Breast Cancer Xenografts Research Articles

Abstract LB268: Discovery of a potent, selective and brain penetrating PARP1 inhibitor, XZP-7797

Abstract First-generation PARP1/2 inhibitors are approved for the treatment of cancers, such as ovarian, prostate, pancreas, and breast cancers, with maximal activity against tumors harboring BRCA1/2 mutation or homologous recombination deficiency (HRD). However, PARP1/2 inhibitors in clinical use have severe hematological toxicities due to the inhibition of PARP2, which has been shown to play an important role in the survival of hematopoietic progenitor cells. Furthermore, the current data indicate that synthetic lethality with BRCA mutations is primarily caused by PARP1 inhibition and trapping, whereas PARP2 inhibition and trapping are not critical for anticancer activity. Therefore, the development of selective PARP1 inhibitors is expected to reduce the hematological adverse effects associated with PARP2 inhibition while maintaining the required efficacy. XZP-7797 is a potent, selective, and brain-penetrating PARP1 inhibitor with trapping ability. In biochemical assays, XZP-7797 is more than 1000-fold selective for PARP1 over PARP2 and other members of the PARP family, including PARP3, PARP5a, PARP5b, and PARP6. XZP-7797 can significantly inhibit MDA-MB-436 cell proliferation in vitro (IC50=2.4nM). In MDA-MB-436 tumor cells, XZP-7797 inhibits PARylation and increases γH2AX level in a concentration-dependent manner. XZP-7797 demonstrates rapid tumor regression in a dose-dependent manner in the BRCA1 mutant MDA-MB-436 breast cancer xenograft model. In a pancreatic cancer xenograft model, XZP-7797 can also significantly inhibit tumor growth. To evaluate the ability of XZP-7797 to cross the blood-brain barrier, an intracranial xenograft model of breast cancer is used. The results show that XZP-7797 can significantly inhibit the growth of intracranial tumors in mice at a dose of 10 mg/kg, demonstrating the brain-penetrating ability of XZP-7797. Additionally, XZP-7797 has great PK profiles in preclinical species after oral dosing and good ADME properties. In a 14-day toxicology study of XZP-7797 in SD Rats, XZP-7797 has no hematological adverse effects at the exposure that is 10 times higher than the exposure required to achieve superior efficacy. Citation Format: Yeqing Gao, Yuqian Lu, Bo Chen, Benke Jiang, Feng Wang, Genyan Zhang, Xifeng Ma, Dapeng Zhou, Chunmin Shi, Yunling Wang, Zhipeng Liu, Jun Sun, Huimin Zhou, Mei Xu, Jiakui Li, Bin Liu. Discovery of a potent, selective and brain penetrating PARP1 inhibitor, XZP-7797 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB268.

XBP1s activates METTL3/METTL14 for ER-phagy and paclitaxel sensitivity regulation in breast cancer

Cancer cells employ the unfolded protein response (UPR) or induce autophagy, especially selective removal of certain ER domains via reticulophagy (termed ER-phagy), to mitigate endoplasmic reticulum (ER) stress for ER homeostasis when encountering microenvironmental stress. N6-methyladenosine (m6A) is one of the most abundant epitranscriptional modifications and plays important roles in various biological processes. However, the molecular mechanism of m6A modification in the ER stress response is poorly understood. In this study, we first found that ER stress could dramatically elevate m6A methylation levels through XBP1s-dependent transcriptional upregulation of METTL3/METTL14 in breast cancer (BC) cells. Further MeRIP sequencing and relevant validation results confirmed that ER stress caused m6A methylation enrichment on target genes for ER-phagy. Mechanistically, METTL3/METTL14 increased ER-phagy machinery formation by promoting m6A modification of the ER-phagy regulators CALCOCO1 and p62, thus enhancing their mRNA stability. Of note, we further confirmed that the chemotherapeutic drug paclitaxel (PTX) could induce ER stress and increase m6A methylation for ER-phagy. Furthermore, the combination of METTL3/METTL14 inhibitors with PTX demonstrated a significant synergistic therapeutic effect in both BC cells and xenograft mice. Thus, our data built a novel bridge on the crosstalk between ER stress, m6A methylation and ER-phagy. Most importantly, our work provides novel evidence of METTL3 and METTL14 as potential therapeutic targets for PTX sensitization in breast cancer.

JHD205, A Novel Abemaciclib Derivative, Exerts Antitumor Effects on Breast Cancer by CDK4/6.

Efficient targeted molecular therapeutics are needed for the treatment of triple-negative breast cancer (TNBC), a highly invasive and difficult-to-treat form of breast cancer associated with a poor prognosis. This study aims to evaluate the potential of selective CDK4/6 inhibitors as a therapeutic option for TNBC by impairing the cell cycle G1 phase through the inhibition of retinoblastoma protein (Rb) phosphorylation. In this study, we synthesized a compound called JHD205, derived from the chemical structure of Abemaciclib, and examined its inhibitory effects on the malignant characteristics of TNBC cells. Our results demonstrated that JHD205 exhibited superior tumor growth inhibition compared to Abemaciclib in breast cancer xenograft chicken embryo models. Western blot analysis revealed that JHD205 could dosedependently degrade CDK4 and CDK6 while also causing abnormal changes in other proteins associated with CDK4/6, such as p-Rb, Rb, and E2F1. Moreover, JHD205 induced apoptosis and DNA damage and inhibited DNA repair by upregulating Caspase3 and p-H2AX protein levels. Collectively, our findings suggest that JHD205 holds promise as a potential treatment for breast carcinoma.

