Abstract Background The clinical standard practice of [177Lu]Lu-PSMA-617 therapy is a single injection per treatment cycle, with 6 weeks between cycles. While clinical schedules currently utilize single-bolus cycles, splitting a treatment cycle into multiple smaller injections has demonstrated benefits in other radionuclide therapies, preclinically and in clinical studies. Potential mechanisms for improved therapeutic efficacy include receptor recycling, receptor upregulation, or targeting new cell growth between fractions. This study aims to investigate the effects on tumor size and animal survival, in a mouse model of prostate cancer, of fractionating [177Lu]Lu-PSMA-617 therapy compared to the same total activity in a single injection. Results BALB/c mice bearing subcutaneous LNCaP prostate cancer tumors, below 650 mm3 in volume, were treated with either 1 × 30 MBq, 2 × 15 MBq (24-hour window), or 2 × 15 MBq (6-day window). SPECT/CT imaging showed a higher, but not significantly so, tumor uptake in the 24-hour window group than in the unfractionated one. Differences in tumor sizes were primarily visible during regrowth after therapy, with significantly smaller relative tumor sizes in the 24-hour window group compared to the unfractionated group day 89–95 post inoculation. The median survival for the 24-hour group (71.5 days) was significantly longer than that of the unfractionated group (46 days; p = 0.024). The 6-day group tumor sizes and survival came close to the 24-hour one, but was not significantly better than the unfractionated group. Conclusion This study demonstrates that fractionation gives therapeutic benefit in an animal model of [177Lu]Lu-PSMA-617 therapy of prostate cancer for tumors in this size range. A shorter 24-hour window outperformed a longer of 6 d between fractions. The outlook for clinical translation will depend on if the mechanism is relevant at conditions, blood ligand concentration etc., that differs between the animal model and human patients.

Despite new therapies, castration-resistant prostate cancer (CRPC) is still incurable. Intercellular Adhesion Molecule 1 (ICAM-1) is a well-characterized cell surface protein involved in prostate cancer pathogenesis, differentially expressed during transition from hormone-sensitive to CRPC. This study aimed to investigate ICAM-1 as a target for imaging and radioimmunotherapy of CRPC.Anti-ICAM-1 antibody R6.5 was labeled with 111In or 177Lu, and a non-specific antibody with 177Lu. In vitro uptake of R6.5 was tested in PC-3 prostate cancer cells. Biodistribution studies, SPECT/CT imaging, and autoradiography were performed in a PC-3 xenograft model.In vitro uptake of R6.5 ([177Lu]Lu-R6.5) increased during 6 h of incubation. The uptake was higher at lower mAb concentration and could be blocked by 500 nM of unlabeled R6.5. In vivo and ex vivo biodistribution showed that [111In]In-R6.5 and [177Lu]Lu-R6.5 targeted the xenograft tumors better than the control Ab, however [111In]In-R6.5 had better tumor uptake than [177Lu]Lu-R6.5, probably due to less aggressive conjugation with chelator and smaller tumor sizes. From 24 h post-injection, the tumors in mice injected with [111In]In-R6.5 and [177Lu]Lu-R6.5 were visible on SPECT, optimal contrast at 48 h. Uptake was low in normal organs except the spleen and liver for all mAbs. Autoradiography showed [111In]In-R6.5 and [177Lu]Lu-R6.5 accumulated along the edges of viable tumor. The control Ab tended to accumulate in partly necrotic areas.This study demonstrates ICAM-1 as a potential target for theragnostics in CRPC.

