Consistent with the BrdU assays, we observed inhibition of pRb at 2��M. As 77% of BSGs harbor p53 mutations, we were also interested in determining the efficacy of PD in our PDGF-B; p53 deficient BSG cell lines. We again used two independent cell lines and repeated the same course of CL 82198 hydrochloride experiments. Similar to our observations with the PDGF-B; Ink4a-ARF deficient BSG cell lines, PD was only minimally cytotoxic to the PDGF-B; p53 deficient BSG cells at a dose of 5��M but not at lower doses. In contrast, BrdU assays showed that p53 deficient cell lines were less sensitive to PD treatment; the IC50 was not achieved with doses up to 5��M. Concordantly, we found that apoptosis was not induced in PDGF-B; p53 deficient BSG cells by DIM-C-pPhOH treatment with PD. To validate these findings we then examined pRb levels. After 48 hours of treatment, pRb inhibition was not achieved at doses up to 2��M. Collectively, our results suggest that treatment with PD is more effective against PDGF-B; Ink4-ARF deficient cell lines than PDGF-B; p53 deficient cell lines. Cells were treated with PD-0332991 for 48 hours before being harvested for MTT or BrdU assays to assess cell survival and proliferation, respectively. MTT assays show minimal cytotoxic activity at doses up to 5��M in cell lines derived from PDGF-B; Ink4a-ARF deficient BSGs. BrdU assays showed inhibition of proliferation with an IC50 of 1.8��M. Assays performed in two independent cell lines. Apoptosis assays showed a very small but significant increase in apoptosis at 2��M and 5��M. Western blot analysis shows inhibition of Rb phosphorylation at the protein level, with inhibition observed at 2��M in the PDGF-B; Ink4a-ARF deficient line after only 24 hours of treatment. MTT assays show the minimal cytotoxic activity only at doses of 5��M in cell lines derived from PDGF-B; p53 deficient BSGs. BrdU assays showed significant inhibition of proliferation at 5��M but IC50 was not reached. Apoptosis assays did not show any difference in apoptosis between vehicle and up to 5��M PD. Assays performed in two independent cell lines. Error bars represent SEM from three independent experiments. Statistical significance was determined using One-way ANOVA; paired student��s t-test was used to compare within groups. PDGFB; p53 deficient BSG cells show no decrease in pRb at doses up to 2��M even after 48 hours of treatment with PD. Upon observing that PDGF-B; Ink4a-ARF deficient BSG cells were more sensitive to PD, we continued our study with this model. To confirm our observations with the BrdU assay, we performed cell cycle analysis. Indeed, cell cycle analysis of PDGF-B; Ink4a-ARF deficient cell lines treated with PD demonstrated a significant increase in the percentage of cells in G0/G1 in response to a 48-hour treatment with 2��M PD. We also noted that while it was not significant, there was a trend of a decrease in the percentage of cells in M phase. Lastly, we did not observe a sub-G0 population in the cell cycle analysis at PD doses up to 2��M.