Comparing Magnetic Resonance Imaging and Prostate-Specific Membrane Antigen-Positron Emission Tomography for Prediction of Extraprostatic Extension of Prostate Cancer and Surgical Guidance: A Prospective Nonrandomized Clinical Trial.

PURPOSE: Survivors of surgically managed prostate cancer may experience urinary incontinence and erectile dysfunction. Our aim was to determine if 68Ga-prostate-specific membrane antigen-11 positron emission tomography CT (PSMA-PET) in addition to multiparametric (mp) MRI scans improved surgical decision-making for nonnerve-sparing or nerve-sparing approach. MATERIALS AND METHODS: We prospectively enrolled 50 patients at risk for extraprostatic extension (EPE) who were scheduled for prostatectomy. After mpMRI and PSMA-PET images were read for EPE prediction, surgeons prospectively answered questionnaires based on mpMRI and PSMA-PET scans on the decision for nerve-sparing or nonnerve-sparing approach. Final whole-mount pathology was the reference standard. Sensitivity, specificity, positive predictive value, negative predictive value, and receiver operating characteristic curves were calculated and McNemar's test was used to compare imaging modalities. RESULTS: The median age and PSA were 61.5 years and 7.0 ng/dL. The sensitivity for EPE along the posterior neurovascular bundle was higher for PSMA-PET than mpMRI (86% vs 57%, P = .03). For MRI, the specificity, positive predictive value, negative predictive value, and area under the curve for the receiver operating characteristic curves were 77%, 40%, 87%, and 0.67, and for PSMA-PET were 73%, 46%, 95%, and 0.80. PSMA-PET and mpMRI reads differed on 27 nerve bundles, with PSMA-PET being correct in 20 cases and MRI being correct in 7 cases. Surgeons predicted correct nerve-sparing approach 74% of the time with PSMA-PET scan in addition to mpMRI compared to 65% with mpMRI alone (P = .01). CONCLUSIONS: PSMA-PET scan was more sensitive than mpMRI for EPE along the neurovascular bundles and improved surgical decisions for nerve-sparing approach. Further study of PSMA-PET for surgical guidance is warranted in the unfavorable intermediate-risk or worse populations. CLINICALTRIALS.GOV IDENTIFIER: NCT04936334.

Assessing extra-prostatic extension for surgical guidance in prostate cancer: Comparing two PSMA-PET tracers with the standard-of-care.

BACKGROUND: Incontinence and impotence occur following radical prostatectomy due to injury to nerves and sphincter muscle. Preserving nerves and muscle adjacent to prostate cancer risks positive surgical margins. Advanced imaging with MRI has improved cancer localization but limitations exist. OBJECTIVE: To measure the accuracy for assessing extra-prostatic extension at nerve bundles for 2 PSMA-PET tracers and to compare the PET accuracy to standard-of-care predictors including MRI and biopsy results. MATERIALS AND METHODS: We studied men with PSMA-targeted PET imaging, performed prior to prostatectomy in men largely with intermediate to high-risk prostate cancer, and retrospectively evaluated for assessment of extra-prostatic extension with whole-mount analysis as reference standard. Two different PSMA-PET tracers were included: 68Ga-PSMA-11 and 68Ga-P16-093. Blinded reviews of the PET and MRI scans were performed to assess extra-prostatic extension (EPE). Sensitivity and specificity for extra-prostatic extension were compared using McNemar's Chi2. RESULTS: Pre-operative PSMA-PET imaging was available for 71 patients with either 68Ga-P16-093 (n = 25) or 68Ga-PSMA-11 (n = 46). There were 24 (34%) with pT3a (EPE) and 16 (23%) with pT3b (SVI). EPE Sensitivity (87% vs. 92%), Specificity (77% vs. 76%), and ROC area (0.82 vs. 0.84) were similar between P16-093 and PSMA-11, respectively (P = 0.87). MRI (available in only 45) found high specificity (83%) but low sensitivity (60%) for EPE when using a published grading system. MRI sensitivity was significantly lower than the PSMA-PET (60% vs. 90%, P = 0.02), but similar to PET when using a >5 mm capsular contact (76% vs. 90%, P = 0.38). A treatment change to "nerve sparing" was recommended in 21 of 71 (30%) patients based on PSMA-PET imaging. CONCLUSIONS: Presurgical PSMA-PET appeared useful as a tool for surgical planning, changing treatment plans in men with ≥4+3 or multi-core 3+4 prostate cancer resulting in preservation of nerve-bundles.

