Efficacy In Breast Cancer Models Research Articles

Efficacy of futibatinib, an irreversible fibroblast growth factor receptor inhibitor, in FGFR-altered breast cancer

Several alterations in fibroblast growth factor receptor (FGFR) genes have been found in breast cancer; however, they have not been well characterized as therapeutic targets. Futibatinib (TAS-120; Taiho) is a novel, selective, pan-FGFR inhibitor that inhibits FGFR1-4 at nanomolar concentrations. We sought to determine futibatinib’s efficacy in breast cancer models. Nine breast cancer patient–derived xenografts (PDXs) with various FGFR1-4 alterations and expression levels were treated with futibatinib. Antitumor efficacy was evaluated by change in tumor volume and time to tumor doubling. Alterations indicating sensitization to futibatinib in vivo were further characterized in vitro. FGFR gene expression between patient tumors and matching PDXs was significantly correlated; however, overall PDXs had higher FGFR3-4 expression. Futibatinib inhibited tumor growth in 3 of 9 PDXs, with tumor stabilization in an FGFR2-amplified model and prolonged regression (> 110 days) in an FGFR2 Y375C mutant/amplified model. FGFR2 overexpression and, to a greater extent, FGFR2 Y375C expression in MCF10A cells enhanced cell growth and sensitivity to futibatinib. Per institutional and public databases, FGFR2 mutations and amplifications had a population frequency of 1.1%–2.6% and 1.5%–2.5%, respectively, in breast cancer patients. FGFR2 alterations in breast cancer may represent infrequent but highly promising targets for futibatinib.

Abstract P4-04-09: New oral SERD elacestrant (RAD1901) shows efficacy in breast cancer models harbouring ESR1 mutations and enhances the antiproliferative activity of mTORC1 and CDK4/6 inhibitors

Abstract Background: Targeting estrogen receptor (ER) signalling is the main therapeutic option for ER+ breast cancer (BC). However, over 30% of patients relapse with endocrine resistance emphasising the need for improved therapeutic strategies. The prevalence of ESR1 mutations in relapsed tumours highlights the sustained reliance on ER signalling, rationalising continued targeting of ER. Unlike other endocrine therapies such as aromatase inhibitors (AI) and tamoxifen, selective ER degraders (SERDs) are competitive ER antagonists, that induce a conformational change in ER resulting in ubiquitination and degradation via the proteasomal pathway. Fulvestrant has shown clinical utility in advanced BC but is limited by its pharmaceutical properties highlighting the need for SERDs with enhanced bioavailability and pharmacokinetic properties. Here, we show that elacestrant (RAD1901) an orally bioavailable SERD, has antitumor activity in endocrine sensitive and resistant models of ER+ BC. Furthermore, elacestrant enhances the efficacy of mTORC1 inhibitor, everolimus and CDK4/6 inhibition, in model systems. Methods: Several ER+ BC lines adapted to long-term E deprivation (LTED) and harbouring wild-type or a naturally occurring ESR1 mutation, were treated with elacestrant or fulvestrant +/- estradiol (E2). Effects on cell proliferation, cell signalling, cell cycle, transcription, ER protein stability and ER genomic binding were assessed. Efficacy in combination with everolimus, palbociclib and abemaciclib was also evaluated. Results: Cell proliferation assays in 2D and spheroids in the presence of 0.01nM E2 showed a concentration-dependent decrease in proliferation in response to elacestrant and fulvestrant. GI50 values for elacestrant in general were 10-fold higher than fulvestrant but equated to doses that are clinically achievable for the drug. Most importantly, elacestrant suppressed proliferation of two LTED models harbouring ESR1 mutations, MCF7 LTEDY537C (GI50 5nM) and SUM44-LTEDY537S (GI50 100nM). GI50 values of elacestrant and fulvestrant showed similar reduction of ER, progesterone receptor (PGR) and cyclinD1 together with decreased phosphorylation of retinoblastoma (RB), concordant with cell cycle arrest. Chromatin immunoprecipitation (ChIP) for ER in response to elacestrant or fulvestrant showed a reduction in recruitment of ER to TFF1, GREB1 and PGR promoters and concomitant reduction in mRNA expression of these genes in the presence of E2. Elacestrant-mediated ER depletion was dependent on the 26S proteasome, as addition of the proteasome inhibitor MG132, fully blocked elacestrant depletion of ER, similar to the effect of MG132 treatment in preventing fulvestrant-mediated ER turnover. The combination of elacestrant with CDK4/6 inhibitors, palbociclib or abemaciclib, demonstrated additivity compared with monotherapy. In addition, elacestrant inhibited growth of palbociclib-resistant MCF7 LTED cells. Conclusion: These findings highlight the potential utility of elacestrant as a 1st or 2nd line drug in the treatment of ER+ BC. The results support the testing of elacestrant versus fulvestrant after relapse on an AI, either alone or in combination with a CDK4/6 inhibitor. Citation Format: Martin L-A, Pancholi S, Simigdala N, Nikitorowicz-Buniak J, Ribas R, Garner F, Bihani T, Dowsett M. New oral SERD elacestrant (RAD1901) shows efficacy in breast cancer models harbouring ESR1 mutations and enhances the antiproliferative activity of mTORC1 and CDK4/6 inhibitors [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-04-09.

