P-PSMA-101 Generates Long-Lasting Response to Prostate Cancer, Mouse Study Shows

P-PSMA-101 Generates Long-Lasting Response to Prostate Cancer, Mouse Study Shows

Poseida Therapeutics’ P-PSMA-101 eliminated prostate cancer in all mice that were treated in a study and prevented it from returning in two-thirds, researchers reported.

The long-lasting nature of the therapy surfaced in the finding that two out of three mice remained cancer-free at the end of the 42-day study, the team said.

P-PSMA-101 is a CAR T-cell therapy that targets the PSMA protein found at high levels in prostate cancer. The name CAR T-cell comes from the approach used to fight cancer — modifying a person’s own immune T-cells. Scientists said the treatment’s long-lasting effect comes from the type of cells they modified: stem cell memory T-cells, or Tscms.

Poseida presented the study’s findings at the Society for Immunotherapy of Cancer 32nd Annual Meeting, in National Harbor, Maryland, Nov. 8-12. The title of the poster session was titled “PSMA‐specific CARTyrin T‐stem cell memory therapy eliminates solid tumor in subcutaneous prostate cancer model.”

P-PSMA has outperformed other CAR T-cell prostate cancer therapies in animal studies, Dr. Eric Ostertag, Poseida’s CEO, said in a press release. “Future efforts will continue towards clinical application of P‐PSMA‐101 in patients with metastatic castrate resistance prostate cancer” — an advanced, hard-to-treat type.

Studies suggest that P-PSMA-101 is better at keeping the cancer at bay than other PSMA-targeted CAR T-cell therapies.

This is likely related to how Poseida delivers the re-engineered cells to the cancer, the company said. Unlike most CAR T-cell therapies, it does not use a virus to carry the new genetic material to T-cells.

Along with other features of the therapy, its process makes it easier to produce the high numbers of modified T-cells needed to treat cancer.

Another unique feature of Poseida’s approach is that most of its CAR T-cells are stem cell memory T-cells. Researchers believe Tscm cells make treatment responses particularly durable.

In their study, researchers found that P-PSMA-101 cells eliminated cancer cells not only in a lab, but also when injected into mice implanted with aggressive and previously incurable prostate cancer cells.

This contrasted with another PSMA-targeting CAR T-cell therapy that is in clinical trials — J591 CAR T-cells. It had only had marginal effects in a lab and was unable to control the cancer in mice, Poseida said.

P-PSMA-101 cells also stayed in the blood for a long time, researchers said.

Poseida is testing a myeloma-focused CAR T-cell therapy, P-BCMA-101, in a Phase 1 clinical trial (NCT03288493).

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