Synthesis and formulation of [64Cu]Cu-PTSM for PET perfusion imaging in small animal models.

PURPOSE: The [64Cu]Cu-PTSM radiopharmaceutical, pyruvaldehyde bis(N4-methylthiosemicarbazonato)copper(II), is suitable for use in microPET and autoradiographic imaging to assess regional tissue perfusion in small animal models. We report here an approach to synthesis and formulation of the [64Cu]Cu-PTSM radiopharmaceutical at the high concentrations required for use in imaging with rodent models of human disease. METHODS: The [64Cu]Cu-PTSM radiopharmaceutical was prepared at small volumes by addition of the H2PTSM ligand to acetate-buffered [64Cu]copper chloride, followed by solid phase extraction to isolate and purify the product, which was then recovered and formulated in 2-mL normal saline containing 5% ethanol and 5% propylene glycol. RESULTS: The [64Cu]Cu-PTSM radiopharmaceutical has been produced over the range of 0.41-1.85 GBq (11-50 mCi) [64Cu]Cu-PTSM in the 2.0-mL final product volume. Radiochemical purity of the [64Cu]Cu-PTSM radiopharmaceutical product averaged 99.8 ± 0.4% (n = 64), with the final formulated product produced at an 83 ± 5% radiochemical yield. CONCLUSIONS: The approach to [64Cu]Cu-PTSM synthesis and formulation has proven to be reliable and robust, supporting radiopharmaceutical delivery at the high concentrations required for PET studies in mouse and other rodent models.

In Vivo Quantitative Whole-Body Perfusion Imaging Using Radiolabeled Copper(II) Bis(Thiosemicarbazone) Complexes and Positron Emission Tomography (PET).

Traditional quantitative perfusion imaging methods require complex data acquisition and analysis strategies; typically require ancillary arterial blood sampling for measurement of input functions; are limited to single organ or tissue regions in an imaging session; and because of their complexity, are not well suited for routine clinical implementation in a standardized fashion that can be readily repeated across diverse clinical sites. The whole-body perfusion method described in this chapter has the advantages of on-demand radiotracer production; simple tissue pharmacokinetics enabling standardized estimation of perfusion; short-lived radionuclides, facilitating repeat or combination imaging procedures; and scalability to support widespread clinical implementation. This method leverages the unique physiological characteristics of radiolabeled copper(II) bis(thiosemicarbazone) complexes and the detection sensitivity of positron emission tomography (PET) to produce quantitatively accurate whole-body perfusion images. This chapter describes the synthesis of ethylglyoxal bis(thosemicarbazonato)copper(II) labeled with copper-62 ([62Cu]Cu-ETS), its unique physiological characteristics, a simple tracer kinetic model for estimation of perfusion using image-derived input functions, and validation of the method against a reference standard perfusion tracer. A detailed description of the methods is provided to facilitate implementation of the perfusion imaging method in PET imaging facilities.

[68Ga]Ga-P16-093 as a PSMA-Targeted PET Radiopharmaceutical for Detection of Cancer: Initial Evaluation and Comparison with [68Ga]Ga-PSMA-11 in Prostate Cancer Patients Presenting with Biochemical Recurrence.