Background: For breast cancer staging, radiolabeled colloids and superparamagnetic iron oxide nanoparticles (SPIONs) are used for sentinel lymph node (SLN) imaging. This study characterized the intranodal activity distribution and absorbed dose distribution.Material and Methods: Six patients diagnosed with primary breast cancer were intradermally injected with 99mTc-Nanocoll. The SLNs were resected, weighed, and measured for activity. Three groups of six rats were subcutaneously injected into the hind paw with either 99mTc-Nanocoll, 99mTc-SPIONs, or 68Ga-SPIONs. Macro- and small-scale dosimetry calculations were performed using autoradiography images of cryosections of SLNs from patients and animals.Results: The mean absorbed dose in patient SLNs was 0.5 +/- 0.3 mGy/MBq for 99mTc-Nanocoll and 3.4 +/- 1.8 mGy/MBq, assuming a 99mTc-Nanocoll-based distribution of 68Ga-SPIONs. Due to different decay characteristics, the heterogeneity in the absorbed dose differed between 99mTc-SPIONs and 68Ga-SPIONs with a maximum to mean absorbed dose ratio of 2.7 +/- 0.3 and 1.6 +/- 0.2, respectively.Conclusions: This study shows that 99mTc- and 68Ga-SPIONs and 99mTc-nanocolloids have similar activity distribution in human and animal lymph nodes. Small-scale dosimetry models combined with clinical patient biokinetics may serve as a bridge between organ and tissue dosimetry and the interpretation of intrinsic geometric variation and its uncertainties in absorbed dose.

Radioligand therapy with [177Lu]Lu-PSMA-617 can be used to prolong life and reduce tumor burden in terminally ill castration resistant prostate cancer patients. Still, accumulation in healthy tissue limits the activity that can be administered. Therefore, fractionated therapy is used to lower toxicity. However, there might be a need to reduce toxicity even further with e.g. radioprotectors. The aim of this study was to (i). establish a preclinical mouse model with fractionated high activity therapy of three consecutive doses of 200 MBq [177Lu]Lu-PSMA-617 in which we aimed to (ii). achieve measurable hematotoxicity and nephrotoxicity and to (iii). analyze the potential protective effect of co-injecting recombinant α1-microglobulin (rA1M), a human antioxidant previously shown to have radioprotective effects. In both groups, three cycles resulted in increased albuminuria for each cycle, with large individual variation. Another marker of kidney injury, serum blood urea nitrogen (BUN), was only significantly increased compared to control animals after the third cycle. The number of white and red blood cells decreased significantly and did not reach the levels of control animals during the experiment. rA1M did reduce absorbed dose to kidney but did not show significant protection here, but future studies are warranted due to the recent clinical studies showing a significant renoprotective effect in patients.

Introduction: Prostate-specific membrane antigen (PSMA) is a target for diagnostic positron emission tomography (PET)-tracers and radiopharmaceutical therapy (RPT), for example, [177Lu]Lu-PSMA-617, in prostate cancer. This autoradiography study investigates [177Lu]Lu-PSMA-617 intratumoral distribution over time, compared with PSMA expression, proliferation (Ki67), and [68Ga]Ga-PSMA-11, [18F]F-PSMA-1007, [18F]-fluorodeoxyglucose, and [18F]-fluorocholine distribution. Mice with LNCaP, 22Rv1, or PC-3 PIP xenografts got [177Lu]Lu-PSMA-617 i.v. Sacrificed 1 h p.i. if coinjected with diagnostic tracers, otherwise at 20 min, 1-2, 12, 24, 48, 72 h, or 2-3 weeks p.i. Cryosectioned tumors imaged by autoradiography, adjacent sections Ki67 or PSMA stained.Results: Heterogeneous distribution of [177Lu]Lu-PSMA-617 was seen 20 min p.i., with visible overlap between tumor cells, Ki67, PSMA, and radioactivity at 1-2 h p.i. Strongest Ki67-correlation at 48 h, which became negative at 72 h and beyond with some Ki67+/PSMA+ low radioactivity areas. Uptake in necrotic tissue was only observed at 2-3 weeks p.i. PSMA-targeted tracers distributed identically to [177Lu]Lu-PSMA-617 whereas other tracers only had some overlap.Conclusion: Regrowth of the tumor post-[177Lu]Lu-PSMA-617 administration creates Ki67+/PSMA+ areas that have no radioactivity uptake and need additional therapy fractions. The identical intratumoral distribution of [177Lu]Lu-PSMA-617 and PSMA-targeted PET-tracers indicate that these will reveal the areas inside the tumor targeted by RPT at least at 1 h p.i.

