Description: Disulfiram has been used for several decades in the treatment of alcoholism. It now shows promise as an anticancer drug and radiosensitizer. Proposed mechanisms of action include the induction of oxidative stress and inhibition of proteasome activity. Our purpose was to determine the potential of disulfiram to enhance the antitumor efficacy of external-beam -irradiation and 131 I-metaiodobenzylguanidine ( 131 I-MIBG), a radiopharmaceutical used for the therapy of neuroendocrine tumors. Methods: The role of copper in disulfiram-induced toxicity was investigated by clonogenic assay after treatment of human SK-N-BE(2c) neuroblastoma and UVW/noradrenaline transporter (NAT) glioma cells. The synergistic interaction between disulfiram and radiotherapy was evaluated by combination-index analysis. Tumor growth delay was determined in vitro using multicellular tumor spheroids and in vivo using human tumor xenografts in athymic mice. Results: Escalating the disulfiram dosage caused a biphasic reduction in the surviving fraction of clonogens. Clonogenic cell kill after treatment with disulfiram concentrations less than 4 μM was copper-dependent, whereas cytotoxicity at concentrations greater than 10 μM was caused by oxidative stress. The cytotoxic effect of disulfiram was maximal when administered with equimolar copper. Likewise, disulfiram radiosensitization of tumor cells was copper-dependent. Furthermore, disulfiram treatment enhanced the toxicity of 131 I-MIBG to spheroids and xenografts expressing the noradrenaline transporter. Conclusion: The results demonstrate that the cytotoxicity of disulfiram was copper-dependent, the molar excess of disulfiram relative to copper resulted in attenuation of disulfiram-mediated cytotoxicity, copper was required for the radiosensitizing activity of disulfiram, and copper-complexed disulfiram enhanced the efficacy not only of external-beam radiation but also of targeted radionuclide therapy in the form of 131 I-MIBG. Therefore, disulfiram may have anticancer potential in combination with radiotherapy.

Description: Radioactive ligands for the prostate-specific membrane antigen (PSMA) are under development for therapy of metastasized prostate cancer. Since PSMA expression is also found in the kidneys, renal tracer uptake can be dose-limiting. Because kidney kinetics differ from tumor kinetics, serial application of PSMA inhibitors such as 2-(phosphonomethyl)pentanedioic acid (PMPA) may improve the kidney-to-tumor ratio. In this study, we evaluated the effect of PMPA on the biodistribution of 2 promising PSMA ligands. Methods: Human prostate cancer xenografts (LNCaP) were transplanted subcutaneously into mice. After injection of 125 I-MIP1095, a 16-h latency period was allowed for tracer clearance from the blood and renal calices. After baseline scintigraphy, PMPA was injected in doses of 0.2–50 mg/kg ( n = 3 per dose, 5 controls), followed by scans at 2, 4, 6, and 24 h after PMPA injection. Kidney and tumor displacement was determined as a percentage of baseline. A shortened but similar design was used to evaluate the PSMA ligand MIP1404, which contains a chelate for 99m Tc/rhenium. Results: PMPA injection 16 h after MIP1095 translated into a rapid and quantitative relevant displacement of renal activity. Tumor uptake was reduced to a significantly lesser extent in a dose-dependent manner. PMPA doses of 0.2–1 mg/kg appear optimal for sustaining nearly complete tumor uptake while simultaneously achieving near-total blocking of specific renal PSMA binding. The effect was successfully validated with the PSMA ligand MIP1404. Conclusion: PSMA-targeted radionuclide therapy can benefit from serial PMPA comedication by reducing off-target radiation to the kidneys. These data will be used for a first approximation in clinical translation, although in patients an optimization of the dose and time schedule may be necessary.

