Time-resolved fluorescence polarization dynamics and optical imaging of Cytate: a prostate cancer receptor-targeted contrast agent

Abstract

Cypate-octreote peptide analogue conjugate (Cytate) was investigated as a prostate cancer receptortargeted contrast agent. The absorption and fluorescence spectra of Cytate were ranged in the nearinfrared "tissue optical window." Time-resolved investigation of polarization-dependent fluorescence emitted from Cytate in solution as well as in cancerous and normal prostate tissues was conducted. Polarization preservation characteristics of Cytate in solution and tissues were studied. Fluorescence intensity emitted from the Cytate-stained cancerous prostate tissue was found to be much stronger than that from the Cytate-stained normal prostate tissue, indicating more Cytate uptake in the former tissue type. The polarization anisotropy of Cytate contained in cancerous prostate tissue was found to be larger than that in the normal prostate tissue, indicating a larger degree of polarization preservation in Cytate-stained cancerous tissue. The temporal profiles of fluorescence from Cytate solution and from Cytate-stained prostate tissue were fitted using a time-dependent fluorescence depolarization model. The photoluminescence imaging of Cytate-stained cancerous and normal prostate tissues was accomplished, showing the potential of Cytate as a fluorescence marker for prostate cancer detection.

Study of rotational dynamics of receptor-targeted contrast agents in cancerous and normal prostate tissues using time-resolved picosecond emission spectroscopy

“…However, the maximum elapsed time is less than 30 h. The preparation of prostate tissue samples used for time-resolved studies follows this protocol: (1) samples (cancerous and normal prostate tissues) were cut into ∼2 × ∼1 × ∼0:5 cm ðlength × width × thicknessÞ pieces, (2) samples were soaked in the same aqueous Cybesin (Cytate) with a concentration of ∼3:2 × 10 −6 M for ∼10 min, (3) samples were put into sodium phosphate buffer (SigmaAldrich) to wash off and consequently reduce the amount of unbound Cybesin (Cytate) in particular on the surface and subsurface. Six pairs of samples were investigated for Cybesin targeting to overexpressed BR [7,8,10] in cancerous tissue and six for Cytate to SSTR [7,9,11]. For each prostate tissue sample, three to six different locations were measured to get an average value.…”

“…In order to investigate the time evolution of emission from receptor-targeted contrast agents (Cybesin and Cytate) bound with prostate cancer cells [7,10,11] in prostate tissue, an analytical model dealing with high viscous media was developed. It is well known that the properties of biological living tissues are somehow similar to the behavior of liquid with very high viscosity [16,17], and the human body has a volume of 70% to 80% water.…”

“…Cybesin (Cytate) in prostate tissue can be considered as a fluorescent contrast agent in "highly viscous liquid." After cancerous prostate tissue was soaked into the Cybesin (Cytate) solution and washed off using sodium phosphate buffer consequently, a large proportion of Cybesin (Cytate) was conjugated to the corresponding receptor on cells [7,10,11]. Although a large amount of free Cybesin (Cytate) molecules in surface and subsurface were removed by the buffer, some free contrast agents were still conserved in the deep tissue area.…”

“…Although a large amount of free Cybesin (Cytate) molecules in surface and subsurface were removed by the buffer, some free contrast agents were still conserved in the deep tissue area. For the case of normal prostate tissue, a smaller portion of contrast agent was conjugated to tissue cells in comparison with cancerous tissue [7,10,11], and some free fluorescent molecules exist in the interstitial fluid of deep tissue areas. The cell-bound mechanism and reorientation of Cybesin (Cytate) molecules in prostate tissue is schematically shown in Fig.…”

“…Two kinds of receptor-targeted contrast agents, namely Cybesin and Cytate, were demonstrated to target the overexpressed bombesin receptor (BR) [8] and somatostatin receptor (SSTR) [9], respectively, on prostate cancer tissues in vitro [10,11]. The advantages of optical receptor-targeted contrast agents include a high affinity of specific 0003-6935/11/101312-11$15.00/0 © 2011 Optical Society of America ligand corresponding to overexpressed receptor for the localization of tumors [7], rapid clearance of the applied contrast, possibilities of preparing a library of peptides for rapid identification of bioactive molecules [7], and preservation of spectral advantage in the NIR range of the "tissue optical window" [10,11]. Time-resolved polarization-dependent fluorescence spectroscopy provides not only the intensity information but also relaxation and rotation information of fluorophores in the microenvironment of media [3].…”