PURPOSE: This study was undertaken to evaluate radiation dosimetry for the prostate-specific membrane antigen targeted [68Ga]Ga-P16-093 radiopharmaceutical, and to initially assess agent performance in positron emission tomography (PET) detection of the site of disease in prostate cancer patients presenting with biochemical recurrence. PROCEDURES: Under IND 133,222 and an IRB-approved research protocol, we evaluated the biodistribution and pharmacokinetics of [68Ga]Ga-P16-093 with serial PET imaging following intravenous administration to ten prostate cancer patients with biochemical recurrence. The recruited subjects were all patients in whom a recent [68Ga]Ga-PSMA-11 PET/X-ray computed tomography (CT) exam had been independently performed under IND 131,806 to assist in decision-making with regard to their clinical care. Voided urine was collected from each subject at ~ 60 min and ~ 140 min post-[68Ga]Ga-P16-093 injection and assayed for Ga-68 content. Following image segmentation to extract tissue time-activity curves and corresponding cumulated activity values, radiation dosimetry estimates were calculated using IDAC Dose 2.1. The prior [68Ga]Ga-PSMA-11 PET/CT exam (whole-body PET imaging at 60 min post-injection, performed with contrast-enhanced diagnostic CT) served as a reference scan for comparison to the [68Ga]Ga-P16-093 findings. RESULTS: [68Ga]Ga-P16-093 PET images at 60 min post-injection provided diagnostic information that appeared equivalent to the subject's prior [68Ga]Ga-PSMA-11 scan. With both radiopharmaceuticals, sites of tumor recurrence were found in eight of the ten patients, identifying 16 lesions. The site of recurrence was not detected with either agent for the other two subjects. Bladder activity was consistently lower with [68Ga]Ga-P16-093 than [68Ga]Ga-PSMA-11. The kidneys, spleen, salivary glands, and liver receive the highest radiation exposure from [68Ga]Ga-P16-093, with estimated doses of 1.7 × 10-1, 6.7 × 10-2, 6.5 × 10-2, and 5.6 × 10-2 mGy/MBq, respectively. The corresponding effective dose from [68Ga]Ga-P16-093 is 2.3 × 10-2 mSv/MBq. CONCLUSIONS: [68Ga]Ga-P16-093 provided diagnostic information that appeared equivalent to [68Ga]Ga-PSMA-11 in this limited series of ten prostate cancer patients presenting with biochemical recurrence, with the kidneys found to be the critical organ. Diminished tracer appearance in the urine represents a potential advantage of [68Ga]Ga-P16-093 over [68Ga]Ga-PSMA-11 for detection of lesions in the pelvis.

Synthesis and biodistribution of lipophilic and monocationic gallium radiopharmaceuticals derived from N,N'-bis(3-aminopropyl)-N,N'-dimethylethylenediamine: potential agents for PET myocardial imaging with 68Ga.

INTRODUCTION: In locations that lack nearby cyclotron facilities for radionuclide production, generator-based (68)Ga radiopharmaceuticals might have clinical utility for positron emission tomography (PET) studies of myocardial perfusion and other physiological processes. METHODS: The lipophilic and monocationic (67)Ga-labeled gallium chelates of five novel hexadentate bis(salicylaldimine) ligands the bis(salicylaldimine), bis(3-methoxysalicylaldimine), bis(4-methoxysalicylaldimine), bis(6-meth,oxysalicylaldimine), and bis(4,6-dimethoxysalicylaldimine) of N,N'-bis(3-aminopropyl)-N,N'-dimethylethylenediamine (BAPDMEN), were prepared. The structure of the unlabeled [Ga(4-MeOsal)(2)BAPDMEN](+)PF(6)(-) salt was determined by X-ray crystallography, and the biodistribution of each of the (67)Ga-labeled gallium chelates was determined in rats following intravenous administration and compared with the biodistribution of [(86)Rb]rubidium chloride. RESULTS: The [Ga(4-MeOsal)(2)BAPDMEN](+)PF(6)(-) complex exhibited the expected pseudo-octahedral N(4)O(2)(2-) coordination sphere about the Ga(3+) center with a trans disposition of the phenolate oxygen atoms. All five (67)Ga radiopharmaceuticals were found to afford the desired myocardial retention of the radiogallium. The [(67/68)Ga][Ga(3-MeOsal)(2)BAPDMEN](1+) radiopharmaceutical appears to have the best properties for myocardial imaging, exhibiting 2% of the injected dose in the heart 1 min and 2 h postinjection and very high heart/nontarget ratios (heart/blood ratios of 7.6+/-1.0 and 54+/-10 at 1 and 120 min, respectively; heart/liver ratios of 1.8+/-0.4 and 39+/-3 at 1 and 120 min, respectively). CONCLUSIONS: Most of these new agents, particularly [(67/68)Ga][Ga(3-MeOsal)(2)BAPDMEN](1+), would appear superior to previously reported bis(salicylaldimine) ligands of N,N'-bis(3-aminopropyl)ethylenediamine as candidates for PET imaging of the heart with (68)Ga.

