Fig 2: Screening for modulators of Cdc7-dependent phosphorylation of Ser40/41 MCM2.Results of the screening of the Johns Hopkins Clinical Compound Library and Tocris kinase inhibitor library using In Cell Western Technology. Each dot represents a compound and the normalized pSer40/41 MCM2 intensity is reported - See text for experimental details. The names of the hits producing the strongest reduction in phosphorylation at Ser40/41MCM2 are indicated.

Fig 3: Ryuvidine and Mitoxantrone reduce CDC7 levels and pSer40/41 MCM2 phosphorylation.A) Molecular structure of PHA-767491, Ryuvidine and Mitoxantrone. B) HeLa cells were incubated with either CDC7 inhibitor PHA-767491, Ryuvidine or Mitoxantrone at 10 micromolar each for the indicated time. Protein extracts were prepared and analyzed by western blot with the indicated antibodies. C) Levels of Cdc7-independent pSer41MCM2 and Cdc7-dependent pSer40/41MCM2 phosphorylation assessed in HeLa cells treated with the indicated concentration of PHA-767491, Ryuvidine or Mitoxantrone. D) Cells were incubated with either PHA-767491, Ryuvidine or Mitoxantrone at the indicated concentration for nine hours. Protein extracts were then prepared and analyzed by western blot with the indicated antibodies. E) HeLa cells incubated with either PHA-767491, Ryuvidine or Mitoxantrone at 10 micromolar each for nine hours in the presence or absence of 20 micromolar of caspase inhibitor Boc-D-fmk. Levels of Ser40/41MCM2 phosphorylation, CDC7 and MCM2 abundance as well as PARP cleavage, were assessed by western blotting.

Fig 4: Confirmation and in vitro characterization of Hit compounds.A) HeLa cells were treated with the ten compounds that produced the strongest reduction in pSer40/41MCM2 levels in the primary screen. Protein extracts were prepared and levels of residual pSer40/41MCM2 phosphorylation were measured by western blot analysis with the indicated antibodies. B) The same compounds were tested for their ability to inhibit CDC7 kinase activity in in vitro kinase assay. Kinase reactions were performed on a synthetic MCM2 substrate in the absence or presence of the indicated drug and reactions were run on SDS-PAGE gels. CDC7 activity on the synthetic MCM2 substrate was monitored by Western blotting with an anti-pSer108MCM2 antibody. As a control the levels of CDC7 kinase and synthetic MCM2 substrate present in each reaction were also assessed and shown to be similar in all reactions.