Eva Forssell-Aronsson

Biological sex can influence radiation response, but sex is rarely considered in biodistribution studies of radionuclides. ¹³¹ I is used clinically and may be released at nuclear accidents. The aim was to investigate differences in biodistribution and dosimetry of ¹³¹ I (iodide) between male and female mice. C57BL/6N mice received 170 kBq ¹³¹ I i.v. and separate groups were euthanised at seven time points from 1 h to 7 days after administration. ¹³¹ I concentration was determined in various collected organs and tissues, and mean absorbed dose per injected activity, D/A _inj , was calculated. Results showed higher ¹³¹ I concentration and D/A _inj in most organs in females than males except for kidneys, where males received fourfold higher D/A _inj after 7 days (120 versus 31 mGy/MBq). The D/A _inj in most organs in females was about up to approximately twofold higher than in males, while thyroid D/A _inj was also higher in females, at 180,000 versus 140,000 mGy/MBq. In conclusion, sex-related differences in ¹³¹ I biodistribution between males and females were found in all investigated tissues at one or more time points, but the magnitude and timing of these differences varied between tissues. These findings support consideration of biological sex as a variable in preclinical biodistribution and dosimetry studies of radionuclides.

Radionuclide therapy with ¹⁷⁷Lu-octreotate improves survival and quality of life in patients with metastatic neuroendocrine tumors, but outcomes are limited by radiation-induced renal and bone marrow toxicity. To reduce the absorbed dose to the kidneys, kidney blocking is routinely performed by co-injection of amino acids. However, more efficient kidney-blocking strategies may allow further optimization of ¹⁷⁷Lu-octreotate treatment. The aim of this study was to evaluate DMSA as a kidney-blocking agent during ¹⁷⁷Lu-octreotate treatment. DMSA and the amino acid L-lysine, alone or in combination, were given to female C57BL/6N mice at different doses and time points relative to administration of 5 MBq ¹⁷⁷Lu-octreotate. All animals were euthanized 24 h after ¹⁷⁷Lu-octreotate administration, and ¹⁷⁷Lu activity concentrations in the kidneys, blood, and other organs were measured and compared to controls. Reduced ¹⁷⁷Lu kidney uptakes were found across all DMSA dosages (adjusted p < 0.05), with generally larger reductions at higher DMSA doses. The largest kidney-protective effect was seen for 32 mg DMSA given simultaneously with ¹⁷⁷Lu-octreotate, with a mean reduction in ¹⁷⁷Lu kidney uptake of approximately 65%. DMSA combined with L-lysine showed no statistically significant additive kidney-protective effect. Overall, DMSA shows potential as a kidney-blocking agent for treatment with ¹⁷⁷Lu-octreotate.

Gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) are the most common subtype of NETs, and their incidence continues to increase worldwide. Many NETs express somatostatin receptors (SSTRs), enabling molecular imaging and treatment with radiolabeled somatostatin analogs (SSTAs). [¹⁷⁷Lu]Lu-DOTATATE is an established treatment for advanced SSTR-positive NETs, but complete and durable responses remain uncommon. This review summarizes current clinical experience with [¹⁷⁷Lu]Lu-DOTATATE and emerging SSTR-targeting radiopharmaceuticals and examines strategies to improve PRRT efficacy. Treatment may be enhanced at several interconnected steps, including increasing receptor availability and tumor targeting, improving radiopharmaceutical uptake and absorbed dose, preventing repair of radiation-induced damage, suppressing cellular stress adaptation and survival, and promoting tumor cell elimination. These approaches include radiation priming and fractionation, somatostatin analog pretreatment, epigenetic modifiers, inhibitors of DNA repair and cellular survival pathways, immunotherapy, and chemotherapy-based combinations. PARP, DNA-PK, and HSP90 inhibitors and chemotherapy-based combinations have shown particularly strong preclinical or clinical evidence, whereas mTOR inhibitors, tyrosine kinase inhibitors, Hedgehog inhibitors, immunotherapy, NAMPT inhibitors, p53 stabilization, and epigenetic modifiers remain under investigation. Ongoing development of novel radiopharmaceuticals, personalized dosimetry, retreatment strategies, and rational combinations is expected to refine PRRT and improve outcomes for patients with NETs.