Species dependence of [64Cu]Cu-Bis(thiosemicarbazone) radiopharmaceutical binding to serum albumins.

INTRODUCTION: Interactions of three copper(II) bis(thiosemicarbazone) positron emission tomography radiopharmaceuticals with human serum albumin, and the serum albumins of four additional mammalian species, were evaluated. METHODS: 64Cu-labeled diacetyl bis(N4-methylthiosemicarbazonato)copper(II) (Cu-ATSM), pyruvaldehyde bis(N4-methylthiosemicarbazonato)copper(II) (Cu-PTSM) and ethylglyoxal bis(thiosemicarbazonato)copper(II) (Cu-ETS) were synthesized and their binding to human, canine, rat, baboon and porcine serum albumins quantified by ultrafiltration. Protein binding was also measured for each tracer in human, porcine, rat and mouse serum. RESULTS: The interaction of these neutral, lipophilic copper chelates with serum albumin is highly compound- and species-dependent. Cu-PTSM and Cu-ATSM exhibit particularly high affinity for human serum albumin (HSA), while the albumin binding of Cu-ETS is relatively insensitive to species. At HSA concentrations of 40 mg/ml, "% free" (non-albumin-bound) levels of radiopharmaceutical were 4.0+/-0.1%, 5.3+/-0.2% and 38.6+/-0.8% for Cu-PTSM, Cu-ATSM and Cu-ETS, respectively. CONCLUSIONS: Species-dependent variations in radiopharmaceutical binding to serum albumin may need to be considered when using animal models to predict the distribution and kinetics of these compounds in humans.

Assessment of Cu-ETS as a PET radiopharmaceutical for evaluation of regional renal perfusion.

UNLABELLED: The copper(II) complex of ethylglyoxal bis(thiosemicarbazone) (Cu-ETS) was evaluated as a positron emission tomography (PET) radiopharmaceutical for assessment of regional renal perfusion. METHODS: The concordance of renal flow estimates obtained with 11- and 15-microm microspheres was confirmed in four immature farm pigs using co-injected (46)Sc- and (57)Co-microspheres administered into the left ventricle. With the use of both immature farm pigs (n=3) and mature Göttingen minipigs (n=6), regional renal radiocopper uptake following intravenous [(64)Cu]Cu-ETS administration was compared to microsphere measurements of renal perfusion. The distribution and kinetics of [(64)Cu]Cu-ETS were further studied by PET imaging of the kidneys. The rate of [(64)Cu]Cu-ETS decomposition by blood was evaluated in vitro, employing octanol extraction to recover intact [(64)Cu]Cu-ETS. RESULTS: The co-injected 11- and 15-microm microspheres provided similar estimates of renal flow. A linear relationship was observed between the renal uptake of intravenous [(64)Cu]Cu-ETS and regional renal perfusion measured using microspheres. [(64)Cu]Cu-ETS provided high-quality PET kidney images demonstrating the expected count gradient from high-flow outer cortex to low-flow medulla. When incubated with pig blood in vitro at 37 degrees C, the [(64)Cu]Cu-ETS radiopharmaceutical was observed to decompose with a half-time of 2.8 min. CONCLUSION: Cu-ETS appears suitable for use as a PET radiopharmaceutical for evaluation of regional renal perfusion, affording renal uptake of radiocopper that varies linearly with microsphere perfusion measurements. Quantification of renal perfusion (in ml min(-1) g(-1)) with [(60,61,62,64)Cu]Cu-ETS will require correcting the arterial input function for the fraction of blood radiocopper remaining present as the intact Cu-ETS radiopharmaceutical, since the Cu-ETS chelate has limited chemical stability in blood. Rapid octanol extraction of blood samples appears suitable as an approach to capturing the actual blood concentration of [(60/61/62/64)Cu]Cu-ETS.

