Versipelostatin (VST), a macrocyclic compound, was isolated from Streptomyces versipellis 4083-SVS6 by Park et al (Tetrahedron Lett. 43:6941, 2002). VST has been found to suppress gene activation of molecular chaperon GRP78 during glucose deprivation, a microenvironmental stress condition commonly seen in poorly vasculized solid tumors (JNCI 96:1300, 2006). Consistent with inhibition of GRP78 induction, VST showed a selective cytotoxicity to glucose-deprived cancer cells. Moreover, VST can inhibit tumor growth of stomach adenocarcinoma MKN74 xenografts in nude mice and is a potential therapeutic agent against solid tumors. However, little is known about the mechanisms of VST action in tumor growth inhibition. In this study, we conducted DNA microarray analysis to investigate changes in gene expression of xenografted tumors with or without VST treatment.
We prepared MKN74-xenografted Balb/c nu/nu mice and treated them with VST intravenously at 6 or 9 mg/kg for three days after the tumor volumes reached about 100 mm³. Eight hours after administering the VST, the tumors were excised to isolate mRNA for gene expression analysis with Human Genome U133 Plus 2.0 Array™ (Affymetrix Co. Ltd). DNA microarray data were extracted on the basis of the criteria of signal intensity and signal log ratio.
VST treatment (9 mg/kg/day, 3 days/week for 3 weeks) for MKN74-xenografted nude mice suppressed tumor growth compared with vehicle-treated control mice. Then, we screened the gene expression pattern in the tumors in the first round of VST treatment (the first week) using the DNA microarray technique. On the whole, no drastic changes in gene expression could be detected, but some interesting changes were observed. For example, increased expression was seen in vascular endotherial growth factor (VEGF) and prostaglandin-endoperoxide synthase 2 (COX-2), while decreased expression was seen in metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), fibronectin 1, and cyclin E2. Interestingly, the expression signature was detected significantly in tumors treated with 9 mg/kg of VST, but less significantly in tumors treated with 6 mg/kg of VST, a dose that showed marginal tumor growth inhibition. To validate the expression signature, we are examining gene expression pattern in xenograft models of pancreatic cancer cells as well as MKN74 cells in greater detail.
We identified changes in gene expression pattern that are associated with tumor growth inhibition by VST. Our present results, together with further analysis in other xenograft models, will be useful in understanding the antitumor action mechanisms of VST and in identifying biomarkers for clinical trials of this new type of antitumor drug.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA