KLF4 defines the efficacy of the epidermal growth factor receptor inhibitor, erlotinib, in triple-negative breast cancer cells by repressing the EGFR gene.

BACKGROUND: Triple-negative breast cancer (TNBC) is characterized by high rates of recurrence and poor overall survival. This is due, in part, to a deficiency of targeted therapies, making it essential to identify therapeutically targetable driver pathways of this disease. While epidermal growth factor receptor (EGFR) is expressed in 60% of TNBCs and drives disease progression, attempts to inhibit EGFR in unselected TNBC patients have had a marginal impact on outcomes. Hence, we sought to identify the mechanisms that dictate EGFR expression and inhibitor response to provide a path for improving the utility of these drugs. In this regard, the majority of TNBCs express low levels of the transcription factor, Krüppel-like factor 4 (KLF4), while a small subset is associated with high expression. KLF4 and EGFR have also been reported to have opposing actions in TNBC. Thus, we tested whether KLF4 controls the expression of EGFR and cellular response to its pharmacological inhibition. METHODS: KLF4 was transiently overexpressed in MDA-MB-231 and MDA-MB-468 cells or silenced in MCF10A cells. Migration and invasion were assessed using modified Boyden chamber assays, and proliferation was measured by EdU incorporation. Candidate downstream targets of KLF4, including EGFR, were identified using reverse phase protein arrays of MDA-MB-231 cells following enforced KLF4 expression. The ability of KLF4 to suppress EGFR gene and protein expression and downstream signaling was assessed by RT-PCR and western blot, respectively. ChIP-PCR confirmed KLF4 binding to the EGFR promoter. Response to erlotinib in the context of KLF4 overexpression or silencing was assessed using cell number and dose-response curves. RESULTS: We report that KLF4 is a major determinant of EGFR expression and activity in TNBC cells. KLF4 represses transcription of the EGFR gene, leading to reduced levels of total EGFR, its activated/phosphorylated form (pEGFR), and its downstream signaling intermediates. Moreover, KLF4 suppression of EGFR is a necessary intermediary step for KLF4 to inhibit aggressive TNBC phenotypes. Most importantly, KLF4 dictates the sensitivity of TNBC cells to erlotinib, an FDA-approved inhibitor of EGFR. CONCLUSIONS: KLF4 is a major regulator of the efficacy of EGFR inhibitors in TNBC cells that may underlie the variable effectiveness of such drugs in patients.

LIN9 and NEK2 Are Core Regulators of Mitotic Fidelity That Can Be Therapeutically Targeted to Overcome Taxane Resistance.

A significant therapeutic challenge for patients with cancer is resistance to chemotherapies such as taxanes. Overexpression of LIN9, a transcriptional regulator of cell-cycle progression, occurs in 65% of patients with triple-negative breast cancer (TNBC), a disease commonly treated with these drugs. Here, we report that LIN9 is further elevated with acquisition of taxane resistance. Inhibiting LIN9 genetically or by suppressing its expression with a global BET inhibitor restored taxane sensitivity by inducing mitotic progression errors and apoptosis. While sustained LIN9 is necessary to maintain taxane resistance, there are no inhibitors that directly repress its function. Hence, we sought to discover a druggable downstream transcriptional target of LIN9. Using a computational approach, we identified NIMA-related kinase 2 (NEK2), a regulator of centrosome separation that is also elevated in taxane-resistant cells. High expression of NEK2 was predictive of low survival rates in patients who had residual disease following treatment with taxanes plus an anthracycline, suggesting a role for this kinase in modulating taxane sensitivity. Like LIN9, genetic or pharmacologic blockade of NEK2 activity in the presence of paclitaxel synergistically induced mitotic abnormalities in nearly 100% of cells and completely restored sensitivity to paclitaxel, in vitro. In addition, suppressing NEK2 activity with two distinct small molecules potentiated taxane response in multiple in vivo models of TNBC, including a patient-derived xenograft, without inducing toxicity. These data demonstrate that the LIN9/NEK2 pathway is a therapeutically targetable mediator of taxane resistance that can be leveraged to improve response to this core chemotherapy. SIGNIFICANCE: Resistance to chemotherapy is a major hurdle for treating patients with cancer. Combining NEK2 inhibitors with taxanes may be a viable approach for improving patient outcomes by enhancing mitotic defects induced by taxanes alone.