Estimation of radiation dosimetry for 68Ga-HBED-CC (PSMA-11) in patients with suspected recurrence of prostate cancer.

INTRODUCTION: This study was performed to estimate the human radiation dosimetry for [68Ga]Ga-HBED-CC (PSMA-11) (68Ga PSMA-11). METHODS: Under an RDRC-approved research protocol, we evaluated the biodistribution and pharmacokinetics of 68Ga PSMA-11 with serial PET imaging following intravenous administration to nine prostate cancer patients in whom clinical [11C]acetate PET/CT exams had been independently performed under Expanded Access IND 118,204. List-mode imaging was performed over the initial 0-10min post-injection with the pelvis in the field-of-view. Whole-body images were acquired, pelvis-to-head, at 15, 60, and 90-min post-injection. Additional images of the pelvis were acquired at 40-min and 115-min, and voided urine collected from each subject at 48-min and 120-min post-injection. Radiation dosimetry estimates were calculated from these data using the OLINDA software package. RESULTS: Renal uptake was high and relatively invariant, ranging from 11% to 14% of the injected dose between 15 and 90-min post-injection. Radioactivity collected in the voided urine accounted for 14% of the injected dose over a period of 120-min. Lymph nodes and skeletal metastases suspicious for prostate cancer recurrence were detected in a greater number of patients using 68Ga PSMA-11 than using 11C-acetate. CONCLUSION: Kidneys are the critical organ following 68Ga PSMA-11 administration, receiving an estimated dose of 0.413mGy/MBq. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: This study confirms that the kidneys will be the critical organ following intravenous administration of 68Ga PSMA-11, and provided data consistent with the expectation that 68Ga PSMA-11 will be superior to [11C]acetate for defining sites of recurrence in prostate cancer patients presenting with biochemical relapse.

Experience in production of (68)Ga-DOTA-NOC for clinical use under an Expanded Access IND.

[(68)Ga]Ga-DOTA-NOC was produced under an Expanded Access IND for 174 clinical PET/CT studies to evaluate patients with neuroendocrine tumors. Production employed either the TiO2-based Eckert & Ziegler (EZAG) (68)Ge/(68)Ga-generator (with fractionated elution), or the SiO2-based ITG (68)Ge/(68)Ga-generator. In both cases, [(68)Ga]Ga-DOTA-NOC was reliably produced, without pre-synthesis purification of the(68)Ga generator eluate, using readily-implemented manual synthesis procedures. [(68)Ga]Ga-DOTA-NOC radiochemical purity averaged 99.2±0.4%. Administered (68)Ga dose averaged 181±22 MBq, and administered peptide mass averaged 43.2±5.2µg (n=47) and 23.9±5.7µg (n=127), respectively, using the EZAG and ITG generators. At dose expiration, (68)Ge breakthrough in the final product averaged 2.7×10(-7)% and 5.4×10(-5%) using the EZAG and ITG generators, respectively.

Whole-body PET/CT evaluation of tumor perfusion using generator-based 62Cu-ethylglyoxal bis(thiosemicarbazonato)copper(II): validation by direct comparison to 15O-water in metastatic renal cell carcinoma.

