Development of a Radioiodinated Triazolopyrimidine Probe for Nuclear Medical Imaging of Fatty Acid Binding Protein 4

Abstract

Fatty acid binding protein 4 (FABP4) is the most well-characterized FABP isoform. FABP4 regulates inflammatory pathways in adipocytes and macrophages and is involved in both inflammatory diseases and tumor formation. FABP4 expression was recently reported for glioblastoma, where it may participate in disease malignancy. While FABP4 is a potential molecular imaging target, with the exception of a tritium labeled probe there are no reports of other nuclear imaging probes that target this protein. Here we designed and synthesized a nuclear imaging probe, [123I]TAP1, and evaluated its potential as a FABP4 targeting probe in in vitro and in vivo assays. We focused on the unique structure of a triazolopyrimidine scaffold that lacks a carboxylic acid to design the TAP1 probe that can undergo facilitated delivery across cell membranes. The affinity of synthesized TAP1 was measured using FABP4 and 8-anilino-1-naphthalene sulfonic acid. [125I]TAP1 was synthesized by iododestannylation of a precursor, followed by affinity and selectivity measurements using immobilized FABPs. Biodistributions in normal and C6 glioblastoma-bearing mice were evaluated, and excised tumors were subjected to autoradiography and immunohistochemistry. TAP1 and [125I]TAP1 showed high affinity for FABP4 (K i = 44.5±9.8 nM, K d = 69.1±12.3 nM). The FABP4 binding affinity of [125I]TAP1 was 11.5- and 35.5-fold higher than for FABP3 and FABP5, respectively. In an in vivo study [125I]TAP1 displayed high stability against deiodination and degradation, and moderate radioactivity accumulation in C6 tumors (1.37±0.24% dose/g 3 hr after injection). The radioactivity distribution profile in tumors partially corresponded to the FABP4 positive area and was also affected by perfusion. The results indicate that [125I]TAP1 could detect FABP4 in vitro and partly in vivo. As such, [125I]TAP1 is a promising lead compound for further refinement for use in in vivo FABP4 imaging.

Radiofluorinated probe for PET imaging of fatty acid binding protein 4 in cancer

“…4). Cell differentiation and FABP4 expression in differentiated adipocytes were confirmed by Oil red O staining and western blot analysis, respectively, in a similar way to that described in our previous report [9]. [ 18 F]FTAP1 showed significantly higher radioactivity in adipocytes than 3T3-L1 preadipocytes.…”

“…In the present study we developed [ 18 F]FTAP1 for in vivo PET imaging of FABP4, which is closely related to CAA functions [5], tumor progression [5], and atherosclerotic plaque instability [13]. This probe is based on our previous radioiodinated probe, [ 123/125 I]TAP1 [9]. [ 18 F]FTAP1 showed high affinity and selectivity for FABP4, adequate cellular membrane permeability, and high uptake into differentiated adipocytes expressing FABP4 that could be perfectly blocked by a selective FABP4 inhibitor.…”

“…The medium was then changed every other day with DMEM supplemented with 10% FBS and 10 μM pioglitazone hydrochloride. After 8-10 days, the differentiated adipocytes were confirmed by western blotting and Oil red O staining following our previous studies [9,10] and used for experiments.…”

“…We recently developed a FABP4 imaging probe, [ 123/125 I]TAP1, for use in nuclear imaging with single photon emission computed tomography (SPECT) [9]. Although the design of [ 123/125 I]TAP1 was based on the structures of selective FABP4 inhibitors and showed high affinity and selectivity for FABP4, this probe had high lipophilicity that caused significant nonspecific distribution in vivo.…”

The Construction and Identification of Induced Pluripotent Stem Cells Derived from Acute Myelogenous Leukemia Cells

“…Hematopoietic stem cell transplantation has been one of the available therapies to treat AML [6]. Previous studies have demonstrated that evaluating the efficiency of both ESCs and iPSCs in cardiac cell therapy in an in vitro analysis is currently the focus of mainstream research [7, 8], but in recent years, iPSCs have become a great alternative for the treatment of AML [9]. These cells share many similarities with embryonic stem cells (ESCs), which serve as a model to study molecular embryogenesis and have a great potential for applications in regenerative medicine [10], including multilineage differentiation and self-renewal [11].…”