HER2/neu antisense targeting of human breast carcinoma

Therapeutic Antisense Oligonucleotides in Oncology: From Bench to Bedside

Advancements in our comprehension of tumor biology and chemoresistance have spurred the development of treatments that precisely target specific molecules within the body. Despite the expanding landscape of therapeutic options, there persists a demand for innovative approaches to address unmet clinical needs. RNA therapeutics have emerged as a promising frontier in this realm, offering novel avenues for intervention such as RNA interference and the utilization of antisense oligonucleotides (ASOs). ASOs represent a versatile class of therapeutics capable of selectively targeting messenger RNAs (mRNAs) and silencing disease-associated proteins, thereby disrupting pathogenic processes at the molecular level. Recent advancements in chemical modification and carrier molecule design have significantly enhanced the stability, biodistribution, and intracellular uptake of ASOs, thereby bolstering their therapeutic potential. While ASO therapy holds promise across various disease domains, including oncology, coronary angioplasty, neurological disorders, viral, and parasitic diseases, our review manuscript focuses specifically on the application of ASOs in targeted cancer therapies. Through a comprehensive examination of the latest research findings and clinical developments, we delve into the intricacies of ASO-based approaches to cancer treatment, shedding light on their mechanisms of action, therapeutic efficacy, and prospects.

The Role of Tumor-Associated Antigen HER2/neu in Tumor Development and the Different Approaches for Using It in Treatment: Many Choices and Future Directions

The treatment of HER2-positive cancers has changed significantly over the past ten years thanks to a significant number of promising new approaches that have been added to our arsenal in the fight against cancer, including monoclonal antibodies, inhibitors of tyrosine kinase, antibody-drug conjugates, vaccination, and particularly, adoptive-T-cell therapy after its great success in hematological malignancies. Equally important is the new methodology for determining patients eligible for targeted HER2 therapy, which has doubled the number of patients who can benefit from these treatments. However, despite the initial enthusiasm, there are still several problems in this field represented by drug resistance and tumor recurrence that require the further development of new more efficient drugs. In this review, we discuss various approaches for targeting the HER2 molecule in cancer treatment, highlighting their benefits and drawbacks, along with the different mechanisms responsible for resistance to HER2-targeted therapies and how to overcome them.

Functional Relationship and Gene Ontology Classification of Breast Cancer Biomarkers

Breast cancer is a complex disease that still imposes a significant healthcare burden on women worldwide. The etiology of breast cancer is not known but significant advances have been made in the area of early detection and treatment. The advent of advanced molecular biology techniques, mapping of the human genome and availability of high throughput genomic and proteomic strategies opens up new opportunities and will potentially lead to the discovery of novel biomarkers for early detection and prognostication of breast cancer. Currently, many biomarkers, particularly the hormonal and epidermal growth factor receptors, are being utilized for breast cancer prognosis. Unfortunately, none of the biomarkers in use have sufficient diagnostic, prognostic and/or predictive power across all categories and stages of breast cancer. It is recognized that more useful information can be generated if tumors are interrogated with multiple markers. But choosing the right combination of biomarkers is challenging, because 1) multiple pathways are involved, 2) up to 62 genes and their protein products are potentially involved in breast cancer-related mechanisms and 3) the more markers evaluated, the more the time and cost involved. This review summarizes the current literature on selected biomarkers for breast cancer, discusses the functional relationships, and groups the selected genes based on a Gene Ontology™ classification.

Intermolecular biparatopic trapping of ErbB2 prevents compensatory activation of PI3K/AKT via RAS-p110 crosstalk

Compensatory mechanisms, such as relief of AKT-ErbB3-negative feedback, are known to desensitize ErbB2-dependent tumours to targeted therapy. Here we describe an adaptation mechanism leading to reactivation of the PI3K/AKT pathway during trastuzumab treatment, which occurs independently of ErbB3 re-phosphorylation. This signalling bypass of phospho-ErbB3 operates in ErbB2-overexpressing cells via RAS-PI3K crosstalk and is attributable to active ErbB2 homodimers. As demonstrated by dual blockade of ErbB2/RAS and ErbB3 by means of pharmacological inhibition, RNA interference or by specific protein binders obstructing the RAS–p110α interaction, both routes must be blocked to prevent reactivation of the PI3K/AKT pathway. Applying these general principles, we developed biparatopic designed ankyrin repeat proteins (DARPins) trapping ErbB2 in a dimerization-incompetent state, which entail pan-ErbB inhibition and a permanent OFF state in the oncogenic signalling, thereby triggering extensive apoptosis in ErbB2-addicted tumours. Thus, these novel insights into mechanisms underlying network robustness provide a guide for overcoming adaptation response to ErbB2/ErbB3-targeted therapy.

