Intratumoural Cytochrome P450 Expression in Breast Cancer: Impact on Standard of Care Treatment and New Efforts to Develop Tumour-Selective Therapies

Despite significant advances in treatment strategies over the past decade, selective treatment of breast cancer with limited side-effects still remains a great challenge. The cytochrome P450 (CYP) family of enzymes contribute to cancer cell proliferation, cell signaling and drug metabolism with implications for treatment outcomes. A clearer understanding of CYP expression is important in the pathogenesis of breast cancer as several isoforms play critical roles in metabolising steroid hormones and xenobiotics that contribute to the genesis of breast cancer. The purpose of this review is to provide an update on how the presence of CYPs impacts on standard of care (SoC) drugs used to treat breast cancer as well as discuss opportunities to exploit CYP expression for therapeutic intervention. Finally, we provide our thoughts on future work in CYP research with the aim of supporting ongoing efforts to develop drugs with improved therapeutic index for patient benefit.

Abstract 5210: Differential cytotoxic effects of Piperlongumine analogues and their radiotherapeutic response in breast cancer

Background: Breast cancer is the most common cancer in women in the United Kingdom. The glutathione (GSH) system is a major redox buffering system involved in regulating radioresponse of cancer cells. Overexpression has been shown to cause multidrug and radiation resistance. Its modulation may increase radiosensitivity and improve radiotherapy efficacy. Piperlongumine (PL) can reportedly inhibit GSH system function and reduce proliferation of a variety cancer cells in vitro. The current study investigates novel PL analogues to determine efficacy in triple-negative (TNBC) and luminal breast cancer cell lines, as both single agents and in combination with ionising radiation.

Methods: Two novel PL analogues (LH91 and LH92) were used along with the parental drug, PL. Cell proliferation assays were conducted in MDA-MB-231 (TNBC) and T47D (luminal) lines at various drug concentrations and times. At 48hr post treatment, cells were also assessed for clonogenic survival. Clonogenic radiosensitisation was assessed by treating with PL agents or L-buthionine-S, R-sulfoximine (BSO, a well characterised GSH radiosensitiser) for 48hr then irradiation with 0-8Gy X-rays. ROS levels were evaluated using H2DCFDA flow cytometry following IC50 drug treatment alone or with subsequent exposure to 1mM H2O2 for 1hr.

Results: PL, LH91 and LH92 inhibited proliferation and decreased clonogenic survival in both lines. From proliferation assays, MDA-MB-231 cells were more sensitive to PL at 48hr (P=0.047) and 72hr (P=0.01) with an IC50 dose of approx. 4μM versus approx. 12μM in T47D’s. There was a significant difference between IC50 doses of LH91 in MDA-MB-231 (5μM) and T47D (12μM) cell lines at 72hr (P=0.006), however this was not observed at 48hr treatment (P=0.178). In contrast, there was no differential sensitivity of LH92 in cell proliferation between the two cell lines at 48 and 72hr. Interestingly, in clonogenic assays, MDA-MB-231’s were more sensitive to LH92 (P=0.01) with an IC50 of 4μM versus 11μM in T47D’s. There were no significant differences in clonogenic survival between each line after treatment with PL or LH91. No radiosensitisation was observed with PL or PL analogues in MDA-MBA-231 however BSO, as a drug comparator, enhanced radiation response with a sensitizer enhancement ratio (SER) of 1.13 at 1% iso-survival. Radiation and drug combinations in T47D cells are ongoing. There were no changes in ROS levels with the drug alone in MDA-MB-231; however, with subsequent exposure of H2O2, there was a 1.7-fold increase in ROS level with LH91 at 48hr (P=0.002).

Conclusion: The TNBC cell line is more sensitive to the cytotoxic effect of PL agents (PL and LH91 in cell proliferation and LH92 in clonogenic assays) in comparison to the luminal cell line; however no altered radiosensitisation was observed. The mechanism of such differential sensitivity is yet to be determined.

Note: This abstract was not presented at the meeting.

