Assessing high-intensity focused ultrasound treatment of prostate cancer with hyperpolarized 13 C dual-agent imaging of metabolism and perfusion.

The goal of the study was to establish early hyperpolarized (HP) 13 C MRI metabolic and perfusion changes that predict effective high-intensity focused ultrasound (HIFU) ablation and lead to improved adjuvant treatment of partially treated regions. To accomplish this a combined HP dual-agent (13 C pyruvate and 13 C urea) 13 C MRI/multiparametric 1 H MRI approach was used to measure prostate cancer metabolism and perfusion 3-4 h, 1 d, and 5 d after exposure to ablative and sub-lethal doses of HIFU within adenocarcinoma of mouse prostate tumors using a focused ultrasound applicator designed for murine studies. Pathologic and immunohistochemical analysis of the ablated tumor demonstrated fragmented, non-viable cells and vasculature consistent with coagulative necrosis, and a mixture of destroyed tissue and highly proliferative, poorly differentiated tumor cells in tumor tissues exposed to sub-lethal heat doses in the ablative margin. In ablated regions, the intensity of HP 13 C lactate or HP 13 C urea and dynamic contrast-enhanced (DCE) MRI area under the curve images were reduced to the level of background noise by 3-4 h after treatment with no recovery by the 5 d time point in either case. In the tissues that received sub-lethal heat dose, there was a significant 60% ± 12.4% drop in HP 13 C lactate production and a significant 30 ± 13.7% drop in urea perfusion 3-4 h after treatment, followed by recovery to baseline by 5 d after treatment. DCE MRI Ktrans showed a similar trend to HP 13 C urea, demonstrating a complete loss of perfusion with no recovery in the ablated region, while having a 40%-50% decrease 3-4 h after treatment followed by recovery to baseline values by 5 d in the margin region. The utility of the HP 13 C MR measures of perfusion and metabolism in optimizing focal HIFU, either alone or in combination with adjuvant therapy, deserves further testing in future studies.

Simultaneous Metabolic and Perfusion Imaging Using Hyperpolarized 13C MRI Can Evaluate Early and Dose-Dependent Response to Radiation Therapy in a Prostate Cancer Mouse Model.

PURPOSE: To investigate use of a novel imaging approach, hyperpolarized (HP) 13C magnetic resonance imaging (MRI) for simultaneous metabolism and perfusion assessment, to evaluate early and dose-dependent response to radiation therapy (RT) in a prostate cancer mouse model. METHODS AND MATERIALS: Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice (n = 18) underwent single-fraction RT (4-14 Gy steep dose across the tumor) and were imaged serially at pre-RT baseline and 1, 4, and 7 days after RT using HP 13C MRI with combined [1-13C]pyruvate (metabolic active agent) and [13C]urea (perfusion agent), coupled with conventional multiparametric 1H MRI including T2-weighted, dynamic contrast-enhanced, and diffusion-weighted imaging. Tumor tissues were collected 4 and 7 days after RT for biological correlative studies. RESULTS: We found a significant decrease in HP pyruvate-to-lactate conversion in tumors responding to RT, with concomitant significant increases in HP pyruvate-to-alanine conversion and HP urea signal; the opposite changes were observed in tumors resistant to RT. Moreover, HP lactate change was dependent on radiation dose; tumor regions treated with higher radiation doses (10-14 Gy) exhibited a greater decrease in HP lactate signal than low-dose regions (4-7 Gy) as early as 1 day post-RT, consistent with lactate dehydrogenase enzyme activity and expression data. We also found that HP [13C]urea MRI provided assessments of tumor perfusion similar to those provided by 1H dynamic contrast-enhanced MRI in this animal model. However, apparent diffusion coefficien , a conventional 1H MRI functional biomarker, did not exhibit statistically significant changes within 7 days after RT. CONCLUSION: These results demonstrate the ability of HP 13C MRI to monitor radiation-induced physiologic changes in a timely and dose-dependent manner, providing the basic science premise for further clinical investigation and translation.

High-contrast fluorescence imaging in fixed and living cells using optimized optical switches.

We present the design, synthesis and characterization of new functionalized fluorescent optical switches for rapid, all-visible light-mediated manipulation of fluorescence signals from labelled structures within living cells, and as probes for high-contrast optical lock-in detection (OLID) imaging microscopy. A triazole-substituted BIPS (TzBIPS) is identified from a rational synthetic design strategy that undergoes robust, rapid and reversible, visible light-driven transitions between a colorless spiro- (SP) and a far-red absorbing merocyanine (MC) state within living cells. The excited MC-state of TzBIPS may also decay to the MC-ground state emitting near infra-red fluorescence, which is used as a sensitive and quantitative read-out of the state of the optical switch in living cells. The SP to MC transition for a membrane-targeted TzBIPS probe (C12-TzBIPS) is triggered at 405 nm at an energy level compatible with studies in living cells, while the action spectrum of the reverse transition (MC to SP) has a maximum at 650 nm. The SP to MC transition is complete within the 790 ns pixel dwell time of the confocal microscope, while a single cycle of optical switching between the SP and MC states in a region of interest is complete within 8 ms (125 Hz) within living cells, the fastest rate attained for any optical switch probe in a biological sample. This property can be exploited for real-time correction of background signals in living cells. A reactive form of TzBIPS is linked to secondary antibodies and used, in conjunction with an enhanced scope-based analysis of the modulated MC-fluorescence in immuno-stained cells, for high-contrast immunofluorescence microscopic analysis of the actin cytoskeleton.