Loredana Mauro

Role of the IGF-I receptor in the regulation of cell-cell adhesion: Implications in cancer development and progression

The insulin‐like growth factor‐I receptor (IGF‐IR) is a ubiquitous multifunctional tyrosine kinase that has an important role in normal cell growth and development. However, abnormal stimulation of IGF‐IR signaling has been implicated in the development of different types of tumors. The strong antiapoptotic activity of IGF‐IR has been recognized as critical in IGF‐I‐dependent tumorigenesis, however, the impact of other IGF‐IR functions, such as regulation of cell–cell and cell–matrix adhesion are also increasingly acknowledged. Here, on the model of breast cancer cells, we discuss how IGF‐IR‐dependent regulation of intercellular adhesion may affect cell survival, resistance to antiestrogens, and invasion.

Insulin receptor substrate 1 is a target for the pure antiestrogen ICI 182,780 in breast cancer cells.

The pure antiestrogen ICI 182,780 inhibits insulin‐like growth factor (IGF)‐dependent proliferation in hormone‐responsive breast cancer cells. However, the interactions of ICI 182,780 with IGF‐I receptor (IGF‐IR) intracellular signaling have not been characterized. Here, we studied the effects of ICI 182,780 on IGF‐IR signal transduction in MCF‐7 breast cancer cells and in MCF‐7‐derived clones overexpressing either the IGF‐IR or its 2 major substrates, insulin receptor substrate 1 (IRS‐1) or src/collagen homology proteins (SHC). ICI 182,780 blocked the basal and IGF‐I‐induced growth in all studied cells in a dose‐dependent manner; however, the clones with the greatest IRS‐1 overexpression were clearly least sensitive to the drug. Pursuing ICI 182,780 interaction with IRS‐1, we found that the antiestrogen reduced IRS‐1 expression and tyrosine phosphorylation in several cell lines in the presence or absence of IGF‐I. Moreover, in IRS‐1‐overexpressing cells, ICI 182,780 decreased IRS‐1/p85 and IRS‐1/GRB2 binding. The effects of ICI 182,780 on IGF‐IR protein expression were not significant; however, the drug suppressed IGF‐I‐induced (but not basal) IGF‐IR tyrosine phosphorylation. The expression and tyrosine phosphorylation of SHC as well as SHC/GRB binding were not influenced by ICI 182,780. In summary, downregulation of IRS‐1 may represent one of the mechanisms by which ICI 182,780 inhibits the growth of breast cancer cells. Thus, overexpression of IRS‐1 in breast tumors could contribute to the development of antiestrogen resistance. Int. J. Cancer 81:299–304, 1999.

Transferrin-Conjugated Pluronic Niosomes as a New Drug Delivery System for Anticancer Therapy

An efficient tumor-targeted niosomal delivery system for the vehiculation of doxorubicin hydrochloride as an anticancer agent was designed. Niosomes were prepared from a mixture of an opportunely modified Pluronic L64 surfactant and cholesterol as a membrane additive and characterized in terms of size and related distribution function and drug entrapment efficiency. After the preparation, transferrin was conjugated to niosomes to produce transferrin (Tf) niosomes, and the cytotoxicity of the final formulation was studied. The specific uptake of Tf niosomes into cells was evaluated via incubation of MCF-7 and MDA-MB-231 cells with fluorescently rhodamine-loaded Tf niosomes for various times and concentration intervals and further investigated by fluorescence microscopy. Results showed that doxorubicin can be easily encapsulated into niosomes, which are regular and spherical in shape. Moreover, transferrin conjugate niosomes demonstrated far greater extents of cellular uptake by MCF-7 and MDA-MB-231 cells, suggesting that they were mainly taken up by transferrin receptor-mediated endocytosis. Doxorubicin-loaded niosome anticancer activity was also achieved against MCF-7 and MDA-MB-231 tumor cell lines, and a significant reduction in viability in a dose- and time-related manner was observed. Finally, our formulation could be potentially useful as a target doxorubicin delivery system in anticancer therapy.

