Destabilization of β-catenin and RAS by targeting the Wnt/β-catenin pathway as a potential treatment for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a severe and heterogeneous disease that lacks an approved targeted therapy and has a poor clinical outcome to chemotherapy. Although the RAS-ERK signaling axis is rarely mutated in TNBC, ~50% of TNBCs show an increased copy number and overexpression of epidermal growth factor receptor (EGFR). However, EGFR-targeted therapies have offered no improvement in patient survival, underscoring the need to explore downstream targets, including RAS. We found that both β-catenin and RAS, as well as epidermal growth factor receptor (EGFR), are overexpressed and correlated with one another in tumor tissues of TNBC patients. KYA1797K, an Axin-binding small molecule reducing β-catenin and RAS expression via degradation and suppressing EGFR expression via transcriptional repression, inhibited the proliferation and the metastatic capability of stable cell lines as well as patient-derived cells (PDCs) established from TNBC patient tissues. KYA1797K also suppressed the stemness of 3D-cultured PDCs and xenografted tumors established by using residual tumors from TNBC patients and those established by the TNBC cell line. Targeting both the Wnt/β-catenin and RAS-ERK pathways via small molecules simultaneously reducing the levels of β-catenin, RAS, and EGFR could be a potential therapeutic approach for TNBC.

The triple-negative breast cancer (TNBC), a highly aggressive form of breast cancer may be susceptible to drug therapy that targets two critical signaling pathways, one that governs cell fate and the other that controls the cell cycle. Researchers from Yonsei University in Seoul, South Korea, had previously synthesized a small-molecule called KYA1797K and found that could lower levels of the proteins, β-catenin (a master regulator of cell fate decisions) and RAS (which controls cell division), in colorectal cancer cells. Now, Kang-Yell Choi, Soonmyung Paik, and colleagues have shown that KYA1797K has the same effects on β-catenin and RAS levels in cells taken from patients with TNBC. In cell lines and mouse models, KY1797K suppressed the proliferation and metastatic capability of TNBC, highlighting the therapeutic potential of this strategy degrading both β-catenin and RAS.

Ixabepilone alone or with cetuximab as first-line treatment for advanced/metastatic triple-negative breast cancer

BACKGROUND

Despite high initial sensitivity to chemotherapy, TNBC is associated with a poor prognosis, highlighting the need for novel therapeutic strategies. The aim of this multicenter, randomized, open-label phase II trial was to assess the efficacy of ixabepilone as monotherapy, and the combination of ixabepilone with cetuximab, as first-line treatment in patients with triple-negative locally advanced nonresectable and/or metastatic breast cancer.

PATIENTS AND METHODS

Women were randomly assigned to receive either ixabepilone (40 mg/m(2)) every 21 days (n = 40), or ixabepilone (40 mg/m(2)) every 21 days with cetuximab (400 mg/m(2) loading dose, followed by 250 mg/m(2)) once weekly (n = 39). The primary end point of the trial was to estimate the response rates of ixabepilone monotherapy and ixabepilone with cetuximab combination therapy.

RESULTS

Of 79 randomized patients, 77 were treated. Based on an intent-to-treat analysis, an objective response rate of 30% (95% confidence interval [CI], 16.6-46.5) was observed in the monotherapy arm, and 35.9% (95% CI, 21.2-52.8) in the combination arm. Median progression-free survival was 4.1 months in both treatment groups. Safety findings were consistent with the known individual toxicity profiles of ixabepilone and cetuximab. Skin and subcutaneous tissue disorders were more common with combination therapy, as were discontinuations because of adverse events.

CONCLUSION

Ixabepilone monotherapy and the ixabepilone and cetuximab combination demonstrated similar levels of clinical activity in first-line treatment of advanced TNBC, with a predictable safety profile. Further investigation of novel therapies for TNBC is required to improve patient outcomes.

The paradox of triple negative breast cancer: novel approaches to treatment

Breast cancer that lacks expression of estrogen/progesterone receptors and overexpression of the human epidermal growth factor receptor2 (HER2), i.e. triple-negative breast cancer (TNBC), is not amenable to current targeted therapies and carries a poor prognosis. This review discusses the natural history of TNBC and published literature in the relevant treatment landscape, with a focus on newer therapies. Compared with other subtypes of breast cancer, TN tumors have higher response rates to neoadjuvant chemotherapy; however, this advantage is not clearly translated into the metastatic setting and has not improved these patients' overall survival. Numerous cytotoxic and targeted strategies have demonstrated efficacy or are under investigation. Strategies showing promise in this difficult-to-treat group of patients include cytotoxic therapy with platinum-containing agents, ixabepilone, and novel targeted approaches such as poly(ADP-ribose) polymerase inhibitors.

Management options in triple-negative breast cancer

Notorious for its poor prognosis and aggressive nature, triple-negative breast cancer (TNBC) is a heterogeneous disease entity. The nature of its biological specificity, which is similar to basal-like cancers, tumors arising in BRCA1 mutation carriers, and claudin-low cancers, is currently being explored in hopes of finding the targets for novel biologics and chemotherapeutic agents. In this review, we aim to give a broad overview of the disease's nomenclature and epidemiology, as well as the basic mechanisms of emerging targeted therapies and their performance in clinical trials to date.

Triple-negative breast cancer: disease entity or title of convenience?

This Review outlines the understanding and management of triple-negative breast cancer (TNBC). TNBC shares morphological and genetic abnormalities with basal-like breast cancer (BLBC), a subgroup of breast cancer defined by gene-expression profiling. However, TNBC and BLBC tumors are heterogeneous and overlap is incomplete. Breast cancers found in BRCA1 mutation carriers are also frequently triple negative and basal like. TNBC and BLBC occur most frequently in young women, especially African Americans, and tend to exhibit aggressive, metastatic behavior. These tumors respond to conventional chemotherapy but relapse more frequently than hormone receptor-positive, luminal subtypes and have a worse prognosis. New systemic therapies are urgently needed as most patients with TNBC and/or BLBC relapse with distant metastases, and hormonal therapies and HER2-targeted agents are ineffective in this group of tumors. Poly (ADP-ribose) polymerase inhibitors, angiogenesis inhibitors, EGFR-targeted agents, and src kinase and mTOR inhibitors are among the therapeutic agents being actively investigated in clinical trials in patients with TNBC and/or BRCA1-associated tumors. Increased understanding of the genetic abnormalities involved in the pathogenesis of TNBC, BLBC and BRCA1-associated tumors is opening up new therapeutic possibilities for these hard-to-treat breast cancers.