Paola B. Campodónico

Autophagy: Friend or Foe in Breast Cancer Development, Progression, and Treatment

Autophagy is a catabolic process responsible for the degradation and recycling of long-lived proteins and organelles by lysosomes. This degradative pathway sustains cell survival during nutrient deprivation, but in some circumstances, autophagy leads to cell death. Thereby, autophagy can serve as tumor suppressor, as the reduction in autophagic capacity causes malignant transformation and spontaneous tumors. On the other hand, this process also functions as a protective cell-survival mechanism against environmental stress causing resistance to antineoplastic therapies. Although autophagy inhibition, combined with anticancer agents, could be therapeutically beneficial in some cases, autophagy induction by itself could lead to cell death in some apoptosis-resistant cancers, indicating that autophagy induction may also be used as a therapy. This paper summarizes the most important findings described in the literature about autophagy and also discusses the importance of this process in clinical settings.

The neural cell adhesion molecule is involved in the metastatic capacity in a murine model of lung cancer.

Neural cell adhesion molecule (NCAM) is involved in cell growth, migration, and differentiation. Its expression and/or polysialylation appear to be deregulated in many different cancer types. We employed the lung tumor cell line LP07, syngeneic in BALB/c mice to investigate the role of NCAM in malignant progression. LP07 cells express the three main NCAM isoforms, all of them polysialylated. This cells line, pretreated with an anti‐NCAM antibody and inoculated intravenously (i.v.) into syngeneic mice, developed less and smaller lung metastases. In vitro studies showed that NCAM bound antibody inhibited cell growth, mainly due to an increase in apoptosis, associated with a decrease of cyclin D1 and enhanced expression of active caspase 3 and caspase 9. Anti‐NCAM‐treated LP07 cells showed impairment in their ability to migrate and adhere to several extracellular matrix components. Secreted uPA activity was also reduced. NCAM‐140 knocked‐down by siRNA in LP07 cells pretreated or not with anti‐NCAM showed an impaired metastasizing ability upon i.v. inoculation into mice. These results suggest that anti‐NCAM treatment could be mimicking homophilic trans‐interactions and NCAM‐140 knocked‐down impairs heterophilic interactions, both leading to inhibition of metastatic dissemination. The involvement of NCAM in lung tumor progression was confirmed in human NSCLC tumors. Sixty percent of the cases expressed NCAM at tumor cell level. A multivariate analysis indicated that NCAM expression was associated with a shorter overall survival in this homogeneous series of Stages I and II NSCLC patients. NCAM may be able to modulate mechanisms involved in lung carcinoma progression and represents an attractive target to control metastatic progression. Mol. Carcinog.

Involvement of PKC delta (PKCδ) in the resistance against different doxorubicin analogs

Doxorubicin is an anti-tumor antibiotic widely used in the management of cancer patients. Its main mechanism of action involves the generation of DNA damage and the inhibition of topoisomerase II, promoting apoptosis. AD 198 is a novel doxorubicin analog devoid of DNA binding and topoisomerase II inhibitory capacities. It has been proposed that AD 198 induces apoptosis by activating protein kinase C delta (PKCδ); a PKC isoform described as growth inhibitory in a large number of cell types. We have previously demonstrated that PKCδ overexpression in NMuMG cells induced the opposite effect, promoting proliferation and cell survival. In this study, we found that PKCδ overexpression confers an enhanced cell death resistance against AD 198 cytotoxic effect and against AD 288, another doxorubicin analog that preserves its mechanism of action. These resistances involve PKCδ-mediated activation of two well-known survival pathways: Akt and NF-κB. While the resistance against AD 198 could be abrogated upon the inhibition of either Akt or NF-κB pathways, only NF-κB inhibition could revert the resistance to AD 288. Altogether, our results indicate that PKCδ increases cell death resistance against different apoptosis inductors, independently of their mechanism of action, through a differential modulation of Akt and NF-κB pathways. Our study contributes to a better understanding of the mechanisms involved in PKCδ-induced resistance and may greatly impact in the rationale design of isozyme-specific PKC modulators as therapeutic agents.

A clinically relevant bi-cellular murine mammary tumor model as a useful tool for evaluating the effect of retinoic acid signaling on tumor progression.

BackgroundThe effect of retinoic acid (RA) on breast cancer progression is controversial. Our objective was to obtain information about breast cancer progression, taking advantage of the ER-negative murine mammary adenocarcinoma model LM38 (LM38-LP constituted by luminal (LEP) and myoepithelial-like cells (MEP), LM38-HP mainly composed of spindle-shaped epithelial cells, and LM38-D2 containing only large myoepithelial cells), and to validate the role of the retinoic acid receptors (RARs) in each cell-type compartment.Materials and methodsWe studied the expression and functionality of the RARs in LM38 cell lines. We analyzed cell growth and cell cycle distribution, apoptosis, the activity of proteases, motility properties, and expression of the molecules involved in these pathways. We also evaluated tumor growth and dissemination in vivo under retinoid treatment.ResultsLM38 cell lines expressed most retinoic receptor isotypes that were functional. However, only the bi-cellular LM38-LP cells responded to retinoids by increasing RARβ2 and CRBP1 expression. The growth of LM38 cell sublines was inhibited by retinoids, first by inducing arrest in MEP cells, then apoptosis in LEP cells. Retinoids induced inhibitory effects on motility, invasiveness, and activity of proteolytic enzymes, mainly in the LM38-LP cell line. In in-vivo assays with the LM38-LP cell line, RA treatment impaired both primary tumor growth and lung metastases dissemination.ConclusionThese in-vivo and in-vitro results show that to achieve maximum effects of RA on tumor progression both the LEP and MEP cell compartments have to be present, suggesting that the interaction between the LEP and MEP cells is crucial to full activation of the RARs.

Abstract 3015: Crosstalk between ≤ and ≤ PKC isoforms and retinoic acid system in malignant phenotype reversion

Retinoids may exert some of their effects on cell differentiation and malignant phenotype reversion through interaction with different PKC isoforms. In this work we studied the crosstalk between retinoid acid system (RA) and PKC signaling pathway and its implication in malignant phenotype reversion using a murine mammary tumor cell line (LM3) and a human breast cancer-derived cell line (MDA-MB231). ATRA (all trans RA) treatment (1uM,72h) induced a significant growth inhibition in vitro in LM3 cell line. This result was confirmed in vivo when LM3 cells were injected orthotopically in female BALB/c mice while carrying subcutaneous slow release ATRA pellets (10 mg). This phenomenon was associated with the reduction of pErk1 levels (80±9%) and the increase of the cell cycle inhibitor p27 in the nuclear fraction without altering Cyclin D1 expression in LM3 cell line. None of these modulations were observed in ATRA unresponsive MDA-MB231 cell line. We determined by Western blot that 24h treatment with ATRA induced an increase of PKC∈ and PKC∈ levels, detecting alpha isoform only in the membrane fraction and delta isoform in the nuclear fraction. In contrast, in MDA-MB231 cells, PKC∈ and PKC∈ expression was reduced after ATRA exposure. Interestingly, pharmacological inhibition of PKC∈ and PKC∈ prevented retinoid receptors activation by ATRA in LM3 cells, as evidenced by a reporter gene assay (RARE-Luciferase). Western blot showed that pharmacological inhibition of PKC∈ (Rottlerin 1μM, 24h) impaired ATRA-induced RARα1 translocation to the nucleus while the pharmacological inhibition of PKC∈ (Go6976 5μM, 24h) did not affect this translocation. Moreover, immunoprecipitation assays showed that only PKC∈ co-immunoprecipitated with RARα1 after ATRA treatment, suggesting a physical interaction between both molecules. Rottlerin-ATRA treatment (72h) reversed the effect on proliferation rate exerted by retinoid treatment. Go6976-ATRA treatment (72h) significantly decreased cell duplication rate compared with ATRA or Go6976 treatment alone, in an additive manner. Pre-treated LM3 cells with Go6976 were intravenously injected in female BALB/c mice that carried subcutaneous slow release ATRA pellets in order to evaluate the importance of combination therapy in the last stages of metastatic spread. We noticed that this combined therapy produced a higher decrease in the number of lung metastases, suggesting an additive effect. Our results indicate that PKC/Retinoid Crosstalk is implicated in growth inhibition through the induction of RA transcription genes that lead to cell cycle arrest and differentiation. Finally we speculate that retinoid treatment combined with PKC∈ isoform modulators could be considered for treatment of PKC∈ positive breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3015. doi:1538-7445.AM2012-3015

