A phase 1 trial to determine the maximum tolerated dose and patient-specific dosimetry of [177Lu]Lu-LNC1003 in patients with metastatic castration-resistant prostate cancer

Biodistribution and dosimetry of [177Lu]Lu-SibuDAB in patients with metastatic castration-resistant prostate cancer

PURPOSE

Several prostate-specific membrane antigen (PSMA) radiopharmaceuticals have been used for the treatment of metastatic, castration-resistant prostate cancer (mCRPC). In an attempt to improve the tumour accumulation, new PSMA ligands were developed with an albumin-binding entity to enhance the blood circulation and, hence, tumour accumulation. In preclinical studies, [177Lu]Lu-SibuDAB, a radiopharmaceutical with moderate albumin-binding properties, outperformed [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T. The aim of this study was to evaluate the dosimetry of [177Lu]Lu-SibuDAB in patients diagnosed mCRPC.

METHODS

Seventeen patients (median age 72 years, range 63‒83) diagnosed with progressive disease of mCRPC were included in this prospective study after exhausting all available treatment options. They were injected with 5.3 ± 0.5 GBq (mean ± standard deviation) [177Lu]Lu-SibuDAB as a first treatment cycle. Sixteen of these patients underwent sequential whole-body SPECT/CT and activity determination in venous blood samples for dosimetry purposes. Absorbed doses to the salivary glands, liver, spleen, kidneys, and red marrow as well as selected tumour lesions were calculated in OLINDA/EXM™ and compared to published values for previously established PSMA radiopharmaceuticals.

RESULTS

Absorbed dose coefficients (ADC) to tumours (9.9 ± 5.4 Gy/GBq) were about 2-fold higher than those reported for clinically approved PSMA radiopharmaceuticals. ADC to salivary glands, liver, spleen, kidneys and red marrow were higher (0.5 ± 0.2, 0.2 ± 0.05, 0.2 ± 0.1, 1.8 ± 0.6, 0.1 ± 0.04 Gy/GBq, respectively) than for [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T, but lower than for [177Lu]Lu-PSMA-ALB-56, a previously investigated long-circulating PSMA radiopharmaceutical. The tumour-to-kidneys, tumour-to-red marrow, tumour-to-salivary glands ADC ratio were 6.6, 102, 33.1. These ratios were comparable to those of [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T for kidneys and red-marrow, but higher for salivary glands.

CONCLUSION

[177Lu]Lu-SibuDAB showed a prolonged blood circulation time and, hence, a significantly increased absorbed tumour dose, while tumour-to-organ ADC ratios were similar to conventional PSMA radiopharmaceuticals. Further clinical investigations to evaluate the efficacy and safety of [177Lu]Lu-SibuDAB are, thus, warranted.

Development of Novel Radiotheranostic Ligand with Positively Charged Unit Targeting Prostate-Specific Membrane Antigen

Prostate-specific membrane antigen (PSMA) is an ideal target of prostate cancer (PCa) for theranostics, combining diagnosis and therapy in the field of nuclear medicine. [177Lu]Lu-PSMA-617 is a gold standard in PSMA-targeting radioligands, whereas its rapid clearance from the tumor and high uptake in the kidney may compromise the efficacy of theranostics. In this study, we developed novel PSMA-targeting radioligands, [111In]In/[225Ac]Ac-PDI2 and [111In]In/[225Ac]Ac-PDI4, by introducing a positively charged diethylenetriamine (PEI2) or tetraethylenepentamine (PEI4) structure, respectively, to PSMA-617. In the biodistribution study, higher tumor retention and lower renal uptake of [111In]In-PDI2 and [111In]In-PDI4 were observed than those of [111In]In-PSMA-617, and [111In]In-PDI2 exhibited higher tumor-residualizing properties than [111In]In-PDI4. [111In]In-PDI2 and [111In]In-PDI4 clearly visualized PSMA-expressing tumors by single photon emission computed tomography/computed tomography (SPECT/CT). The administration of [225Ac]Ac-PDI2 led to a higher antitumor effect than [225Ac]Ac-PDI4 and [225Ac]Ac-PSMA-617. These findings suggest the utility of [111In]In/[225Ac]Ac-PDI2 as theranostic ligands for PCa.

