Kate Amato Foundation Awarded Projects

Project Description:

Rhabdomyosarcoma (RMS) is a cancer that mostly affects children. It starts in soft tissues, including arms and legs, eyes, head, neck, abdomen, and around the genital or urinary systems. Current treatments for RMS include surgery, chemotherapy and radiation therapy. These treatments do not work long-term for late-stage or metastatic disease or against disease that relapses after treatment. These children desperately need new, innovative therapies. It is unacceptable to have had no new treatments for decades when none currently in the clinic are effective against relapsed or metastatic disease.

In the past ten years, a new type of therapy that uses the patient’s own immune cells has been incredibly successful in children with a type of blood cancer called Acute Lymphoblastic Leukemia (ALL). Children with relapsed/refractory ALL now have an over 80% survival rate at 2 years compared to just 20% before. This new therapy engineers the patient’s immune cells, T cells, to recognize the tumor, activates them and grows them to large numbers. The newly engineered “Chimeric Antigen Receptor-T cells,” or CAR-Ts, are re-introduced into the patient. They then travel through the blood, find and recognize the cancer cells and kill them. CAR-Ts can also be a safer alternative to traditional therapies without the short- or long-term side effects that are common with chemotherapy and radiation. Patients remark on their improved quality

of life with CAR-Ts compared to chemotherapy or radiation, and formal studies support their long-term benefits and safety. Though CAR-T therapy has been highly successful for leukemia, there are challenges to treating solid tumors, and, to date, there has been limited success in these patients. One challenge for solid tumors is that the targets are highly variable between patients’ tumors and even between the cancer cells in one patient’s tumor. It has been difficult to find broadly expressed solid tumor proteins that could be targeted by CAR-Ts. One major reason CAR-T therapy has been so successful in children and young adult patients with leukemia is because all their tumor cells have the CD19 protein. Therefore, a

CD19-CAR-T can recognize and kill all the patient’s tumor cells. Secondly, a common obstacle for CAR-T therapy in leukemias and solid tumors is a phenomenon known as target escape. This is a means by which some cancer cells become invisible or resistant to the CAR-T therapy by losing the protein being targeted. In a clinical trial of adults with lymphoma, simultaneously targeting two proteins with a bispecific CAR-T prevented this form of disease relapse. Our goal is to utilize a bispecific CAR-T to develop a safer, more effective treatment for pediatric cancers, focusing first on RMS.

We have identified two broadly expressed proteins, found on several pediatric cancer types, that we aim to co-target using bispecific CAR-Ts. The protein alphavbeta3 (αvβ3) is known to play a role in cancer progression and metastasis in many types of cancers, and it also plays a role in the development of new blood vessels that feed tumors. HER2 is expressed on many pediatric cancers, including RMS, and one child with metastatic RMS even experienced a temporary remission with HER2-CAR-Ts. We previously developed CAR-Ts that recognize either αvβ3 or HER2 and demonstrated that both CAR-Ts were highly effective at controlling or curing pediatric brain tumors in mice. We recently demonstrated that both αvβ3- and HER2-CAR-Ts are very effective in mice against RMS tumors growing in the leg muscle, a common location for cancer. These promising results support incorporating these two CARs into a bispecific CAR-T for pediatric RMS.

What is most interesting about the αvβ3- and HER2-CAR-T treatment results is that, despite both CAR-Ts nearly curing these aggressive RMS tumors, small tumor nests, similar to minimal residual disease (MRD) in patients, persist almost two months later. At this later timepoint, CAR-Ts are located in the tumor nests, and tumors still have the targeted proteins. Even so, the CAR-Ts appear unable to fully eliminate all cancer cells. We believe this is similar to MRD in patients, which often comes back as relapsed/refractory disease and no longer responds well to treatments. This is a huge challenge for treating solid tumors, not just for CAR-T therapy but for most types of therapy. A treatment that initially works very well eventually stops working, and the cancer grows back. For CAR-T treatment, we believe there are two phenomena

happening: over time, the CAR-Ts have become less effective at killing tumors cells, and the tumor cells have become less vulnerable to being killed by CAR-Ts, what is called “resistance.” For us to create better CAR-T therapies or better combinatorial therapies that prevent MRD that no longer responds to therapy, we need to first understand how it happens.

There is still much we do not understand about acquired CAR-T dysfunction and tumor resistance to CAR-T

therapy, and most of the research thus far has been in adult tumors, which, quite frankly, are not the same as pediatric solid tumors. Adult and pediatric solid cancers have very different origins and characteristics. Therefore, it is reasonable to anticipate that the mechanisms underlying CAR-T failure and tumor resistance to therapy will be distinct in pediatric solid tumors. We need to understand how these obstacles arise so we can design better treatments that prevent or anticipate them.

Here we propose to identify and begin to understand how CAR-Ts become dysfunctional and how tumor cells acquire resistance by using targeted and unbiased experimental approaches. We aim to meet this need for safer and more effective treatments for pediatric solid cancers by identifying mechanisms of CAR-T failure and tumor resistance driving persistence of MRD so we can engineer more effective αvβ3/HER2 bispecific CAR-Ts. We are prioritizing pediatric RMS because there are currently no effective treatments for relapsed/refractory or metastatic disease, and we plan to later test our therapy against other pediatric solid tumors, with the ultimate goal of eventually bringing it into a clinical trial for children.