Keith M. Stantz

Delivery of nanoparticles to brain metastases of breast cancer using a cellular Trojan horse.

As systemic cancer therapies improve and are able to control metastatic disease outside the central nervous system, the brain is increasingly the first site of relapse. The blood–brain barrier (BBB) represents a major challenge to the delivery of therapeutics to the brain. Macrophages originating from circulating monocytes are able to infiltrate brain metastases while the BBB is intact. Here, we show that this ability can be exploited to deliver both diagnostic and therapeutic nanoparticles specifically to experimental brain metastases of breast cancer.

Thermoacoustic CT of the breast

We have completed the design and testing of a thermoacoustic computed tomography scanner for whole-breast imaging. We report on the technical changes in this design form our previous TCT scanner, and how these design changes have improved image quality. Improvements to the design include: greater angular coverage of TCT measurements, increased sensitivity of the ultrasound detector array, and improved delivery of radio wave energy. These improvements resulted in higher fidelity 3D reconstructions, reduced scan time, and fewer image artifacts. These improvements were documented by imaging simple, 3D phantoms, formulated from salinated agar spheres. We confirmed improvements in breast image quality by comparing images of patient volunteers taken with our previous TCT scanner and this new TCT scanner.

Photoacoustic Spectroscopic Imaging of Intra-Tumor Heterogeneity and Molecular Identification

Purpose. To evaluate photoacoustic spectroscopy as a potential imaging modality capable of measuring intra-tumor heterogeneity and spectral features associated with hemoglobin and the molecular probe indocyanine green (ICG). Material and Methods. Immune deficient mice were injected with wildtype and VEGF enhanced MCF-7 breast cancer cells or SKOV3x ovarian cancer cells, which were allowed to grow to a size of 6-12 mm in diameter. Two mice were imaged alive and after euthanasia for (oxy/deoxy)-hemoglobin content. A 0.4 mL volume of 1 μg/mL concentration of ICG was injected into the tail veins of two mice prior to imaging using the photoacoustic computed tomography (PCT) spectrometer (Optosonics, Inc., Indianapolis, IN 46202) scanner. Mouse images were acquired for wavelengths spanning 700-920 nm, after which the major organs were excised, and similarly imaged. A histological study was performed by sectioning the organ and optically imaging the fluorescence distribution. Results. Calibration of PCT-spectroscopy with different samples of oxygenated blood reproduced a hemoglobin dissociation curve consistent with empirical formula with an average error of 5.6%. In vivo PCT determination of SaO2 levels within the tumor vascular was measurably tracked, and spatially correlated to the periphery of the tumor. Statistical and systematic errors associated with hypoxia were estimated to be 10 and 13%, respectively. Measured ICG concentrations determined by contrast-differential PCT images in excised organs (tumor, liver) were approximately 0.8 μg/mL, consistent with fluorescent histological results. Also, the difference in the ratio of ICG concentration in the gall bladder-to-vasculature between the mice was consistent with excretion times between the two mice. Conclusion. PCT spectroscopic imaging has shown to be a noninvasive modality capable of imaging intra-tumor heterogeneity of (oxy/deoxy)-hemoglobin and ICG in vivo, with an estimated error in SaO2 at 17% and in ICG at 0.8 μg/mL in excised tissue. Ongoing development of spectroscopic analysis techniques, probe development, and calibration techniques are being developed to improve sensitivity to both exogenous molecular probes and (oxy/deoxy)-hemoglobin fraction.