Abstract 3092: U3-1402a, a novel HER3-targeting ADC with a novel DNA topoisomerase I inhibitor, demonstrates a potent antitumor efficacy

Abstract Background HER3 (human epidermal growth factor receptor 3) is a member of HER family, and overexpressed in breast cancer, NSCLC, melanoma, gastric cancer and pancreatic cancer patients` tissues. U3-1402a is an antibody-drug conjugate (ADC) comprised of a fully human anti-HER3 monoclonal immunoglobulin G1 (IgG1) antibody (U3-1287) covalently conjugated via a cleavable peptide linker to exatecan derivative (DXd). The DXd is released after internalization of U3-1402a and leads to apoptosis of the target tumor cells by the inhibition of topoisomerase I. This ADC achieves a high drug-to-antibody-ratio (DAR 7 to 8) with homogeneous conjugation with the topoisomerase I inhibitor. The aim of this study was to preclinically evaluate the efficacy of U3-1402a in breast cancer models. Materials and methods In order to evaluate the pharmacological potential of U3-1402a, in vitro and in vivo studies were performed. In vitro growth inhibition assay evaluated the sensitivity of U3-1402a in HER3-positive human breast cancer cell line (HCC1569) and HER3-negative human cervical carcinoma cell line (C33A). Cells were treated with U3-1402a or MAAA-1181 (payload of U3-1402a) depending on its concentration (U3-1402a: 0.153 to 10 000 ng/mL, MAAA-1181: 2.44 to 160,000 pg/mL). In vivo growth inhibition study evaluated the dose-dependent sensitivity of U3-1402a in HER3-positive breast cancer xenograft model, MDA-MB-453. In addition, several xenograft models with different HER3 expression were tested with its sensitivity to U3-1402a. These models were HCC1569 (human breast cancer cell line, HER3 IHC score 3+), MDA-MB-453 (human breast cancer cell line, HER3 IHC score 2+), NIBIO-G016 (human gastric cancer patient-derived xenograft, HER3 IHC score 1+) and MDA-MB-231 (human breast cancer cell line, HER3 IHC score 0). R esults In vitro study, U3-1402a exhibited anti-tumor killing activity in HER3-positive human breast cancer cell line, HCC1569. C-33A human cervical carcinoma cell line was not sensitive to U3-1402a even MAAA-1181 itself exhibited anti-tumor killing activity to this cell line. In vivo study, U3-1402a showed dose-dependent anti-tumor killing activity in a HER3-positive breast cancer MDA-MB-453 xenograft model. Finally, in vivo tumor regression was only observed in HER3 2+ and 3+ models. Conclusions U3-1402a preclinically exhibited its efficacy in breast cancer model in vitro and in vivo. In vivo efficacy was correlated with HER3 expression. These studies suggest that U3-1402a, a novel HER3-targeting ADC, would be efficacious in a broader patient population with HER3 expression like breast cancer, melanoma, NSCLC, gastric cancer and pancreatic cancer. Citation Format: Suguru Ueno, Kenji Hirotani, Reimar Abraham, Sabine Blum, Birgit Frankenberger, Mauricio Redondo-Muller, Johannes Bange, Yusuke Ogitani, Akiko Zembutsu, Koji Morita, Takashi Nakada, Shuji Majima, Yuki Abe, Toshinori Agatsuma. U3-1402a, a novel HER3-targeting ADC with a novel DNA topoisomerase I inhibitor, demonstrates a potent antitumor efficacy [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 3092. doi:10.1158/1538-7445.AM2017-3092

Abstract 392: Combined targeting of MET and PI3K improves efficacy in breast cancer models with concurrent MET/PI3K aberrations

