Breast Cancer Xenograft Model Research Articles

Letter to the editor regarding “Hsp90 inhibitor-loaded IR780 micelles for mitochondria-targeted mild-temperature photothermal therapy in xenograft models of human breast cancer”

Letter to the editor regarding “Hsp90 inhibitor-loaded IR780 micelles for mitochondria-targeted mild-temperature photothermal therapy in xenograft models of human breast cancer”

Preclinical safety assessment of MV-s-NAP, a novel oncolytic measles virus strain armed with an H. pylori immunostimulatory bacterial transgene

Despite recent therapeutic advances, metastatic breast cancer (MBC) remains incurable. Engineered measles virus (MV) constructs based on the attenuated MV Edmonston vaccine platform have demonstrated significant oncolytic activity against solid tumors. The Helicobacter pylori neutrophil-activating protein (NAP) is responsible for the robust inflammatory reaction in gastroduodenal mucosa during bacterial infection. NAP attracts and activates immune cells at the site of infection, inducing expression of pro-inflammatory mediators. We engineered an MV strain to express the secretory form of NAP (MV-s-NAP) and showed that it exhibits anti-tumor and immunostimulatory activity in human breast cancer xenograft models. In this study, we utilized a measles-infection-permissive mouse model (transgenic IFNAR KO-CD46Ge) to evaluate the biodistribution and safety of MV-s-NAP. The primary objective was to identify potential toxic side effects and confirm the safety of the proposed clinical doses of MV-s-NAP prior to a phase I clinical trial of intratumoral administration of MV-s-NAP in patients with MBC. Both subcutaneous delivery (corresponding to the clinical trial intratumoral administration route) and intravenous (worst case scenario) delivery of MV-s-NAP were well tolerated: no significant clinical, laboratory or histologic toxicity was observed. This outcome supports the safety of MV-s-NAP for oncolytic virotherapy of MBC. The first-in-human clinical trial of MV-s-NAP in patients with MBC (ClinicalTrials.gov: NCT04521764) was subsequently activated.

Chimeric Oncolytic Adenovirus Armed Chemokine Rantes for Treatment of Breast Cancer.

The immunosuppressive state in the tumor microenvironment (TME) of breast cancer makes it difficult to treat with immunotherapy. Oncolytic viruses not only lyse tumor cells but also reshape the TME. Therefore, they can play a multi-mechanism synergistic effect with immunotherapy. In this study, an oncolytic adenovirus Ad5F11bSP-Rantes was constructed and used as a vector to express the chemokine Rantes. The objective of this study was to test the dual mechanisms of the oncolytic effect mediated by virus replication and the enhanced anticancer immune response mediated by Rantes chemotaxis of immune cells. It was found that Ad5F11bSP-Rantes has strong infectivity and effective killing activity against breast cancer cells. In the established triple negative breast cancer (TNBC) xenograft model in NCG mice whose immune system was humanized with human peripheral blood mononuclear cells (PBMCs), Ad5F11bSP-Rantes achieved 88.33% tumor inhibition rate. Rantes expression was high in mouse blood, a large number of CD3+ lymphocytes infiltrated in tumor tissues and E-cadherin was up-regulated in cancer cells, suggesting that Ad5F11bSP-Rantes altered the TME and induced a reversal of cancer cell epithelial–mesenchymal transition (EMT). In conclusion, oncolytic adenovirus can exert the oncolytic effect and the chemotactic effect of immune cells and realize the synergy of multiple anticancer effects. This strategy creates a candidate treatment for the optimization of breast cancer, especially TNBC, combination therapy.

Reduced CREB3L1 expression in triple negative and luminal a breast cancer cells contributes to enhanced cell migration, anchorage-independent growth and metastasis.

Women with metastatic breast cancer have a disheartening 5-year survival rate of only 28%. CREB3L1 (cAMP-responsive element binding protein 3 like 1) is a metastasis suppressor that functions as a transcription factor, and in an estrogen-dependent model of rat breast cancer, it repressed the expression of genes that promote breast cancer progression and metastasis. In this report, we set out to determine the expression level of CREB3L1 across different human breast cancer subtypes and determine whether CREB3L1 functions as a metastasis suppressor, particularly in triple negative breast cancers (TNBCs). CREB3L1 expression was generally increased in luminal A, luminal B and HER2 breast cancers, but significantly reduced in a high proportion (75%) of TNBCs. Two luminal A (HCC1428, T47D) and two basal TNBC (HCC1806, HCC70) CREB3L1-deficient breast cancer cell lines were characterized as compared to their corresponding HA-CREB3L1-expressing counterparts. HA-CREB3L1 expression significantly reduced both cell migration and anchorage-independent growth in soft agar but had no impact on cell proliferation rates as compared to the CREB3L1-deficient parental cell lines. Restoration of CREB3L1 expression in HCC1806 cells was also sufficient to reduce mammary fat pad tumor formation and lung metastases in mouse xenograft models of breast cancer as compared to the parental HCC1806 cells. These results strongly support a metastasis suppressor role for CREB3L1 in human luminal A and TNBCs. Further, the ability to identify the subset of luminal A (7%) and TNBCs (75%) that are CREB3L1-deficient provides opportunities to stratify patients that would benefit from additional treatments to treat their more metastatic disease.

Therapeutic Response Monitoring with 89Zr-DFO-Pertuzumab in HER2-Positive and Trastuzumab-Resistant Breast Cancer Models.