Abstract 172: Utility of retinoid treatment in the reversion of the malignant phenotype of mammary tumors with alterations in the expression of protein kinase C (PKC) isoforms

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Some of the most promising signaling pathways for breast cancer treatment include the PKC family, involved in proliferation and apoptosis, and the retinoid system mainly involved in differentiation. In this work we have developed a murine model of mammary adenocarcinoma-derived cells (LM3) that overexpress α or ≤ PKC isoforms in order to analyze whether elevated levels of these kinases alter cell sensitivity to retinoid treatment (ATRA). LM3 cells are poorly responsive to ATRA. The overexpression of PKCα induced alterations in LM3 in vitro behavior that could be associated with tumor progression. In this sense, PKCα increased proliferation and motility (wound coverage: 69.3±8.3% vs 41.2±5.1% in control cells p<0.05) of the transfected LM3 cells. Interestingly, at the same time PKCα sensitized LM3 cells to ATRA treatment as evidenced by a significant reduction in both parameters. Upon othotopic inoculation into syngeneic mice LM3-PKCα cells formed tumors with higher growth rate and metastatic potential than LM3-vector cells. In vivo treatment with an ATRA pellet reduced both the local tumor growth and the number of spontaneous lung metastases (Md [Range]: 9 [0-27] vs 55 [20-75] for LM3-PKCα treated or not respectively p<0.05). On the contrary PKC ≤ overexpression did not affect LM3 cells behavior either in vitro or in vivo. LM3 cells response to ATRA was not modulated by PKC∈ either. However, through a RARE-luciferase gene reporter assay, we could determine that the overexpression of PKC∈ increased the activity of the retinoic acid receptors. Our results show that PKCα overexpression induced a more aggressive phenotype but also conferred ATRA sensitivity to mammary tumor cells. On the other side high PKC∈ levels increased the activity of retinoid receptors but did not modulate biological cell responses to retinoids. We believe that the use of retinoids may be beneficial in patients with aggressive breast tumors associated with high PKCα expression levels. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 172. doi:1538-7445.AM2012-172

Abstract 1199: Implications of protein kinase C (PKC)α and PKCΔ on murine mammary tumor growth and metastatic dissemination; effect of retinoids

The retinoid system exerts some of its effects on cell differentiation and malignant phenotype reversion through the interaction of its receptors (RAR) with different PKC isoforms. In this work, using a murine mammary tumor cell line (LM3), we studied the interaction between RARs and PKC in vitro as well as whether the overexpression of α and Δ PKC isoforms could influence the effect of retinoids on cell proliferation both in vivo and in vitro. Western blot assays showed that the pharmacological inhibition of PKCΔ (Rottlerin 5μM, 24h) impaired all trans retinoic acid (ATRA)-induced RARα1 translocation to the nucleus while the pharmacological inhibition of PKCα (Go6976 5μM, 24h) did not affect this translocation. Moreover, immunoprecipitation assays showed that only PKCΔ co-immunoprecipitated with RARα1 after ATRA treatment, suggesting a physical interaction between both molecules. However, both PKC isoforms seemed to be necessary for RARs activation as determined by a gene reporter assay. Next, by a stable transfection procedure, we overexpressed PKCα and PKCΔ in LM3 cell line. In vitro assays showed that LM3-PKCα cells presented the highest proliferative rate and were highly responsive to ATRA treatment reducing their growth capability. These genetically modified lines were also inoculated orthotopically into the mammary glands of female BALB/c mice. Ten days later, when tumors were palpable, mice were implanted with ATRA pellets (10 mg/mouse). Tumors overexpressing PKCα presented a higher growth rate and were more metastatic than control vector-transfected LM3 cells, but showed a significant response to ATRA treatment, impairing primary tumor growth and reducing lung metastases number [Md (range) 55 (20-75) vs. 16 (0-27) in non-treated and ATRA-treated LM3-PKCα cells respectively (P Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1199. doi:10.1158/1538-7445.AM2011-1199

Abstract 2142: Signaling pathways involved in apoptosis-resistance against doxorubicin analogues in murine mammary cells; Role of protein kinase C delta (PKCΔ)

