The aim of this study was to examine the expression of
methylthioadenosine phosphorylase (MTAP) in 21 fresh
tumor samples from patients with
soft tissue sarcomas (STS) and 11 human
soft tissue sarcoma cell lines, and to determine if loss of expression of this
enzyme was correlated with increased sensitivity to
L-alanosine and/or
6-methylmercaptopurine. We used a polyclonal antibody to measure the expression of MTAP in
soft tissue sarcoma cell lines and in fresh
tumor samples. Transfection of the HT-1080 cell line with a plasmid containing the
cDNA for the MTAP gene was also performed to generate cell lines for in vitro and in vivo comparative sensitivity studies. MTAP was not expressed in 8 of 21 fresh STS
tumors. The expression of MTAP was also not detectable in 3 of the 11
soft tissue sarcoma cell lines (HT-1080, HS42, and M-9 110). These three cell lines were more sensitive to
L-alanosine, a potent inhibitor of de novo
AMP synthesis, and to an inhibitor of de novo
purine nucleotide synthesis,
6-methylmercaptopurine riboside (MMPR). The IC50 values for
L-alanosine and MMPR were >20-fold lower in MTAP-deficient cells than in MTAP-positive cells. Restoration of MTAP into HT-1080 MTAP-deficient cells also led to decreased sensitivity to
L-alanosine and MMPR. An in vivo study using HT-1080 cell
tumors with and without MTAP expression confirmed that
tumors lacking MTAP were more sensitive to
L-alanosine than
tumors expressing MTAP. These results provide the basis for selective
therapy using inhibitors of de novo
purine nucleotide synthesis such as
L-alanosine or MMPR to treat patients with STS lacking this
enzyme.