The claudin connection: exploring the potential of claudins in oncology

Astellas Pharma Ltd commissioned the article, reviewed and amended the final copy. Diarmuid Moran is an Astellas employee. Professor Chau received a fee for the interview. Views are his own and not necessarily those of Astellas Pharma Ltd. This article is for UK healthcare professionals only.

Claudins, a family of proteins integral to cell junctions, have emerged as pivotal players in the field of oncology, particularly due to their role in tumor progression and metastasis. Among these, claudin 18.2 has garnered significant interest due to its potential as a target for cancer therapeutics. In this interview, Professor Ian Chau (The Royal Marsden NHS Foundation Trust, London, UK) and Diarmuid Moran (Head of Precision Medicine and Diagnostics; Astellas Pharma, Chicago, US) provide an overview of the nature of claudins and discuss what may be on the horizon for claudin 18.2.

What are claudins and why are they of interest to oncology research?

Diarmuid Moran (DM): Claudins are very important physiological proteins. They are tight-junction proteins which means they exist within tight junctions, the close cell contacts between epithelial or endothelial cells. Within epithelial sheets, claudins play important roles in maintaining the polarization of cells and keeping the cells in the right order, in addition to controlling the permeability between cells, which means the passage of molecules between cells.

There are approximately 27 claudin family members. One of the unique aspects of claudins is that they are expressed throughout the body, but often with each claudin family member being expressed in a highly tissue-specific manner. Claudins share many functions; however, dependent upon the claudin and the tissues in which they are expressed, they often have tissue-specific roles as well.

Ian Chau (IC): Many of these claudin functions are important in cancer proliferation and metastasis. Therefore, with different cancers, they will have differential expression of various claudins.  Many different cancer-related genes, which are important in cancer signaling pathways, are amplified or overexpressed into proteins. Importantly, the expression of some of these proteins may indicate whether they are prognostic and relate to the patient’s survival. Some could also be predictive of cancer therapeutics’ effectiveness.

A well-established example, which is frequently used in oncology, is HER2. HER2-targeted therapeutics are now used in multiple cancers and were originally developed in breast cancer, where the presence of HER2 is a prognostic factor. Patients with HER2-overexpressed breast cancer were initially found to have poorer prognosis. Later, it translated to be a predictive biomarker for drugs, which subsequently transformed the prognosis. We now have many different HER2-targeted agents. Claudins have been assessed in a similar way. Multiple claudins have been investigated in terms of their prognostic values. Now we are developing cancer therapeutics against certain claudins and understanding the predictive value of claudin expression.

What are some of the claudin family members of interest in cancer research?

DM: Multiple claudins are under research at different stages and recently the claudin research space has become very active. We see the largest development area, for both therapeutics and as a biomarker, for claudin 18. However, we also see drugs being developed in clinical studies targeting claudin 6, which is very commonly overexpressed in ovarian cancer. We also see drug development activities for claudin 4, which is expressed in many gastrointestinal cancers.

Why is claudin 18.2 an area of particular interest?

DM: Claudin 18.2 is particularly of interest for a few reasons. There are two known isoforms of claudin 18 – claudin 18.1, which is expressed in lung tissue and claudin 18.2, which is expressed in normal gastric tissue. What is particularly interesting is the restricted expression of claudin 18.2. It is typically only seen in normal gastric tissue and has very limited expression in other normal tissues. As gastric cancer develops, while some gastric tumors lose it, the majority retain claudin 18.2 expression. It’s also been observed that claudin 18.2 can become overexpressed in other cancers such as pancreatic cancer, ovarian cancer and non-small cell lung cancer.

Another unique aspect of claudin 18.2 and the reason it probably has generated the greatest interest, is the way that it’s expressed and localized in gastric cancer tumors. When we spoke about the normal function of claudin proteins, we described it being buried in tight junctions which may make it relatively inaccessible to therapeutics. It is proposed that as the gastric tumor develops and cells lose polarization, the cells begin to expose claudin 18.2, which may allow binding of treatments that can deliver chemotherapeutics or an immune attack into the tumor. So that unique property is a very important aspect of claudin 18.2.

Astellas and others have also done substantial research on claudin 18.2 in terms of understanding its global prevalence, and how it is expressed across different tumor types, particularly for gastric and gastroesophageal junction cancers. Claudin 18.2 is expressed in approximately 75–80% of all gastric cancers. Higher expression [1] (in some of the larger studies) occurs in the tumors of more than a third of patients. So the data supports that it’s a highly prevalent biomarker in these cancers.

