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Identification of gene expression profiles predicting tumor cell response to L-alanosine
Thomas Efferth1, Erich Gebhart, Douglas D Ross
1Center for Molecular Biology of the University of Heidelberg (ZMBH), Im Neuenheimer Feld 282, 69120 Heidelberg, Germany. thomas.efferth@web.de
Abstract:
The methylthioadenosine phosphorylase (MTAP) gene gained considerable interest as therapeutic target for tumors with the 9p21 deletion. This gene maps to 9p21 and loss of this chromosomal region in tumors offers an unique opportunity for chemoselective treatment, since MTAP is an important salvage enzyme for the formation of adenine that is needed for DNA synthesis. L-Alanosine, an antibiotic from Streptomyces alanosinicus, blocks the common de novo purine biosynthesis pathway and, thereby, inhibits tumor cells with MTAP deficiency. Normal cells escape the detrimental effects of L-alanosine due to their proficiency in the MTAP salvage pathway. The present analysis was undertaken to gain insights into the molecular architecture of tumor cells that determines the response to L-alanosine apart from the MTAP gene. Analysis of cell doubling times and IC(50) values for L-alanosine showed that slowly growing cell lines were more resistant to L-alanosine than rapidly growing ones. Mining the database of the National Cancer Institute (N.C.I.), for the mRNA expression of 9706 genes in 60 cell lines by means of Kendall's tau-test, false discovery rate calculation, and hierarchical cluster analysis pointed to 11 genes or expressed sequence tags whose mRNA expression correlated with the IC(50) values for L-alanosine. Furthermore, we tested L-alanosine for cross-resistance in multidrug-resistant cell lines which overexpress selectively either the P-glycoprotein/MDR1 (CEM/ADR5000), MRP1 (HL-60/AR), or BCRP (MDA-MB-231-BCRP) genes. None of the multidrug-resistant cell lines was cross-resistant to L-alanosine indicating that L-alanosine may be suitable to treat multidrug-resistant, refractory tumors in the clinic. Finally, the IC(50) values for L-alanosine of the 60 cell lines were correlated to the p53 mutational status and expression of p53 downstream genes. We found that p53 mutated cell lines were more resistant to L-alanosine than p53 wild type cell lines.
Insights
Methylthioadenosine phosphorylase (MTAP) deficiency in tumors presents a therapeutic target. L-alanosine selectively inhibits MTAP-deficient cells, showing promise for treating refractory cancers, including multidrug-resistant types.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Therapeutics
Background:
- Methylthioadenosine phosphorylase (MTAP) is a key salvage enzyme, crucial for adenine synthesis and DNA replication.
- Tumors with a 9p21 deletion often lack MTAP, creating a vulnerability for targeted therapies.
- L-alanosine, an antibiotic, inhibits de novo purine biosynthesis, selectively targeting MTAP-deficient cancer cells.
Purpose of the Study:
- To investigate molecular factors beyond MTAP that influence tumor cell response to L-alanosine.
- To assess the potential of L-alanosine in treating multidrug-resistant and refractory cancers.
- To explore the correlation between L-alanosine efficacy and p53 mutational status.
Main Methods:
- Analysis of cell doubling times and IC(50) values for L-alanosine across 60 cancer cell lines.
- Utilizing the National Cancer Institute's database for mRNA expression analysis (Kendall's tau-test, FDR, hierarchical clustering).
- Testing L-alanosine for cross-resistance in multidrug-resistant cell lines overexpressing P-glycoprotein, MRP1, or BCRP.
- Correlating L-alanosine IC(50) values with p53 mutational status and downstream gene expression.
Main Results:
- Slower-growing cell lines exhibited greater resistance to L-alanosine compared to rapidly growing ones.
- 11 genes/ESTs were identified whose mRNA expression correlated with L-alanosine IC(50) values.
- No cross-resistance to L-alanosine was observed in multidrug-resistant cell lines.
- p53-mutated cell lines demonstrated increased resistance to L-alanosine compared to p53 wild-type cell lines.
Conclusions:
- Tumor growth rate and p53 status are significant determinants of L-alanosine sensitivity, independent of MTAP deficiency.
- L-alanosine shows potential as a therapeutic agent for multidrug-resistant and refractory tumors.
- Further investigation into the identified gene expression patterns could refine L-alanosine treatment strategies.