Shedding light on the effect of radiation therapy on circulating tumor cells

Many common treatments for cancer – including radiation therapy (RT) – have the unfortunate side effect of promoting the spread of cancer to other organs [1-3]. While the ‘pro-metastatic’ effects of RT have been known for some time, it has garnered renewed attention in recent years in part due to the widespread study of circulating tumor cells (CTCs). In hematogenous metastasis, CTCs detach from the primary tumor and spread via the blood to other organs and tissues of the body. There are three main hypotheses for RT induced metastasis (RTIM) as reviewed in [1]: i) RT causes disruption of the primary tumor and vasculature, which leads to immediate shedding of CTCs, iii) RT induces biomolecular changes in tumor cells, such as epithelial to mesenchymal transition, leading to increased CTC shedding over time as the tumor cells die, and, iii) Systemic effects, such as the elimination of suppressive signaling molecules by the primary tumor resulting in the proliferation of existent but previously dormant micro-metastases [3]. Our team recently developed a new instrument called ‘Diffuse in vivo Flow Cytometry’ (DiFC; figure 1) [4]. The main advantage of DiFC is that it samples large circulating blood volumes (hundreds of µL per minute), allowing in vivo detection of very rare CTCs. DiFC uses specially designed fiber-optic probe bundles with built-in filters and lenses for efficient collection of weak fluorescent signals and blocking of tissue autofluorescence. As labeled cells pass through the DiFC field of view, transient fluorescent peaks are detected. A custom signal processing algorithm allowed us to determine the number, direction, speed, and depth of circulating cells, and reject false alarm signals from motion artifacts. For example, we recently showed that DiFC allowed detection of early dissemination of green fluorescent protein (GFP)-labeled multiple myeloma cells in a disseminated xenograft model at CTC burdens below 1 cell per mL, as well as rare CTC clusters (fig. 1). Please click Additional Files below to see the full abstract

Improved diffuse fluorescence flow cytometer prototype for high sensitivity detection of rare circulating cells in vivo

Abstract. Detection and enumeration of rare circulating cells in mice are important problems in many areas of preclinical biomedical research. Recently, we developed a new method termed “diffuse fluorescence flow cytometry” (DFFC) that uses diffuse photons to increase the blood sampling volume and sensitivity versus existing in vivo flow cytometry methods. In this work, we describe a new DFFC prototype with approximately an order-of-magnitude improvement in sensitivity compared to our previous work. This sensitivity improvement is enabled by a number of technical innovations, which include a method for the removal of motion artifacts (allowing interrogation of mouse hindlegs that was less optically attenuating versus the tail) and improved collection optics and signal preamplification. We validated our system first in limb mimicking optical flow phantoms with fluorescent microspheres and then in nude mice with fluorescently labeled mesenchymal stem cells at injected concentrations of 5×103 cells/mL. In combination, these improvements resulted in an overall cell counting sensitivity of about 1 cell/mL or better in vivo

Near-infrared fluorescence imaging platform for quantifying in vivo nanoparticle diffusion from drug loaded implants

Drug loaded implants are a new, versatile technology platform to deliver a localized payload of drugs for various disease models. One example is the implantable nanoplatform for chemo-radiation therapy where inert brachytherapy spacers are replaced by spacers doped with nanoparticles (NPs) loaded with chemotherapeutics and placed directly at the disease site for long-term localized drug delivery. However, it is difficult to directly validate and optimize the diffusion of these doped NPs in in vivo systems. To better study this drug release and diffusion, we developed a custom macroscopic fluorescence imaging system to visualize and quantify fluorescent NP diffusion from spacers in vivo. To validate the platform, we studied the release of free fluorophores, and 30 nm and 200 nm NPs conjugated with the same fluorophores as a model drug, in agar gel phantoms in vitro and in mice in vivo. Our data verified that the diffusion volume was NP size-dependent in all cases. Our near-infrared imaging system provides a method by which NP diffusion from implantable nanoplatform for chemo-radiation therapy spacers can be systematically optimized (eg, particle size or charge) thereby improving treatment efficacy of the platform

The effect of temporal impulse response on experimental reduction of photon scatter in time- resolved diffuse optical tomography The effect of temporal impulse response on experimental reduction of photon scatter in time-resolved diffuse optical tomograph

Abstract New fast detector technology has driven significant renewed interest in timeresolved measurement of early photons in improving imaging resolution in diffuse optical tomography and fluorescence mediated tomography in recent years. In practice, selection of early photons results in significantly narrower instrument photon density sensitivity functions (PDSFs) than the continuous wave case, resulting in a better conditioned reconstruction problem. In this work, we studied the quantitative impact of the instrument temporal impulse response function (TIRF) on experimental PDSFs in tissue mimicking optical phantoms. We used a multimode fiber dispersion method to vary the system TIRF over a range of representative literature values. Substantial disagreement in PDSF width-by up to 40%-was observed between experimental measurements and Monte Carlo (MC) models of photon propagation over the range of TIRFs studied. On average, PDSFs were broadened by about 0.3 mm at the center plane of the 2 cm wide imaging chamber per 100 ps of the instrument TIRF at early times. Further, this broadening was comparable on both the source and detector sides. Results were confirmed by convolution of instrument TIRFs with MC simulations. These data also underscore the importance of correcting imaging PDSFs for the instrument TIRF when performing tomographic image reconstruction to ensure accurate data-model agreement