UNLABELLED: This study was undertaken to demonstrate the feasibility of whole-body (62)Cu-ethylglyoxal bis(thiosemicarbazonato)copper(II) ((62)Cu-ETS) PET/CT tumor perfusion imaging in patients with metastatic renal carcinoma and to validate (62)Cu-ETS as a quantitative marker of tumor perfusion by direct comparison with (15)O-water perfusion imaging. METHODS: PET/CT imaging of 10 subjects with stage IV renal cell cancer was performed after intravenous administration of (15)O-water (10-min dynamic list-mode study) with the heart and at least 1 tumor in the PET field of view, followed 10 min later by intravenous (62)Cu-ETS (6-min list-mode study). Whole-body (62)Cu imaging was then performed from 6 to 20 min at 2-3 min/bed position. Blood flow (K1) was quantified with both agents for normal and malignant tissues in the 21.7-cm dynamic field of view. The required arterial input functions were derived from the left atrium and, in the case of (62)Cu-ETS, corrected for partial decomposition of the agent by blood with data from an in vitro analysis using a sample of each patient's blood. This imaging protocol was repeated at an interval of 3-4 wk after initiation of a standard clinical treatment course of the antiangiogenic agent sunitinib. RESULTS: All subjects received the scheduled (62)Cu-ETS doses for the dynamic and subsequent whole-body PET/CT scans, but technical issues resulted in no baseline (15)O-water data for 2 subjects. Direct comparisons of the perfusion estimates for normal tissues and tumor metastases were made in 18 paired baseline and treatment studies (10 subjects; 8 baseline studies, 10 repeated studies during treatment). There was an excellent correlation between the blood flow estimates made with (62)Cu-ETS and (15)O-water for normal tissues (muscle, thyroid, myocardium) and malignant lesions (pulmonary nodules, bone lesions); the regression line was y = 0.85x + 0.15, R(2) = 0.83, for the 88 regions analyzed. CONCLUSION: (62)Cu-ETS provided high-quality whole-body PET/CT images, and (62)Cu-ETS measures of blood flow were highly and linearly correlated with (15)O-water-derived K1 values (mL(-1) ⋅ min(-1) ⋅ g). This tracer is suitable for use as a PET tracer of tumor perfusion in patients with metastatic renal cell carcinoma.

Folate-receptor-targeted radionuclide imaging agents.

The cell-membrane folate receptor is a potential molecular target for tumor-selective drug delivery, including delivery of radiolabeled folate-chelate conjugates for diagnostic imaging. This review surveys the growing literature on tumor imaging with radionuclide agents targeted to the folate receptor. Successful folate-receptor targeting has been reported, both in vitro and in vivo, using a variety of radionuclides that are suitable for clinical diagnostic imaging (67Ga, 111In, 99mTc, 66Ga, and 64Cu). While none of these agents has, to date, been demonstrated to have clinical efficacy as a diagnostic tool, existing data indicates that it is feasible to noninvasively assess (at least qualitatively) tissue folate receptor levels by external radionuclide imaging.

Evaluation of 111In-DTPA-folate as a receptor-targeted diagnostic agent for ovarian cancer: initial clinical results.

UNLABELLED: The cell-membrane folate receptor is a potential molecular target for tumor-selective drug delivery, including radiolabeled folate-chelate conjugates for diagnostic imaging. We report here the initial clinical study of such an agent, (111)In-diethylenetriaminepentaacetic acid (DTPA)-folate, evaluated for diagnosis of ovarian malignancy. METHODS: Thirty-five women were enrolled in a phase I/II clinical study, with 33 completing the surgical follow-up required by the study protocol for definition of disease status. Patients either had a pathologically proven malignancy or were scheduled for surgery for suspected new ovarian cancer (n = 26), recurrent ovarian cancer (n = 5), or endometrial cancer (n = 2). (111)In-DTPA-folate was administered as an intravenous bolus, and whole-body images were obtained at 30 min, 4 h, and (for the first 19 patients) 24 h after injection; SPECT also was done at the delayed imaging times. For 19 of the patients, unlabeled free folic acid was injected before administration of (111)In-DTPA-folate to also assess the impact of folate loading on tracer biodistribution. Masked and unmasked readings of the images by 2 nuclear medicine physicians were compared with the pathologic findings after surgery. RESULTS: Among 33 patients who had surgical intervention, 14 had new or recurrent malignant tumors. All of 7 newly diagnosed ovarian carcinomas were identified by both masked readers (sensitivity, 100%). The sensitivity for detection of 7 recurrent malignancies was 38% for masked readings and 85% for unmasked readings, indicating that correlation with anatomic imaging studies (CT) was highly important in diagnosis of these lesions. Eighteen of the studied patients were found to have benign masses; for this limited population, the specificity of (111)In-DTPA-folate scintigraphy was 76% and 82% for the masked and unmasked analyses, respectively. CONCLUSION: (111)In-DTPA-folate is safe, and possibly effective, for scintigraphy differentiating between malignant and benign ovarian masses.

