Repurposing mebendazole against triple-negative breast cancer CNS metastasis.

PURPOSE: Triple-negative breast cancer (TNBC) often metastasizes to the central nervous system (CNS) and has the highest propensity among breast cancer subtypes to develop leptomeningeal disease (LMD). LMD is a spread of cancer into leptomeningeal space that speeds up the disease progression and severely aggravates the prognosis. LMD has limited treatment options. We sought to test whether the common anti-helminthic drug mebendazole (MBZ) may be effective against murine TNBC LMD. METHODS: A small-molecule screen involving TNBC cell lines identified benzimidazoles as potential therapeutic agents for further study. In vitro migration assays were used to evaluate cell migration capacity and the effect of MBZ. For in vivo testing, CNS metastasis was introduced into BALB/c athymic nude mice through internal carotid artery injections of brain-tropic MDA-MB-231-BR or MCF7-BR cells. Tumor growth and spread was monitored by bioluminescence imaging and immunohistochemistry. MBZ was given orally at 50 and 100 mg/kg doses. MBZ bioavailability was assayed by mass spectrometry. RESULTS: Bioinformatic analysis and migration assays revealed higher migratory capacity of TNBC compared to other breast cancer subtypes. MBZ effectively slowed down migration of TNBC cell line MDA-MB-231 and its brain tropic derivative MDA-MB-231-BR. In animal studies, MBZ reduced leptomeningeal spread, and extended survival in brain metastasis model produced by MDA-MB-231-BR cells. MBZ did not have an effect in the non-migratory MCF7-BR model. CONCLUSIONS: We demonstrated that MBZ is a safe and effective oral agent in an animal model of TNBC CNS metastasis. Our findings are concordant with previous efforts involving MBZ and CNS pathology and support the drug's potential utility to slow down leptomeningeal spread.

Repurposing mebendazole against triple-negative breast cancer leptomeningeal disease.

Purpose: Triple-negative breast cancer (TNBC) is an aggressive subtype that often metastasizes to the brain. Leptomeningeal disease (LMD), a devastating brain metastasis common in TNBC, has limited treatment options. We sought to test whether the common anti-helminthic drug mebendazole (MBZ) may be effective against murine TNBC LMD. Methods: A small-molecule screen involving TNBC cell lines identified benzimidazoles as potential therapeutic agents for further study. In vitro migration assays were used to evaluate cell migration capacity and the effect of MBZ. For in vivo testing, LMD was introduced into BALB/c athymic nude mice through internal carotid artery injections of brain-tropic MDA-MB-231-BR or MCF7-BR cells. Tumor growth and spread was monitored by bioluminescence imaging. MBZ was given orally at 50 and 100 mg/kg doses. MBZ bioavailability was assayed by mass spectrometry. Results: Bioinformatic analysis and migration assays revealed higher migratory capacity of TNBC compared to other breast cancer subtypes. MBZ effectively slowed down migration of TNBC cell line MDA-MB-231 and its brain tropic derivative MDA-MB-231-BR. In animal studies, MBZ reduced tumor growth and extended survival in the LMD model produced by MDA-MB-231-BR cells. MBZ did not have an effect in the non-migratory MCF7-BR model. Conclusions: We demonstrated that MBZ is a safe and effective oral agent in an animal model of TNBC LMD. Our findings are concordant with previous efforts involving MBZ and central nervous system pathology and further support the drug's potential utility as an alternative therapeutic for TNBC LMD.

Silver nanoparticles selectively treat triple-negative breast cancer cells without affecting non-malignant breast epithelial cells in vitro and in vivo.