Deciphering the Tumor Uptake of Heterobivalent (SST2/Albumin) [64Cu]Cu-NODAGA-cLAB-TATEs

Radioligands with albumin-binding moieties exhibit a great potential for the treatment of tumor diseases owing to the general finding of an increased integral tumor uptake compared to radioligands without such moieties. However, the reasons for this pharmacokinetic behavior are less explored. Herein, we focused on identifying potential mechanisms for our previously developed heterobivalent (SST2/albumin) [64Cu]Cu-NODAGA-cLAB-TATEs. For this purpose, we designed two novel derivatives that show either negligible binding to albumin or lack the SST2-targeting capability. Based on the in vivo results, we hypothesize that binding of the albumin-bound radioligand to SST2 in addition to that of the free radioligand causes the increased tumor uptake. This is supported by saturation binding analyses in the presence of albumin and compartment modeling considerations. Overall, the results of this study provide a first tentative explanation for the phenomenon of increased tumor uptake for albumin-binding radioligands, which may support the prospective design of such radioligands.

Dansylated Amino Acid-Modified Long-Acting PSMA Derivatives 68Ga/177Lu-LNC1011 as Prostate Cancer Theranostics

Prostate-specific membrane antigen (PSMA)-targeted radiopharmaceutical therapy has demonstrated promising potential for treating metastatic castration-resistant prostate cancer. Recently, albumin-binding motif-modified PSMA radioligands with prolonged blood circulation were developed to improve tumor uptake and therapeutic effectiveness, properties which, however, were associated with an increased risk of bone marrow toxicity. This study presents new PSMA-targeted radioligands incorporating dansylated amino acids as relatively weak and preferable albumin binders to achieve a fine balance between increased tumor accumulation, safety, and diagnostic efficacy, facilitating a unified approach to theranostics within a single molecular framework. Methods: Three novel PSMA ligands ([68Ga]Ga-Dan-Gly-PSMA, [68Ga]Ga-Dan-Nva-PSMA, and [68Ga]Ga-Dan-Phe-PSMA, denoted as [68Ga]Ga-LNC1011) were synthesized with dansylated amino acids and measured the albumin-binding properties with human serum albumin through ultrafiltration experiments. Binding affinity and PSMA-targeting specificity were investigated using a saturation binding assay and cell uptake in the PSMA-induced prostate cancer 3 cell line (PC3-PIP). PET imaging in PC3-PIP tumor-bearing mice was performed to evaluate the preclinical pharmacokinetics and diagnostic efficiency of 68Ga-labeled PSMA ligands. Tumor uptake of [177Lu]Lu-LNC1011 was evaluated through SPECT/CT imaging and biodistribution studies. Radiopharmaceutical therapy studies were conducted to systematically assess the therapeutic effect of the radioligand. Results: Three novel PSMA radioligands ([68Ga]Ga-Dan-Gly-PSMA, [68Ga]Ga-Dan-Nva-PSMA, and [68Ga]Ga-LNC1011) with various dansylated amino acids were successfully synthesized with a radiochemical yield greater than 97%. In the PC3-PIP xenograft tumor model, the tumor/heart, tumor/liver, tumor/kidney, and tumor/muscle ratios were 9.82 ± 2.35, 12.42 ± 3.71, 4.36 ± 0.29, and 52.88 ± 12.08 at 4 h after injection, respectively. Biodistribution studies confirmed the significantly higher tumor uptake of [177Lu]Lu-LNC1011 (127.36 ± 16.95 %ID/g) over [177Lu]Lu-PSMA-617 (17.44 ± 6.29 %ID/g) at 4 h after injection, and no decrease was measured for the [177Lu]Lu-LNC1011 at up to 72 h after injection, which was corroborated with SPECT imaging. A single injection of 9.3 MBq of [177Lu]Lu-LNC1011 achieved 89.43% inhibition of tumor growth, equivalent to 18.5 MBq of [177Lu]Lu-PSMA-617 (90.87%). [68Ga]Ga-LNC1011 PET/CT scans of patients with metastatic castration-resistant prostate cancer identified as many lesions as [68Ga]Ga-PSMA-11 did, confirming its diagnostic efficacy. Conclusion: 68Ga/177Lu-LNC1011, characterized by high tumor uptake and retention along with timely clearance from normal organs and tissues, thus emerges as a promising single-molecule theranostic radioligand.

Comparison of Radionuclide Drug Conjugates With Boron Neutron Capture Therapy: An Overview of Targeted Charged Particle Radiation Therapy

Targeted charged alpha- and beta-particle therapies are currently being used in clinical radiation treatments as newly developed methods for either killing or controlling tumor cell growth. The alpha particles can be generated either through a nuclear decay reaction or in situ by a nuclear fission reaction such as the boron neutron capture reaction. Different strategies have been employed to improve the selectivity and delivery of radiation dose to tumor cells based on the source of the clinically used alpha particles. As a result, the side effects of the treatment can be minimized. The increasing attention and research efforts on targeted alpha-particle therapy have been fueled by exciting results of both academic research and clinical trials. It is highly anticipated that alpha-particle therapy will improve the efficacy of treating malignant tumors. In this overview, we compare radionuclide drug conjugates (RDC) with boron neutron capture therapy (BNCT) to present recent developments in targeted alpha-particle therapy.

