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Combination Strategies to Improve Targeted Radionuclide Therapy.

ABSTRACT: In recent years, targeted radionuclide therapy (TRT) has emerged as a promising strategy for cancer treatment. In contrast to conventional radiotherapy, TRT delivers ionizing radiation to tumors in a targeted manner, reducing the dose that healthy tissues are exposed to. Existing TRT strategies include the use of ¹⁷⁷Lu-DOTATATE, ¹³¹I-metaiodobenzylguanidine, Bexxar, and Zevalin, clinically approved agents for the treatment of neuroendocrine tumors, neuroblastoma, and non-Hodgkin lymphoma, respectively. Although promising results have been obtained with these agents, clinical evidence acquired to date suggests that only a small percentage of patients achieves complete response. Consequently, there have been attempts to improve TRT outcomes through combinations with other therapeutic agents; such strategies include administering concurrent TRT and chemotherapy, and the use of TRT with known or putative radiosensitizers such as poly(adenosine diphosphate ribose) polymerase and mammalian-target-of-rapamycin inhibitors. In addition to potentially achieving greater therapeutic effects than the respective monotherapies, these strategies may lead to lower dosages or numbers of cycles required and, in turn, reduce unwanted toxicities. As of now, several clinical trials have been conducted to assess the benefits of TRT-based combination therapies, sometimes despite limited preclinical evidence being available in the public domain to support their use. Although some clinical trials have yielded promising results, others have shown no clear survival benefit from particular combination treatments. Here, we present a comprehensive review of combination strategies with TRT reported in the literature to date and evaluate their therapeutic potential.

SUBMITTER: Chan TG

PROVIDER: S-EPMC8679619 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundRadiolabelled bombesin (BN) conjugates are promising radiotracers for imaging and therapy of breast and prostate tumours, in which BN2/gastrin-releasing peptide receptors are overexpressed. We describe the influence of the specific activity of a 177Lu-DOTA-PEG5k-Lys-B analogue on its therapeutic efficacy and compare it with its non-PEGylated counterpart.MethodsDerivatisation of a stabilised DOTA-BN(7-14)[Cha13,Nle14] analogue with a linear PEG molecule of 5?kDa (PEG5k) was performed by PEGylation of the ?-amino group of a ?3hLys-?Ala-?Ala spacer between the BN sequence and the DOTA chelator. The non-PEGylated and the PEGylated analogues were radiolabelled with 177Lu. In vitro evaluation was performed in human prostate carcinoma PC-3 cells, and in vivo studies were carried out in nude mice bearing PC-3 tumour xenografts. Different specific activities of the PEGylated BN analogue and various dose regimens were evaluated concerning their therapeutic efficacy.ResultsThe specificity and the binding affinity of the BN analogue for BN2/GRP receptors were only slightly reduced by PEGylation. In vitro binding kinetics of the PEGylated analogue was slower since steady-state condition was reached after 4?h. PEGylation improved the stability of BN conjugate in vitro in human plasma by a factor of 5.6. The non-PEGylated BN analogue showed favourable pharmacokinetics already, i.e. fast blood clearance and renal excretion, but PEGylation improved the in vivo behaviour further. One hour after injection, the tumour uptake of the PEG5k-BN derivative was higher compared with that of the non-PEGylated analogue (3.43?±?0.63% vs. 1.88?±?0.4% ID/g). Moreover, the increased tumour retention resulted in a twofold higher tumour accumulation at 24?h p.i., and increased tumour-to-non-target ratios (tumour-to-kidney, 0.6 vs. 0.4; tumour-to-liver, 8.8 vs. 5.9, 24?h p.i.). In the therapy study, both 177Lu-labelled BN analogues significantly inhibited tumour growth. The therapeutic efficacy was highest for the PEGylated derivative of high specific activity administered in two fractions (2?×?20?MBq?=?40?MBq) at day 0 and day 7 (73% tumour growth inhibition, 3?weeks after therapy).ConclusionsPEGylation and increasing the specific activity enhance the pharmacokinetic properties of a 177Lu-labelled BN-based radiopharmaceutical and provide a protocol for targeted radionuclide therapy with a beneficial anti-tumour effectiveness and a favourable risk-profile at the same time.

Project description:Very late antigen-4 (VLA-4; also known as integrin α4β1) is expressed at high levels in aggressive and metastatic melanoma tumors and may provide an ideal target for imaging and targeted radiotherapy. 177Lu-DOTA-PEG4-LLP2A (177Lu-LLP2A) shows high affinity for VLA-4 and had high uptake in B16F10 mouse melanoma tumors in vivo. Here, we report efficacy studies of 177Lu-LLP2A, alone and combined with immune checkpoint inhibitors (ICI) in B16F10 tumor-bearing mice. Methods: B16F10 tumor cells (1 x 106) were implanted subcutaneously in C57BL/6 mice. After 8-10 days, the mice were randomized into eight groups (n = 8). 177Lu-LLP2A was injected i.v. on day 8 or 9 (single dose), and ICI antibodies were administered i.p. in 3 doses. Tumor growth was monitored over time via calipers. TUNEL staining for apoptosis was performed on fixed tumors. In a separate study, Cy3-LLP2A or Cy3-scramble LLP2A were injected in tumor-bearing mice, tumors were collected after 4 h post-injection, and then analyzed by flow cytometry and immunofluorescence microscopy using different immune cell markers. Results:177Lu-LLP2A alone showed comparable efficacy to combination anti-PD-1/PD-L1 + anti-CTLA-4 antibody treatment, while 177Lu-LLP2A together with combination ICI significantly enhanced survival. TUNEL staining showed the highest levels of apoptosis were found in the 177Lu-LLP2A + ICI groups. In addition to targeting tumor cells, 177Lu-LLP2A also binds immune cells in the B16F10 tumor microenvironment. Based on flow cytometry data, the tumor consists of ~77 % tumor cells/fibroblasts (CD45-CD49d+) and ~23 % immune cells (CD45+CD49d+), and immune cells express higher levels of VLA-4. Cy3-LLP2A and CD49d colocalized with macrophages (CD68), T cells (CD8, CD4), and B cells (CD19). Immunohistochemical analysis identified a significant colocalization of Cy3-LLP2A and CD68. Conclusion: Combination treatment of 177Lu-LLP2A and ICI targets both tumor cells and immune cells and has potential as a therapeutic agent in patients with metastatic melanoma.

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Combination Strategies to Improve Targeted Radionuclide Therapy.

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