Citation Format: Nurul Akmaryanti Abdullah, John Moses, Li Chen Han, Sarah Storr, Aula Ammar, Stewart G. Martin. Differential cytotoxic effects of Piperlongumine analogues and their radiotherapeutic response in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5210. doi:10.1158/1538-7445.AM2017-5210

Abstract 890: The role of calpastatin isoforms in breast cancer progression

Calpastatin is the endogenous inhibitor of the ubiquitously expressed m-calpain and μ-calpain. Both of them are important regulators of various cellular pathways including proliferation, apoptosis, adhesion, and migration. Dysregulation of the calpain system is associated with a wide range of pathologies including tumour invasion and metastasis. In breast cancer, down-regulation of calpastatin mRNA, in particular an exon 3 containing variant, is associated with lymphatic vessel invasion which is the predominant form of lymphovascular invasion (LVI) (96%), a critical initial step of metastases. The current project seeks to determine the role that individual calpastatin isoforms play in regulating breast cancer cell migration and endothelial interactions to understand processes involved in regulating LVI.

Seven breast cancer cell lines were assessed for calpain system protein expression (calpain-1, -2, -4 and calpastatin) and calpastatin (CAST) mRNA expression (total CAST, CASTexon3, CAST I, II and III) by Western blotting and qRT-PCR, respectively. T47D and MDA-MB-231 cell lines showed low calpastatin but high calpain expression. From haptotaxis cell migration data, T47D migrated more slowly than MDA-MB-231 (35.49±6.14 and 80.34±5.52 percent wound closure at 24 hours post-scratch respectively) (P value=0.0233). These cell lines, that represent different subtypes of breast cancer (luminal and basal respectively), were therefore selected to study the role of differential calpastatin type/isoform expression.

GFP-tagged XL and Leader domains of calpastatin type I, II and III, with or without exon 3 were overexpressed in each cell line. The different calpastatin types show differential subcellular localization. In MDA-MB-231, type I, III, IΔ3, IIIΔ3 were expressed generally in cytoplasm whereas type II and IIΔ3 were located as punctate nuclear invaginations. To assess if overexpression of the different calpastatin types cause phenotypic changes, full length HA-tagged calpastatin type I, II and III were transfected into MDA-MB-231 and T47D and stable clones produced. Thus far stable type II overexpression in MDA-MB-231 and type III in T47D have been obtained with others under single cell selection. The localization of full length type II in MDA-MB-231 was similar to the localization of the truncated form that showing a strong single perinuclear signal. In T47D, the full length and truncated type III also show similarly localization that expressed throughout the cytoplasm. For the effect of calpastatin types on cell proliferation, calpastatin type II in MDA-MB-231, and type III in T47D, had no significant effect on cell doubling time when compared to respective controls (P value=0.6400 and 0.8874, respectively). According to preliminary studies, calpastatin type II seems to have no effect on clonogenicity of MDA-MB-231. Such effect on T47D and other phenotypic changes involved in regulating LVI of transfected cell are being examined.

Citation Format: Bhudsaban Sukkarn, Sarah Storr, Ian O. Ellis, Kirsty Jewell, Tim Parr, Stewart G. Martin. The role of calpastatin isoforms in breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 890. doi:10.1158/1538-7445.AM2017-890

