The accepted model of colorectal cancer assumes the paradigm that aberrant crypt foci (ACF) are the earliest events in tumorigenesis and develop into adenoma, which further develop into adenocarcinoma. Under this assumption, basic research and drug studies have been performed using ACF as substitute markers for fully developed carcinoma. While studies have shown a correlation between the number of ACF present and the presence of adenoma/adenocarcinoma, a causal relationship has yet to be determined. The mouse has shown to be an excellent model for colorectal cancer; however, the outcomes of such experiments require sacrifice and histologic examination of ex vivo tissue. To better utilize the mouse model to study ACF and adenoma development, an endoscope was constructed for non-destructive in vivo surface visualization, molecular imaging and cross-sectional imaging of the colon. Our system combines surface magnifying chromoendoscopy (SMC) and optical coherence tomography (OCT) to image colon microstructure. Sixteen mice, treated with the carcinogen azoxymethane, were imaged at 2 week intervals, to visualize carcinogenesis events. With this dual-modality system we are able to visualize crypt structure alteration over time as well as adenoma development over time.
Many diseases involve changes in cell signaling cascades, as seen commonly in drug resistant cancers. To better
understand these intricate signaling events in diseased cells and tissues, experimental methods of probing cellular
communication at a single to multi-cell level are required. We recently introduced a general platform for activation of
selected signaling pathways by optically controlled delivery and release of water soluble factors using gold-coated
liposomes. In the example presented here, we encapsulated inositol trisphosphate (IP3), a ubiquitous intracellular
secondary messenger involved in GPCR and Akt signaling cascades, within 100 nm gold-coated liposomes. The high
polarizability of the liposome’s unique gold pseudo-shell allows stable optical trapping for subcellular manipulation in
the presence of cells. We take this optical manipulation further by optically injecting IP3-containing liposomes into the
cytosol of a single cell to initiate localized cell signaling. Upon optical injection of liposomal IP3 into a single ovarian
carcinoma cell, we observed localized activation as reported by changes in Indo-1 fluorescence intensity. With
established gap junctions between the injected cell and neighboring cells, we monitored propagation of this signaling to
and through nearby cells.
We have developed an experimental system with the potential for the delivery and localized release of an encapsulated
agent with high spatial and temporal resolution. We previously introduced liposome-supported plasmon resonant gold
nanoshells; in this composite structure, the liposome allows for the encapsulation of substances, such as therapeutic
agents, neurotransmitters, or growth factors, and the plasmon resonant structure facilitates the rapid release of
encapsulated contents upon laser light illumination. More recently, we demonstrated that these gold-coated liposomes
are capable of releasing their contents in a spectrally-controlled manner, where plasmon resonant nanoparticles only
release content upon illumination with a wavelength of light matching their plasmon resonance band. We now show that
this release mechanism can be used in a biological setting to deliver a peptide derivative of cholecystokinin to HEK293
cells overexpressing the CCK2 receptor. Using directed laser light, we may enable localized release from gold-coated
liposomes to enable accurate perturbation of cellular functions in response to released compounds; this system may have
possible applications in signaling pathways and drug discovery.
We recently demonstrated that liposome-supported plasmon resonant gold nanoshells are degradable into
components of a size compatible with renal clearance, potentially enabling their use as multifunctional agents in
applications in nanomedicine, including imaging, diagnostics, therapy, and drug delivery (Troutman et al., Adv.
Mater. 2008, 20, 2604-2608). When illuminated with laser light at the wavelength matching their plasmon resonance
band, gold-coated liposomes rapidly release their encapsulated substances, which can include therapeutic and
diagnostic agents. The present research demonstrates that release of encapsulated agents from gold-coated liposomes
can be spectrally controlled by varying the location of the plasmon resonance band; this spectral tuning is
accomplished by varying the concentration of gold deposited on the surface of liposomes. Furthermore, the amount
of laser energy required for release is qualitatively explained using the concept of thermal confinement (Jacques,
Appl. Opt. 1993, 32(3), 2447-2454). Overlapping thermal confinement zones can be avoided by minimizing the laser
pulse width, resulting in lower energy requirements for liposomal content release and less global heating of the
sample. Control of heating is especially important in drug delivery applications, where it enables spatial and spectral
control of delivery and prevents thermal damage to tissue.
We have recently introduced liposome-supported plasmon resonant gold nanoshells (Troutman et al., Adv. Mater. 2008,
20, 2604-2608). These plasmon resonant gold-coated liposomes are degradable into components of a size compatible
with renal clearance, potentially enabling their use as multifunctional agents in applications in nanomedicine, including
imaging, diagnostics, therapy, and drug delivery. The present research demonstrates that laser illumination at the
wavelength matching the plasmon resonance band of a gold-coated liposome leads to the rapid release of encapsulated
substances, which can include therapeutic and diagnostic agents. Leakage of encapsulated contents is monitored through
the release of self-quenched fluorescein, which provides an increase in fluorescence emission upon release. Moreover,
the resonant peak of these gold-coated liposomes is spectrally tunable in the near infrared range by varying the
concentration of gold deposited on the surface of liposomes. Varying the plasmon resonant wavelengths of gold-coated
liposomes can provide a method for spectrally-coding their light-mediated content release, so that the release event is
initiated by the specific wavelength of light used to illuminate the liposomes. The development of spectrally-coded
release can find applications in controlled delivery of multiple agents to support complex diagnostic tests and therapeutic
interventions.
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