Silver nanoparticles (AgNPs) show promise for treatment of aggressive cancers including triple-negative breast cancer (TNBC) in preclinical cancer models. For clinical development of AgNP-based therapeutics, it will be necessary to clearly define the specific physicochemical features of the nanoparticles that will be used, and to tie these properties to biological outcomes. To fill this knowledge gap, we performed thorough structure/function, mechanistic, safety, and efficacy studies to assess the potential for AgNPs to treat TNBC. We establish that AgNPs, regardless of size, shape, or stabilizing agent, are highly cytotoxic to TNBC cells at doses that are not cytotoxic to non-malignant breast epithelial cells. In contrast, TNBC cells and non-malignant breast epithelial cells are similarly sensitive to exposure to silver cation (Ag+), indicating that the nanoparticle formulation is essential for the TNBC-specific cytotoxicity. Mechanistically, AgNPs are internalized by both TNBC and non-malignant breast cells, but are rapidly degraded only in TNBC cells. Exposure to AgNPs depletes cellular antioxidants and causes endoplasmic reticulum stress in TNBC cells without causing similar damage in non-malignant breast epithelial cells. AgNPs also cause extensive DNA damage in 3D TNBC tumor nodules in vitro, but do not disrupt the normal architecture of breast acini in 3D cell culture, nor cause DNA damage or induce apoptosis in these structures. Lastly, we show that systemically administered AgNPs are effective at non-toxic doses for reducing the growth of TNBC tumor xenografts in mice. This work provides a rationale for development of AgNPs as a safe and specific TNBC treatment.

Correcting errors in the BRCA1 warning system.

Given its important role in human health and disease, remarkably little is known about the full-length three-dimensional (3D) molecular architecture of the breast cancer type 1 susceptibility protein (BRCA1), or its mechanisms to engage the tumor suppressor, TP53 (p53). Here, we show how a prevalent cancer-related mutation in the C-terminal region of the full-length protein, BRCA15382insC, affects its structural properties, yet can be biochemically corrected to restore its functional capacity. As a downstream consequence of restoring the ubiquitin ligase activity of mutated BRCA15382insC, the DNA repair response of p53 was enhanced in cellular extracts naturally deficient in BRCA1 protein expression. Complementary structural insights of p53 tetramers bound to DNA in different stage of the repair process support these biochemical findings in the context of human cancer cells. Equally important, we show how this knowledge can be used to lower the viability of breast cancer cells by modulating the stability of the BRCA1 protein and its associated players.

BRCA1: Beyond double-strand break repair.

Since its discovery, the BRCA1 tumor suppressor has been shown to play a role in multiple DNA damage response pathways. Here, we will review the involvement of BRCA1 in base-excision DNA repair and highlight its clinical implications.

BRCA1: a movement toward cancer prevention.

Breast cancer susceptibility gene 1 (BRCA1) was first identified in 1994 and has since been shown to encode a tumor suppressor protein that maintains genetic stability through DNA damage response pathways. Carriers of mutations in BRCA1 are predisposed to breast and ovarian cancer; however, their cancers lack the targets for existing anticancer drugs. We describe a novel chemoprevention approach that uses DNA repair-activating agents to enhance the repair of oxidative DNA damage and, in turn, prevent tumorigenesis in the presence of mutant BRCA1.

Therapeutic targeting of BRCA1-mutated breast cancers with agents that activate DNA repair.

Cancers due to germline mutations in the BRCA1 gene tend to lack targets for approved chemoprevention agents. This study aimed at a targeted chemoprevention strategy for BRCA1-associated malignancies. Mutant BRCA1 limits the base-excision DNA repair activity that addresses oxidative DNA damage, the accumulation of which heightens one's risk for cancer. Therefore, we conducted a high-throughput chemical screen to identify drug candidates that could attenuate the inhibitory effects of mutant BRCA1 on this repair activity, thereby describing a new class of DNA repair-activating chemopreventive agents. In the screen design, such drugs functioned by enhancing base-excision DNA repair of oxidative DNA damage in the presence of mutant BRCA1, with minimal cytotoxicity. We identified at least one new agent that decreased malignant properties associated with tumorigenesis, including anchorage-independent growth and tumor progression. This work offers a preclinical proof-of-concept for a wholly new approach to chemoprevention in carriers of BRCA1 mutations as a strategy to reduce the prevalence of BRCA1-associated malignancy.

A clinical trial of lovastatin for modification of biomarkers associated with breast cancer risk.

