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Radiopharm Theranostics Limited (ASX: RAD, Nasdaq: RADX) revealed encouraging Phase 1 clinical outcomes for RAD204, a novel PD-L1-targeted lutetium-177 nanobody radiotherapeutic. The initial patient in the third dosing cohort achieved a RECIST-confirmed durable Partial Response sustained through four treatment cycles, remaining progression-free for over seven months. No dose-limiting toxicities were observed across all dosing cohorts, supporting ongoing development of RAD204 for patients with advanced solid tumors refractory to standard treatments.
Key Points
- Radiopharm Theranostics Limited (ASX:RAD) updated Phase 1 clinical data for RAD204 on 22 July 2026
- First patient in Dose 3 cohort achieved a RECIST-confirmed durable Partial Response with 43% reduction in target lesions post Dose 2, maintained through Dose 4
- Patient 1 remains progression-free beyond seven months; Patient 2 exhibits early 7% tumor reduction and continues treatment
- No dose-limiting toxicities reported across Dose levels 1 to 3; kidney uptake limited to 8.1 Gy cumulative dose over four cycles in Patient 1
- Third patient currently under screening; company plans additional data releases and Phase 2 trial initiation
Confirmed Tumor Response Achieved in Third Dose Cohort of RAD204 Phase 1 Trial
Radiopharm Theranostics announced that the first patient treated in the third cohort of the Phase 1 study achieved a RECIST-confirmed Partial Response demonstrating durable clinical benefit. Target lesions reduced by 19% after the initial dose, increasing to 43% following the second dose, meeting RECIST criteria for Partial Response. This response was confirmed and sustained after the third dose, remaining at 43%, with a 35% reduction observed after the fourth dose while still meeting Partial Response criteria. The sustained tumor reduction across multiple cycles represents a significant clinical finding in this advanced solid tumor population.
Extended follow-up data shows Patient 1 has remained progression-free for over seven months since initial treatment, indicating ongoing clinical benefit and tolerability. This is notable given RAD204 is being evaluated in patients with advanced solid tumors who have progressed on standard therapies, a group with limited treatment options. The company’s characterization of the response as "durable" highlights the sustained tumor shrinkage observed during extended monitoring, suggesting meaningful therapeutic potential.
Early Anti-Tumor Activity Observed in Second Patient
The second patient enrolled in the third dosing cohort demonstrated early anti-tumor effects with a 7% reduction in target lesions after the first treatment cycle, described as "early tumor shrinkage." This patient remains on active therapy and progression-free, with ongoing safety and efficacy assessments. Although the response magnitude differs from Patient 1, measurable tumor reduction at this stage supports RAD204’s therapeutic promise.
A third patient in the third cohort is currently undergoing screening, indicating continued enrollment at this dosing level. Preliminary results from the first two patients, combined with prior imaging data showing positive tumor uptake in PD-L1-positive lesions, suggest consistent target engagement and biological activity. Initial data from all Phase 1 cohorts confirmed tumor uptake in PD-L1-expressing lesions, aligning with previously published imaging study results and reinforcing RAD204’s target-specific mechanism.
Strong Safety Profile Enables Further Dose Escalation
A key Phase 1 trial finding is the absence of dose-limiting toxicities across all evaluated dose levels. RAD204 demonstrated a favorable safety and tolerability profile at Dose levels 1, 2, and 3 (up to 90 millicuries). This safety outcome supports further dose escalation and indicates a promising therapeutic window. The lack of dose-limiting toxicities at the highest dose tested (90 mCi) suggests feasibility for advancing to higher dose cohorts.
Kidney uptake, a critical safety parameter for radiopharmaceuticals, remained limited and manageable. Patient 1’s cumulative kidney dose over four cycles was 8.1 Gray, which the company stated "does not represent a potential obstacle for escalation to the next higher dose level (Dose level #4)." This favorable renal dosimetry is significant given repeated dosing is central to RAD204’s therapeutic strategy, supporting the potential for multiple treatment cycles.
PD-L1 Targeting Across Multiple Tumor Types
RAD204 is a single-domain monoclonal antibody (sdAb) targeting PD-L1, a protein involved in immune regulation and overexpressed in various cancers. Potential indications include non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), triple-negative breast cancer (TNBC), cutaneous melanoma, head and neck squamous cell carcinoma (HNSCC), and endometrial cancer. Unlike conventional checkpoint inhibitors that primarily mobilize immune responses, RAD204 combines PD-L1 targeting with lutetium-177 radiotherapy, offering a unique cytotoxic mechanism.