Abstract 6027: 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts

Abstract Background: About 80% of colorectal cancer (CRC) and 50 % of Triple-Negative breast cancer (TNBC) patients overexpress epidermal growth factor receptor (EGFR). Mutations in the KRAS oncogene (present in 40% of mCRC) lead to constitutive over-activation of EGFR and drive de novo resistance to anti-EGFR drugs. Here, we propose to target KRAS-mutant/BRAF mutant EGFR positive mCRC and TNBC using 225Ac-labeled matuzumab, a humanized anti-EGFR monoclonal antibody. Methods: p- -SCN-macropa was used to conjugate matuzumab for radiolabeling with 225Ac and SCN-deferoxamine was used to conjugate matuzumab for labelling with 89Zr. The radioimmunoconjugates were characterized by flow cytometry, HPLC and iTLC. in vitro cytotoxicity was evaluated in EGFR-positive mCRC, TNBC cell lines and 3D spheroids with different levels of EGFR density. Tumor growth was monitored using digital caliper. Mice were treated with either 10 MBq of 89Zr-matuzumab for imaging or three doses of 13 KBq/dose administered of 225Ac-matuzumab 10 days apart. In vivo study endpoint was tumor volume greater than or equal to 1500 mm3. Results: Flow cytometry showed about 95% binding to the cells in all EGFR-positive colorectal cell lines (DLD-1, SW620, SNU-C2B, HT-29) and breast cancer cell lines (MDA-MB-468, MDA-MB-231). in vitro studies showed enhanced cytotoxicity of 225Ac-matuzumab compared with matuzumab. IC50 in the MDA-MB-468 cell line for 225Ac-matuzumab (1.86 ± nM) was 35 times more effective than matuzumab (65.25± 7 nM). Similar trends were observed in the other KRAS-mutant mCRC cell lines and breast cancer cell lines. In 3D spheroid models, the IC50 of 225Ac-matuzumab (3.0 ± 2 nM) in MDA-MB-468, was 20.79 times more effective than matuzumab (62.3 ± 1.38 nM). Similar trends were observed for all the other spheroid models as well. High uptake of 89Zr-matuzumab was observed in both mCRC and TNBC xenografts. 225Ac-matuzumab slowed tumor growth rate in MDA-MB-468 and MDA-MB-231 tumors models compared with control antibody or non-treated controls for 30 days. This study is still ongoing and will last for 2 more months. Conclusion: 225Ac-matuzumab shows very promising outcomes in KRAS-mutant mCRC models and breast cancer models and warrants further investigation. Citation Format: Florence Anjong Tikum, Humphrey Fonge, Fabrice Njotu, Hanan Babeker, Jessica K. Pougoue, Nikita Henning, Alireza Doroudi. 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6027.

Abstract 2616: BCG033, a novel bispecific antibody-drug conjugate targeting PTK7 and TROP2, demonstrates preclinical efficacy against triple-negative breast cancer and other solid tumor xenografts

Abstract Metastatic triple-negative breast cancer (TNBC) patients have poor overall survival, highlighting the need for novel treatments. Although the TROP2-targeting ADC sacituzumab govitecan recently received accelerated approval from the FDA for the treatment of patients with metastatic TNBC, the on-target toxicity of this single-target agent has limited clinical efficacy. We sought to improve the specificity and efficacy of future TNBC-targeted therapies by generating a bispecific antibody-drug conjugate (bsADC) targeting TROP2 and PTK7, another tumor-associated antigen (TAA) that is highly expressed in TNBC and correlates with poor prognosis and metastatic disease. We previously generated fully human antibodies targeting PTK7 and TROP2 from Biocytogen’s fully human, common light chain antibody transgenic RenLite® mice, which were selected such that their monovalent antibodies exhibited reduced internalization profiles for improved tumor selectivity. These antibodies were then constructed into a bispecific antibody targeting PTK7 × TROP2, which demonstrated reactivity to human and cynomolgus monkey antigens and binding to multiple cancer cell lines, including TNBC, with high affinity. PTK7 × TROP2 bsAb also showed enhanced internalization in vitro compared with parental monovalent antibodies. Next, the PTK7 x TROP2 bsAb was conjugated to vcMMAE with a drug-to-antibody ratio (DAR) of 4 to generate a bsADC (BCG033). BCG033-vcMMAE demonstrated superior activity to benchmark and parental ADCs in a cell line-derived xenograft (CDX) TNBC model with low PTK7 expression. Here, we demonstrate that BCG033-vcMMAE ADCs also exhibited superior efficacy to benchmark ADCs in PDX models, including TNBC xenografts and NSCLC xenografts. We next tested the efficacy of the PTK7 x TROP2 bsAb conjugated to BLD1102, Biocytogen’s novel, proprietary linker/payload composed of a DNA Topo I inhibitor payload and a highly hydrophilic protease-cleavable linker, with a DAR of 8. BCG033-BLD1102 showed potent activity in a colorectal cancer PDX model in which benchmark ADCs were inactive, even at high doses. In summary, BCG033 conjugates demonstrate promising preclinical efficacy in vivo, which ultimately could provide a new treatment option for TNBC and other solid tumors expressing PTK7 and TROP2. Citation Format: Sufei Yao, Chengzhang Shang, Gao An, Chaoshe Guo, W. Frk an, Yi Yang. BCG033, a novel bispecific antibody-drug conjugate targeting PTK7 and TROP2, demonstrates preclinical efficacy against triple-negative breast cancer and other solid tumor xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2616.

Abstract 3370: Anti-tumor activity of Debio 0123 in combination with sacituzumab govitecan in preclinical models of breast cancer

Abstract Background: Debio 0123 is a WEE1 inhibitor that has previously shown significant preclinical efficacy in combination with DNA damaging agents and is currently being investigated in phase 1 clinical studies either as a monotherapy or in combination with different standard therapies. Sacituzumab govitecan (SG) is a TROP2 directed antibody-drug-conjugate (ADC) carrying an SN38 payload that has recently gained approval in TNBC and ER+ve breast cancer after demonstrating improvements in survival versus standard therapies. Despite these promising data some patients still do not respond to SG treatment, develop resistance or experience toxic side effects. Herein we present preclinical data that demonstrates Debio 0123 improves tumor response to SG in breast cancer models and provides sustained complete responses and anti-metastatic activity. Methods: Synergy between Debio 0123 and SG was evaluated in breast cancer cell lines, with varying levels of TROP2 expression, in vitro using standard cytotoxicity assay in a matrix combination format. Efficacy of Debio 0123 and SG as monotherapies or in combination was further assessed in vivo, in both TROP2high and TROP2low subcutaneous breast cancer xenograft models at different doses. Results: In vitro, Debio 0123 in combination with SG demonstrated synergistic tumor cell killing in all 4 breast cancer cell lines tested, at all concentrations. In vivo, TROP2high MDA-MB-468 breast cancer xenograft tumors treated with Debio 0123 at 30mg/kg QD resulted in minimal anti-tumor activity as a monotherapy but completely regressed 100% of the tumors in combination with SG. Furthermore, 40% of these complete regressions were sustained for up to 100 days post-treatment initiation. These data were then further replicated at a reduced dose of SG. In the TROP2low MDA-MB-231luc model, Debio 0123 significantly improved response to SG resulting in a 2-fold improvement in tumor growth inhibition. Additionally, combination treatment significantly inhibited metastasis of these tumors to the lung and lymph nodes as monitored by bioluminescence. Collectively, these results lead to a significant improvement in animal survival as a combination compared to either treatment as a monotherapy. Conclusion: These results demonstrate that Debio 0123 synergizes with, and significantly improves breast cancer tumor cell response to, SG regardless of TROP2 expression levels (both in vitro and in vivo), leading to complete regressions and inhibition of metastasis. Collectively these data support Debio 0123 in combination with SG could be a potential therapeutic approach for improving responses in patients with breast cancer. Citation Format: Luke Piggott, Esteban Rodrigo Imedio, Francesco Staehli. Anti-tumor activity of Debio 0123 in combination with sacituzumab govitecan in preclinical models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3370.