Abstract Introduction: Detailed understanding of the genetic abnormalities that drive subsets of cancer has led to the development of highly specific inhibitors targeting key oncogenic pathways. Growing evidence implicates aberrations of both mesenchymal epithelial transition receptor (MET) and its key downstream phosphatidylinositol 3-kinase (PI3K) signaling with poorer prognosis in breast cancer. Co-targeting MET/PI3K and identifying mechanisms of response and resistance could ultimately inform a novel therapeutic strategy for breast cancer treatment. Based on these finding, we hypothesized that concurrent aberrations in PI3K and MET will render breast cancers resistant to therapies targeting each pathway, and that combination therapy targeting the PI3K and MET pathway will improve the efficacy by preventing the acquisition of resistance. Methods: We established cell models that stably express human wild type (WT) MET or MET-T1010I, a functional germline single nucleotide polymorphism, or mutant PI3K-H1047R alone, or variable concurrent aberrations in PI3K and MET using MCF-10A, a non-transformed mammary epithelial cell line, and HCC1954, a breast cancer cell line with an endogenous PI3KCA-H1047R mutation. Cell behaviors, including survival, invasion and response to MET one arm monoclonal antibody onartuzumab (MetMAb, Genentech Inc) and/or pan class I PI3K inhibitor GDC 941 (pictilisib, Genentech Inc), were detected. HCC1954 expressing WT MET or MET-T1010I along with PI3K-H1047R were transplanted into the mammary fat pad of hepatocyte growth factor-transgenic mice on a severe combined immunodeficiency background. Statistical analyses were carried out using the ANOVA and the Student t test. Result: Expression WT MET or MET-T1010I act coordinately with PI3K-H1047R to increase colony formation (P < 0.01, respectively). Concurrent MET-T1010I, but not WT MET, acts coordinately with PI3K-H1047R to increase cell invasion (P < 0.0001). Expression MET-T1010I or WT MET induced cells resistance to GDC941, with MET-T1010I stronger than WT MET. Combined targeting MET with onartuzumab and targeting PI3K with GDC941 significantly inhibited cell growth in matrigel, dose dependently than each monotherapy (P < 0.0001, respectively). Invasion assay showed similar pattern. Combined onartuzumab and GDC941 significantly inhibited invasion, dose dependently (P < 0.001). The effects were confirmed using PI3K/mTOR inhibitor, GDC980. Consistently, combination of onartuzumab/GDC941 significantly inhibited tumor growth (P < 0.01 versus GDC941; P < 0.0001 versus onartuzumab alone). Conclusions: Concurrent aberrations of MET and PI3K render breast cancer cells resistant to therapies blocking either pathway. Targeting both MET and PI3K increases inhibitory efficacy. Citation Format: Shuying Liu, Naoto T. Ueno, Bailiang Wang, Mihai Gagea, Prahlad T. Ram, Mark Merchant, John Mendelsohn, Debasish Tripathy, Gordon B. Mills, Ana M. Gonzalez-Angulo. Combined targeting of MET and PI3K improves efficacy in breast cancer models with concurrent MET/PI3K aberrations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 392.

Abstract P4-16-10: A novel paclitaxel-dendrimer conjugate demonstrates better efficacy in breast cancer models

Abstract BACKGROUND: Breast cancer is the 2nd most common cause of cancer deaths in women. Chemotherapy is an important treatment modality. Yet, delivery of drugs such as paclitaxel (PTX) to cancer cells remains a challenge, mainly due to a drug's low solubility, rapid in vivo clearance, high systemic toxicity, and low drug delivery to tumor. Nanotechnology has been proposed as a solution to these problems. In active targeting, increased tumor specificity of nanoparticles is achieved through attachment of agents that target the molecular differences between normal and malignant cells. Dendrimers are a category of synthetic, monodisperse and multivalent nanopolymers, capable of high drug-loading and multiple covalent bonding of bioactive moieties. Conjugation using enzyme cleavable linkers allows for specific, targeted release. While PTX delivery through dendrimers has been established, such vehicles have not used active targeting for specific delivery to cancer cells. Thus, a need exists for specific delivery of PTX through an active-targeting dendrimer-based vehicle, while maintaining high-drug loading properties of dendrimers. This study reports the synthesis, characterization, and biological assessment of polyamidoamine (PAMAM) dendrimers conjugated to PTX via a peptide spacer cleavable by a cancer-upregulated enzyme, Cathepsin B (CatB). METHODS: PAMAM was conjugated to PTX via an enzyme-cleavable, peptide spacer resulting in formation of a PTX-laden dendrimer (PLD). Structure confirmation of PLD was done by 1H-NMR and mass spectrometry (MS). MDA-MB-231 breast cancer cells and MCF10A immortalized normal breast cells served as in vitro models for tumor efficacy and specificity. WST-1 based cytotoxicity assays were performed after 72h drug incubation at various concentrations of PTX or PTX-equivalent dendrimer. In vivo tumor efficacy of PLD as compared to PTX alone or vehicle alone was performed on MDA-MB-231 xenografts in athymic nude mice. RESULTS: MS data showed a broad peak centered at 24 kDa. NMR proton integration revealed a PTX:dendrimer ratio of 7:1. This ratio was used to deliver specific molar amounts of PTX in PLD form during assays. Cytotoxicity assays for the MDA-MB-231 demonstrated a marked shift in the relative IC50 values of PTX incorporated in PLD. The IC50 of paclitaxel for MDA-MB-231 cancer cells was 0.640 nM for PLD relative to 3.29 nM for PTX. By contrast, the IC50 of PLD for MCF10A normal cells was 2.45 nM as compared to 2.85 nM for PTX. This smaller shift in relative IC50 values correlates to reported CatB activity. When compared at 10 nM PTX/PLD, negative control PAMAM had no effect on cell growth, while PLD had a statistically-significant reduced proliferation compared PTX for MDA-MB-231 cells only. In vivo studies revealed PLD had a strong reduction in tumor volume growth compared to vehicle alone (p<0.05) up to 2 weeks after treatment while PTX treatment showed a smaller reduction (p>0.05). CONCLUSIONS: PTX when delivered through PLD showed increased cytotoxicity to MDA-MB-231 cancer cells but not normal MCF10A cells, correlating with previous reports on CatB activity. PLD demonstrates enhanced reduction in tumor growth as compared to PTX. This suggests successful development of a cancer-specific active targeting delivery vehicle. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-16-10.