IC: To add onto this in terms of prevalence, through some large-scale global screening studies, we’ve seen other variations in the prevalence of claudin 18.2. In terms of age, sex, geographical regions and histological subtype (diffuse vs. intestinal). Whereas there might be statistical differences in the prevalence for several patient or clinical characteristics, the absolute differences are generally small.

We should also consider if claudin 18.2 is a prognostic or predictive biomarker. This has led to a series of questions. Firstly, how do you define claudin 18.2 positivity? Multiple studies over the years have used different thresholds because when we run protein expression, we predominantly use immunohistochemistry (IHC). So, we must work out which IHC antibody to assess. In addition, it also matters which IHC antibody platform you are using, not just an antibody. Then we need to decide what percentage we would class as overexpressed and whether it’s moderate or strong stain intensity. That all feeds into how we define claudin 18.2 as a biomarker.

There is no evidence at present to show that CLDN 18.2 is a prognostic factor despite multiple studies [2].

The next thing we’re trying to do, as more cancer therapeutics are targeted towards claudin 18.2, is decide what the threshold is for claudin 18.2 positivity to decide whether that drug will be effective.

Diarmuid, do you want to add more detail about how we try to work out what’s the best cutoff for claudin 18.2 and about clinical trials?

DM: Certainly, there’s a lot of research ongoing in this area. There are many therapeutic modalities being developed that target claudin 18.2. As Ian pointed out, establishing a cut-off for claudin 18.2 expression is dependent on many factors such as what drug is being developed and the potency of the mechanism of action. There is a lot of work that has to be done in clinical research to be able to understand the biomarker and how its expression might relate to therapeutic activity. Generally, it is through clinical studies that we identify the patient populations who benefit the most from new treatments.

IC: It’s an interesting biomarker and I think the ongoing clinical trials with several compounds also suggest it’s a predictive biomarker [3],[4]. There are multiple mechanisms of action being investigated to target claudin 18.2, such as monoclonal antibodies, bispecific antibodies, antibody-drug conjugates and CAR-T [5],[6],[7]. So, for the monoclonal antibodies, you may need a higher expression of the biomarker in the cancer cells.

What’s on the horizon for claudin 18.2 and what’s on the horizon for other claudins?

IC: Early on we mentioned that there are different therapeutic classes that can target claudin 18.2. Certainly, the most advanced drug development area involves monoclonal antibodies. We know the approach will probably be similar to the approach we use for monoclonal antibodies for other targets, where we tend to combine them with cytotoxic chemotherapy. That is probably closest on the horizon. There is also preclinical and clinical data looking at these monoclonal antibodies together with both chemotherapy and chemotherapy plus immunotherapy.

There are other therapeutics in development to target claudin 18.2. These antibody-drug conjugates are well known in terms of therapeutic targets for the HER2 biomarker. Regarding claudin 18.2, gastric cancer is the main focus for this drug class due to the claudin 18.2 prevalence but there are studies ongoing in pancreatic cancer. Other therapeutics would be bispecific antibodies. These are bispecific T-cell engagers. They have one arm targeting claudin 18.2 [8], but another arm targeting an immune molecule such as CD3 [9]. They are starting to come into human Phase I studies now. That is a little bit further on the horizon, but there is very intense research interest in this area at the moment.

Then CAR-T is another potential approach against claudin 18.2. There are some initially very encouraging results coming from one of the CAR-T molecules in East Asia and that is now being tested in Western populations. The important thing is that they potentially require lower expression of claudin 18.2 to be effective. They are showing good activity even for heavily pretreated patients, including those who have already received immunotherapy [5],[6],[7],[10].

In terms of other claudins, there are now quite early first-in-human Phase I small-scale studies. For example, claudin 3 is often looked at in colorectal cancer [11] and there are CAR-Ts being developed against claudin 3 and being explored further. Claudin 6, is observed in ovarian cancer [12] and is common in germ-cell tumors [13], a rare cancer type, which is very sensitive to chemotherapy.

There is a smaller group of patients who have refractory disease, but they are highly expressing claudin 6. A recent study looked at the use of CAR-T, but on top of giving CAR-T against claudin 6, they also used a form of RNA vaccine to expand or amplify the CAR-T cells [14]. It’s being tested in both germ cell tumors (testicular cancers) and ovarian cancer.

