Figure 2.

RS67333 shows suitable kinetics for intermittent vs. continuous administration. A, Measurements of RS67333 serum levels in individual wild-type FVB/N mice receiving continuous infusion of 3 mg/kg · d of drug solubilized in 20% cyclodextrin by osmotic pump. Assessment of a prebleed taken before osmotic pump implantation is plotted before d 0. B, Measurements of RS67333 serum levels in wild-type FVB/N mice after receiving a single sc dose of 3 mg/kg of drug. Error bars, mean ± 1 sd. C and D, Representative expression levels of the osteoblastic marker collagen 1α1 (C) and Rs1 (D) determined by qPCR on whole femurs isolated from 6- or 12-wk-old animals and normalized to glyceraldehyde-3-phosphate dehydrogenase. The 6-wk-old ColI(2.3)+/Rs1+ mice were either raised off doxycycline (continuous Rs1 expression, leading to the bone overgrowth phenotype), or on doxycycline (suppressed Rs1 expression, leading to a normal skeleton). Whole femur from a 6-wk-old wild-type mouse maintained on doxycycline is shown as a control. The ColI/Rs1–late femurs were isolated from 12-wk-old animals that had been removed from doxycycline at 4 wk of age. The left femur was analyzed whole and the right femur was divided into the diaphysis and epiphysis regions. E, The Rs1/collagen I expression ratios, used to assess the relative levels of Rs1 expression in osteoblasts, show no differences in Rs1 levels between the diaphysis and epiphysis. The analyses for C–E were performed on three individual sets of mice with similar results. Error bars, mean ± 1 sd of technical triplicates from representative femurs. RNAs from the mice used for the 6-wk-old femurs shown in C–E were used in a prior publication (4).