Trevor Mitcham

Fluorinated Graphene Oxide; a New Multimodal Material for Biological Applications

Fluorinated graphene oxide (FGO) is reported for the first time as a magnetically responsive drug carrier that can serve both as a magnetic resonance imaging (MRI) and photoacoustic contrast agent, under preclinical settings, and as a type of photothermal therapy. Its hydrophilic nature facilitates biocompatibility. FGO as a broad wavelength absorber, with high charge transfer and strong non-linear scattering is optimal for NIR laser-induced hyperthermia.

In vitro and in vivo mapping of drug release after laser ablation thermal therapy with doxorubicin-loaded hollow gold nanoshells using fluorescence and photoacoustic imaging

Doxorubicin-loaded hollow gold nanoshells (Dox@PEG-HAuNS) increase the efficacy of photothermal ablation (PTA) not only by mediating efficient PTA but also through chemotherapy, and therefore have potential utility for local anticancer therapy. However, in vivo real-time monitoring of Dox release and temperature achieved during the laser ablation technique has not been previously demonstrated before. In this study, we used fluorescence optical imaging to map the release of Dox from Dox@PEG-HAuNS and photoacoustic imaging to monitor the tumor temperature achieved during near-infrared laser-induced photothermal heating in vitro and in vivo. In vitro, treatment with a 3-W laser was sufficient to initiate the release of Dox from Dox@PEG-HAuNS (1:3:1 wt/wt, 1.32 × 10(12)particles/mL). Laser powers of 3 and 6W achieved ablative temperatures of more than 50°C. In 4T1 tumor-bearing nude mice that received intratumoral or intravenous injections of Dox@PEG-HAuNS, fluorescence optical imaging (emission wavelength = 600 nm, excitation wavelength = 500 nm) revealed that the fluorescence intensity in surface laser-treated tumors 24h after treatment was significantly higher than that in untreated tumors (p = 0.015 for intratumoral, p = 0.008 for intravenous). Similar results were obtained using an interstitial laser to irradiate tumors following the intravenous injection of Dox@PEG-HAuNS (p = 0.002 at t = 24h). Photoacoustic imaging (acquisition wavelength = 800 nm) revealed that laser treatment caused a substantial increase in tumor temperature, from 37 °C to ablative temperatures of more than 50 °C. Ex vivo analysis revealed that the fluorescence intensity of laser-treated tumors was twice as high as that of untreated tumors (p = 0.009). Histological analysis confirmed that intratumoral injection of Dox@PEG-HAuNS and laser treatment caused significantly more tumor necrosis compared to tumors that were not treated with laser (p<0.001). On the basis of these findings, we conclude that fluorescence optical imaging and photoacoustic imaging are promising approaches to assessing Dox release and monitoring temperature, respectively, after Dox@PEG-HAuNS-mediated thermal ablation therapy.

Croconaine rotaxane for acid activated photothermal heating and ratiometric photoacoustic imaging of acidic pH

Absorption of 808 nm laser light by liposomes containing a pH sensitive, near-infrared croconaine rotaxane dye increases dramatically in weak acid. A stealth liposome composition permits acid activated, photothermal heating and also acts as an effective nanoparticle probe for ratiometric photoacoustic imaging of acidic pH in deep sample locations, including a living mouse.

Modulation of photoacoustic signal generation from metallic surfaces

Abstract. The ability to image metallic implants is important for medical applications ranging from diagnosis to therapy. Photoacoustic (PA) imaging has been recently pursued as a means to localize metallic implants in soft tissue. The work presented herein investigates different mechanisms to modulate the PA signal generated by macroscopic metallic surfaces. Wires of five different metals are tested to simulate medical implants/tools, while surface roughness is altered or physical vapor deposition (PVD) coatings are added to change the wires’ overall optical absorption. PA imaging data of the wires are acquired at 970 nm. Results indicate that PA signal generation predominately occurs in a wire’s metallic surface and not its aqueous surroundings. PA signal generation is similar for all metals tested, while addition of PVD coatings offers significant modulations (i.e., 4-dB enhancement and 26-dB reduction achieved) in PA signal generation. Results also suggest that PA signal increases with increasing surface roughness. Different coating and roughness schemes are then successfully utilized to generate spatial PA signal patterns. This work demonstrates the potential of surface modifications to enhance or reduce PA signal generation to permit improved PA imaging of implants/tools (i.e., providing location/orientation information) or to allow PA imaging of surrounding tissue.

