Spectral Polarization Imaging of Human Prostate Cancer Tissue Using a Near-infrared Receptor-targeted Contrast Agent

Abstract

The Cypate-Bombesin Peptide Analogue Conjugate (Cybesin) was used as a prostate tumor receptor-targeted contrast agent. The absorption and fluorescence spectra of Cybesin were measured and shown to exist in the NIR tissue "optical window". The spectral polarization imaging of Cybesin-stained prostate cancerous and normal tissues shows that prostate cancerous tissue takes-up more Cybesin than that of prostate normal tissue, making Cybesin a potential marker of prostate cancer.Keywords: Prostate cancer; Receptor-targeted; Peptide analogue conjugate; Contrast agent; Spectral polarization imaging; Near-infrared; Absorption; and Fluorescence. IntroductionThe increasing incidence and mortality rate of prostate cancers in men makes early tumor detection research a challenge for oncological specialists. The region of the highest incidence is in the western world, where there are 10-11% chances for a man to develop prostate cancer, and 3-4% chances of dying from the disease (1). Conventional oncology imaging methods for prostate cancer diagnosis, still depend on bulk physical properties of cancer tissue and are not effective for earlystage primary tumors (2). It is well known that diagnosis of a small premalignant lesion is critical for the success of cancer therapy and a key to increase survival rates. Scientists have been looking for methods that emphasize gene-specific or receptor-specific, minimally invasive diagnosis for early-stage tumors (2).Near-infrared (NIR) optical imaging is a powerful tool in cancer research that relies on activating endogenous chromophores or applying contrast agents that can target cancer cells. The use of intrinsic chromophores to differentiate the optical properties of diseased and healthy human tissues has been reported in some studies using fluorescence and absorption (3, 4). The most attractive advantage of optical imaging is the high sensitivity, which can be superior to other in vivo imaging techniques (2). Over the past decade, cyanine dyes have been investigated by several groups (5, 6) as contrast agents for optical detection of tumors. In order to observe fluorescence from a substantial distance within the body, the emission wavelength must be in the NIR wavelength window in which light passing through tissue is less likely to be absorbed or scattered (7). Researchers are interested in cyanine dyes because their emission range of 700 nm to 900 nm is in the tissue "optical window" (8 absorption bands at 950nm and 1195nm due to water which is the main chromophore component in human tissue (4, 9).The investigations of receptor expression in normal and cancer tissue suggest that small peptide-dye conjugates can be used to target over-expressed receptors on tumors contrary to the traditional approach of dyes conjugated to large proteins and antibodies (5, 10, 11). As a small ICG-derivative dyepeptide, Cypate-Bombesin Peptide Analogue Conjugate (Cybesin) was synthesized and used as a contrast agent to detect pancreas tumors in an animal model a few years ago (5). The prior experimenta...

Molecular Imaging of Breast Cancer Tissue via Site-Directed Radiopharmaceuticals

“…Alternative optical imaging technologies such as fluorescence molecular tomography are emerging as new and exciting molecular imaging tools for diagnosis of human disease (Montet et al, 2006;Young & Rozengurt, 2005;Pu et al, 2005). Studies show that the highthroughput signal afforded by fluorescence imaging might offer an alternative to traditional tomographic imaging by alleviating many of the imaging artifacts seen in imaging systems of this general type (Weissleder & Ntziachristos, 2003;Zacharakis et al, 2005;Kwon et al, 2005).…”

“…This study well demonstrates the potential of dualmodality imaging for diagnosis of human cancers. Young and co-workers have recently described the use of quantum dots conjugated to bombesin to successfully image living mouse Swiss 3T3 and Rat-1 cells in vitro (Young & Rozengurt, 2005) and Pu et al, have described a new Cypate-bombesin Peptide Analogue Conjugate (Cybesin) that has potential use as a prostate tumor receptor-mediated contrast agent (Pu et al, 2005). All of these studies provide either in vivo or in vitro evidence for production of fluorescence-based targeting vectors of bombesin for early detection of human cancers.…”

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

“…The spectral polarization imaging set up used for imaging Cybesin-and Cytate-stained cancerous and normal prostate tissues has been described in our early work [10]. Light from a white light source is used to illuminate the prostate tissue sample with average power of ∼50 μW=cm 2 .…”

“…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.…”

“…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].…”