Immuno-positron emission tomography (PET) has great potential to evaluate the target expression level and therapeutic response for targeted cancer therapy. Immuno-PET imaging with pertuzumab, due to specific recognition in different binding sites of HER2, could be useful for the determination of the therapeutic efficacy of HER2-targeted therapy, trastuzumab, and heat shock protein 90 (HSP90) inhibitor, in HER2-expressing breast cancer. The aim of this study is to evaluate the feasibility of monitoring therapeutic response with 89Zr-DFO-pertuzumab for the treatment of HER2-targeted therapeutics, trastuzumab, or the HSP90 inhibitor 17-DMAG, in trastuzumab-resistant JIMT-1 breast cancer models. We prepared an immuno-PET imaging agent using desferoxamine (DFO)-pertuzumab labeled with 89Zr and performed the biodistribution and PET imaging in breast cancer xenograft models for monitoring therapeutic response to HER2-targeted therapy. 89Zr-DFO-pertuzumab was successfully prepared and showed specific binding to HER2 in vitro and clearly visualized HER2 expressing JIMT-1 tumors. 89Zr-DFO-pertuzumab had prominent tumor uptake in HER2 expressing JIMT-1 tumors. JIMT-1 tumors showed trastuzumab-resistant and HSP90 inhibitor sensitive characterization. In immuno-PET imaging, isotype antibody-treated JIMT-1 tumors had similar uptake in trastuzumab-treated JIMT-1 tumors, but 17-DMAG-treated JIMT-1 tumors showed greatly reduced uptake compared to vehicle-treated tumors. Additionally, HER2 downregulation evaluated by immuno-PET imaging was verified by western blot analysis and immunofluorescence staining which resulted in a significant reduction in the tumor’s HER2 level in 17-DMAG-treated JIMT-1 tumors. 89Zr-DFO-pertuzumab immuno-PET may be clinically translated to select pertinent patients for HER2-targeted therapy and to monitor the therapeutic response in HER2-positive cancer patients under various HER2-targeted therapeutics treatments.

Synthesis and Evaluation of Small Molecule Drug Conjugates Harnessing Thioester-Linked Maytansinoids.

Ligand-targeting drug conjugates are a class of clinically validated biopharmaceutical drugs constructed by conjugating cytotoxic drugs with specific disease antigen targeting ligands through appropriate linkers. The integrated linker-drug motif embedded within such a system can prevent the premature release during systemic circulation, thereby allowing the targeting ligand to engage with the disease antigen and selective accumulation. We have designed and synthesized new thioester-linked maytansinoid conjugates. By performing in vitro cytotoxicity, targeting ligand binding assay, and in vivo pharmacokinetic studies, we investigated the utility of this new linker-drug moiety in the small molecule drug conjugate (SMDC) system. In particular, we conjugated the thioester-linked maytansinoids to the phosphatidylserine-targeting small molecule zinc dipicolylamine and showed that Zn8_DM1 induced tumor regression in the HCC1806 triple-negative breast cancer xenograft model. Moreover, in a spontaneous sorafenib-resistant liver cancer model, Zn8_DM1 exhibited potent antitumor growth efficacy. From quantitative mRNA analysis of Zn8_DM1 treated-tumor tissues, we observed the elevation of gene expressions associated with a “hot inflamed tumor” state. With the identification and validation of a plethora of cancer-associated antigens in the “omics” era, this work provided the insight that antibody- or small molecule-based targeting ligands can be conjugated similarly to generate new ligand-targeting drug conjugates.

Abstract 1756: Antitumor effect of XMT1660, a B7H4 targeting antibody drug conjugate, in an unselected panel of patient derived xenograft models of breast cancer

Abstract Introduction: XMT-1660 is a first-in-class Dolasynthen Antibody-Drug Conjugate (ADC) targeting B7-H4 and carrying a DolaLock payload with controlled bystander effect. B7-H4 is an immunoregulatory protein that is expressed in breast, ovarian and endometrial tumors. Expression of B7-H4 has been described in both tumor cells and in tumor associated macrophages, and B7-H4 shows infrequent co-expression with PD-L1, suggesting distinct immunoregulatory functions. XMT-1660 is built on the Dolasynthen platform which incorporates several attributes, including site-specific bioconjugation and precise control over drug-antibody ratio (DAR). The XMT-1660 ADC contains 6 DolaLock Auristatin F-hydroxypropyl amide (AF-HPA) anti-tubulin payloads per antibody (DAR-6). Previously, we demonstrated the cytotoxic effect of XMT-1660 in cell line xenograft and patient derived xenograft models of breast cancer known to have B7-H4 target expression. The purpose of this study was to evaluate the anti-tumor activity of XMT-1660 across an unselected panel of breast cancer patient derived xenograft (PDX) models, evaluate the level of B7-H4 expression across this panel of breast PDX models, and assess the correlation between B7-H4 expression and anti-tumor activity following a single dose of XMT-1660. Methods: A panel of 30 breast cancer patient-derived xenograft models, annotated by prior treatment history, and divided between TNBC and ER-positive subtypes, was implanted into athymic Nude-Foxn1n mice. When tumors reached an average volume of 150-300 mm3, animals (n=3) were treated with a single administration of either XMT-1660 0.15mg/kg (calculated by payload dose)/4.71 mg/kg (calculated by antibody dose) IV/QD X1 or saline vehicle. Tumor volumes were evaluated until the planned endpoint of mean tumor volume of control group of 1500 mm3 or day 28. At the endpoint, xenografts, or tumor beds (in the case of no palpable mass) were collected as formalin fixed paraffin embedded material. The xenograft material was evaluated for B7-H4 expression by protein and RNA methods and expression was compared to the anti-tumor activity. Results: In this panel of breast patient derived xenograft models, a range of anti-tumor activities has been observed following administration of a single dose of XMT-1660. The relationship between XMT-1660 anti-tumor activity and B7-H4 expression was demonstrated. Conclusion: XMT-1660 elicits a range of anti-tumor activity across a series of primary breast cancer xenograft models. XMT-1660 is currently in IND-enabling studies and is expected to enter a Phase I dose escalation clinical study in 2022. The efficacy/expression relationship of B7-H4 will be further evaluated in an upcoming clinical study with a goal to identify patients most likely to respond to XMT-1660. Citation Format: Scott D. Collins, Pamela S. Shaw, Shawn P. Fessler, Jason Wang, Rebecca Mosher. Antitumor effect of XMT1660, a B7H4 targeting antibody drug conjugate, in an unselected panel of patient derived xenograft models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1756.

