Abstract PD5-6: Sustained hyperactivated mTOR & JAK2/STAT3 pathways in inflammatory breast cancer (IBC): Evidence for mTOR plus JAK2 therapeutic targeting

Background: IBC is an aggressive form of breast cancer with poor prognosis. Combined multi-modality therapy results in a 5 year OS of 30%, underscoring the unmet need for targeted therapy. Our preclinical research in cell lines & xenograft tumor models has identified a role for hyper-activated PI3K/mTOR signaling in IBC. IBC cells express IL-6 and IL-8, which recruit tumor activated macrophages (TAMs) that further induce inflammatory cytokines and activate the JAK2/STAT3 pathway. We investigated the independent and combined activity of these pathways in IBC patient tissues.

Methods: Archived tissue specimens of 42 IBC patients (dx 1999-2009) and 27 non-IBC patients (dx 2001-2005) with invasive ductal carcinoma (IDC) were obtained. Surrounding non-tumor normal tissue from IBC (companion controls) was also utilized. All specimens were analyzed using immunohistochemistry (IHC) and scored by 3 independent pathologists. Results were defined as 0 = negative; 1+,2+ = positive for activated mTOR (P-S6); activated JAK2/STAT3 (P-JAK2; P-STAT3); cytokine (IL-6); macrophage infiltration (CD68) and TAM (CD163). Proportions of IBC cases with positive expression were compared with non-IBC cases (Fisher's exact test) & companion controls (McNemar's test). Clinical & survival data were obtained.

Results: Median age at diagnosis: 46 yrs (31-62) in early stage IBC [EIBC] (n = 37) & 41 yrs (29-57) in pts with de novo metastatic IBC [MIBC] (n = 5). In EIBC, 19/36: HER2+ (1 unk); 8/19: ER+/HER2+; 8/36: ER-/HER2-. In MIBC, all were ER- (1 unk) & 3/4 were HER2+ (1 unk). 88% were rx with neoadjuvant &/or adjuvant anthracycline & taxane w/o adjuvant trastuzumab. There were 24 pt deaths (5/5 MIBC). Median f/u for EIBC: 6.3 yrs and for MIBC: 3.4 yrs. Median OS: 81.4 mo (95% CI lower 48 mo) for EIBC & 41 mo (95% CI 8-81 mo) for MIBC. Median RFS: 18 mo (95% CI 18-79 mo) for 23 pts (13 NED; 1 unk). The non-IBC patients were all stage 2-3 with median age at diagnosis: 58 yrs (39-94). 19/27: ER+; 7/25 HER2+ (2 unk); 15/25 ER+/HER2-; 3/25 ER-/HER2-. 78% were rx with adjuvant anthracycline & taxane, 4% were rx with FEC and 18% did not receive adjuvant chemotherapy. 18% received adjuvant trastuzumab. Median f/u: 8.0 yrs. Median OS: not yet reached and median RFS: 111.3 mo (95% CI lower 34.5 mo). EIBC cases were compared with non-IBC cases & companion controls (Table 1). PS6, pJAK2 and pSTAT3 expression was significantly increased in IBC compared to non-IBC. Of the 29 EIBC patients with complete biomarker data who were PS6+, 28/29 (97%) were JAK2+, 15/29 (52%) were STAT3+, 26/29 (90%) were CD68+, 20/29 (69%) were CD163+ and 28/29 (97%) were IL6+.

Conclusion: This is the first study to validate preclinical findings & show a strong co-association between hyper-activation of mTOR & JAK/STAT pathways in most IBC patient tumors when compared to surrounding non-tumor tissue and non-IBC (IDC) tumors and tissues. These findings suggest a key role for dual blockade of mTOR & JAK/STAT pathways for IBC in phase I trials.

BiomarkerMcNemars p-value: Early Stage IBC vs companion controls (N = 37)Fishers p-value: Early stage IBC (N = 37)vs non-IBC (N = 27)PS6<0.00010.0315pJAK2<0.0001<0.0001pSTAT30.0003<0.0001CD163<0.00010.0908CD68<0.00010.0582IL60.00030.3882

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD5-6.

Abstract P5-03-02: Targeting mRNA Translation to Enhance the Radiosensitivity of Inflammatory Breast Cancer Stem Cells

Purpose/Objective(s): Inflammatory breast cancer (IBC) is a highly aggressive and radiation resistant malignancy with a dismal prognosis despite multimodality therapy, including ionizing radiation. We have previously shown that the unique pathogenic properties of IBC result in part from over-expression of translation initiation factor eIF4G1, which is part of the eIF4F translation initiation complex, along with eIF4E and eIF4A. eIF4F is regulated by mTOR, providing a promising target for anti-cancer therapeutics. We demonstrated that protein synthesis is highly regulated during IR by the DNA-damage response (DDR) pathway through mTOR signaling. Many key proteins required for the DDR pathway are encoded by mRNAs that require high levels of the eIF4F complex and mTOR activity for their efficient translation. We hypothesized that upregulation of eIF4F in IBC plays a crucial role in the radio-resistance of disease.

