<b>Introduction:</b> Brain tumor margin detection remains a challenging problem in the operative resection of gliomas. A novel nanoparticle, a PEGylated quantum dot, has been shown to be phagocytized by macrophages <i>in vivo</i>. This feature may allow quantum dots to co-localize with brain tumors and serve as an optical aid in the surgical resection of brain tumors. <b>Methods:</b> Sprague-Daly rats were injected intracranially with C6 gliosarcoma cell lines to establish tumors. Two weeks after implantation of brain tumors, PEGylated quantum dots emitting at 705 nm (PEG-705 QD) were injected via the tail vein. Twenty-four hours post PEG-705 QD injection, the animals were sacrificed and their tissues examined. <b>Results:</b> PEGylated quantum dots are avidly phagocytized by macrophages and are taken up by liver, spleen and lymph nodes. Macrophages and microglia co-localize with glioma cells, carrying the optical nanoparticle, the quantum dot. Excitation of the PEG-705 quantum dots gives off a deep red fluorescence detectable with charge coupled device (CCD) cameras, optical spectroscopy units, and in dark field fluorescence microscopy. <b>Conclusions:</b> PEG-705QDs co-localize with brain tumors and may serve as an optical adjunct to aid in the operative resection of gliomas. The particles may be visualized in surgery with CCD cameras or detected by optical spectroscopy.
<b>OBJECTIVE:</b> Optical spectroscopic tools exist that allow open surgical and minimally invasive assays of intrinsic tissue optics. Optical detection of cellular and tissue viability may offer a minimally invasive way to assess tumor responsiveness to chemotherapies. We report on an optical spectroscopic change that precedes apoptotic cell death and appears related to NAD(P)H autofluorescence.
<b>METHODS:</b> The cell lines SW 480 and U87-MG were grown in culture and treated with cisplatin 100 μg/ml and tamoxifen 10 μM, respectively. Fluorescence spectroscopy at 355 nm excitation and 460 nm emission were collected. MTS assays were used to determine cell viability. Cell lysates were analyzed for NAD(P)H concentrations by mass spectroscopy. <b>RESULTS:</b> Autoflourescence at 355 nm excitation and 460 nm emission declines markedly despite normalization for cell number and total protein concentration after treatment with tamoxifen or cisplatin. The autofluorescence drop precedes the loss of cell viability as measured by MTS assay. For example, the relative viability of the U87-MG cell treated with tamoxifen at hours 0, 8, 12 and 24 of treatment was 100 ± 6, 85 ± 6, 53 ± 9 and 0 ± 3. The relative fluorescence at the same time points were 100 ± 2, 57 ± 6, 47 ± 3, and 0 ± 1. TUNNEL assays confirm that cell death is via apoptosis. The key cellular fluorophore at these wavelengths is NAD(P)H. Mass spectroscopic analysis of cell lysates at these time points reveals a drop in NAD(P)H concentrations that is parallel to the loss of fluorescence signal. <b>CONCLUSIONS:</b> NAD(P)H autofluoresence decline precedes apoptotic cell death. This may allow the design of minimally invasive spectroscopic tools to monitor chemotherapeutic response.
Quantum dots (QDs) are optical semiconductor nanocrystals that exhibit stable, bright fluorescence over narrow, size tunable emission bands. The size tunable optical properties of QDs allow multiplexing with multiple emission wavelengths from a single excitation source. QDs may be linked to antibodies, peptides, and nucleic acids for use as fluorescence probes <i>in vitro</i> and <i>in vivo</i>. The electron dense construction of QDs makes it possible to detect QDs with radiographic techniques such as computed tomography. The intravenous injection of QDs may be exploited to optically label brain tumors, potentially leading to improved techniques for surgical biopsy and resection. Macrophage-mediated delivery of QDs to areas of neoplasm and inflammation may represent a novel technique that might be exploited in a variety of surgical situations in which optical feedback control could be useful in aiding the completeness of resection of a lesion or in the accurate localization of pathology for biopsy.
Conference Committee Involvement (2)
Optical Methods in Drug Discovery and Development II
1 October 2006 | Boston, Massachusetts, United States