Preclinical rationale for combined use of endocrine therapy and 5-fluorouracil but neither doxorubicin nor paclitaxel in the treatment of endocrine-responsive breast cancer

Tamoxifen resistance alters sensitivity to 5-fluorouracil in a subset of estrogen receptor-positive breast cancer

Sequential treatment with endocrine or chemotherapy is generally used in the treatment of estrogen receptor (ER)-positive recurrent breast cancer. To date, few studies have investigated the effect of long-term endocrine therapy on the response to subsequent chemotherapy in ER-positive breast cancer. We examined whether a preceding endocrine therapy affects the sensitivity to subsequent chemotherapy in ER-positive breast cancer cells. Three ER-positive breast cancer cell lines (T47D, MCF7, BT474) and tamoxifen-resistant sublines (T47D/T, MCF7/T, BT474/T) were analyzed for sensitivity to 5-fluorouracil, paclitaxel, and doxorubicin. The mRNA levels of factors related to drug sensitivity were analyzed by RT-PCR. MCF7/T cells became more sensitive to 5-fluorouracil than wild-type (wt)-MCF7 cells. In addition, the apoptosis induced by 5-fluorouracil was significantly increased in MCF7/T cells. However, no difference in sensitivity to chemotherapeutic agents was observed in T47D/T and BT474/T cells compared with their wt cells. Dihydropyrimidine dehydrogenase (DPYD) mRNA expression was significantly decreased in MCF7/T cells compared with wt-MCF7 cells. The expression of DPYD mRNA was restored with 5-azacytidine treatment in MCF7/T cells. In addition, DPYD 3'-UTR luciferase activity was significantly reduced in MCF7/T cells. These data indicated that the expression of DPYD mRNA was repressed by methylation of the DPYD promoter region and post-transcriptional regulation by miRNA in MCF7/T cells. In the mouse xenograft model, capecitabine significantly reduced the tumor volume in MCF7/T compared with MCF7. The results of this study indicate that endocrine therapy could alter the sensitivity to chemotherapeutic agents in a subset of breast cancers, and 5-fluorouracil may be effective in tamoxifen-resistant breast cancers.

Estrogen Down-regulator Fulvestrant Potentiates Antitumor Activity of Fluoropyrimidine in Estrogen-responsive MCF-7 Human Breast Cancer Cells

BACKGROUND

Endocrine therapy is clinically administered in hormone-responsive breast cancer. Combinations of fluoropyrimidine S-1 and an aromatase inhibitor or anti-estrogen are considered beneficial in Japan. Herein we assessed new combinations of S-1 and fulvestrant.

PATIENTS AND METHODS

Cytotoxicity of fulvestrant and 5-fluorouracil (5-FU) was assessed in hormone-responsive (MCF-7) and non-responsive (MDA-MB-231) breast cancer cell cultures. Fulvestrant and S-1 were evaluated for antitumor activity in mice and their effects on estrogen receptor (ER)-α and progesterone receptor (PgR) levels in MCF-7 xenografts using immunohistochemical methods.

RESULTS

Fulvestrant inhibited growth of MCF-7, but not of MDA-MB-231 xenografts. Combinations of 5-FU and fulvestrant were superior to monotherapy in vitro. In vivo antitumor activity of S-1/fulvestrant combination therapy was significantly (p<0.05) enhanced compared to that of both monotherapies. Fulvestrant partially down-regulated expression of ERα and PgR, but in combination with S-1, it almost completely blocked their expression.

CONCLUSION

Chemo-endocrine combination therapy using S-1 and fulvestrant is beneficial in estrogen-responsive breast cancer.

Tamoxifen suppresses paclitaxel-, vincristine-, and bortezomib-induced neuropathy via inhibition of the protein kinase C/extracellular signal-regulated kinase pathway

Chemotherapy-induced neuropathy is a highly problematic, dose-limiting effect of potentially curative regimens of cancer chemotherapy. When neuropathic pain is severe, patients often either switch to less-effective chemotherapy agents or choose to discontinue chemotherapy entirely. Conventional chemotherapy drugs used to treat lung and breast cancer, multiple myeloma, and lymphoma include paclitaxel, vincristine, and bortezomib. Approximately 68% of patients receiving these anticancer drugs develop neuropathy within the first month of treatment, and while strategies to prevent chemotherapy-induced neuropathy have been investigated, none have yet been proven as effective. Recent reports suggest that chemotherapy-induced neuropathy is associated with signal transduction molecules, including protein kinase C and mitogen-activated protein kinases. It is currently unclear whether protein kinase C inhibition can prevent chemotherapy-induced neuropathy. In this study, we found that tamoxifen, a protein kinase C inhibitor, suppressed paclitaxel-, vincristine-, and bortezomib-induced cold and mechanical allodynia in mice. In addition, chemotherapy drugs induce neuropathy via the protein kinase C/extracellular signal-regulated kinase pathway in the spinal cord in lumbar segments 4-6 and dorsal root ganglions. In addition, tamoxifen was shown to act synergistically with paclitaxel to inhibit tumor-growth in mice injected with tumor cells. Our results indicated that paclitaxel-, vincristine-, and bortezomib-induced neuropathies were associated with the protein kinase C/extracellular signal-regulated kinase pathway in the lumbar spinal cord and dorsal root ganglions, which suggest that protein kinase C inhibitors may be therapeutically effective for the prevention of chemotherapy-induced neuropathy when administered with standard chemotherapy agents.