Materials/Methods: Experiments were conducted in IBC SUM149 cells. eIF4G1, eIF4E and eIF4A were silenced through the generation of stable cell lines that express tetracycline-inducible shRNAs. eIF4A was also inhibited using the pharmacologic investigational inhibitor DAMD-PatA. Radiation sensitivity in vitro was determined by cell survival assay. Tumor xenografts were generated by the injection of stable shRNA inducible cell lines into nude mice. IBC SUM149 cancer stem cells (CSC) from both in vitro and in vivo experiments were analyzed by a combination of cell surface marker analysis, mammosphere formation and Aldefluor assays.

Results: We show that moderate inhibition by silencing of individual components (or by pharmacologic inhibition of eIF4A) of the eIF4F complex prevents IBC xenograft tumor growth and strongly enhances radiosensitivity. In contrast to results obtained for non-transformed breast epithelial cells, reducing the high levels of eIF4G1 in epithelial IBC cells in 2D cultures provides no enhancement in radiation sensitivity. Rather, SUM149 IBC cells harbor a substantial population of CSCs, which are the cells that are strongly dependent on high levels of eIF4G1, and which are selectively radio-sensitized as a result of eIF4G1-silencing. CSCs also require eIF4E and eIF4A activity in order to survive radiation treatment. We also demonstrate that silencing of eIF4G1 radio-sensitizes the stem cell population within IBC tumor xenografts. Radio-resistance of IBC cells is likely mediated by differential responses to the DDR in the stem-cell populations and by selective mRNA translation of proteins involved in the DDR pathway.

Conclusions: Our results demonstrate that regulation of mRNA translation plays an important role in conferring radio-resistance to advanced breast cancers, particularly by allowing the survival of the CSC compartment. While inhibition of eIF4F enhances radiation sensitivity in non-transformed cells, this process is abrogated in IBC due to enrichment of a radiation resistant CSC population, demonstrating translational control of the breast cancer stem cell population, and providing a novel understanding of the role of the regulation of mRNA translation in radiation resistance of breast cancer.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-03-02.

Abstract P5-06-05: Catalytic mTOR Inhibition with pp242 but Not Allosteric Inhibition with Rapamycin RAD001 Enhances the Radiosensitivity of Inflammatory Breast Cancer in an Animal Model

Purpose/Objective(s): Inflammatory breast cancer (IBC) is a highly aggressive and radiation resistant cancer that continues to have a dismal prognosis despite aggressive multimodality therapy, which includes ionizing radiation (IR). The PI3K/Akt/mTOR pathway is frequently dysregulated in human cancers, including IBC. mTOR (mammalian target of rapamycin) is a central regulator of protein synthesis, linking mRNA translation to the metabolic state of the cell, playing a key role in the signaling of malignant cell growth, proliferation, differentiation, migration, and survival. We have shown that mTOR activation following treatment with DNA damaging agents such as ionizing radiation (IR) is a primary protector of advanced breast cancer cells, including IBC cells, through selectively increased translation of mRNAs for survival and DNA repair genes, including survivin, PARP, and DNA repair enzymes, among other radio-protective mRNAs. Thus, treatment with an mTOR inhibitor, coupled with IR, would be expected to provide a synergistic ability to control IBC. Therefore we compared the cytotoxic effects of combining mTOR inhibition and radiation in an IBC xenograft model, using either the selective mTORC1/2 inhibitor pp242, or the partial mTORC1 inhibitor RAD001 (Everlimus), a rapamcyin analog.

Methods: Experiments were conducted using SUM149 cells, a well-established model for IBC. Cells were treated with RAD001 or TORC1/2 inhibitor pp242 alone or in combination with increasing doses of radiation from 0-8 Gy. In vitro studies preformed included; cell survival assays, immunoblot analysis of key proteins, and 35S-methionine labeling to evaluate protein synthesis. In vivo studies were performed in a SUM149 xenograft nude mouse model; animals were treated with RAD001 or pp242 alone or in combination with IR.

