Fusion Pharmaceuticals (FUSN) Announces Preliminary Safety and Dosimetry Results from its Single-Dose Portion of the Phase 1 Study of FPI-1434

Fusion Pharmaceuticals Inc. (Nasdaq: FUSN), a clinical-stage oncology company focused on developing next-generation radiopharmaceuticals as precision medicines, today announced the presentation of preliminary Phase 1 data from the single-dose portion of the study at the Society of Nuclear Medicine and Molecular Imaging (SNMMI) Virtual Annual Meeting. The presentations and posters highlight the potential of Fusion's targeted alpha therapies (TATs) to enable delivery of alpha particle emitting isotopes (225Ac) to targeted tumor cells.

"The data from our ongoing clinical study of FPI-1434 presented at SNMMI demonstrated that treatment with our actinium-based targeted alpha therapy was well tolerated, and imaging shows uptake of the drug across multiple tumor types," said Chief Executive Officer John Valliant, Ph.D. "Importantly, these data supported our ability to initiate the multi-dosing portion of the study, in which we would expect to begin reaching total cumulative levels of radiation necessary to demonstrate anti-tumor activity."

In both the oral session and the poster titled, "Preliminary Dosimetry Results from a First-in-Human Phase 1 Study Evaluating the Efficacy and Safety of [225Ac]-FPI-1434 in Patients with IGF-1R Expressing Solid Tumors," results from the first three patient cohorts (n=12) demonstrated a favorable safety profile for [225Ac]-FPI-1434. No drug-related serious adverse events and/or dose limiting toxicity were reported in administered activity up to 40 kBq/kg body weight and dosimetric results were within normal organ radiation tolerability limits. The single dose escalation portion of the study has concluded, while enrollment into the multi-dosing cohorts are ongoing.

Preclinical Results Combining FPI-1434 with DNA Damage Response Inhibitor (DDRi) and Immune Checkpoint InhibitorsIn separate oral and poster presentations, Fusion presented preclinical data demonstrating synergistic efficacy against olaparib-resistant colorectal and radioresistant lung cancer xenografts when combining FPI-1434 with olaparib.

The combination of the two therapeutics, using doses that were non-effective as single agents, resulted in anti-tumor efficacy against colorectal and non-small cell lung cancer tumor models. The strongest combination effect appeared to occur at the lowest single agent doses, as FPI-1434's efficacy dominated at higher dose levels.

Fusion also presented preclinical data showing that treatment with FPI-1434 in combination with immune checkpoint inhibitors resulted in complete tumor eradication. Additionally, an increase in antigen-specific CD8 positive T cells and a strong "vaccine" effect were observed with the combination of IGF-1R TAT and immune checkpoint inhibitors, as noted by the prevention of tumor growth in animals that were reinoculated with the same tumor cells.

Dr. Valliant continued, "We are excited by our preclinical data that show the power of combining a potent TAT with the latest generation of cancer therapies, such as checkpoint inhibitors and DDRis. We view these combinations as an opportunity to bring these next-generation radiopharmaceuticals into earlier lines of therapy for patients, and we look forward to initiating combination studies in human once we have achieved the recommended Phase 2 dose for FPI-1434 monotherapy. Our previously announced collaborations with both Merck and AstraZeneca provide us with multiple opportunities to explore these exciting combination therapies."

Following the conclusion of the SNMMI Annual Meeting, copies of the presentations can be found at https://fusionpharma.com/fusion-scientific-presentations/.

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