Dietary restriction (DR) extends lifespan and increases resistance to multiple forms of stress, including ischemia reperfusion injury to the brain and heart in rodents. While maximal effects on lifespan require long-term restriction, the kinetics of onset of benefits against acute stress are not known. Here we show that 2–4 weeks of 30% dietary restriction improved survival and kidney function following renal ischemia reperfusion injury in mice. Brief periods of water-only fasting were similarly effective at protecting against ischemic damage. Significant protection occurred within one day, persisted for several days beyond the fasting period and extended to another organ, the liver. Protection by both short-term DR and fasting correlated with improved insulin sensitivity, increased expression of markers of antioxidant defense and reduced expression of markers of inflammation and insulin/insulin-like growth factor-1 signaling. Unbiased transcriptional profiling of kidney from mice subject to short-term DR or fasting revealed a significant enrichment of signature genes of long-term DR. These data demonstrate that brief periods of reduced food intake, including short-term daily restriction and fasting, can increase resistance to ischemia reperfusion injury in rodents and suggest a rapid onset of benefits of DR in mammals.

The folate receptor (FR) has proven a valuable target for nuclear imaging using folic acid radioconjugates. However, using folatebased radiopharmaceuticals for therapy has long been regarded as an unattainable goal because of their considerable renal accumulation. Herein, we present a novel strategy in which a DOTA-folate conjugate with an albumin-binding entity (cm09) was designed with the aim of prolonging circulation in the blood and therewith potentially improving tumor-to-kidney ratios. Methods: The folate conjugate cm09 was radiolabeled with 177 LuCl 3 , and stability experiments were performed in plasma. Cell uptake studies were performed on FR-positive KB tumor cells, and an ultrafiltration assay was used to determine the plasma protein-binding properties of 177 Lu-cm09. In vivo, 177 Lu-cm09 was tested in KB tumor-bearing mice using SPECT/CT. The therapeutic anticancer effect of 177 Lu-cm09 (20 MBq) applied as a single injection or as fractionated injections was investigated in different groups of mice (n 5 5) by monitoring tumor size and the survival time of treated mice, compared with untreated controls. Results: Compound cm09 was radiolabeled at a specific activity of 40 MBq/nmol, a radiochemical yield of more than 98%, and a stability of more than 99% over 5 d in plasma. Ultrafiltration revealed significant binding of 177 Lu-cm09 to serum proteins (;91%) in plasma, compared with folate radioconjugate without an albumin-binding entity. Cell uptake and internalization of 177 Lu-cm09 was FR-specific and comparable to other folate radioconjugates. In vivo studies resulted in high tumor uptake (17.56 percentage injected dose per gram [%ID/g] at 4 h after injection), which was almost completely retained for at least 72 h. Renal accumulation was significantly reduced (28 % ID/g at 4 h after injection), compared with folate conjugates that lack an albumin-binding entity (;70 %ID/g at 4 h after injection). These circumstances enabled SPECT imaging of excellent quality. Radionuclide therapy (1 · 20 MBq) revealed complete remission of tumors in 4 of 5 cases and a significantly prolonged survival time, compared with untreated controls. Conclusion: The modification of a folate radioconjugate with an albuminbinding entity resulted in a significant increase of the tumor-tokidney ratio of radioactivity, enabling for the first time, to our knowledge, the preclinical application of folic acid-targeted radionuclide therapy in mice.

