The overall goal of this patient derived glioblastoma 3D microtumor culture system is to enable high-throughput drug testing with a corresponding molecular profiling assay, such as kinomic testing. This method can help answer key questions in the cancer field, such as, why do certain therapies work well in one patient's tumor but not in another? The main advantage of this technique is that it provides a miniature yet realistic tumor culture system suitable for therapy testing.
Generally, individuals new to this method will struggle because handling the patient derived xenograft cells is not like handling long established, immortalized tumor cells. This is due to their fragility and sensitivity to changing culture conditions. Visual demonstration of this method is critical, as the microtumor generation steps are difficult to learn through description only, due to their unique and complex method of production.
Demonstrating the tumor disaggregation procedure will be Catherine Langford, the senior technician and lab manager in my laboratory. Demonstrating the microtumor generation and drug dosing procedures will be Rachael Shevin, a technician in my lab. Using forceps, blunt dissect to gently free the tumor mass from the peritoneal wall and the skin, and transfer the tumor mass to a sterile glass Petri dish.
Then, use a sterile scalpel with a number 11 blade and sterile semi-curved forceps to debride the tumor tissue of any necrotic tissue and membranous host connective tissue. Wash the cleaned tumors with sterile RPMI three to five times to remove the excess blood, gently tilting the dish between rinses to remove the wash. After the final wash, use two number 11 scalpel blades to finely mince the tumors.
Then, use sterile semi-curved forceps to transfer the tumors into a dissociation tube containing enzyme solution. Place the tube into a cellular dissociator, and select the Tumor 2 program. Click Start"to run the dissociator for 37 seconds.
Then transfer the tube to a rotator and place the rotator in a 37 degree Celsius incubator for 40 minutes. At the end of the incubation, place the tube back on the dissociator and run the Tumor 3 program for 37 seconds. At the end of the program, centrifuge the cells and re-suspend the pellet in 10 milliliters of serum free RPMI with gentle mixing.
Next, slowly load the cells onto a 40 micron cell strainer in a new 50 milliliter tube, and allow the suspension to drip through the filter by gravity. Gently lift the tab of the cell strainer in between each new addition of cells, breaking the vacuum between the strainer and the tube to allow the suspended cells to pass freely through the mesh. When all of the cells have been filtered, spin down the single cell suspension and re-suspend the pellet in 10 milliliters of complete Neurobasal Medium.
Then, determine the number of viable cells by trypan blue exclusion, and place the cells on ice. To generate the microtumors, spin down the dissociated patient derived glioblastoma xenoline cells and re-suspend the pellet at 50, 000 cells per two microliters of FBS. Next, dilute the cells in ice cold high density human biogel at a one to four cell to biogel ratio.
Then, use an electronic multichannel pipette to dispense 10 microliters of cell mixture per pin onto a 96 pin steel plate with hydrophobic coating. It's important to prevent bubbles when mixing the cells, medium, and biogel, while still working quickly and efficiently to generate the microtumors before the human biogel begins to solidify on the pins. When all of the microtumors have been plated, transfer the 3D tumors into a tissue culture incubator for 20 minutes to gelate the tumor beads.
At the end of the incubation, transfer the microtumors to a 10 centimeter culture dish containing complete Neurobasal Medium and return the tumors to the incubator. After one to two days, use a wide mouth dispensing pipette to transfer the microtumors into the wells of a 96 well culture plate, containing 50 microliters of Neurobasal Medium per well, and add 50 microliters of the appropriate dosing solution to each well. Maintain the treated microtumors in the tissue culture incubator for one to 14 days, feeding the tumors twice weekly with a fresh medium and drug solution.
To evaluate the microtumor cell morphology, on days one, seven, and fourteen of culture, label the microtumors with one micromolar of freshly diluted Calcein-AM per well in the tissue culture incubator for 20 minutes. Then, image the tumors by flourescence microscopy at two, four, and 10x magnifications. To assess the microtumor growth, and days one, seven, and 14, treat the cultures with 20 microliters of freshly prepared MTT for two hours in the tissue culture incubator.
At the end of the incubation, lyse the tumors with freshly prepared, 10%SDS lysis buffer at a one to one ratio to the culture well volumes, and seal the plate. Then incubate the microtumors in the lysis buffer overnight at 37 degrees Celsius, and read the absorbance at 570 nanometers on a multi-plate reader the next morning. Through live cell imaging Calcein-AM as just demonstrated, the cell growth and viability of the microtumors, as well as the effects of the drug therapies on these functions, can be evaluated.
As observed, untreated microtumors and microtumors with a known resistance to the experimental drug treatment display a continuous growth pattern over a two week culture period. These TMZ sensitive tumor cells, however, demonstrate a reduced cell growth by the end of the culture in response to the highest concentration of TMZ treatment by MTT assay. Interestingly, kinase signaling in TMZ resistant microtumors reveals a number of peptides with significantly altered intensities after the 10 micromolar TMZ treatment.
Indeed, in this representative experiment, analysis of these altered kinomic profiles using upstream kinase prediction software identified specific alterations in SYK, LCK, and CTK tyrosine kinase and a number of serine/threonine kinase intensities, suggesting potential novel therapeutic targets that may help overcome tumor treatment resistance. Once mastered, the tumor disaggregation can be completed in two hours if it is performed properly. The microtumor generation and drug dosing techniques can be completed in three hours total if they are performed properly.
In the future, this model system could be used as a proband style avatar system, in which a patient's tumor is molecularly matched to an existing patient derived microtumor library to inform the clinician of the best choice of therapy.