Targeted therapy of ErbB2-dependent tumours often provokes an adaptive response leading to reactivation of the PI3K/AKT pathway. Here the authors identify an ErbB3-independent compensatory mechanism comprising Ras/PI3K activation directly by ErbB2, and develop biparatopic panErbB inhibitors to block this mode of resistance.

Anti-tumor activities and apoptotic mechanism of ribosome-inactivating proteins

Ribosome-inactivating proteins (RIPs) belong to a family of enzymes that attack eukaryotic ribosomes and potently inhibit cellular protein synthesis. RIPs possess several biomedical properties, including anti-viral and anti-tumor activities. Multiple RIPs are known to inhibit tumor cell proliferation through inducing apoptosis in a variety of cancers, such as breast cancer, leukemia/lymphoma, and hepatoma. This review focuses on the anti-tumor activities of RIPs and their apoptotic effects through three closely related pathways: mitochondrial, death receptor, and endoplasmic reticulum pathways.

Modification of HER2 pre-mRNA alternative splicing and its effects on breast cancer cells

The oncogene HER2 is overexpressed in a variety of human tumors, providing a target for anti-cancer molecular therapies. Here, we employed a 2'-O-methoxyethyl (MOE) splice switching oligonucleotide, SSO111, to induce skipping of exon 15 in HER2 pre-mRNA, leading to significant downregulation of full-length HER2 mRNA, and simultaneous upregulation of Delta15HER2 mRNA. SSO111 treatment of SK-BR-3 cells, which highly overexpress HER2, led to inhibition of cell proliferation and induction of apoptosis. The novel Delta15HER2 mRNA encodes a soluble, secreted form of the receptor. Treating SK-BR-3 cells with exogenous Delta15HER2 protein reduced membrane-bound HER2 and decreased HER3 transphosphorylation. Delta15HER2 protein thus has similar activity to an autoinhibitory, natural splice variant of HER2, Herstatin, and to the breast cancer drug Herceptin. Both SSO111 and Delta15HER2 may be potential candidates for the development of novel HER2-targeted cancer therapeutics.

Activity of suberoylanilide hydroxamic Acid against human breast cancer cells with amplification of her-2

PURPOSE

We determined the effects of suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, on hsp90 and its client proteins Her-2, AKT, and c-Raf, as well as evaluated the cytotoxic effects of co-treatment of SAHA with trastuzumab or docetaxel in human breast cancer BT-474 and SKBR-3 cells containing amplification of Her-2.

EXPERIMENTAL DESIGN

The cells were treated with SAHA (1.0-5.0 micromol/L) and/or trastuzumab (5-40 microg/mL) or docetaxel (5-20 nmol/L). Following this, apoptosis and the levels of p21(WAF1), p27(KIP1), AKT, c-Raf, and Her-2, as well as of the key regulators of apoptosis were determined. Synergistic interaction between drugs was evaluated by median dose-effect analysis.

RESULTS

Treatment with SAHA up-regulated p21(WAF1) and p27(KIP1) levels, increased the percentage of cells in G2-M phase of the cell cycle, as well as induced apoptosis in a dose-dependent manner. This was associated with up-regulation of the pro-death Bak and Bim, as well as with attenuation of the levels of Her-2 and XIAP, survivin, Bcl-2, and Bcl-x(L) proteins. SAHA treatment induced acetylation of hsp90. This reduced the chaperone association of Her-2 with hsp90, promoting polyubiquitylation and degradation of Her-2. SAHA also attenuated the levels of c-Raf and AKT. Co-treatment with SAHA significantly increased trastuzumab or docetaxel-induced apoptosis of BT-474 and SKBR-3 cells. Additionally, median dose-effect analysis revealed that co-treatment with SAHA and trastuzumab or docetaxel induced synergistic cytotoxic effects against the breast cancer cells.

CONCLUSIONS

These preclinical findings support the development of SAHA in combination with docetaxel and/or trastuzumab against Her-2-amplified breast cancer.

