Fatty acid synthase (FAS): a target for cytotoxic antimetabolites in HL60 promyelocytic leukemia cells.

Many human cancers express elevated levels of fatty acid synthase (FAS), with correspondingly increased fatty acid synthesis and abnormal fatty acid utilization. Recent studies have shown that the FAS inhibitor, cerulenin, is selectively cytotoxic to cell lines derived from human malignancies, suggesting that those carcinoma cells are dependent upon endogenous fatty acid synthesis for growth. These data further suggest that the fatty acid synthesis pathway is a potential target for chemotherapy development. The present studies demonstrate that cerulenin cytotoxicity is mediated by fatty acid pathway inhibition. Proliferating HL60 promyelocytic leukemia cells express high levels of FAS mRNA and protein and synthesize fatty acid predominantly for membrane phospholipid. Following exposure to 12-O-tetradecanoylphorbol-13-acetate, the FAS expression in HL60 cells is abolished, fatty acid synthesis diminishes, and the cells become insensitive to cerulenin while acquiring a differentiated, macrophage-like phenotype. HL60 cells adapted to growth in serum- and fatty acid-free medium show a dose-dependent sensitivity to cerulenin, which is reversed by palmitate, the major product of FAS, indicating that cerulenin cytotoxicity is mediated through fatty acid starvation. Cells grown in the presence of exogenous fatty acid partially downmodulate FAS expression and increase mean cell volume (phospholipid mass/cell) but retain their sensitivity to cerulenin, which is reversed by 3-fold excess oleate supplementation. These results demonstrate that malignant cells can retain dependence on endogenous fatty acid synthesis and sensitivity to FAS inhibitors in the presence of physiological fatty acid levels and thus support the notion that FAS inhibitors may be useful in treating cancer in vivo.

Inhibition of fatty acid synthesis induces programmed cell death in human breast cancer cells.

One of the key limiting factors in the treatment of advanced stage human epithelial malignancies is the lack of new, selective molecular targets for antineoplastic therapy. A substantial subset of human breast, ovarian, endometrial, colorectal, and prostatic cancers express elevated levels of fatty acid synthase, the major enzyme required for endogenous fatty acid biosynthesis, and carcinoma lines are growth inhibited by cerulenin, a noncompetitive inhibitor of fatty acid synthase. We have shown previously that the difference in fatty acid biosynthesis between cancer and normal cells is an exploitable target for metabolic inhibitors in the in vitro setting and in vivo in a human ovarian carcinoma xenograft in nude mice. Here, we report that cerulenin treatment of human breast cancer cells inhibits fatty acid synthesis within 6 h after exposure, that loss of clonogenic capacity occurs within the same interval, and that DNA fragmentation and morphological changes characteristic of apoptosis ensue.

Inhibition of fatty acid synthesis delays disease progression in a xenograft model of ovarian cancer.

One of the key limiting factors in the treatment of advanced stage human epithelial malignancies is the lack of selective molecular targets for antineoplastic therapy. A substantial subset of human ovarian, endometrial, breast, colorectal, and prostatic cancers exhibit increased endogenous fatty acid biosynthesis and overexpress certain enzymes in the pathway. Cell lines derived from these tumors use endogenously synthesized fatty acids for cellular functions, whereas normal cells and tissues appear to utilize dietary lipids preferentially. We have previously shown that the difference in fatty acid biosynthesis between cancer and normal cells is an exploitable target for metabolic inhibitors in vitro. Here, we report observations in vivo using the i.p. model of the multiply drug-resistant OVCAR-3 human ovarian carcinoma in nude mice which demonstrate that: (a) fatty acid synthase overexpression in OVCAR-3 is comparable to levels in primary human tumors assessed by immunohistochemistry; (b) fatty acid synthetic activity of OVCAR-3 is comparably elevated in vitro and in vivo and is 4 to >20-fold higher than normal murine tissues; (c) treatment with the specific fatty acid synthase inhibitor, cerulenin, markedly reduces tumor cell fatty acid biosynthesis in vivo; (d) fatty acid synthase inhibition produces regression of established ascites tumor; and (e) treatment with cerulenin causes reduction in ascites incidence, delay in onset of ascites, and significantly increased survival (P<0.04).

Fatty acid synthesis: a potential selective target for antineoplastic therapy.

OA-519 is a prognostic molecule found in tumor cells from breast cancer patients with markedly worsened prognosis. We purified OA-519 from human breast carcinoma cells, obtained its peptide sequence, and unambiguously identified it as fatty acid synthase through sequence homology and enzymology. Tumor fatty acid synthase is an approximately 270-kDa polypeptide which specifically abolished immunostaining of human breast cancers by anti-OA-519 antibodies. Tumor fatty acid synthase oxidized NADPH in a malonyl-CoA-dependent fashion and synthesized fatty acids composed of 80% palmitate, 10% myristate, and 10% stearate from acetyl-CoA, malonyl-CoA, and NADPH with a specific activity of 624 nmol of NADPH oxidized per min per mg. Tumor cell lines with elevated fatty acid synthase showed commensurate increases in incorporation of [U-14C]acetate into acylglycerols demonstrating that fatty acid synthase increases occur in the context of overall increases in endogenous fatty acid synthesis. Cerulenin inhibited acylglycerol synthesis in tumor cells and fibroblast controls in a dose-dependent fashion and also caused a growth inhibition which generally paralleled the level of endogenous fatty acid synthesis. Supraphysiologic levels of palmitate, 14 microM in dimethyl sulfoxide, significantly reversed the growth inhibition caused by cerulenin at concentrations of up to 5 micrograms/ml, indicating that cerulenin-mediated growth inhibition was due to fatty acid synthase inhibition.