Abstract 6039: Application of triple negative breast cancer patient-derived organoid and xenograft model for drug screening

Abstract Background: Breast cancer Patient Derived Organoids (PDOs) and patient-derived xenografts (PDXs) which recapitulate the tumor heterogeneity and molecular signatures of original tumor tissue, are useful tools to enable greater precision of both approved and experimental medicines through personalized therapeutic approaches. We focus on use of ex vivo PDOs, PDX-derived organoids (PDXOs), and vivo PDXs models for drug testing and personalized therapy. In this study, we investigated the oncogenic role and therapeutic potency of targeting WEE1 in breast cancer. Methods: Fresh surgical specimens of primary TNBC breast tumor (N=3) were used for PDOs. PDOs and PDX-derived organoids (PDXOs) were cultured in previously reported media compositions based on ECM hydrogel. PODs and PDXOs were subjected to drug screening for 22 anticancer drugs including chemoreagents and targeted drugs in the 3D HTS system. Drug sensitivity was tested in triplicate in different concentration ranges for 7 days. The IC50 for each drug was calculated by a sigmoidal dose-response curve, using the GraphPad Prism 9 program. For drug screening in PDXs models, PDOs were injected into the fourth mammary fat pads of NOD.Cg-Prkdcscid Il2rgtm1wjl/SzJ mice. WEE1 inhibitor (AZD1775) was administered by oral gavage (AZD1775, 30 mg/kg) for 3 weeks. Immunostaining of ER, PR, Her2, CK5 and Ki67 was performed in PODs, PODXs and PDX tumor tissues. Results: All PDOs, PDXs, and PDXOs were ER-, PR- and HER2- negative. PDOs and PDXOs (172T, 185T, 207T) showed differential response to 22 anticancer drugs. In PDOs and PDXOs models, 172T and 207T PDOs and PDXOs are highly sensitive to AZD1775, but 185T PDOs and PDXOs less sensitive or never respond to treatment with AZD1775 (10 µM). In PDX models, treatment with AZ1775 decreased tumor growth (P<0.0079) as well as distance metastasis in 207T-PDX mice, whereas in 172T- and 185T-PDX mice, the tumor growth and metastasis were not reduced compared with the vehicle group. Conclusion: Consequently, PDOs, PDXOs and PDXs recapitulated immunohistological signatures of original tumor tissues. The results of WEE1 inhibitor response between PDOs, PDXOs and PDXs were consistent. This study may provide a preclinical tool to screen drug responses to standard-of-care and newly identified drugs. Citation Format: Seungyeon Ryu, Hoe Suk Kim, Jung Eun KIM, So-Hyun Yoon, Sangeun Lee, Moonjou Baek, Han-Byoel Lee, Dong Woo Lee, Bosung Ku, Wonshik Han. Application of triple negative breast cancer patient-derived organoid and xenograft model for drug screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6039.

Abstract LB006: In vivo programming of myeloid cells by mRNA mediated delivery of novel Fc alpha fusion receptor activates anti-tumor immunity

Abstract Immunotherapy has revolutionized cancer treatment. However, for the majority of patients with advanced solid tumors, sustained clinical benefit has yet to be achieved. Myeloid cells such as monocytes and macrophages readily accumulate in tumors, in some cases contributing up to 75% of the tumor mass. Reprogramming circulating and tumor associated myeloid cells to activate their ability to elicit anti-tumor adaptive immunity by phagocytosis, cytokine secretion and antigen presentation is an attractive approach to harness and orchestrate systemic anti-tumor immunity. It remains challenging to specifically target and activate myeloid cells in vivo. To overcome this hurdle, we have developed a novel in vivo myeloid cell engineering platform: Fc-alpha Receptor Fusion Constructs. Unlike other chimeric antigen receptors (CARs) the construct was engineered by fusing a tumor recognition scFv with the alpha chain of human Fc receptors. The stable expression and function of these receptors requires endogenously expressed Fc receptor gamma chain, a protein with limited expression to immune cells, mostly myeloid cells. Here, we present that intravenous infusion of lipid-nanoparticle (LNP) encapsulating the Fc-alpha Receptor Fusion Construct mRNA results in the uptake and expression of the construct by myeloid cells. In immunodeficient xenograft models of hepatocellular carcinoma and triple negative breast cancer, delivery of LNP mRNA encoding for GPC3 or TROP2 targeted Fc-alpha Receptor Fusion Constructs resulted in tumor killing, confirming the ability of this approach to program myeloid cells. Furthermore, in the B16 syngeneic melanoma model, treatment with the melanoma antigen GP75 targeted Fc-alpha Receptor Fusion Constructs was also associated with the initiation of broad systemic immune responses, characterized by tumoral accumulation of activated CD8+ T cells, reduced tumor associated Tregs and activation of antigen presenting cells in spleen. Together these studies highlight the potential of Fc-alpha Receptor Fusion Construct delivered directly in vivo to program myeloid cells to recognize and kill cancer. Citation Format: Hongyun Zhao, Inna Shcherbakova, Thomas Prod’homme, Bruce McCreedy, Yuxiao Wang, Daniel Getts. In vivo programming of myeloid cells by mRNA mediated delivery of novel Fc alpha fusion receptor activates anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB006.