Differential sensitivities of trastuzumab (Herceptin)-resistant human breast cancer cells to phosphoinositide-3 kinase (PI-3K) and epidermal growth factor receptor (EGFR) kinase inhibitors

Her2 (erbB2/neu) is overexpressed in 25-30% of human breast cancers. Herceptin is a recombinant humanized Her2 antibody used to treat breast cancer patients with Her2 overexpression. Over a 5-month selection process, we isolated clones of BT474 (BT) human breast carcinoma cells (BT/Her(R)) that were resistant to Herceptin in vitro. In BT/Her(R) subclones, cell-surface, phosphorylated and total cellular Her2 protein remained high in the continuous presence of Herceptin. Likewise, the levels of cell-surface, phosphorylated, and total cellular Her3 and EGFR were either unchanged or only slightly elevated in BT/Her(R) subclones relative to BT cells. One BT/Her(R) subclone had substantially upregulated cell-surface EGFR, but this did not correlate with a higher relative resistance to Herceptin. In looking at the downstream PI-3K/Akt signaling pathway, phosphorylated and total Akt levels and Akt kinase activities were all sustained in BT/Her(R) subclones in the presence of Herceptin, but significantly downregulated in BT cells exposed to Herceptin. Whereas BT cells lost sensitivity to the PI-3K inhibitor LY294002 in the presence of Herceptin, BT/Her(R) subclones were equally sensitive to this agent in the presence and absence of Herceptin. This suggests that BT/Her(R) subclones acquired a Herceptin-resistant mechanism of PI-3K signaling. BT/Her(R) subclones were also sensitive to the EGFR kinase inhibitor AG1478 in the presence of Herceptin, to the same extent as BT cells. The BT/Her(R) subclones provide new insights into mechanisms of Herceptin resistance and suggest new treatment strategies in combination with other inhibitors targeted to signal transduction pathways.

Silencing of the HER2/neu gene by siRNA inhibits proliferation and induces apoptosis in HER2/neu-overexpressing breast cancer cells

In eukaryotes, double-stranded (ds) RNA induces sequence-specific inhibition of gene expression referred to as RNA interference (RNAi). We exploited RNAi to define the role of HER2/neu in the neoplastic proliferation of human breast cancer cells. We transfected SK-BR-3, BT-474, MCF-7, and MDA-MB-468 breast cancer cells with short interfering RNA (siRNA) targeted against human HER2/neu and analyzed the specific inhibition of HER2/neu expression by Northern and Western blots. Transfection with HER2/neu-specific siRNA resulted in a sequence-specific decrease in HER2/neu mRNA and protein levels. Moreover, transfection with HER2/neu siRNA caused cell cycle arrest at G0/G1 in the breast cancer cell lines SK-BR-3 and BT-474, consistent with a powerful RNA silencing effect. siRNA treatment resulted in an antiproliferative and apoptotic response in cells overexpressing HER2/neu, but had no influence in cells with almost no expression of HER2/neu proteins like MDA-MB-468 cells. These data indicate that HER2/neu function is essential for the proliferation of HER2/neu-overexpressing breast cancer cells. Our observations suggest that siRNA targeted against human HER2/neu may be valuable tools as antiproliferative agents that display activity against neoplastic cells at very low doses.

The carcinoma-associated antigen EpCAM upregulates c-myc and induces cell proliferation

Epithelial cell adhesion molecule (EpCAM) is a membrane glycoprotein expressed on adenomatous and simple epithelia, where it is involved in homophilic adhesion at the basolateral membrane. Carcinomas strongly overexpress EpCAM through an, as yet, unknown mechanism. Interestingly, otherwise EpCAM-negative squamous epithelia are seen to express EpCAM concomitant with their transformation and de-differentiation. The amount of EpCAM and the number of expressing cells both increase with the grade of dysplasia. Despite an important amount of data correlating the expression of EpCAM with cellular proliferation and de-differentiation, such as the coexpression with Ki-67, a marker for proliferation, it is unknown whether EpCAM may directly contribute to carcinogenesis. Here, we show that EpCAM has a direct impact on cell cycle and proliferation, and the ability to rapidly upregulate the proto-oncogene c-myc and cyclin A/E. Human epithelial 293 cells as well as murine NIH3T3 fibroblasts expressing EpCAM had a decreased requirement for growth factors, enhanced metabolic activity and colony formation capacity. Importantly, the inhibition of EpCAM expression with antisense mRNA led to a strong decrease in proliferation and metabolism in human carcinoma cells. Moreover, domain swapping experiments demonstrated that the intracellular part of EpCAM is necessary and sufficient to transduce the effects described. Thus, the data presented here highlight the role of EpCAM, demonstrating for the first time a direct link to cell cycle and proliferation.

