Combined CDK2 and CDK4/6 Inhibition Overcomes Palbociclib Resistance in Breast Cancer by Enhancing Senescence

Abstract

Breast cancer represents the number one global cancer burden in women and the hormone receptor (HR)-positive subtype comprises approximately 70% of breast cancers. Unfortunately, acquired resistance ultimately occurs in almost all cases, even though cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are a highly effective therapy for HR-positive/human epidermal growth factor receptor 2-negative subtype. Here, we investigated mechanisms of resistance to CDK4/6 inhibitor and potential therapeutic strategies using our palbociclib-resistant preclinical model. We observed that cyclin E was significantly overexpressed in palbociclib-resistant cells, and similar association was also confirmed in pleural effusion samples collected from HR-positive breast cancer patients. After confirmation of cyclin E-CDK2 interaction by co-immunoprecipitation, we demonstrated CDK2 inhibition combined with palbociclib synergistically suppressed proliferation of palbociclib-resistant cells and growth of palbociclib-resistant xenograft in mice. We also proved that enhancing C-MYC-mediated senescence is a novel mechanism behind the synergism created by targeting both CDK2 and CDK4/6. Furthermore, the clinical relevance of cyclin E as a therapeutic target was supported by significant association between CCNE1 overexpression and poor prognosis based on large-scale public gene expression data sets in HR-positive breast cancer patients. Therefore, we propose cyclin E-CDK2 signaling as a promising therapeutic target for overcoming cyclin E-associated resistance to CDK4/6 inhibitor.

Kinase drug discovery 20 years after imatinib: progress and future directions

“…114 ), resulting in less effective inhibition of CDK6 by these drugs. The upregulation of CDK2/cyclin E activity is another cause of resistance to palbociclib 115 , which can be suppressed by the combined use of CDK2 and CDK4/CDK6 inhibitors 116 .…”

Pharmacoinformatics and Preclinical Studies of NSC765690 and NSC765599, Potential STAT3/CDK2/4/6 Inhibitors with Antitumor Activities against NCI60 Human Tumor Cell Lines

“…These higher numbers of interactions undoubtedly contributed to the higher affinity that NSC765690 has for CDK2, CDK4, and CDK6 than do NSC765599 and palbociclib. Palbociclib has been actively applied in multiple preclinical models and was approved for targeting CDK4/6 as anticancer therapy for breast cancer; however, acquired resistance occurs in almost all cases [ 20 ]. Although docking STAT3 with a known inhibitor, SH-4-54, revealed a higher number of conventional H-bond and halogen bond interactions with STAT3, the pi interactions were fewer, and consequently, the overall binding affinity was less negative.…”

“…Therefore, since dysfunctional cell cycle regulation via oncogenic aberrations of CDKs is a hallmark of all human cancers [ 15 ], pharmacological targeting of CDKs will undoubtedly affect cancer proliferation and survival [ 16 , 17 ]. Hence, CDK inhibitors have been developed and evaluated; however, disappointingly, while first-generation inhibitors of CDK were non-selective and besieged with toxicity [ 18 , 19 ], second-generation CDK4/6 inhibitors, although showing promising outcomes, are plagued with acquired resistance, which develops in almost all cases [ 20 ] due to the activation of other oncogenic pathways, including c-Myc, signal transducer and activator of transcription 3 (STAT3), and phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathways [ 21 , 22 ].…”

Deregulated Immune Pathway Associated with Palbociclib Resistance in Preclinical Breast Cancer Models: Integrative Genomics and Transcriptomics

“…Regarding gene expression analyses associated with CDK4/6 inhibitor resistance, only CCNE1 (cyclin E) overexpression [ 42 ] and RB loss [ 43 , 44 ] were clinically confirmed in the literatures. In our resistant model, we also observed CCNE overexpression i.e., activation of cyclinE-CDK2 pathway and RB loss associated with palbociclib resistance [ 20 ]. Additionally, in search of other possible pathways that could be responsible for the development of resistance to CDK4/6 inhibitor, we analyzed genomics and transcriptomics of palbociclib-sensitive and resistant breast cancer cells.…”

“…The CDK4/6 inhibitor palbociclib was provided by Pfizer Inc. (North Peapack, NJ 07977, USA). Palbociclib-resistant cells, indicated as MCF7-PR and T47D-PR, were generated from MCF7 and T47D cells by treating with palbociclib for approximately 9 months in a stepwise dose escalating fashion as described previously [ 20 ] ( Figure 1 A). Resistant cells gained a more than 10-fold higher half-maximal inhibitory concentration (IC 50 ) than their parental counterparts: 7.15 μM in MCF7-PR vs. 0.75 μM in MCF7 and 3.37 μM in T47D-PR vs. 0.26 μM in T47D-PR.…”