Elena Strekalova

NanoFlares for the detection, isolation, and culture of live tumor cells from human blood

Significance To our knowledge, as the first genetic-based approach for the simultaneous isolation and intracellular genetic analysis of live circulating tumor cells, NanoFlares provide opportunities for invasive cancer study, diagnosis, prognosis, and personalized therapy. Metastasis portends a poor prognosis for cancer patients. Primary tumor cells disseminate through the bloodstream before the appearance of detectable metastatic lesions. The analysis of cancer cells in blood—so-called circulating tumor cells (CTCs)—may provide unprecedented opportunities for metastatic risk assessment and investigation. NanoFlares are nanoconstructs that enable live-cell detection of intracellular mRNA. NanoFlares, when coupled with flow cytometry, can be used to fluorescently detect genetic markers of CTCs in the context of whole blood. They allow one to detect as few as 100 live cancer cells per mL of blood and subsequently culture those cells. This technique can also be used to detect CTCs in a murine model of metastatic breast cancer. As such, NanoFlares provide, to our knowledge, the first genetic-based approach for detecting, isolating, and characterizing live cancer cells from blood and may provide new opportunities for cancer diagnosis, prognosis, and personalized therapy.

Photoexpulsion of surface-grafted ruthenium complexes and subsequent release of cytotoxic cargos to cancer cells from mesoporous silica nanoparticles

Ruthenium(II) polypyridyl complexes have emerged both as promising probes of DNA structure and as anticancer agents because of their unique photophysical and cytotoxic properties. A key consideration in the administration of those therapeutic agents is the optimization of their chemical reactivities to allow facile attack on the target sites, yet avoid unwanted side effects. Here, we present a drug delivery platform technology, obtained by grafting the surface of mesoporous silica nanoparticles (MSNPs) with ruthenium(II) dipyridophenazine (dppz) complexes. This hybrid nanomaterial displays enhanced luminescent properties relative to that of the ruthenium(II) dppz complex in a homogeneous phase. Since the coordination between the ruthenium(II) complex and a monodentate ligand linked covalently to the nanoparticles can be cleaved under irradiation with visible light, the ruthenium complex can be released from the surface of the nanoparticles by selective substitution of this ligand with a water molecule. Indeed, the modified MSNPs undergo rapid cellular uptake, and after activation with light, the release of an aqua ruthenium(II) complex is observed. We have delivered, in combination, the ruthenium(II) complex and paclitaxel, loaded in the mesoporous structure, to breast cancer cells. This hybrid material represents a promising candidate as one of the so-called theranostic agents that possess both diagnostic and therapeutic functions.

αB-Crystallin: A Novel Regulator of Breast Cancer Metastasis to the Brain

Purpose: Basal-like breast tumors are typically (ER/PR/HER2) triple-negative and are associated with a high incidence of brain metastases and poor clinical outcomes. The molecular chaperone αB-crystallin is predominantly expressed in triple-negative breast cancer (TNBC) and contributes to an aggressive tumor phenotype in preclinical models. We investigated the potential role of αB-crystallin in brain metastasis in TNBCs. Experimental Design: αB-crystallin expression in primary breast carcinomas and brain metastases was analyzed by immunohistochemistry among patients with breast cancer with brain metastases. αB-crystallin was overexpressed or silenced in two different TNBC cell lines. The effects on cell adhesion to human brain microvascular endothelial cells (HBMEC) or extracellular matrix proteins, transendothelial migration, and transmigration across a HBMEC/astrocyte coculture blood–brain barrier (BBB) model were examined. In addition, the effects of overexpressing or silencing αB-crystallin on brain metastasis in vivo were investigated using orthotopic TNBC models. Results: In a cohort of women with breast cancer brain metastasis, αB-crystallin expression in primary breast carcinomas was associated with poor overall survival and poor survival after brain metastasis, even among patients with TNBC. Stable overexpression of αB-crystallin in TNBC cells enhanced adhesion to HBMECs, transendothelial migration, and BBB transmigration in vitro, whereas silencing αB-crystallin inhibited these events. αB-crystallin promoted adhesion of TNBC cells to HBMECs, at least in part, through an α3β1 integrin–dependent mechanism. αB-crystallin overexpression promoted brain metastasis, whereas silencing αB-crystallin inhibited brain metastasis in orthotopic TNBC models. Conclusion: αB-crystallin is a novel regulator of brain metastasis in TNBC and represents a potential biomarker and drug target for this aggressive disease. Clin Cancer Res; 20(1); 56–67. ©2013 AACR.

