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New method of synthesis of water-soluble polymer-drug conjugates, exhibiting remarkable anticancer activity in mice models, has been developed. In the conjugates, an anticancer drug doxorubicin (DOX) is attached to a polymer carrier based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer via a hydrolytically labile hydrazone bond. New methacrylamide-type comonomers, containing either hydrazide group or hydrazon of DOX, were used for copolymerization with HPMA. In contrast to the synthetic procedure described earlier the new method is simpler, cheaper, and results in a better-defined conjugate structure. The conjugates are fairly stable in buffer at pH 7.4 (model of blood stream) but release DOX under mild acid conditions modeling the tumor microenvironment. The conjugates showed significant in vivo antitumor activity in treatment of T-cell lymphoma EL-4 bearing mice with up to 100% long-term survivors.