Description: Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer, and small-molecule radiopharmaceuticals targeting PSMA rapidly detect the location and extent of disease. Here we evaluated preclinically 4 novel 99m Tc-labeled small-molecule inhibitors of PSMA with the potential for clinical translation for molecular imaging of prostate cancer in humans. Methods: Four PSMA inhibitors derived from the glutamate-urea-glutamate or glutamate-urea-lysine pharmacophores conjugated to CIM or TIM chelators were radiolabeled with 99m Tc and evaluated in vitro and in vivo. Results: High-affinity, saturable binding to PSMA on LNCaP cells was observed with K d values of 0.64 ± 0.46 nM for 99m Tc-MIP-1427, 1.07 ± 0.89 nM for 99m Tc-MIP-1404, 1.75 ± 0.32 nM for 99m Tc-MIP-1428, and 4.35 ± 0.35 nM for 99m Tc-MIP-1405. 99m Tc-labeled PSMA inhibitors did not bind human prostate cancer PC3 cells, which lack PSMA, demonstrating specificity, and binding was abolished with 2-(phosphonomethyl)pentanedioic acid (PMPA), a structurally unrelated PSMA inhibitor. 99m Tc-labeled PSMA inhibitors were shown to internalize at 37°C. Uptake in LNCaP xenografts ranged from 9.3% to 12.4% injected dose per gram at 1 h after injection and from 7.2% to 11.0% at 4 h, with tumor-to-blood ratios ranging from 29:1 to 550:1 and tumor–to–skeletal muscle ratios ranging from 31:1 to 157:1 at 4 h. 99m Tc-MIP-1404 exhibited the best combination of high tumor uptake and rapid clearance from kidney and nontarget tissues. 99m Tc-MIP-1404 specifically bound to PSMA in vivo as demonstrated by the absence of uptake in PC3 xenografts and by competition with PMPA. SPECT/CT imaging corroborated the tissue distribution results, demonstrating uptake only in PSMA-expressing kidney and tumor tissue and clearance through the urinary bladder. Conclusion: These 99m Tc-labeled radiopharmaceuticals targeting PSMA may provide a SPECT molecular imaging option to assist in the initial diagnosis of prostate cancer and the management of patient care by monitoring disease progression.

Description: The performance of cytotoxic drugs is defined by their selectivity of uptake and action in tumor tissue. Recent clinical responses achieved by treating metastatic malignant melanoma with therapeutic modalities based on gene expression profiling showed that malignant melanoma is amenable to systemic treatment. However, these responses are not persistent, and complementary targeted treatment strategies are required for malignant melanoma. Methods: Here we provide our experience with different labeling procedures for the radioiodination of benzamides and report on initial dosimetry data and the first therapeutic application of 131 I-BA52, a novel melanin-binding benzamide in patients with metastatic malignant melanoma. Twenty-six adults with histologically documented metastasized malignant melanoma received a single dose of 235 ± 62 MBq of 123 I-BA52 for planar and SPECT/CT imaging. Nine patients were selected for radionuclide therapy and received a median of 4 GBq (minimum, 0.51 GBq; maximum, 6.60 GBq) of the β-emitting radiopharmaceutical 131 I-BA52. Results: A trimethyltin precursor–based synthesis demonstrated high radiochemical yields in the large-scale production of radioiodinated benzamides required for clinical application. 123 I-BA52 showed specific uptake and long-term retention in tumor tissue with low transient uptake in the excretory organs. In tumor tissue, a maximum dose of 12.2 Gy per GBq of 131 I-BA52 was calculated. The highest estimated dose to a normal organ was found for the lung (mean, 3.1 Gy/GBq). No relevant acute or mid-term toxicity was observed with the doses administered until now. Even though dosimetric calculations reveal that the doses applied in this early phase of clinical application can be significantly increased, we observed antitumor effects with follow-up imaging, and single patients of the benzamide-positive cohort of patients (3/5 of the patients receiving a dose 〉 4.3 GBq) demonstrated a surprisingly long survival of more than 2 y. Conclusion: These data indicate that systemic radionuclide therapy using 131 I-BA52 as a novel approach for the therapy of malignant melanoma is of considerable potential. Future trials should be done to enhance the precision of dosimetry, validate the maximum tolerable dose, and evaluate the effectiveness of the treatment in a prospective manner.

Description: Prostate-specific membrane antigen (PSMA)–targeted radiotherapy of prostate cancer (PCa) has emerged recently as a promising approach to the treatment of disseminated disease. A small number of ligands have been evaluated in patients, and although early tumor response is encouraging, relapse rate is high and these compounds localize to the parotid, salivary, and lacrimal glands as well as to the kidney, leading to dose-limiting toxicities and adverse events affecting quality of life. We envision that dual-target binding ligands displaying high affinity for PSMA and appropriate affinity for human serum albumin (HSA) may demonstrate a higher therapeutic index and be suitable for treatment of PCa by targeted α-therapy. Methods: Six novel urea-based ligands with varying affinities for PSMA and HSA were synthesized, labeled with 131 I, and evaluated by in vitro binding and uptake assays in LNCaP cells. Four compounds were advanced for further evaluation in a preclinical model of PCa. The compounds were compared with MIP-1095, a PSMA ligand currently in clinical evaluation. Results: The compounds demonstrated affinity for PSMA on the order of 4–40 nM and affinity for HSA in the range of 1–53 μM. Compounds with relatively high affinity for HSA (≤2 μM) showed high and sustained blood-pool activity and reduced uptake in the kidneys. 131 I-RPS-027, with a 50% inhibitory concentration (PSMA) of 15 nM and a dissociation constant (HSA) of 11.2 μM, cleared from the blood over the course of 48 h and showed good tumor uptake (10 percentage injected dose per gram) and retention and a greater than 5-fold decrease in kidney uptake relative to MIP-1095. The tumor-to-kidney ratio of 131 I-RPS-027 was greater than 3:1 at 24 h after injection, increasing to 7:1 by 72 h. Conclusion: RPS-027 shows dual targeting to PSMA and albumin, resulting in a high tumor uptake, highly favorable tissue distribution, and promising therapeutic profile in a preclinical model of prostate cancer. In comparison to existing ligands proposed for targeted therapy of prostate cancer, RPS-027 has tumor-to-tissue ratios that predict a significant reduction in side effects during therapy. Using iodine/radioiodine as a surrogate for the radiohalogen 211 At, we therefore propose dual-target binding ligands such as RPS-027 as next-generation radiopharmaceuticals for targeted α-therapy using 211 At.

