Ethynylcytidine is a nucleoside antimetabolite.

The cytotoxicity of Ethynylcytidine tends to become stronger as the exposure time becomes longer. The IC50 values of Ethynylcytidine in the five human tumors with 4, 24 and 72 h exposure range from 0.114 to 1.032 μM, 0.015 to 0.067 μM, and 0.008 to 0.058 μM, respectively. The differences in IC50 values between the 24 and 72 h exposure times are not large, and Ethynylcytidine appears to show sufficiently potent cytotoxicity at the 24 h exposure time in all 5 human tumors.

In both OCUM-2MD3 and LX-1 xenograft models, Ethynylcytidine exhibits significant tumor regression and potent antitumor efficacy, achieving a tumor growth inhibition (IR) rate of around 90% or higher by day 15 at minimally toxic doses across all three dosing schedules. A weekly administration of Ethynylcytidine at 6 mg/kg results in a substantial reduction in LX-1 tumor size, with an IR of 98%. Conversely, administering Ethynylcytidine three or five times weekly yields a strong antitumor response with an IR of approximately 85%, while a once-weekly treatment results in an IR of less than 60%, indicating comparatively weaker antitumor activity.