Evaluation of ⁶⁸Ga- and ¹⁷⁷Lu-DOTA-PEG₄-LLP2A for VLA-4-Targeted PET Imaging and Treatment of Metastatic Melanoma

Abstract

Malignant melanoma is a highly aggressive cancer, and the incidence of this disease is increasing worldwide at an alarming rate. Despite advances in the treatment of melanoma, patients with metastatic disease still have a poor prognosis and low survival rate. New strategies, including targeted radiotherapy, would provide options for patients who become resistant to therapies such as BRAF inhibitors. Very late antigen-4 (VLA-4) is expressed on melanoma tumor cells in higher levels in more aggressive and metastatic disease and may provide an ideal target for drug delivery and targeted radiotherapy. In this study, we evaluated 177Lu- and 68Ga-labeled DOTA-PEG4-LLP2A as a VLA-4-targeted radiotherapeutic with a companion PET agent for diagnosis and monitoring metastatic melanoma treatment. DOTA-PEG4-LLP2A was synthesized by solid-phase synthesis. The affinity of 177Lu- and 68Ga-labeled DOTA-PEG4-LLP2A to VLA-4 was determined in B16F10 melanoma cells by saturation binding and competitive binding assays, respectively. Biodistribution of the LLP2A conjugates was determined in C57BL/6 mice bearing B16F10 subcutaneous tumors, while PET/CT imaging was performed in subcutaneous and metastatic models. 177Lu-DOTA-PEG4-LLP2A showed high affinity to VLA-4 with a Kd of 4.1 ± 1.5 nM and demonstrated significant accumulation in the B16F10 melanoma tumor after 4 h (31.5 ± 7.8%ID/g). The tumor/blood ratio of 177Lu-DOTA-PEG4-LLP2A was highest at 24 h (185 ± 26). PET imaging of metastatic melanoma with 68Ga-DOTA-PEG4-LLP2A showed high uptake in sites of metastases and correlated with bioluminescence imaging of the tumors. These data demonstrate that 177Lu-DOTA-PEG4-LLP2A has potential as a targeted therapeutic for treating melanoma as well as other VLA-4-expressing tumors. In addition, 68Ga-DOTA-PEG4-LLP2A is a readily translatable companion PET tracer for imaging of metastatic melanoma.

Zirconium tetraazamacrocycle complexes display extraordinary stability and provide a new strategy for zirconium-89-based radiopharmaceutical development

“…Finally, clinicians are increasingly using 89 Zr–DFO–mAbs in dosimetry and therapeutic planning before targeted systemic radiotherapy. 47–51 Since DOTA can effectively chelate 89 Zr and other therapeutic radionuclides, 52–54 it is plausible to imagine that one DOTA–mAb conjugate would be needed to accomplish dosimetry and radiotherapy with 89 Zr and a therapeutic radionuclide, respectively. This approach may increase dosimetric accuracy, reduce regulatory burden, and minimize costs associated with cGMP-compliant radiopharmaceutical development, so that these precision medicine applications may be used more effectively in the future.…”

Combined VLA-4–Targeted Radionuclide Therapy and Immunotherapy in a Mouse Model of Melanoma

“…DOTA-PEG 4 -LLP2A (12,13), scrambled LLP2A (sLLP2A) (12), and Cy3-PEG 4 -conjugated LLP2A and sLLP2A (15) were synthesized as previously described. 177 Lu-and 68 Ga-labeled DOTA-PEG 4 -LLP2A ( 177 Lu-LLP2A; 68 Ga-LLP2A) were prepared in greater than 99% purity as previously described (13).…”

“…The half-life of 68 Ga is amenable to imaging with peptides and small molecules. We previously reported that 68 Ga-and 177 Lu-labeled LLP2A have high uptake in B16F10 mouse melanoma tumors (13).…”

Imaging of Programmed Cell Death Ligand 1: Impact of Protein Concentration on Distribution of Anti-PD-L1 SPECT Agents in an Immunocompetent Murine Model of Melanoma

“…Receptor Binding Assay. The binding affinity of 111 In-DTPA-anti-PD-L1 was determined in B16F10 cells as described previously, with modifications (12,15). Briefly, cells were seeded in 24-well plates (50,000 cells) 48 h before the experiment.…”

“…Biodistribution of 111 In-DTPA-Anti-PD-L1. Biodistribution experiments were conducted as previously described, with minor modifications (15,19,20). Briefly, healthy B16F10 tumor-bearing female C57BL/6 mice (5 per time point) were injected intravenously with 111 In-DTPA-anti-PD-L1 (0.37 MBq [specific activity, 21.3 MBq/ nmol]; 0.13 mg of antibody protein per kilogram of mouse mass) 10 d after the B16F10 cell injections.…”