PSMA-targeted radioligand therapy with [177Lu]Lu-LNC1011 for metastatic castration-resistant prostate cancer: a pilot study

BACKGROUND

Preclinical studies have shown that the long-acting PSMA-targeting radiopharmaceutical [177Lu]Lu-LNC1011 based on dansylated amino acid modification had high tumor uptake and prolonged retention. This study aimed to explore its safety and efficacy in patients with metastatic castration-resistant prostate cancer (mCRPC).

METHODS

Eight mCRPC patients who met the inclusion criteria received intravenous treatment with [177Lu]Lu-LNC1011. Treatment was repeated every 6 weeks for up to a maximum of 6 cycles. Molecular imaging and hematology markers were the main evaluation indicators. The primary endpoints were biochemical (PSA) response and molecular imaging response. Toxicity grading was assessed using the Common Terminology Criteria for Adverse Events version 5.0.

RESULTS

Hematological toxicity was the primary side effect. In all patients, adverse events (AEs) after [177Lu]Lu-LNC1011 treatment were primarily characterized by decreased levels of hemoglobin, white blood cells and platelets. Grade 3 anemia was recorded in 1 patient, and grade 2 leukopenia and thrombocytopenia were recorded in 4 patients. The average systemic effective dose was 0.18 mSv/MBq, and the kidney was the organ with the highest absorbed dose (3.11 ± 0.26 mSv/MBq). Long half-life (71.30 ± 8.23 h) and high absorbed dose [5.77, (range 5.5-14 Gy/GBq)] were calculated in the lesions. All patients had a more than 50% decline of PSA during treatment, and one patient dropped to 0 ng/mL. According to assessment criteria adapted from the PERCIST v.1.0 criteria, complete response, partial response, and disease progression were observed in 2 (25%), 4 (50%), and 2 (25%) patients, respectively.

CONCLUSION

[177Lu]Lu-LNC1011 was well tolerated and had acceptable side effects for PSMA-targeted radioligand therapy. Tumor lesions received high radiation doses and had excellent responses to the treatment. Dose escalation studies in a larger number of patients are worth pursuing and necessary to confirm these results. URL OF REGISTRY: https://clinicaltrials.gov/study/NCT06809426?term=NCT06809 .

TRIAL REGISTRATION

NCT06809426, registration date: 2025-01-23.

Development of [225Ac]Ac‑LNC1011 for targeted alpha-radionuclide therapy of prostate cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) radioligand therapy (PRLT) has become a promising option for treating metastatic castration-resistant prostate cancer (mCRPC). Radioligands labelled with the 68Ga/177Lu theranostic pair have been most widely used in the clinic for diagnosis and therapy, respectively. This study aims to develop a novel PSMA-targeted radioligand, LNC1011, radiolabeled with alpha-emitter 225Ac, to optimise pharmacokinetic properties and assess its potential for targeted alpha therapy (TAT) in prostate cancer treatment.

METHODS

LNC1011 (Dan-PSMA) was synthesised based on a PSMA-binding ligand with the addition of a dansylated amino acid. Systematic radiochemical analyses were conducted to confirm the successful synthesis and radiolabelling of [225Ac]Ac-LNC1011. Cell uptake and competition binding assays were performed in PSMA-positive PC3-PIP tumour cells to evaluate the binding affinity and PSMA targeting specificity. The pharmacokinetics properties and tumour uptake were characterised by biodistribution studies using healthy mice and a PC3-PIP xenograft mouse model injected with [225Ac]Ac-LNC1011. Radioligand therapy studies and maximum tolerated dose (MTD) assays were conducted to systematically evaluate the therapeutic efficacy and the safety of [225Ac]Ac-LNC1011.

