Libraries of 2β-(N-substituted piperazino)-5α-androstane-3α, 17β-diols: chemical synthesis and cytotoxic effects on human leukemia HL-60 cells and on normal lymphocytes

Libraries of steroid derivatives with two levels of molecular diversity were prepared to optimize the antiproliferative activity on leukemia HL-60 cells by first varying the amino acid (AA) at R¹ (libraries A, B, C, and D: with 45, 45, 20, and 20 members, respectively) and, subsequently, the capping group at R² (library E: 168 members). The screening of these aminosteroids revealed interesting structure–activity relationships. In library A, the compounds bearing a tetrahydroisoquinolone residue as the first element of diversity showed potent cytotoxicity, principally when isovaleric or cyclohexyl acetic acid was used as a capping group (>40% of cell growth inhibition at 1 μM). In library B, the phenylalanine (Phe) derivatives bearing a cyano group induced a higher growth inhibition than the other Phe derivatives. The screening of library C indicated the increase of hydrophobicity of proline (Pro) seems to preserve the cytotoxic effect achieved by the lead compound. However, the synthesis of structural Pro variants (library D) clearly shows weaker activities when compared to L-Pro building blocks. Finally, by incorporating some of the most active AA of libraries A–D in library E, we observed that the amide coupling functionality gave stronger cytotoxic activity compared to the corresponding sulfonamides or benzylamines. Six of the most active amide derivatives (E-37P, E-41P, E-42P, E-46P, E-48F, and E-12T) were selected and IC₅₀ determined on HL-60 cells as well as on normal human lymphocytes. Among this series of new anticancer agents, good to high selectivity indices (SI = IC₅₀ (lymphocytes)/IC₅₀ (HL-60 cells) = 5 - 55) were obtained.