Cancer Research: Sequential Targeting of Retinoblastoma and DNA Synthesis Pathways Is a Therapeutic Strategy for Sarcomas That Can Be Monitored in Real Time (Houghton)

m_canres_83_6_coverTuyen Duong;Thanh Nguyen; Yan Wang;  Tuyen N. Bui; Rossana Lazcano;  Davis R. Ingram;  Min Yi; Varshini Vakulabharanam; Linjie Luo; Marc A. Pina; Cansu Karakas ; Mi Li; Nicole M. Kettner; Neeta Somaiah; Peter J. Hougton; Osama Mawlawi; Alexander J. Lazar; Kelly K. Hunt; Khandan Keyomarsi

Treatment strategies with a strong scientific rationale based on specific biomarkers are needed to improve outcomes in patients with advanced sarcomas. Suppression of cell-cycle progression through reactivation of the tumor suppressor retinoblastoma (Rb) using CDK4/6 inhibitors is a potential avenue for novel targeted therapies in sarcomas that harbor intact Rb signaling. Here, we evaluated combination treatment strategies (sequential and concomitant) with the CDK4/6 inhibitor abemacicib to identify optimal combination strategies. Expression of Rb was examined in 1,043 sarcoma tumor specimens, and 50% were found to be Rb-positive. Using in vitro and in vivo models, an effective two-step sequential combination strategy was developed. Abemaciclib was used first to prime Rb-positive sarcoma cells to reversibly arrest in G1 phase. Upon drug removal, cells synchronously traversed to the S phase, where a second treatment with S-phase targeted agents (gemcitabine or Wee1 kinase inhibitor) mediated a synergistic response by inducing DNA damage. The response to treatment could be noninvasively monitored using real-time positron emission tomography imaging and serum thymidine kinase activity. Collectively, these results show that a novel, sequential treatment strategy with a CDK4/6 inhibitor followed by a DNA-damaging agent was effective, resulting in synergistic tumor cell killing. This approach can be readily translated into a clinical trial with noninvasive functional imaging and serum biomarkers as indicators of response and cell cycling.

Read Full Text

Article Categories: IF 10+, Research Paper