RESULTS

[225Ac]Ac-LNC1011 was successfully radiolabelled with high radiochemical purity (> 97%) and high stability within 96 h (radiochemical purity > 96%). The high binding affinity of LNC1011 (IC50 = 16.28 nM) to PSMA was comparable to that of PSMA-617 (IC50 = 27.93 nM). Biodistribution studies confirmed that [225Ac]Ac-LNC1011 had moderate blood elimination half-life (T1/2z = 13.4 ± 0.57 h), which was at an optimised level between [225Ac]Ac-PSMA-617 (T1/2z = 5.19 ± 0.12 h) and [225Ac]Ac-PSMA-EB-01 (T1/2z = 25.18 ± 2.78 h). In addition, high tumour uptake of [225Ac]Ac-LNC1011 was identified to be 38.28 ± 10.04%ID/g at 1 h post-injection. The specific uptake gradually increased and peaked at 24 h (80.57 ± 3.00%ID/g) and persisted at a high level up to 72 h post-injection (50.58 ± 5.37%ID/g). Targeted alpha therapy results showed the complete inhibition of PC3-PIP tumour growth after administration of a single dose of 1 µCi and 0.5 µCi of [225Ac]Ac-LNC1011 similar to 0.5 µCi [225Ac]Ac-PSMA-617. At the 0.1 µCi dose level, partial remission was observed for [225Ac]Ac-LNC1011, as recurrence was found 20 days after administration. In contrast, mice treated with 0.1 µCi [225Ac]Ac-PSMA-617 showed incomplete tumour inhibition under the same conditions.

CONCLUSION

[225Ac]Ac-LNC1011 was successfully radiolabelled with high radiochemical purity and stability. With significantly improved tumour uptake and retention over PSMA-617, [225Ac]Ac-LNC1011 showed significantly better therapeutic efficacy than [225Ac]Ac-PSMA-617 for targeted alpha therapy of prostate cancer.

Novel Radiopharmaceuticals and Future of Theranostics in Genitourinary Cancers

BACKGROUND AND OBJECTIVE

This review aims to provide an overview of novel diagnostic and therapeutic radiopharmaceuticals tested recently or used currently in genitourinary cancers within prospective phase 1-2 clinical trials, summarizing progresses and future directions.

METHODS

A systematic search was conducted using the PubMed/MEDLINE and ClinicalTrials.gov databases for original prospective research studies following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

KEY FINDINGS AND LIMITATIONS

Forty-six papers were systematically reviewed; 74 ongoing clinical trials were identified. The results of 27 novel radiopharmaceuticals (ie, not approved by the Food and Drug Administration/European Medicines Agency and not listed in the Pharmacopeia) prospectively investigated in genitourinary cancers, mostly prostate, for diagnostic, theranostic, or therapeutic purposes (21, one, and five of the 27 radiopharmaceuticals, respectively) over the past 5 yr were presented. Most were prostate-specific membrane antigen-targeting agents (17/27); other targets included gastrin-releasing peptide receptor, carbonic anhydrase IX, Cu, six transmembrane epithelial antigen of the prostate 1, tumor-associated glycoprotein 42, and urokinase-type plasminogen activator receptor. Ongoing research confirms the same trend. Fibroblast activation protein inhibitor, PD-L1, CD8, nectin-4, and HER2 are other targets under investigation. Among the 22 ongoing therapeutic trials (out of the 74 ongoing clinical trials), targeted alpha therapy is being explored in 12, and five are evaluating combinations of radioligand therapy with other treatments. We confirmed the safety of radiopharmaceuticals (regardless of the diagnostic/therapeutic purpose) and showed promising results in terms of diagnostic accuracy and therapeutic efficacy in genitourinary cancers.

CONCLUSIONS AND CLINICAL IMPLICATIONS

There continues to be expansion in radiopharmaceutical approaches to genitourinary cancers, reflecting a strong emphasis on improving tumor detection and treatment, which will likely impact future management across the disease spectrum, with the potential for improved patient care and outcomes.

Therapeutic co-assemblies for synergistic NSCLC treatment through dual topoisomerase I and tubulin inhibitors

Camptothecin (CPT) and podophyllotoxin (PPT) function as topoisomerase (TOP) I and tubulin inhibitors, respectively, with potent anticancer effects in a variety of cancers. Despite its promise, the clinical applicability of the combination of CPT and PPT faces challenges, including potential side effect and limited therapeutic efficacy. In this study, we designed co-assembly nanomedicines with the different weight (w/w) ratios of amphiphilic Evans blue conjugated CPT prodrug (EB-ss-CPT) and PPT molecules, denoted as ECT Nano. The co-assembly of EB-ss-CPT and PPT without other excipients has nearly 100% drug loading efficiency and high drug loading content of PPT of up to 74.29 ± 0.90 wt%. Notably, the ECT Nano (1:2) equipped with the ability to inhibit TOP I activity and tubulin polymerization, which provided a highly efficient strategy to improve synergistic efficacy and decrease side toxicity in non-small cell lung cancer mouse model. This work represents a step forward to the development of practical applications for dual TOP I and tubulin inhibitors and especially hopeful to the rational design of combination nanomedicine for therapeutic purposes.