Drug-induced interstitial lung disease (ILD) is crucial to detect early to achieve the best treatment outcome. Optimally, non-invasive imaging biomarkers can be used for early detection of disease progression and treatment follow-up. Therefore, reliable in vivo models are warranted in new imaging biomarker development to accelerate better-targeted treatment options. Single-dose bleomycin models have, for a long time, served as a reference model in fibrosis and lung injury research. Here, we aimed to use a clinically more relevant animal model by systemic exposure to bleomycin and assessing disease progression over time by combined magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging.MethodsC57BL/6 mice received bleomycin (i.p. 35iU/kg) or saline as control twice per week for 4 weeks. Mice were monitored until 2 weeks after cessation of bleomycin administration (w4 + 1 and w4 + 2), referred to as the resting period. MRI scans were performed in weeks 3 and 4 and during the resting weeks. [18F]FDG-PET was performed at the last week of dosing (w4) and 2 weeks after the last dosing (w4 + 2). Lung tissue sections were stained with Masson’s trichrome and evaluated by modified Ashcroft scoring. Lung volume and lesion volumes were assessed using MRI, as well as 3D mapping of the central airways.Results and discussionBleomycin-challenged mice showed increased lung weights (p < 0.05), while total lung volume was unchanged (w4 and onward). Histology analysis demonstrated fibrotic lesions emanating from the distal parts of the lung. Fibrosis progression was visualized by MRI with significantly increased high signal in bleomycin-exposed lungs compared to controls (p < 0.05). In addition, a significant increase in central airway diameter (p < 0.01) was displayed in bleomycin-exposed animals compared to controls and further continued to dilate as the disease progressed, comparing the bleomycin groups over time (p < 0.05–0.001). Lung [18F]FDG uptake was significantly elevated in bleomycin-exposed mice compared to controls (p < 0.05).ConclusionNon-invasive imaging displayed progressing lesions in the lungs of bleomycin-exposed mice, using two distinct MRI sequences and [18F]FDG-PET. With observed fibrosis progression emanating from distal lung areas, dilation of the central airways was evident. Taken together, this chronic bleomycin-exposure model is translationally more relevant for studying lung injury in ILD and particularly in the context of DIILD.

One novel option for treating metastatic castration resistant prostate cancer is radionuclide therapy targeting prostate-specific membrane antigen (PSMA), e.g. [177Lu]Lu-PSMA-617. Overexpression of HER2 has been found in 80% of metastatic cases of prostate cancer. Previous research showed that HER2 is elevated post irradiation in PC-3 prostate cancer cells. Co-treating with anti-HER2 antibody Trastuzumab gave less proliferation of irradiated tumor cells in vitro, and when using radionuclide therapy, also in vivo. The aim of this study is to determine whether the same holds true in PSMA-expressing PC-3 PIP cells using [177Lu]Lu-PSMA-617 radionuclide therapy. PC-3 PIP and 22Rv1 prostate cancer cells were tested in vitro, treated with 6 Gy of x-rays with or without Trastuzumab incubation. We measured uptake of HER2-targeting affibody [68Ga]Ga-ABY-025 and cell survival, e.g. using the WST-1 assay. Three groups (n=10 each) of male nude Balb/c mice were inoculated with PC-3 PIP xenograft tumors and treated with just [177Lu]Lu-PSMA-617 (20 MBq), [177Lu]Lu-PSMA-617 (20 MBq) and Trastuzumab (4 × 5 mg/kg), or left untreated. Tumor sizes and animal survival was observed. In vitro, x-ray irradiation did reduce survival in 22Rv1 but not PC-3 PIP cells, and there was no significant effect of Trastuzumab treatment. Cells expressed HER2 but not significantly elevated post irradiation. In vivo, mice co-treated with Trastuzumab had significantly longer survival than untreated mice, but not than only [177Lu]Lu-PSMA-617. Staining of tumor sections showed similar HER2 and PSMA expression across groups. In conclusion, these results give no support for any benefit from co-treatment with anti-HER2 antibody for PSMA-targeted radioligand therapy.