Description: This phase 1 study was performed to determine the pharmacokinetics and ability to visualize prostate cancer in bone, soft-tissue, and the prostate gland using 123 I-MIP-1072 and 123 I-MIP-1095, novel radiolabeled small molecules targeting prostate-specific membrane antigen. Methods: Seven patients with a documented history of prostate cancer by histopathology or radiologic evidence of metastatic disease were intravenously administered 370 MBq (10 mCi) of 123 I-MIP-1072 and 123 I-MIP-1095 2 wk apart in a crossover trial design. 123 I-MIP-1072 was also studied in 6 healthy volunteers. Whole-body planar and SPECT/CT imaging was performed and pharmacokinetics studied over 2–3 d. Target-to-background ratios were calculated. Absorbed radiation doses were estimated using OLINDA/EXM. Results: 123 I-MIP-1072 and 123 I-MIP-1095 visualized lesions in soft tissue, bone, and the prostate gland within 0.5–1 h after injection, with retention beyond 48 h. Target-to-background ratios from planar images averaged 2:1 at 1 h, 3:1 at 4–24 h, and greater than 10:1 at 4 and 24 h for SPECT/CT. Both agents cleared the blood in a biphasic manner; clearance of 123 I-MIP-1072 was approximately 5 times faster. 123 I-MIP-1072 was excreted in the urine, with 54% and 74% present by 24 and 72 h, respectively. In contrast, only 7% and 20% of 123 I-MIP-1095 had been renally excreted by 24 and 72 h, respectively. Estimated absorbed radiation doses were 0.054 versus 0.110 mGy/MBq for the kidneys and 0.024 versus 0.058 mGy/MBq for the liver, for 123 I-MIP-1072 and 123 I-MIP-1095, respectively. Conclusion: 123 I-MIP-1072 and 123 I-MIP-1095 detect lesions in soft tissue, bone, and the prostate gland at as early as 1–4 h. These novel radiolabeled small molecules have excellent pharmacokinetic and pharmacodynamic profiles and warrant further development as diagnostic and potentially when labeled with 131 I therapeutic radiopharmaceuticals.

Description: A first-in-human phase 1 clinical study was performed on 12 healthy adults with a high-specific-activity carrier-free formulation of 123 I-iobenguane. Clinical data are presented on the behavior of this receptor-targeting imaging agent. Methods: Whole-body and thoracic planar and SPECT imaging were performed over 48 h for calculation of tissue radiation dosimetry and for evaluation of clinical safety and efficacy. Results: A reference clinical imaging database acquired over time for healthy men and women injected with high-specific-activity 123 I-iobenguane showed organ distribution and whole-body retention similar to those of conventional 123 I-iobenguane. The heart-to-mediastinum ratios for the high-specific-activity formulation were statistically higher than for conventional formulations, and the predicted radiation dosimetry estimations for some organs varied significantly from those based on animal distributions. Conclusion: Human normal-organ kinetics, radiation dosimetry, clinical safety, and imaging efficacy provide compelling evidence for the use of high-specific-activity 123 I-iobenguane.