Design and conduct of theranostic trials in neuro-oncology: Challenges and opportunities

Theranostics is a new treatment modality integrating molecular imaging with targeted radionuclide therapy. Theranostic agents have received regulatory approval for some systemic cancers and have therapeutic potential in neuro-oncology. As clinical trials are developed to evaluate the efficacy of theranostic agents in brain tumors, specific considerations will have to be considered, taking into account lessons learned from previous studies examining other treatment modalities in neuro-oncology. These include the need for molecular imaging or surgical window-of-opportunity studies to confirm adequate passage across the blood-brain barrier, optimize eligibility criteria, and selection of the most appropriate response criteria and endpoints to address issues such as pseudoprogression. This review will discuss some of the issues that should be considered when designing clinical trials for theranostic agents.

Comparison of novel PSMA-targeting [177Lu]Lu-P17-087 with its albumin binding derivative [177Lu]Lu-P17-088 in metastatic castration-resistant prostate cancer patients: a first-in-human study

PURPOSE

Prostate-specific membrane antigen (PSMA) is a promising target for diagnosis and radioligand therapy (RLT) of prostate cancer. Two novel PSMA-targeting radionuclide therapy agents, [177Lu]Lu-P17-087, and its albumin binder modified derivative, [177Lu]Lu-P17-088, were evaluated in metastatic castration-resistant prostate cancer (mCRPC) patients. The primary endpoint was dosimetry evaluation, the second endpoint was radiation toxicity assessment (CTCAE 5.0) and PSA response (PCWG3).

METHODS

Patients with PSMA-positive tumors were enrolled after [68Ga]Ga-PSMA-11 PET/CT scan. Five mCRPC patients received [177Lu]Lu-P17-087 and four other patients received [177Lu]Lu-P17-088 (1.2 GBq/patient). Multiple whole body planar scintigraphy was performed at 1.5, 4, 24, 48, 72, 120 and 168 h after injection and one SPECT/CT imaging was performed at 24 h post-injection for each patient. Dosimetry evaluation was compared in both patient groups.

RESULTS

Patients showed no major clinical side-effects under this low dose treatment. As expected [177Lu]Lu-P17-088 with longer blood circulation (due to its albumin binding) exhibited higher effective doses than [177Lu]Lu-P17-087 (0.151 ± 0.036 vs. 0.056 ± 0.019 mGy/MBq, P = 0.001). Similarly, red marrow received 0.119 ± 0.068 and 0.048 ± 0.020 mGy/MBq, while kidney doses were 0.119 ± 0.068 and 0.046 ± 0.022 mGy/MBq, respectively. [177Lu]Lu-P17-087 demonstrated excellent tumor uptake and faster kinetics; while [177Lu]Lu-P17-088 displayed a slower washout and higher average dose (7.75 ± 4.18 vs. 4.72 ± 2.29 mGy/MBq, P = 0.018). After administration of [177Lu]Lu-P17-087 and [177Lu]Lu-P17-088, 3/5 and 3/4 patients showed reducing PSA values, respectively.

CONCLUSION

[177Lu]Lu-P17-088 and [177Lu]Lu-P17-087 displayed different pharmacokinetics but excellent PSMA-targeting dose delivery in mCRPC patients. These two agents are promising RLT agents for personalized treatment of mCRPC. Further studies with increased dose and frequency of RLT are warranted to evaluate the potential therapeutic efficacy.

TRIAL REGISTRATION

177Lu-P17-087/177Lu-P17-088 in Patients with Metastatic Castration-resistant Prostate Cancer (NCT05603559, Registered at 25 October, 2022). URL OF REGISTRY: https://classic.

CLINICALTRIALS

gov/ct2/show/NCT05603559 .

New Drugs for Targeted Radionuclide Therapy in Metastatic Prostate Cancer

Metastatic prostate cancer is a frequent and fatal disease. Targeted radionuclide therapy (TRT) has become a readily available therapeutic option since the approval of [177Lu]Lu-PSMA-617. Various molecules are currently being studied for TRT in prostate cancer. We review various combinations of isotopes and vectors being used to target prostate cancer cells and optimize pharmacokinetics. Promising innovations include chemical modifications to improve biodistribution, identification of new targets, and the use of novel radioisotopes such as α emitters. PATIENT SUMMARY: Our mini review summarizes research on targeted radioactive drugs for treatment of metastatic prostate cancer. Several promising radioactive pharmaceuticals are being evaluated in clinical trials, but more studies are necessary before these can be used in routine clinical practice.