Prediction of Pathological Complete Response to Neoadjuvant Chemotherapy for Primary Breast Cancer Comparing Interim Ultrasound, Shear Wave Elastography and MRI

BACKGROUND

 Prediction of pathological complete response (pCR) of primary breast cancer to neoadjuvant chemotherapy (NACT) may influence planned surgical approaches in the breast and axilla. The aim of this project is to assess the value of interim shear wave elastography (SWE), ultrasound (US) and magnetic resonance imaging (MRI) after 3 cycles in predicting pCR.

METHODS

 64 patients receiving NACT had baseline and interim US, SWE and MRI examinations. The mean lesion stiffness at SWE, US and MRI diameter was measured at both time points. We compared four parameters with pCR status: a) Interim mean stiffness ≤ or > 50 kPa; b) Percentage stiffness reduction; c) Percentage US diameter reduction and d) Interim MRI response using RECIST criteria. The Chi square test was used to assess significance.

RESULTS

 Interim stiffness of ≤ or > 50 kPa gave the best prediction of pCR with pCR seen in 10 of 14 (71 %) cancers with an interim stiffness of ≤ 50 kPa, compared to 7 of 50 (14 %) of cancers with an interim stiffness of > 50 kPa, (p < 0.0001) (sensitivity 59 %, specificity 91 %, PPV 71 %, NPV 86 % and diagnostic accuracy 83 %). Percentage reduction in stiffness was the next best parameter (sensitivity 59 %, specificity 85 %, p < 0.0004) followed by reduction in MRI diameter of > 30 % (sensitivity 50 % and specificity 79 %, p = 0.03) and % reduction in US diameter (sensitivity 47 %, specificity 81 %, p = 0.03). Similar results were obtained from ROC analysis.

CONCLUSION

 SWE stiffness of breast cancers after 3 cycles of NACT and changes in stiffness from baseline are strongly associated with pCR after 6 cycles.

p53 controls expression of the DNA deaminase APOBEC3B to limit its potential mutagenic activity in cancer cells

Cancer genome sequencing has implicated the cytosine deaminase activity of apolipoprotein B mRNA editing enzyme catalytic polypeptide-like (APOBEC) genes as an important source of mutations in diverse cancers, with APOBEC3B (A3B) expression especially correlated with such cancer mutations. To better understand the processes directing A3B over-expression in cancer, and possible therapeutic avenues for targeting A3B, we have investigated the regulation of A3B gene expression. Here, we show that A3B expression is inversely related to p53 status in different cancer types and demonstrate that this is due to a direct and pivotal role for p53 in repressing A3B expression. This occurs through the induction of p21 (CDKN1A) and the recruitment of the repressive DREAM complex to the A3B gene promoter, such that loss of p53 through mutation, or human papilloma virus-mediated inhibition, prevents recruitment of the complex, thereby causing elevated A3B expression and cytosine deaminase activity in cancer cells. As p53 is frequently mutated in cancer, our findings provide a mechanism by which p53 loss can promote cancer mutagenesis.

Expression of CDK7, Cyclin H, and MAT1 Is Elevated in Breast Cancer and Is Prognostic in Estrogen Receptor-Positive Breast Cancer

PURPOSE

CDK-activating kinase (CAK) is required for the regulation of the cell cycle and is a trimeric complex consisting of cyclin-dependent kinase 7 (CDK7), Cyclin H, and the accessory protein, MAT1. CDK7 also plays a critical role in regulating transcription, primarily by phosphorylating RNA polymerase II, as well as transcription factors such as estrogen receptor-α (ER). Deregulation of cell cycle and transcriptional control are general features of tumor cells, highlighting the potential for the use of CDK7 inhibitors as novel cancer therapeutics.

EXPERIMENTAL DESIGN

mRNA and protein expression of CDK7 and its essential cofactors cyclin H and MAT1 were evaluated in breast cancer samples to determine if their levels are altered in cancer. Immunohistochemical staining of >900 breast cancers was used to determine the association with clinicopathologic features and patient outcome.

RESULTS

We show that expressions of CDK7, cyclin H, and MAT1 are all closely linked at the mRNA and protein level, and their expression is elevated in breast cancer compared with the normal breast tissue. Intriguingly, CDK7 expression was inversely proportional to tumor grade and size, and outcome analysis showed an association between CAK levels and better outcome. Moreover, CDK7 expression was positively associated with ER expression and in particular with phosphorylation of ER at serine 118, a site important for ER transcriptional activity.