Feasibility of RACT for 3D dose measurement and range verification in a water phantom

PURPOSE The objective of this study is to establish the feasibility of using radiation-induced acoustics to measure the range and Bragg peak dose from a pulsed proton beam. Simulation studies implementing a prototype scanner design based on computed tomographic methods were performed to investigate the sensitivity to proton range and integral dose. METHODS Derived from thermodynamic wave equation, the pressure signals generated from the dose deposited from a pulsed proton beam with a 1 cm lateral beam width and a range of 16, 20, and 27 cm in water using Monte Carlo methods were simulated. The resulting dosimetric images were reconstructed implementing a 3D filtered backprojection algorithm and the pressure signals acquired from a 71-transducer array with a cylindrical geometry (30 × 40 cm) rotated over 2π about its central axis. Dependencies on the detector bandwidth and proton beam pulse width were performed, after which, different noise levels were added to the detector signals (using 1 μs pulse width and a 0.5 MHz cutoff frequency/hydrophone) to investigate the statistical and systematic errors in the proton range (at 20 cm) and Bragg peak dose (of 1 cGy). RESULTS The reconstructed radioacoustic computed tomographic image intensity was shown to be linearly correlated to the dose within the Bragg peak. And, based on noise dependent studies, a detector sensitivity of 38 mPa was necessary to determine the proton range to within 1.0 mm (full-width at half-maximum) (systematic error < 150 μm) for a 1 cGy Bragg peak dose, where the integral dose within the Bragg peak was measured to within 2%. For existing hydrophone detector sensitivities, a Bragg peak dose of 1.6 cGy is possible. CONCLUSIONS This study demonstrates that computed tomographic scanner based on ionizing radiation-induced acoustics can be used to verify dose distribution and proton range with centi-Gray sensitivity. Realizing this technology into the clinic has the potential to significantly impact beam commissioning, treatment verification during particle beam therapy and image guided techniques.

Dimethylaminoparthenolide and gemcitabine: a survival study using a genetically engineered mouse model of pancreatic cancer

BackgroundPancreatic cancer remains one of the deadliest cancers due to lack of early detection and absence of effective treatments. Gemcitabine, the current standard-of-care chemotherapy for pancreatic cancer, has limited clinical benefit. Treatment of pancreatic cancer cells with gemcitabine has been shown to induce the activity of the transcription factor nuclear factor-kappaB (NF-κB) which regulates the expression of genes involved in the inflammatory response and tumorigenesis. It has therefore been proposed that gemcitabine-induced NF-κB activation may result in chemoresistance. We hypothesize that NF-κB suppression by the novel inhibitor dimethylaminoparthenolide (DMAPT) may enhance the effect of gemcitabine in pancreatic cancer.MethodsThe efficacy of DMAPT and gemcitabine was evaluated in a chemoprevention trial using the mutant Kras and p53-expressing LSL-KrasG12D/+; LSL-Trp53R172H; Pdx-1-Cre mouse model of pancreatic cancer. Mice were randomized to treatment groups (placebo, DMAPT [40 mg/kg/day], gemcitabine [50 mg/kg twice weekly], and the combination DMAPT/gemcitabine). Treatment was continued until mice showed signs of ill health at which time they were sacrificed. Plasma cytokine levels were determined using a Bio-Plex immunoassay. Statistical tests used included log-rank test, ANOVA with Dunnett’s post-test, Student’s t-test, and Fisher exact test.ResultsGemcitabine or the combination DMAPT/gemcitabine significantly increased median survival and decreased the incidence and multiplicity of pancreatic adenocarcinomas. The DMAPT/gemcitabine combination also significantly decreased tumor size and the incidence of metastasis to the liver. No significant differences in the percentages of normal pancreatic ducts or premalignant pancreatic lesions were observed between the treatment groups. Pancreata in which no tumors formed were analyzed to determine the extent of pre-neoplasia; mostly normal ducts or low grade pancreatic lesions were observed, suggesting prevention of higher grade lesions in these animals. While gemcitabine treatment increased the levels of the inflammatory cytokines interleukin 1α (IL-1α), IL-1β, and IL-17 in mouse plasma, DMAPT and DMAPT/gemcitabine reduced the levels of the inflammatory cytokines IL-12p40, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1 beta (MIP-1β), eotaxin, and tumor necrosis factor-alpha (TNF-α), all of which are NF-κB target genes.ConclusionIn summary, these findings provide preclinical evidence supporting further evaluation of agents such as DMAPT and gemcitabine for the prevention and treatment of pancreatic cancer.

