Dr. Hope Rugo and Dr. Giuseppe Curigliano discuss recent developments in the field of bispecific antibodies for hematologic and solid tumors, including strategies to optimize the design and delivery of the immunotherapy.

TRANSCRIPT

Dr. Hope Rugo: Hello and welcome to By the Book, a podcast series from ASCO that features engaging conversations between editors and authors of the ASCO Educational Book. I am your host, Dr. Hope Rugo. I am the director of the Women's Cancers Program and division chief of breast medical oncology at the City of Hope Cancer Center. I am also the editor-in-chief of the Educational Book.

Bispecific antibodies represent an innovative and advanced therapeutic platform in hematologic and solid tumors. And today, I am delighted to be joined by Dr. Giuseppe Curigliano to discuss the current landscape of bispecific antibodies and their potential to reshape the future of precision oncology.

Dr. Curigliano was the last author of an ASCO Educational Book piece for 2025 titled, "Bispecific Antibodies in Hematologic and Solid Tumors: Current Landscape and Therapeutic Advances." Dr. Curigliano is a breast medical oncologist and the director of the Early Drug Development Division and chair of the Experimental Therapeutics Program at the European Institute of Oncology in Milan. He is also a full professor of medical oncology at the University of Milan.

You can find our disclosures in the transcript of this episode.

Dr. Curigliano, Giuseppe, welcome and thanks for being here.

Dr. Giuseppe Curigliano: Thanks a lot for the invitation.

Dr. Hope Rugo: Giuseppe, I would like to first ask you to provide some context for our listeners on how these novel therapeutics work. And then perhaps you could tell us about recent developments in the field of bispecific antibodies for oncology. We are at a time when antibody-drug conjugates (ADCs) are all the rage and, trying to improve on the targeting of specific antigens, proteins, receptors in the field of oncology is certainly a hot and emerging topic.

Dr. Giuseppe Curigliano: So, thanks a lot. I believe really it was very challenging to try to summarize all the bispecific antibodies that are under development in multiple solid tumors. So, the first thing that I would like to highlight is the context and the mechanism of action of bispecific antibodies.

Bispecific antibodies represent a groundbreaking advancement in cancer immunotherapy, because these engineered molecules have the unique ability to target and simultaneously bind to two distinct antigens. That is why we call them bispecific. So typically, one antigen is expressed on the tumor cell and the other one is expressed on the immune effectors, like T-cell or natural killer cells. So this dual targeting mechanism offers several key advantages over conventional monoclonal antibodies because you can target at the same time the tumor antigen, downregulating the pathway of proliferation, and you can activate the immune system. So the primary mechanism through which bispecific antibodies exert their therapeutic effects are: First, T-cell redirecting. I mean, many bispecific antibodies are designed to engage tumor-associated antigens like epidermal growth factor receptor, HER2, on the cancer cell and a costimulatory molecule on the surface of T-cell. A typical target antigen on T-cell is CD3. So what does it mean? That you activate the immune system, immune cells will reach the tumor bed, and you have a dual effect. One is downregulating cell proliferation, the other one is activation of the immune system. This is really important in hematological malignancies, where we have a lot of bispecifics already approved, like acute lymphoblastic leukemia or non-Hodgkin lymphoma.

The second, in fact, is the engagement of the tumor microenvironment. So, if you engage immune effector cells like NK cells or macrophages, usually the bispecific antibodies can exploit the immune system's ability to recognize and kill the immune cells, even if there is a lack of optimal antigen presentation.

And finally, the last mechanism of action, this may have a role in the future, maybe in the early cancer setting, is overcoming immune evasion. So bispecific antibodies can overcome some of the immune evasion mechanisms that we see in cancer. For example, bispecific antibodies can target immune checkpoint receptors, like PD-L1 and CTLA-4. Actually, there is a bispecific under development in breast cancer that has a dual targeting on vascular endothelial growth factor receptor and on PD-L1. So you have a dual effect at the same time.

So, what is really important, as a comment, is we need to focus first on the optimal format of the bispecific, the optimal half-life, the stability, because of course even if they are very efficient in inducing a response, they may give also a lot of toxicities. So in clinical trials already, we have several bispecifics approved. In solid tumors, very few, specifically amivantamab for non-small cell lung cancer, but we have a pipeline of almost 40 to 50 bispecifics under development in multiple solid tumors, and some of them are in the context of prospective randomized trials.

Dr. Hope Rugo: So this is really a fascinating area and it's really exciting to see the expansion of the different targets for bispecific antibodies. One area that has intrigued me also is that some of the bispecifics actually will target different parts of the same receptor or the same protein, but presumably those will be used as a different strategy. It's interesting because we have seen that, for example, in targeting HER2.

Dr. Giuseppe Curigliano: Oh, yes, of course. You may consider some bispecifics like margetuximab, I suppose, in which you can target specifically two different epitopes of the same antigen. This is really an example of how a bispecific can potentially be more active and downregulating, let us say, a pathway, by targeting two different domains of a specific target antigen. This is an important point.

Of course, not all the bispecifics work this way, because some of the target antigen may dimerize, and so you have a family of target antigen; an example is epidermal growth factor receptor, in which you have HER1, HER2, HER3, and HER4. So some of them can inhibit the dimerization between one target antigen and the other one, in order to exert a more antiproliferative effect. But to be honest, the new generation of them are more targeting two different antigens, one on the tumor and one on the microenvironment, because according to the clinical data, this is a more efficient way to reduce proliferation and to activate the immune system.

Dr. Hope Rugo: Really interesting, and I think it brings us to the next topic, which is really where bispecific antibodies have already shown success, and that is in hematologic malignancies where we have seen very interesting efficacy and these are being used in the clinic already. But the expansion of bispecific antibodies into solid tumors faces some key challenges. It's interesting because the challenges come in different shapes and forms. Tell us about some of those challenges and strategies to optimize bispecific antibody design, delivery, patient selection, and how we are going to use these agents in the right kind of clinical trials.

Dr. Giuseppe Curigliano: This is really an excellent question because despite bispecific antibodies having shown a remarkable efficacy in hematological malignancies, their application in solid tumors may have some challenges. The first one is tumor heterogeneity. In hematological malignancy, you have a clear oncogene addiction. Let us say that 90% of the cells may express the same antigen. In solid tumors, it is not the same. Tumor heterogeneity is a typical characteristic of solid tumors, and you have high heterogeneity at the genetic, molecular, and phenotypic levels. So tumor cells can differ significantly from one another, even if within the same tumor. And this heterogeneity sometimes makes it difficult to identify a single target antigen that is universally expressed in an hematological malignancy. So furthermore, sometimes the antigen expressed on a tumor cell can be also present on the normal tissue. And so you may have a cross-targeting. So let's say, if you have a bispecific against epidermal growth factor receptor, this will target the tumor but will target also the skin with a lot of toxicity.

The second challenge is the tumor microenvironment. The solid tumor microenvironment is really complex and often immunosuppressive. It is characterized by the presence of immunosuppressor cells like the T regulators, myeloid derived suppressor cells, and of course the extracellular matrix. All these factors hinder immune cell infiltration and also may reduce dramatically the effectiveness of bispecific antibodies. And as you know, there is also an hypoxic condition in the tumor.

The other challenge is related to the poor tumor penetration. As you know also with antibody-drug conjugate, only 1 to 3% of the drug will arrive in the tumor bed. Unlike hematological malignancies where tumor cells are dispersed in the blood and easily accessible, the solid tumors have a lot of barriers, and so it means that tumor penetration can be very low. Finally, the vascularity also of the tumor can be different across solid tumors. T...