Results: We found that only the combination of IR and catalytic mTOR inhibition by pp242 led to a number of striking additive/synergistic effects that were not observed with the combination of IR and the partial mTORC 1 inhibitor RAD001. These effects included; decreased clonogenic survival, inhibition of both endogenous and radiation-induced Akt activation, greater inhibition of mTOR signaling to its downstream effectors, efficient inhibition of protein synthesis, and greater induction of apoptotic cell death, as indicated by induction of caspase-3 cleavage. Importantly, SUM149 IBC xenografts treated with pp242 and concurrent radiation treatment exhibited significantly greater tumor control and survival compared to radiation treatment alone or RAD001 with radiation. Conclusions: These studies demonstrate that targeted inhibition of mTORC1/2 catalytic activity synergizes with radiation therapy in a model system of IBC. Mechanistically, mTORC1/2 inhibition likely prevents radiation induced pro-survival signals mediated through constitutively active Akt, which is not blocked by Rapamycin and its analogs. Experiments examining whether inhibition by pp242 prevents the selective increase in translation of prosurvival mRNAs in IBC as a result of IR treatment will be presented.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-06-05.

The N-terminal K homology domain of the poly(rC)-binding protein is a major determinant for binding to the poliovirus 5'-untranslated region and acts as an inhibitor of viral translation

The poly(rC)-binding proteins (PCBP1 and PCBP2) are RNA-binding proteins whose RNA recognition motifs are composed of three K homology (KH) domains. These proteins are involved in both the stabilization and translational regulation of several cellular and viral RNAs. PCBP1 and PCBP2 specifically interact with both the 5'-element known as the cloverleaf structure and the large stem-loop IV RNA of the poliovirus 5'-untranslated region. We have found that the first KH domain of PCBP2 (KH1) specifically interacts with the viral RNAs, and together with viral protein 3CD, KH1 forms a high affinity ternary ribonucleoprotein complex with the cloverleaf RNA, resembling the full-length PCBP protein. Furthermore, KH1 acts as a dominant-negative mutant to inhibit translation from a poliovirus reporter gene in both Xenopus laevis oocytes and HeLa cell in vitro translation extracts.

Intracellular determinants of picornavirus replication

Viruses replicate in a restricted number of hosts and tissues. In addition to viral receptors, several intracellular factors can be involved in determining tissue tropism. Many proteins have recently been implicated in picornavirus translation and RNA replication. Although the functional role of these proteins has not been established in vivo, it is possible that they determine cell-type tropism and the pathogenic outcome of the infection.

Toward a poliovirus-based simian immunodeficiency virus vaccine: correlation between genetic stability and immunogenicity

Recombinant polioviruses expressing foreign antigens may provide a convenient vaccine vector to engender mucosal immunity. Replication-competent chimeric viruses can be constructed by fusing foreign antigenic sequences to several positions within the poliovirus polyprotein. Artificial cleavage sites ensure appropriate proteolytic processing of the recombinant polyprotein, yielding mature and functional viral proteins. To study the effect of the position of insertion, two different recombinant polioviruses were examined. A small amino-terminus insertion delayed virus maturation and produced a thermosensitive particle. In contrast, insertion at the junction between the P1 and P2 regions yielded a chimeric poliovirus that replicated like the wild type. Eight different chimeras were constructed by inserting simian immunodeficiency virus (SIV) sequences at the P1/P2 junction. All recombinant viruses replicated with near-wild-type efficiency in tissue culture cells and expressed high levels of the SIV antigens. One of the inserted fragments corresponding to gp41 envelope protein was N-glycosylated but was not secreted. Inserted sequences were only partially retained after few rounds of replication in HeLa cells. This problem could be remedied to some extent by altering the sequences flanking the insertion point. Reducing the homology of the direct repeats by 37% decrease the propensity of the recombinant viruses to delete the insert. To determine the immunogenic potential of the recombinants, mice susceptible to poliovirus infection were inoculated intraperitoneally. The antibody titers elicited against Gag p17 depended on the viral doses and the number of inoculations. In addition, recombinants which display higher genetic stability were more effective in inducing an immune response against the SIV antigens, and inoculation with a mix of recombinants carrying different SIV antigens (a cocktail of recombinants) elicited humoral responses against each of the individual SIV sequences.

Engineering poliovirus as a vaccine vector for the expression of diverse antigens

As a step toward developing poliovirus as a vaccine vector, poliovirus recombinants were constructed by fusing exogenous peptides (up to 400 amino acids) and an artificial cleavage site for viral protease 3Cpro to the amino terminus of the viral polyprotein. Viral replication proceeded normally. An extended polyprotein was produced in infected cells and proteolytically processed into the complete array of viral proteins plus the foreign peptide, which was excluded from mature virions. The recombinants retained exogenous sequences through successive rounds of replication in culture and in vivo. Infection of animals with recombinants elicited a humoral immune response to the foreign peptides.