Kinematic modeling and its implication in longitudinal chemotherapy study of tumor physiology: ovarian xenograft mouse model and contrast-enhanced dynamic CT (Honorable Mention Poster Award)

The purpose of this study is to demonstrate that dynamic CT provides the necessary sensitivity to quantify tumor physiology and differences in chemotherapeutic response. A compartmental mouse model utilizing measured contrast-enhanced dynamic CT scans is used to simulate systematic and statistical errors associated with tumor physiology: perfusion, permeability (PS), fractional plasma volume (fp), and fractional interstitial volume. The solute utilized is a small molecular weight radio-opaque contrast agent (isovue). For such an intravascular-interstitial medium, the kinematics simplifies to a two compartmental diffusive dominated set of coupled differential equations. Each combination of physiological parameters is repeatedly simulated fifteen times from which statistical errors calculated. The fractional change relative to the true value (systematic error) and standard deviation (statistical error) are plotted as a function of PS, fp, scanner temporal resolution and noise, and contrast media injection rates. By extrapolating from experimental data found in literature, a relative change in PS and fp of approximately 40% is required. Thus, the longitudinal response of two chemotherapeutic drugs under investigation - proteasome and IMPDH inhibitors - are hypothesized to induce different physiological responses. The first set of simulations varies PS from 0.05 to 0.40 mL/min/mL and fp from 0.01 to 0.07 mL/mL while holding all other physiological parameters constant. Errors in PS remain below 3% while statistical errors for fp increase significantly as the volume decreases toward 1-2%: errors remain less than 6% for fp>0.03 while increasing to above 15% for fp<0.02. The second set of simulations are performed quantifying the relationship between scanner temporal resolution and contrast media injection rate for various tumor permeabilities. For the majority of cases, the errors remain below 5%. As PS approaches perfusion, a total error less than 6% can be maintained for a temporal resolution less than or equal to 3 seconds, and an error less than 9% up to 5-7 seconds. As the injection rate decreases from 2 mL/min down to 0.25 mL/min, inadequate sampling of the contrast dynamics necessary to decouple the physiological parameters is lost increasing both systematic and statistical errors from 10% when sampling at 5 seconds in excess of 20-25% at a 9 second sampling rate. In each case, dynamic CT provides the necessary sensitivity to distinguish between the differing therapeutic reponses of proteasome and IMPDH inhibitors.

Molecular Imaging of Neutropilin-1 Receptor Using Photoacoustic Spectroscopy in Breast Tumors

Purpose: Our purpose is to develop and test a molecular probe that can detect the expression of neutropilin-1 receptor (NPR-1) in vivo using fluorescence imaging and photoacoustic spectroscopy. Introduction: NPR-1 is expressed on endothelial cells and some breast cancer cells, and binds to vascular endothelial growth factor VEGF165, a growth factor associated with pathological tumor angiogenesis. This receptor is coexpressed with VEGFR2 and shown to enhance the binding of VEGF165; therefore, it has the potential to be used as a marker of angiogenic activity and targeted for therapy. Material and Methods: A peptide specific to NPR-1 receptor was synthesized and conjugated to a NIR fluorochrome (IRDye800CW) and was intravenously injected into mice with breast tumors (MCF7VEGF). Probe kinetics was monitored in vivo via near infrared fluorescence (NIRF) within an optical imager for up to 72 hours within the tumor and compared to other organs (liver, muscle) for binding specificity. A multivariate fitting algorithm was used to spectrally deconvolve the IRDye800CW from endogenous hemoglobin signature (hemoglobin concentration and oxygen saturation). Results: Dynamics of the NIR fluorescence signal within the first hour after injection indicates specific binding compared to muscle, with an average tumor-to-muscle ration of 2.00 (+/- 0.27). Spectral analysis clearly indentified the presence of the NPR-1 probe. Based on calibration data, the average tumor concentration from both NIRF and PCT-S was measured to be ~200-300nM. Conclusion: These preliminary results show the capability of PCT to image an exogenous probe in vivo in addition to its hemoglobin state.

Development of Follicle-Stimulating Hormone Receptor Binding Probes to Image Ovarian Xenografts.

