Abstract 4144: Identification of molecules involved in PpIX accumulation in brain tumor induced by oral administration of 5-ALA

Abstract

Abstract [Background and Purpose] 5-aminolevulinic acid (5-ALA) is one of leading compounds widely used in photodynamic diagnosis and therapy of solid tumors: 5-ALA is metabolically converted to protoporphyrin IX (PpIX), a fluorescent molecule in response to excitation with a laser beam of 405 nm wavelength, that accumulates specifically in tumor lesions. This is found to be very effective for intra-operative detection of malignant brain tumors such as glioblastoma multiforme (GBM). On the other hand, we occasionally encountered cancerous lesions that are apparently malignant under a white light, while showing no fluorescence of the PpIX during cyto-reductive operation of the GBM. In order to overcome this problem, we hereby searched for factors associated with either presence or absence of the PpIX fluorescence by means of comprehensive gene expression analysis. [Materials and Methods] Thirty-one patients of brain tumor (21 GBM, 3 pilocytic astrocytoma and 7 oligodendroglial tumors), orally-administrated with 5-ALA followed by operation under a fluorescence-guide, were enrolled in this study. Tumor specimens with or without the 5-ALA induced-fluorescence were collected from these patients and snap-frozen in liquid nitrogen. Total RNAs were extracted from the frozen tissues and were subjected to a comprehensive gene expression analysis using Whole Human Genome 4×44K Oligo Microarray (Agilent). We then compared gene expression levels between specimens with or without the fluorescence among individuals and selected candidate genes of which gene expression levels significantly differ between these. For validation, quantitative gene expression analyses were conducted for the candidates with real-time RT-PCR using gene specific-primers and probes. Knockdown experiments using specific siRNAs were also performed in cell lines derived from GBM to test their biological significance. [Results and Discussion] A total of 14 genes were initially selected as candidates that were associated with PpIX accumulation in GBM in the microarray analysis. Among these, CDH13 (cadherin 13) gene was expressed significantly higher in the fluorescence-positive GBMs than in negative ones. Knockdown of CDH13 gene expression in GBM cells treated with 5-ALA, attenuated the fluorescence intensity, indicating its possible role in PpIX accumulation. Further experiments are underway to elucidate molecular mechanisms of CDH13 in 5-ALA-induced PpIX fluorescence in brain tumor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4144. doi:10.1158/1538-7445.AM2011-4144