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Targeting and killing of malignant gliomas
by specific stem cells expressing a suicide gene
Gliomas are tumors that arise from glial cells
Located in the brain or spinal cord
Current treatment: Neurosurgery, Radio- & Chemotherapy
After diagnosis, 30% of human patients live to 1 year and 14% live to 2 years.
Glioma cells can migrate and form new tumors
Malignant Gliomas
Have the ability to migrate to a pathological focus (e.g. to brain tumors)
Limitations: Cost, low population doublings, ability to subculture, and pathological focus
Adult Stem Cells
Different types of stem cells were tested and selected for, based on:
Ability to be subcultured Highly proliferative No antigenic surface markers Ability to migrate to gliomas and track tumorous cells
Bone Marrow-derived Tumor-Infiltrating Cells (BM-TICs)
showed the most promise in these experiments
Selecting the best cellular vehicle
Transduced with a retro-viral vector containing the Thymidine Kinase gene from HSV & the green fluorescent protein gene.
Tumor infiltration and ability to track migrating tumor cells
Examined by Fluorescence Microscopy
BM-TIC genetic modification
Gap junction formation? Glioma cells dyed with DiI
BM-TICs are dyed with Calcein-AM
Intially two distinct populations after mixing (a)
Incubated for 3 hours
Glioma cells taken in Calcein-AM & BM-TICs have lost intensity
DiI is a membrane bound protein
Increase in Glioma cells Calcein-AM concentration
explained by Gap Junction communication
Ganciclovir & Gap Junctions
Rats with BM-TIC-tk-GFP injections were treated with Ganciclovir
Ganciclovir is a prodrug that reacts with viral thymidine kinase
Results in production of a toxic triphosphate
Incorporates into DNA and stops replication, signaling apoptosis
Gap Junctions between the tumor cells and therapeutic cells allow viral thymidine kinase diffusion
Rendering tumor cells susceptible to Ganciclovir
In vivo testing Rats were injected with BM-TIC-tk-GFP, into or near tumors
4 days after injection the rats were treated with Ganciclovir daily for 10 days
Over 65% of treated rats showed long term survival
Statistical significance (P<0.001)
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Future Treatment in humans
This method was highly effective in rats and shows promise for the treatment of malignant gliomas in humans
Thymidine kinase based gene therapy techniques have reached clinical trials
References:Rachet B, Mitry E, Quinn MJ, et al; Survival from brain tumours in England and Wales up to 2001. Br J Cancer. 2008 Sep 23;99 Suppl 1:S98-101
Goodenberger ML, Jenkins RB (2012). “Genetics of adult glioma”. Cancer genet. doi:10.1016/j.cancergen.2012.10.009
Miletic, Hrvoie, et. al. “Bystander Killing Of Malignant Glioma By Bone Marrow-Derived Tumor-Infiltrating Progenitor Cells Expressing A Suicide Gene.” Molecular Therapy: The Journal Of The American Society Of Gene Therapy 15.7 (2007): 1373-1381.
Questions?