Multifunctional Cu 2'x Te Nanocubes Mediated Combination Therapy for Multi-Drug Resistant MDA MB 453

Hypermethylated cancer populations are hard to treat due to their enhanced chemo-resistance, characterized by aberrant methylated DNA subunits. Herein, we report on invoking response from such a cancer lineage to chemotherapy utilizing multifunctional copper telluride (Cu2−XTe) nanocubes (NCs) as photothermal and photodynamic agents, leading to significant anticancer activity. The NCs additionally possessed photoacoustic and X-ray contrast imaging abilities that could serve in image-guided therapeutic studies.

Highly versatile SPION encapsulated PLGA nanoparticles as photothermal ablators of cancer cells and as multimodal imaging agents

We have designed versatile polymeric nanoparticles with cancer cell specific targeting capabilities via aptamer conjugation after the successful encapsulation of curcumin and superparamagnetic iron oxide nanoparticles (SPIONs) inside a PLGA nanocapsule. These targeted nanocomposites were selectively taken up by tumor cells, under in vitro conditions, demonstrating the effectiveness of the aptamer targeting mechanism. Moreover, the nanocomposite potentially functioned as efficient multiprobes for optical, magnetic resonance imaging (MRI) and photoacoustic imaging contrast agents in the field of cancer diagnostics. The hyperthermic ability of these nanocomposites was mediated by SPIONs upon NIR-laser irradiation. In vitro cytotoxicity was shown by curcumin-loaded nanoparticles as well as the photothermal ablation of cancer cells mediated by the drug-encapsulated nanocomposite demonstrated the potential therapeutic effect of the nanocomposite. In short, we portray the aptamer-conjugated nanocomposite as a multimodal material capable of serving as a contrast agent for MR, photoacoustic and optical imaging. Furthermore, the nanocomposite functions as a targetable drug nanocarrier and a NIR-laser inducible hyperthermic material that is capable of ablating PANC-1 and MIA PaCa-2 cancer cell lines.

Plasmonic fluorescent CdSe/Cu2S hybrid nanocrystals for multichannel imaging and cancer directed photo-thermal therapy

A simple, crude Jatropha curcas (JC) oil-based synthesis approach, devoid of any toxic phosphine and pyrophoric ligands, to produce size and shape tuned CdSe QDs and a further copper sulfide (Cu2S) encasing is presented. The QDs exhibited excellent photoluminescent properties with narrow band gap emission. Furthermore, the Cu2S shell rendered additional cytocompatibility and stability to the hybrid nanomaterial, which are major factors for translational and clinical applications of QDs. The nanocomposites were PEGylated and folate conjugated to augment their cytoamiability and enhance their specificity towards cancer cells. The nanohybrids possess potentials for visible, near infrared (NIR), photoacoustic (PA) and computed tomography (μCT) imaging. The diverse functionality of the composite was derived from the multi-channel imaging abilities and thermal competence on NIR laser irradiation to specifically actuate the photo-thermal ablation of brain cancer cells.

Photoacoustic-based sO2 estimation through excised bovine prostate tissue with interstitial light delivery

Photoacoustic (PA) imaging is capable of probing blood oxygen saturation (sO2), which has been shown to correlate with tissue hypoxia, a promising cancer biomarker. However, wavelength-dependent local fluence changes can compromise sO2 estimation accuracy in tissue. This work investigates using PA imaging with interstitial irradiation and local fluence correction to assess precision and accuracy of sO2 estimation of blood samples through ex vivo bovine prostate tissue ranging from 14% to 100% sO2. Study results for bovine blood samples at distances up to 20 mm from the irradiation source show that local fluence correction improved average sO2 estimation error from 16.8% to 3.2% and maintained an average precision of 2.3% when compared to matched CO-oximeter sO2 measurements. This work demonstrates the potential for future clinical translation of using fluence-corrected and interstitially driven PA imaging to accurately and precisely assess sO2 at depth in tissue with high resolution.