BackgroundThe targeting of the prostate-specific membrane antigen (PSMA) is of particular interest for radiotheragnostic purposes of prostate cancer. Radiolabeled PSMA-617, a 1,4,7,10-tetraazacyclododecane-N,N′,N′′,N′′′-tetraacetic acid (DOTA)-functionalized PSMA ligand, revealed favorable kinetics with high tumor uptake, enabling its successful application for PET imaging (68Ga) and radionuclide therapy (177Lu) in the clinics. In this study, PSMA-617 was labeled with cyclotron-produced 44Sc (T 1/2 = 4.04 h) and investigated preclinically for its use as a diagnostic match to 177Lu-PSMA-617.Results 44Sc was produced at the research cyclotron at PSI by irradiation of enriched 44Ca targets, followed by chromatographic separation. 44Sc-PSMA-617 was prepared under standard labeling conditions at elevated temperature resulting in a radiochemical purity of >97% at a specific activity of up to 10 MBq/nmol. 44Sc-PSMA-617 was evaluated in vitro and compared to the 177Lu- and 68Ga-labeled match, as well as 68Ga-PSMA-11 using PSMA-positive PC-3 PIP and PSMA-negative PC-3 flu prostate cancer cells. In these experiments it revealed similar in vitro properties to that of 177Lu- and 68Ga-labeled PSMA-617. Moreover, 44Sc-PSMA-617 bound specifically to PSMA-expressing PC-3 PIP tumor cells, while unspecific binding to PC-3 flu cells was not observed. The radioligands were investigated with regard to their in vivo properties in PC-3 PIP/flu tumor-bearing mice. 44Sc-PSMA-617 showed high tumor uptake and a fast renal excretion. The overall tissue distribution of 44Sc-PSMA-617 resembled that of 177Lu-PSMA-617 most closely, while the 68Ga-labeled ligands, in particular 68Ga-PSMA-11, showed different distribution kinetics. 44Sc-PSMA-617 enabled distinct visualization of PC-3 PIP tumor xenografts shortly after injection, with increasing tumor-to-background contrast over time while unspecific uptake in the PC-3 flu tumors was not observed.ConclusionsThe in vitro characteristics and in vivo kinetics of 44Sc-PSMA-617 were more similar to 177Lu-PSMA-617 than to 68Ga-PSMA-617 and 68Ga-PSMA-11. Due to the almost four-fold longer half-life of 44Sc as compared to 68Ga, a centralized production of 44Sc-PSMA-617 and transport to satellite PET centers would be feasible. These features make 44Sc-PSMA-617 particularly appealing for clinical application.Electronic supplementary materialThe online version of this article (doi:10.1186/s13550-017-0257-4) contains supplementary material, which is available to authorized users.

The treatment of metastatic castration-resistant prostate cancer (mCRPC) remains challenging with current treatment options. The development of more effective therapies is, therefore, urgently needed. Targeted radionuclide therapy with prostate-specific membrane antigen (PSMA)-targeting ligands has revealed promising clinical results. In an effort to optimize this concept, it was the aim of this study to design and investigate PSMA ligands comprising different types of albumin binders. PSMA-ALB-53 and PSMA-ALB-56 were designed by combining the glutamate-urea-based PSMA-binding entity, a DOTA chelator and an albumin binder based on the 4-( p-iodophenyl)-moiety or p-(tolyl)-moiety. The compounds were labeled with Lu (50 MBq/nmol) resulting in radioligands of high radiochemical purity (≥98%). Both radioligands were stable (≥98%) over 24 h in the presence of l-ascorbic acid. The uptake into PSMA-positive PC-3 PIP tumor cells in vitro was in the same range (54-58%) for both radioligands; however,Lu-PSMA-ALB-53 showed a 15-fold enhanced binding to human plasma proteins. Biodistribution studies performed in PC-3 PIP/flu tumor-bearing mice revealed high tumor uptake of Lu-PSMA-ALB-53 andLu-PSMA-ALB-56, respectively, demonstrated by equal areas under the curves (AUCs) for both radioligands. The increased retention of Lu-PSMA-ALB-53 in the blood resulted in almost 5-fold lower tumor-to-blood AUC ratios when compared toLu-PSMA-ALB-56. Kidney clearance of Lu-PSMA-ALB-56 was faster, and hence, the tumor-to-kidney AUC ratio was 3-fold higher than in the case ofLu-PSMA-ALB-53. Due to the more favorable tissue distribution profile, Lu-PSMA-ALB-56 was selected for a preclinical therapy study in PC-3 PIP tumor-bearing mice. The tumor growth delay after application ofLu-PSMA-ALB-56 and Lu-PSMA-617 applied at the same activities (2 or 5 MBq per mouse) revealed better antitumor effects in the case ofLu-PSMA-ALB-56. As a consequence, the survival of mice treated with Lu-PSMA-ALB-56 was prolonged when compared to the mice, which received the same activity ofLu-PSMA-617. Our results demonstrated the superiority of Lu-PSMA-ALB-56 overLu-PSMA-ALB-53 indicating that the p-(tolyl)-moiety was more suited as an albumin binder to optimize the tissue distribution profile. Lu-PSMA-ALB-56 was more effective to treat tumors thanLu-PSMA-617 resulting in complete tumor remission in four out of six mice. This promising results warrant further investigations to assess the potential for clinical application of Lu-PSMA-ALB-56.

