Small-Animal PET of Tumor Damage Induced by Photothermal Ablation with ⁶⁴Cu-Bis-DOTA-Hypericin

Abstract

The purpose of this study was to investigate the potential application of small-molecular-weight 64 Cu-labeled bis-DOTAhypericin in the noninvasive assessment of response to photothermal ablation therapy. Methods: Bis-DOTA-hypericin was labeled with 64 Cu with high efficiency (.95% without purification). Nine mice bearing subcutaneous human mammary BT474 tumors were used. Five mice were injected intratumorally with semiconductor CuS nanoparticles, followed by near-infrared laser irradiation 24 h later (12 W/cm 2 for 3 min), and 4 mice were not treated (control group). All mice were intravenously injected with 64 Cu-bis-DOTA-hypericin (24 h after laser treatment in treated mice). Small-animal PET images were acquired at 2, 6, and 24 h after radiotracer injection. All mice were killed immediately after the imaging session for biodistribution and histology study. In vitro cell uptake and surface plasmon resonance studies were performed to validate the small-animal PET results. Results: 64 Cu-bis-DOTA-hypericin uptake was significantly higher in the treatment group than in the control group. The percentage injected dose per gram of tissue in the treated and control groups was 1.72 6 0.43 and 0.76 6 0.19, respectively (P 5 0.017), at 24 h after injection. Autoradiography and histology results were consistent with selective uptake of the radiotracer in the necrotic zone of the tumor induced by photothermal ablation therapy. In vitro results showed that treated BT474 cells had a higher uptake of 64 Cu-bis-DOTA-hypericin than nontreated cells. Surface plasmon resonance study showed that bis-DOTA-hypericin had higher binding affinity to phosphatidylserine and phosphatidylethanolamine than to phosphatidylcholine. Conclusion: 64 Cu-bis-DOTA-hypericin has a potential to image thermal therapy-induced tumor cell damage. The affinity of 64 Cu-bis-DOTA-hypericin for injured tissues may be attributed to the breakdown of the cell membrane and exposure of phosphatidylserine or phosphatidylethanolamine to the radiotracer, which binds selectively to these phospholipids.

Influence of the vascular damaging agents DMXAA and ZD6126 on hypericin distribution and accumulation in RIF-1 tumors

“…Hypericin, bearing a negative charge in physiological conditions, may interact with positively charged proteins such as histones or histone fragments, which are typically exposed in necrotic tissue. Alternatively, a 64 Cu-Bis-DOTA conjugate to hypericin has been shown to interact with phospholipids that are normally present at the inner leaflet of the cell membrane, yet become exposed during necrotic cell death (Song et al 2011). Because of this, it is of interest to experimentally investigate the impact of timing and sequence of administration on hypericin accumulation in tumors that have been treated with a VDA.…”

A single-dose toxicity study on non-radioactive iodinated hypericin for a targeted anticancer therapy in mice

“…Hyp and its radio-derivatives have been investigated in animal models with ischemic heart diseases and malignancies for diagnostic and therapeutic purposes [11,14,15,18,32] . Toxicity information is an indispensable part for exploring and integrating the targeting anticancer theragnostic strategy using radioiodi- Figure 4.…”

Transbilayer phospholipids molecular imaging

“…PET distribution also showed higher uptake in the liver and the kidneys. Bis-DOTA-hypericin had a selective binding affinity for PS and PE phospholipids [45]. In necrosis, PS and PE are exposed to 64 Cu-labelled hypericin probe in the inner leaflet of damaged cell membrane.…”

“…131 I-hypericin) and 99m Tc (i.e. 99m Tc-hypericin) for imaging of necrosis in preclinical and clinical research as described above in the PS target section [45-50]. Table 3 summarises the PE-based radiolabelled molecular probes.…”