Construction and Preclinical Evaluation of 211At Labeled Anti-mesothelin Antibodies as Potential Targeted Alpha Therapy Drugs

Our plain-English summary of Construction and Preclinical Evaluation of 211At Labeled Anti-mesothelin Antibodies as Potential Targeted Alpha Therapy Drugs, by X. Wang, W. Ma, W. Liu, et al (Journal of Radiation Research, 2020).

The study

• Authors: X. Wang, W. Ma, W. Liu, H. Ma, Y. Yang, Y. Wang, N. Liu, G. Yang
• Journal: Journal of Radiation Research
• Published: 2020;61(5):684-690
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Targeted alpha therapy (TAT) is a promising tumor therapy that can specifically transport α particle to the vicinity of tumor cells while the normal cells are only slightly irradiated. Mesothelin is a highly promising molecular signature for many types of solid tumors including malignant mesothelioma, pancreatic cancer, ovarian cancer and lung adenocarcinoma etc., while the expression in normal human tissues are limited, thus making mesothelin a promising antigen for TAT. Previously we developed a theoretical model that could predict and optimize in vitro screening of potential TAT drugs. The aim of the study is construction and preclinical evaluation of 211At labeled anti-mesothelin antibodies as potential TAT drugs. Mesothelin expression of two tumor cell lines were confirmed by flow cytometry, and their radiosensitivities were also evaluated. We used two kinds of anti-mesothelin antibodies, ET210-6 and ET210-28, to construct TAT drugs. Then, radiochemical purity, stability in vitro, affinity of the conjugates and mesothelin expression level were assessed. The specific killing of mesothelin-positive cancer cells treated by 211At-ET210-28 and 211At-ET210-6 were studied via Cell Counting Kit-8 assay and colony formation assay. 211At-ET210-28 and 211At-ET210-6 revealed excellent affinity and stability in both phosphate buffer saline and fetal bovine serum environment. Radiolabeled antibody conjugates bound specifically to mesothelin-positive cells in vitro. Both 211At-ET210-28 and 211At-ET210-6 could specifically kill mesothelin-positive cells with negligible damages to mesothelin-negative cells. Our findings provide initial proof-of-concept for the potential use of 211At labeled ET210-28/ET210-6 anti-mesothelin antibody in specific killings of mesothelin-positive tumor cells.

© The Author(s) 2020. Published by Oxford University Press on behalf of The Japanese Radiation Research Society and Japanese Society for Radiation Oncology.

In plain English

This laboratory study tested two experimental anti-mesothelin antibodies, ET210-28 and ET210-6, each attached to the alpha-particle-emitting radioactive element astatine-211, as possible targeted alpha therapy drugs. Mesothelin is a protein found on several cancers, including malignant mesothelioma. The work used only laboratory-grown cells: the human tumor cell line MDA-MB-231, which showed nearly no mesothelin, and a version engineered to carry mesothelin. No patients, animals, mesothelioma cells or asbestos exposure were studied. In phosphate buffer saline or fetal bovine serum, not in a living body, the labeled antibodies stayed stable for up to 48 hours. In a binding test using iodine-131-labeled rather than astatine-211-labeled ET210-28, the antibody bound mesothelin with a dissociation constant of 0.251 nM. At 0.82 kBq/mL, astatine-211-labeled ET210-28 left 9.83 ± 1.83% of mesothelin-positive cells surviving. Labeled ET210-6 left 3.76 ± 0.98% surviving at 7.41 kBq/mL. At 0.80 kBq/mL of labeled ET210-28, 1.94 ± 0.20% of mesothelin-positive cells survived, against 97.32 ± 10.61% of mesothelin-negative cells. A radiolabeled control antibody was much less damaging. The authors concluded that the two drugs might be promising potential treatments for mesothelin-expressing tumors.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) preclinical study using cultured cell lines; no animal or human experiments
• Who was studied: Two human cell lines grown in the laboratory: MDA-MB-231, which was mesothelin-negative, and MDA-MB-231-mesothelin, a line engineered (stably transfected) to express human mesothelin. No mesothelioma cells, patients or animals were studied.
• Exposure: No asbestos exposure was studied. The cells were treated with the anti-mesothelin antibodies ET210-28 and ET210-6, and with a control IgG antibody, each labeled with the alpha emitter astatine-211, at doses from 0.02 to 500 kBq/mL. Iodine-131-labeled ET210-28 was used for the binding tests, and cobalt-60 gamma rays at 1, 2, 4 and 6 Gy were used to test how sensitive the cells were to radiation.
• Main results:
  • Flow cytometry showed high mesothelin expression in MDA-MB-231-mesothelin cells and nearly no mesothelin in MDA-MB-231 cells
  • In laboratory (in vitro) tests, the astatine-211-labeled antibodies stayed stable in phosphate buffer saline and in fetal bovine serum for up to 48 hours, with only a slight drop in radiochemical purity. Stability in a living organism was not tested.
  • In a binding assay that used iodine-131-labeled ET210-28 (not the astatine-211-labeled antibody), ET210-28 had a dissociation constant (Kd) of 0.251 nM. The mesothelin expression level on MDA-MB-231-mesothelin cells was printed as 4.37 × 105, which appears to be 4.37 × 10^5 (binding sites per cell) with the superscript lost in scanning. The 1.25 nM value given for ET210-6 comes from the authors' earlier study, not this one.
  • In the CCK-8 viability test on mesothelin-positive cells, survival after astatine-211-labeled ET210-28 was 83.74 ± 10.64% at 0.27 kBq/mL and 9.83 ± 1.83% at 0.82 kBq/mL
  • Survival of mesothelin-positive cells treated with astatine-211-labeled ET210-6 was 3.76 ± 0.98% at 7.41 kBq/mL. The authors reported that labeled ET210-28 was more cytotoxic than labeled ET210-6.
  • At the same dose (0.80 kBq/mL) of astatine-211-labeled ET210-28, survival was 1.94 ± 0.20% for mesothelin-positive cells versus 97.32 ± 10.61% for mesothelin-negative cells (P less than 0.001, per the figure legend)
  • In colony formation tests on mesothelin-positive cells, survival after labeled ET210-28 and labeled ET210-6 was much lower than after labeled control IgG
  • From the CCK-8 results, the authors set a 'meaningful dose interval' of 0.82 to 22.22 kBq/mL for labeled ET210-28 and 2.47 to 22.22 kBq/mL for labeled ET210-6
  • Mesothelin-positive cells treated with labeled control IgG at 0.09, 0.27 and 0.82 kBq/mL showed survival of 104.03 ± 3.87%, 103.91 ± 5.13% and 103.22 ± 3.92%. The authors interpreted this as radiation hormesis.
• The authors' conclusion: The authors concluded that astatine-211-labeled ET210-28 and ET210-6 bound mesothelin well and specifically killed mesothelin-positive tumor cells, suggesting they might be promising potential targeted alpha therapy drugs for mesothelin-expressing tumors
• Limitations the authors state:
  • Because there was not enough astatine-211 or antibody available, iodine-131-labeled antibodies (not astatine-211-labeled ones) were used for the receptor saturation and binding affinity tests

Topics

Medical terms in this study, explained in our Lexicon: Mesothelin, Mesothelioma, Ovarian Cancer, Lung Adenocarcinoma, Damages.

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