Differential Expression Patterns of Eph Receptors and Ephrin Ligands in Human Cancers

Eph receptors constitute the largest family of receptor tyrosine kinases, which are activated by ephrin ligands that either are anchored to the membrane or contain a transmembrane domain. These molecules play important roles in the development of multicellular organisms, and the physiological functions of these receptor-ligand pairs have been extensively documented in axon guidance, neuronal development, vascular patterning, and inflammation during tissue injury. The recognition that aberrant regulation and expression of these molecules lead to alterations in proliferative, migratory, and invasive potential of a variety of human cancers has made them potential targets for cancer therapeutics. We present here the involvement of Eph receptors and ephrin ligands in lung carcinoma, breast carcinoma, prostate carcinoma, colorectal carcinoma, glioblastoma, and medulloblastoma. The aberrations in their abundances are described in the context of multiple signaling pathways, and differential expression is suggested as the mechanism underlying tumorigenesis.

Antitumor and anticancer stem cell activities of eribulin mesylate and antiestrogens in breast cancer cells

BACKGROUND

Eribulin mesylate (eribulin), a non-taxane microtubule dynamic inhibitor, has been widely used in the treatment of patients with advanced or metastatic breast cancer. The combined antitumor and anticancer stem cell (CSC) activities of eribulin with endocrine therapeutic agents have not yet been examined in breast cancer cells. We herein investigated the combined effects of eribulin and antiestrogens.

METHODS

A panel of eight breast cancer cell lines, including five estrogen receptor (ER)-positive and three ER-negative cell lines, was used. These cells were treated with eribulin and/or the antiestrogen, 4-hydroxytamoxifen or fulvestrant. Their growth inhibitory activities and effects on cell cycle progression, apoptosis, and the CSC population were investigated. CSCs were detected using the CD44/CD24/EpCAM, Aldefluor, and mammosphere assays.

RESULTS

The 50% growth inhibitory concentrations of eribulin were 0.38-2.64 nM for the eight cell lines tested. Eribulin exhibited significant antitumor activity under estrogen-supplemented conditions in ER-positive breast cancer cells. The combined antitumor activity of eribulin with an antiestrogen was evaluated using the combination index. The combination index was 0.43-1.46 for ER-positive cell lines. The additive antitumor effect of eribulin with 4-OHT was only significant in MCF-7 cells. Eribulin induced the accumulation of G2/M and apoptosis, while antiestrogens induced the retardation of G1-S cell cycle and apoptosis, respectively. Estrogen markedly increased the proportion of CSCs, whereas antiestrogens inhibited increases in ER-positive cell lines. Moreover, eribulin decreased the proportion of CSCs in either ER-positive or ER-negative cell lines. The combined treatment of eribulin with an antiestrogen did not additively decrease the proportion of CSCs in ER-positive cell lines.

DISCUSSION

The results of the present study demonstrated that eribulin had potent antitumor effects on estrogen-stimulated ER-positive breast cancer cells and the combined treatment of eribulin with an antiestrogen resulted in a weakly additive antitumor effect. We herein suggested for the first time that eribulin exhibited anti-CSC effects on either ER-positive or ER-negative breast cancer cells.

Evidence produced in Japan: tegafur-based preparations for postoperative chemotherapy in breast cancer

Oral fluoropyrimidine anticancer agents (oral 5-fluorouracil [5-FU]) able to be used as chemotherapy for breast cancer include tegafur–uracil (UFT), tegafur–gimeracil–oteracil potassium (S-1), doxifluridine, and capecitabine. Since the 1980s, UFT has been most widely used for postoperative chemotherapy in breast cancer. UFT is an oral preparation that was designed to achieve and maintain high concentrations of 5-FU in plasma by combining tegafur, a prodrug of 5-FU, with uracil. UFT is characterized by mild adverse events, allowing long-term treatment. The prolonged maintenance of high plasma 5-FU concentrations has been suggested to inhibit micrometastases after surgery. Recently, large clinical trials conducted in Japan have shown that UFT-based postoperative chemotherapy is therapeutically useful in patients with node-negative (n0), high-risk breast cancer. We review the results of clinical trials of postoperative chemotherapy with UFT in Japan and discuss its roles and future prospects.

Oral fluoropyrimidine may augment the efficacy of aromatase inhibitor via the down-regulation of estrogen receptor in estrogen-responsive breast cancer xenografts

The present preclinical study was designed to evaluate a new combination therapy comprised of the aromatase inhibitor anastrozole (ANA) and the oral fluoropyrimidines, UFT and S-1 against the estrogen receptor (ER)-positive human breast cancer cell line MCF-7/Arom 14, which was stably transfected with the cDNA of human aromatase. MCF-7/Arom 14 cells showed a high aromatase activity and notably were able to grow in the presence of testosterone and estradiol (E(2)) in vitro. ANA and 5-fluorouracil (5-FU) inhibited cell growth at concentrations of 0.005-10 and 0.2-5 μM, respectively, and the combination of both drugs additively inhibited cell growth. The growth of MCF-7/Arom 14 tumors was significantly inhibited by ANA and S-1 or UFT in vivo. The combination of ANA with S-1 or UFT administered using a 21-day consecutive, metronomic-like regimen significantly enhanced the antitumor efficacy, suppressing tumor growth for 2-4 times longer than monotherapy. To investigate the mechanisms by which S-1 enhances the antitumor activity of ANA, the protein and mRNA expression levels of ER-α in tumor tissue after treatment with S-1, ANA, and the typical chemotherapeutic agents doxorubicin (ADM) or paclitaxel (TXL) were analyzed. The protein and mRNA expression levels of ER-α in the tumor tissue were markedly decreased after treatment with S-1 or S-1 + ANA, but not after treatment with either ADM or TXL. The reduced ER-α level after S-1 treatment might contribute to the increased antitumor activity of ANA by reducing ER-α-induced growth signaling in addition to the decrease in estrogen production induced by ANA. Based on these results, the combination of ANA and S-1 might yield a greater benefit than other chemotherapeutic agents in postmenopausal women with ER-positive breast cancer.