Previously published Phase 1 imaging data from 16 NSCLC patients treated with 99-technetium-RAD204 demonstrated favorable tumor targeting and biodistribution correlating with PD-L1 expression. This imaging evidence provided the rationale to advance to therapeutic dosing with the lutetium-177 variant. The company highlights that radioimmunotherapies like 177Lu-RAD204 may overcome resistance to current standard-of-care treatments, addressing a critical unmet need.
Innovative Radiopharmaceutical Platform Enables Repeat Dosing
RAD204’s proprietary platform offers advantages over traditional monoclonal antibodies, including "hidden epitope access, exceptional stability, rapid tumor penetration, favorable pharmacokinetics, and repeat dosing potential." Rapid tumor penetration is vital for radiopharmaceutical efficacy, minimizing systemic exposure. The favorable pharmacokinetics and demonstrated repeat dosing in Phase 1 suggest RAD204 may allow flexible dosing schedules distinct from conventional therapies.
Patient 1’s four treatment cycles with maintained response and tolerability exemplify this repeat dosing capability. Unlike fixed schedules typical for PD-L1 inhibitors, the radiopharmaceutical approach with lutetium-177 may enable adaptive dosing strategies. The company emphasizes that repeat dosing was an intentional design feature, potentially enhancing clinical management and therapeutic optimization.
Phase 1 Trial Design and Progression to Phase 2
The Phase 1 study evaluates RAD204’s safety, tolerability, dosimetry, pharmacokinetics, and preliminary anti-tumor activity in patients with advanced solid tumors refractory to standard therapies. Primary objectives include establishing the recommended Phase 2 dose and safety characterization; secondary endpoints assess tumor response rates and duration. This design aligns with standard early-stage radiopharmaceutical development protocols.
CEO Riccardo Canevari stated the company "anticipates releasing additional data supporting RAD204’s therapeutic potential in PD-L1-associated malignancies," and that data across dose cohorts "support confidence in the program and will inform the recommended Phase 2 dose." The Data and Safety Monitoring Committee has endorsed progression to the current highest dose (90 mCi, Dose level #3), with safety data permitting advancement to Dose level #4. The transition from Phase 1 dose escalation to Phase 2 efficacy evaluation is expected to span several years.
Company Pipeline and Market Positioning
Radiopharm Theranostics is a clinical-stage radiotherapeutics company with a diverse pipeline including peptide, small molecule, and monoclonal antibody platforms targeting oncology indications. Listed on the ASX (RAD) and NASDAQ (RADX), the company has international investor access and regulatory oversight. Beyond RAD204, the pipeline includes one Phase 2 and five Phase 1 trials addressing lung, breast, and brain metastases cancers, providing multiple clinical and commercial development pathways.
Operating in the radiopharmaceutical oncology sector, Radiopharm combines targeting precision with radioisotope cytotoxicity. The company’s dual headquarters in Sydney, Australia, and Malvern, Pennsylvania, support its ASX and NASDAQ operations and global clinical programs.
Addressing Unmet Needs in Post-Immunotherapy Advanced Cancers
RAD204 targets a patient population with significant unmet medical needs: advanced solid tumors progressing after standard therapies, including checkpoint inhibitor immunotherapies. These patients typically have limited treatment options and poor prognoses. Indications under study include NSCLC, SCLC, TNBC, melanoma, HNSCC, and endometrial cancer, collectively affecting millions worldwide.
By combining PD-L1 targeting with direct radiotherapy-mediated cytotoxicity, RAD204 aims to overcome resistance mechanisms to immunotherapy. The company notes that "tumor targeting with radioimmunotherapies such as 177Lu-RAD204 has the potential to address resistance mechanisms to current standard-of-care treatments," positioning RAD204 as a promising option for this challenging patient subset.
Upcoming Milestones and Development Outlook
Next steps include continued enrollment in the Phase 1 trial, completion of Cohort 3, and potential initiation of Cohort 4 (Dose level #4). A third patient in Cohort 3 is under screening, indicating ongoing recruitment. Additional clinical data releases are planned but not yet scheduled. The company is preparing for Phase 2 trial initiation, with dose escalation informing the recommended Phase 2 dose.
Key investor milestones will include Phase 1 dose escalation completion, recommended Phase 2 dose announcement, Phase 2 enrollment start, and interim or final Phase 2 efficacy results. Extended follow-up of treated patients, including Patient 1 at seven months post-treatment, will provide durability data critical for Phase 2 design. RAD204 is a flagship program for Radiopharm Theranostics, with successful Phase 1 to Phase 2 progression essential for regulatory approval and commercialization.
