Project description:Triple-Negative Breast Cancer (TNBC) has a poor prognosis and adverse clinical outcomes among all breast cancer subtypes as there is no available targeted therapy. Overexpression of Enhancer of zeste homolog 2 (EZH2) has been shown to correlate with TNBC's poor prognosis, but the contribution of EZH2 catalytic (H3K27me3) versus non-catalytic EZH2 (NC-EZH2) function in TNBC progression remains elusive. We reveal that selective hyper-activation of functional EZH2 (H3K27me3) over NC-EZH2 alters TNBC metastatic landscape and fosters its peritoneal metastasis, particularly splenic. Instead of H3K27me3-mediated repression of gene expression; here, it promotes KRT14 transcription by attenuating binding of repressor Sp1 to its promoter. Further, KRT14 loss significantly reduces TNBC migration, invasion, and peritoneal metastasis. Consistently, human TNBC metastasis displays positive correlation between H3K27me3 and KRT14 levels. Finally, EZH2 knockdown or H3K27me3 inhibition by EPZ6438 reduces TNBC peritoneal metastasis. Altogether, our preclinical findings suggest a rationale for targeting TNBC with EZH2 inhibitors.
Project description:Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer, associated with poor response to therapies and high mortality. We identify that phosphodiesterase 7A (PDE7A) is overexpressed in the majority of TNBC, and a higher level of PDE7A associates with poor prognosis. The PI3K/AKT pathway, via the transcription factor IRF1, stimulates the expression of PDE7A in TNBC cells. PDE7A inhibition attenuates TNBC growth in both cell culture and mouse models of TNBC. Inhibition of PDE7A suppresses de novo pyrimidine biosynthesis, in part through the downregulation of the enzyme dihydroorotate dehydrogenase (DHODH). DHODH suppression attenuates TNBC tumor growth, mirroring the effects of PDE7A inhibition, and ectopic DHODH expression rescues PDE7A-inhibition-induced tumor suppression. Pharmacological co-targeting of PDE7A and DHODH potently inhibits TNBC tumor growth and metastasis. These findings identify the PDE7A→ DHODH→ de novo pyrimidine biosynthesis pathway as a key driver of TNBC, offering additional therapeutic opportunities for TNBC patients.
Project description:Triple-negative breast cancer (TNBC) is the breast cancer (BC) subtype with the poorest outcome. The PIM family of kinases has recently emerged as a factor that is both overexpressed in TNBC samples and associated with poor outcomes. Preclinical data suggest that TNBC that exhibits an elevated MYC oncoprotein expression (MYC+TNBC), accounting for 50% of TNBC cases, is sensitive to PIM inhibition. However, ongoing clinical observations indicate that the efficacy of PIM inhibitors as single agents may be limited in solid tumors, suggesting the need for combination therapies. We conducted drug combination screens to identify a combination that targets PIM and the 20S proteasome (the PIMi/20Si combination) as the most synergistic combination. Following the screening, we used a chemical genetic approach to reveal that the mechanisms of drug synergy involve disruption of protein homeostasis and obstruction of an adaptive resistance mechanism associated with proteasome inhibition. Thus, the PIMi/20Si combination could represent a rational combination therapy against MYC+ TNBC that is readily translatable to early-stage clinical investigations.
Project description:We profiled gene expression and splicing changes in HCC1806 human TNBC cells overexpressing three splicing factor genes (SRSF2-SRSF3-SRSF7), all three splicing factors (called 3xSR) or MYC. We performed RNA-seq, in triplicate on 3xSR, MYC-OE, triple plasmid control, SRFS2, SRSF3, SRSF7, or single plasmid control HCC1806 cells.
Project description:The MYC oncogene is frequently amplified in triple negative breast cancer (TNBC). Here, we show that MYC suppression induces immune-related hallmark gene set signatures and tumor infiltrating T cells in MYC-hyperactivated TNBCs. Mechanistically, MYC repressed stimulator of interferon genes (STING) expression via direct binding to the STING enhancer region, resulting in downregulation of the T cell chemokines CCL5, CXCL10 and CXCL11. In primary and metastatic TNBC cohorts, tumors with high MYC expression or activity exhibited low STING expression. Using a CRISPR-mediated enhancer perturbation approach, we demonstrated that MYC-driven immune evasion is mediated by STING repression. STING repression induced resistance to PD-L1 blockade in mouse models of TNBC. Finally, a small molecule inhibitor of MYC combined with PD-L1 blockade elicited a durable response in immune-cold TNBC with high MYC levels, suggesting a strategy to restore PD-L1 inhibitor sensitivity in MYC-overexpressing TNBC.
Project description:The MYC oncogene is frequently amplified in triple negative breast cancer (TNBC). Here, we show that MYC suppression induces immune-related hallmark gene set signatures and tumor infiltrating T cells in MYC-hyperactivated TNBCs. Mechanistically, MYC repressed stimulator of interferon genes (STING) expression via direct binding to the STING enhancer region, resulting in downregulation of the T cell chemokines CCL5, CXCL10 and CXCL11. In primary and metastatic TNBC cohorts, tumors with high MYC expression or activity exhibited low STING expression. Using a CRISPR-mediated enhancer perturbation approach, we demonstrated that MYC-driven immune evasion is mediated by STING repression. STING repression induced resistance to PD-L1 blockade in mouse models of TNBC. Finally, a small molecule inhibitor of MYC combined with PD-L1 blockade elicited a durable response in immune-cold TNBC with high MYC levels, suggesting a strategy to restore PD-L1 inhibitor sensitivity in MYC-overexpressing TNBC.
Project description:Efforts to therapeutically target EZH2 have generally focused on inhibition of its methyltransferase activity, although it remains less clear whether this is the central mechanism whereby EZH2 promotes cancer. We demonstrate that EZH2 directly interacts with both MYC family oncoproteins, MYC and MYCN, and promotes their stabilization in a methyltransferase-independent manner. By competing against the SCFFBW7 ubiquitin ligase to bind MYC and MYCN, EZH2 counteracted FBW7-mediated MYC(N) polyubiquitination and proteasomal degradation. Depletion, but not enzymatic inhibition, of EZH2 induced robust MYC(N) degradation and inhibited tumor cell growth in MYC(N) driven neuroblastoma and small cell lung cancer. These findings unveil the MYC family proteins as global EZH2 oncogenic effectors and EZH2 pharmacologic degraders as potential MYC(N) targeted cancer therapeutics, pointing out that MYC(N) driven cancers may develop inherent resistance to the canonical EZH2 enzymatic inhibitors currently in clinical development.