Molecular markers of therapeutic resistance in breast cancer

Summary

Resistance to chemotherapy and endocrine therapy is a serious obstacle in the treatment of breast cancer. Highly specific biomarkers for predicting therapeutic resistance have not yet been identified. In this study, the amounts of aldehyde dehydrogenase 1, cleaved caspase 3, cyclooxygenase 2, phosphorylated Akt, Ki-67, and H2AX proteins were measured by immunohistochemical staining in 113 breast cancer tissues, and their predictive ability for therapeutic resistance was investigated. The patients were receiving chemotherapy (n = 30), endocrine therapy (n = 22), or combined chemotherapy and endocrine therapy (n = 61). Expression of aldehyde dehydrogenase 1, cleaved caspase 3, and cyclooxygenase 2 correlated significantly with a higher relapse rate (P < .05 or P < .01) and shorter survival (P < .01 or P < .001) in triple-negative patients receiving chemotherapy. In addition, cyclooxygenase 2 expression was an independent predictor of a poor prognosis (P < .05). On the other hand, aldehyde dehydrogenase 1 expression correlated significantly with shorter survival in patients receiving combined therapy (P < .01) but showed no association with relapse. No correlation was observed between Ki-67, phosphorylated Akt, and H2AX expression and survival or relapse in any group of patients. These data suggest that aldehyde dehydrogenase 1, cleaved caspase 3, and cyclooxygenase 2 are useful markers for therapeutic resistance in breast cancer.

Introduction

Despite numerous advances in prevention, surgical technology, and various therapies for breast cancer (BC), an estimated 450 000 patients die from the disease annually [1], [2]. The survival rate differs greatly depending on cancer type, disease stage, and treatment. Overall, the 5-year survival rate is approximately 84% in the Western world [3] but much lower in developing countries.

BC usually is treated with surgery followed by chemotherapy, radiotherapy, or hormone therapy according to its clinical features and risk of recurrence. For example, the presence of estrogen and progesterone receptors on the cancer cells is an important index for hormone treatments because cancer cells that lack such receptors usually are unresponsive to such therapy [4]. Chemotherapy can be given before surgery (neoadjuvant therapy) or after surgery (adjuvant therapy) [5]. Despite the early efficacy of both chemotherapy and endocrine therapy, BCs may recur and form metastases. Therapeutic resistance is one of the major hurdles to successful treatment. It is widely accepted that therapeutic resistance is caused by a series of complex molecular events that include decreased intracellular drug concentrations mediated by drug transporters and metabolic enzymes; impaired cellular responses that affect cell cycle arrest, apoptosis, and DNA repair; and the induction of signaling pathways that promote the progression of cancer cell populations [6]. In addition, the observation that targeting any single molecule is ineffective against chemotherapy-resistant BC suggests that multiple molecular pathways may be responsible for this resistance [7], [8].

Identification of biological markers able to predict the sensitivity of BC cells to chemotherapy or endocrine therapy is important for making treatment decisions because patients with poor tumor sensitivity require more aggressive treatment. A recent study demonstrated that aldehyde dehydrogenase 1 (ALDH1) expression was associated with shorter survival and a poor clinical response to neoadjuvant chemotherapy but had no effect on the outcome of hormone receptor–positive BC [8], [9]. However, the predictive role of ALDH1 in adjuvant chemotherapy of BC has rarely been reported, especially in patients receiving combined endocrine therapy and chemotherapy. Cyclooxygenase 2 (Cox-2) is involved in drug and endocrine resistance in BC [10], [11], [12]. The chemoresistance role of Ki-67 [13] and phosphorylated Akt (p-Akt) [14] has been found only in cultured BC cells, although Akt has been widely demonstrated to be involved in endocrine resistance [15], [16]. Our recent studies suggest that cleaved caspase 3 (CC3) is also a proliferation and differentiation factor in cancer cells [17]. Activated caspase 3 exerts its role through activating calcium-independent phospholipase A2 and arachidonic acid production by paracrine signaling. Arachidonic acid is the chemical precursor of prostaglandin E2, a key regulator of tumor growth. However, the role of CC3 in drug and endocrine resistance has not been reported in BC.

We collected 113 breast cancer samples and categorized them into chemotherapy alone, endocrine therapy alone, or combined therapy (chemotherapy and endocrine therapy) groups. The correlation of CC3, ALDH1, Ki-67, p-Akt, Cox-2, and H2AX protein expression with overall survival and relapse rate was analyzed in each group.