Abstract
Acquired drug resistance represents a major obstacle to using sunitinib for the treatment of solid tumors. Here, we examined the cellular and molecular alterations in tumors that are associated with acquired brain tumor resistance to sunitinib by using an in vivo model. U87MG tumors obtained from nude mice that received sunitinib (40 mg/kg/day) for 30 days were classified into sunitinib-sensitive and -resistant groups based on tumor volume and underwent targeted gene microarray and protein array analyses. The expression of several angiogenesis-associated genes was significantly modulated in sunitinib-treated tumors compared with those in control tumors (p < 0.05), whereas no significant differences were observed between sunitinib-sensitive and -resistant tumors (p > 0.05). Tumor vasculature based on microvessel density, neurogenin 2 chondroitin sulfate proteoglycan density, and α-smooth muscle actin density was also similar in sunitinib-treatment groups (p > 0.05). The moderate increase in unbound sunitinib tumor-to-plasma area-under-the-curve ratio in sunitinib-resistant mice was accompanied by up-regulated ATP-binding cassette G2 expression in tumor. The most profound difference between the sunitinib-sensitive and -resistant groups was found in the expression of several phosphorylated proteins involved in intracellular signaling. In particular, phospholipase C-γ1 phosphorylation in sunitinib-resistant tumors was up-regulated by 2.6-fold compared with that in sunitinib-sensitive tumors (p < 0.05). In conclusion, acquired sunitinib resistance in U87MG tumors is not associated with revascularization in tumors, but rather with the activation of alternate prosurvival pathways involved in an escape mechanism facilitating tumor growth and possibly insufficient drug uptake in tumor cells caused by an up-regulated membrane efflux transporter.
Footnotes
This study was supported by the National Institutes of Health National Cancer Institute [Grant CA072937]; and the National Institutes of Health National Institute of General Medical Sciences [Grant P50GM071558-03].
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
ABBREVIATIONS:
- VEGF
- vascular endothelial growth factor
- ABCB1
- ATP-binding cassette B1
- ABCG2
- ATP-binding cassette G2
- ANOVA
- analysis of variance
- AUC
- area under the curve
- c-Jun
- Jun proto-oncogene
- CREB
- cAMP response element-binding protein
- CT
- cycle threshold
- CT
- control tumor
- ERK1/2
- extracellular signal-regulated kinase 1/2
- p-ERK1/2
- phosphorylated ERK1/2
- GSK3α/β
- glycogen synthase kinase 3α/β
- p-GSK3α/β
- phosphorylated GSK3α/β
- HSP27
- heat shock protein 27
- IF
- interstitial fluid
- IL-8
- interleukin-8
- JNK
- c-Jun NH2-terminal kinase
- p-c-Jun
- phosphorylated c-Jun
- MMP
- matrix metallopeptidase
- NG2
- neurogenin 2 chondroitin sulfate proteoglycan
- NIH
- National Institutes of Health
- PCA
- principal component analysis
- PCR
- polymerase chain reaction
- PK
- pharmacokinetic
- PLC-γ1
- phospholipase C-γ1
- p-PLC-γ1
- phosphorylated PLC-γ1
- RSK1/2/3
- ribosomal S6 kinase 1/2/3
- RT
- resistant tumor
- α-SMA
- α-smooth muscle actin
- ST
- sensitive tumor
- STAT5α/β
- signal transducers and activators of transcription 5α/β
- U73122
- 1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione.
- Received May 2, 2012.
- Accepted August 3, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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