Methionine Deprivation Induces a Targetable Vulnerability in Triple-negative Breast Cancer Cells by Enhancing TRAIL Receptor-2 Expression

Purpose: Many neoplasms are vulnerable to methionine deficiency by mechanisms that are poorly understood. Because gene profiling studies have revealed that methionine depletion increases TNF-related apoptosis-inducing ligand receptor-2 (TRAIL-R2) mRNA, we postulated that methionine stress sensitizes breast cancer cells to proapoptotic TRAIL-R2 agonists. Experimental Design: Human triple (ER/PR/HER2)-negative breast carcinoma cell lines were cultured in control or methionine-free media. The effects of methionine depletion on TRAIL receptor expression and sensitivity to chemotherapy or a humanized agonistic TRAIL-R2 monoclonal antibody (lexatumumab) were determined. The melanoma-associated antigen MAGED2 was silenced to delineate its functional role in sensitizing TNBC cells to methionine stress. An orthotopic TNBC model was utilized to evaluate the effects of dietary methionine deficiency, lexatumumab, or the combination. Results: Methionine depletion sensitized TNBC cells to lexatumumab-induced caspase activation and apoptosis by increasing TRAIL-R2 mRNA and cell surface expression. MCF-10A cells transformed by oncogenic H-Ras, but not untransformed cells, and matrix-detached TNBC cells were highly sensitive to the combination of lexatumumab and methionine depletion. Proteomics analyses revealed that MAGED2, which has been reported to reduce TRAIL-R2 expression, was suppressed by methionine stress. Silencing MAGED2 recapitulated features of methionine deprivation, including enhanced mRNA and cell surface expression of TRAIL receptors and increased sensitivity to TRAIL receptor agonists. Dietary methionine deprivation enhanced the antitumor effects of lexatumumab in an orthotopic metastatic TNBC model. Conclusions: Methionine depletion exposes a targetable defect in TNBC cells by increasing TRAIL-R2 expression. Our findings provide the foundation for a clinical trial combining dietary methionine restriction and TRAIL-R2 agonists. Clin Cancer Res; 21(12); 2780–91. ©2015 AACR.

ERK-regulated αB-crystallin induction by matrix detachment inhibits anoikis and promotes lung metastasis in vivo

Evasion of extracellular matrix detachment-induced apoptosis (‘anoikis’) is a defining characteristic of metastatic tumor cells. The ability of metastatic carcinoma cells to survive matrix detachment and escape anoikis enables them to disseminate as viable circulating tumor cells and seed distant organs. Here we report that αB-crystallin, an antiapoptotic molecular chaperone implicated in the pathogenesis of diverse poor-prognosis solid tumors, is induced by matrix detachment and confers anoikis resistance. Specifically, we demonstrate that matrix detachment downregulates extracellular signal-regulated kinase (ERK) activity and increases αB-crystallin protein and messenger RNA (mRNA) levels. Moreover, we show that ERK inhibition in adherent cancer cells mimics matrix detachment by increasing αB-crystallin protein and mRNA levels, whereas constitutive ERK activation suppresses αB-crystallin induction during matrix detachment. These findings indicate that ERK inhibition is both necessary and sufficient for αB-crystallin induction by matrix detachment. To examine the functional consequences of αB-crystallin induction in anoikis, we stably silenced αB-crystallin in two different metastatic carcinoma cell lines. Strikingly, silencing αB-crystallin increased matrix detachment-induced caspase activation and apoptosis but did not affect cell viability of adherent cancer cells. In addition, silencing αB-crystallin in metastatic carcinoma cells reduced the number of viable circulating tumor cells and inhibited lung metastasis in two orthotopic models, but had little or no effect on primary tumor growth. Taken together, our findings point to αB-crystallin as a novel regulator of anoikis resistance that is induced by matrix detachment-mediated suppression of ERK signaling and promotes lung metastasis. Our results also suggest that αB-crystallin represents a promising molecular target for antimetastatic therapies.

