1999, we backcrossed the Tsc2 genotype onto A J and C57BL 6 backgrounds, compared kidney disease severity, and found that the A J strain shows a much higher kidney tumor burden than mice in the C57BL 6 background at 9 and 12 months of different age as shown by the average score per kidney and average number of cystade nomas per kidney. Similar to TSC related kidney disease in humans, the tumor burden increases with age in both mouse strains. Interestingly, the A J Tsc2 strain shows a significantly higher tumor burden at 5 months of age than the C57BL 6 Tsc2 strain at 12 months of age. Based on the findings of this study, the A J strain Tsc2 mice have a 5 10 fold higher disease burden than C57BL 6 strain Tsc2 mice and are a superior and higher through put Tsc2 mouse model for preclinical studies relevant to TSC kidney disease and tumors.

Furthermore, because there is a dramatic difference in the severity of the kidney Inhibitors,Modulators,Libraries tumor phenotype in these two mouse strains, they could be used to identify modifier genes that impact the severity of TSC renal manifestations. The potential utility of rapamycin treatment for a pro longed duration Inhibitors,Modulators,Libraries was suggested by the results of a pre vious preclinical study using C57BL 6 Tsc2 mice in which we noted that a rapamycin dosing schedule that included daily treatment for 2 months and weekly treat ment for 6 months, resulted in a dramatic 94. 5% reduc tion in kidney tumor severity. In that study, rapamycin was given at a dose of 8 mg kg Monday through Friday from 6 to 7 months of age, followed by a maintenance dose of 16 mg kg once a week from 7 to 12 months of age, followed by daily rapamycin treat ment from 12 to 13 months of age.

We also note that in previous CCI 779 preclinical studies, giving a lower dose over 3 months seemed to be more effective than a higher dose for 2 months. We found that opti mal treatment correlated with duration of treatment, not total dose given. Inhibitors,Modulators,Libraries There was a 66% reduction with a total dose of 4. 8 mg per mouse in the group treated daily 4 weeks, an 82% reduction with a total dose of 6. 72 mg per mouse in the group treated daily 4 weeks plus weekly 8 weeks, and an 81% reduction with a total dose of 2. 88 mg per mouse in the group treated weekly 12 weeks. These findings demon strate that low dose rapamycin treatment for a longer duration of time is most effective in the Tsc2 mouse, and it would be reasonable to evaluate Inhibitors,Modulators,Libraries this dosing strat egy in future TSC clinical trials.

Our findings also clearly demonstrate that the response of kidney tumors to rapamycin in the Tsc2 mouse correlates well with observations in early TSC angiomyolipoma clinical trials. In A J Tsc2 mice, cystadenoma score per kidney in untreated animals at 9 months of age Inhibitors,Modulators,Libraries is 74. 4, and cystadenoma score per kid ney is 41. 13 in the groups treated daily 4 weeks, but Epigenetic Reader Do 21. 50 in the group treated daily 4 weeks then weekly 8 weeks.