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.

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.

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.

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.

Autoradiography is defined as technologies and methods used to produce a two-dimensional image of the distribution of activity in, or on, a thin and solid sample that is in close proximity to the detector. The images are usually formed by charged particles (α or β±), and image characteristics are determined both by the detector and the properties of the particles detected. This method is not widely employed in the clinic, but in a number of research settings such as pharmaceutical development. The application of the method can be done either ex vivo using tissue from animal models, or in vitro where the radiotracer is applied to tissue samples post sacrifice. This chapter will primarily discuss different detection systems used for autoradiography, beginning with the classical film emulsion and continuing to detail phosphor storage plates, scintillation-based detectors, gaseous detectors, and semiconductor-based imaging systems. A special focus is also made on detectors being capable of imaging alpha-particles. For each type of detector, applications of the system are presented from recent academic work to show the possibilities of using autoradiography to produce scientific data.

A large number of systemically administered drugs have the potential to cause drug-induced interstitial lung disease (DIILD). We aim to characterize a model of DIILD in the rat and develop imaging biomarkers (IBs) for detection and quantification of DIILD. In this study, Sprague-Dawley rats received one single dose of intratracheal (i.t.) bleomycin and were longitudinally imaged at day 0, 3, 7, 14, 21, and 28 post dosing, applying the imaging techniques magnetic resonance imaging (MRI) and positron emission tomography (PET)/computed tomography (CT). Bronchoalveolar lavage fluid (BALF) was analyzed for total protein and inflammatory cells. Lungs were saved for further evaluation by gene analysis using quantitative-PCR and by histology. Lung sections were stained with Masson's-Trichrome staining and evaluated by modified Ashcroft score. Gene expression profiling of inflammatory and fibrotic markers was performed on lung tissue homogenates. Bleomycin induced significant increase in total protein concentration and total cell count in bronchoalveolar lavage (BAL), peaking at day 3 (p > 0.001) and day 7 (p > 0.001) compared to control, respectively. Lesions measured by MRI and PET signal in the lungs of bleomycin challenged rats were significantly increased during days 3-14, peaking at day 7. Two subgroups of animals were identified as low- and high-responders by their different change in total lung volume. Both groups showed signs of inflammation initially, while at later time points, the low-responder group recovered toward control, and the high-responder group showed sustained lung volume increase, and significant increase of lesion volume (p < 0.001) compared to control. Lastly, important inflammatory and pro-fibrotic markers were assessed from lung tissue, linking observed imaging pathological changes to gene expression patterns. In conclusion, bleomycin-induced lung injury is an adequate animal model for DIILD studies and for translational lung injury assessment by MRI and PET imaging. The scenario comprised disease responses, with different fractions of inflammation and fibrosis. Thereby, this study improved the understanding of imaging and biological biomarkers in DIILD and lung injury.

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.

A large number of systemically administered drugs have the potential to cause DIILD. We aim to characterize a model of DIILD in the rat and develop imaging biomarkers for detection and quantification of DIILD. Methods: Sprague-Dawley rats received one single dose of intratracheal bleomycin and were longitudinally imaged at day 0, 3, 7, 14, 21 and 28 post dosing, applying imaging techniques MRI and PET/CT. Bronchoalveolar lavage fluid (BALF) was analyzed for total protein and inflammatory cells. Lungs were taken for further analyses by histology, and stained for inflammation and collagen deposition. Results: Bleomycin induced significant increase in total protein concentration and total cell count in BALF, peaking at day3 (p>0.001) and day7 (p>0.001) compared to control, respectively. The lesion measured by MRI and the FDG-PET signal in the lungs of bleomycin challenged rats was significantly increased during day3-14, peaking at day7. Two subgroups of animals were identified as low- and high responders to bleomycin challenge, by their different change in total lung volume. Both groups showed signs of inflammation initially, while at later time points the low-responder group recovered towards control, and the high-responder group showed progressive fibrosis with significant increase of lesion volume (p<0.001), compared to control. Conclusion: Bleomycin-induced lung injury with MRI and PET readout in rats, is an adequate and translational animal model for DIILD studies. The scenario comprised different disease responses, with different fractions of inflammation and fibrosis. Thereby, this study improved the understanding biological- and imaging biomarkers in DIILD.

