Treatment with the sialic acid precursor ManNAc reduces the number of lesions and tumor load in vivo. (A) Twenty mice were given an intravenous injection of 2 × 10⁶ of 5TGM1 mouse multiple myeloma cells and treated with ManNAc and the corresponding vehicle (mannose), both administered at 10 g/L in the drinking water for the duration of the study. After ∼30 days, the mice were euthanized. (B) IgG2abc-Fc sialylation before tumor challenge, 21 days’ post–tumor challenge, and at euthanasia as indicated. (C-D) The lesion number and lesion area in hind limbs were determined from radiographic images with MetaMorph image analysis software. (E-G) Serum levels of the osteoclast marker CTX-1, the osteoblast marker P1NP, and the M component IgG2b in animals treated as indicated were measured by enzyme-linked immunosorbent assay at the end of the study. (H) Spleens were harvested and weighed at end point. Significance was determined by 2-way ANOVA followed by Tukey’s multiple comparisons test (panel B) or by unpaired Student t test (panels C-H). *P < .05, **P < .01 ****P < .0001. ns, not significant.