CONCLUSIONS

Expressions of components of the CAK complex, CDK7, MAT1, and Cyclin H are elevated in breast cancer and correlate with ER. Like ER, CDK7 expression is inversely proportional to poor prognostic factors and survival. Clin Cancer Res; 22(23); 5929-38. ©2016 AACR.

Abstract P5-03-13: The anticancer effects of Supinoxin® (RX-5902) in triple-negative breast cancer MDA-MB-231 through phosphorylated p68 on Tyr593

Several studies have indicated that the DEAD box RNA helicase DDX5/p68 plays several important roles in cancer (1, 2). In particular, p68 that is phosphorylated on Tyr593 has been shown to be associated with cell transformaton, epithelial mesenchymal transition (EMT) and cell migration (3). Therefore, phosphorylated p68 may be a promising target for novel anti-cancer therapeutics. We previously reported that 1-(3,5-dimethoxyphenyl)-4-[(6-fluoro-2-methoxyquinoxalin-3-yl) aminocarbonyl] piperazine (RX-5902, Supinoxin®) inhibits the growth of cancer cells at low nanomolar concentrations by interacting with phosphorylated p68 on Tyr593, interfering with the phosphorylated p68-β-catenin signaling pathway (4). In this study, we sought to determine whether phosphorylated p68 on Tyr593 plays a key role in RX-5902's ability to inhibit cancer cell growth by knocking down p68. p68-siRNA efficiently down-regulated the expression of phosphorylated p68 on Tyr593 as well as p68 in the triple-negative (TN) breast cancer cell line, MDA-MB-231. Exposure of p68-siRNA-transfected cells to the IC50 concentration of RX-5902 protected MDA-MB-231 cells from the cytotoxic effects of RX-5902, indicating the phosphorylated p68 on Tyr593 is a key molecule for RX-5902 cytotoxic effects. We also examined the tumor growth inhibition (TGI) of RX-5902 in the human TN-breast tumor (MDA-MB-231) xenograft mouse model. Not only did RX-5902 demonstrate potent efficacy in this model but also oral administration with RX-5902 resulted in dose-dependent TGI and extended the overall survival of these animals. Oral administration of 160, 320 and 600 mg/kg of RX-5902 showed 54.4%, 84.4% and 100% TGI, respectively whereas 5 mg/kg of Abraxane (iv) showed only 48.2% TGI at day 29. Further studies demonstrated the inhibitory effects of RX-5902 on cellular motility in MDA-MB-231 in wound healing assays, suggesting the potential function of phosphorylated p68 on Tyr593 in cell migration (5). These data support the potential therapeutic activity of RX-5902 in triple negative breast cancers. A Phase 1 study of RX-5902 on relapse/refractory solid tumors is ongoing.

References

1. Fuller-Pace, FV, RNA Biology 10, 121–132 (2013)

2. Dai et al. Journal of Experimental & Clinical Cancer Research, 33, 64-71 (2014

3. Yang et al., Cell, 127, 139–155 (2006)

4. Kost et al., Journal of Cellular Biochemistry ;online: 3 FEB 2015 05:14PM EST | DOI: 10.1002/jcb.25113) (2015).

5. Remenyi et al, presented at 2015 AACR (2015).

Citation Format: Kim DJ, Yang MY, Lee YB, Remenyi J, Fuller-Pace F. The anticancer effects of Supinoxin® (RX-5902) in triple-negative breast cancer MDA-MB-231 through phosphorylated p68 on Tyr593. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-03-13.

APOBEC3B-Mediated Cytidine Deamination Is Required for Estrogen Receptor Action in Breast Cancer

Estrogen receptor α (ERα) is the key transcriptional driver in a large proportion of breast cancers. We report that APOBEC3B (A3B) is required for regulation of gene expression by ER and acts by causing C-to-U deamination at ER binding regions. We show that these C-to-U changes lead to the generation of DNA strand breaks through activation of base excision repair (BER) and to repair by non-homologous end-joining (NHEJ) pathways. We provide evidence that transient cytidine deamination by A3B aids chromatin modification and remodelling at the regulatory regions of ER target genes that promotes their expression. A3B expression is associated with poor patient survival in ER+ breast cancer, reinforcing the physiological significance of A3B for ER action.

