Componentes del estándar H.323

i. FLOW CYTOMETRY

Flow cytometry was used for studying dynamics o f drug uptake in sensitive and resistant cells.

This technique allows us to measure and record the fluorescence intensity, size and granularity o f any particle, normally whole cells or nuclei. The flow cytometer used in these studies was the Becton Dickinson FACScan (fluorescence activated cell sorting device) combined with an Apple M acintosh Quadra 650 running CellQuest software. The instrument is equipped with a single 15mW air cooled argon ion laser emitting light at 488nm. The main experiments were done at the Imperial Cancer Research Fund (ICRF), London, with the kind permission and help o f Derek Davies.

The mechanics are as follows: as a particle i.e. an event, passes through the laser beam o f the instrument, it scatters laser light and its attached fluorochromes emit light. In this case, the cells (events) scatter the laser light whilst the anthracycline within them emits light, i.e. fluorescence. Photodetectors collect forward scattered light (FSC), side scattered light (SSC), emitted green fluorescence (F L l, 530 ± 15nm), orange fluorescence (FL2, 585 ± 21nm) and red fluorescence (FL3, above 620nm). FSC is related to the size o f event and SSC is related to the internal complexity (granularity) o f the particle. The three FL channels pick up emitted fluorescence within their respective ranges. The drugs used in this study all have their photon absorption maximum close to 488nm and emit fluorescence in the red / far red range which is detected by FL3. The detection o f scattered and emitted light results in a pulse of electrical energy, which is converted to a digital signal for each measured parameter o f each cell. These values can be stored for a requested number o f events, usually 1 0 0 0 0 cells’

The computer displays these digital signals on the screen. Two different types o f data plots are displayed o f the events as they are being acquired, dual

parameter dot plots and single parameter histograms. Forward scatter signals are read on a linear scale o f 1024 channels with a default threshold level set at 52, i.e.

for an event to be recorded its measurement must be greater than the threshold level. This allows much o f the cellular debris to be excluded from the measurements. To reduce further acquisition of events other than single live cells, an inclusion gate or region is drawn around the main population o f live cells, shown on the dot plot o f FSC and SSC and only cells within that region are acquired and recorded (see Appendix 2). The main population o f live cells is determined by running a control containing propidium iodide, a dye detected in FL2 which only enters the nuclei o f dead cells, before each series o f experiments. PI cannot be used simultaneously with the anthracyclines due to spectral overlap o f the two emission spectra. The nature o f the inclusion polygon gate meant that large clumps o f cells are also excluded. This method means a defined distinct population o f mainly live single cells was acquired producing more accurate results recorded as clumped cells had increased levels o f drug.

For analysis, both dot plots and histograms o f the total events acquired are displayed along with a statistical analysis. The amount o f fluorescence emitted by each cell, which is proportional to the amount of drug within the cell, is recorded and the mean fluorescence intensity per 1 0 0 0 0 cells displayed along with the median and the peak channel o f fluorescence. All data is shown as arbitrary units. The parameters and detector values were saved on the hard disc drive and kept as constant as possible. Slight variation, such as adjusting the forward scatter and FL3 channel, was necessary depending on the cells’ condition and the anthracycline being investigated so the dot plot o f the control cells fell completely within the inclusion gate .

A standard procedure was maintained (unless otherwise stated) for all flow cytometry experiments regardless o f cell line or anthracycline used. A 12.5cm^ flask o f cells >90% confluent per cell line was used for each drug dose per experiment with or without pre-incubation with GLA. For dose response uptake curves, the cells were incubated in 5mis o f medium, each flask containing a different drug dilution. This resulted in 7 flasks o f 7 different drug concentration per cell line per experiment. Each flask contained similar numbers o f cells. This

meant dose response curves could be repeated for each cell line using different cell passage numbers. A wide variation in cell numbers and confluence drastically changed the amount o f cellular drug uptake; depending on the type o f drug incubation protocol, I e. whether the cells were in suspension or attached to flasks. The effect o f GLA on drug uptake was also studied using flow cytometry for only 3 different drug concentrations: i) no drug, ii) a drug concentration taken from the uptake part o f the dose response curve and iii) a drug concentration taken from the plateau region o f the dose response curve. The cells were incubated on the flasks with a set dose o f GLA for 24h before the addition o f anthracycline, while negative controls were not exposed to GLA.

For all drug uptake studies, the cells were incubated at 37°C with the drug. From previous experiments it was noted that it was preferable to use FIEPES (N-2-

hydroxyethylpiperazine-N’-2-ethanesulfonic acid) buffered medium. HEPES

buffered medium was used to help maintain pFI levels and cell integrity in the flasks during travel to the ICRF. The cells were then harvested and the amount o f drug uptake per cell recorded on the FACScan. This method produced reliable and consistent results with an easily defined main cell population. Previously the cells were incubated in suspension with the drug medium but this proved to be damaging to their integrity giving inconsistent results. The latter method also gave a more realistic comparison to the in vivo situation where cells are layered and cellular connections are still intact.

ii. CONFOCAL MICROSCOPY

Confocal microscopy was used for visualising either the intracellular distribution o f drugs or the fluorescent profile o f resistance proteins (also see 2.B.3).

In conventional light or fluorescence microscopy, two dimensional images o f the object are formed. This is also true o f confocal microscopy but each image represents only part o f the thickness o f the sample. This is possible because the microscope optics exclude features outside the plane o f focus. A series o f images at different positions through the thickness o f the object can be obtained by changing

the plane o f focus or moving the object. Such a series o f images can be reconstructed to a three dimensional representation o f the object produced by optical (as opposed to physical) sectioning. This is the main feature and major advantage o f confocal microscopy over conventional microscopy (Fig.2.1). The confocal principle is effectively implemented when combined with a point scanning system using a laser light source. This builds up an image by scanning a point of laser light across the sample in the X and Y directions in a raster pattern. The detector in the laser scanning system is usually a photomultiplier tube. An image is displayed by using a computer to store the intensity value o f each point from the detector and then presenting these in the correct order on a high resolution video monitor. To collect a series o f images the computer then shifts the focus by a fixed amount and the object is scanned again to produce the next image at a different Z position. This image is stored and the process repeated to build the 3D data set. The combination o f confocal microscopy and laser scanning microscopy (CLSM) was implemented in the drug localisation studies using the Leica TCS 4D confocal microscope system Fig. 2.2.

As mentioned a digital record o f the image is produced by recording the brightness o f each pixel in the image as it is scanned. In the case o f the Leica TCS each point is allocated a value between 0 (black) and 255 (white). Therefore the image is stored in black and white, although often displayed in ‘false’ colour. On the monitor each point o f the image is displayed in the correct position and is allocated a colour using a ‘look-up’ table (LUT). The scanning laser source in this system is an air cooled, mixed gas (Argon / Krypton) 3 micron fibre-optic. The endogenous fluorescence o f the drug localised within the cells could be directly viewed using a mercury vapour light source and a filter. The microscope used was the Leitz DMR BE research microscope. This is a high resolution, light microscope with semi-automatic focusing controls and a galvanometric stage facilitating automatic specimen scanning in both the X/Y and X/Z directions. A variety o f objectives of both water and oil immersion type allow ‘w et’ preparations as well as permanently mounted specimens to be examined at low and high power magnifications up to 1 0 0 0 times life size’^°.

CONFOCAL PRINCIPLE