One of the longstanding questions for DIPG has been."Why doesn't chemo work?"
There have been dozens of trials using all kinds of agents and all of them have virtually the identical Kaplan Meier Curve. The think we don't know is why that is. Often times one hears about something in the blood brain barrier that limits chemotherapy effectiveness. Other times one wonders if it is something in the glioma cells themselves that make them more resistant. The Netherlands paper tried to answer one part of this in better defining ABC transporters in pediatric glioma.
ABC transporters essentially function as little door ways in the cell's membrane either usher substances into the cell (importers) or out of the cells (exporters). The exporters are tone ones that are a problem withe drug resistance. The transporters pump drugs and toxins out of the cells.
There have been 3 different ABC transporters found that escort drugs out of cells. These include P-glcyoprotein (P-gp, ABCB1), breast cancer resistance protein (BCRP, ABCG2) and multidrug resistance associated proteins (MRPs, ABCC1).
This Netherlands study looked at the above 3 ABC transporters in each of the glioma cell lines. All cell lines were negative for P-gp. Only one supratentorial pediatric glioma cell line had BRCP1. High levels of MRP1 was found in 4 of the 9 glioma cell lines. That included 2 of 3 of the DIPG cell lines.
The researchers then looked at actual tumor sample sections to try to determine the amount of ABC transporters in the glioma cells versus the blood vessels. They found that P-gp was not present in most of the glioma cells but was presesnt moderately in the tumor's blood vessels. BCRP1 was not present in the glioma cells but was highly pressent in the blood vessels. Only MRP1 was seen in both the glioma cells and the blood vessels. A chart on the cell lines tested (including 2 of the 3 DIPG samples) is available (click here to see chart).
So, what does this mean for DIPG now?
That is hard to say. So far tying to inhibit the ABC transporters with different agents have been problematic because of significant toxic side effects. These ABC transporters are meant to protect normal cells as well. However, since most of the ABC transporters seem to be in the blood vessels a way around this blood-brain barrier could be direct tumor delivery (i.e., convenction enhanced delivery). The researchers also suggest developing drugs that are not a substract for these transporters could also increase chemotherapy effectiveness.
It does tell us that in trying to find a cure for DIPG that we can not just focus on finding targets within the cancer biology but also need to work on finding ways for new agents to be able reach these targets.
Note: The ATP-binding cassette transporters issue was featured in a recent blogspot regarding a new abstract out of Oren Becher's lab in Duke.
This work was funded by KiKa "Stichting Kinderen Kankervrij"- Dutch Children Cancer-free Foundation.
References:
In vitro drug response and efflux transporters associated with drug resistance in pediatric high grade glioma and diffuse intrinsic pontine glioma
PLoS One. 2013 Apr 29;8(4):e61512. doi: 10.1371/journal.pone.0061512. Print 2013.
Free Full Text- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639279/
KiKa Stichting Kinderen Kankervrij- Dutch Children Cancer-free Foundation
http://www.kika.nl/
ABC transporters limit dansantinib efficacy in mice
http://dipg.blogspot.com/2013/04/abc-transported-limit-dasatinib.html
Showing posts with label KiKa. Show all posts
Showing posts with label KiKa. Show all posts
Tuesday, May 7, 2013
Monday, May 6, 2013
New Publication- Are DIPGs just resistant to chemo? No!
Last week the highly productive, DIPG-focused Netherlands group from VU University Medical Center in Amsterdam put forth another publication which happens to have free full text available!
This research focuses on unravelling the reasons why chemotherapy has not been beneficial against DIPGs and pediatric high-grade gliomas. Are DIPGs just resistant to the agents? Or, is it that something is protecting the cells which causes an otherwise good option to be ineffective?
Part 1- Are glioma cells just resistant to chemotherapy?
To look at the first question, the researchers evaluated 9 pediatric glioma cell lines to eliminate questions of adequate drug delivery. Three of these cell lines were from children with DIPGs and 6 were from supratentorial high grade gliomas. Of the 3 DIPG cell lines, all were of different histologic grades- one GBM, one anaplastic astrocytoma and one diffuse fibrillary asrocytomas. Two of these DIPG cell lines came from children who had not had any treatment. The other cell line came from an autopsy donation done approximately 2 hours after death.