Abstract 1595: Analysis of spatiotemporal phenotypic heterogeneity in chemoresistant triple negative breast cancer using imaging mass cytometry

Abstract Shifts in tumor cell phenotype in response to selective pressures (i.e. changing microenvironments, drug treatments) pose one of the biggest obstacles to successful breast cancer therapies. Phenotypically diverse breast tumor and stroma subpopulations, and interactions between them that alter tumor cell biology, represent unique and spatially distinct niches. We hypothesize that localized neighborhoods of breast tumor cells possess specialized phenotypes that mediate chemoresistance and represent novel therapeutic vulnerabilities. In order to assess these potential phenotypes, we utilized imaging mass cytometry (IMC), a highly multiplexed imaging modality that allows simultaneous measurement of 30-40 antigens while retaining the spatial architecture of the cancer tissue. We constructed an IMC antibody panel that combines markers for tissue architecture, tumor and stromal cell phenotyping, and signaling pathway activation. IMC was applied to patient-derived xenograft (PDX) models of triple negative breast cancer (TNBC).Our TNBC PDX collection was established from tumors obtained before and after neoadjuvant Adriamycin and cyclophosphamide (AC). IMC analysis of 18 PDX models representing eight patients revealed that stromal cell phenotypes were generally shared between all models, but tumor cell phenotypes were largely patient-specific. While every model was comprised primarily of a few major tumor cell phenotypes, we noted that each case also harbored several minor, unique populations, suggesting that specialized neighborhoods may exist within the tumor mass. Comparison of paired PDX models showed a wide range of phenotypic responses to chemotherapy, ranging from stable tumor composition to widespread changes in tumor phenotypes. These phenotypic changes arose despite relatively consistent genomic architecture. Vimentinhi fibroblasts were present more often in post-AC models, while SMAhi fibroblasts were unchanged after treatment. Comparison of pre-/post-AC PDX pairs revealed spatially constrained MAPK activation emerged after treatment. To capture acute changes in tumor phenotype, we treated treatment-naïve PDX models with AC and evaluated tumors by IMC. As tumors regressed and then regrew, we identified novel phenotypic shifts, again including increased MAPK signaling localized to discrete neighborhoods, suggesting this property may be a common feature of chemoresistant TNBC. Analysis of adjacent cells revealed seven distinct neighborhoods, and ongoing work is aimed at determining whether these neighborhoods are altered in response to chemotherapy treatment. Taken together, our findings suggest that distinct tumor phenotypes arise following treatment. Our goal is to determine whether these unique phenotypic niches functionally contribute to chemoresistance and if disruption of these niches enhances chemosensitivity. Citation Format: Amanda L. Rinkenbaugh, Vidya C. Sinha, Pankaj Singh, Yuan Qi, Jiansu Shao, Xiaomei Zhang, Gloria V. Echeverria, W. Fraser Symmans, Stacy L. Moulder, Helen Piwnica-Worms. Analysis of spatiotemporal phenotypic heterogeneity in chemoresistant triple negative breast cancer using imaging mass cytometry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1595.

Abstract 964: Tumor cell plasticity promotes metastasis across heterogeneous tumors

Abstract Metastasis, the growth of secondary tumors in distant organs, is the major cause of cancer-related deaths due to insufficient therapeutic effects of conventional treatment. Individual tumor cells exhibit heterogeneous features and growth potentials within the same tumor that may influence metastasis formation. During the metastatic cascade, tumor cells adapt their phenotype to various microenvironments that are distinct from their original site resulting in heterogeneous metastatic cells that often are resistant to conventional treatment. The underlying mechanisms of why some tumor cells can give rise to metastases, whereas others cannot are remarkably poorly understood. We established patient-derived xenograft (PDX) models of breast cancer with different metastatic potential and preserved tumor heterogeneity. We analyzed the intrinsic cellular programs of individual tumor cells that influence the metastatic potential of breast cancers using different single-cell RNA-sequencing protocols (MULTI-Seq and Smart-Seq2). Using gene expression profiling of matched primary tumor and metastatic cells of 13 human breast cancers, we demonstrated that while human tumors showed profound inter-patient heterogeneity, they also shared signatures of differentially expressed genes between primary tumor and metastatic cells. Tumors with similar metastatic capabilities shared similar signatures, suggesting potential targets to directly treat metastasis. Additionally, we found that the plasticity of tumor cells is a common feature across tumors that is beneficial for the formation of metastasis. Tumors with higher levels of plastic tumor cells have a greater ability to form metastases. Moreover, we identified a subset of tumor cells expressing both markers of epithelial and mesenchymal characteristics, demonstrating in-vivo evidence for tumor epithelial-mesenchymal plasticity (EMP) in the metastatic cascade. The EMP is a continuum of states with epithelial and mesenchymal cell states as the two extremes of this continuum. The identified transition cells express distinct markers suggesting that these cells may represent a novel and overlooked cell type within the EMP continuum. Given the importance of tumor plasticity in the metastatic cascade, inhibiting the subset of tumor cells that are currently undergoing EMP may represent a novel treatment strategy for metastasis. Citation Format: Juliane Winkler, Weilun Tan, Angela O. Pisco, Andrei Goga, Spyros Darmanis, Zena Werb. Tumor cell plasticity promotes metastasis across heterogeneous tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 964.

