Figure 6.

Palbociclib does not protect RB1-mutant cancer cells against SN-38.

Note: a. Scheme of co-treatment with SN-38 and palbociclib. RB1-mutant cancer cells were pretreated with palbociclib for 24 hrs with a renewal for 24 hrs (total 48 hrs, blue lines). For the final 24 hrs, SN-38 or DMSO was added (red box). On day 3, the drugs were removed and the cells were further cultured for 4 d, followed by analyses.

b. Panc02.03 (left) and SW837 (right) cells were handled as described in a to reveal that little or no protection by palbociclib was provided to them. On day 7, CellTiter-Glo assays were performed to assess cell viability. Mean ± SEM from two independent experiments, each with three in-plate replicates (n = 6). DMSO served as control treatment (0 nM SN-38 and 0 µM palbociclib) and was set 100%. Two-way ANOVA with Dunnett’s multiple comparison test, *p < 0.05, **p < 0.01, n.s. not significant.

c. Cancer cells were treated as in a. Daily measurements of cell growth of Panc02.03 (left) and SW837 (right) cells were performed via a bright field imaging system, indicating the lack of protection by palbociclib. The percentage of area covered by cells was calculated as cell confluency. Mean ± SEM from two biological replicates with ≥2 in-plate replicates (n ≥ 5). Control (DMSO treatment, gray line) was used for both SN-38 concentrations. Blue lines, palbociclib for 48 hrs. Red rectangle, co-treatment with SN-38. Student’s t-test on day 7, n.s. not significant.