Molecule imaging is an indispensible tool for diagnosis, treatment and basic mechanism studies. For a specific disease, the majority of research has been focusing on a single-biomarker imaging, which is particularly important for the purpose of diagnosis. However, given the complex nature of most diseases, systemic molecular imaging (SYMI) of multiple biomarkers of a single disease can be crucial for understanding its mechanism, and for designing more efficient therapeutics.
Alzheimer’s disease (AD) is a multi-facet neurodegenative disease with multi-dimensional biomarkers. If the biomarkers of AD are considered in a multi-dimensional space, each category of biomarkers could be considered as one coordination axis. Amyloid beta (Ab) deposits and tau tangles are the most prominent pathological hallmarks of AD, and Ab and tau species respectively represent two essential axis of biomarkers of AD. It is also well accepted that oxidative stress is highly associated with AD, and reactive oxygen species (ROS) could also be considered as another important biomarker dimension of AD. Considering AD biomarkers in a three-dimensional (3D) space, Ab, tau and ROS could be considered as x, y, z-coordination axis correspondingly.
This presentation will focus on our recent results from our laboratory in systemic molecular imaging of AD, particularly on the biomarker dimensions of Aβs and ROS. On the axis of Aβ, multiple sub-species, including insoluble and soluble Aβs consist a complex family of biomarkers. Currently, it is not clear which sub-species could serve as a better biomarker for AD severity and progression. In the past few years, our research has been concentrated on three-phase development of “smart” NIRF probes for various Aβ species. In phase (I), we developed a new family of NIR fluorescent dyes (termed CRANAD-X) for insoluble Aβs. In phase (II), we have successfully developed NIRF probes for both soluble and insoluble Aβ species. In phase (III) we have concentrated our efforts on developing imaging probes that are selective for soluble Aβs. On the ROS axis, we have first designed NIRF probes for detection of H2O2, and then designed NIRF probes that are sensitive to various ROS. Our data showed the excellent correlation between ROS levels and the progression of AD. Taken together, with imaging probes for different dimensions of AD biomarkers, we believe that systemic molecular imaging will be a vital approach for understanding the complexity of AD, and for efficiently assisting AD drug development.
Ran C, Xu X, Raymond SB, Ferrara BJ, Neal K, Bacskai BJ, Medarova Z, Moore A, J. Amer. Chem. Soc.,2009,131(42):15257-61.
Zhang X, Tian Y, Li Z, Tian X, Sun H, Liu H, Moore A, Ran C.*, J. Amer. Chem. Soc., 2013, 135(44):16397-409.
Zhang X, Tian Y, Yuan P, Li Y., Yaseen MA, Grutzendler J, Moore A, Ran C.*, Chem. Commun., 2014, 50(78):11550-3.
Zhang X, Tian Y, Zhang C, Tian X, Ross AW, Moir RD, Sun H, Tanzi RE, Moore A, and Ran C*, Proc. Natl. Aca Sci. USA, 2015, 112(31):9734-9.
Turn-on fluorescence imaging is routinely studied; however, turn-on chemiluminescence has been rarely explored for in vivo imaging. Herein, we report the design and validation of chemiluminescence probe ADLumin-1 as a turn-on probe for amyloid beta (Aβ) species. Two-photon imaging indicates that ADLumin-1 can efficiently cross the blood–brain barrier and provides excellent contrast for Aβ plaques and cerebral amyloid angiopathy. In vivo brain imaging shows that the chemiluminescence signal of ADLumin-1 from 5-month-old transgenic 5xFAD mice is 1.80-fold higher than that from the age-matched wild-type mice. Moreover, we demonstrate that it is feasible to further dually-amplify signal via chemiluminescence resonance energy transfer (DAS-CRET) using two non-conjugated smart probes (ADLumin-1 and CRANAD-3) in solutions, brain homogenates, and in vivo whole brain imaging. Our results show that DAS-CRET can provide a 2.25-fold margin between 5-month-old 5xFAD mice and wild type mice. We believe that our strategy could be extended to other aggregating-prone proteins.
