A human single-domain antibody elicits potent antitumor activity by targeting an epitope in mesothelin close to the cancer cell surface

Our plain-English summary of A human single-domain antibody elicits potent antitumor activity by targeting an epitope in mesothelin close to the cancer cell surface, by Z. Tang, M. Feng, W. Gao, et al (Molecular Cancer Therapeutics, 2013).

The study

• Authors: Z. Tang, M. Feng, W. Gao, Y. Phung, W. Chen, A. Chaudhary, B. St Croix, M. Qian, D.S. Dimitrov, M. Ho
• Journal: Molecular Cancer Therapeutics
• Published: 2013;12(4):416-26
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Monoclonal antibodies against mesothelin are being evaluated for the treatment of mesothelioma and multiple forms of cancers, and show great promise for clinical development for solid cancers. Antibodies against mesothelin have been shown to act via immunotoxin-based inhibition of tumor growth and induction of antibody-dependent cell-mediated cytotoxicity (ADCC). However, complement-dependent cytotoxicity (CDC), considered an important additional mechanism of therapeutic antibodies against tumors, is inactive for such antibodies. Here, we used phage display antibody engineering technology and synthetic peptide screening to identify SD1, a human single-domain antibody to mesothelin. SD1 recognizes a conformational epitope at the C-terminal end (residues 539-588) of mesothelin close to the cell surface. To investigate SD1 as a potential therapeutic agent, we generated a recombinant human Fc (SD1-hFc) fusion protein. Interestingly, the SD1-hFc protein exhibits strong CDC activity, in addition to ADCC, against mesothelin-expressing tumor cells. Furthermore, it causes growth inhibition of human tumor xenografts in nude mice as a single agent. SD1 is the first human single-domain antibody targeting mesothelin-expressing tumors, shows potential as a cancer therapeutic candidate, and may improve current antibody therapy targeting mesothelin-expressing tumors.

In plain English

This was a laboratory study, not a study of people or of asbestos exposure. The authors developed SD1, a human single-domain antibody that binds mesothelin, a protein highly expressed in mesothelioma and other solid tumors. They fused it to part of a human antibody to make SD1-hFc and tested it on cancer cell lines, including the NCI-H226 mesothelioma line, and in nude mice carrying A431/H9 tumors. SD1-hFc bound human mesothelin. In tests using human serum, it killed 40% of A431/H9 cells and more than 30% of NCI-H226 mesothelioma cells. With human blood immune cells, it killed more than 40% of A431/H9 and more than 30% of NCI-H226 cells. A comparison antibody, HN1, showed no serum-based killing at the same concentrations. Twenty days after tumor implantation, average tumor size was about 300 mm3 in treated mice and about 1000 mm3 in controls. In the authors' cell growth tests, the antibody did not directly slow tumor cell growth. The authors concluded that SD1 is a promising therapeutic candidate. They called for direct comparisons with MORAb-009 and complement depletion studies in mice.

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 study: antibody discovery by phage display, tests on cancer cell lines, and a tumor experiment in mice (animal experiment)
• Who was studied: Human cancer cell lines, including the NCI-H226 mesothelioma line, ovarian, cholangiocarcinoma and lung cancer (NSCLC) lines, and A431/H9 cells engineered to carry human mesothelin. Also female athymic nude mice aged four to six weeks with implanted A431/H9 tumors. The number of mice is not stated.
• Exposure: No asbestos or fiber exposure was studied. The treatment tested was the SD1-hFc antibody. Mice received 50 mg/kg by intravenous injection on days 7, 9, 11, 14, 17 and 20 after tumor implantation. Control mice received PBS.
• Main results:
  • SD1-hFc bound full-length human mesothelin with a dissociation constant (KD) of 13.59 nM. It bound the C-terminal mesothelin peptide with a KD of 16.08 nM.
  • In complement-dependent killing tests with human serum, SD1-hFc killed 40% of A431/H9 cells
  • In the same type of test, SD1-hFc killed more than 30% of NCI-H226 mesothelioma cells
  • The control single-domain antibody and the HN1 antibody showed no complement-dependent killing at the same concentrations
  • In immune-cell-mediated killing (ADCC) tests, SD1-hFc killed more than 40% of A431/H9 cells and more than 30% of NCI-H226 mesothelioma cells
  • Twenty days after tumor implantation, the average tumor size in mice treated with SD1-hFc alone was about 300 mm3. In control mice it was about 1000 mm3.
  • With mouse serum, SD1-hFc killed 11% of A431/H9 cells
  • In the cell proliferation assays the authors performed, neither SD1 nor HN1 directly inhibited tumor cell growth (data not shown). The authors noted it remains uncertain whether any anti-mesothelin antibodies can do so.
• The authors' conclusion: The authors concluded that SD1 represents a new class of anti-mesothelin antibody and is a promising therapeutic candidate for mesothelin-targeted therapy. They also concluded that complement-dependent killing likely contributes to its anti-tumor activity.
• Limitations the authors state:
  • The role of complement-dependent killing in mice was not confirmed. The authors suggested complement depletion studies to test it.
  • SD1 was not directly compared with MORAb-009 in the same experiments
  • Mouse complement was 10-fold less active than human complement for SD1-hFc

Topics

Medical terms in this study, explained in our Lexicon: Mesothelin, Monoclonal, Mesothelioma.

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