Abstract 3274: Targeting NSD family histone methyltransferase activity with irreversible inhibitors

Abstract Nuclear SET domain containing (NSD) family member proteins are histone methyltransferases that mono- and di-methylate histone 3 at lysine 36 (H3K36) to alter gene expression in a context-dependent manner. NSD1 and NSD3 are two members of this family which share greater than 80 percent sequence similarity in the catalytic SET domain. NSD1 is found as a fusion with NUP98 in aggressive cases of pediatric leukemia, and the lysine methyltransferase (KMTase) activity of NUP98-NSD1 drives bone marrow progenitor proliferation. Similarly, high levels of enzymatically active NSD3 mRNA are correlated with reduced disease-free survival in breast cancer and catalytic NSD3 expression is sufficient to rescue tumor growth in a xenograft model of triple negative breast cancer. Selective and potent inhibitors of NSD1 and NSD3 KMTase activity are needed to further investigate the therapeutic potential of targeting this function in leukemia and/or solid cancers. Here, we report the development of irreversible small molecule inhibitors of the NSD1 and NSD3 SET domains. We utilized a NMR-based fragment screen of the NSD1 SET domain to identify the hit BT1, which binds reversibly to the SET domain of NSD1. BT1 was extensively optimized into a series of potent irreversible ligands. Mass spectrometry and structural studies revealed that these compounds react with a cysteine near the autoinhibitory loop, providing a rational for the strong inhibition of KMTase activity we observe in biochemical assays. These inhibitors also bind to the NSD1 and NSD3 SET domains in cells and exhibit potent anti-proliferative effects against leukemia cells containing NUP98-NSD1 and breast cancer cells with high levels of NSD3 expression. In summary, we present novel irreversible inhibitors of NSD1 and NSD3 KMTase activity which represent important chemical probes that can be used to investigate the therapeutic potential of targeting NSD family member catalytic activity in cancers. Citation Format: Christina Howard, Sergei Zari, Shuangjiang Li, Huang Huang, EunGi Kim, Se Ra Park, Trupta Purohit, Hongzhi Miao, Xiaotian Zhang, Caroline Nikolaidis, Hao Li, Juliano Ndoj, HyoJe Cho, Jolanta Grembecka, Tomasz Cierpicki. Targeting NSD family histone methyltransferase activity with irreversible inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3274.

Abstract 2300: Brain penetrant CDK4/6 inhibitor PRT3645 demonstrates anti-tumor activity and enhances survival in glioblastoma and breast cancer brain metastasis models

Abstract Cell cycle deregulation is a hallmark of cancer and CDK inhibitors, specifically inhibiting CDK4/6 and blocking cells transition from the G1 to the S phase of the cell cycle are the first and only class of highly specific CDK inhibitors approved for cancer treatment to date. CDK4/6 inhibitors have transformed the treatment paradigm of estrogen receptor-positive (ER+), HER2- breast cancer with three CDK4/6 inhibitors currently FDA approved. Brain metastasis commonly arises in patients with breast, lung, melanoma and other cancer types, is associated with poor survival outcomes and poses distinct challenges in clinical management. Due to advances in imaging technologies, the detection of brain metastases is increasing and there is a dearth of novel therapies to combat brain metastatic cancers and impact patient survival. Here, we describe a novel brain penetrant CDK4/6 inhibitor, PRT3645 exhibiting single digit nanomolar biochemical potency against CDK 4/6 and >2000-fold selectivity against other CDK family members (CDK1, CDK2, and CDK9). In cellular assays, PRT3645 inhibits cellular phosphorylation of RB with low nanomolar activity. Consistent with this, PRT3645 treatment resulted in concentration-dependent inhibition of cell proliferation in glioblastoma (GBM) cell lines and in HER2- and HER2+ breast cancer lines (EC50 values < 125 nM). Furthermore, PRT3645 demonstrated additive in vitro activity with fulvestrant or tucatinib in ER+ and HER2+ breast cancer lines. PRT3645 exhibits favorable in vitro safety pharmacology and ADME profiles, including brain exposure in rodents at steady state, and demonstrates oral bioavailability across rodents, dog and nonhuman primates. In vivo, oral PRT3645 was well tolerated and highly efficacious in a dose-dependent manner in subcutaneous xenograft models of GBM and breast cancer and in orthotopic human breast cancer brain metastasis (BCBM) and GBM models in mice as a monotherapy. PRT3645 showed tumor regression as single agent in the MCF7 ER+ breast cancer model and a combinatorial benefit with the estrogen receptor blocker, fulvestrant. In a HER2+ BT474-luc orthotopic model, similarly efficacious single agent activity of PRT3645 was achieved, as well as a significant combinatorial benefit on tumor growth and median survival when administered with the brain penetrant HER2 kinase inhibitor, tucatinib. PRT3645 was highly efficacious in a U87-luc GBM orthotopic model and demonstrated enhanced median survival benefit when combined with an orally active brain penetrant PRMT5 inhibitor. In summary, PRT3645 demonstrates an excellent balance of potency, selectivity, PK parameters across species, brain penetrance and favorable tissue distribution relative to brain exposure, and currently has advanced into IND-enabling preclinical studies. Citation Format: Ashish Juvekar, Yang Zhang, Andrew Buesking, Min Wang, Dave Rominger, Joseph Rager, Stefan Ruepp, Kirsten Gallagher, Yue Zou, Miles Cowart, Xiaowei Wu, Sarah Pawley, Ryan Holmes, William Gowen-MacDonald, Kris Vaddi, Andrew Combs, Bruce Ruggeri, Peggy Scherle. Brain penetrant CDK4/6 inhibitor PRT3645 demonstrates anti-tumor activity and enhances survival in glioblastoma and breast cancer brain metastasis models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2300.

