Imaging prostate cancer invasion with multi-nuclear magnetic resonance methods: the Metabolic Boyden Chamber

Abstract

The physiological milieu within solid tumors can influence invasion and metastasis. To determine the impact of the physiological environment and cellular metabolism on cancer cell invasion, it is necessary to measure invasion during well-controlled modulation of the physiological environment. Recently, we demonstrated that magnetic resonance imaging can be used to monitor cancer cell invasion into a Matrigel layer [Artemov D, Pilatus U, Chou S, Mori N, Nelson JB, and Bhujwalla ZM (1999). Dynamics of prostate cancer cell invasion studied in vitro by NMR microscopy. Mag Res Med 42, 277-282.]. Here we have developed an invasion assay ("Metabolic Boyden Chamber") that combines this capability with the properties of our isolated cell perfusion system. Long-term experiments can be performed to determine invasion as well as cellular metabolism under controlled environmental conditions. To characterize the assay, we performed experiments with prostate cancer cell lines preselected for different invasive characteristics. The results showed invasion into, and degradation of the Matrigel layer, by the highly invasive/metastatic line (MatLyLu), whereas no significant changes were observed for the less invasive/metastatic cell line (DU-145). With this assay, invasion and metabolism was measured dynamically, together with oxygen tensions within the cellular environment and within the Matrigel layer. Such a system can be used to identify physiological and metabolic characteristics that promote invasion, and evaluate therapeutic interventions to inhibit invasion.

Figure 1

Schematic of the design of the perfusion system. The insert shows a magnified view of the sample structure within the 10-mm NMR tube.

Figure 2

¹H MR image of sample (right), ¹⁹F MR image (center), and two panels (left) showing the recovery of the inverted ¹⁹F signal of perfluorocarbons at the top and within the Matrigel layer of the sample.

Figure 3

Expanded ¹H MR image of sample showing the Matrigel layer in the filter cup for (a) DU-145 cells after 58.5 hours and (b) MatLyLu after 56.5 hours. The Matrigel forms a well-defined bright layer in the filter cup. Images were obtained with TR = 1 second; TE = 30 msec; FOV = 40 mm; slice thickness = 2 mm; in-plane resolution of 78 µm. The ¹H MR spectra on the left side of the ¹H MR images are from localized slices (310 µm thick) from within the sample.

Figure 4

Comparison of T₁ weighted ¹H MR images from MatLyLu and DU-145 cells showing continuous degradation of Matrigel by MatLyLu compared to DU-145.

Figure 5

Zoomed cell density profiles of MatLyLu and DU-145 cells. The MatLyLu cells invade the Matrigel, whereas DU-145 cells remain at the surface of the Matrigel layer. Each profile corresponds to an individual time point.

Figure 6

Cell density profiles of the entire sample for MatLyLu and DU-145 cells. The profiles, representing the diffusion-weighted cellular water signal (see Materials and Methods section), were taken at consecutive days starting from day 0. Cell growth is represented by increased signal intensity. The lines in the center mark the border between cells, filter (F) and Matrigel (M). Each profile corresponds to an individual time point.

Figure 7

Invasion index I for the highly invasive MatLyLu cells and the less invasive DU-145 cells. Values are mean ± SEM.

Figure 8

Representative ³¹P MR spectra obtained from the samples 24 and 48 hours after transferring the cells to the perfusion system. The spectra demonstrate the stability of the energy levels of the cells while in the perfusion system.