The folate receptor as a molecular target for tumor-selective radionuclide delivery.

The cell-membrane folate receptor is a potential molecular target for tumor-selective drug delivery, including radiolabeled folate-chelate conjugates for diagnostic imaging. We review here some background on the folate receptor as tumor-associated molecular target for drug delivery, and briefly survey the literature on tumor-targeting with radiolabeled folate-chelate conjugates.

Synthesis and evaluation of 99mTc(CO)(3)-DTPA-folate as a folate-receptor-targeted radiopharmaceutical.

A folate-receptor-targeted 99mTc-radiopharmaceutical, [99mTc]Tc(CO)(3)DTPA-folate, was prepared by heating [99mTc]Tc(CO)(3)(H(2)O)(3)(+) in an aqueous solution of the previously reported DTPA-folate conjugate. The radiotracer was HPLC purified (> 98% radiochemical purity) and evaluated in vitro and in vivo as an agent for targeting folate-receptor-positive cells. [99mTc]Tc(CO)(3)DTPA-folate experienced high, folate-receptor-specific uptake in human KB tumor cells. Intravenous administration of [99mTc]Tc(CO)(3)DTPA-folate to athymic mice bearing KB cell tumor xenografts resulted in 99mTc tumor uptake of 1.8 +/- 0.5 and 3.3 +/- 0.2%ID/g (n = 3) at 30 minutes and 4 hours post-injection, respectively. Tumor uptake was reduced when folic acid was co-administered with the intravenous [99mTc]Tc(CO)(3)DTPA-folate, consistent with radiopharmaceutical localization being mediated by the folate receptor.

Preparation of 66Ga- and 68Ga-labeled Ga(III)-deferoxamine-folate as potential folate-receptor-targeted PET radiopharmaceuticals.

A folate-receptor-targeting radiopharmaceutical, Ga(III)-deferoxamine-folate (Ga-DF-Folate), was radiolabeled with two positron-emitting isotopes of gallium, cyclotron-produced (66)Ga (9.5 hour half-life) and generator-produced (68)Ga (68 minute half-life). The [(66)Ga]Ga-DF-Folate was administered to athymic mice with folate-receptor-positive human KB cell tumor xenografts to demonstrate that microPET mouse tumor imaging is feasible with (66)Ga, despite the relatively high positron energy of this radionuclide. Using the athymic mouse KB tumor xenograft model, dual-isotope autoradiography was also performed following i.v. co-administration of [(18)F]-FDG, a marker of regional metabolic activity, and folate-receptor-targeted [(111)In]In-DTPA-Folate. The autoradiographic images of 1 mm tumor sections demonstrate the gross heterogeneity of the KB cell tumor xenograft, as well as subtle disparity in the regional accumulation of the two radiotracers.

Elucidation of the human serum albumin (HSA) binding site for the Cu-PTSM and Cu-ATSM radiopharmaceuticals.

