Non-invasive imaging biomarkers (IBs) are warranted to enable improved diagnostics and follow-up monitoring of interstitial lung disease (ILD) including drug-induced ILD (DIILD). Of special interest are IB, which can characterize and differentiate acute inflammation from fibrosis. The aim of the present study was to evaluate a PET-tracer specific for Collagen-I, combined with multi-echo MRI, in a rat model of DIILD. Rats were challenged intratracheally with bleomycin, and subsequently followed by MRI and PET/CT for four weeks. PET imaging demonstrated a significantly increased uptake of the collagen tracer in the lungs of challenged rats compared to controls. This was confirmed by MRI characterization of the lesions as edema or fibrotic tissue. The uptake of tracer did not show complete spatial overlap with the lesions identified by MRI. Instead, the tracer signal appeared at the borderline between lesion and healthy tissue. Histological tissue staining, fibrosis scoring, lysyl oxidase activity measurements, and gene expression markers all confirmed establishing fibrosis over time. In conclusion, the novel PET tracer for Collagen-I combined with multi-echo MRI, were successfully able to monitor fibrotic changes in bleomycin-induced lung injury. The translational approach of using non-invasive imaging techniques show potential also from a clinical perspective.

Anti-prostate specific membrane antigen (PSMA) radioligand therapy is promising but not curative in castration resistant prostate cancer. One way to broaden the therapeutic index could be to administer higher doses in combination with radioprotectors, since administered radioactivity is kept low today in order to avoid side-effects from a high absorbed dose to healthy tissue. Here, we investigated the human radical scavenger α₁-microglobulin (A1M) together with 177-Lutetium (¹⁷⁷Lu) labeled PSMA-617 in preclinical models with respect to therapeutic efficacy and kidney toxicity. Nude mice with subcutaneous LNCaP xenografts were injected with 50 or 100 MBq of [¹⁷⁷Lu]Lu-PSMA-617, with or without injections of recombinant A1M (rA1M) (at T = 0 and T = 24 h). Kidney absorbed dose was calculated to 7.36 Gy at 4 days post a 100 MBq injection. Activity distribution was imaged with Single-Photon Emission Computed Tomography (SPECT) at 24 h. Tumor volumes were measured continuously, and kidneys and blood were collected at termination (3–4 days and 3–4 weeks after injections). In a parallel set of experiments, mice were given [¹⁷⁷Lu]Lu-PSMA-617 and rA1M as above and dynamic technetium-99m mercaptoacetyltriglycine ([^99mTc]Tc-MAG3) SPECT imaging was performed prior to injection, and 3- and 6-months post injection. Blood and urine were continuously sampled. At termination (6 months) the kidneys were resected. Biomarkers of kidney function, expression of stress genes and kidney histopathology were analyzed. [¹⁷⁷Lu]Lu-PSMA-617 uptake, in tumors and kidneys, as well as treatment efficacy did not differ between rA1M and vehicle groups. In mice given rA1M, [^99mTc]Tc-MAG3 imaging revealed a significantly higher slope of initial uptake at three months compared to mice co-injected with [¹⁷⁷Lu]Lu-PSMA-617 and vehicle. Little or no change compared to control was seen in urine albumin, serum/plasma urea levels, RT-qPCR analysis of stress response genes and in the kidney histopathological evaluation. In conclusion, [^99mTc]Tc-MAG3 imaging presented itself as a sensitive tool to detect changes in kidney function revealing that administration of rA1M has a potentially positive effect on kidney perfusion and tubular function when combined with [¹⁷⁷Lu]Lu-PSMA-617 therapy. Furthermore, we could show that rA1M did not affect anti-PSMA radioligand therapy efficacy.

Prostate cancer (PC) is one of the most common malignancies affecting men, with poor prognosis after progression to metastatic castration-resistant prostate cancer (mCRPC). Radioligand therapy (RLT) targeting the overexpressed PSMA on PC cells, with, e.g., ¹⁷⁷Lu-PSMA-617, has been effective in reducing tumor burden and prolonging survival in mCRPC. However, it is not a curative method with kidney and bone marrow toxicity limiting the activity given to patients. Previous preclinical models have reported transient hematotoxicity for up to 120 MBq. This activity may still be too low to investigate the effect on renal function since it corresponds to an absorbed dose below 10 Gy, whereas the kidneys in a clinical setting usually receive an absorbed dose more than double. Here we investigated the hematotoxicity and recovery after administered activities of 120, 160, and 200 MBq in a ¹⁷⁷Lu-PSMA-617 BALB/cAnNRj mouse model. The animals had an initial drop in white blood cells (WBC) starting 4 days post injection, which recovered after 21 days. The effect on red blood cells (RBC) and platelets was detected later; 17 days post-injection levels decreased compared to the control group. The reduction was restored again 32 days post injection. No correlation between injected activity and hematotoxicity was found. Our results suggest that activities up to 200 MBq of ¹⁷⁷Lu-PSMA-617 give transient hematotoxicity from which animals recover within a month and no radiation-related deaths. Injecting these high activities could allow animal studies with increased clinical relevance when studying renal toxicity in animal models.

