Synthesis, Screening, and Evaluation of Theranostic Molecular CPCR4-Based Probe Targeting CXCR4

Chemokines and chemokine receptors are indispensable to play a key role in the development of malignant tumors. As one of the most widely expressed chemokine receptors, chemokine (C-X-C motif) receptor 4 (CXCR4) has been a popular research focus. In most tumors, CXCR4 expression is significantly upregulated. Moreover, integrated nuclide diagnosis and therapy targeting CXCR4 show great potential. [⁶⁸Ga]Ga-pentixafor, a radioligand targeting CXCR4, exhibits a strong affinity for CXCR4 both in vivo and in vitro. However, [¹⁷⁷Lu]Lu-pentixather, the therapeutic companion of [⁶⁸Ga]Ga-pentixafor, requires significant refinement to mitigate its pronounced hepatic biodistribution. The objective of this study was to synthesize theranostic molecular tracers with superior CXCR4 targeting functions. The Daudi cell line, which highly expressed CXCR4, and the MM.1S cell line, which weakly expressed CXCR4, were used in this study. Based on the pharmacophore cyclo (-d-Tyr-n-me-d-Orn-l-Arg-L-2-NAL-Gly-) (CPCR4) of pentixafor, six tracers were synthesized: [¹²⁴I]I-1 ([¹²⁴I]I-CPCR4), [^99mTc]Tc-2 ([^99mTc]Tc-HYNIC-CPCR4), [¹²⁴I]I-3 ([¹²⁴I]I-pentixafor), [¹⁸F]AlF-4 ([¹⁸F]AlF-NETA-CPCR4), [^99mTc]Tc-5 ([^99mTc]Tc-MAG₃-CPCR4) and [¹²⁴I]I-6 ([¹²⁴I]I-pentixafor-Ga) and their radiochemical purities were all higher than 95%. After positron emission tomography (PET)/single-photon emission computed tomography (SPECT) imaging, the [¹²⁴I]I-6 group exhibited the best target-nontarget ratio. At the same time, comparing the [⁶⁸Ga]Ga-pentixafor group with the [¹²⁴I]I-6 group, we found that the [¹²⁴I]I-6 group had a better target-nontarget ratio and lower uptake in nontarget organs. Therefore, compound 6 was selected for therapeutic radionuclide (¹³¹I) labeling, and the tumor-bearing animal models were treated with [¹³¹I]I-6. The volume of the tumor site was significantly reduced in the treatment group compared with the control group, and no significant side effects were found. [¹²⁴I]I-6 and [¹³¹I]I-6 showed excellent affinity for targeting CXCR4, and they showed great potential for the integrated diagnosis and treatment of tumors with high CXCR4 expression.