Imaging CXCR4 Expression with Iodinated and Brominated Cyclam Derivatives

Abstract

Purpose: CXCR4 is one of several "chemokine" receptors expressed on malignant tumors (including GBM and PCNSL) and hematopoietic stem cells. Although 68 Ga-pentixafor and 68 Ga-NOTA-NFB have been shown to effectively image CXCR4 expression in myeloma and other systemic malignancies, imaging CXCR4 expression in brain tumors has been more limited due to the blood-brain barrier (BBB) and a considerable fraction of CXCR4 staining is intracellular. Methods: We synthesized 6 iodinated and brominated cyclam derivatives with high affinity (low nM range) for CXCR4, since structure-based estimates of lipophilicity suggested rapid transfer across the BBB and tumor cell membranes. Results: We tested 3 iodinated and 3 brominated cyclam derivatives in several CXCR4(+) and CXCR4(−) cell lines, with and without cold ligand blocking. To validate these novel radiolabeled cyclam derivatives for diagnostic CXCR4 imaging efficacy in brain tumors, we established appropriated murine models of intracranial GBM and PCNSL. Based on initial studies, 131 I-HZ262 and 76 Br-HZ270-1 were shown to be the most avidly accumulated radioligands. 76 Br-HZ270-1 was selected for further study in the U87-CXCR4 and PCNSL #15 intracranial tumor models, because of its high uptake (9.5 ± 1.3 %ID/g, SD) and low non-specific uptake (1.6 ± Hanwen Zhang and Masatomo Maeda contributed equally to this work. Key Points • New derivatives of AMD3100 and AMD3465, based on radiohalogenating the phenyl moiety directly, were successfully designed and synthesized with greater than 98% purity. • Selected halogenated cyclam derivatives successfully imaged CXCR4expressing subcutaneous tumors, but not intracranial tumors. • The halogenated cyclam analogues were expected to be hydrophobic, as suggested by structure-based estimates of their lipophilicity, but the estimates were significantly different from the "measured" octanol/PBS partition coefficient (LogD) of the synthesized radioligands. • Due to a comparatively intact blood-tumor barrier in the experimental animal models, intracranial CXCR4 expressing gliomas and PCNSL were not well visualized. Electronic supplementary material The online version of this article (https:// 0.7 %ID/g, SD) in the s.c. U87-CXCR4 tumor models. However, imaging CXCR4 expression in intracranial U87-CXCR4 and PCNSL #15 tumors with 76 Br-HZ270-1 was unsuccessful, following either i.v. or spinal-CSF injection. Conclusions: Imaging CXCR4 expression with halogenated cyclam derivatives was successful in s.c. located tumors, but not in CNS located tumors. This was largely due to the following: (i) the hydrophilicity of the radiolabeled analogues-as reflected in the "measured" radiotracer distribution (LogD) in octanol/PBS-which stands in contrast to the structure-based estimate of LogP, which was the rationale for initiating the study and (ii) the presence of a modest BTB in intracranial U87-CXCR4 gliomas and an intact BBB/BTB in the intracranial PCNSL animal model.

CXCR4-Targeted Radiopharmaceuticals for the Imaging and Therapy of Malignant Tumors

“…The modification of the phenyl ring did not show an obvious change in binding affinity toward the CXCR4 binding target. Among the six studied radioligands, 76 Br-HZ270-1 (Figure 3) exhibited the best performance for the imaging of CXCR4 expression in s.c.-located tumors rather than CNS-located tumors [35].…”

“…Molecules 2023, 28, x FOR PEER REVIEW 6 of 22 radioligands, 76 Br-HZ270-1 (Figure 3) exhibited the best performance for the imaging of CXCR4 expression in s.c.-located tumors rather than CNS-located tumors [35]. In 2014, Prof. Nimmagadda and his colleagues [36] developed a facile synthetic route to RAD1-24 and RAD1-52, which are cross-bridged analogs of cyclams, to evaluate their radiochemical properties.…”

Novel insights into the biomarkers and therapies for primary central nervous system lymphoma

“…38 CXCR4 is highly expressed on PCNSL cells and binds to CXCL12 to establish the CXCL12/ CXCR4 signaling pathway, which is important in the homing of tumor cells. 39 PET imaging using 68 Ga-Pentixafor, a CXCR4-directed tracer, could exhibit PCNSL in excellent contrast to the surrounding brain parenchyma, and might be a novel diagnostic biomarker for PCNSL. 40 Considering the high CXCR4 expression levels in glioblastoma, 39 the efficacy of CXCR4-directed imaging in distinguishing PCNSL from glioma should be investigated further in prospective clinical trials.…”

In Vivo Targeting of CXCR4—New Horizons

“…When an excess of the OCT-substrate metformin was co-administered with [ 18 F]MCFB, a reduction of tracer accumulation in the liver by approximately 25% was observed, with a less pronounced effect in the kidneys [70]. Another interesting effect that was observed during the evaluation of different radio-iodinated and radio-brominated mono-cyclam analogs [73] is the dependence of their general pharmacokinetics and targeting efficiency on the radiolabeling site. Of the two radio-brominated isomers investigated, [ 76 Br]HZ270-1 (entry 5, Table 1, 2-[ 76 Br]bromo-analog) showed distinctly lower background accumulation in all organs, and a doubled tumor accumulation compared to the corresponding 3-[ 76 Br]bromoanalog, highlighting the importance of establishing detailed structure activity relationships in tracer development.…”