Androgen ablating drugs increase life expectancy in men with metastatic prostate cancer, but resistance inevitably develops. In a majority of these recurrent tumors, the androgen axis is reactivated in the form of increased androgen receptor (AR) expression. Targeting proteins that are expressed as a down-stream effect of AR activity is a promising rationale for management of this disease. The humanized IgG1 antibody hu11B6 internalizes into prostate and prostate cancer (PCa) cells by binding to the catalytic cleft of human kallikrein 2 (hK2), a prostate specific enzyme governed by the AR-pathway. In a previous study, hu11B6 conjugated with Actinium-225 (225Ac), a high linear energy transfer (LET) radionuclide, was shown to generate an AR-upregulation driven feed-forward mechanism that is believed to enhance therapeutic efficacy. We assessed the efficacy of hu11B6 labeled with a low LET beta-emitter, Lutetium-177 (177Lu) and investigated whether similar tumor killing and AR-enhancement is produced. Moreover, single-photon emission computed tomography (SPECT) imaging of 177Lu is quantitatively accurate and can be used to perform treatment planning. [177Lu]hu11B6 therefore has significant potential as a theranostic agent. Materials and Methods: Subcutaneous PCa xenografts (LNCaP s.c.) were grown in male mice. Biokinetics at 4-336 h post injection and uptake as a function of the amount of hu11B6 injected at 72 h were studied. Over a 30 to 120-day treatment period the therapeutic efficacy of different activities of [177Lu]hu11B6 were assessed by volumetric tumor measurements, blood cell counts, molecular analysis of the tumor as well as SPECT/CT imaging. Organ specific mean absorbed doses were calculated, using a MIRD-scheme, based on biokinetic data and rodent specific S-factors from a modified MOBY phantom. Tumor tissues of treated xenografts were immunohistochemically (IHC) stained for Ki-67 (proliferation) and AR, SA-β-gal activity (senescence) and analyzed by digital autoradiography (DAR). Results: Organ-to-blood and tumor-to-blood ratios were independent of hu11B6 specific activity except for the highest amount of antibody (150 µg). Tumor accumulation of [177Lu]hu11B6 peaked at 168 h with a specific uptake of 29 ± 9.1 percent injected activity per gram (%IA/g) and low accumulation in normal organs except in the submandibular gland (15 ± 4.5 %IA/g), attributed to a cross-reaction with mice kallikreins in this organ, was seen. However, SPECT imaging with therapeutic amounts of [177Lu]hu11B6 revealed no peak in tumor accumulation at 7 d, probably due to cellular retention of 177Lu and decreasing tumor volumes. For [177Lu]hu11B6 treated mice, tumor decrements of up to 4/5 of the initial tumor volume and reversible myelotoxicity with a nadir at 12 d were observed after a single injection. Tumor volume reduction correlated with injected activity and the absorbed dose. IHC revealed retained expression of AR throughout treatment and that Ki-67 staining reached a nadir at 9-14 d which coincided with high SA- β-gal activity (14 d). Quantification of nuclei staining showed that Ki-67 expression correlated negatively with activity uptake. AR expression levels in cells surviving therapy compared to previous timepoints and to controls at 30 d were significantly increased (p = 0.017). Conclusions: This study shows that hu11B6 labeled with the low LET beta-emitting radionuclide 177Lu can deliver therapeutic absorbed doses to prostate cancer xenografts with transient hematological side-effects. The tumor response correlated with the absorbed dose both on a macro and a small scale dosimetric level. Analysis of AR staining showed that AR protein levels increased late in the study suggesting a therapeutic mechanism, a feed forward mechanism coupled to AR driven response to DNA damage or clonal lineage selection, similar to that reported in high LET alpha-particle therapy using 225Ac labeled hu11B6, however emerging at a later timepoint.