Abstract 991: OVO-like genes are master regulators of the epithelial fate in breast cancer

Abstract The OVO-like genes are evolutionary conserved C2H2 zinc finger transcription factors (TFs) with SNAG repressor domains involved in the maintenance of epithelial homeostasis. From the three Ovo-like family genes identified in mammals, Ovol-like1 (Ovol1) and Ovol-like2 (Ovol2) are the most studied members with multiple reports pinpointing relevant roles in development and disease. In cancer, one of the hallmarks of invasive carcinoma involves the loss of E-cadherin expression by the repression of SNAG transcription factors. Interestingly, contrary to the other SNAG domain family members the OVO-like genes regulate epithelial cell fate. We performed data analysis in breast cancer cell lines and patient data obtained from GEO, CCLE, TCGA and METABRIC to assess the potential of the OVO-like genes as relevant regulators of gene expression in breast carcinoma. In addition, we stablished breast cancer models with inducible expression or repression of the OVO-like genes. We also analyzed the cellular systems we generated using naïve high-throughput methods such as RNA-Seq. Likewise, we studied the effect of OVO-like genes on tumor progression and metastasis using inducible expression systems in both xenograft and syngeneic breast cancer models. We observed that Ovol1 and Ovol2 are constitutively expressed in human breast cancer cell lines, and they are upregulated due to chromosomal gains in breast cancer patients. We observed how the introduction of Ovol1 and Ovol2 into mesenchymal-like breast cancer cell lines modified their transcriptome in a way that promoted expression of epithelial marker genes (e.g., Amphiregulin) and downregulated mesenchymal markers (e.g., Vimentin). In addition, introducing Ovo-like genes in mesenchymal-like cells greatly affected their viability and function. Surprisingly, we observed a similar effect by downregulating the Ovo-like genes in epithelial-like cells. We propose a model where a common epigenetic machinery is shared between structurally related transcription factors with opposing effects, such as OVO-like proteins and other SNAG-containing transcription factors, such as Snail and Slug, such that the abundance of the transcription factors and their co-repressors defines the state of the system as either epithelial or mesenchymal. Citation Format: Diana Drago Garcia, Yosef Yarden. OVO-like genes are master regulators of the epithelial fate in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 991.

Abstract 1763: Gastric cancer antibody fragment drug-conjugates (FDCs): Succeeding in solid tumors where ADCs fail

Abstract Antibody Drug Conjugates (ADCs) are failing due to 3 critical limitations: Low potency, ineffective solid-tumor penetration and poor tolerability. The industry is full of approaches where full-length Immunoglobulins have been engineered to carry defined numbers of payloads with higher-loadings of less potent payloads appearing to be well-tolerated. However, antibody fragments (e.g. single-chain Fcs-scFvs), which have many advantages including rapid tumor penetration, faster clearance, inexpensive manufacture, have been technologically challenging to apply in oncology. Our novel approach enables scFvs to have a high Drug:Antibody loading ratio (DAR) whilst retaining effective binding and other favorable biophysical properties, leading to a new product class tailored for solid tumors. Antikor has two FDC products in development for solid tumors, notably gastric: anti-HER2 FDC (ANT-043) and a second target (ANT-045) which will be disclosed during this presentation. ANT-043 has pM potencies in a range of HER2-expressing cell-lines, including trastuzumab-resistant models, excellent tumor ablation effects in breast, ovarian and gastric cancer xenograft models and superior tolerability compared to an ADC in rat toxicology studies at a dose of 1mg/kg/weekly. Quantitative payload tumor uptake and fluorescent immuno-histological studies demonstrate superior solid tumor penetration across the entire tumor and diffusion from blood vessels. In collaboration with our partners, Essex Biotechnology, Antikor is taking ANT-043 into IND-enabling studies for clinical development. ANT-045, which emerged from Antikor’s proprietary FDC ‘discovery engine’, is progressing towards IND-filing and updated data will illustrate how ANT-045 could have a broader patient benefit in gastro-intestinal cancers. ANT-045 has excellent in vitro cell-kill potency (pM IC50s) and excellent stability and superior in vivo tumor cure efficacy, compared to a leading clinical stage benchmark ADC. This presentation will focus on Antikor’s FDC discovery platform (stable high-DAR scFv-display libraries, tailored linker-payloads and design features) that has the potential to generate first-in-class products for difficult to treat solid tumors for patient benefit and promising to succeed where ADCs have failed to deliver. Citation Format: Mahendra P. Deonarain, Gokhan Yahioglu, Ioanna Stamati, Bryan Edwards, Soraya Diez-Posada, Isabel Perez-Castro, Anja Pomowski, Laura Bouche, Ashleigh Stewart, Monika Maciuszek, Sam Ness, Malcolm Ngiam, Quinn Xue. Gastric cancer antibody fragment drug-conjugates (FDCs): Succeeding in solid tumors where ADCs fail [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1763.

Abstract 6280: Preclinical development of a bispecific antibody-trap selectively targeting CD47 and HER2 for the treatment of breast as well as gastric cancer

