Anticancer conjugates and cocktails based on methotrexate and nucleoside synergism

Conjugates of methotrexate (MTX) and the nucleoside analogs 3-azidodeoxythymidine (AZT), iododeoxyuridine (IUdR) and dideoxycytidine (ddC) linked using poly(ethyleneglycol) are presented. In vitro cytotoxicity assays of the conjugates against drug resistant ovarian cell line A2780/AD are preformed and comparisons made to such assays performed for unconjugated (cocktail) systems. All systems tested were inactive, or had low activity, at 24 h. After 72 hr incubation however, the cocktails of MTX and AZT, IUdR or ddC showed high cytotoxicity in the low nanomolar range. The conjugates were only very moderately active with IC₅₀ values in the [0.1 to 1.0 mM] range. Conjugation of the antifolate to the nucleoside analogs has it seems reduced the activity significantly when compared to a cocktail of the components, indicating a conjugate approach is unlikely to translate into success in vivo. The positive note comes from the observation that by combining two of the new conjugates, namely those based on MTX with IUdR or AZT, an IC50 at 24 hours of ∼ [180 μM] was produced.