In the screening of these cell lines, several agents had high level of killing tumor cells.
When looking at targeted small molecule agents, these did not fare as well as classical chemotherapies. Some did show some efficacy . The best of these was bortezomib which resulted in more than 50% reduction in cell line surival in 6/9 cell lines. There was little or no effect with erlotinib and everolimus. A hypothesis for this result include that the cell lines were not checked for the targets. If there was a matching of targets and agents the results might have been better. Also since there are multiple messed up pathways combined therapy is generally thought to be needed and a single agents is very unlikely to be effective.
In looking at classic chemotherapy agents, melphalan was the only drug that had significiant toxicity in all cell lines. Interestly that is the exact agent of the new intra-arterial Hopkins DIPG trial!
Other agents that were found to have a signficant effect included doxorubicin, mitoxantrone and BCNU. The next level included etoposide, thiotepa and carboplatin. Carboplatin was of special note since that is what the UK in their CED report.
What this means for DIPG is that DIPG is not necessarily resistant to chemotherapy! Effective drgus might not be the biggest hurdle for a cure for DIPG. It might be getting them to the tumor cells.
This work was funded by KiKa "Stichting Kinderen Kankervrij"- Dutch Children Cancer-free Foundation.
Tomorrow.....
Part 2- Do the efflux transporters protect the glioma cells?
References:
In vitro drug response and efflux transporters associated with drug resistance in pediatric high grade glioma and diffuse intrinsic pontine glioma
PLoS One. 2013 Apr 29;8(4):e61512. doi: 10.1371/journal.pone.0061512. Print 2013.
Free Full Text- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639279/
KiKa Stichting Kinderen Kankervrij- Dutch Children Cancer-free Foundation
http://www.kika.nl/
This research focuses on unravelling the reasons why chemotherapy has not been beneficial against DIPGs and pediatric high-grade gliomas. Are DIPGs just resistant to the agents? Or, is it that something is protecting the cells which causes an otherwise good option to be ineffective?
Part 1- Are glioma cells just resistant to chemotherapy?
To look at the first question, the researchers evaluated 9 pediatric glioma cell lines to eliminate questions of adequate drug delivery. Three of these cell lines were from children with DIPGs and 6 were from supratentorial high grade gliomas. Of the 3 DIPG cell lines, all were of different histologic grades- one GBM, one anaplastic astrocytoma and one diffuse fibrillary asrocytomas. Two of these DIPG cell lines came from children who had not had any treatment. The other cell line came from an autopsy donation done approximately 2 hours after death.
In the screening of these cell lines, several agents had high level of killing tumor cells.
When looking at targeted small molecule agents, these did not fare as well as classical chemotherapies. Some did show some efficacy . The best of these was bortezomib which resulted in more than 50% reduction in cell line surival in 6/9 cell lines. There was little or no effect with erlotinib and everolimus. A hypothesis for this result include that the cell lines were not checked for the targets. If there was a matching of targets and agents the results might have been better. Also since there are multiple messed up pathways combined therapy is generally thought to be needed and a single agents is very unlikely to be effective.
In looking at classic chemotherapy agents, melphalan was the only drug that had significiant toxicity in all cell lines. Interestly that is the exact agent of the new intra-arterial Hopkins DIPG trial!
Other agents that were found to have a signficant effect included doxorubicin, mitoxantrone and BCNU. The next level included etoposide, thiotepa and carboplatin. Carboplatin was of special note since that is what the UK in their CED report.
What this means for DIPG is that DIPG is not necessarily resistant to chemotherapy! Effective drgus might not be the biggest hurdle for a cure for DIPG. It might be getting them to the tumor cells.
This work was funded by KiKa "Stichting Kinderen Kankervrij"- Dutch Children Cancer-free Foundation.
Tomorrow.....
Part 2- Do the efflux transporters protect the glioma cells?
References:
In vitro drug response and efflux transporters associated with drug resistance in pediatric high grade glioma and diffuse intrinsic pontine glioma
PLoS One. 2013 Apr 29;8(4):e61512. doi: 10.1371/journal.pone.0061512. Print 2013.
Free Full Text- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639279/
KiKa Stichting Kinderen Kankervrij- Dutch Children Cancer-free Foundation
http://www.kika.nl/
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