Metformin sensitizes triple-negative breast cancer to proapoptotic TRAIL receptor agonists by suppressing XIAP expression

AbstractPurpose Despite robust antitumor activity in diverse preclinical models, TNF-related apoptosis-inducing ligand (TRAIL) receptor agonists have not demonstrated efficacy in clinical trials, underscoring the need to identify agents that enhance their activity. We postulated that the metabolic stress induced by the diabetes drug metformin would sensitize breast cancer cells to TRAIL receptor agonists.MethodsHuman triple (estrogen receptor, progesterone receptor, and HER2)-negative breast cancer (TNBC) cell lines were treated with TRAIL receptor agonists (monoclonal antibodies or TRAIL peptide), metformin, or the combination. The effects on cell survival, caspase activation, and expression of TRAIL receptors and the antiapoptotic protein XIAP were determined. In addition, XIAP was silenced by RNAi in TNBC cells and the effects on sensitivity to TRAIL were determined. The antitumor effects of metformin, TRAIL, or the combination were evaluated in an orthotopic model of metastatic TNBC.ResultsMetformin sensitized diverse TNBC cells to TRAIL receptor agonists. Metformin selectively enhanced the sensitivity of transformed breast epithelial cells to TRAIL receptor agonist-induced caspase activation and apoptosis with little effect on untransformed breast epithelial cells. These effects of metformin were accompanied by robust reductions in the protein levels of XIAP, a negative regulator of TRAIL-induced apoptosis. Silencing XIAP in TNBC cells mimicked the TRAIL-sensitizing effects of metformin. Metformin also enhanced the antitumor effects of TRAIL in a metastatic murine TNBC model.ConclusionsOur findings indicate that metformin enhances the activity of TRAIL receptor agonists, thereby supporting the rationale for additional translational studies combining these agents.

αB-crystallin: Portrait of a malignant chaperone as a cancer therapeutic target.

αB-crystallin is a widely expressed member of the small heat shock protein family that protects cells from stress by its dual function as a molecular chaperone to preserve proteostasis and as a cell death antagonist that negatively regulates components of the conserved apoptotic cell death machinery. Deregulated expression of αB-crystallin occurs in a broad array of solid tumors and has been linked to tumor progression and poor clinical outcomes. This review will focus on new insights into the molecular mechanisms by which oncogenes, oxidative stress, matrix detachment and other tumor microenvironmental stressors deregulate αB-crystallin expression. We will also review accumulating evidence pointing to an essential role for αB-crystallin in the multi-step metastatic cascade whereby tumor cells colonize distant organs by circumventing a multitude of barriers to cell migration and survival. Finally, we will evaluate emerging strategies to therapeutically target αB-crystallin and/or interacting proteins to selectively activate apoptosis and/or derail the metastatic cascade in an effort to improve outcomes for patients with metastatic disease.

Abstract 3849: The antidiabetic drug metformin increases pro-apoptotic effect of TRAIL therapy by reducing X-linked inhibitor of apoptosis protein (XIAP) levels in triple-negative breast cancer cells

Most metastatic tumors, such as triple negative breast cancer (TNBC) respond poorly to conventional chemotherapy. We have previously demonstrated that targeting TNF-related apoptosis-inducing ligand receptor-2 (TRAIL-R2) might be an effective pathway against metastatic TNBC. However, many TNBCs are resistant to TRAIL receptor agonists. Here we demonstrate that diabetes drug metformin, previously linked to preventing and treating several types of cancer, enhances sensitivity of TNBC cells to recombinant TRAIL and TRAIL-R2 agonistic humanized monoclonal antibody (lexatumumab)-induced apoptosis. We have demonstrated that combination of metformin with lexatumumab or TRAIL augments response to TRAIL therapy and reduce cancer cell viability via induction of apoptosis and inhibiting long-term survival of three different metastatic TNBC cell lines. Intriguingly, metformin treatment also sensitized transformed MCF10A-RasV12 cells, but not untransformed MCF10A-Vector cells, to TRAIL agonist therapy. This effect was associated with reduction of X-linked Inhibitor of Apoptosis Protein (XIAP) levels after metformin treatment. Similar to metformin treatment, inhibition of XIAP by small interfering RNA sensitized breast cancer cells to TRAIL-induced apoptosis. Moreover, metformin treatment in combination with TRAIL more efficiently inhibited primary tumor growth and lung metastases in orthotopic model of TNBC. Overall, our results demonstrate that metformin treatment in combination with targeting TRAIL receptors may be a good strategy to augment the antitumor effects of TRAIL receptors agonistic therapy and provide the foundation for a clinical trial combining dietary metfomin and TRAIL agonists. Citation Format: Elena Strekalova, Dmitry Malin, Vincent Cryns. The antidiabetic drug metformin increases pro-apoptotic effect of TRAIL therapy by reducing X-linked inhibitor of apoptosis protein (XIAP) levels in triple-negative breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3849.

