New CAR-T cell therapy using scorpion venom developed to treat brain tumors

Contributed by Wikimedia Commons (Public Domain)

Glioblastoma (GBM) is an aggressive form of cancer that begins in the brain and results in tumors that can be very difficult to treat. This condition has claimed the lives of Beau Biden, former Vice President Joe Biden’s son, and John McCain, former Senator of Arizona. However, a new approach to combat this condition is being developed at City of Hope and has just received approval from the FDA to conduct clinical trials. The innovative approach involves using a combination of chimeric antigen receptor (CAR)-T cell therapy and specific components of scorpion venom!

Before we dive into how the scorpion venom is being used, what exactly is CAR-T cell therapy?

Diagram of CAR-T Cell Therapy
Image Source: National Cancer Institute

This approach consists of using T cells, which are an immune system cell that can destroy foreign or abnormal cells, and modifying them with a protein called a chimeric antigen receptor (CAR). These newly designed CAR-T cells are able to identify and destroy cancer cells by detecting a specific protein on these cells. What makes CAR-T cell even more promising is that the specific protein detected can be set to virtually anything.

This is where the scorpion venom comes into play. One of the components of this venom is called chlorotoxin (CLTX), which has the ability to specifically bind to brain tumor cells.

Michael Barish, Ph.D. (Left), Christine Brown, Ph.D. (Center), Dongrui Wang (Right)
Photo Credit: Business Wire

For this study, Dr. Christine Brown, Dr. Michael Barish, and a team of researchers at City of Hope designed CAR-T cells using chlorotoxin in order to specifically detect and destory brain tumor cells. Now referred to as CLTX-CAR-T cells, they found that these newly engineered cells were highly effective at selectively killing brain tumor cells in animal models. What’s more remarkable is that the CLTX-CAR-T cells ignored non-tumor cells in the brain and other organs.

In a press release, Dr. Barish describes the CLTX-CAR-T cell approach in more detail.

“Much like a scorpion uses toxin components of its venom to target and kill its prey, we’re using chlorotoxin to direct the T cells to target the tumor cells with the added advantage that the CLTX-CAR T cells are mobile and actively surveilling the brain looking for appropriate target. We are not actually injecting a toxin, but exploiting CLTX’s binding properties in the design of the CAR. The idea was to develop a CAR that would target T cells to a wider variety of GBM tumor cells than the other antibody-based CARs.”

In the same press release, Dr. Brown talks about the promise of this newly developed therapy.

“Our chlorotoxin-incorporating CAR expands the populations of solid tumors potentially targeted by CAR T cell therapy, which is particularly needed for patients with cancers that are difficult to treat such as glioblastoma. This is a completely new targeting strategy for CAR T therapy with CARs incorporating a recognition structure different from other CARs.”

The first-in-human clinical trial using the CLTX-CAR T cells is now screening potential patients.

CIRM has funded a separate clinical trial conducted by Dr. Brown that also involves CAR-T cell therapy for brain tumors.

The full results of this study was published in Science Translational Medicine.

A video talking about this approach can also be found here.

Scientists find switch that targets immunotherapies to solid tumors

Cancer immunotherapies harness the power of the patient’s own immune system to fight cancer. One type of immunotherapy, called adoptive T cell therapy, uses immune cells called CD8+ Killer T cells to target and destroy tumors. These T cells are made in the spleen and lymph nodes and they can migrate to different locations in the body through a part of our circulatory system known as the lymphatic system.

CD8+ T cells can also leave the circulation and travel into the body’s tissues to fight infection and cancer. Scientists from the Scripps Research Institute and UC San Diego are interested in learning how these killer T cells do just that in hopes of developing better immunotherapies that can specifically target solid tumors.

In a study published last week in the journal Nature, the teams discovered that a gene called Runx3 acts as a switch that programs CD8+ T cells to set up shop within tissues outside of the circulatory system, giving them access to solid tumors.

“Runx3 works on chromosomes inside killer T cells to program genes in a way that enables the T cells to accumulate in a solid tumor,” said Matthew Pipkin, co-senior author and Associate Professor at The Scripps Research Institute.

Study authors Adam Getzler, Dapeng Wang and Matthew Pipkin of The Scripps Research Institute collaborated with scientists at the University of California, San Diego.

They discovered Runx3 by comparing what genes were expressed in CD8+ T cells found in the lymphatic system to CD8+ T cells that were found in tissues outside of the circulation. They then screened thousands of potential factors for their ability to influence CD8+ T cells to infiltrate solid tumors.

“We found a distinct pattern,” Pipkin said. “The screens showed that Runx3 is one at the top of a list of regulators essential for T cells to reside in non-lymphoid tissues.”

The team then set out to prove that Runx3 was a key factor in getting CD8+ T cells to localize at the site of solid tumors. To do this, they took T cells that either overexpressed Runx3 or did not express Runx3 in these cells. The T cells were then transplanted into mice with melanoma through a process known as adoptive cell transfer. Overexpression of Runx3 in T cells not only reduced tumor size but also extended lifespan in the mice. On the other hand, removing Runx3 expression had a negative impact on their survival rate.

This research, which was supported in part by CIRM funding, offers a new strategy for developing better cancer immunotherapies for solid tumors.

Pipkin concluded in a Scripps Research Institutes News Release,

“Knowing that modulating Runx3 activity in T cells influences their ability to reside in solid tumors opens new opportunities for improving cancer immunotherapy. We could probably use Runx3 to reprogram adoptively transferred cells to help drive them to amass in solid tumors.”