Preclinical and Clinical Feasibility Studies as the First Step Before Forthcoming Intravesical Instillation of [211At]At-anti-CA-IX Antibody (ATO-101™) Study in Patients with Non-Muscle-Invasive Bladder Cancer Unresponsive to Standard of Care

Abstract

Introduction: Recently, alpha-emitting radionuclides like astatine-211 have offered promising results in clinical development. Non-muscle-invasive bladder cancer (NMIBC) presents a need for novel therapies. One promising approach is radioimmunotherapy targeting Carbonic Anhydrase IX (CA-IX), which is supported by preclinical and clinical evidence. The aim of our preclinical and clinical studies was to evaluate the [²¹¹At]At-anti-CA-IX antibody (ATO-101™) for future use in NMIBC patient care.

Methods: The anti-CA-IX antibody, girentuximab (TLX250), was labeled with lutetium-177 and astatine-211 for in vitro studies. Affinity constant measurements of [²¹¹At]At-girentuximab in RT-112 cells were taken, and toxicity evaluations were conducted in vitro and in healthy mice. Additionally, a clinical proof-of-concept study, PERTINENCE, that used [⁸⁹Zr]Zr-girentuximab for PET/CT imaging in bladder cancer patients was conducted.

Results: The measurement of the affinity constant of [²¹¹At]At-girentuximab in RT112 cells revealed high binding affinity and significant cytotoxicity compared to [177Lu]Lu-girentuximab. Biodistribution studies in healthy mice indicated low systemic radioactivity uptake, and a bladder post-instillation examination showed no abnormalities in bladder mucosa, suggesting safety. In the PERTINENCE study, which involved patients with NMIBC tumors expressing CA-IX, [⁸⁹Zr]Zr-girentuximab PET/CT showed no extravesical leakage. Wall bladder uptake spots correlated with recurrence or inflammatory reaction. A dosimetric study suggested the potential efficacy and favorable safety profile of intravesical alpha therapy with the [²¹¹At]At-anti-CA-IX antibody (ATO-101™) in NMIBC treatment.

Conclusions: Preclinical and clinical data demonstrate the promising therapeutic role of ²¹¹At-targeted alpha agents in NMIBC, and the [²¹¹At]At-anti-CA-IX antibody (ATO-101™) could fulfill this role. A phase I FIH clinical trial is in preparation, and results are expected within the next years.

Keywords: PET/CT; [211At]At; [89Zr]Zr-girentuximab; carbonic anhydrase IX; dosimetry; non-muscle-invasive bladder cancer; radioimmunotherapy.

Figure 1

Decay scheme of astatine-211. Equivalent of one alpha particle is emitted within disintegration of astatine-211. Alpha particle emitted by astatine-211 in a 41.8% ratio with bismuth-207 has a kinetic energy of 5869.5 keV and a maximum path in water equal to 47.4 µm. Alpha particle emitted by polonium-211 in a 58.2% ratio with stable lead-207 has a kinetic energy of 7594.5 keV and a corresponding maximum path in water equal to 68.7 µm.

Figure 2

Compared cytotoxic effect of girentuximab labeled with either 177Lu (green square) and 211At (orange triangle) on RT112 cells at D5 after exposure.

Figure 3

Biodistribution of 1200 kBq of [²¹¹At]At-anti-CA-IX antibody (ATO-101™) at 30 (blue square), 60 (yellow square), and 240 min (violet square) after intravesical instillation in bladders of tumor-free mice. Biodistribution data of [²¹¹At]At-anti-CA-IX antibody (ATO-101™). Three animals were sacrificed at each time point. Data are expressed as the percentages of injected dose per gram of tissue (%ID/g). Means and SDs are depicted.

Figure 4

CA-IX staining is observed on papillary structure luminal surface (arrow) in direct contact with bladder cavity.

Figure 5

(A) CT coronal and (A′) [⁸⁹Zr]Zr-TLX250 PET of the whole body with no radioactivity in the body, except for a bladder residue (2 h after instillation and urination) (bold arrow); (B) Day 1, uptake focus (yellow arrow) on fusion axial [⁸⁹Zr]Zr-TLX250 PET-CT corresponding to TURB-controlled CA-IX IHC tumor recurrence in patient 1 (detailed in Table 1); (C) Day 1, uptake focus (yellow arrow) on fusion axial [⁸⁹Zr]Zr-TLX250 PET-CT showed TURB-controlled CA-IX IHC scar in patient 2 (detailed in Table 1).