Abstract A265: L-methionine restriction sensitizes triple-negative breast cancer cells to a TRAIL receptor-2 agonist by reducing the expression of the melanoma-associated antigen MAGE-D2.

The prognosis for most women with metastatic breast cancer remains poor due to a dearth of effective adjuvant therapies for this advanced stage of the disease. We have previously demonstrated that targeting TNF-related apoptosis-inducing ligand receptor-2 (TRAIL-R2) suppressed metastases in a murine model of triple-negative breast cancer (TNBC). However, many TNBCs are resistant to TRAIL receptor agonists. Restriction of the essential amino acid L-methionine has been reported to inhibit growth of transformed cells in preclinical models. We postulated that methionine restriction would sensitize TNBC cells to TRAIL-R2 agonists such as the humanized monoclonal antibody lexatumumab. Here we demonstrate that methionine restriction sensitized TNBC cells to lexatumumab-induced caspase activation and apoptosis. Intriguingly, methionine restriction also sensitized transformed MCF10A-RasV12 cells, but not untransformed MCF10A-Vector cells, to lexatumumab. Methionine restriction enhanced the cell surface expression of TRAIL-R2. To delineate the underlying mechanism(s), we performed proteomics analyses of TNBC cells grown in methionine restricted media and observed that methionine restriction dramatically reduced the expression of the melanoma-associated antigen MAGE-D2, which has recently been reported to inhibit TRAIL-R2 expression. siRNAs targeting MAGE-D2 mimicked the actions of methionine restriction by augmenting cell surface expression of TRAIL-R2 and sensitizing TNBC cells to lexatumumab. Overall, our results demonstrate that methionine restriction sensitizes TNBC cells to TRAIL-R2 agonists and suggest that dietary methionine restriction may be a strategy to augment the antitumor effects of TRAIL receptor agonists in vivo. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A265. Citation Format: Elena Strekalova, Dmitry Malin, David Good, Vincent Cryns. L-methionine restriction sensitizes triple-negative breast cancer cells to a TRAIL receptor-2 agonist by reducing the expression of the melanoma-associated antigen MAGE-D2. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A265.

Abstract A69: aB-crystallin: A novel regulator of breast cancer metastasis to the brain

Brain metastases are a devastating complication of advanced breast cancer that result in disabling neurologic deficits and death within one year in the vast majority of patients. Triple-negative breast tumors, which lack expression of the estrogen receptor, progesterone receptor and HER2, commonly metastasize to the brain. However, the genes regulating brain metastasis are poorly understood. The molecular chaperone aB-crystallin is frequently expressed in triple-negative breast cancer and has been reported to play important roles in cytoskeletal organization, cell migration and invasion. As such, we hypothesized that aB-crystallin promotes metastasis in triple-negative breast cancer. To test this hypothesis, we stably overexpressed aB-crystallin in triple-negative breast cancer cells with low endogenous expression of the protein and stably silenced aB-crystallin in triple-negative breast cancer cells with high endogenous levels. We examined the effects of altering aB-crystallin levels on adhesion to human brain microvascular endothelial cells (HBMECs) and penetration of an in vitro model of the blood-brain barrier (BBB). In addition, orthotopic models of triple-negative breast cancer in which fluorescently labeled breast cancer cells metastasize from the mammary gland to the brain were utilized to evaluate the effects of aB-crystallin on primary and metastatic tumor burden in vivo. We observed that silencing aB-crystallin inhibited adhesion to HBMECs and penetration of an in vitro BBB model, while overexpression of aB-crystallin enhanced adhesion to HBMECs and penetration of the BBB in vitro. Consistent with these results, overexpression of aB-crystallin in triple-negative breast cancer cells increased brain metastasis in female NSG mice with transplanted mammary tumors, while silencing aB-crystallin inhibited brain metastasis. We also demonstrated that aB-crystallin enhanced adhesion to HBMECs by a b1 integrin-dependent mechanism. Taken together, our results point to a novel role of aB-crystallin in breast cancer brain metastasis and suggest that aB-crystallin may be a promising drug target for this rapidly fatal disease. Citation Format: Dmitry Malin, Elena Strekalova, Andrey Ugolkov, Vladimir Petrovic, Vincent Cryns. aB-crystallin: A novel regulator of breast cancer metastasis to the brain. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A69.