By its very nature the movement of cancer cells is a highly dynamic process. Our group uses time-lapse imaging to gain insights into the behaviour of moving cells. In particular, we are interested in how cells move in three-dimensional environments and the interplay between different cell types in tumours.
Simple analysis of the morphology of breast cancer cells cultured on rigid two-dimensional or deformable three-dimensional substrates reveals very striking differences. Cells on 2D substrates are very flat when viewed 'side-on' with their prominent actin stress fibres that generate contractile force. However in 3D environments the same cells are rounded, lack stress fibres and have a more complex zone of polymerisation.
The video above is of a three-dimensional reconstruction of the actin cytoskeleton of breast cancer cells moving on a 2D surface or in 3D collagen matrix. [Olson and Sahai Clinical and Experimental Metastasis , in press].
The actin network in cells in invading cancer cells in 3D environments is largely cortical and can be clearly visualised using electron microscopy.
Invading cancer cells can use their acto-myosin machinery to deform the extra-cellular matrix or to constrict the cell body such that it can squeeze through gaps in the extra-cellular matrix. Both these mechanisms can enable these cells to invade in the absence of matrix proteolysis.
The movie above shows rapidly changing morphology of a melanoma cell expressing fluorescently tagged ROCK1 (in purple). Note the cortical localisation of ROCK1 and its accumulation at the rear every time the moves its position; filmed over 2 minutes [Pinner and Sahai, Nature Cell Biology 2008 ].
We are now seeking to extend our analysis of 3D models to live tumour imaging. Interestingly, only a minority of cancer cells are motile in vivo and these are frequently concentrated in particular areas, or micro-environments, of the tumour. The following movie shows a tumour invading into surrounding tissue.
The movie above shows a melanoma (in red) and surrounding collagen matrix (in purple). Note 'amoeboid' melanoma cell breaking away from the bulk of the primary tumour and moving into the surrounding extra-cellular matrix seemingly by moving on and between collagen fibres; filmed over 20 minutes. [Pinner and Sahai, Nature Cell Biology 2008 ].
Analysis of squamous cell carcinomas has provided insights into another mechanism that cancer cells can use to invade. Instead of invading as single cells they invade as collective chains.
The movie above shows a tumour fibroblast (in red) being followed by a collection of squamous cell carcinoma cells (in green); filmed over 4 hours. [Gaggioli et al. , Nature Cell Biology 2007 ].
In addition to observing cell motility, we can also monitor the organisation of the cytoskeleton. In particular, we have imaged the organisation of myosin light chain in live tumours. The following movie shows myosin light chain localising to the cleavage furrow of a mitotic cell in vivo (the chromosomes are visible as a dark shadow).
The movie above shows breast cancer cells expressing fluorescently tagged MLC (in green) and surrounding collagen fibres (in red). Note dividing cell near *; filmed over 20 minutes.
