The invention provides novel methods of determining or comparing potency of a test interferon relative to rSIFN-co (an interferon having therapeutic effects on solid tumors)； methods of establishing substantial equivalence between a test interferon and rSIFN-co； methods for down-regulation of expression of Wnt-related receptors or co-receptors, such as LRP6/FZD6； down-regulation of expression of Wnt-related target genes, such as, Axin2, CD24, Survivin and/or ID2； inhibition of beta-catenin/TCF transcriptional activities； suppression of expression of beta-catenin； up-regulation of tumor suppressor genes, such as DKK-3, BATF2 and/or KLF4； inhibition of tumor cell viability in vitro； inhibition of tumor growth and metastases in vivo； inhibition of tumor cell migration, pseudopod formation, and colony formation in vitro； as well as methods for determining potency of a test interferon, kits for determination of such methods, and an interferon or an interferon substitute having said activities.