Combining doxorubicin and liposomal anti-HER-2/NEU antisense oligodeoxynucleotides to treat HER-2/NEU-expressing MDA-MB-435 breast tumor model

This study assessed the in vivo therapeutic activity of an antisense molecule targeted against HER-2/neu expressing mRNA. Antisense activity was evaluated in female SCID/Rag2m mice bearing subcutaneous tumors derived from HER-2/neu-transfected MDA-MB-435 (MDA-MB-435(HER2)) cells, a transfected line derived from the human breast cancer MDA-MB-435 cell line. Animals were treated with free or liposome-encapsulated antisense. The area under the curve (AUC(0-24h)) of the liposomal formulated antisense was demonstrated to be more than 30-fold greater than that of free antisense following intravenous administration. Efficacy was determined by assessing changes in tumor growth rate as well as by an immunohistological end-point evaluating HER-2/neu expression. HER-2/neu protein expression was reduced in mice bearing HER-2/neu-transfected MDA-MB-435 tumors when treated with liposomal antisense. However, tumors in these mice grew at a faster rate than the control, a result that was interpreted to be a consequence of selection of a more rapidly proliferating HER-2/neu-negative subpopulation of cells. Effective control of the MDA-MB-435(HER2) tumors was achieved when antisense treatment was combined with doxorubicin. Tumors derived from animals treated with the combination of doxorubicin and the liposomal antisense against HER-2/neu exhibited no detectable levels of HER-2/neu expression. Antisense targeted against HER-2/neu mRNA was effective in reducing or eliminating HER-2/neu protein expression, and when combined wtih doxorubicin treatment was efficacious in the treatment of mice bearing HER-2/neu-overexpressing human xenograft tumors.

ErbB receptors: directing key signaling networks throughout life

The epidermal growth factor (EGF)-related peptides bind the ErbB receptors, inducing the formation of different homo- and heterodimers. Receptor dimerization promotes activation of the intrinsic kinase, leading to phosphorylation of specific tyrosines located in the ErbB's cytoplasmic region. These phosphorylated residues serve as docking sites for a variety of signaling molecules whose recruitment stimulates intracellular signaling cascades, which ultimately control diverse genetic programs. Particular ligand-receptor complexes have essential roles in embryonic development as well as in the adult. Finally, ErbB receptors are being pursued as therapeutic targets because aberrant ErbB activity has been observed in many human cancers. In this review, we discuss these data in more detail, illustrating the importance of tightly regulated ErbB signaling throughout life.

External control of Her2 expression and cancer cell growth by targeting a Ras-linked coactivator

Overproduction of the Her2 oncoprotein has been found in approximately 30% of breast tumors, and patients who have Her2 excesses typically have more aggressive disease. Here we show that the expression of the Her2 gene can be decreased by inhibiting the interaction of the two cancer-linked proteins, DRIP130/CRSP130/Sur-2 (a Ras-linked subunit of human mediator complexes) and ESX (an epithelial-restricted transcription factor). Disruption of the interaction by a short cell-permeable peptide reduced the expression of the Her2 gene and specifically impaired the growth and viability of Her2-overexpressing breast cancer cells. The association of ESX with DRIP130 is mediated by a small hydrophobic face of an 8-aa helix in ESX, suggesting a therapeutic approach to incapacitating the Her2 gene by small organic molecules.

Development and effects of immunoliposomes carrying an antisense oligonucleotide against DHFR RNA and directed toward human breast cancer cells overexpressing HER2

The development and the effect of immunoliposomes directed against human breast cancer cells overexpressing p185/HER2 are described. These immunoliposomes carry an antisense oligonucleotide directed toward the translational start site of dihydrofalate reductase (DHFR) RNA, which causes high cytotoxicity. To prepare the immunoliposomes, we followed two methodologies based on the high affinity between streptavidin and biotin and the use of biotinylated antibodies. In the first approach, the streptavidin molecule is covalently attached to the phospholipid DOPE, which is mixed with the cationic liposome DOTAP complexed with the antisense oligonucleotide. The second approach, which is much easier to perform, involves the binding of streptavidin to antibody and oligonucleotide, both biotinylated, and the latter complexed with DOTAP. The formation of the intermediary complexes of this immunoliposome was studied sequentially by gel electrophoresis. The uptake of the oligonucleotide carried by the immunoliposome was monitored by flow cytometry and confocal microscopy. As a model, we used SKBR3 cells that overexpress p185. The full immunoliposomes were more toxic than the antisense oligonucleotide in the absence of the antibody, thus increasing the sensitivity of the treatment.