The Follicle-Stimulating Hormone Receptor (FSHR) is used as an imaging biomarker for the detection of ovarian cancer (OC). FSHR is highly expressed on ovarian tumors and involved with cancer development and metastatic signaling pathways. A decapeptide specific to the FSHR extracellular domain is synthesized and conjugated to fluorescent dyes to image OC cells in vitro and tumors xenograft model in vivo. The in vitro binding curve and the average number of FSHR per cell are obtained for OVCAR-3 cells by a high resolution flow cytometer. For the decapeptide, the measured EC50 was 160 μM and the average number of receptors per cell was 1.7 × 107. The decapeptide molecular imaging probe reached a maximum tumor to muscle ratio five hours after intravenous injection and a dose-dependent plateau after 24–48 hours. These results indicate the potential application of a small molecular weight imaging probe specific to ovarian cancer through binding to FSHR. Based on these results, multimeric constructs are being developed to optimize binding to ovarian cells and tumors.

TH‐C‐144‐01: BEST IN PHYSICS (THERAPY) – Use of Radiation‐Induced Ultrasound to Image Proton Dosimetry

PURPOSE The objectives of this study are to simulate the ionizing radiation induced thermoacoustic signal from scanning proton beam; and investigate the various designs and techniques of ultrasound tomographic imaging to map three dimensional dose (3D) proton dose distributions. METHODS A 3D dose and proton fluence distribution in a water phantom from a scanning spot beam from a treatment nozzle was simulated using a Monte Carlo (MC) code FLUKA (v. 2012) for 6.5, 16 and 27 cm proton range. An initial radio-acoustic computed tomographic (RCT) scanner design of a cylinder with 128 transducer array (0.5MHz center frequency; 50% bandwidth at -6dB; flat surface) centered along the height of the cylinder (z-axis) at a radial distance of 15 cm was evaluated. The thermoacoustic generated pressure signals from the proton beam were simulated and digitally sampled for each transducer over time, which was rotated over 30 angles about isocenter. A 3D filtered backprojection algorithm was used to reconstruct the dosimetric image volume consisting of the Bragg peak (initially at 5×5×5mm3), and then compared to the MC results. RESULTS The comparison between the beam profiles as simulated by MC and measured from commissioning of the beam had an estimated deviation of about 2%. An analysis of the RCT intensity dependence on depth as compared to MC simulated data demonstrated that the distal edge of the Bragg peak was within binning size of the reconstruction image and MC position prediction, with an average variation in RCT intensity around 6%. CONCLUSION This feasibility study demonstrates that RCT can be used to monitor the dose distribution and proton range in proton therapy. Additional scanner designs (geometry, transducer bandwidth consideration, phantom designs) will be investigated and presented, such as phase-array methods. Acquiring measurement data to compare with the simulated data is work in progress.

Assessment of photoacoustic computed tomography to classify tissue in a polycystic-kidney disease mouse model

Purpose: The purpose of this study is to evaluate PCT Imaging technique to classify tissue and extract kidney cysts in pcy mice model of human adolescent nephronophthisis. Method: Four mice with late stages of nephronophthisis with polycystic kidney disease-PKD and one normal mouse were scanned in the PCT Small Animal Scanner. Both vivo and ex-vivo images of mice kidney were taken at wavelength from 680 nm to 940 nm. The ex-vivo PCT images were compared with histology photographs to check the sensitivity of detecting cysts. Histograms of kidney images were generated over slices and fitted to Gaussian-curve model for volumetric analysis. The portions of cysts in kidneys were estimated and kidney images were segmented by three different colors to present the distribution of different tissues. Result: A good correspondence between PCT imaging findings and PKD histology result was observed. Histogram curves from images of pcy kidneys and normal kidneys were fitted to Gaussian-curve model. Portions of cysts, parenchyma and area of high level hemoglobin were estimated according to the curve fit result. A growth of cysts associated with relatively volume decrease of parenchyma and tissues with high perfusion of hemoglobin was observed. Conclusion: The PCT enabled visualization of renal cysts for mouse model and had the potential for volumetric measurements of kidney.