Abstract Trastuzumab executes anti-tumor efficacy mainly via antibody-dependent cell cytotoxicity (ADCC). However due to the fact that majority of the populations including patients with cancers carry a CD16A-158F allele which has low binding affinity to the Fc fragment of trastuzumab, response to trastuzumab treatment is hindered. Furthermore, overexpression of CD47 on cancer cells prevent macrophages from activation via Fc-FcγRIIa interaction due to the so called “Don’t eat me” signal. We therefore designed a bispecific mAb-trap designated as IMM2902. Extensive in vitro as well as in vivo characterization demonstrated that IMM2902 binds to both CD47 and HER2 with high affinity (KD = 5.8x10-10M for HER2; KD = 8.9x10-9M for CD47) and has stronger ADCC activity against NCI-N87 (EC50 = 0.054nM for IMM2902, v.s. 0.868nM for trastuzumab). In vivo efficacy studies in several xenograft tumor models revealed a robust anti-tumor activity as reflected by the complete elimination of established tumors in BT-474 breast cancer and NCI-N87 gastric xenograft models even at the dose as low as 3.5mg/kg. Interestingly, even in Herceptin-resistant breast tumor model, when administered at a dose of 10mg/kg, the established HCC-1954 tumors were also eliminated. Immunohistochemistry staining of the tumor tissues demonstrated an accelerated HER2 degradation which is highly correlated with tumor volume. IMM2902 has no impact on hemagglutination, nor does it have significant hemotoxicity following single as well as multiple administrations in non-human primate animals at different dosage. Our study suggests that IMM2902 has the potential to be an alternative promising treatment option for patients with her2-positive cancers refractory to trastuzumab treatment. Citation Format: Wenzhi Tian, Song Li, Dianze Chen, Dandan Liu, Huiqin Guo, Chunmei Yang, Li Zhang, Wei Zhang, Xiaoping Tu, Liang Peng, Gui Zhao, Ruliang Zhang, Fan Zhang. Preclinical development of a bispecific antibody-trap selectively targeting CD47 and HER2 for the treatment of breast as well as gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6280.

Abstract ND01: KSQ-4279: A first-in-class USP1 inhibitor for the treatment of cancers with homologous recombination deficiencies

Abstract Tumors with BRCA1/2 mutations and other homologous repair deficiencies (HRD) are vulnerable to agents that target the remaining DNA repair pathways, including platinum-containing chemotherapy agents and molecules targeting poly (ADP-ribose) polymerase-1 (PARP1). Despite the clinical benefit achieved with these drugs, many patients achieve incomplete disease control and resistance often emerges. With the goal of addressing this clinical need, we applied our proprietary CRISPRomics technology to identify novel targets in cancer indications characterized by defects in DNA repair pathways. One of the top ranked targets was the deubiquitinating enzyme USP1. USP1 has established roles in DNA damage repair processes including Translesion Synthesis and the Fanconi Anemia pathway. We developed KSQ-4279, a potent, highly selective inhibitor of USP1. KSQ-4279 was active in cells, leading to the accumulation of mono-ubiquitinated substrates of USP1 and inhibited the proliferation of cancer cell lines with BRCA mutations or other HRD alterations. Studies investigating the effect of combining KSQ-4279 with PARP inhibitors revealed clear evidence of synergy in cell lines with partial or no sensitivity to each agent alone. To investigate how the distinct mechanisms of action of KSQ-4279 and PARP inhibitors would be reflected in their resistance profiles, we used our CRISPRomics technology to perform functional genomic resistance screens. The top scoring resistance genes for KSQ-4279 were distinct from those identified for PARP inhibitors, which raised the possibility that combining PARP and USP1 inhibitors may provide more durable disease control by reducing the emergence of resistance. Evaluation of KSQ-4279 in patient-derived ovarian and triple-negative breast cancer xenograft models demonstrated dose-dependent tumor growth inhibition as a single agent and in combination with PARP inhibitors. In xenograft models that were insensitive or only partially sensitive to PARP inhibitors, the combination of KSQ-4279 and Olaparib led to tumor regressions and durable tumor control. This data supports the ongoing clinical trial of KSQ-4279 in patients with tumors harboring BRCA1/2 or other HRD mutations, both as a single agent and in combination with PARP inhibitors. Citation Format: Louise Cadzow, Erica Tobin, Pamela Sullivan, Sol Shenker, Sumeet Nayak, Janid Ali, Hugh Gannon, Anne Dodson, Paula Grasberger, Alyssa Carlson, Michael McGuire, Jehrod Brenneman, Hanlan Liu, Andrew Olaharski, Kerstin Sinkevicius, Jeff Hixon, Elsa Krall, Mike Schlabach, Matt Goulet, Jeremy Wilt, Patricia Harris, Frank Stegmeier, Andrew Wylie. KSQ-4279: A first-in-class USP1 inhibitor for the treatment of cancers with homologous recombination deficiencies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr ND01.

Abstract 1399: Discovery and development of PARP inhibitor senaparib

Abstract Poly (ADP-ribose) polymerase (PARP) is a key enzyme for DNA repair. PARP inhibitors have been shown to be effective against cancers with DNA repair defects, such as with BRCA1 or BRCA2 mutations. Several PARP inhibitors, including olaparib, rucaparib, niraparib, talazoparib, fluzoparib and pamiparib have been approved for the treatment of several types of cancer. In this presentation, we will report our discovery and development of senaparib (IMP4297) as a potent PARP inhibitor. We will present studies led to the identification of senaparib as a clinical candidate, as well as IND enabling in vitro and in vivo characterization of senaparib. Preclinical data indicated that senaparib had a wide therapeutic window (single agent effective dose of 2.5-21 mg/kg QD, in a BRCA1 mutated MDA-MB-436 human breast cancer xenograft model), which was confirmed in clinical studies (effective dose of 20-120 mg QD, and no DLT was found up to 150 mg QD). Senaparib is currently in several phase I/II, phase II and phase III clinical studies for the treatment of multiple tumor types either as single agent or in combination with temozolomide (TMZ). The most advanced study of senaparib is a phase III study as maintenance therapy in platinum-sensitive advanced ovarian cancer patients following first-line chemotherapy (ClinicalTrials.gov Identifier: NCT04169997). Citation Format: Sui Xiong Cai, Ning Ma, Xiaozhu Wang, Yangzhen Jiang, Mingchuan Guo, Chih-Yi Hsieh, Ye Edward Tian. Discovery and development of PARP inhibitor senaparib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1399.