In this work we have analyzed whether the overexpression of PKCΔ in murine mammary cells (NMuMG) is able to alter cell death susceptibility to two chemotherapeutic drugs derived from doxorubicin (AD198 and AD288), and evaluate the signaling pathways involved in this process. Similarly to doxorubicin, the mechanism of action of AD288 involves the generation of DNA damage whereas, it has been proposed that AD198 induces apoptosis by activating PKC isoforms, in particular PKCΔ. By western blot we could determine that NMuMG-PKCΔ cells showed an increase in the activation and/or expression of different molecules and signaling pathways involved in cell survival such as Bcl-2, pBad, PI3K/Akt y NFκB. Therefore PKCΔ overexpression induced an increase in cell death resistance against both ADs (survival: AD198: 80±10% vs. 41±8% and AD288: 90±15% vs. 60±10% in NMuMG-PKCΔ and NMuMG-vector cells respectively). In order to evaluate the role of PI3K/Akt pathway in cell death resistance induced by both ADs, cells were treated with LY294002, a PI3K inhibitor. The inhibition of this signaling pathway in NMuMG-PKCΔ cells increased 3-fold AD198 cytotoxic effect, whereas did not alter AD288 effect. The role of NFκB signaling pathway in the resistance against cell death induced by each AD was determined by transient transfection with a variant of its repressor IκB. The inhibition of this signaling pathway significantly increased cell death susceptibility to both drugs (P In this work we have demonstrated that the anti-apoptotic signals generated by PKCΔ in NMuMG mammary cells could be reverted by inhibiting PI3K/Akt and/or NFκB signaling pathways. In addition, it was shown that the pathway involved was dependent on the mechanism of action of the cytotoxic drug used. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2142. doi:10.1158/1538-7445.AM2011-2142

Abstract 339: Importance of retinoic acid receptors alpha, beta and gamma on the in vivo tumor growth of a murine mammary bi-cellular tumor cell line: Differential response of luminal and myoepithelial components to retinoids treatment

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The incidence of breast cancer has apparently increased throughout the world during the last century. Caucasian women in the western world have a considerably higher breast cancer risk. Due to their role in the regulation of cell growth and differentiation through binding to RAR/RXR receptors, retinoids (Rds) are being evaluated in clinical trials of cancer prevention. We focus our studies in LM38-LP, a murine mammary tumor cell line composed by luminal (LEP) and myoepithelial (MEP) cells that express all functional retinoic acid receptors RAR/RXR. We studied the mechanisms involved in Rds effects in LEP/MEP interactions. By using anti E-cadherin/immunobeads we managed to temporarily separate LEP and MEP compartments in LM38-LP cell line. We determined that ATRA (all trans retinoic acid) induced a significant increase of RARb2 and RARg2 only in LEP cells (RT-PCR). Rds treatment increased the adhesive capacity of the bicellular LM38-LP cell line to fibronectin (FN). When the two components of the cell line were analyzed separately, Rds only induced an increase in the adhesion to FN. of MEP cells Also to understand the importance of each RAR regarding metastatic dissemination and tumor growth, we generated LM38-LP cell lines stably transfected with shRNA against RARa, RARb or RARg. These cells were inoculated into the mammary fat pad of syngeneic BALB/c mice. Ten days post-inoculation, when tumors were palpable, mice received a pellet with or without ATRA (10mg/mouse) during 3 weeks and we analyzed tumor volume and number and size of spontaneous lung metastasis. ATRA treatment markedly decreased the tumor volume and the number of spontaneous metastasis in those mice inoculated with LM38-LP control cells. Tumors and/or metastases grown from cells transfected with shRNA against RARa, b or g did not respond to ATRA. Interestingly the absence of RARb led to a total loss of the metastatic capacity, suggesting the involvement of RARb in malignant progression. On the contrary, loss of RARa and RARg decreased orthotopic growth but promoted lung metastases formation, suggesting that these RARs could participate in the prevention of metastatic dissemination. In sum our in vitro studies allow us to conclude that the LEP compartment of LM38-LP cell line responds to ATRA by a classical pathway through RARb. On the other hand, ATRA modulation of the adhesiveness of LM38-LP cells to FN could be mediated by the MEP component. In vivo experiments demonstrated that the three retinoic receptors are implicated, but in a different manner, both in tumor growth and in the colonization of the target organ. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 339.