Happy birthday: 25 years of DEAD-box proteins

RNA helicases of the DEAD-box family are found in all eukaryotes, most bacteria and many archaea. They play important roles in rearranging RNA-RNA and RNA-protein interactions. DEAD-box proteins are ATP-dependent RNA binding proteins and RNA-dependent ATPases. The first helicases of this large family of proteins were described in the 1980s. Since then our perception of these proteins has dramatically changed. From bona fide helicases, they became RNA binding proteins that separate duplex RNAs, in a local manner, by binding and bending the target RNA. In the present review we describe some of the experiments that were important milestones in the life of DEAD-box proteins since their birth 25 years ago.

p53-dependent repression of polo-like kinase-1 (PLK1)

PLK1 is a critical mediator of G₂/M cell cycle transition that is inactivated and depleted as part of the DNA damage-induced G₂/M checkpoint. Here we show that downregulation of PLK1 expression occurs through a transcriptional repression mechanism and that p53 is both necessary and sufficient to mediate this effect. Repression of PLK1 by p53 occurs independently of p21 and of arrest at G₁/S where PLK1 levels are normally repressed in a cell cycle-dependent manner through a CDE/CHR element. Chromatin immunoprecipitation analysis indicates that p53 is present on the PLK1 promoter at two distinct sites termed p53RE1 and p53RE2. Recruitment of p53 to p53RE2, but not to p53RE1, is stimulated in response to DNA damage and/or p53 activation and is coincident with repression-associated changes in the chromatin. Downregulation of PLK1 expression by p53 is relieved by the histone deacetylase inhibitor, trichostatin A, and involves recruitment of histone deacetylase to the vicinity of p53RE2, further supporting a transcriptional repression mechanism. Additionally, wild type, but not mutant, p53 represses expression of the PLK1 promoter when fused upstream of a reporter gene. Silencing of PLK1 expression by RNAi interferes with cell cycle progression consistent with a role in the p53-mediated checkpoint. These data establish PLK1 as a direct transcriptional target of p53, independently of p21, that is required for efficient G₂/M arrest.

A novel site of AKT-mediated phosphorylation in the human MDM2 onco-protein

MDM2 is an E3 ubiquitin ligase which mediates ubiquitylation and proteasome-dependent degradation of the p53 tumor suppressor protein. Phosphorylation of MDM2 by the protein kinase AKT is thought to regulate MDM2 function in response to survival signals, but there has been uncertainty concerning the identity of the sites phosphorylated by AKT. In the present study, we identify Ser-166, a site previously reported as an AKT target, and Ser-188, a novel site which is the major site of phosphorylation of MDM2 by AKT in vitro. Analysis of MDM2 in cultured cells confirms that Ser-166 and Ser-188 are phosphorylated by AKT in a physiological context.

Cellular RNA helicase p68 relocalization and interaction with the hepatitis C virus (HCV) NS5B protein and the potential role of p68 in HCV RNA replication

Chronic infection by hepatitis C virus (HCV) can lead to severe hepatitis and cirrhosis and is closely associated with hepatocellular carcinoma. The replication cycle of HCV is poorly understood but is likely to involve interaction with host factors. In this report, we show that NS5B, the HCV RNA-dependent RNA polymerase (RdRp), interacts with a human RNA helicase, p68. Transient expression of NS5B alone, as well as the stable expression of all the nonstructural proteins in a HCV replicon-bearing cell line (V. Lohmann, F. Korner, J.-O. Koch, U. Herian, L. Theilmann, and R. Bartenschlager, Science 285:110-113), causes the redistribution of endogenous p68 from the nucleus to the cytoplasm. Deletion of the C-terminal two-thirds of NS5B (NS5BDeltaC) dramatically reduces its coimmunoprecipitation (co-IP) with endogenous p68, while the deletion of the N-terminal region (NS5BDeltaN1 and NS5BDeltaN2) does not affect its interaction with p68. In consistency with the co-IP results, NS5BDeltaC does not cause the relocalization of p68 whereas NS5BDeltaN1 does. With a replicon cell line, we were not able to detect a change in positive- and negative-strand synthesis when p68 levels were reduced using small interfering RNA (siRNA). In cells transiently transfected with a full-length HCV construct, however, the depletion (using specific p68 siRNA) of endogenous p68 correlated with a reduction in the transcription of negative-strand from positive-strand HCV RNA. Overexpression of NS5B and NS5BDeltaN1, but not that of NS5BDeltaC, causes a reduction in the negative-strand synthesis, indicating that overexpressed NS5B and NS5BDeltaN1 sequesters p68 from the replication complexes (thus reducing their replication activity levels). Identification of p68 as a cellular factor involved in HCV replication, at least for cells transiently transfected with a HCV expression construct, is a step towards understanding HCV replication.