Anticancer effects of PARP1 hyperactivation by a decoy oligodeoxynucleotide in vitro and in vivo.

e15060 Background: Poly (ADP-ribose) polymerase (PARP) inhibitors mediate significant anticancer effects against homologous recombination defective (HRD) tumors but have limited efficacy against homologous recombination proficient (HRP) neoplasms. Moreover, HRD tumors often become resistant to PARP inhibitors during treatment, constituting a major limitation to the clinical use of these agents. Here, we describe the metabolic, antineoplastic and immunomodulatory effects of a first-in-class oligodeoxynucleotide that operates as a PARP1 decoy (OX413), resulting in constitutive hyperactivation of PARP1 and consequent exhaustion of the DNA damage response. Methods: OX413-induced PARP trapping and hyperactivation, NAD+ consumption and cell cytotoxicity were monitored using (HRP and HRD) breast, ovarian or prostate cancer cells as well as normal fibroblasts and leukocytes. DNA repair abrogation was monitored by analyzing repair protein recruitment to damage sites. Accumulation of cytoplasmic DNA fragments was monitored after DNA staining and microscopy analysis. Effects on the innate immune response was assessed by following STING pathway activation and T-cell mediated anti-tumor cytotoxicity. In a mouse xenograft model of breast cancer, OX413-induced PARP activation and tumor infiltration by immune cells were analyzed ex-vivo by flow cytometry. Antitumor efficacy of OX413 alone or combined to a PD1 blocker was assessed in MPA/DMBA-driven HR+ HER2- mouse mammary carcinomas. Results: At odds with conventional PARP inhibitors, OX413 bound to and hyperactivated PARP1 with high affinity and in a dose-dependent manner, resulting in elevated cytotoxicity in multiple cancer (but not normal) cells irrespective of HR status. OX413 impaired DNA repair due to PARP trapping and rapid NAD+ consumption, leading to the accumulation of cytoplasmic chromatin fragments (CCFs). Consistent with this, OX413 triggered activation of the CGAS/STING pathway, CCL5 secretion and potentiation of tumor-targeting T cell responses. PARP1 engagement and STING activation were corroborated in vivo in EMT6 mouse mammary carcinomas, correlating with anticancer effects coupled to tumor infiltration by innate and adaptive immune cells. In MPA/DMBA-driven tumors, OX413 mediated considerable anticancer effects that could be exacerbated by PD1 inhibition. Conclusions: Our results provide preclinical rationale for using OX413 to trigger metabolic exhaustion in cancer cells and initiate inflammatory responses that can be actioned by immune checkpoint inhibitors in patients bearing HRD as well as HRP tumors.

Phase 1 study of SGN-B7H4V, a novel, investigational vedotin antibody–drug conjugate directed to B7-H4, in patients with advanced solid tumors (SGNB7H4V-001, trial in progress).

TPS3155 Background: B7-H4, a B7 immune checkpoint ligand, is expressed at low levels in normal tissue and negatively regulates T-cell function by inhibiting T-cell proliferation and cytokine production. B7-H4 expression is elevated in solid tumors, including breast, ovarian, and endometrial cancers. Targeting B7-H4–expressing tumor cells may relieve B7-H4–mediated T-cell inhibition. SGN-B7H4V is a novel, investigational vedotin antibody–drug conjugate directed to B7-H4 with proposed mechanisms of action including monomethyl auristatin E (MMAE)-directed cytotoxicity, bystander effect, antibody-dependent cellular cytotoxicity, and antibody-dependent cellular phagocytosis. SGN-B7H4V elicited antitumor activity in cell line-derived xenograft models of triple-negative breast cancer (TNBC) and patient-derived xenograft models of TNBC and ovarian cancer (Gray et al 2021), providing a rationale to evaluate SGN-B7H4V in patients (pts) with advanced solid tumors. Methods: SGNB7H4V-001 (NCT05194072) is a phase 1, first-in-human, multicenter, open-label trial evaluating the safety, tolerability, pharmacokinetics (PK), and antitumor activity of SGN-B7H4V in pts with advanced solid tumors. This study includes 3 parts: dose escalation (Part A), dose and schedule optimization (Part B), and dose expansion in disease-specific cohorts and a biology cohort (Part C). Adult pts (≥18 years) with histologically/cytologically confirmed locally advanced unresectable or metastatic solid tumors including high-grade serous epithelial ovarian cancer, primary peritoneal cancer, fallopian tube cancer, human epidermal growth factor receptor 2-negative and hormone receptor-positive breast cancer, TNBC, endometrial carcinoma, squamous non-small cell lung cancer, cholangiocarcinoma, or gallbladder carcinoma, are eligible. Pts must have ECOG PS 0–1 and relapsed/refractory disease or be intolerant to standard-of-care therapies. Prior treatment with an MMAE-containing agent or a B7-H4–targeted agent is not permitted. Primary endpoints include the rate of adverse events, laboratory abnormalities, dose-limiting toxicities, and cumulative dose-level safety. Secondary endpoints are objective response rate (ORR), complete response rate, duration of objective response (DOR), progression-free survival (PFS), overall survival (OS), PK, and incidence of antidrug antibodies. Exploratory endpoints include pharmacodynamic (PD) analyses, PD and PK exposure measurements, B7-H4 characterization on malignant cells, and biomarker analyses. Safety and antitumor activity endpoints will be assessed using descriptive statistics. ORR will be analyzed by tumor type and dose. DOR, PFS, and OS will be estimated using the Kaplan–Meier method. Enrollment for Part A is ongoing in North America and is planned in Europe. Clinical trial information: NCT05194072.