Plus Therapeutics (NASDAQ: PSTV) is a pharmaceutical company engaged in the development of targeted radiotherapeutics for difficult-to-treat cancers. Currently, it is advancing a pipeline of product candidates with lead programs in leptomeningeal metastases and recurrent glioblastoma. In an email conversation with AlphaStreet, Dr. Marc Hedrick, chief executive officer of Plus Therapeutics, provided insights into the company’s strategic vision and its potential to transform oncology treatments.
Can you provide a brief overview of Plus Therapeutics and its clinical programs?
Listed on Nasdaq under the ticker symbol PSTV, Plus Therapeutics is a clinical-stage pharmaceutical company developing targeted radiotherapeutics designed to deliver a safe and effective dose of radiation directly to the tumor for adults and children with rare and difficult-to-treat cancers. We are based in the U.S. with headquarters in Houston. Our lead radiotherapeutic, REYOBIQ, is specifically formulated to treat central nervous system (CNS) cancers. We have three REYOBIQ clinical trial programs for leptomeningeal metastases (LM), recurrent glioblastoma (GBM), and pediatric brain cancer (PBC).
The company’s three trials are supported by grants from the NIH, DoD, and CPRIT. The first trial, ReSPECT-GBM, is for recurrent GBM and we expect to finish enrolling in Phase 2 soon. GBM is a fatal, treatment-resistant, malignant brain tumor affecting about 15K people each year. The second trial, ReSPECT-LM, is for LM. Our phase two trial is currently enrolling. LM is a late-stage cancer complication in which cancer cells spread from many primary cancers, such as breast, lung, melanoma, and gastrointestinal – to the CNS and affects about 150K people each year, but more recent studies indicate the actual instances are much higher. Our PBC trial, ReSPECT-PBC, expects to begin enrolling soon. PBCs, such as high-grade glioma and ependymoma, are malignant tumors in the brain or spinal cord that account for approximately 26% of all childhood cancers.
Our completed phase 1 clinical trials in GBM and LM show REYOBIQ’s safety and strong signs of efficacy. The data demonstrates that high radiation doses were successfully delivered locally to tumors and are well-tolerated with no significant safety issues. The findings provided evidence of prolonged survival and improved patient outcomes. Additionally, the U.S. FDA has granted Fast Track & Orphan Drug Designation for REYOBIQ, underscoring the regulatory support we have as well.
Plus Therapeutics also has a direct subsidiary, CNSide Diagnostics, which offers the CNSide CSF Assay Platform. CNSide is a highly sensitive, cerebrospinal fluid-based assay platform used to detect, quantify, and characterize tumor cells in patients with LM from carcinomas and melanomas. It is the first and only such diagnostic platform available commercially in the U.S.
What unique advantages does Plus Therapeutics’ targeted radiotherapeutics program offer over existing or emerging therapies in this area?
Radiation therapy is a crucial treatment modality for cancer and serves as the gold standard for fighting CNS cancers. However, traditional External Radiation Beam Therapy (EBRT) is limited by low doses to minimize potential damage to healthy tissues and organs and the need for frequent treatment sessions over several weeks, which are inconvenient and time-consuming for the patient. EBRT is associated with a variety of complications, including the loss of taste, hair loss, skin changes, and other negative effects that stem from toxic radiation levels in the body.
What makes Plus Therapeutics different is that we have developed a targeted radiotherapeutic that addresses these limitations with EBRT. Plus Therapeutics’ REYOBIQ targeted radiotherapeutic is an internal radiation therapy in which radiation is delivered locally to the tumor via catheter injection or infusion into the tumor space. This approach delivers radiation near or in the tumor, mitigating the risk of radiation damage to surrounding healthy tissues and organs.
Compared to EBRT, our REYOBIQ product candidate allows for the precise delivery of 15-20 times the radiation dose directly into the tumor in a single patient visit.
What are the main challenges in bringing REYOBIQ to market, and how do you see your proprietary radiotherapeutic platform evolving in the next five years?
One challenge is that we are focused on rarer and more difficult-to-treat cancers, which means it can be difficult to find patients to participate in our clinical trials or we face greater competition for patients. We are overcoming this challenge by establishing new clinical trial sites in more major cities across the U.S., thereby improving patient access. Another difficulty is ensuring that we can get our radiotherapeutic to the right patient at the right time. However, by establishing a robust supply chain for drug production and transportation, we are alleviating this issue.
Getting through the FDA approval process is also a challenge, but by generating compelling clinical data for GBM and LM, leveraging our FDA designations, and seeking accelerated approval to bring our radiotherapeutic to these patients who have few to no treatment options, we are well on our way. Over the next five years, we expect to expand our REYOBIQ portfolio to non-CNS cancers.
Beyond GBM, LM, and PBC, what other pipeline candidates are you actively exploring?
For REYOBIQ, we are performing preclinical studies evaluating the combination of our targeted radiotherapeutic with immune checkpoint inhibitors. Further, we have published preclinical data in several other indications including peritoneal carcinomatosis, head and neck cancer, and breast cancer. This can serve as a foundation for future FDA IND approvals. In addition to REYOBIQ, we also have a Rhenium-based radioembolization therapy in preclinical development for the treatment of primary and secondary liver cancer.
Primary liver cancer, or hepatocellular carcinoma (HCC), occurs most often in people with chronic liver diseases, including fatty liver disease and cirrhosis being the top risk factors, and affects about 42K people each year. Secondary liver cancer, or metastatic colorectal cancer (mCRC), is an advanced, stage IV cancer that has spread to the liver from the colon or rectum and affects about 75K people each year. Our next-generation radioembolization therapy is designed for the injection of biodegradable microspheres and a single high dose of radiation directly into the hepatic artery, blocking the tumor’s blood flow and shrinking the tumor. We expect this therapy will minimize radiation exposure to normal tissues, and improve patients’ survival expectancy and quality of life.
Given the positive data from the REYOBIQ clinical trial, what milestones do you foresee Plus Therapeutics achieving in the near term?
We expect to complete enrollment of our ReSPECT-GBM Phase 2 clinical trial of REYOBIQ for recurrent GBM soon. Our ReSPECT-LM multidose clinical trial for LM will begin in 2025. We are hopeful for positive results from both trials and given our FDA Fast Track and Orphan Designations, we hope to bring REYOBIQ to market within the next few years. We also expect to initiate enrollment of our ReSPECT-PBC Phase 1 clinical trial for pediatric brain cancer in 2025 and to launch CNSide in Q3 2025.