Abstract 6582: Preclinical characterization of IPH45, a novel topoisomerase I inhibitor ADC targeting Nectin-4 for the treatment of Nectin-4 expressing tumors

Abstract Background: Nectin-4 is a cell membrane adhesion protein overexpressed in several solid tumors, including urothelial, breast, lung, ovarian, and pancreatic cancers, with limited expression in normal tissues, making it an ideal target for antibody-drug conjugates (ADC). Enfortumab Vedotin (EV, PADCEV®) is an ADC targeting Nectin-4 with a monomethyl auristatin E (MMAE) payload approved for the treatment of patients with urothelial carcinoma (UC), but with limited clinical activity reported beyond UC. In addition, EV causes peripheral neuropathy and skin toxicity, leading to treatment discontinuation. To overcome these limitations and the mechanism of resistance to EV, IPH45, a novel topoisomerase I inhibitor ADC targeting Nectin-4 with an improved therapeutic index, was developed. Methods: In vitro studies were performed to investigate internalization, tumor cell killing and bystander effect, antibody-dependent cellular cytotoxicity (ADCC) and complement activation. In vivo efficacy studies were performed on cell line-derived xenografts (CDX) of triple negative breast cancer, patient-derived xenografts (PDX) of urothelial carcinoma and syngeneic tumor models expressing human Nectin-4. IPH45 efficacy was compared to EV. Toxicology studies to determine the dose range were conducted in rat and non-human primates (NHP). Results: IPH45 consists of a humanized IgG1 targeting a unique epitope in human Nectin-4, non-overlapping with EV, a cleavable linker, and a topoisomerase I inhibitor with a high drug-to-antibody ratio (DAR). In vitro, IPH45 is internalized upon binding to its target and induces direct killing of Nectin-4 expressing tumor cells as well as bystander killing of Nectin-4 non-expressing tumor cells in mixed culture. IPH45 mediates ADCC and complement-mediated killing. IPH45 demonstrates activity in CDX and PDX models with similar effective dose as EV. Moreover, IPH45 shows anti-tumor efficacy in vitro and in vivo in primary and secondary EV resistant models. In dose-range finding toxicology studies in rats and NHP, IPH45, unlike EV, does not elicit skin toxicity. IPH45 remains well tolerated up to the highest dose tested, suggesting a potentially larger therapeutic index than MMAE-based ADCs. Pharmacokinetic analyses in mice, rats, and NHP show minimal release of free toxin in the serum and half-life compatible with Q2W or less frequent dosing schedules in clinic. Conclusion: IPH45 is a topoisomerase I ADC targeting Nectin-4 with the potential for larger therapeutic index than EV, improved safety and dosing regimen, and ability to overcome primary and secondary resistance to EV or other Nectin-4 ADC in development. IPH45 is progressing to the clinic where the translatability of this unique profile into improved patient outcomes will be assessed across indications. Citation Format: Romain Remark, Cécile Bonnafous, Laura Chiossone, Caroline Soulas, Cyril Perrier, Guillaume Habif, Sivan Bokobza, Aurélie Maguer, Rachel Courtois, Julie Lopez, Grégory Fenaux, Olivier Benac, Barbara Carrette, Robin Letay-Drouet, Raja Bonifay, Séverine Augier, Léa Simon, Benjamin Rossi, Ariane Morel, Agnès Represa, Nicola Beltraminelli, Yannis Morel, Carine Paturel, Eric Vivier. Preclinical characterization of IPH45, a novel topoisomerase I inhibitor ADC targeting Nectin-4 for the treatment of Nectin-4 expressing tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6582.

Abstract 674: Novel anti-cancer small molecule targeting the protein regulator of cytokinesis pathway

Abstract Aberrant migration and proliferation of cancer cells are the hallmark of metastatic tumors. Protein Regulator of Cytokinesis 1 (PRC1) is a scaffold protein that regulates metabolic pathways of cancer cell proliferation, survival, and metastasis. BKT300 is a small molecule (MW 399.33, C22H25NO6), that selectively inhibits the migration and survival of hematological and solid cancer cells. BKT300 inhibits, at high affinity, both actin and microtubule formation and organization leading to G2/M cell cycle arrest, mitotic catastrophe, and apoptosis through the caspase 3 pathway. These effects are selective to cancer cells and were not observed on normal cells. BKT300 was found to arrest PRC1 in a phosphorylated form at position T481, down regulates the expression of CDC25C and up regulate p21. Suppression of PRC1 using SiRNA ablation inhibited BKT300 induced apoptosis on several tumor cell lines and inhibited the effect of BKT300 on G2M cell cycle arrest. Furthermore, using Biacore SPR, microscale thermophoresis (MST), and ELISA assays we were able to demonstrate the direct binding of BKT300 to PRC1. Beyond its single agent activity, BKT300 was shown to synergize with standard of care (SoC) treatments, including anti PD-1 immunotherapy, BCL-2 inhibitor (Ventoclax), topoisomerase I inhibitor (Irinotecan) topoisomerase II inhibitor (Doxorubicin), anti-metabolite Fluorouracil (5-FU) and alkylating agent (Temozolomide). BKT300 has a remarkable safety profile when administered at high doses to mice rats, minipigs and non-human primates. Treatment with BKT300 showed almost no effects on hematopoiesis and biochemistry in doses far higher than the affective ones. The in-vivo activity of BKT300 was demonstrated in multiple Xenograft, Syngeneic and PDX models in mice. In-vivo treatment with BKT300 resulted in preventive (small tumors) as well as therapeutic (large tumors) activity in triple negative breast cancer (TNBC) xenograft, MDA-MB-453 and MDA-MB-468 models leading to over then 70%-90% reduction in tumor size following one to two treatments cycles. Similar results were obtained using PDX models derived from patients with Colon, Ovarian and Pancreatic cancer. BKT300 is a novel, first in class, targeted anti-cancer treatment that inhibits the activity of the scaffold protein PRC1. BKT300 is expected to provide a new treatment option to, the high unmet medical need of, advanced difficult to treat cancers, specifically ones that overexpress PRC1 and CDC25C. Citation Format: Amnon Peled, Michal Abraham, Hanna Wald, Rakefet Rosenfeld, Orly Eizenberg, Arnon Aharon. Novel anti-cancer small molecule targeting the protein regulator of cytokinesis pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 674.

