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.

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.

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.