Induction of apoptosis in a human breast cancer cell overexpressing ErbB-2 receptor by alpha-tocopheryloxybutyric acid

The overexpression of ErbB-2 receptor relates to malignant transformation of breast cancer. The present study was carried out to establish the usefulness of alpha-tocopheryloxybutyric acid (TE) as a chemotherapeutic agent for human breast cancer. TE caused induction of apoptosis in MDA-MB-453 cells overexpressing the ErbB-2 receptor. TE reduced levels of activated ErbB-2 receptor and Akt. In contrast, TE induced the activation of p38, and SB203580, a specific inhibitor for p38, attenuated the TE-induced apoptosis. These data indicate that simultaneous occurrences of Akt inhibition and p38 activation by TE result in the cell death.

Direct measurement of the association constant of HER2/neu antisense oligonucleotide to its target RNA sequence using a molecular beacon

A molecular beacon approach was developed to directly determine the association constant of RNA-DNA hybrid formation. The molecular beacon was composed of a 15-nt loop structure containing the antisense sequence that can hybridize with the AUG translational start site of the HER2/neu gene, which is overexpressed in a significant proportion of breast, ovarian, and lung tumors. The equilibrium association constant (Ka) of DNA binding to the RNA oligonucleotide was 6.4 +/- 0.14 x 10(7) M(-1) in the presence of 150 mM NaCl at 22 degrees C. The free energy change (AG) associated with RNA-DNA hybrid formation was -10.7 kcal/mole. The melting temperature (Tm) of RNA-DNA hybrid was 64.4 degrees C +/- 1 degree C in the presence of 150 mM NaCl. The RNA-DNA hybrid was more stable than the corresponding DNA-DNA duplex in 150 mM NaCl, as judged by both Ka and Tm data. We also determined the Ka, deltaG, and Tm values of RNA-DNA and DNA-DNA duplex formation in the presence of three monovalent cations, Li+, K+, and Cs+. The feasibility of this method was also investigated using a phosphorothioate molecular beacon. The information generated through this new approach for thermodynamic measurements might be useful for the design of oligonucleotides for antisense therapeutics.

ErbB2-overexpressing human mammary carcinoma cells display an increased requirement for the phosphatidylinositol 3-kinase signaling pathway in anchorage-independent growth

The proto-oncogene ErbB2 is known to be amplified and to play an important role in the development of about one-third of human breast cancers. Phosphatidylinositol 3-kinase (PI3K), which is often activated in ErbB2-overexpressing breast cancer cells, is known to regulate cell proliferation and cell survival. Selective inhibitors of the PI3K pathway were used to assess the relevance of PI3K signaling in the anchorage-independent growth of a series of human mammary carcinoma cell lines. Wortmannin, LY294002, and rapamycin at concentrations that did not affect MAPK phosphorylation but substantially inhibited PI3K, Akt, and p70(S6K) significantly suppressed the soft agar growth of tumor cell lines that overexpress ErbB2 but not the growth of tumor lines with low ErbB2 expression. A similar growth inhibition of ErbB2-overexpressing carcinoma lines was observed when a dominant negative p85(PI3K) mutant was introduced into these cells. Forced expression of ErbB2 in breast cancer lines originally expressing low ErbB2 levels augmented receptor expression and sensitized those lines to LY294002- and rapamycin-mediated inhibition of colony formation. Furthermore, treatment with LY294002 resulted in the selective increase of cyclin-dependent kinase inhibitors p21(Cip1) or p27(Kip1) and suppression of cyclin E-associated Cdk2 kinase activity in ErbB2-overexpressing lines, which may account for their hypersensitivity toward inhibitors of the PI3K pathway in anchorage-independent growth. Our results indicate that the PI3K/Akt/p70(S6K) pathway plays an enhanced role in the anchorage-independent growth of ErbB2-overexpressing breast cancer cells, therefore providing a molecular basis for the selective targeting of this signaling pathway in the treatment of ErbB2-related human breast malignancies.

Apoptosis and cancer chemotherapy

The explosion of interest in apoptosis amongst cancer biologists has been underpinned by the hope that a mechanistic understanding of cell death will inform our understanding of tumour drug resistance. A framework for drug-induced apoptosis can now be described in which a balance exists between intrinsic and extrinsic survival signals and drug-induced death signals. Pro- and anti-apoptotic signals impact upon pro-apoptotic members of the Bcl-2 family of proteins, which ultimately control the cellular fate. This framework suggests multiple points at which therapeutic interventions could be made to overcome drug resistance and, in addition, generates novel molecular targets for the induction of apoptosis in cancer cells.