Multiple pathways regulate Cten in colorectal cancer without a Tensin switch

CTEN/TNS4 is a member of the Tensin gene family. It localizes to focal adhesions and induces cell motility. The mechanisms regulating Cten expression are unclear although we have shown regulation by Kras in the colon and pancreas. In normal mammary cell lines, it is reportedly upregulated by epidermal growth factor receptor (EGFR) and STAT3 signalling and upregulation is accompanied by downregulation of Tensin 3 (Tensin switch). In this study, we investigated the roles of EGFR and STAT3 signalling in the regulation of Cten in colorectal cancer (CRC). In addition, we investigated calpain--a regulator of focal adhesion-associated proteins whose relevance to Cten has not been investigated. CRC cell lines were stimulated with epidermal growth factor (EGF). This resulted in an increase in Cten and Tensin 3 protein. Kras was knocked down and this resulted in downregulation of Cten and Tensin 3. We next investigated the role of STAT3 signalling. Activation and knockdown of STAT3 resulted in downregulation and upregulation, respectively, of Cten. Inhibition of calpain resulted in upregulation of both Cten and Tensin 3. As the regulators of Cten also seemed to regulate Tensin 3, we tested the interaction between Cten and Tensin 3. Cten was forcibly expressed or knocked down resulting, respectively, in upregulation and downregulation of Tensin 3. We conclude that in CRC, Cten is upregulated by EGFR and Kras but downregulated by STAT3. We show that calpain may be a negative regulator of Cten and that a Tensin switch does not occur and, if anything, Cten stabilizes Tensin 3.

Lymphovascular invasion: assessment and prognostic impact in melanoma and breast cancer

The presence of lymphovascular invasion is a recognised poor prognostic factor in a wide range of tumour types. Vascular invasion was historically identified through haematoxylin and eosin staining, however this technique is non-specific and differentiates poorly between blood and lymphatic vessels. Newer techniques using immunohistochemistry allow more sensitive and specific identification of lymphovascular invasion and are able to accurately differentiate between lymphatic and blood vessels. This review will discuss the current methods available for the assessment of lymphovascular invasion. Additionally, it will focus on the role of lymphovascular invasion in breast cancer and melanoma, discussing the relative importance of lymphatic and blood vessel invasion in each tumour type.

The clinicopathological and gene expression patterns associated with ulceration of primary melanoma

Ulceration of primary melanomas is associated with poor prognosis yet is reported to predict benefit from adjuvant interferon. To better understand the biological processes involved, clinicopathological factors associated with ulceration were determined in 1804 patients. From this cohort, 348 primary tumor blocks were sampled to generate gene expression data using a 502-gene cancer panel and 195 blocks were used for immunohistochemistry to detect macrophage infiltration and vessel density. Gene expression results were validated using a whole genome array in two independent sample sets. Ulceration of primary melanomas was associated with more proliferative tumors, tumor vessel invasion, and increased microvessel density. Infiltration of tumors with greater number of macrophages and gene expression pathways associated with wound healing and up-regulation of pro-inflammatory cytokines suggests that ulceration is associated with tumor-related inflammation. The relative benefit from interferon reported in patients with ulcerated tumors may reflect modification of signaling pathways involved in inflammation.

Are DNA repair factors promising biomarkers for personalized therapy in gastric cancer?

Chronic inflammation is a driving force for gastric carcinogenesis. Reactive oxygen species (ROS) generated during the inflammatory process generates DNA damage that is processed through the DNA repair pathways. In this study, we profiled key DNA repair proteins (single-strand-selective monofunctional uracil-DNA glycosylase 1 [SMUG1], Flap endonuclease 1 [FEN1], X-ray repair cross-complementing gene 1 [XRCC1], and Ataxia telangiectasia mutated [ATM]) involved in ROS-induced oxidative DNA damage repair in gastric cancer and correlated to clinicopathological outcomes. High expression of SMUG1, FEN1, and XRCC1 correlated to high T-stage (T3/T4) (p-values: 0.001, 0.005, and 0.02, respectively). High expression of XRCC1 and FEN1 also correlated to lymph node-positive disease (p-values: 0.009 and 0.02, respectively). High expression of XRCC1, FEN1, and SMUG1 correlated with poor disease-specific survival (DSS) (p-values: 0.001, 0.006, and 0.05, respectively) and poor disease-free survival (DFS) (p-values: 0.001, 0.001, and 0.02, respectively). Low expression of ATM correlated to lymph node positivity (p=0.03), vascular invasion (p=0.05), and perineural invasion (p=0.005) and poor DFS (p=0.001) and poor DSS (p=0.003). In the multivariate Cox model, high XRCC1 and low ATM were independently associated with poor survival (p=0.008 and 0.011, respectively). Our observation supports the hypothesis that DNA repair factors are promising biomarkers for personalized therapy in gastric cancer.