Description: Prostate-specific membrane antigen (PSMA) is a well-established target for developing radiopharmaceuticals for imaging and therapy of prostate cancer (PCa). We have recently reported that novel 99m Tc-labeled small-molecule PSMA inhibitors bind with high affinity to PSMA-positive tumor cells in vitro and localize in PCa xenografts. This study reports the first, to our knowledge, human data in men with metastatic PCa and in healthy male subjects. Methods: Under an exploratory investigational new drug, using a cross-over design, we compared the pharmacokinetics, biodistribution, and tumor uptake of 99m Tc-MIP-1404 and 99m Tc-MIP-1405 in 6 healthy men and 6 men with radiographic evidence of metastatic PCa. Whole-body images were obtained at 10 min and 1, 2, 4, and 24 h. SPECT was performed between 3 and 4 h after injection. Results: Both agents cleared the blood rapidly, with MIP-1404 demonstrating significantly lower urinary activity (7%) than MIP-1405 (26%). Both agents showed persistent uptake in the salivary, lacrimal, and parotid glands. Uptake in the liver and kidney was acceptable for imaging at 1–2 h. In men with PCa, both agents rapidly localized in bone and lymph node lesions as early as 1 h. SPECT demonstrated excellent lesion contrast. Good correlation was seen with bone scanning; however, more lesions were demonstrated with 99m Tc-MIP-1404 and 99m Tc-MIP-1405. The high-contrast images exhibited tumor-to-background ratios from 3:1 to 9:1 at 4 and 20 h. Conclusion: Compared with the standard-of-care bone scanning, 99m Tc-MIP-1404 and 99m Tc-MIP-1405 identified most bone metastatic lesions and rapidly detected soft-tissue PCa lesions including subcentimeter lymph nodes. Because 99m Tc-MIP-1404 has minimal activity in the bladder, further work is planned to correlate imaging findings with histopathology in patients with high-risk metastatic PCa.

Description: Key issues for prostate cancer patients are the detection of recurrent disease and the treatment of metastasized cancer. Early detection is a major challenge for all conventional imaging modalities. Furthermore, therapy of patients with hormone-resistant tumor lesions presents a major clinical challenge. Because the prostate-specific membrane antigen (PSMA) is frequently overexpressed in prostate cancer, several PSMA-targeting molecules are under development to detect and treat metastatic castration-resistant prostate cancer (mCRPC). mCRPC represents a situation where cure is no longer achievable and novel therapeutic approaches for palliation and increase of survival are needed. In this article, we discuss the recent development for noninvasive detection of recurrent disease and therapy of mCRPC with corresponding PSMA-targeted radioligands. Clin Cancer Res; 22(1); 9–15. ©2016 AACR .

Description: A good-manufacturing-practices (GMP) 68 Ge/ 68 Ga generator that uses modified dodecyl-3,4,5-trihydroxybenzoate hydrophobically bound to a octadecyl silica resin (C-18) as an adsorbent has been developed that allows for dilute HCl (0.05N) to efficiently elute metal-impurity-free 68 Ga 3+ ready for peptide labeling. We characterized the performance of this generator system over a year in conjunction with the production of 68 Ga-labeled DOTATOC and Glu-NH-CO-NH-Lys(Ahx)-HBED-CC (PSMA-HBED-CC) intended for clinical studies and established protocols for batch release. Methods: A 2,040-MBq self-shielded 68 Ge/ 68 Ga generator provided metal-free 68 GaCl 3 ready for peptide labeling in the fluidic labeling module after elution with 4 mL of 0.05N HCl. The compact system was readily housed in a laminar flow cabinet allowing an ISO class-5 environment. 68 Ga labeling of peptides using GMP kits was performed in 15–20 min, and the total production time was 45–50 min. Batch release quality control specifications were established to meet investigational new drug submission and institutional review board approval standards. Results: Over a period of 12 mo, 68 Ga elution yields from the generator averaged 80% (range, 72.0%–95.1%), and 68 Ge breakthrough was less than 0.006%, initially decreasing with time to 0.001% (expressed as percentage of 68 Ge activity present in the generator at the time of elution), a unique characteristic of this generator. The radiochemical purity of both 68 Ga-DOTATOC and 68 Ga-PSMA-HBED-CC determined by high-performance liquid chromatography analysis was greater than 98%, with a minimum specific activity of 12.6 and 42 GBq/μmol, respectively. The radionuclidic ( 68 Ge) impurity was 0.00001% or less (under the detection limit). Final sterile, pyrogen-free formulation was provided in physiologic saline with 5%–7% ethanol. Conclusion: The GMP-certified 68 Ge/ 68 Ga generator system was studied for a year. The generator system is contained within the fluidic labeling module, and it is compact, self-shielded, and easy to operate using simple manual techniques. The system provides radiolabeled peptides with high (〉98%) radiochemical purity and greater than 80% radiochemical yield. The 68 Ge levels in the final drug products were under the detection limits at all times. 68 Ga-DOTATOC and 68 Ga-PSMA-HBED-CC investigational radiopharmaceuticals are currently being studied clinically under investigational new drug (IND) applications submitted to the U.S. Food and Drug Administration.