CDK4/6 Inhibitors Sensitize Rb-positive Sarcoma Cells to Wee1 Kinase Inhibition through Reversible Cell-Cycle Arrest

Abstract

Research into the biology of soft tissue sarcomas has uncovered very few effective treatment strategies that improve upon the current standard of care which usually involves surgery, radiation, and chemotherapy. Many patients with large (>5cm), high-grade sarcomas develop recurrence, and at that point have limited treatment options available. One challenge is the heterogeneity of genetic drivers of sarcomas, and many of these are not validated targets. Even when such genes are tractable targets, the rarity of each subtype of sarcoma makes advances in research slow. Here we describe the development of a synergistic combination treatment strategy that may be applicable in both soft tissue sarcomas as well as sarcomas of bone that takes advantage of targeting the cell cycle. We show that Rb-positive cell lines treated with the CDK4/6 inhibitor palbociclib reversibly arrest in the G1 phase of the cell cycle, and upon drug removal cells progress through the cell cycle as expected within 6–24 hours. Using a long-term high-throughput assay that allows us to examine drugs in different sequences or concurrently, we found that palbociclib-induced cell cycle arrest poises Rb-positive sarcoma cells (SK-LMS1 and HT-1080) to be more sensitive to agents that work preferentially in S-G2 phase such as doxorubicin and Wee1 kinase inhibitors (AZD1775). The synergy between palbociclib and AZD1775 was also validated in vivo using SK-LMS1 xenografts as well as Rb-positive patient-derived xenografts (PDX) developed from leiomyosarcoma patients. This work provides the necessary preclinical data in support of a clinical trial utilizing this treatment strategy.

Microtubules play an essential role in the survival of primary acute lymphoblastic leukemia cells advancing through G1 phase

“…For example, CDK4/6 inhibitors cooperate with PI3K inhibitors in breast cancer models [46] and sensitize pancreatic cancer cell lines to MEK and mTOR inhibitors [34,47]. Another study showed that RB-proficient sarcoma cells were sensitized to Wee1 kinase inhibition after prior transient treatment with PCB [48]. This novel sequential combination treatment exploited the reversibility of PCB to synchronize the cells thus maximizing the effects of the kinase inhibitor during the ensuing S and G2 phases.…”

Overcoming CDK4/6 inhibitor resistance in ER-positive breast cancer

“…For example, palbociclib treatment of melanoma cells for more than 3 days led to the induction of senescence in association with a decreased sensitivity to vemurafenib (Yoshida et al 2016). Likewise, Rb-expressing sarcoma cell lines with reversible palbociclib-induced cell cycle arrest were sensitive to co-treatment with the WEE1 kinase inhibitor AZD1775 (Francis et al 2017). Unfortunately, CDK4/6 inhibitor-induced senescence may also result in an undesirable outcome in the stroma through the promotion of a proinflammatory, senescence-associated secretory phenotype (SASP).…”

CDKs in Sarcoma: Mediators of Disease and Emerging Therapeutic Targets

“…Many of the studies demonstrated that monotherapy targeting specific CDKs induces a reversible cell cycle arrest, as expected. Some studies, however, revealed additional benefits of CDK inhibition including downregulation of other CDKs [200,201], decreased migration [141,202], and enhanced efficacy of other targeted agents [203,204]. Among the rationale combination therapies evaluated, THZ531, a CDK12 inhibitor, was found to synergize with PARP inhibitors to prevent DNA damage repair and induce tumor cell death in EwS, significantly diminishing the tumor growth in mouse xenograft and PDX models of the disease [205].…”