Side effects caused by various drugs may induce lung injury known as drug induced interstitial lung disease (DIILD). Clinical and pre-clinical studies within the TRISTAN-consortium aim to find translational imaging biomarkers that can indicate progression of DIILD at an early stage. Methods: Sprague-Dawley rats received Bleomycin i.t. (dose 750U, 1000U or 1250U) or Saline and were longitudinally imaged at day 0, 3, 7, 14 and 21 post-stimuli. Scans were performed on a small-animal 9.4T MRI, using two different ultra-short echo (UTE) sequences (0.32ms vs 1ms echo time). MRI scans were evaluated qualitatively and quantitatively (histogram-based thresholding). At termination, bronchoalveolar lavage fluid (BALF) was collected and analysed for inflammatory cells and proteins. Lungs were harvested, stained and scored. Results: MRI scans showed increased signal (oedema) at d.3-7 and again at d.21 (fibrosis) in the lungs of Bleomycin exposed rats. Total lung volume increased significantly (p=0.001) and dose-dependently compared to Saline, although the functional lung volume decreased due to development of lesions (oedema or fibrotic tissue formation). Lung volume and body weight correlated significantly (p=0.016). Increased total protein and cells in BALF were significantly decreased (p=0.05) at d.30. Histological score resembled the lung injury found on MRI, where disease severity was linked to the MRI data in a dose-dependent matter. Conclusion: Non-invasive biomarkers are warranted, to assess incidence and disease progression in the clinic. In our DIILD model, using Bleomycin, we observed dose dependent MRI signal increase correlating to inflammation and fibrosis as confirmed by BAL and tissue markers.

PURPOSE:The most commonly used technology currently used for autoradiography is storage phosphor screens, which has many benefits such as a large field of view but lacks particle-counting detection of the time and energy of each detected radionuclide decay. A number of alternative designs, using either solid state or scintillator detectors, have been developed to address these issues. The aim of this study is to characterize the imaging performance of one such instrument, a double-sided silicon strip detector (DSSD) system for digital autoradiography. A novel aspect of this work is that the instrument, in contrast to previous prototype systems using the same detector type, provides the ability for user accessible imaging with higher throughput. Studies were performed to compare its spatial resolution to that of storage phosphor screens and test the implementation of multiradionuclide ex vivo imaging in a mouse preclinical animal study.METHODS:Detector background counts were determined by measuring a nonradioactive sample slide for 52 h. Energy spectra and detection efficiency were measured for seven commonly used radionuclides under representative conditions for tissue imaging. System dead time was measured by imaging (18)F samples of at least 5 kBq and studying the changes in count rate over time. A line source of (58)Co was manufactured by irradiating a 10 μm nickel wire with fast neutrons in a research reactor. Samples of this wire were imaged in both the DSSD and storage phosphor screen systems and the full width at half maximum (FWHM) measured for the line profiles. Multiradionuclide imaging was employed in a two animal study to examine the intratumoral distribution of a (125)I-labeled monoclonal antibody and a (131)I-labeled engineered fragment (diabody) injected in the same mouse, both targeting carcinoembryonic antigen.RESULTS:Detector background was 1.81 × 10(-6) counts per second per 50 × 50 μm pixel. Energy spectra and detection efficiency were successfully measured for seven radionuclides. The system dead time was measured to be 59 μs, and FWHM for a (58)Co line source was 154 ± 14 μm for the DSSD system and 343 ± 15 μm for the storage phosphor system. Separation of the contributions from (125)I and (131)I was performed on autoradiography images of tumor sections.CONCLUSIONS:This study has shown that a DSSD system can be beneficially applied for digital autoradiography with simultaneous multiradionuclide imaging capability. The system has a low background signal, ability to image both low and high activity samples, and a good energy resolution.