Does atractylenolide I synergize the anti-melanoma effects of MK-8776 by inhibiting cyclin-dependent kinase 2 signaling?

Malignant melanoma is aggressive and intractable. The 5-year survival rate of patients with metastatic melanoma is only 18%. Novel treatment modalities for melanoma are needed. Checkpoint kinase 1 (Chk1) is a central component of the DNA damage response and plays a crucial role in controlling melanoma cell cycle progression. A Chk1 inhibitor MK-8776 has been tested in a phase I clinical trial for treating melanoma. Although the treatment was safe, only 1/3 of melanoma patients responded to it. Therefore, the efficacy of MK-8776 needs to be improved. Through inhibiting Chk1 signaling, MK-8776 induces DNA damage in melanoma cells. Simultaneously, MK-8776 activates cyclin-dependent kinase 2 (Cdk2), a critical kinase for DNA repair. MK-8776-activated Cdk2 might in turn attenuate the effect of MK-8776 in killing melanoma cells. Silencing Cdk2 selectively induces melanoma cell death without affecting normal cells. Thus, combination of a Cdk2 inhibiting agent and MK-8776 should be effective yet relatively nontoxic for treating melanoma. Our laboratory has a long history of studying atractylenolide I (AT-I), a Chinese medicinal herb-derived sesquiterpene that has anti-melanoma effects and can lower the protein level of Cdk2 in melanoma cells. Recently, we found that AT-I alone or in combination with MK-8776 inhibits Cdk2 activation; and the AT-I/MK-8776 combination downregulates mRNA levels of Cdk2 and several DNA repair genes regulated by Cdk2 in cultured melanoma cells. Furthermore, the AT-I/MK-8776 combination produces synergism in reducing the viability of melanoma cells. Importantly, intraperitoneal co-administration of AT-I and MK-8776 displays synergistic anti-melanoma effects in allograft mouse models. We hypothesize that AT-I synergizes the anti-melanoma effects of MK-8776 by inhibiting Cdk2 signaling. To prove this hypothesis, we propose:
1) to determine whether intragastric administration of AT-I synergizes the anti-melanoma effects of MK-8776 in xenograft mouse models;
2) to determine the contribution of inhibiting Cdk2 signaling in the anti-melanoma effects of the AT-I/MK-8776 combination in cell models;
3) to explore how Cdk2 is inhibited by the AT-I/MK-8776 combination; and
4) to determine whether the AT-I/MK-8776 combination exerts synergistic anti-melanoma effects and inhibits Cdk2 signaling in diverse melanoma cell lines.

This study will for the first time demonstrate the Cdk2 signaling-related anti-melanoma mechanisms of the AT-I/MK-8776 combination. Its success should facilitate the development of this combination as a novel modality for melanoma treatment.