Abstract 1899: Novel combinations of aplitabart, a DR5 agonist IgM antibody, with ADCs or chemotherapeutic agents lead to robust anti-tumor responses in solid tumor models

Abstract Agonism of death receptor 5 (DR5), a tumor necrosis factor receptor superfamily member, induces the killing of tumor cells via the extrinsic apoptotic pathway upon receptor multimerization. We have engineered a multivalent IgM DR5 agonist antibody, aplitabart (IGM-8444), that induces robust anti-tumor activity in both in vitro and in vivo preclinical models. We also demonstrated potent synergistic in vitro activity of aplitabart with different classes of chemotherapeutic agents including microtubule inhibitors, nucleoside analogs and topoisomerase inhibitors in a range of solid cancer cell lines. Preliminary results from an ongoing phase 1a/ab clinical study show that aplitabart has an encouraging safety profile and promising activity in combination with FOLFIRI ± bevacizumab in heavily pretreated metastatic colorectal cancer patients. To further explore the combination therapies for aplitabart in lung and breast cancers, we evaluated standard of care chemotherapies, such as paclitaxel, carboplatin, and antibody drug conjugates (ADCs) in vitro on a range of human lung and breast cancer cell lines. We observed dose-dependent synergistic cytotoxic effects of aplitabart on tumor cells when combined with these agents. Additionally, these agents increased the expression of DR5 on tumor cells and could explain their synergistic combinatorial activity with aplitabart. Representative cancer cell lines were selected to evaluate these combinations in vivo using xenograft mouse models where robust anti-tumor responses were demonstrated in the xenograft lung and breast cancer models, resulting in enhanced tumor growth inhibition and extended survival. Our findings demonstrate potent in vitro synergistic cytotoxicity and enhanced anti-tumor response in preclinical models in vivo by combining aplitabart with ADCs, or carboplatin and paclitaxel. These results support the combination of DR5 agonist IgM antibodies with agents known to upregulate DR5 expression on solid tumors. Aplitabart is currently under evaluation in a randomized clinical study in combination with FOLFIRI + bevacizumab in comparison with FOLFIRI + bevacizumab in patients with colorectal cancer (NCT04553692). Citation Format: Mélanie Desbois, Susan E. Calhoun, Kevin C. Hart, Carolyn R. Denson, Poonam Yakkundi, Thomas J. Matthew, Maya K. Leabman, Sanela Bilic, Genevive Hernandez, Eric W. Humke, Albert F. Candia, Bruce Keyt, Angus M. Sinclair, Maya F. Kotturi, Beatrice T. Wang. Novel combinations of aplitabart, a DR5 agonist IgM antibody, with ADCs or chemotherapeutic agents lead to robust anti-tumor responses in solid tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1899.

Abstract 5911: In vivo efficacy of a novel peptide-conjugated drug in patient-derived xenograft models of breast cancer

Abstract Introduction: Antibody and peptide-conjugated drugs are rapidly entering the clinic for the treatment of patients with early and advanced breast cancer. These drugs are designed to achieve more targeted delivery of cytotoxic agents to tumor cells with robust clinical activity. ARB-1-6, a sortilin (SORT1) targeted peptide conjugated to the cytotoxic agent MMAE, has demonstrated pre-clinical activity and tolerability in cell line xenografts of breast cancer. To further characterize its spectrum of antitumor activity and biomarker correlates we evaluated ARB-1-6 in a collection of clinically and genomically annotated breast cancer patient-derived xenografts (PDX). Methods: Breast cancer PDX models were generated and propagated under IRB approved protocols [14-8358]. ARB-1-6 was dosed in tumor-bearing SCID mice by tail vein injection at 3 mg/kg weekly x 4 doses. Tumor volume was measured twice weekly until day 35 or until models reached humane endpoints, after which tumors were collected. Animals were weighed regularly and assessed for treatment-related toxicity. Results: 7 models (5 TN and 2 HR) have completed efficacy assessment to date. 3/7 models were derived from treatment naïve patients while 4/7 were derived from pre-treated patients (Table 1). Complete response (mRECIST) was seen in 5/7 (71.4%) models with stable disease occurring in 2/7 (28.6%). ARB-1-6 was well tolerated with no weight loss observed. Complete tumor regression was seen in a PDX derived from a patient with clinical resistance to a TROP2 antibody drug conjugate (ADC). Antitumor activity was observed in models with low SORT1 RNA expression; SORT1 IHC and other correlatives studies are underway. Conclusion: ARB-1-6 demonstrates substantial preclinical activity in PDX models at doses that are well tolerated in mice. Treatment of additional models is ongoing. Full results and correlative analyses including relationships between antitumor activity and target protein expression will be presented. PDX Model Characteristics and Patient Treatment PDX Subtype Pt. Treatment 1 TN AC-T 2 TN FEC-D, Gem+Carbo 3 TN AC-T 4 TN No 5 TN No 6 HR No 7 HR TC, ET, Cape, Gem+Cis, TROP2-ADC Citation Format: Mitchell J. Elliott, Meghan Mcguire, Jennifer Silvester, Chantal Tobin, Samah El Ghamrasni, Francine Lui, Andrew Zhai, Ozge Yoluk, Aron Broom, Tracy Stone, Glenn Butterfoss, Serban Popa, Tianyu Lu, Chris Ing, David White, David W. Cescon. In vivo efficacy of a novel peptide-conjugated drug in patient-derived xenograft models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5911.