FGF-7 (keratinocyte growth factor) expression during mouse development suggests roles in myogenesis, forebrain regionalisation and epithelial-mesenchymal interactions

We have isolated cDNA and genomic clones for the murine FGF-7 gene and examined its expression throughout development. Transcripts were transiently detected in the developing myocardium, differentially regulated between the atrium and ventricle. The gene was also expressed in the myotomes of the somites, coincident with FGF-4 and FGF-5 transcripts, and was detected transiently in cleaved muscles. Regional expression was detected in the ventricular zone of the developing forebrain at 14.5 d.p.c. Later in development, FGF-7 RNA was detected in mesenchymal tissues suggesting a role in epithelial-mesenchymal interactions and in the dermis consistent with its proposed role as a keratinocyte mitogen. Our results suggest that FGF-7 is likely to have diverse roles during development.

Large induction of keratinocyte growth factor expression in the dermis during wound healing

Recent studies have shown that application of basic fibroblast growth factor (basic FGF) to a wound has a beneficial effect. However, it has not been assessed whether endogenous FGF also plays a role in tissue repair. In this study we found a 160-fold induction of mRNA encoding keratinocyte growth factor (KGF) 1 day after skin injury. This large induction was unique within the family of FGFs, since mRNA levels of acidic FGF, basic FGF, and FGF-5 were only slightly induced (2- to 10-fold) during wound healing, and there was no expression of FGF-3, FGF-4, and FGF-6 detected in normal and wounded skin. High levels of FGF receptor 1 and FGF receptor 2 mRNA and low levels of FGF receptor 3 mRNA were found in both normal and wounded skin. No change in the levels of these transcripts was detected during wound healing. In situ hybridization studies revealed highest levels of KGF mRNA expression in the dermis at the wound edge and in the hypodermis below the wound. In contrast, mRNA encoding the receptor of this growth factor (a splice variant of FGF receptor 2) was predominantly expressed in the epidermis. These results suggest that basal keratinocytes are stimulated by dermally derived KGF during wound healing and implicate a unique role of this member of the FGF family in wound repair.

Cell transformation by kFGF requires secretion but not glycosylation

The Kfgf gene, which encodes a member of the fibroblast growth factor family, was originally discovered by assaying human tumor DNA for dominantly transforming oncogenes. The 22-kD kFGF product contains a single site for asparagine-linked glycosylation and an amino-terminal signal peptide for vectorial synthesis into the endoplasmic reticulum and eventual secretion. To determine whether these features are necessary for transformation, we have constructed mutants of kFGF that are impaired for glycosylation or secretion. All mutants retained the ability to induce DNA synthesis when added to quiescent cells, and the absence of glycosylation had no appreciable effect on the transformation efficiency on NIH3T3 cells. In contrast, mutants of kFGF that remain in the cytoplasm or are retained in the secretory pathway, through addition of a KDEL motif, score negative in standard transformation assays. Since transformation by either the glycosylated or unglycosylated form of kFGF can be reversed by addition of suramin, the data imply that secretion of kFGF, or surface localization of the ligand/receptor complex, is a prerequisite for transformation.

Characterization of int-2: a member of the fibroblast growth factor family

int-2 was discovered as a proto-oncogene transcriptionally activated by MMTV proviral insertion during mammary tumorigenesis in the mouse. Sequence analysis showed int-2 to be a member of the fibroblast growth factor family of genes. In normal breast and most other adult mouse tissues, int-2 expression was not detected except for low levels in brain and testis. However, using in situ hybridization, expression was found at a number of sites during embryonic development, from day 7 until birth. An analysis of the int-2 transcripts found in embryonal carcinoma cells revealed six major classes of RNA initiating at three promoters and terminating at either of two polyadenylation sites. Despite the transcriptional complexities, all size classes of RNA encompass the same open reading frame. Using an SV40 early promoter to drive transcription of an int-2 cDNA in COS-1 cells, several proteins were observed. These were shown to be generated by initiation from either of two codons: One, a CUG, leads to a product which localizes extensively to the cell nucleus and partially to the secretory pathway. In contrast, initiation at a downstream AUG codon results in quantitative translocation across the endoplasmic reticulum and the accumulation of products ranging in size from 27.5 x 10(3) Mr to 31.5 x 10(3) Mr in organelles of the secretory pathway. These proteins represented glycosylated and non-glycosylated forms of the same primary product with or without the signal peptide removed. These findings suggest the potential for a dual role of int-2; an autocrine function acting at the cell nucleus, and a possible paracrine action through a secreted product.