Based on the clinical success of platinum-based anti-cancer drugs, a variety of other metal-based anti-cancer compounds are being investigated.

In recent years, 47 Sc has attracted attention because of its favorable decay characteristics (half-life, 3.35 d; average energy, 162 keV; Eγ, 159 keV) for therapeutic application and for SPECT imaging. The aim of the present study was to investigate the suitability of 47 Sc for radionuclide therapy in a preclinical setting. For this purpose a novel DOTA-folate conjugate (cm10) with an albumin-binding entity was used. Methods: 47 Sc was produced via the 46 Ca(n,γ) 47 Ca! b − 47 Sc nuclear reaction at the high-flux reactor at the Institut Laue-Langevin. Separation of the 47 Sc from the target material was performed by a semi-automated process using extraction chromatography and cation exchange chromatography. 47 Sc-labeled cm10 was tested on folate receptor-positive KB tumor cells in vitro. Biodistribution and SPECT imaging experiments were performed in KB tumor-bearing mice. Radionuclide therapy was conducted with two groups of mice, which received either 47 Sc-cm10 (10 MBq) or only saline. Tumor growth and survival time were compared between the two groups of mice. Results: Irradiation of 46 Ca resulted in approximately 1.8 GBq of 47 Ca, which subsequently decayed to 47 Sc. Separation of 47 Sc from 47 Ca was obtained with 80% yield in only 10 min. The 47 Sc was then available in a small volume (∼500 μL) of an ammonium acetate/HCl (pH 4.5) solution suitable for direct radiolabeling. 47 Sc-cm10 was prepared with a radiochemical yield of more than 96% at a specific activity of up to 13 MBq/nmol. In vitro 47 Sccm10 showed folate receptor-specific binding and uptake into KB tumor cells. In vivo SPECT/CT images allowed the visualization of accumulated radioactivity in KB tumors and in the kidneys. The therapy study showed a significantly delayed tumor growth in mice, which received 47 Sc-cm10 (10 MBq, 10 Gy) resulting in a more than 50% increase in survival time, compared with untreated control mice. Conclusion: With this study, we demonstrated the suitability of using 47 Sc for therapeutic purposes. On the basis of our recent results obtained with 44 Sc-folate, the present work confirms the applicability of 44 Sc/ 47 Sc as an excellent matched pair of nuclides for PET imaging and radionuclide therapy.

The prostate-specific membrane antigen (PSMA) has emerged as an attractive prostate cancer associated target for radiotheragnostic application using PSMA-specific radioligands. The aim of this study was to design new PSMA ligands modified with an albumin-binding moiety in order to optimize their tissue distribution profile. The compounds were prepared by conjugation of a urea-based PSMA-binding entity, a DOTA chelator, and 4-( p-iodophenyl)butyric acid using multistep solid phase synthesis. The three ligands (PSMA-ALB-02, PSMA-ALB-05, and PSMA-ALB-07) were designed with varying linker entities. Radiolabeling with Lu was performed at a specific activity of up to 50 MBq/nmol resulting in radioligands of>98% radiochemical purity and high stability. In vitro investigations revealed high binding of all three PSMA radioligands to mouse (>64%) and human plasma proteins (>94%). Uptake and internalization into PSMA-positive PC-3 PIP tumor cells was equally high for all radioligands. Negligible accumulation was found in PSMA-negative PC-3 flu cells, indicating PSMA-specific binding of all radioligands. Biodistribution and imaging studies performed in PC-3 PIP/flu tumor-bearing mice showed enhanced blood circulation of the new radioligands when compared to the clinically employed Lu-PSMA-617. The PC-3 PIP tumor uptake of all three radioligands was very high (76.4 ± 2.5% IA/g, 79.4 ± 11.1% IA/g, and 84.6 ± 14.2% IA/g, respectively) at 24 h post injection (p.i.) resulting in tumor-to-blood ratios of ∼176, ∼48, and ∼107, respectively, whereas uptake into PC-3 flu tumors was negligible. Kidney uptake at 24 h p.i. was lowest forLu-PSMA-ALB-02 (10.7 ± 0.92% IA/g), while Lu-PSMA-ALB-05 andLu-PSMA-ALB-07 showed higher renal retention (23.9 ± 4.02% IA/g and 51.9 ± 6.34% IA/g, respectively). Tumor-to-background ratios calculated from values of the area under the curve (AUC) of time-dependent biodistribution data were in favor of Lu-PSMA-ALB-02 (tumor-to-blood, 46; tumor-to-kidney, 5.9) when compared toLu-PSMA-ALB-05 (17 and 3.7, respectively) and Lu-PSMA-ALB-07 (39 and 2.1, respectively). The high accumulation of the radioligands in PC-3 PIP tumors was visualized on SPECT/CT images demonstrating increasing tumor-to-kidney ratios over time. Taking all of the characteristics into account,Lu-PSMA-ALB-02 emerged as the most promising candidate. The applied concept may be attractive for future clinical translation potentially enabling more potent and convenient prostate cancer radionuclide therapy.