Abstract 4149: Real-time intravital trafficking of tumor infiltrating lymphocytes in breast cancer models

Abstract Cancer immunotherapy utilizing the immunoreactive efficiency of immune cells via adoptive cell therapy (ACT) has been a novel method of cancer treatment. In tumor microenvironment, immune cell reactivity of tumor-infiltrating lymphocytes (TILs) can facilitate cancer cell attack, which finally derives efficient suppression of tumor growth. However, the conventional evaluation for cancer immunotherapy has been generally performed by ex vivo methods, providing restricted information on lymphocyte motility and immune cell dynamics within the tumor microenvironment. In vivo data with the dynamic behavior of TILs in breast cancer can provide new insight to investigate novel targets of immune checkpoint inhibitors. In this research, longitudinal intravital imaging of motility trafficking of TILs in breast cancer animal models has been performed by utilizing intravital microscopy to unveil the immunoreactive dynamics of T cell activity in early stage. In vivo analysis of TIL motility within different breast cell lines, including 4T1 (mouse breast cancer cell), MDA-MB-231 (human triple-negative breast cancer cell), and MCF7 (human breast cancer cell), respectively, has been investigated for immune responses to cancer. We’ve monitored spatiotemporal dynamics of TIL over 11 days in breast cancer xenograft mouse model generated by tumor implantation into the dorsal skinfold imaging chamber and adoptive T cell transfer by blood circulation. In the results, the adoptive immunoreactivity of TIL has been differentiated by the timepoint of adoptive T cell transfer, distance proximity of T cells in tumors, and breast cancer types. Furthermore, anti-cancer effect coordinated with dendritic cells behaviors showed induced immune responses with accumulated dendritic cells with increased TIL count over time in breast cancer model treated with various cancer therapy such as immunotherapy, radiation therapy and anti-cancer drug (anti-PD-L1), which implied a relationship between programmed death-ligand 1 expression levels and TIL/dendritic cell motility. The result demonstrates that intravital TIL motility trafficking analysis in cancer model can be an invaluable assessment method to explain the detailed cellular/molecular mechanism of immune response to cancer involved with T lymphocytes, dendritic cells, and immune checkpoint inhibitors to accelerate the efficiency of cancer immunotherapy. Citation Format: Soyeon Ahn, Kubra Akyildiz, Hyunseok Kim, Pilhan Kim. Real-time intravital trafficking of tumor infiltrating lymphocytes in breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4149.

Abstract 7215: Nectin-4 targeted therapy with MMAE protodrug results in anti-tumor efficacy mediated by click chemistry

Abstract Shasqi is advancing the Click Activated Protodrugs Against Cancer (CAPAC®) platform based on click chemistry, a Nobel Prize winning technology. The platform is modular and comprises 1) an activator that target specific antigens, and 2) inert cancer drugs, protodrugs, which are selectively activated at tumors via click chemistry. The CAPAC technology separates the tumor targeting function from the payload and reunite them at the tumor creating the flexibility to optimize activity while limiting toxicity during preclinical and clinical development. The modularity of the platform enables the rapid development of new therapies as well as unlocking unique treatment benefits such as tunable combinations and payload cycling. We envision that CAPAC will expand the scope of potential targets, widen the therapeutic index of antibody drug conjugates (ADCs). Here we present a Nectin-4-targeting activator with a monomethyl auristatin E (MMAE) payload. Nectin-4 is a clinically validated tumor target expressed in a wide range of solid tumors, making Nectin-4 an attractive target for developing new therapeutic approaches for cancer patients. Substantial numbers of Nectin-4 targeting drugs are being developed but exhibit high rates of drug toxicities and highlight the need for alternative approaches that are efficacious and safe. We have developed a Nectin-4 Fab binder conjugated with tetrazine (~2.3 tetrazines per protein), SQT03, and tested it in combination with SQP22, an attenuated protodrug of MMAE conjugated to trans-cyclooctene (TCO). The reaction between tetrazine and TCO moieties releases MMAE at the tumor site. We have previously demonstrated that SQP22 is highly attenuated in vivo at doses that are > 20x the toxic dose of free MMAE, and in combination with a HER2 targeting activator, led to significant tumor growth inhibition in NCI-N87 gastric cancer xenograft model. The separation of an antigen-targeting activator from the payload by CAPAC technology allowed the rapid development and subsequent testing of SQT03 in combination with SQP22 in vitro and in vivo. SQT03 displayed <10nM binding affinity to Nectin-4 positive cells by flow cytometry analysis. In vivo, dosing of SQT03 occurs 8-24hrs prior to SQP22 to reduce systemic activation and to enable specific release of the active cytotoxic payload at the tumor site. In the T47D breast cancer xenograft model, a single dose of SQP22 at 8-24hrs after SQT03 led to tumor regression without body weight loss, in contrast to the 5% of body weight loss presented by two doses of Enfortumab-vedotin required to lead to similar activity. The presented data illustrates how the CAPAC platform can be used to test various therapeutic combinations, accelerating development, and reducing the time it takes to bring treatments to the clinic. The results support further development and testing of MMAE protodrug with Nectin-4 targeting agent in clinical settings. Citation Format: George Coricor, Jesse M. McFarland, Sangeetha Srinivasan, Stefanie Wagner, Nathan Yee, Tri-Hung Nguyen, Jose M. Mejia Oneto. Nectin-4 targeted therapy with MMAE protodrug results in anti-tumor efficacy mediated by click chemistry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7215.

Abstract 3134: SDP03923-000-9106, a novel and optimized LIV-1 ADC with superior anti-tumor efficacy in breast cancer xenograft models