Pre-clinical and epidemiologic studies provide rationale for evaluating lipophilic statins for breast cancer prevention. We conducted a single-arm, biomarker modulation trial of lovastatin among women with increased risk of breast cancer. Eligibility criteria included a deleterious germline mutation in BRCA1, BRCA2, CDH1, or TP53; lifetime breast cancer risk of ≥20 % as estimated by the Claus model; or personal history of estrogen receptor and progesterone receptor-negative breast cancer. Participants received 40 mg of lovastatin orally twice daily for 6 months. We evaluated the following biomarkers before and after lovastatin use: breast duct cytology (primary endpoint), serum lipids, C-reactive protein, insulin-like growth factor-1, IGF binding protein-3, lipid peroxidation, oxidative DNA damage, 3-hydroxy-3-methylglutaryl CoA reductase genotype, and mammographic density. Thirty women were enrolled, and 26 (86.7 %) completed the study. For the primary endpoint of changes in breast duct cytology sampled by random periareolar fine needle aspiration, most participants [57.7 %, 95 % confidence interval (CI) 38.9-74.5 %] showed no change after lovastatin; 19.2 % (CI 8.1-38.3 %) had a favorable change in cytology, 7.7 % (95 % CI 1.0-25.3 %) had an unfavorable change, and 15.4 % (95 % CI 5.5-34.2 %) had equivocal results due to acellular specimens, usually after lovastatin. No significant changes were observed in secondary biomarker endpoints. The study was generally well-tolerated: 4 (13.3 %) participants did not complete the study, and one (3.8 %) required a dose reduction. This trial was technically feasible, but demonstrated no significant biomarker modulation; contributing factors may include insufficient sample size, drug dose and/or duration. The results are inconclusive and do not exclude a favorable effect on breast cancer risk.

Breast cancers with compromised DNA repair exhibit selective sensitivity to elesclomol.

The basal-like subtype of breast cancers, including those that contain germline mutations in BRCA1, tend to be triple-negative (i.e. lack expression of estrogen and progesterone receptors and lack overexpression/amplification of the HER2/neu oncogene), which renders them relatively insensitive to existing "targeted" therapy. BRCA1-mutated and basal-like breast cancers harbor compromised ability for repairing oxidative DNA damage by the DNA base-excision repair pathway. We found that this defective repair mechanism predicts sensitivity to elesclomol, an experimental therapeutic that produces elevated levels of oxidative DNA damage. In conclusion, BRCA1-mutated and/or basal-like breast cancers may benefit from treatment regimens that include elesclomol.

Enhanced sensitivity to cisplatin and gemcitabine in Brca1-deficient murine mammary epithelial cells.

BACKGROUND: Breast cancers due to germline mutations or altered expression of the BRCA1 gene associate with an aggressive clinical course and frequently exhibit a "triple-negative" phenotype, i.e. lack of expression of the estrogen and progesterone hormone receptors and lack of overexpression of the HER2/NEU oncogene, thereby rendering them relatively insensitive to hormonal manipulation and targeted HER2 therapy, respectively. BRCA1 plays a role in multiple DNA repair pathways, and thus, when mutated, results in sensitivity to certain DNA damaging drugs. RESULTS: Here, we used a Brca1 murine mammary epithelial cell (MMEC) model to examine the effect of loss of Brca1 on cellular sensitivity to various chemotherapy drugs. To explore novel therapeutic strategies, we included DNA damaging and non-DNA damaging drugs whose mechanisms are dependent and independent of DNA repair, respectively, and drugs that are used in standard and non-standard lines of therapy for breast cancer. To understand the cellular mechanism, we also determined the role that DNA repair plays in sensitivity to these drugs. We found that cisplatin and gemcitabine had the greatest specific therapeutic benefit to Brca1-deficient MMECs, and that when used in combination produced a synergistic effect. This sensitivity may be attributed in part to defective NER, which is one of the DNA repair pathways normally responsible for repairing DNA adducts produced by cisplatin and is shown in this study to be defective in Brca1-deficient MMECs. Brca1-deficient MMECs were not differentially sensitive to the standard breast cancer chemotherapy drugs doxorubicin, docetaxel or 5-FU. CONCLUSIONS: Both cisplatin and gemcitabine should be explored in clinical trials for first line regimens for BRCA1-associated and triple-negative breast cancer.

