CXCR4 expression in glioblastoma tissue and the potential for PET imaging and treatment with [68Ga]Ga-Pentixafor /[177Lu]Lu-Pentixather

Abstract

Purpose: CXCR4 (over)expression is found in multiple human cancer types, while expression is low or absent in healthy tissue. In glioblastoma it is associated with a poor prognosis and more extensive infiltrative phenotype. CXCR4 can be targeted by the diagnostic PET agent [68Ga]Ga-Pentixafor and its therapeutic counterpart [177Lu]Lu-Pentixather. We aimed to investigate the expression of CXCR4 in glioblastoma tissue to further examine the potential of these PET agents.

Methods: CXCR4 mRNA expression was examined using the R2 genomics platform. Glioblastoma tissue cores were stained for CXCR4. CXCR4 staining in tumor cells was scored. Stained tissue components (cytoplasm and/or nuclei of the tumor cells and blood vessels) were documented. Clinical characteristics and information on IDH and MGMT promoter methylation status were collected. Seven pilot patients with recurrent glioblastoma underwent [68Ga]Ga-Pentixafor PET; residual resected tissue was stained for CXCR4.

Results: Two large mRNA datasets (N = 284; N = 540) were assesed. Of the 191 glioblastomas, 426 cores were analyzed using immunohistochemistry. Seventy-eight cores (23 tumors) were CXCR4 negative, while 18 cores (5 tumors) had both strong and extensive staining. The remaining 330 cores (163 tumors) showed a large inter- and intra-tumor variation for CXCR4 expression; also seen in the resected tissue of the seven pilot patients-not directly translatable to [68Ga]Ga-Pentixafor PET results. Both mRNA and immunohistochemical analysis showed CXCR4 negative normal brain tissue and no significant correlation between CXCR4 expression and IDH or MGMT status or survival.

Conclusion: Using immunohistochemistry, high CXCR4 expression was found in a subset of glioblastomas as well as a large inter- and intra-tumor variation. Caution should be exercised in directly translating ex vivo CXCR4 expression to PET agent uptake. However, when high CXCR4 expression can be identified with [68Ga]Ga-Pentixafor, these patients might be good candidates for targeted radionuclide therapy with [177Lu]Lu-Pentixather in the future.

Keywords: CXCR4; Glioblastoma; Molecular imaging; PET; [177Lu]Lu-Pentixather; [68Ga]Ga-Pentixafor.

Conflict of interest statement

The authors declare that they have no competing interests.

© 2021. The Author(s).

Figures

Fig. 1

Example of a single tissue microarray (TMA) with CXCR4 stained glioblastoma tissue cores: (a) TMA grid in blue; green square indicating empty core due to missing tissue; orange rectangle indicating row of empty cores being part of the grid for orientation; yellow and red square representing CXCR4 positive versus CXCR4 negative glioblastoma tissue cores, higher magnification in, respectively, (b) and (c)

Fig. 2

CXCR4 mRNA expression according to WHO glioma grade and in normal brain tissue determined with GEO dataset GSE16011 (N = 284), showing a relatively higher expression in high grade gliomas, with highest (very variable) expression in glioblastoma, while normal brain tissue did not show expression. Data are presented as box and whisker plots: boxes extend from the 25th to 75th percentile, with a black line at the median. Statistical significance was determined by ANOVA, p < 0.05

Fig. 3

Variation in CXCR4 staining of glioblastoma tissue cores. Every dot represents a CXCR4 positive glioblastoma tissue core with positive CXCR4 staining

Fig. 4

Examples of positive and negative CXCR4 stained glioblastoma tissue cores with different IDH status. The brown color represents staining with the CXCR4 antibody. (a) CXCR4 positive IDH mutant glioblastoma tissue of a 62-year-old male with strong CXCR4 staining as well as > 75% staining of the core; (b) CXCR4 positive IDH wildtype glioblastoma tissue of a 82-year-old male with strong CXCR4 staining as well as > 75% staining of the core; (c) CXCR4 negative IDH mutant glioblastoma tissue of a 54-year-old male and (d) CXCR4 negative IDH wildtype glioblastoma tissue of a 59-year-old male. Scale bar is 20 μm

Fig. 5

Axial [68Ga]Ga-Pentixafor PET (A1; B1; C1), T2-weighted MRI (A2; B2; C2) and fused [68Ga]Ga-Pentixafor PET/MRI (A3; B3; C3) images of three patients with suspicion of recurrent glioblastoma. (A) Male (patient no. 4 in Table 4) showing higher uptake (SUVmax 3.5) in the MR-enhancing tissue in the left cerebellar hemisphere compared to the other patients and than bloodpool activity (SUVmean 1.48). (B) Female (patient no. 2) showing low to moderate uptake (SUVmax 1.82) in the MR-enhancing tissue in the left frontal lobe slightly higher than bloodpool activity (SUVmean 1.23). (C) Male (patient no. 6) showing low uptake (SUVmax 1.46) in the MR-enhancing tissue in the left frontal lobe equal to bloodpool activity (SUVmean 1.48)

Fig. 6

Example of intra-tumoral heterogeneity of CXCR4 staining in recurrent glioblastoma tissue of patient no. 6. (a) No staining. (b) Extensive and partly strong cytoplasmic staining of tumor and microvascular cells. (c) Strong cytoplasmic staining of small subset of neurons (with the appearance of “dark neurons”) in tumor-infiltrated cortex. Scale bar is 50 μm