Novel lysine-spermine conjugate inhibits polyamine transport and inhibits cell growth when given with DFMO

Polyamines are ubiquitous molecules with multiple intracellular functions. Cells tightly regulate their levels through feedback mechanisms affecting s ynthesis, intracellular conversion, and transport. Because polyamines have an important role in regulating cell growth, they are a target for cancer t herapeutic development. However, to effectively inhibit cell growth through polyamine depletion one needs to inhibit both polyamine synthesis and impo rt. Although the mammalian polyamine transporter has not been cloned, we ha ve identified ORI 1202, an N-1-spermine-L-lysinyl amide, as an effective po lyamine transport inhibitor. ORI 1202 prevents the cellular accumulation of [H-3]spermidine over a 20-h test period. ORI 1202 (30-100 muM) effectively inhibits cell growth when used in conjunction with the polyamine synthesis inhibitor alpha -difluoromethylornithine (DFMO; greater than or equal to 2 30 muM). Human breast, prostate, and bladder carcinoma cell lines and melan oma cell lines show ORI 1202 EC,, values in the low micromolar range when t ested in conjunction with DFMO. This cytostatic effect correlates with a re duction in the intracellular levels of putrescine and spermidine. When ORI 1202 (45 mg/kg, i.p., tidx5) and DFMO (1% in drinking water) were delivered over 14 days, MDA-MB-231 breast tumor xenografts in nude mice showed 50% g rowth inhibition. Polyamine depletion therapy provides a cytostatic therapy that could be useful against cancer and other diseases resulting from unco ntrolled cell growth. (C) 2000 Academic Press.