AML mouse model to study the efficacy of PD0332991 in vivo. (A) Phospho-pRb staining in human CD45 cells. 6 NOD/SCID mice were inoculated with MOLM13 cells. On day 9 after inoculation, 3 mice were dosed with PD0332991 (150 mg/kg), and 3 mice were dosed with vehicle (lactic acid buffer). On day 10, the mice were dosed a second time with PD0332991 (150 mg/kg) or vehicle 4 hours before sacrificing them. The bone marrow was isolated, stained with anti-human CD45 plus anti-phospho-pRb, and analyzed by flow cytometry. The cells detected in the upper right and lower right quadrant are human leukemia cells because they stain positive for human CD45. The cells in the upper right quadrant stain positive for phospho-pRb. The cells in the lower right are negative for phospho-pRb. (B) Kaplan-Meyer survival plot. NOD/SCID mice were inoculated with MOLM13 cells. Starting on day 6 after inoculation, one group (10 mice) was dosed with PD0332991 (150 mg/kg), the other group (10 mice) was dosed with vehicle (lactic acid buffer). The survival of both groups was analyzed by Kaplan-Meyer plot. The survival benefit of mice treated with PD0332991 was statistically significant (P=.001, logrank test). (C) Immunohistochemistry. 10 NOD/SCID mice were engrafted as above. Five mice were each dosed with PD0332991 (150 mg/kg) or lactic acid buffer (control) starting on day 5 after inoculation. On day 10, all mice were killed. Sections of the sterna were prepared and stained as indicated with H&E, anti-human CD45, and anti-phospho pRb. The arrows point at the human leukemia cells. Images were visualized using an Olympus BX41 microscope equipped with an Olympus 3040 camera and a Plan 40×/0.65 NA objective lens (Olympus America, Melville, NY). The image medium was air. Adobe Photoshop CS version 8 (Adobe Systems, San Jose, CA) was used for image acquisition and processing.