Background: Assessing the biodistribution and absorbed dose of ¹³¹I is crucial for optimisation of radionuclide therapy, as well as for improving risk assessment following nuclear emergencies. After the Chernobyl accident, an increase in thyroid cancer among children was observed in regions affected by ¹³¹I fallout, particularly among young girls. Reasons for these age- and sex-specific differences in response to low doses of ¹³¹I are not fully understood, but variations in biodistribution and absorbed dose may be contributing factors. The aim of this study was therefore to assess the influence of sex and age at exposure on the biodistribution and dosimetry of ¹³¹ I. Methods: Male and female Sprague Dawley rats were internally exposed to 0.36 MBq ¹³¹I at 5 or 17 weeks of age, corresponding to young and adult exposure groups. The ¹³¹ I activity concentration of 16 vital tissues was measured at six time points (1–144 h post-injection) and used to estimate the mean absorbed dose to each organ. Sodium-iodide symporter (NIS) protein expression was assessed using immunohistochemistry and western blot. Results: The thyroid showed the highest ¹³¹I activity concentration at 18 h in males and 24 h in females, regardless of age. All non-thyroid tissues showed substantially lower activity concentrations, with the stomach having the second-highest levels. Statistically significant sex differences were determined in all tissues, with the most pronounced effect in the thyroid, where females consistently had higher activity concentrations compared to males. Age at exposure also impacted the biodistribution in some tissues. These differences led to pronounced variations in the absorbed dose. The absorbed dose to the thyroid ranged from 23 Gy/MBq in adult males to 100 Gy/MBq in young females. Protein quantification of NIS showed high individual variability but no clear difference between the groups. Conclusions: The results demonstrate that sex and age at exposure affect ¹³¹I biodistribution and absorbed dose in rats, particularly in the thyroid. The observed differences in absorbed dose may partly explain the variation in susceptibility to thyroid cancer in exposed populations reported after the Chernobyl accident. Further research is needed to clarify the underlying biological and mechanistic drivers of these differences.

Background: Peptide receptor radionuclide therapy with [ ¹⁷⁷ Lu]Lu-DOTATATE is an established treatment for somatostatin receptor–expressing neuroendocrine tumors. Although strong anti-tumor effects have been demonstrated in experimental models, curative responses in patients remain limited. Improved understanding of the molecular responses induced by [ ¹⁷⁷ Lu]Lu-DOTATATE may help identify strategies for treatment optimization. This study aimed to characterize proteomic alterations in GOT1 small intestinal neuroendocrine tumor xenografts following [ ¹⁷⁷ Lu]Lu-DOTATATE therapy. Methods: GOT1 tumor–bearing BALB/c nude mice received a non-curative intravenous administration of 15 MBq [ ¹⁷⁷ Lu]Lu-DOTATATE or saline control. Tumors were collected 1 or 13 days after treatment to represent early response and regrowth phases. Tumor volumes were monitored using magnetic resonance imaging. Proteomic profiling was performed using liquid chromatography tandem mass spectrometry with tandem mass tag labeling. Differential protein expression was analyzed using Welch’s t-test with significance defined as fold change ≥ 1.5 and p < 0.01. Functional enrichment and pathway analyses were conducted using Gene Ontology annotation and Ingenuity Pathway Analysis. Results: Treatment induced a transient reduction in tumor volume followed by regrowth. In total, 3861 proteins were quantified, of which 155 showed significantly altered expression after treatment. Affected proteins were associated with cytoskeletal organization, oxidative stress response, protein metabolism, and systemic regulation. Pathway analyses identified inhibition of several signaling pathways linked to cell migration and invasiveness, including RhoA, Rac, integrin, and CXCR4 signaling. Upstream regulator analysis suggested activation of RABL6 and inhibition of p53 signaling during tumor regrowth. Proteins related to endoplasmic reticulum stress and ubiquitin-proteasome activity were also altered. Selected findings were validated by ELISA. Conclusions: [ ¹⁷⁷ Lu]Lu-DOTATATE therapy induced extensive proteomic changes in GOT1 tumors, including suppression of pathways associated with invasiveness and modulation of p53- and stress-related signaling. These findings suggest potential therapeutic benefits of combining [ ¹⁷⁷ Lu]Lu-DOTATATE with agents targeting p53 regulation or endoplasmic reticulum stress pathways to improve treatment efficacy in neuroendocrine tumors.

Gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) are the most common subtype of NETs, and their incidence continues to increase worldwide. Many NETs express somatostatin receptors (SSTRs), enabling molecular imaging and treatment with radiolabeled somatostatin analogs (SSTAs). [¹⁷⁷Lu]Lu-DOTATATE is an established treatment for advanced SSTR-positive NETs, but complete and durable responses remain uncommon. This review summarizes current clinical experience with [¹⁷⁷Lu]Lu-DOTATATE and emerging SSTR-targeting radiopharmaceuticals and examines strategies to improve PRRT efficacy. Two complementary approaches are emphasized: increasing tumor uptake through modulation of SSTR expression and enhancing radiation response through radiosensitization. SSTR upregulation has been investigated using radiation priming, somatostatin analog pretreatment, epigenetic modifiers, and selected pharmacological agents. Radiosensitization strategies include inhibition of DNA repair, cellular stress-response and oncogenic signaling pathways, tumor metabolism, and immune checkpoint signaling. PARP, DNA-PK, and HSP90 inhibitors and chemotherapy-based combinations have shown particularly strong preclinical or clinical evidence, whereas mTOR inhibitors, tyrosine kinase inhibitors, Hedgehog inhibitors, immunotherapy, NAMPT inhibitors, and epigenetic modifiers remain under investigation. Ongoing development of novel radiopharmaceuticals, personalized dosimetry, retreatment strategies, and rational combinations is expected to refine PRRT and improve outcomes for patients with NETs.