The Cu-PTSM (pyruvaldehyde bis(N(4)-methylthiosemicarbazonato)copper(II)) and Cu-ATSM (diacetyl bis(N(4)-methylthiosemicarbazonato)copper(II)) radiopharmaceuticals exhibit strong, species-dependent binding to human serum albumin (HSA), while Cu-ETS (ethylglyoxal bis(thiosemicarbazonato)copper(II)) appears to only exhibit nonspecific binding to human and animal serum albumins. This study examines the structural basis for HSA binding of Cu-PTSM and Cu-ATSM via competition with drugs having known albumin binding sites. Warfarin, furosemide, ibuprofen, phenylbutazone, benzylpenicillin, and cephmandole were added to HSA solutions at drug:HSA mole ratios from 0 to 8:1, followed by quantification of radiopharmaceutical binding to HSA by ultrafiltration. Warfarin, a site IIA drug, progressively displaced both [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM from HSA. At 8:1 warfarin:HSA mole ratios, free [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM levels increased 300-500%. This was in contrast to solutions containing ibuprofen, a site IIIA drug; no increase in free [(64)Cu]Cu-PTSM or [(64)Cu]Cu-ATSM was observed except at high ibuprofen:HSA ratios, where secondary ibuprofen binding to the IIA site may cause modest radiopharmaceutical displacement. By contrast, and consistent with earlier findings suggesting Cu-ETS exhibits only nonspecific associations, [(64)Cu]Cu-ETS binding to HSA was unaffected by the addition of drugs that bind in either site. We conclude that the species-dependence of Cu-PTSM and Cu-ATSM albumin binding arises from interaction(s) with the IIA site of HSA.

A convenient route to [68Ga]Ga-MAA for use as a particulate PET perfusion tracer.

A convenient method is described for compounding [(68)Ga]Ga-MAA (MAA=macroaggregated human serum albumin) with the eluate of a commercially available TiO(2)-based (68)Ge/(68)Ga generator. The final [(68)Ga]Ga-MAA product was obtained with an 81.6+/-5.3% decay-corrected radiochemical yield and a radiochemical purity of 99.8+/-0.1% (n=5). Microscopic examination showed the [(68)Ga]Ga-MAA product to remain within the original particle size range. The entire procedure, from generator elution to delivery of the final [(68)Ga]Ga-MAA suspension, could be completed in 25 min. Only 4.4+/-0.9% of the total (68)Ge breakthrough remaining associated with the final [(68)Ga]Ga-MAA product. The procedure allows reasonably convenient preparation of [(68)Ga]Ga-MAA in a fashion that can be readily adapted to sterile product compounding for human use.

Targeting the tumor-associated folate receptor with an 111In-DTPA conjugate of pteroic acid.

The cell membrane folate receptor is a potential molecular target for tumor-selective drug delivery. To probe structural requirements for folate receptor targeting with low molecular weight radiometal chelates, specifically the role of the amino acid fragment of folic acid (pteroylglutamic acid) in mediating targeting selectivity, the amide-linked conjugate pteroyl-NHCH(2)CH(2)OCH(2)CH(2)OCH(2)CH(2)NH-DTPA was prepared by a three-step procedure from pteroic acid, 2,2'-(ethylenedioxy)-bis(ethylamine), and t-Bu-protected DTPA. This conjugate, 1-{2-[2-[(2-(biscarboxymethyl-amino)ethyl)-carboxymethyl-amino]ethyl]-carboxymethyl-amino}-acetylamino-3,6-dioxa-8-pteroylamino-octane (1), was employed for synthesis of the corresponding (111)In(III) radiopharmaceutical. Following intravenous administration to athymic mice, the (111)In complex of 1 was found to selectively localize in folate receptor-positive human KB tumor xenografts and to afford prolonged tumor retention of the (111)In radiolabel (5.4 +/- 0.8, 5.6 +/- 1.1, and 3.6 +/- 0.6% of the injected dose per gram of tumor at 1, 4, and 24 h, respectively). The observed tumor localization was effectively blocked by co-administration of folic acid with the (111)In-1 complex, consistent with a folate receptor-mediated targeting process. In control studies, tumor targeting with this pteroic acid conjugate appears as effective as that seen using (111)In-DTPA-folate, a radiopharmaceutical that has progressed to clinical trials for detection of folate receptor-expressing gynecological tumors.