Abstract Background: LIV-1, also known as SLC39A6 or ZIP6, is a transmembrane protein belonging to the zinc transporter family. LIV-1 is a promising target for antibody-drug conjugate (ADC) therapy due to its broad expression in tumors and limited normal tissue expression. Ladiratuzumab vedotin, a LIV-1 targeting ADC with payload of MMAE, is now in phase I clinical trial stage and is the only LIV-1 ADC under clinical development worldwide. The preliminary clinical results demonstrated promising efficacy in TNBC (ORR=32%) but no response in HR+/HER2- breast cancer (ORR=0%), and typical MMAE-related adverse events were observed. Herein, we presented a novel LIV-1 directed ADC, SDP03923-000-9106, consisting of a LIV-1 mAb developed in house conjugated to a proprietary topoisomerase I inhibitor via a cleavable linker with an optimized average drug-to-antibody ratio (DAR) of 6. Method: The in vitro binding affinity of SDP03923-000-9106 against LIV-1 protein was measured by Surface Plasmon Resonance (SPR) assays. The expression levels of LIV-1 in different cancer cell lines were detected by flow cytometry and IHC staining. In vitro activity against cancer cell lines was analyzed by CellTiter Glo assays following 10 days of treatment. The in vivo anti-tumor activities were investigated in both CDX and PDX models of breast cancer. Results: SDP03923-000-9106 is a novel anti-LIV-1 ADC comprised of a humanized LIV-1 monoclonal antibody conjugated to the potent topoisomerase I inhibitor (a novel exatecan derivative designed by Hengrui with a better liposolubility and cellular permeability) by a cleavable linker. SDP03923-000-9106 had an optimal drug-to-antibody ratio (DAR) of 6 and showed strong binding affinity to LIV-1 and favorable internalization. SDP03923-000-9106 exhibited robust anti-tumor activity in cell lines across breast cancer, esophageal squamous cancer, gastric cancer, prostate cancer and non-small cell lung cancer. In the LIV-1 highly expressed breast cancer cell line of MCF-7, SDP03923-000-9106 demonstrated a strong inhibitory effect with IC50 of 5.36 nM. Moreover, in a LIV-1 high-expressing patient-derived xenograft model of breast cancer, SDP03923-000-9106 showed pronounced tumor regression at both doses of 3 and 10 mg/kg and showed stronger anti-tumor activity (TGI: 109%) at the same dose of 3 mg/kg versus BMK-MMAE (TGI: 75%; BMK-MMAE is synthesized by Hengrui using the published structure of Ladiratuzumab vedotin). Conclusion: In summary, SDP03923-000-9106 is a novel LIV-1 targeted ADC with a highly permeable payload demonstrating great anti-tumor activity across multiple types of tumors in preclinical studies. The promising preclinical data support advancing SDP03923-000-9106 into clinical testing, and Investigational New Drug (IND) application to NMPA has been submitted. Citation Format: Yanling Gong, Xing Sun, Changyong Yang, Simeng Chen, Wei Zhang, Cheng Liao. SDP03923-000-9106, a novel and optimized LIV-1 ADC with superior anti-tumor efficacy in breast cancer xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3134.

Abstract 6068: Discovery of BTX-9341, a bifunctional degrader of CDK4 and CDK6 for HR+/HER2- breast cancer

Abstract CDK4/6 inhibitors (CDK4/6i) such as palbociclib, abemaciclib and ribociclib are used to treat HR+/HER2- breast cancer, but patients can develop resistance via many mechanisms, several of which converge on the upregulation of the cyclin D-CDK4/6 signaling node. This has been shown to limit the effectiveness of CDK4/6i in ER+ breast cancer with up to 20% patients exhibiting innate resistance and up to 70% patients developing acquired resistance after 3 years on therapy (Scheidemann, 2021). To address acquired resistance, we sought a degrader approach. We utilized our PRODEGY platform of Cereblon (CRBN) binders to synthesize CRBN mediated CDK4/6 bifunctional degraders and identified BTX-9341 as a development candidate. Breast cancer cell lines treated with BTX-9341 showed up to 85% degradation of CDK4 and CDK6 with DC50s <1nM. CDK4/6 phosphorylates the protein RB which releases the transcription factor E2F, inducing the expression of genes which promote cell cycle progression. We examined RB phosphorylation by in-cell western, E2F target gene expression by qPCR and cell cycle progression by propidium iodide staining followed by flow cytometry. BTX-9341 was potent in all downstream assays, with phospho-RB IC50s <30nM, E2F target gene downregulation and G0/G1 cell cycle arrest at concentrations as low as 10nM. These downstream effects were sustained throughout 72 hours with BTX-9341 treatment but recovered more rapidly with Palbociclib treatment. We used a 2D colony formation assay (CFA) to assess inhibition of proliferation by cell cycle arrest. BTX-9341 potently inhibited cell proliferation with CFA IC50s of 20-50nM while CDK4/6i had CFA IC50s of 50-1000nM. This increased activity was due to CRBN mediated target degradation, as demonstrated by a shift in CFA IC50 values in a CRBN knockout cell line towards the values seen with the inhibitors. In palbociclib-resistant HR+/HER2- cell line models BTX-9341 maintained a low CFA IC50 (<150nM) while CDK4/6i displayed micromolar CFA IC50s. BTX-9341 displays excellent pharmacokinetic properties which allowed for oral dosing in xenograft studies. In several breast cancer xenograft models, BTX-9341 showed dose-dependent tumor growth inhibition, tumor regression at higher dose levels, and was effective with multiple alternate dosing regimens. These results show that BTX-9341 displays excellent single agent activity in vitro and in vivo and that this activity is maintained in CDK4/6i resistant models. This indicates that a degrader approach to targeting this pathway may be more effective than current therapies, and that using this modality in a post CDK4/6i setting may be more effective than switching CDK4/6 inhibitors. Reference: Scheidemann, Erin R, and Ayesha N Shajahan-Haq. “Resistance to CDK4/6 Inhibitors in Estrogen Receptor-Positive Breast Cancer.” International journal of molecular sciences vol. 22,22 12292. 14 Nov. 2021, doi:10.3390/ijms222212292 Citation Format: Hannah Majeski, Akinori Okano, Kirti Chahal, Angela Pasis, Casey Carlson, Arvind Shakya, Qiao Liu, Shenlin Huang, Aparajita Hoskote Chourasia, Leah Fung. Discovery of BTX-9341, a bifunctional degrader of CDK4 and CDK6 for HR+/HER2- breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6068.

