SPECT Imaging of Treatment-Related Tumor Necrosis Using Technetium-99m-Labeled Rhein

Design and Evaluation of Rhein-Based MRI Contrast Agents for Visualization of Tumor Necrosis Induced by Combretastatin A-4 Disodium Phosphate

PURPOSE

Visualization of tumor necrosis can determine tumor response to therapy. Our previous study showed that the rhein-based magnetic resonance imaging (MRI) contrast agent with alkane linker (GdL₂) could clearly image tumor necrosis. However, its water solubility and cell safety needed to be improved. Herein, three rhein-based MRI agents with ether or lysine linkers were designed.

PROCEDURES

Three rhein-based MRI agents were synthesized with a tetracarbon ether (GdP1), a hexacarbon ether (GdP2), and a lysine (GdP3) linker, respectively. Their octanol-water partition coefficients (log P) and cytotoxicity were determined. Necrosis avidity of the leading agent was explored on HepG2 cells and ischemia reperfusion-induced liver necrosis (IRLN) rats by MRI. The effect of visualization of tumor necrosis was tested on nude mice with W256 tumor treated by combretastatin-A4 phosphate (CA4P). DNA binding assays were applied to evaluate the possible necrosis-avidity mechanism of the leading agent.

RESULTS

The log P of three agents (- 1.66 ± 0.09, - 1.74 ± 0.01, - 1.95 ± 0.01) decreased when compared with GdL₂, indicating higher water solubility. GdP1 not only presented lower cytotoxicity and good necrotic affinity in vitro and in vivo, but also can be fast excreted by renal. According to MRI results of tumor, distinct visualization of tumor necrosis can be discernible from 3 to 4.5 h post-injection of GdP1. In DNA-binding assays, the fluorescence quenching constant K_SV (1.00 × 10⁴ M^-1) and the ultraviolet binding constant K_b (1.11 × 10⁴ M^-1) suggested that GdP1 may bind to DNA through intercalation.

CONCLUSION

GdP1 may serve as a potential candidate for early evaluation of tumor response to CA4P treatment.

Discovery of necrosis avidity of rhein and its applications in necrosis imaging

Necrosis-avid agents possess exploitable theragnostic utilities including evaluation of tissue viability, monitoring of therapeutic efficacy as well as diagnosis and treatment of necrosis-related disorders. Rhein (4,5-dihydroxyl-2-carboxylic-9,10-dihydrodiketoanthracene), a naturally occurring monomeric anthraquinone compound extensively found in medicinal herbs, was recently demonstrated to have a newly discovered necrosis-avid trait and to show promising application in necrosis imaging. In this overview, we present the discovering process of rhein as a new necrosis-avid agent as well as its potential imaging applications in visualisation of myocardial necrosis and early evaluation of tumour response to therapy. Moreover, the molecular mechanism exploration of necrosis avidity behind rhein are also presented. The discovery of necrosis avidity with rhein and the development of rhein-based molecular probes may further expand the scope of necrosis-avid compounds and highlight the potential utility of necrosis-avid molecular probes in necrosis imaging.

Imaging Cell Death: Focus on Early Evaluation of Tumor Response to Therapy

Cell death plays a prominent role in the treatment of cancer, because most anticancer therapies act by the induction of cell death including apoptosis, necrosis, and other pathways of cell death. Imaging cell death helps to identify treatment responders from nonresponders and thus enables patient-tailored therapy, which will increase the likelihood of treatment response and ultimately lead to improved patient survival. By taking advantage of molecular probes that specifically target the biomarkers/biochemical processes of cell death, cell death imaging can be successfully achieved. In recent years, with the increased understanding of the molecular mechanism of cell death, a variety of well-defined biomarkers/biochemical processes of cell death have been identified. By targeting these established cell death biomarkers/biochemical processes, a set of molecular imaging probes have been developed and evaluated for early monitoring treatment response in tumors. In this review, we mainly present the recent advances in identifying useful biomarkers/biochemical processes for both apoptosis and necrosis imaging and in developing molecular imaging probes targeting these biomarkers/biochemical processes, with a focus on their application in early evaluation of tumor response to therapy.

Molecular imaging of myocardial necrosis: an updated mini-review

Acute myocardial infarction (AMI) remains the most severe and common cardiac emergency among various ischaemic heart diseases. Both unregulated (necrosis) and regulated (apoptosis, autophagy and necroptosis et al.) forms of cell death can occur during AMI. Non-invasive imaging of cardiomyocyte death represents an attractive approach to acquire insights into the pathophysiology of AMI, track the temporal and spatial evolution of MI, guide therapeutic decision-making, evaluate response to therapeutic intervention and predict prognosis. Although several forms of cell death have been identified during AMI, to date, only apoptosis- and necrosis-detecting probes compatible with currently available tomographic imaging modalities have been successfully developed for non-invasive visualisation of cardiomyocyte death. Myocardial apoptosis imaging has gained more attention because of its potential controllability while less attention has been paid to myocardial necrosis imaging. In our opinion, although cardiomyocyte necrosis is unsalvageable, imaging necrosis can play an important role in early diagnosis, risk stratification, prognostic prediction and guidance in therapeutic decision-making of AMI. In this mini-review, we summarise the updated advances achieved by us and others and discuss the challenges in the development of molecular imaging probes for visualisation of myocardial necrosis.

Synthesis and Evaluation of Diindole-Based MRI Contrast Agent for In Vivo Visualization of Necrosis

PURPOSE

Noninvasive imaging of cell necrosis can provide an early evaluation of tumor response to treatments. Here, we aimed to design and synthesize a novel diindole-based magnetic resonance imaging (MRI) contrast agent (Gd-bis-DOTA-diindolylmethane, Gd-DIM) for assessment of tumor response to therapy at an early stage.

PROCEDURES

The oil-water partition coefficient (Log P) and relaxivity of Gd-DIM were determined in vitro. Then, its necrosis avidity was examined in necrotic cells in vitro and in rat models with microwave ablation-induced muscle necrosis (MAMN) and ischemia reperfusion-induced liver necrosis (IRLN) by MRI. Visualization of tumor necrosis induced by combretastatin A-4 disodium phosphate (CA4P) was evaluated in rats bearing W256 orthotopic liver tumor by MRI. Finally, DNA binding assay was performed to explore the possible necrosis-avidity mechanism of Gd-DIM.

RESULTS

The Log P value and T1 relaxivity of Gd-DIM is - 2.15 ± 0.01 and 6.61 mM^-1 s^-1, respectively. Gd-DIM showed predominant necrosis avidity in vitro and in vivo. Clear visualization of the tumor necrosis induced by CA4P was achieved at 60 min after administration of Gd-DIM. DNA binding study indicated that the necrosis-avidity mechanism of Gd-DIM may be due to its binding to exposed DNA in necrotic cells.

CONCLUSION

Gd-DIM may serve as a promising necrosis-avid MRI contrast agent for early assessment of tumor response to therapy.