EFFECTS OF 4'-MODIFIED ANALOGS OF ARISTEROMYCIN ON THE METABOLISM OF S-ADENOSYL-L-HOMOCYSTEINE IN MURINE L929 CELLS

(1 S,3'R)-9-(2',3'-Dihydroxycyclopentan-1'-yl)adenine (DHCaA), -(2',3' -dihydroxycyclopentan-l'-yl)-3-deazaadenine (3-deaza-DHCaA), (4'R)-4'- methyl-DHCaA, and (4'R)-4'-vinyl-DHCaA, which are analogs of the carbo cyclic nucleoside aristeromycin, were synthesized earlier by our labor atory and were shown to be potent inhibitors of purified bovine liver S-adenosylhomocysteine (AdoHcy) hydrolase (EC 3.3.1.1). In the present study, these analogs were shown to produce rapid (within 15 min) and concentration-dependent (0.03-10 mum) inhibition of AdoHcy hydrolase i n cultured murine L929 cells [relative order of inhibitory activity, D HCaA = 3-deaza-DHCaA >> (4'R)-4'-vinyl-DHCaA = (4'R)-4'-methyl-DHCaA]. The relative potencies of these inhibitors on the L929 AdoHcy hydrola se were consistent with their inhibitory effects on the recombinant fo rms of rat liver and human placental enzymes. This inhibition of L929 cellular AdoHcy hydrolase persisted for up to 48 hr. The inhibition of the L929 AdoHcy hydrolase resulted in a significant increase in the c ellular concentrations of AdoHcy, whereas the cellular S-adenosylmethi onine (AdoMet) levels remained relatively constant, thereby elevating the AdoHcy/AdoMet ratios. Maximum increases in AdoHcy levels and AdoHc y/AdoMet ratios occurred within 6 hr of exposure to the inhibitors and persisted for at least 24 hr. At a concentration of 1 mum, DHCaA and 3-deaza-DHCaA increased AdoHcy/AdoMet ratios to approximately 0.8 (aft er 24 hr of exposure to the inhibitors), whereas (4'R)-4'-vinyl-DHCaA and (4'R)-4'-methyl-DHCaA elevated AdoHcy/AdoMet ratios to approximate ly 0.15, compared with control levels of 0.05. Treatment of L929 cells with concentrations of DHCaA, 3-deaza-DHCaA, (4'R)-4'-vinyl-DHCaA, an d (4'R)-4'-methyl-DHCaA up to 10 muM did not result in changes in cell ular levels of endogenous nucleotides (e.g., CTP, UTP, ATP, and GTP). In contrast, cells treated with 1 0 mu m aristeromycin for 6 hr contai ned reduced cellular levels of CTP, ATP, and GTP and significant level s of aristeromycin triphosphate and a GTP metabolite of this carbocycl ic nucleoside. These data clearly show that the 4'-modified analogs [D HCaA, 3-deaza-DHCaA, (4'R)-4'-vinyl-DHCaA, and (4'R)-4'-methyl-DHCaA] retain inhibitory activity toward cellular AdoHcy hydrolase, causing e levated levels of AdoHcy and elevated AdoHcy/AdoMet ratios. However, t hese analogs are devoid of substrate or inhibitory activity toward cel lular adenosine kinase. In addition, aristeromycin is rapidly metaboli zed in murine L929 cell lysates, i.e., >60% of the aristeromycin had b een metabolized in 6 hr. In contrast, neither DHCaA nor 3-deaza-DHCaA showed any decrease in concentration after incubation with cell lysate s for up to 6 hr.