Synergistic chemosensitivity of triple-negative breast cancer cell lines to poly(ADP-Ribose) polymerase inhibition, gemcitabine, and cisplatin.

The basal-like subtype of breast cancer is characterized by a triple-negative (TN) phenotype (estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2/neu negative). TN breast cancers share similar gene expression profiles and DNA repair deficiencies with BRCA1-associated breast cancers. BRCA1-mutant cells exhibit sensitivity to gemcitabine, cisplatin, and poly(ADP-ribose) polymerase (PARP) inhibition; therefore, we hypothesized that TN cancer cells may also exhibit sensitivity to these drugs. In this study, we report that TN breast cancer cells are more sensitive to these drugs compared with non-TN breast cancer cells. Moreover, combination treatments indicated that PARP inhibition by the small-molecule inhibitor PJ34 or siRNA knockdown synergized with gemcitabine and cisplatin in TN cells but not in luminal cancer cells. TN cells exhibited reduced repair of UV-induced cyclobutane pyrimidine dimers after PARP inhibition, suggesting that the synergistic effect of PJ34 and gemcitabine or cisplatin reflected inefficient nucleotide excision repair. Mechanistic investigations revealed that in TN cells, PJ34 reduced the levels of ΔNp63α with a concurrent increase in p73 and its downstream target p21. Thus, the sensitivity to combination treatment seemed to be mediated by sustained DNA damage and inefficient DNA repair triggering p63/p73-mediated apoptosis. Our results suggest a novel therapeutic strategy to treat women with TN breast cancer, an aggressive disease that presently lacks effective treatment options.

Defective repair of oxidative dna damage in triple-negative breast cancer confers sensitivity to inhibition of poly(ADP-ribose) polymerase.

Subtypes of breast cancer that represent the two major types of epithelial cells in the breast (luminal and basal) carry distinct histopathologic profiles. Breast cancers of the basal-like subtype, which include the majority of hereditary breast cancers due to mutations in the breast cancer susceptibility gene 1 (BRCA1), frequently assume triple-negative status, i.e., they lack expression of estrogen receptor-alpha and progesterone receptor, and lack overexpression or amplification of the HER2/NEU oncogene. Defects in DNA damage response pathways result in genome instability and lead to carcinogenesis, but may also be exploited for therapeutic purposes. We analyzed repair of oxidative DNA damage by the base-excision repair (BER) pathway, which when aberrant leads to genomic instability and breast carcinogenesis, in cell lines that represent the different subtypes of breast cancer and in the presence of BRCA1 deficiency. We found that basal-like and BRCA1-mutated breast cancer cells were defective in BER of oxidative DNA damage, and that this defect conferred sensitivity to inhibition of poly(ADP-ribose) polymerase, a DNA repair enzyme. The defect may be attributed, at least in part, to a novel role for BRCA1 in the BER pathway. Overall, these data offer preventive, prognostic, and therapeutic usefulness.

Reversal of stathmin-mediated resistance to paclitaxel and vinblastine in human breast carcinoma cells.

Antimicrotubule agents are commonly used chemotherapy drugs for the treatment of breast and other cancers. However, these agents have variable activity partly because of microtubule regulatory proteins. Stathmin, an 18-kDa phosphoprotein that promotes microtubule depolymerization, was found to be frequently overexpressed in breast cancer. We previously identified stathmin-mediated mechanisms of resistance to antimicrotubule agents, including altered drug binding and delayed transit from G(2) into M phase, where these agents are effective in disrupting microtubule dynamics. We hypothesized that by reversing stathmin-mediated depolymerization of microtubules or by promoting entry into mitosis, this could increase sensitivity to antimicrotubule agents in human breast cancer cells overexpressing stathmin. We found that targeting stathmin or wee-1 expression with RNA interference can induce microtubule polymerization and promote G(2)/M progression, respectively, and sensitize stathmin-overexpressing breast cancer cells to paclitaxel and vinblastine. Furthermore, targeting wee-1 led to the phosphorylation of stathmin, which is known to attenuate its activity. Therefore, these data suggest a novel approach to improving the efficacy of certain antimicrotubule agents against breast cancer by regulating the function of stathmin.

