Antitumor effect of lonidamine alone or combined with tamoxifen or medroxyprogesterone acetate in breast cancer cells.

The effect of Lonidamine (LND) alone or combined with the antiestrogen Tamoxifen (TAM) or Medroxyprogesterone acetate (MPA) on cell proliferation and steroid hormone receptor content of a human estrogen sensitive breast cancer cell line was investigated. LND has a direct growth inhibitory action, even if used at relatively low concentrations (10(-7) M), and shows the maximum effect at 10(-4) M. The combination of LND with the antiestrogen does not produce a potentiation of the TAM-induced reduction of cell number, while the association of the drug with MPA seems more effective with respect to MPA alone, at least at certain concentrations. The negative interference observed between LND and TAM may be due to the LND-induced decrease of estrogen receptor levels.