There are some other potentially interesting therapeutics in preclinical and even early clinical development. For example, there’s a form of lipid nanoparticle being investigated to deliver mRNA to manufacture the claudin 18.2 antibody inside the body of the patient. Preclinical studies have shown that the mechanism is feasible [15]. They’ve started to study this in humans, but we are awaiting further data on this approach.

There are very interesting therapeutic approaches against this big family of claudins. Some of these are in very advanced clinical development. Hopefully, we’ll be able to use these in our patients very soon.

Sources:

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2. Kim HD, Choi E, Shin J, Lee IS, Ko CS, Ryu MH, Park YS. Clinicopathologic features and prognostic value of claudin 18.2 overexpression in patients with resectable gastric cancer. Sci. Rep. 13, 20047 (2023).

3. Cao W, Xing H, Li Y et al. Claudin18.2 is a novel molecular biomarker for tumor-targeted immunotherapy. Biomark. Res. 10, 38 (2022). 

4. Klempner SJ, Janjigian YY, Wainberg ZA. Claudin 18.who? Examining biomarker overlap and outcomes in claudin18.2-positive gastroesophageal adenocarcinomas. ESMO Open. 8(2), 100778 (2023).

5. Nakayama I, Qi C, Chen Y et al. Claudin 18.2 as a novel therapeutic target. Nat. Rev. Clin. Oncol. 21, 354–369 (2024).

6. Shitara K, Lordick F, Bang YJ et al. Zolbetuximab plus mFOLFOX6 in patients with CLDN18.2-positive, HER2-negative, untreated, locally advanced unresectable or metastatic gastric or gastro-oesophageal junction adenocarcinoma (SPOTLIGHT): a multicentre, randomised, double-blind, phase 3 trial. Lancet. 401(10389):1655–1668 (2023).

7. Shah MA, Shitara K, Ajani JA et al. Zolbetuximab plus CAPOX in CLDN18.2-positive gastric or gastroesophageal junction adenocarcinoma: the randomized, phase 3 GLOW trial. Nat. Med. 29, 2133–2141 (2023).

8. Lordick F, Chao J, Buxo E et al. 1496TiP Phase I study evaluating safety and tolerability of AMG 910, a half-life extended bispecific T cell engager targeting claudin-18.2 in gastric and gastroesophageal junction adenocarcinoma. Ann. Oncol. 31, S928–S929 (2020).

9. Zhu G, Foletti D, Liu X, Ding S et al. Targeting CLDN18.2 by CD3 bispecific and ADC modalities for the treatments of gastric and pancreatic cancer. Sci. Rep. 9, 8420 (2019).

10. Qi C, Gong J, Li J. et al. Claudin18.2-specific CAR T cells in gastrointestinal cancers: phase 1 trial interim results. Nat. Med. 28,1189–1198 (2022).

11. Mees ST, Mennigen R, Spieker T et al. Expression of tight and adherens junction proteins in ulcerative colitis associated colorectal carcinoma: upregulation of claudin-1, claudin-3, claudin-4, and β-catenin. Int. J. Colorectal Dis. 24, 361–368 (2009). 

12. Du H, Yang X, Fan J, Du X. Claudin 6: Therapeutic prospects for tumours, and mechanisms of expression and regulation. Mol. Med. Rep. doi:10.3892/mmr.2021.12316 (2021) (Epub ahead of print). 

13. Skowron MA, Kotthoff M, Bremmer F, Ruhnke K et al. Targeting CLDN6 in germ cell tumors by an antibody-drug-conjugate and studying therapy resistance of yolk-sac tumors to identify and screen specific therapeutic options. Mol. Med. 29(1), 40 (2023). 

14. Mackensen A, Haanen JB, Koenecke C et al. CLDN6-specific CAR-T cells plus amplifying RNA vaccine in relapsed or refractory solid tumors: the phase 1 BNT211-01 trial. Nat. Med. 29, 2844–2853 (2023).

15. Bähr-Mahmud H, Ellinghaus U, Stadler CR et al. Preclinical characterization of an mRNA-encoded anti-Claudin 18.2 antibody. Oncoimmunology. 12(1), 2255041 (2023).

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The opinions expressed in this article are those of the author and do not necessarily reflect the views of Oncology Central or Taylor & Francis Group.

Astellas Pharma Ltd commissioned the article, reviewed and amended the final copy. Diarmuid Moran is an Astellas employee. Professor Chau received a fee for the interview. Views are his own and not necessarily those of Astellas Pharma Ltd. This article is for UK HCPs only.

MAT-GB-NON-2024-00314

July 2024