Safety, dosimetry, and efficacy of an optimized long-acting somatostatin analog for peptide receptor radionuclide therapy in metastatic neuroendocrine tumors: From preclinical testing to first-in-human study

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.

Radiopharmaceuticals and their applications in medicine

Radiopharmaceuticals involve the local delivery of radionuclides to targeted lesions for the diagnosis and treatment of multiple diseases. Radiopharmaceutical therapy, which directly causes systematic and irreparable damage to targeted cells, has attracted increasing attention in the treatment of refractory diseases that are not sensitive to current therapies. As the Food and Drug Administration (FDA) approvals of [177Lu]Lu-DOTA-TATE, [177Lu]Lu-PSMA-617 and their complementary diagnostic agents, namely, [68Ga]Ga-DOTA-TATE and [68Ga]Ga-PSMA-11, targeted radiopharmaceutical-based theranostics (radiotheranostics) are being increasingly implemented in clinical practice in oncology, which lead to a new era of radiopharmaceuticals. The new generation of radiopharmaceuticals utilizes a targeting vector to achieve the accurate delivery of radionuclides to lesions and avoid off-target deposition, making it possible to improve the efficiency and biosafety of tumour diagnosis and therapy. Numerous studies have focused on developing novel radiopharmaceuticals targeting a broader range of disease targets, demonstrating remarkable in vivo performance. These include high tumor uptake, prolonged retention time, and favorable pharmacokinetic properties that align with clinical standards. While radiotheranostics have been widely applied in tumor diagnosis and therapy, their applications are now expanding to neurodegenerative diseases, cardiovascular diseases, and inflammation. Furthermore, radiotheranostic-empowered precision medicine is revolutionizing the cancer treatment paradigm. Diagnostic radiopharmaceuticals play a pivotal role in patient stratification and treatment planning, leading to improved therapeutic outcomes in targeted radionuclide therapy. This review offers a comprehensive overview of the evolution of radiopharmaceuticals, including both FDA-approved and clinically investigated agents, and explores the mechanisms of cell death induced by radiopharmaceuticals. It emphasizes the significance and future prospects of theranostic-based radiopharmaceuticals in advancing precision medicine.

Development of [177Lu]Lu-LNC1010 for peptide receptor radionuclide therapy of nasopharyngeal carcinoma

PURPOSE

Somatostatin Receptor 2 (SSTR2)-targeted radiopharmaceutical [68Ga]Ga-DOTATATE has potential advantages in the diagnosis of nasopharyngeal carcinoma (NPC). This study introduces a novel long-lasting SSTR2 analogue, LNC1010, based on DOTATATE, a truncated Evans blue-binding moiety, and a polyethylene-glycol linker. We hypothesised that peptide receptor radionuclide therapy (PRRT) is more effective with [177Lu]Lu-LNC1010 than with [177Lu]Lu-DOTATATE in treating metastatic NPC.

METHODS

We assessed binding characteristics of LNC1010 in vitro using C666-1 NPC cells and in-vivo pharmacokinetics of [68Ga]Ga/[177Lu]Lu-LNC1010 in C666-1 NPC xenografts via PET and SPECT imaging, biodistribution studies, and PRRT, and compared them with [68Ga]Ga/[177Lu] Lu-labelled DOTATATE. Furthermore, a proof-of-concept approach for imaging and therapy was conducted in a patient with metastatic NPC.

RESULTS

LNC1010 exhibited strong uptake and specific affinity for SSTR2 in C666-1 NPC cells. PET and SPECT imaging demonstrated higher uptake and longer tumour retention of [68Ga]Ga/[177Lu]Lu-LNC1010 than [68Ga]Ga/[177Lu]Lu-DOTATATE in C666-1 NPC xenografts, indicating its suitability for PRRT applications in NPCs. Biodistribution studies confirmed the higher uptake and prolonged retention of [177Lu]Lu-LNC1010 than [177Lu]Lu-DOTATATE. In preclinical PRRT studies, [177Lu]Lu-LNC1010 showed greater inhibition of tumour growth in C666-1 NPC xenografts than [177Lu]Lu-DOTATATE. In a subsequent pilot clinical study, PRRT with [177Lu]Lu-LNC1010 achieved favourable therapeutic and negligible side effects in a patient with metastatic NPC.

CONCLUSION

[177Lu]Lu-LNC1010 demonstrated increased tumour uptake and prolonged retention in SSTR2-positive NPCs, with superior anti-tumour efficacy to that of [177Lu]Lu-DOTATATE in preclinical studies. These findings suggest that PRRT with [177Lu]Lu-LNC1010 is a promising treatment for advanced NPC, extending the clinical scope of PRRT beyond neuroendocrine tumours.