In recent years, implementation of 68 Ga-radiometalated peptides for PET imaging of cancer has attracted the attention of clinicians. Herein, we propose the use of 44 Sc (half-life 5 3.97 h, average b 1 energy [Eb 1 av ] 5 632 keV) as a valuable alternative to 68 Ga (half-life 5 68 min, Eb 1 av 5 830 keV) for imaging and dosimetry before 177 Lu-based radionuclide therapy. The aim of the study was the preclinical evaluation of a folate conjugate labeled with cyclotronproduced 44 Sc and its in vitro and in vivo comparison with the 177 Lulabeled pendant. Methods: 44 Sc was produced via the 44 Ca(p,n) 44 Sc nuclear reaction at a cyclotron (17.6 6 1.8 MeV, 50 mA, 30 min) using an enriched 44 Ca target (10 mg 44 CaCO 3 , 97.00%). Separation from the target material was performed by a semiautomated process using extraction chromatography and cation exchange chromatography. Radiolabeling of a DOTA-folate conjugate (cm09) was performed at 95°C within 10 min. The stability of 44 Sc-cm09 was tested in human plasma. 44 Sc-cm09 was investigated in vitro using folate receptor-positive KB tumor cells and in vivo by PET/CT imaging of tumor-bearing mice Results: Under the given irradiation conditions, 44 Sc was obtained in a maximum yield of 350 MBq at high radionuclide purity (.99%). Semiautomated isolation of 44 Sc from 44 Ca targets allowed formulation of up to 300 MBq of 44 Sc in a volume of 200-400 mL of ammonium acetate/HCl solution (1 M, pH 3.5-4.0) within 10 min. Radiolabeling of cm09 was achieved with a radiochemical yield of greater than 96% at a specific activity of 5.2 MBq/nmol. In vitro, 44 Sc-cm09 was stable in human plasma over the whole time of investigation and showed folate receptor-specific binding to KB tumor cells. PET/CT images of mice injected with 44 Sc-cm09 allowed excellent visualization of tumor xenografts. Comparison of cm09 labeled with 44 Sc and 177 Lu revealed almost identical pharmacokinetics. Conclusion: This study presents a highyield production and efficient separation method of 44 Sc at a quality suitable for radiolabeling of DOTA-functionalized biomolecules. An in vivo proof-of-concept study using a DOTA-folate conjugate demonstrated the excellent features of 44 Sc for PET imaging. Thus, 44 Sc is a valid alternative to 68 Ga for imaging and dosimetry before 177 Luradionuclide tumor therapy. In the past decade, applications of radiometal-based PET have rapidly increased, particularly for oncologic imaging purposes (1). Clinical implementation of 68 Ga-labeled somatostatin analogs (e.g., 68 Ga-DOTATATE, 68 Ga-DOTATOC) for imaging of neuroendocrine tumors has raised attention because of the excellent imaging quality that can be achieved and the on-site availability of 68 Ga (half-life [T 1/2 ] 5 68 min, average b 1 energy [Eb 1 av ] 5 830 keV, intensity 5 89%) by the 68 Ge/ 68 Ga generator (2-6). Somatostatin receptor-targeted PET is currently used for dosimetry before application of 177 Lu-based radionuclide therapy (7). These facts have established the basis of a new era of PET applicat...