Patients with neuroendocrine tumours may receive higher total amount of [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr ³ )-octreotate and achieve better tumor control if the risk of kidney toxicity could be predicted individually for each patient. One strategy for such a prediction includes the evaluation of early responding biomarkers for kidney damage during treatment to decide the number of treatment cycles. The aims of this study were to (1) evaluate if urinary RBP4, NGAL, creatinine and cystatin C levels may serve as early responding biomarkers for kidney damage, (2) assess the expression of NGAL, KIM-1, CDKN1A, S100A6 and ADIPOQ in kidney tissue to validate their use as histological indicators of toxicity, and to (3) examine the long-term effects of the proposed radioprotector α ₁ -microglobulin (A1M) in mice exposed to [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr3)-octreotate. Mice were injected with 90 or 150 MBq [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr3)-octreotate with or without A1M. Urine was collected at several time-points, and the animals were sacrificed after 9 months. Urinary RBP4 increased from day 35 after injection of 150 MBq [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr ³ )-octreotate, creatinine decreased from day 131 and cystatin C increased from day 223. KIM-1, CDKN1A and S100A6 showed a dose dependent kidney expression. Morphological signs of kidney injury were observed in mice injected with 150 MBq [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr ³ )-octreotate. No clear kidney protective effect was detected when A1M was co-administered with [ ¹⁷⁷ Lu]Lu-DOTA-(Tyr ³ )-octreotate.

The antioxidant α1-microglobulin (A1M) has been suggested as kidney protector during 177Lu-octreotate treatment. The aim of this work was to evaluate apoptotic-related transcript expression in kidney cortex and medulla following injection of 177Lu-octreotate and/or A1M. Mice were injected with 177Lu-octreotate, A1M, or 177Lu-octreotate + A1M. Control groups received PBS or vehicle solution. Animals were killed after 24 hours or 7 d. mRNA was isolated from kidney medulla and cortex. Expression of 84 apoptosis-related genes was assessed by q-PCR. Gene expression profiles in kidney cortex were generally similar in the 177Lu-octreotate and 177Lu-octreotate + A1M groups. This was also seen in kidney medulla at 24 hours, but at 7 d anti-apoptotic response of A1M was observed. Altogether, 177Lu-octreotate exposure induced pro-apoptotic response (e.g. Apaf1, Bax, and Tnfrsf10b genes) in kidney medulla and cortex. A1M co-administration did not inhibit pro-apoptotic response in kidney cortex, while A1M initiated pro-survival mechanisms in kidney medulla.

131I (iodide) accumulates in the thyroid and may affect thyroid tissue. Mechanisms behind such effects are not known. The aim was to investigate early changes in protein expression in thyroid and plasma from mice injected with 131I as iodide. Female Balb/c nude mice were i.v. injected with 0 or 490 kBq 131I and killed after 24 h. Thyroid and blood samples were collected from each animal. Protein levels were determined by mass spectrometry. Data are available via ProteomeXchange with identifier PXD062861. Altogether, 17 and 20 proteins showed statistically significant altered levels in thyroid gland and plasma, respectively, after 131I exposure. Most of these proteins had decreased and increased levels in thyroid and plasma, respectively. Few of them were previously proposed radiation responsive proteins. Functional annotation suggests impact on haematopoiesis, reduced oxygen levels, and hypothyroidism. The role of CHIA and PGAM2 in radiation-induced response should be further examined, together with identification and validation of biomarkers of 131I exposure.

131I is recognised, both for its significance in nuclear medicine, and for its association with a rise in paediatric but not adult thyroid cancer cases following the Chornobyl accident. However, the detailed radiobiological mechanisms underlying 131I effects on the thyroid remain unknown to date. In the present study, 1 kBq or 100 kBq 131I was administered to mice that were euthanised after 48 h, 3 weeks or 6 months. Thyroid glands were surgically removed, and proteins were extracted and analysed by tandem mass spectrometry. On a group-level, the results showed few alterations in protein abundance, mainly linked to RNA metabolism and DNA damage response. However, individual analysis of protein abundance changes in each animal showed distinct findings suggesting inhibited proliferation in a few individuals across various exposure levels and time points. Future studies should involve larger animal groups to better assess the frequency and variability of proteomic radiation responses.