Fatty acid-binding protein 4 in kidney diseases: From mechanisms to clinics

Considerable evidence indicated the relationship between fatty acid-binding protein 4 (FABP4) and kidney diseases. FABP4, a small molecular lipid chaperone, is identified to regulate fatty acid oxidation, inflammation, apoptosis, endoplasmic reticulum stress and macrophage-to-myofibroblast transition in kidney diseases. Many studies have shown that circulating FABP4 level is related to proteinuria, renal function decline, cardiovascular complications of end-stage renal disease and even the prognosis of kidney transplanted patients. Notably, pharmacological or genetic inhibition of FABP4 attenuated renal injury in the various experimental models of kidney diseases, making it promising to develop potential therapeutic strategies targeting FABP4 in kidney diseases. In this study, we updated and reviewed the mechanisms and clinical significance of FABP4 in kidney diseases.

Radionuclide imaging and therapy directed towards the tumor microenvironment: a multi-cancer approach for personalized medicine

Targeted radionuclide theranostics is becoming more and more prominent in clinical oncology. Currently, most nuclear medicine compounds researched for cancer theranostics are directed towards targets expressed in only a small subset of cancer types, limiting clinical applicability. The identification of cancer-specific targets that are (more) universally expressed will allow more cancer patients to benefit from these personalized nuclear medicine–based interventions. A tumor is not merely a collection of cancer cells, it also comprises supporting stromal cells embedded in an altered extracellular matrix (ECM), together forming the tumor microenvironment (TME). Since the TME is less genetically unstable than cancer cells, and TME phenotypes can be shared between cancer types, it offers targets that are more universally expressed. The TME is characterized by the presence of altered processes such as hypoxia, acidity, and increased metabolism. Next to the ECM, the TME consists of cancer-associated fibroblasts (CAFs), macrophages, endothelial cells forming the neo-vasculature, immune cells, and cancer-associated adipocytes (CAAs). Radioligands directed at the altered processes, the ECM, and the cellular components of the TME have been developed and evaluated in preclinical and clinical studies for targeted radionuclide imaging and/or therapy. In this review, we provide an overview of the TME targets and their corresponding radioligands. In addition, we discuss what developments are needed to further explore the TME as a target for radionuclide theranostics, with the hopes of stimulating the development of novel TME radioligands with multi-cancer, or in some cases even pan-cancer, application.

Inhibition of Fatty Acid Binding Protein 4 in Obese Male Mice Adversely Affects Reproductive Parameters

Background:

As obesity is increasing worldwide, obese people use various methods to get rid of excess weight. BMS309403 (A drug) is a specific inhibitor of fatty acid binding protein 4. In this study, the effects of the BMS309403 on serum biochemical markers, testis tissue spermatogenesis and apoptotic markers were investigated in male mice.

Methods:

Balb/c mice (total=56, each group n=14) were divided into control, obese control, obese solvent and obese drug groups. The obese control, obese solvent and obese drug groups were fed on the high sucrose diet to lead to obesity. After the development of obesity, BMS309403 was orally administered to the obese drug group for six weeks. It was performed in testicular tissues (Johnson Score and apoptosis markers) and biochemical tests (total testosterone, sex hormone binding globulin, inhibin-B tests and free androgen index) were used to evaluate reproductive parameters. The p<0.05 was considered to indicate a statistical significance.

Results:

Serum fatty acid binding protein 4 levels were higher in obese control group and obese solvent group, compared to control (p<0.05) and obese drug groups (p<0.001). Serum total testosterone, free androgen index, inhibin-B, sex hormone binding globulin levels, testicular tissue B-cell lymphoma-2 expression level and Johnson Score parameters were lower in all obese groups compared with the control group. Inhibin-B levels and Johnson Score results were lower in obese drug group compared to other two obese groups (p<0.05).

Conclusion:

Contrary to expectations, the use of BMS309403 negatively affected male reproductive parameters. Negative changes in reproductive parameters may be a result of the increased lee index of obesity.

3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation

Following on the recent publication of pharmacologically relevant effects, small molecule inhibitors of adipocyte fatty-acid binding protein 4 (FABP4) have attracted high interest. FABP4 is mainly expressed in macrophages and adipose tissue, where it regulates fatty acid storage and lipolysis, being also an important mediator of inflammation. In this regard, FABP4 recently demonstrated an interesting molecular target for the treatment of type 2 diabetes, other metabolic diseases and some type of cancers. In the past years, hundreds of effective FABP4 inhibitors have been synthesized. In this paper, a quantitative structure-activity relationship (QSAR) model has been produced, in order to predict the bioactivity of FABP4 inhibitors. The methodology has been combined with a scaffold-hopping approach, allowing to identify three new molecules that act as effective inhibitors of this protein. These molecules, synthesized and tested for their FABP4 inhibitor activity, showed IC₅₀ values between 3.70 and 5.59 μM, with a high level of agreement with the predicted values.

Development of a radioiodinated triazolopyrimidine probe for nuclear medical imaging of fatty acid binding protein 4

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.