The therapeutic effect of radioimmunotherapy depends on the distribution of the absorbed dose in relation to viable cancer cells within the tumor, which in turn is a function of the activity distribution. The aim of this study was to investigate the distribution of ¹⁷⁷Lu-DOTA-BR96 monoclonal antibodies targeting the Lewis Y antigen over 7 d using a syngeneic rat model of colon carcinoma. Methods: Thirty-eight tumor-bearing rats were intravenously given 25 or 50 MBq of ¹⁷⁷Lu-DOTA-BR96 per kilogram of body weight and were sacrificed 2, 8, 24, 48, 72, 96, 120, or 168 h after injection, with activity measured in blood and tumor samples. Adjacent cryosections of each tumor were analyzed in 3 ways: imaging using a silicon-strip detector for digital autoradiography, staining for histologic characterization, or staining to determine the distribution of the antigen, vasculature, and proliferating cells using immunohistochemistry. Absorbed-dose rate distribution images at the moment of sacrifice were calculated using the activity distribution and a point-dose kernel. The correlations between antigen expression and both activity uptake and absorbed-dose rate were calculated for several regions of interest in each tumor. Nine additional animals with tumors were given unlabeled antibody to evaluate possible immunologic effects. Results: At 2–8 h after injection, activity was found in the tumor margins; at 24 h, in viable antigen-expressing areas within the tumor; and at 48 h and later, increasingly in antigen-negative areas of granulation tissue. The correlation between antigen expression and both the mean activity and the absorbed-dose rate in regions of interest changed from positive to negative after 24 h after injection. Antigen-negative areas also increased over time in animals injected with unlabeled BR96, compared with untreated tumors. Conclusion: The results indicate that viable Lewis Y-expressing tumor cells are most efficiently treated during the initial uptake period. The activity then seems to remain in these initial uptake regions after the elimination of tumor cells and formation of granulation tissue. Further studies using these techniques could aid in determining the effects of the intratumoral activity distribution on overall therapeutic efficacy.

α₁-Microglobulin (A1M) is an antioxidant found in all vertebrates, including humans. It has enzymatic reductase activity and can scavenge radicals and bind free heme groups. Infused recombinant A1M accumulates in the kidneys and has therefore been successful in protecting kidney injuries in different animal models. In this review, we focus on A1M as a radioprotector of the kidneys during peptide receptor radionuclide/radioligand therapy (PRRT/RLT). Patients with, e.g., neuroendocrine tumors or castration resistant prostate cancer can be treated by administration of radiolabeled small molecules which target and therefore enable the irradiation and killing of cancer cells through specific receptor interaction. The treatment is not curative, and kidney toxicity has been reported as a side effect since the small, radiolabeled substances are retained and excreted through the kidneys. In recent studies, A1M was shown to have radioprotective effects on cell cultures as well as having a similar biodistribution as the somatostatin analogue peptide ¹⁷⁷Lu-DOTATATE after intravenous infusion in mice. Therefore, several animal studies were conducted to investigate the in vivo radioprotective potential of A1M towards kidneys. The results of these studies demonstrated that A1M co-infusion yielded protection against kidney toxicity and improved overall survival in mouse models. Moreover, two different mouse studies reported that A1M did not interfere with tumor treatment itself. Here, we give an overview of radionuclide therapy, the A1M physiology and the results from the radioprotector studies of the protein.

Background: The humanized monoclonal antibody (mAb) hu5A10 specifically targets and internalizes prostate cancer cells by binding to prostate specific antigen (PSA). Preclinical evaluations have shown that hu5A10 is an excellent vehicle for prostate cancer (PCa) radiotheranostics. We studied the impact of different chelates and conjugation ratios on hu5A10′s target affinity, neonatal fc-receptor interaction on in vivo targeting efficacy, and possible enhanced therapeutic efficacy. Methods: In our experiment, humanized 5A10 (hu5A10) was conjugated with DOTA or DTPA at a molar ratio of 3:1, 6:1, and 12:1. Surface plasmon resonance (SPR) was used to study antigen and FcRn binding to the antibody conjugates. [¹¹¹In]hu5A10 radio-immunoconjugates were administered intravenously into BALB/c mice carrying subcutaneous LNCaP xenografts. Serial Single-photon emission computed tomography (SPECT) images were obtained during the first week. Tumors were harvested and radionuclide distribution was analyzed by autoradiography along with microanatomy and immunohistochemistry. Results: As seen by SPR, the binding to PSA was clearly affected by the chelate-to-antibody ratio. Similarly, FcRn (neonatal fc-receptor) interacted less with antibodies conjugated at high ratios of chelator, which was more pronounced for DOTA conjugates. The autoradiography data indicated a higher distribution of radioactivity to the rim of the tumor for lower ratios and a more homogenous distribution at higher ratios. Mice injected with ratio 3:1 ¹¹¹In-DOTA-hu5A10 showed no significant difference in tumor volume when compared to mice given vehicle over a time period of 3 weeks. Mice given a similar injection of ratio 6:1 ¹¹¹In-DOTA-hu5A10 or 6:1 ¹¹¹In-DTPA-hu5A10 or 12:1 ¹¹¹In-DTPA-hu5A10 showed significant tumor growth retardation. Conclusions: The present study demonstrated that the radiolabeling strategy could positively modify the hu5A10′s capacity to bind PSA and complex with the FcRn-receptor, which resulted in more homogenous activity distribution in tumors and enhanced therapy efficacy.