Abstract
Background. The chemokine receptor CXCR3 and its binding molecules MIG, IP-10 and ITAC have been associated with tumor progression, immune escape and angiogenesis in several human malignancies. In multiple myeloma (MM), CXCR3 binding molecules were shown to induce migration of MM cells without effecting proliferation. More recent results suggest a tumor suppressive activity of IP-10. Presently, information about the precise role of CXCR3 binding chemokines in MM is limited and evidence for their clinical significance is lacking. Therefore we aimed to evaluate the prognostic relevance of CXCR3 binding chemokines in patients with MM.
Patients and Methods. Serum levels of MIG, IP-10 and ITAC were analyzed by FACS-CBA array in 65 newly diagnosed MM patients. Expression of CXCR3 and its binding molecules was also analyzed by quantitative PCR in 7 human MM cell lines (HMCLs) and in a publically available gene expression dataset (GSE2658). Further analysis of MIG serum levels was performed by ELISA in an extended cohort of MM (n=105) and MGUS patients (n=17), and in healthy volunteers (n=37).
Results. Determination of serum levels by FACS-CBA revealed significant expression of MIG (range: 33.4 – 157 960 pg/ml) and IP-10 (12 - 4418.8 pg/ml), while ITAC (0 - 351.5 pg/ml) was only detectable in a subset (20 of 65) of patients. Interestingly, serum levels of all three molecules showed a positive correlation with each other (MIG vs. IP-10, R=0.38, P=0.002; MIG vs. ITAC, R=0.62, P<0.0001; ITAC vs. IP-10, R=0.41, P=0.0007). We also observed a significant correlation with beta 2 microglobulin (B2M) (MIG: R=0.45, P<0.0001; IP-10: R=0.36, P=0.003; ITAC: R=0.3, P=0.016) and a trend regarding ISS stage (MIG: R=0.23, P=0.06; IP-10: R=0.24, P=0.05; ITAC: R=0.11, P=0.39). Importantly, a significant association with overall survival (OS) was observed as well. Survival was significantly worse in patients with high compared to low MIG (median OS 25.3 months vs. not reached, P=0.003) and IP-10 (19.97 months vs. not reached, P=0.0006) as well as in patients with detectable compared to absent ITAC serum levels (19.97 vs. 65.8 months, P=0.019). In multivariate analysis, MIG (P=0.03) and ITAC (P=0.013) along LDH and calcium were revealed as independent predictors of survival.
Expression of CXCR3 binding chemokines was rarely detected in HMCLs (1 of 7 expressed MIG, 3 of 7 IP-10 and 2 of 7 ITAC, respectively). In line with this, in-silico analysis of previously published primary MM cell samples (n=414) (GSE2658), showed a present detection call of MIG, IP-10 and ITAC in 51 (12.3%), 11 (2.7%) and 0 (0%) patients, respectively. In contrast, all three cytokines were detectable in 100% of bone marrow plasma cells of healthy donors, MGUS and smoldering MM patients in this dataset. Hence, CXCR3 binding chemokines are silenced in myeloma cells indicating that the increased serum levels of CXCR3 binding chemokines are derived from other cell types.
As MIG serum concentration was identified as one of the most important predictors for OS, we studied the prognostic relevance of this molecule in an extended cohort (n=105) of MM patients by ELISA. Median MIG levels (161.3 pg/ml, range: 9.4-1966) were significantly elevated in newly diagnosed MM patients compared to MGUS (92.7 pg/ml, range: 6.29-1303.1) and healthy volunteers (106.2, range: 51–390.6 pg/ml). MIG levels were significantly correlated with B2M, ISS stage, calcium, albumin, LDH, hemoglobin and with age (R=0.466, P<0.001). Importantly, high MIG levels predicted adverse survival (17.0 months vs. not reached, P<0.001), which was upheld when age-adjusted cut-off levels were used. In accordance with our findings, in-silico analysis of MIG expression in purified plasma cells of MM patients (n=559) treated within the total therapy 2 and 3 protocol (GSE2658) revealed shorter OS in patients with a present compared to those with an absent detection call for MIG (P=0.004).
Conclusion. Our findings depict MIG, IP-10 and ITAC as novel prognostic markers for shorter survival in newly diagnosed MM patients. High serum levels of CXCR3 binding chemokines in conjunction with silenced expression in MM cells may shield myeloma cells from immune attack as previously shown for T cell lymphomas. Further experiments will aim to confirm these initial results by extending our patient cohort and define the source as well as functional role of CXCR3 chemokines in MM.
Figure 1 Figure 1.
Disclosures
No relevant conflicts of interest to declare.
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