Effect of stathmin on the sensitivity to antimicrotubule drugs in human breast cancer.

Stathmin is a p53-regulated protein known to influence microtubule dynamics. Because several chemotherapeutic agents used to treat breast cancer alter the dynamic equilibrium of tubulin polymerization, stathmin may play an important role in determining the sensitivity to these drugs. Therefore, we evaluated the effect of stathmin expression on the action of taxanes and Vinca alkaloids using a panel of human breast cancer cell lines. Cell lines harboring mutant p53 expressed high levels of stathmin. Two cell lines with different levels of endogenous stathmin expression and isogenic-paired cell lines transfected to overexpress stathmin were used to determine whether or not stathmin modulated the sensitivity to drugs. Overexpression of stathmin decreased polymerization of microtubules, markedly decreased binding of paclitaxel, and increased binding of vinblastine. Stathmin overexpression decreased sensitivity to paclitaxel and, to a lesser extent, to vinblastine. In contrast, stathmin content had no significant effect on the sensitivity to chemotherapeutic drugs that do not target microtubules. Cell lines overexpressing stathmin were more likely to enter G(2) but less likely to enter mitosis as determined by fluorescence-activated cell sorting and mitotic index. This effect was magnified when stathmin-overexpressing cells were treated with vinblastine as measured by the detection of proteins phosphorylated in early mitosis. These data suggest that the action of antimicrotubule drugs can be affected by stathmin in at least two ways: (a) altered drug binding; and (b) growth arrest at the G(2) to M boundary. Mutant p53 breast cancers exhibiting high levels of stathmin may be resistant to antimicrotubule agents.

A Phase I/pilot study of sequential doxorubicin/vinorelbine: effects on p53 and microtubule-associated protein 4.

PURPOSE: Few molecular determinants of sensitivity to cancer chemotherapy exist. In experimental systems, p53 regulates the sensitivity to antimicrotubule drugs through its effect on microtubule-associated protein 4 (MAP4). MAP4 is the major microtubule-associated protein in nonneuronal tissues and promotes microtubule polymerization. We reported that wild-type p53 induction by doxorubicin in C127 breast cancer cells repressed MAP4, decreased microtubule polymerization, and increased Vinca alkaloid sensitivity. The goals of this Phase I/pilot clinical trial were to determine: (a) the safety of delivering a DNA-damaging agent (doxorubicin) followed in sequence by treatment with an antimicrotubule drug (vinorelbine); and (b) the feasibility of detecting activation of p53 and repression of MAP4 in patients' tissues. EXPERIMENTAL DESIGN: Peripheral blood mononuclear cells (PBMNCs) and tumor were obtained from 16 women with locally advanced (stage IIIb) or metastatic (stage IV) breast cancer before doxorubicin treatment and immediately before treatment with vinorelbine 24 or 48 h later. RESULTS: After doxorubicin treatment, p53 increased in 12 of 14 PBMNC and 4 of 10 tumor samples. Changes in MAP4 were variable; however, in samples in which p53 was induced, MAP4 decreased in 7 of 12 PBMNC and 3 of 4 breast cancer specimens. Immunohistochemistry confirmed lower MAP4 expression in tumor cells after doxorubicin treatment. Seven of 16 patients had a partial response, and treatment was well tolerated. CONCLUSIONS: These data demonstrate the ability to detect the activation of p53 and the repression of MAP4 in normal and malignant tissues in patients treated with a DNA-damaging agent, and that an antimicrotubule drug can be administered safely at a time when cells may be more sensitive to treatment.