Design, synthesis of methotrexate-diosgenin conjugates and biological evaluation of their effect on methotrexate transport-resistant cells

[Display omitted] •The lipophilic MTX conjugates with diosgenin were synthesized via various polyamine linkers.•Polyamine linkers could balance the solubility, rapid drug release and cell membrane permeability.•The diosgenin residue aids the transfer of MTX into transport resistant cells.•Disulfide-containing MTX conjugate showed stronger antitumor activity relative to MTX alone.•Antitumor activity of MTX conjugates against transport resistant MDA-MB-231 cell was evaluated. A series of methotrexate-diosgenin conjugates was designed and synthesized to enhance the passive internalization of methotrexate (MTX) into transport-resistant cells. The inhibitory effects of these conjugates on dihydrofolate reductase (DHFR), and their anti-proliferation behaviors against a transport-resistant breast cancer cell line, MDA-MB-231, were investigated. All of the synthesized conjugates retained an ability to inhibit DHFR after the diosgenin substitution. The MTX conjugates were much more potent against methotrexate-resistant MDA-MB-231 cells than MTX. Conjugate 18, containing a disulfide bond, exhibited the most potent anti-proliferative and DHFR inhibitory effects (IC50=4.1μM and 17.21nM, respectively). Anti-proliferative activity was higher in the conjugate with a longer space linker (conjugate 21) than those with shorter linkers (conjugates 19 and 20). These results suggest that diosgenin conjugation of MTX may be an effective way to overcome its transport resistance in cancer cells.