PT  - JOURNAL ARTICLE
AU  - Jaeyeon Choi
AU  - Wissam Beaino
AU  - Ronald J. Fecek
AU  - Kellsye P.L. Fabian
AU  - Charles M. Laymon
AU  - Brenda F. Kurland
AU  - Walter J. Storkus
AU  - Carolyn J. Anderson
TI  - Combined VLA-4–Targeted Radionuclide Therapy and Immunotherapy in a Mouse Model of Melanoma
AID  - 10.2967/jnumed.118.209510
DP  - 2018 Dec 01
TA  - Journal of Nuclear Medicine
PG  - 1843--1849
VI  - 59
IP  - 12
4099  - http://jnm.snmjournals.org/content/59/12/1843.short
4100  - http://jnm.snmjournals.org/content/59/12/1843.full
SO  - J Nucl Med2018 Dec 01; 59
AB  - Very late antigen-4 (VLA-4; also known as integrin α4β1) is expressed at high levels in aggressive and metastatic melanoma tumors and may provide an ideal target for imaging and targeted radionuclide therapy (TRT). 177Lu-DOTA-PEG4-LLP2A (177Lu-LLP2A) is a TRT that shows high affinity for VLA-4 and high uptake in B16F10 mouse melanoma tumors in vivo. Here, we report efficacy studies of 177Lu-LLP2A, alone and combined with immune checkpoint inhibitors (ICIs) (anti-PD-1, anti-PD-L1, and anti-CTLA-4 antibodies), in B16F10 tumor–bearing mice. Methods: Tumor cells (1 × 106) were implanted subcutaneously in C57BL/6 mice. After 8–10 d, the mice were randomized into 8 groups. 177Lu-LLP2A was injected intravenously on day 8 or 9 (single dose), and ICI antibodies were administered intraperitoneally in 3 doses. Tumor growth was monitored over time via calipers. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining for apoptosis was performed on fixed tumors. In a separate study, Cy3-LLP2A or Cy3–scrambled LLP2A was injected in tumor-bearing mice, and tumors were collected 4 h after injection and then analyzed by flow cytometry and immunofluorescence microscopy using different immune cell markers. Results: TRT alone showed efficacy comparable to the dual-ICI anti-PD-1 + anti-CTLA-4 or anti-PD-L1 + anti-CTLA-4, whereas TRT + ICIs significantly enhanced survival. TUNEL staining showed that the highest levels of apoptosis were in the TRT + ICI groups. In addition to targeting tumor cells, TRT also bound immune cells in the tumor microenvironment. Flow cytometry data showed that the tumors consisted of about 77% tumor cells and fibroblasts (CD45-negative/CD49d-positive) and about 23% immune cells (CD45-positive/CD49d-positive) and that immune cells expressed higher levels of VLA-4. Cy3-LLP2A and CD49d colocalized with macrophages (CD68), T cells (CD8, CD4), and B cells (CD19). Immunohistochemical analysis identified a significant colocalization of Cy3-LLP2A and CD68. Conclusion: Combination treatment with TRT + ICIs targets both tumor cells and immune cells and has potential as a therapeutic agent in patients with metastatic melanoma.