Differentiating amyloid beta (Ab) subspecies Ab40 and Ab42 has long been considered as an impossible mission with small-molecule probes. In this report, based on recently published structures of Ab fibrils, we designed iminocoumarin-thiazole (ICT) fluorescence probes to differentiate Ab40 and Ab42, among which Ab42 has much higher neurotoxicity. We demonstrated that ICTAD-1 robustly responds to Ab fibrils, evidenced by turn-on fluorescence intensity and red-shifting of emission peaks. Remarkably, ICTAD-1 showed different spectra towards Ab40 and Ab42 fibrils. In vitro results demonstrated that ICTAD-1 could be used to differentiate Ab40/42 in solutions. Moreover, our data revealed that ICTAD-1 could be used to separate Ab40/42 components in plaques of AD mouse brain slides. In addition, two-photon imaging suggested that ICTAD-1 was able to cross the BBB and label plaques in vivo. Interestingly, we observed that ICTAD-1 was specific toward plaques, but not cerebral amyloid angiopathy (CAA) on brain blood vessels. Given Ab40 and Ab42 species have significant differences of neurotoxicity, we believe that ICTAD-1 can be used as an important tool for basic studies and has the potential to provide a better diagnosis in the future.
Evidence suggests that the abnormal levels of Amyloid beta (A) species in brains appear as early as 30 years before symptom starts in Alzheimer’s disease (AD) patients. However, the early generation PET probes can only detect the abnormal A deposits close to the onset of clinical AD syndrome. In this report, we demonstrated that half-curcuminoid could be a better scaffold for PET tracer development. Through blocking a highly reactive site of half-curcuminoids, F-CRANAD-101 was designed and showed significant responses to both soluble and insoluble Aβs in fluorescent spectral tests. PET imaging results indicated that both 14-month and 5-month APP/PS1 AD mice had higher signals in brain than the age-matched wild type mice. We believe that [18F]-CRANAD-101 could be a potential PET imaging probe for Amyloid betas in Alzheimer’s disease.
Purpose: Brown adipose tissue (BAT) in adult humans has been recently re-discovered and intensively investigated as a new potential therapeutic target for obesity and type 2 diabetes (T2D). However, reliable assessment of BAT mass in vivo represents a considerable challenge. The purpose of this study is to demonstrate for the first time that human BAT depots can be imaged with a TSPO-specific PET tracer [11C]PBR28 under thermoneutral conditions.
Procedures:In this retrospective study, we analyzed the images of three healthy volunteers who underwent PET/MR imaging after injection of 14mCi of [11C]PBR28 at room temperature. Thirty-minute static PET images were reconstructed from the data obtained 60-90 minutes after the injection of the tracer .
Results: [11C]PBR28 uptake in the neck/supraclavicular regions was identified, which was parallel to the known distribution pattern of human BAT depots. These areas co-localized with the areas of hyperintensity and corresponded to fat on T1 weighted MR images. Standardized uptake value (SUV) was used to quantify [11C]PBR28 signal in BAT depots. The average (± SD) SUV(mean) and SUVmax for BAT depots was 2.13 (±0.33) and 3.19 (±0.34) respectively, while the average SUV(mean) for muscle and subcutaneous adipose tissue was 0.79 (±0.1) and 0.18 (±0.04) respectively.
Conclusions: In this brief article, we provide the first evidence suggesting that [11C]PBR28, a widely available TSPO-specific PET tracer, can be used for imaging human BAT mass under thermoneutral conditions.
Amyloid peptides and proteins are associated with pathologies of numerous diseases. In the progression of a disease, amyloids exist in soluble and insoluble forms, which are dominated species at different stages of the disease and have different degree of toxicities. However, differentiating the soluble and insoluble forms is very challenging with small molecule probes, due to multiple layers of hurdles. Inspired by the recognition principle of antibodies for sAβ, we hypothesized that the accessibility/tightness of soluble and insoluble amyloids could be utilized to design imaging probes to recognize different amyloid forms, and stereo-hindrance tuning strategy could be used to design imaging probes for selectively detecting soluble amyloid beta (sAβ) species in Alzheimer’s disease (AD). Herein, we demonstrated that tuning the stereo-hindrance of phenoxy-alkyl chains at 4-position of curcumin scaffold could lead to certain selectivity for sAβ over insoluble Aβs (insAβ). Among the designed compounds, CRANAD-102 showed a 68-fold higher affinity to sAβ than insAβ (7.5±10 nM vs. 505.9±275.9 nM). Moreover, our imaging data indicated that CRANAD-102 was indeed capable of detecting sAβ in vivo using 4-months old APP/PS1 mice, in which sAb are the predominant species in the brains. In addition, we also demonstrted that CRANAD-102 could be used to monitor the increasing of sAβ loading from the ages of 4-months old to 12-months old. We believe that CRANAD-102 can be a useful probe for selectively detecting sAβ species in AD, and our probe designing strategy can be applied to other amyloids, and will have tremendous impact on AD drug development and other amyloid research.