Prognostic and Potentially Therapeutic Implications of MTAP Depletion in Myxofibrosarcoma.
Jen-Wei Tsai, Fu-Min Fang, Chien-Feng Li, Tzu-Ju Chen, Yu-Hui Wang, Hsuan-Ying Huang. E-Da Hospital, Kaohsiung, Taiwan; Chang Gung Memorial Hospital, Kaohsiung, Taiwan; Chi-Mei Hosp., Tainan, Taiwan; Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan; Institute of Biosignal Transduction, NCKU, Tainan, Taiwan
Background: Myxofibrosarcoma (MFS) is genetically complex and remains obscure in molecular determinants of clinical aggressiveness. A large-scale genomic study recently reported deletions of classical tumor suppressor genes (TSGs), CDKN2A/CDKN2B, at 9p21.3, while other potential TSGs on chromosome 9 are less understood in MFS.
Design: Genome-wide 385K array comparative genomic hybridization (aCGH) was profiled for 12 tumors and 2 cell lines (OH931, NMFH-1) of MFS, with special attention to potential TSGs on 9p. Three MFS cell lines (OH931, NMFH-1, NMFH-2) were subjected to immunoblotting and quantitative PCR (qPCR) assays, respectively, to analyze the MTAP protein expression and gene dosage relative to diploid dermal fibroblasts. These cell lines were also examined by XTT assay to evaluate their cell viability upon L-alanosine treatment. An independent cohort of primary MFS on tissue microarrays were immunostained for MTAP protein, yielding 87 cases with assessable results that were further correlated with clincopathological variables and patient survival.
Results: aCGH identified recurrent DNA deletions spanning 90 genes on 9p and 116 genes on 9q. MTAP and CDKN2A/CDKN2B at 9p21.3 were deleted in 5 and 6 cases, respectively, with 1 case homozygously co-deleted at both loci. As for MATP, OH931 and NMFH-2 cells showed neither detectable gene by qPCR nor protein expression by immunoblotting, while NMFH-1 had preserved gene and protein of MTAP, corresponding to aCGH findings. As compared to NMFH-1 cells (IC50∼100 uM), MTAP-depleted OH931 (IC50∼50 uM) and NMFH-2 (IC50< 1 uM) cells were more susceptible to L-alanosine, a MTAP-directed agent inhibiting de novo AMP synthesis. There were 32 of 87 cases showing loss of MTAP protein immunoexpression, which, albeit not related to clincopathological variables, were independently associated with disease-specific survival (p=0.014, RR=4.020) alone and with metastasis-free survival (p=0.0318, risk ratio [RR]=2.527), along with higher grades.
Conclusions: MTAP protein deficiency, present in 37% of primary MFS, independently portends worse prognosis, while its underlying inactivating mechanisms are currently being elucidated by both methylation-specific PCR and qPCR. MTAP-depleted MFS cells are more susceptible to L-alanosine. These findings indicate the potentiality of MTAP as prognostic and/or therapeutic biomarker of MFS.
Category: Bone & Soft Tissue
Monday, February 28, 2011 1:00 PM
Poster Session II # 4, Monday Afternoon