Differences in CXCR7 protein expression on rat versus mouse and human splenic marginal zone B cells

Targeted Imaging of the Atypical Chemokine Receptor 3 (ACKR3/CXCR7) in Human Cancer Xenografts

The atypical chemokine receptor ACKR3 (formerly CXCR7), overexpressed in various cancers compared with normal tissues, plays a pivotal role in adhesion, angiogenesis, tumorigenesis, metastasis, and tumor cell survival. ACKR3 modulates the tumor microenvironment and regulates tumor growth. The therapeutic potential of ACKR3 has also been demonstrated in various murine models of human cancer. Literature findings underscore the importance of ACKR3 in disease progression and suggest it as an important diagnostic marker for noninvasive imaging of ACKR3-overexpressing malignancies. There are currently no reports on direct receptor-specific detection of ACKR3 expression. Here we report the evaluation of a radiolabeled ACKR3-targeted monoclonal antibody (ACKR3-mAb) for the noninvasive in vivo nuclear imaging of ACKR3 expression in human breast, lung, and esophageal squamous cell carcinoma cancer xenografts.

METHODS

ACKR3 expression data were extracted from Cancer Cell Line Encyclopedia, The Cancer Genome Atlas, and the Clinical Lung Cancer Genome Project. (89)Zr-ACKR3-mAb was evaluated in vitro and subsequently in vivo by PET and ex vivo biodistribution studies in mice xenografted with breast (MDA-MB-231-ACKR3 [231-ACKR3], MDA-MB-231 [231], MCF7), lung (HCC95), or esophageal (KYSE520) cancer cells. In addition, ACKR3-mAb was radiolabeled with (125)I and evaluated by SPECT imaging and ex vivo biodistribution studies.

RESULTS

ACKR3 transcript levels were highest in lung squamous cell carcinoma among the 21 cancer type data extracted from The Cancer Genome Atlas. Also, Clinical Lung Cancer Genome Project data showed that lung squamous cell carcinoma had the highest CXCR7 transcript levels compared with other lung cancer subtypes. The (89)Zr-ACKR3-mAb was produced in 80% ± 5% radiochemical yields with greater than 98% radiochemical purity. In vitro cell uptake of (89)Zr-ACKR3-mAb correlated with gradient levels of cell surface ACKR3 expression observed by flow cytometry. In vivo PET imaging and ex vivo biodistribution studies in mice with breast, lung, and esophageal cancer xenografts consistently showed enhanced (89)Zr-ACKR3-mAb uptake in high-ACKR3-expressing tumors. SPECT imaging of (125)I-ACKR3-mAb showed the versatility of ACKR3-mAb for in vivo monitoring of ACKR3 expression.

CONCLUSION

Data from this study suggest ACKR3 to be a viable diagnostic marker and demonstrate the utility of radiolabeled ACKR3-mAb for in vivo visualization of ACKR3-overexpressing malignancies.

Fluctuations in Blood Marginal Zone B-Cell Frequencies May Reflect Migratory Patterns Associated with HIV-1 Disease Progression Status

We have previously shown that overexpression of BLyS/BAFF was associated with increased relative frequencies of innate “precursor” marginal zone (MZ)-like B-cells in the blood of HIV-1-infected rapid and classic progressors. However, along with relatively normal BLyS/BAFF expression levels, these cells remain unaltered in elite-controllers (EC), rather, percentages of more mature MZ-like B-cells are decreased in the blood of these individuals. Fluctuations in frequencies of blood MZ-like B-cell populations may reflect migratory patterns associated with disease progression status, suggesting an important role for these cells in HIV-1 pathogenesis. We have therefore longitudinally measured plasma levels of B-tropic chemokines by ELISA-based technology as well as their ligands by flow-cytometry on blood B-cell populations of HIV-1-infected individuals with different rates of disease progression and uninfected controls. Migration potential of B-cell populations from these individuals were determined by chemotaxis assays. We found important modulations of CXCL13-CXCR5, CXCL12-CXCR4/CXCR7, CCL20-CCR6 and CCL25-CCR9 chemokine-axes and increased cell migration patterns in HIV progressors. Interestingly, frequencies of CCR6 expressing cells were significantly elevated within the precursor MZ-like population, consistent with increased migration in response to CCL20. Although we found little modulation of chemokine-axes in EC, cell migration was greater than that observed for uninfected controls, especially for MZ-like B-cells. Overall the immune response against HIV-1 may involve recruitment of MZ-like B-cells to peripheral sites. Moreover, our findings suggest that “regulated” attraction of these cells in a preserved BLyS/BAFF non-inflammatory environment, such as encountered in EC could be beneficial to the battle and even control of HIV.