Abstract 6351: MUC1*-ADCs are effective against heterogeneous solid tumor cancers

Abstract Purpose: To develop a MUC1*-ADC for the treatment of over 75% of solid tumor cancers. Methods: MUC1* (muk 1 star) is a growth factor receptor created after cleavage and release of the N-terminal portion of MUC1. The targeting antibody, huMNC2, has already demonstrated safety and cancer selectivity in a 1st-in-human CAR-T clinical trial for treatment of metastatic breast cancers. MNC2 is an IgG1 antibody that only recognizes the conformational epitope created when MUC1 is cleaved by specific tumor-associated enzymes. Confocal microscopy and pHlourin2 were employed to measure antibody internalization as a function of time. We conjugated MNC2 to MMAE, MMAF, Dxd and exatecan via several different linkers. MUC1*-ADCs with DARs ranging from 4-8 were tested in vitro and in vivo for efficacy against a panel of solid tumor cancers. Heterogenous MUC1* tumors were made by mixing different ratios of mCherry wild-type cancer cells with GFP MUC1* overexpressed cancer cells. Resulting H scores ranged from 10-280 (max 300). Results: Cancer cells internalized the MUC1* MNC2 antibody within 2 hours. In vitro, MUC1*-ADC IC50s ranged from 1.3nM to 20.0nM, depending on the linker-payload and cancer subtype, wherein the majority had an IC50 of about 10nM. In general, efficacy in animals was seen across multiple cancer sub-types treated with multiple MUC1*-ADCs. Efficacy in animals xenografted with heterogeneous MUC1* tumors showed a dependence on antigen density. Greatest efficacy was observed for breast cancer xenografts with an H Score >10 treated with MNC2-Deruxtecan. However, only pancreatic tumors with higher H Scores were completely eliminated by MNC2-MMAE, MNC2-Deruxtecan and MNC2-exatecan. MNC2-ADC and MNC2-CAR share the same antibody. No off-tumor toxicity was observed in animals treated with MNC2-ADC, which mimicked lack of off-target toxicities for MNC2-CAR T cells in humans. Conclusions: These data, combined with MNC2-CAR T data from our 1st-in-human trial for metastatic breast cancer, supports a conclusion that the MUC1* antibody MNC2 is safe and could have high therapeutic value as a MUC1*-ADC for multiple solid tumors with both high and low antigen density. Citation Format: Cynthia Carol Bamdad, Benoit S. Smagghe, Scott T. Moe, Mark G. Carter, Trevor J. Grant, Kevin R. Yi, Michael J. Nash, Jacy P. Marquez, Natalie K. Miller, Jac-Leen S. Nash, Dan S. Miller, Danica M. Walkley, Andrew K. Stewart. MUC1*-ADCs are effective against heterogeneous solid tumor cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6351.

Abstract 6605: Understanding the role of sumoylated Etv1 in mammary oncogenesis

Abstract The Small Ubiquitin-like Modifier (SUMO) pathway is a major post-translational regulatory mechanism involved in a variety of cellular functions including the DNA damage response, transcriptional regulation, and carcinogenesis. Recent discoveries by our group demonstrated that inhibiting the SUMO pathway can repress the growth of breast cancer xenografts and Neu-driven mammary oncogenesis in a genetically engineered mouse model with conditional knockout (CKO) of the SUMOylation E2 conjugating enzyme, Ube2i. However, despite the consistency of the findings, there remains considerable debate concerning the mechanisms through which SUMO inhibition represses tumorigenesis. Our downstream analysis suggested ETS Translocation Variant 1, encoded by ETV1 gene, acts as a SUMO-sensitive transcription factor that drives mammary oncogenesis and cancer growth. To examine oncogenic properties of SUMO-conjugated ETV1 in breast cancer, we cloned HA-tagged WT Etv1, SUMO-resistant Etv15xKR, or SUMO mimetic SUMO-1-Etv15xKR into a lentiviral vector with a GFP cassette. Proliferation, colony formation in soft agar, and in vivo xenograft assays were evaluated in the Ube2iF/F cell line derived from a tumor in a MMTV-c-neu/Ube2ifl/fl animal. We did ChIP-seq in Ube2iF/F cells using SUMO-1 and Etv1 antibodies to examine the effects of SUMO conjugation on Etv1 genomic occupancy. RNA-seq using siEtv1 or AdCre was also performed to compare changes in gene expression with SUMO-conjugated Etv1 genomic occupancy. Inhibition of SUMOylation via AdCre caused a significant reduction in proliferation and colony formation in vitro and completely block the formation of flank xenografts in vivo. Interestingly, expressing a SUMO-resistant ETV15xKR rescued in vitro growth effects, whereas a SUMO mimetic SUMO-1-ETV15xKR had no effect on restoring proliferation. On the contrary, in vivo xenograft assays demonstrated that the Etv15xKR-SUMO1 efficiently induced tumor formation despite the loss of Ube2i while the sumo-resistant Etv15xKR was unable to rescue tumorigenesis. Bulk RNA-seq and ChIP seq performed demonstrated different patterns of gene regulation between sumoylated and unsumoylated Etv1. Gene set enrichment analysis (GSEA) showed genes associated with cancer stemness were significantly enriched in cells expressing Etv15xKR-SUMO1. Collectively, these observations support Etv1 acting as a SUMO-sensitive transcription factor that drives a stem cell phenotype necessary for mammary oncogenesis and progression. Citation Format: Zhijie Li, Kelsey E. Koch, Dakota T. Thompson, Dana M. Van der Heide, Jeremy Chang, Christopher M. Franke, Mohammed O. Suraju, Anna C. Beck, Allison W. Lorenzen, Jeffrey R. White, Mikhail V. Kulak, David K. Meyerholz, Colin Kenny, Ronald J. Weigel. Understanding the role of sumoylated Etv1 in mammary oncogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6605.

Abstract 7146: HSK39775: A USP1 inhibitor for the treatment of cancers with homologous recombination deficiencies