Abstract 2051: Three-dimensional in vivo photoacoustic tracking of targeted nanoparticles in a pancreatic cancer model

The use of targeted gold nanoparticles (AuNPs) has shown tremendous promise in the early detection and improved therapy of cancer. Successful development and implementation of these new theranostic approaches, however, depends on sufficient transvascular migration and specific accumulation of AuNPs to extravascular tumor tissue. This study utilized photoacoustic (PA) imaging to track - in three dimensions and through 24 hours - the extravasation and accumulation of targeted AuNPs in a subcutaneous murine model of prostate cancer. AuNPs (nanorods; 760-nm peak) targeting the Luteinizing-hormone-releasing hormone receptor were systemically injected into three mice bearing PC-3 human prostate cancer tumors; as a control, three additional mice were injected with PEGylated AuNPs. For all particle-tracking studies, multi-wavelength (680, 760, 800, 920, & 940 nm), volumetric (spherical volume with 25.6-mm diameter) PA imaging was conducted at pre-injection, post-injection, 15-min, 60-min, 240-min, and 24-hr time points; the imaging volume contained the tumor and the spleen (control). Following imaging, tumors were excised and inductively coupled plasma mass spectrometry (ICP-MS) of samples and two-photon imaging of histological sections was performed to confirm AuNP accumulation and diffusion, respectively. Volumetric PA perfusion assessment was then conducted by monitoring the wash-out of indocyanine green (ICG) in near real-time (0.25 Hz for 180 s post-injection). All PA imaging studies were performed on the Nexus 128 preclinical imaging system (Endra Inc., Ann Arbor, MI). Spectral unmixing of the multi-wavelength PA data was achieved to segment AuNPs and deoxy-/oxyhemoglobin (i.e. for local hypoxia assessment). Accumulation and extravasation data of the targeted AuNPs in the tumor were then compared to tumor perfusion data, PA-derived tumor hypoxia data, PEGylated AuNP accumulation data in the tumor, AuNP accumulation data in the spleen, and ICP-MS/histological analysis. Results of the study establish that volumetric PA imaging with multi-wavelength unmixing is able to track nanoparticle accumulation and extravasation throughout an in vivo tumor model. The location and relative degree of particle accumulation was also found to correlate with PA-based perfusion and vascularity assessment. This study demonstrates that volumetric PA imaging has the spatiotemporal resolution and sensitivity to track extravasation of AuNPs in an in vivo tumor model. This in vivo tracking ability - along with concurrent PA-based perfusion and hypoxia mapping - could be of significant benefit in understanding and improving nanoparticle targeting for the diagnosis and treatment of cancer. Citation Format: Richard Bouchard, Tatiana Wolfe, Michael Thornton, Timothy Morgan, Trevor Mitcham, Shanta Bhattarai, Jonathan Grant, Jihyoun Lee, John Hazle, Sunil Krishnan. Three-dimensional in vivo photoacoustic tracking of targeted nanoparticles in a pancreatic cancer model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2051. doi:10.1158/1538-7445.AM2014-2051

Imaging biomarker development based on microbubble perfusion and oxygen saturation in a rat model of liver cancer

Treatment of hepatocellular carcinoma (HCC) with sorafenib, a multikinase inhibitor, results in decreased microvessel density associated with increased levels of tumor hypoxia. However, the response rate is relatively poor, and recently it has been shown that tumor hypoxia and perfusion have predictive correlations with HCC response to sorafenib. In this study, we have investigated the correlation of oxygen saturation (SO2) and perfusion, estimated using photoacoustic-ultrasonic (PAUS) imaging, to the sorafenib treatment response in an orthotopic rat model of HCC. Following spectroscopic photoacoustic (sPA) imaging, microbubble contrast was introduced and harmonic imaging data were acquired for perfusion measurements. An FEM-based fluence correction model based on the diffusion approximation with empirically estimated tissue surface fluence and an SNR-based thresholding approach have been developed and validated on ex vivo and in vivo rat data to estimate SO2 using sPA imaging. The SO2 estimate has been obtained by solving an iterative minimization problem and then thresholded based on a pixel-wise empirically estimated SNR mask. For the treated cohort, the results show that the change in SO2 during an oxygen challenge is positively correlated with disease progression, while it is negatively correlated for the untreated cohort. Additionally, perfusion was significantly decreased in the treated group compared to baseline pretreatment and untreated cohort measurements. The reduced treatment-mediated perfusion leads to lack of oxygen supply and thus reduced oxygen levels. This study shows the potential of PAUS estimation of SO2 and perfusion to monitor and predict HCC sorafenib treatment response, ultimately leading to improved future treatment.