used to calculate radiation doses using the OLINDA/EXM software. The highest mean absorbed dose was received by the renal cortex, with 1.9 mGy per MBq of (86)Y- 6: CONCLUSION: Compound (86)Y- 6: is a promising candidate for quantitative PET imaging of PSMA-expressing tumors. Dosimetry calculations indicate promise for future (90)Y or other radiometals that could use a similar chelator/scaffold combination for radiopharmaceutical therapy based on the structure of 6.

Structural characterization and in vivo evaluation of ß-Hairpin peptidomimetics as specific CXCR4 imaging agents.

The CXCR4 chemokine receptor is integral to several biological functions and plays a pivotal role in the pathophysiology of many diseases. As such, CXCR4 is an enticing target for the development of imaging and therapeutic agents. Here we report the evaluation of the POL3026 peptidomimetic template for the development of imaging agents that target CXCR4. Structural and conformational analyses of POL3026 and two of its conjugates, DOTA (POL-D) and PEG12-DOTA (POL-PD), by circular dichroism, two-dimensional NMR spectroscopy and molecular dynamics calculations are reported. In silico observations were experimentally verified with in vitro affinity assays and rationalized using crystal structure-based molecular modeling studies. [(111)In]-labeled DOTA conjugates were assessed in vivo for target specificity in CXCR4 expressing subcutaneous U87 tumors (U87-stb-CXCR4) through single photon emission computed tomography (SPECT/CT) imaging and biodistribution studies. In silico and in vitro studies show that POL3026 and its conjugates demonstrate similar interactions with different micelles that mimic cellular membrane and that the ε-NH2 of lysine(7) is critical to maintain high affinity to CXCR4. Modification of this group with DOTA or PEG12-DOTA led to the decrease of IC50 value from 0.087 nM for POL3026 to 0.47 nM and 1.42 nM for POL-D and POL-PD, respectively. In spite of the decreased affinity toward CXCR4, [(111)In]POL-D and [(111)In]POL-PD demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors at 90 min and 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled POL3026, indicating specificity of the agents in vivo. These results suggest POL3026 as a promising template to develop new imaging agents that target CXCR4.

Bridged cyclams as imaging agents for chemokine receptor 4 (CXCR4).

Over-expression of chemokine receptor 4 (CXCR4) is present in a majority of cancers, has been linked to an aggressive phenotype, and may indicate the metastatic potential of primary tumor. Several CXCR4 targeted therapeutics are in clinical trials and the development of the corresponding imaging agents is an area of active interest. Previously, (64)Cu-labeled imaging agents for CXCR4 have provided clear images of CXCR4-bearing tissues in relevant experimental models but demonstrated fast washout from tissues harboring receptor. Addition of stabilizing bridges is known to provide more robust chelator-Cu(II) complexes. In addition, bridged cyclam-based CXCR4 binding agents demonstrated increased receptor residence times relative to existing agents. Based on that knowledge we synthesized several bridged cyclam analogs of AMD3465, a monocyclam-based CXCR4 imaging agent, to increase the retention time of the tracer bound to the receptor to allow for protracted imaging and improved target-to-non-target ratios. Specific accumulation of two radiolabeled, cross-bridged analogs ([(64)Cu] RAD1-24 and [(64)Cu]RAD1-52) was observed in U87-stb-CXCR4 tumors in both PET/CT imaging and biodistribution studies. At 90min post-injection of radiotracer, tumor-to-muscle and tumor-to-blood ratios reached 106.05±17.19 and 28.08±4.78, respectively, for cross-bridged pyrimidine analog [(64)Cu]RAD1-52. Receptor blockade performed in vivo denoted target binding specificity. The biodistribution and PET/CT imaging studies with the radiolabeled bridged cyclams demonstrated longer tumor retention and comparable uptake to [(64)Cu]AMD3465, though [(64)Cu]AMD3465 demonstrated superior overall pharmacokinetics.

64Cu-labeled inhibitors of prostate-specific membrane antigen for PET imaging of prostate cancer.

Prostate-specific membrane antigen (PSMA) is a well-recognized target for identification and therapy of a variety of cancers. Here we report five (64)Cu-labeled inhibitors of PSMA, [(64)Cu]3-7, which are based on the lysine-glutamate urea scaffold and utilize a variety of macrocyclic chelators, namely NOTA(3), PCTA(4), Oxo-DO3A(5), CB-TE2A(6), and DOTA(7), in an effort to determine which provides the most suitable pharmacokinetics for in vivo PET imaging. [(64)Cu]3-7 were prepared in high radiochemical yield (60-90%) and purity (>95%). Positron emission tomography (PET) imaging studies of [(64)Cu]3-7 revealed specific accumulation in PSMA-expressing xenografts (PSMA+ PC3 PIP) relative to isogenic control tumor (PSMA- PC3 flu) and background tissue. The favorable kinetics and high image contrast provided by CB-TE2A chelated [(64)Cu]6 suggest it as the most promising among the candidates tested. That could be due to the higher stability of [(64)Cu]CB-TE2A as compared with [(64)Cu]NOTA, [(64)Cu]PCTA, [(64)Cu]Oxo-DO3A, and [(64)Cu]DOTA chelates in vivo.