Abstract Tumors with BRCA1/2 mutations or homologous repair deficiency (HRD) are vulnerable to agents that target DNA repair pathways, including platinum-containing chemotherapeutics and poly (ADP-ribose) polymerase-1 (PARP1) inhibitors. Despite the significant therapeutic benefits in patients with BRCAm or HRD, innate and acquired resistance to PARPi is still a challenge in the clinic. To address this clinical challenge, we developed HSK39775, a potent, highly selective inhibitor of ubiquitin carboxyl-terminal hydrolase 1 (USP1), which acts as an oncogenic and PARP inhibitor resistance driver involved in DNA damage repair pathway through the deubiquitylation of proteins in Translesion Synthesis pathway and Fanconi Anemia pathway, paired with BRCA as a synthetic lethality target. HSK39775 was active in enzymatic level to inhibit USP1/UAF1 complex. Enzymatic panel screening containing 50 deubiquitinase demonstrated high selectivity of HSK39775. Ubiquitinated PCNA was accumulated treated by HSK39775, indicating target engagement. HSK39775 also demonstrated potent anti-proliferation activity against cancer cell lines with BRCA mutation and excellent selectivity between BRCA WT vs. BRCAm. Combining HSK39775 with PARP inhibitors indicated synergy in cell lines with partial or insensitivity to each agent alone. Triple-negative BRCA mutant breast cancer xenograft model demonstrated strong dose-dependent tumor growth inhibition of HSK39775 as a single agent with Tumor Growth Inhibition (TGI) of 63.2% at 30 mg/kg QD, and ubiquitinated PCNA was also accumulated in HSK39775 treated tumor tissue. Meanwhile, combination with PARP inhibitors significantly enhanced the therapeutic efficacy of HSK39775 in xenograft model and led to tumor regressions and durable tumor control even at low dose (TGI:89% (HSK39775, 5 mg/kg + Olaparib, 50 mg/kg)). Interestingly, HSK39775 inhibited the tumor growth of a HRP and BRCA wild-type lung cancer xenograft as a single agent with TGI of 94% at 30 mg/kg QD, suggesting the therapeutic effect of USP1 inhibitors beyond canonical BRCA mutant or HRD tumors. In summary, these results indicate HSK39775 as a potent and selective USP1 inhibitor and support further development. Citation Format: Jun Xu, Yangguang Li, Ju Wang, Pingming Tang, Jianmin Wang, Chen Zhang, Pangke Yan. HSK39775: A USP1 inhibitor for the treatment of cancers with homologous recombination deficiencies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7146.

Factors associated with engraftment success of patient-derived xenografts of breast cancer

BackgroundPatient-derived xenograft (PDX) models serve as a valuable tool for the preclinical evaluation of novel therapies. They closely replicate the genetic, phenotypic, and histopathological characteristics of primary breast tumors. Despite their promise, the rate of successful PDX engraftment is various in the literature. This study aimed to identify the key factors associated with successful PDX engraftment of primary breast cancer.MethodsWe integrated clinicopathological data with morphological attributes quantified using a trained artificial intelligence (AI) model to identify the principal factors affecting PDX engraftment.ResultsMultivariate logistic regression analyses demonstrated that several factors, including a high Ki-67 labeling index (Ki-67LI) (p < 0.001), younger age at diagnosis (p = 0.032), post neoadjuvant chemotherapy (NAC) (p = 0.006), higher histologic grade (p = 0.039), larger tumor size (p = 0.029), and AI-assessed higher intratumoral necrosis (p = 0.027) and intratumoral invasive carcinoma (p = 0.040) proportions, were significant factors for successful PDX engraftment (area under the curve [AUC] 0.905). In the NAC group, a higher Ki-67LI (p < 0.001), lower Miller-Payne grade (p < 0.001), and reduced proportion of intratumoral normal breast glands as assessed by AI (p = 0.06) collectively provided excellent prediction accuracy for successful PDX engraftment (AUC 0.89).ConclusionsWe found that high Ki-67LI, younger age, post-NAC status, higher histologic grade, larger tumor size, and specific morphological attributes were significant factors for predicting successful PDX engraftment of primary breast cancer.

Developing liver-targeted naringenin nanoparticles for breast cancer endocrine therapy by promoting estrogen metabolism

Endocrine therapy is standard for hormone receptor–positive (HR+) breast cancer treatment. However, current strategies targeting estrogen signaling pay little attention to estradiol metabolism in the liver and is usually challenged by treatment failure. In a previous study, we demonstrated that the natural compound naringenin (NAR) inhibited HR+ breast cancer growth by activating estrogen sulfotransferase (EST) expression in the liver. Nevertheless, the poor water solubility, low bio-barrier permeability, and non-specific distribution limited its clinical application, particularly for oral administration. Here, a novel nano endocrine drug NAR-cell penetrating peptide-galactose nanoparticles (NCG) is reported. We demonstrated that NCG presented specific liver targeting and increased intestinal barrier permeability in both cell and zebrafish xenotransplantation models. Furthermore, NCG showed liver targeting and enterohepatic circulation in mouse breast cancer xenografts following oral administration. Notably, the cancer inhibition efficacy of NCG was superior to that of both NAR and the positive control tamoxifen, and was accompanied by increased hepatic EST expression and reduced estradiol levels in the liver, blood, and tumor tissue. Moreover, few side effects were observed after NCG treatment. Our findings reveal NCG as a promising candidate for endocrine therapy and highlight hepatic EST targeting as a novel therapeutic strategy for HR+ breast cancer.Graphical

Cell morphology best predicts tumorigenicity and metastasis in vivo across multiple TNBC cell lines of different metastatic potential

BackgroundMetastasis is the leading cause of death in breast cancer patients. For metastasis to occur, tumor cells must invade locally, intravasate, and colonize distant tissues and organs, all steps that require tumor cell migration. The majority of studies on invasion and metastasis rely on human breast cancer cell lines. While it is known that these cells have different properties and abilities for growth and metastasis, the in vitro morphological, proliferative, migratory, and invasive behavior of these cell lines and their correlation to in vivo behavior is poorly understood. Thus, we sought to classify each cell line as poorly or highly metastatic by characterizing tumor growth and metastasis in a murine model of six commonly used human triple-negative breast cancer xenografts, as well as determine which in vitro assays commonly used to study cell motility best predict in vivo metastasis.MethodsWe evaluated the liver and lung metastasis of human TNBC cell lines MDA-MB-231, MDA-MB-468, BT549, Hs578T, BT20, and SUM159 in immunocompromised mice. We characterized each cell line's cell morphology, proliferation, and motility in 2D and 3D to determine the variation in these parameters between cell lines.ResultsWe identified MDA-MB-231, MDA-MB-468, and BT549 cells as highly tumorigenic and metastatic, Hs578T as poorly tumorigenic and metastatic, BT20 as intermediate tumorigenic with poor metastasis to the lungs but highly metastatic to the livers, and SUM159 as intermediate tumorigenic but poorly metastatic to the lungs and livers. We showed that metrics that characterize cell morphology are the most predictive of tumor growth and metastatic potential to the lungs and liver. Further, we found that no single in vitro motility assay in 2D or 3D significantly correlated with metastasis in vivo.ConclusionsOur results provide an important resource for the TNBC research community, identifying the metastatic potential of 6 commonly used cell lines. Our findings also support the use of cell morphological analysis to investigate the metastatic potential and emphasize the need for multiple in vitro motility metrics using multiple cell lines to represent the heterogeneity of metastasis in vivo.