First-in-Humans Evaluation of Safety and Dosimetry of 64Cu-LLP2A for PET Imaging

Abstract

There remains an unmet need for molecularly targeted imaging agents for multiple myeloma (MM). The integrin very late antigen 4 (VLA4), is differentially expressed in malignant MM cells and in pathogenic inflammatory microenvironmental cells. [⁶⁴Cu]Cu-CB-TE1A1P-LLP2A (⁶⁴Cu-LLP2A) is a VLA4-targeted, high-affinity radiopharmaceutical with promising utility for managing patients diagnosed with MM. Here, we evaluated the safety and human radiation dosimetry of ⁶⁴Cu-LLP2A for potential use in MM patients. Methods: A single-dose [^natCu]Cu-LLP2A (Cu-LLP2A) tolerability and toxicity study was performed on CD-1 (Hsd:ICR) male and female mice. ⁶⁴Cu-LLP2A was synthesized in accordance with good-manufacturing-practice-compliant procedures. Three MM patients and six healthy participants underwent ⁶⁴Cu-LLP2A-PET/CT or PET/MRI at up to 3 time points to help determine tracer biodistribution, pharmacokinetics, and radiation dosimetry. Time-activity curves were plotted for each participant. Mean organ-absorbed doses and effective doses were calculated using the OLINDA software. Tracer bioactivity was evaluated via cell-binding assays, and metabolites from human blood samples were analyzed with analytic radio-high-performance liquid chromatography. When feasible, VLA4 expression was evaluated in the biopsy tissues using 14-color flow cytometry. Results: A 150-fold mass excess of the desired imaging dose was tolerated well in male and female CD-1 mice (no observed adverse effect level). Time-activity curves from human imaging data showed rapid tracer clearance from blood via the kidneys and bladder. The effective dose of ⁶⁴Cu-LLP2A in humans was 0.036 ± 0.006 mSv/MBq, and the spleen had the highest organ uptake, 0.142 ± 0.034 mSv/MBq. Among all tissues, the red marrow demonstrated the highest residence time. Image quality analysis supports an early imaging time (4-5 h after injection of the radiotracer) as optimal. Cell studies showed statistically significant blocking for the tracer produced for all human studies (82.42% ± 13.47%). Blood metabolism studies confirmed a stable product peak (>90%) up to 1 h after injection of the radiopharmaceutical. No clinical or laboratory adverse events related to ⁶⁴Cu-LLP2A were observed in the human participants. Conclusion: ⁶⁴Cu-LLP2A exhibited a favorable dosimetry and safety profile for use in humans.

Keywords: dosimetry; first-in-humans; radiochemistry; radiopharmaceuticals; safety; translational imaging.

Graphical abstract

FIGURE 1.

Aggregated time–activity curves. Orange circles indicate MM participants; black circles indicate healthy participants. %I/A = percentage injected activity.

FIGURE 2.

Anterior maximum-intensity-projection ⁶⁴Cu-LLP2A-PET images of healthy volunteer (MMDN05) and subject with MM (MMDM03) at similar time points after tracer injection. Best-quality images were obtained 1–5 h after injection of radiotracer. Later time points (∼24 h) exhibited relatively lower count and high image noise. Unit of measurement for intensity bars = SUV.

FIGURE 3.

Comparison of ⁶⁴Cu-LLP2A SUV_max of iliac bones in healthy and MM participants at average of 240 min after injection of radiotracer. Mean and SD for SUV_max were 12.05 ± 2.0 for healthy participants (n = 5) and 25.62 ± 9.38 for MM patients (n = 3) (**P < 0.03, 2-tailed).

FIGURE 4.

MM patient underwent PET imaging with ⁶⁴Cu-LLP2A and ¹⁸F-FDG. On PET/CT, osteolytic lesion in right iliac bone (arrows) of MM patient had ¹⁸F-FDG uptake similar to background marrow. On PET/MRI, this same lesion (arrows) had ⁶⁴Cu-LLP2A uptake above background marrow, corresponding to fat-replacing lesion on fat-only Dixon images and hyperintense lesion on DWI. In this lesion, ⁶⁴Cu-LLP2A SUV_max was 29.5 with SUL_peak (per PERCIST) of 18.7; in comparison, ¹⁸F-FDG SUV_max was 2.9 with SUL_peak (per PERCIST) of 2.1. DWI = diffusion-weighted imaging.

FIGURE 5.

Flow cytometry analysis of LLP2A-Cy5 staining of human BM and peripheral blood cell subsets. (A) Heat map showing percentage of different cell subsets found within BM or peripheral blood (PB) of healthy participants from MM tissue bank (UPN1954, UPN2055, and UPN2140) or one of the MM patients (UPN99520/MMDM02) at baseline and after disease progression 4 mo later. (B) Heat map showing mean fluorescence intensity of LLP2A-Cy5 staining of different cell subsets.