The estrogen receptor α is the key regulator of the bifunctional role of FoxO3a transcription factor in breast cancer motility and invasiveness

The role of the Forkhead box class O (FoxO)3a transcription factor in breast cancer migration and invasion is controversial. Here we show that FoxO3a overexpression decreases motility, invasiveness, and anchorage-independent growth in estrogen receptor α-positive (ERα+) cancer cells while eliciting opposite effects in ERα-silenced cells and in ERα-negative (ERα−) cell lines, demonstrating that the nuclear receptor represents a crucial switch in FoxO3a control of breast cancer cell aggressiveness. In ERα+ cells, FoxO3a-mediated events were paralleled by a significant induction of Caveolin-1 (Cav1), an essential constituent of caveolae negatively associated to tumor invasion and metastasis. Cav1 induction occurs at the transcriptional level through FoxO3a binding to a Forkhead responsive core sequence located at position −305/−299 of the Cav1 promoter. 17β-estradiol (E2) strongly emphasized FoxO3a effects on cell migration and invasion, while ERα and Cav1 silencing were able to reverse them, demonstrating that both proteins are pivotal mediators of these FoxO3a controlled processes. In vivo, an immunohistochemical analysis on tissue sections from patients with ERα+ or ERα− invasive breast cancers or in situ ductal carcinoma showed that nuclear FoxO3a inversely (ERα+) or directly (ERα−) correlated with the invasive phenotype of breast tumors. In conclusion, FoxO3a role in breast cancer motility and invasion depends on ERα status, disclosing a novel aspect of the well-established FoxO3a/ERα interplay. Therefore FoxO3a might become a pursuable target to be suitably exploited in combination therapies either in ERα+ or ERα− breast tumors.

Activated FXR Inhibits Leptin Signaling and Counteracts Tumor-promoting Activities of Cancer-Associated Fibroblasts in Breast Malignancy

Cancer-associated fibroblasts (CAFs), the principal components of the tumor stroma, play a central role in cancer development and progression. As an important regulator of the crosstalk between breast cancer cells and CAFs, the cytokine leptin has been associated to breast carcinogenesis. The nuclear Farnesoid X Receptor-(FXR) seems to exert an oncosuppressive role in different tumors, including breast cancer. Herein, we demonstrated, for the first time, that the synthetic FXR agonist GW4064, inhibiting leptin signaling, affects the tumor-promoting activities of CAFs in breast malignancy. GW4064 inhibited growth, motility and invasiveness induced by leptin as well as by CAF-conditioned media in different breast cancer cell lines. These effects rely on the ability of activated FXR to increase the expression of the suppressor of the cytokine signaling 3 (SOCS3) leading to inhibition of leptin-activated signaling and downregulation of leptin-target genes. In vivo xenograft studies, using MCF-7 cells alone or co-injected with CAFs, showed that GW4064 administration markedly reduced tumor growth. Interestingly, GW4064-treated tumors exhibited decreased levels of leptin-regulated proteins along with a strong staining intensity for SOCS3. Thus, FXR ligands might represent an emerging potential anti-cancer therapy able to block the tumor supportive role of activated fibroblasts within the breast microenvironment.

Further Evolution of Multifunctional Niosomes Based on Pluronic Surfactant: Dual Active Targeting and Drug Combination Properties

The loading of chemotherapics into smart nanocarriers that simultaneously possess more than one useful property for specifically targeting a tumor site improves their therapeutic effectiveness, reducing their side effects. Hence, we proposed a combined approach for the treatment of human breast cancer (BC) consisting of the co-encapsulation of doxorubicin and curcumin or doxorubicin and quercetin into multifunctional niosomes, which results in prolonged blood circulation and an ability to spontaneously accumulate at the tumor site (passive target) and to recognize and bind the tumor cells through dual ligand-receptor interactions (active target). The drug-loaded vesicles showed high stability and good capability of loading doxorubicin and antioxidants alone or in combination. Their diameter was around 400 nm. The drugs released from the vesicles were found to be controlled and sustained for over 24 h, with a strong dependence on the co-presence of the loaded molecules. Transferrin and/or folic acid were conjugated on the external surface of the niosomes as ligands, considerably improving the cellular uptake into MCF-7 and MDA-MB-231 malignant cells when compared with the uptake of nonconjugated samples. In vitro evaluation of anticancer activity demonstrated the strong potential of niosomes loaded with a doxorubicin/curcumin combination as useful devices in breast tumor treatment. These features hold great promise for the development of multifunctional devices that combine several advantages such as biocompatibility, stealth properties, loading capability, and active targeting, moving toward the development of more specific and efficient carriers for personalized tumoral therapy.