pyrimidinones and Sarcoma--Ewing

Ewing sarcoma is an aggressive childhood cancer for which treatment options remain limited and toxic. There is an urgent need for the identification of novel therapeutic strategies. Our group has recently shown that Ewing cells rely on the S-phase kinase CDC7 (DDK) to maintain replication rates and cell viability and that DDK inhibition causes an increase in the phosphorylation of CDK1 and a significant delay in mitotic entry. Here, we expand on our previous findings and show that DDK inhibitor-induced mitotic entry delay is dependent upon WEE1 kinase. Specifically, WEE1 phosphorylates CDK1 and prevents mitotic entry upon DDK inhibition due to the presence of under-replicated DNA, potentially limiting the cytotoxic effects of DDK inhibition. To overcome this, we combined the inhibition of DDK with the inhibition of WEE1 and found that this results in elevated levels of premature mitotic entry, mitotic catastrophe, and apoptosis. Importantly, we have found that DDK and WEE1 inhibitors display a synergistic relationship with regards to reducing cell viability of Ewing sarcoma cells. Interestingly, the cytotoxic nature of this combination can be suppressed by the inhibition of CDK1 or microtubule polymerization, indicating that mitotic progression is required to elicit the cytotoxic effects. This is the first study to display the potential of utilizing the combined inhibition of DDK and WEE1 for the treatment of cancer. We believe this will offer a potential therapeutic strategy for the treatment of Ewing sarcoma as well as other tumor types that display sensitivity to DDK inhibitors.

Topics: Antineoplastic Agents; Cell Cycle Proteins; Cell Death; Cell Line, Tumor; Child; Humans; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Pyrimidinones; Sarcoma, Ewing

Inhibition of ribonucleotide reductase (RNR), the rate-limiting enzyme in the synthesis of deoxyribonucleotides, causes DNA replication stress and activates the ataxia telangiectasia and rad3-related protein (ATR)-checkpoint kinase 1 (CHK1) pathway. Notably, a number of different cancers, including Ewing sarcoma tumors, are sensitive to the combination of RNR and ATR-CHK1 inhibitors. However, multiple, overlapping mechanisms are reported to underlie the toxicity of ATR-CHK1 inhibitors, both as single agents and in combination with RNR inhibitors, toward cancer cells. Here, we identified a feedback loop in Ewing sarcoma cells in which inhibition of the ATR-CHK1 pathway depletes RRM2, the small subunit of RNR, and exacerbates the DNA replication stress and DNA damage caused by RNR inhibitors. Mechanistically, we identified that the inhibition of ATR-CHK1 activates CDK2, which targets RRM2 for degradation via the proteasome. Similarly, activation of CDK2 by inhibition or knockdown of the WEE1 kinase also depletes RRM2 and causes DNA damage and apoptosis. Moreover, we show that the concurrent inhibition of ATR and WEE1 has a synergistic effect in Ewing sarcoma cells. Overall, our results provide novel insight into the response to DNA replication stress, as well as a rationale for targeting the ATR, CHK1, and WEE1 pathways, in Ewing sarcoma tumors. IMPLICATIONS: Targeting the ATR, CHK1, and WEE1 kinases in Ewing sarcoma cells activates CDK2 and increases DNA replication stress by promoting the proteasome-mediated degradation of RRM2.

Topics: Apoptosis; Ataxia Telangiectasia Mutated Proteins; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Checkpoint Kinase 1; Cyclin-Dependent Kinase 2; DNA Damage; DNA Repair; Enzyme Inhibitors; HEK293 Cells; Humans; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidinones; Ribonucleoside Diphosphate Reductase; Sarcoma, Ewing; Transfection

Musculoskeletal sarcomas are aggressive malignancies of bone and soft tissues often affecting children and adolescents. Histone deacetylase inhibitors (HDACi) have been proposed to counteract cancer stem cells (CSCs) in solid neoplasms. When tested in human osteosarcoma, rhabdomyosarcoma, and Ewing's sarcoma stem cells, the new HDACi MC1742 (1) and MC2625 (2) increased acetyl-H3 and acetyl-tubulin levels and inhibited CSC growth by apoptosis induction. At nontoxic doses, 1 promoted osteogenic differentiation. Further investigation with 1 will be done in preclinical sarcoma models.

Topics: Aminopyridines; Apoptosis; Bone Neoplasms; Cell Differentiation; Cell Line, Tumor; Cell Proliferation; Drug Screening Assays, Antitumor; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Neoplastic Stem Cells; Osteogenesis; Osteosarcoma; Pyrimidinones; Rhabdomyosarcoma; Sarcoma; Sarcoma, Ewing; Structure-Activity Relationship