Negative Patient-derived Xenografts Research Articles

Theprogrammed death ligand 1 interactome demonstrates bidirectional signaling coordinating immune suppression and cancer progression in head and neck squamous cell carcinoma.

The programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) are validated cancer targets; however, emerging mechanisms and impact of PD-L1 intracellular signaling on cancer behavior are poorly understood. We investigated the cancer cell intrinsic role of PD-L1 in multiple patient-derived models in vitro and in vivo. PD-L1 overexpression, knockdown, and PD-L1 intracellular domain (PD-L1-ICD) deletion (Δ260-290PD-L1) models were assessed for key cancer properties: clonogenicity, motility, invasion, and immune evasion. To determine how PD-L1 transduces signals intracellularly, we used the BioID2 platform to identify the PD-L1 intracellular interactome. Both human papillomavirus-positive and negative patient-derived xenografts were implanted in NOD-scid-gamma and humanized mouse models to investigate the effects of recombinant PD-1, anti-PD-L1, and anti-signal transducer and activator of transcription 3 (STAT3) in vivo. PD-L1 intracellular signaling increased clonogenicity, motility, and invasiveness in multiple head and neck squamous cell carcinoma (HNSCC) models, and PD-1 binding enhanced these effects. Protein proximity labeling revealed the PD-L1 interactome, distinct for unbound and bound PD-1, which initiated cancer cell-intrinsic signaling. PD-L1 binding partners interleukin enhancer binding factors 2 and 3 (ILF2-ILF3) transduced their effect through STAT3. Δ260-290PD-L1 disrupted signaling and reversed pro-growth properties. In humanized HNSCC in vivo models bearing T-cells, PD-1 binding triggered PD-L1 signaling, and dual PD-L1 and STAT3 inhibition were required to achieve tumor control. Upon PD-1 binding, the PD-L1 extracellular and intracellular domains exert a synchronized effect to promote immune evasion by inhibiting T-cell function while simultaneously enhancing cancer cell-invasive properties.

Abstract 1388: ATM inhibitor AZD1390 sensitizes breast cancer brain metastasis to radiation therapy

Abstract Metastasis to the central nervous system (CNS) has remained a major source of morbidity and mortality for patients with breast cancer. This is mainly driven by the lack of therapeutic options, as traditional chemotherapy and targeted therapies have been shown to have limited efficacy in the brain. Ataxia-telangiectasia mutated (ATM) protein orchestrates the cellular DNA damage response (DDR) to cytotoxic DNA double-strand breaks induced by ionizing radiation (IR). ATM genetic ablation or pharmacological inhibition results in tumor cell hypersensitivity to IR.AZD1390 is a potent orally bioavailable ATM inhibitor, specifically optimized for blood brain barrier penetration and has shown to be an effective radiosensitizer in gliomas. We have shown that there are frequent alterations in DNA damage response (DDR) pathways in CNS metastasis (CM), which include frequent mutations in TP53. Incorrect repair of DNA lesions often leads to genomic instability. ATM, a core component of the DNA repair system, is activated to enhance the homologous recombination (HR) repair pathway upon DNA double-strand breaks. Here we show that AZD1390, when used in combination with radiation therapy, can inhibit the growth of breast cancer CM in patient derived xenograft (PDX) tumors. Three PDX models (2 Her2+ and one triple negative), all of which harbor TP53 mutations and other DDR alterations, were implanted into the flank or brain of immunocompromised mice. Pre-treatment with AZD1390 followed by a fractionated regime of radiation therapy (2Gy/day for 5 days) significantly inhibited growth of flank PDX tumors by an average of 81% (85% and 80% in the HER2+ and 77% in the triple negative PDX, p-value < 0.05). This is compared to an average of 7% (8%, 13% and 0% respectively) for tumors treated with AZD1390 alone or 40% (39%, 21% and 58% respectively) for radiation therapy alone in all PDX models. Growth inhibition was sustained until the experiment endpoint at 90 days in 75% of the tumors, and 25% of the tumors regressed below their size at the beginning of treatment. About 31% of tumors across three models started to grow back and gene expression analysis comparing these tumors with complete responders demonstrated changes in oxidative phosphorylation, sirtuin signaling, and ERK/MAPK signaling. Adjuvant therapy of AZD1390 did not further decrease tumor growth. Our results demonstrate that AZD1390 can sensitize breast cancer CM with DDR pathway alterations to radiation therapy. This points to the potential of AZD1390 as a potential novel therapeutic agent for patients with breast cancer CM. Citation Format: Ben Yi Tew, Stephen Durant, Bodour Salhia. ATM inhibitor AZD1390 sensitizes breast cancer brain metastasis to radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1388.

ABT-806 derived antibody drug conjugates (ADCs) inhibit growth of malignant mesothelioma in-vivo.

e14677 Background: Malignant mesothelioma (MM) is an aggressive malignancy of the pleura with limited therapeutic options, and is associated with a poor prognosis. EGFR is known to be highly over-expressed in mesothelioma with reported EGFR overexpression between 44 to 97%. We have investigated an anti-EGFR antibody (ABT-806), which is tumor specific and robustly inhibits EGFR-expressing tumors. We have previously shown that ABT-806 ADCs demonstrate potent anti-tumor activity in 806 immunohistochemistry (IHC) positive MSTO-211H MM cell line xenograft model. We present data in MM using ABT-806 novel ADCs [ABT-414 (ABT-806- monomethyl auristatin F), ABBV-221 (ABT-806- monomethyl auristatin E) and ABBV-321 (ABT-806- pyrrolobenzodiazepine)] in MM patient derived xenografts (PDX). Methods: We evaluated expression of EGFR and mAb 806 IHC in MM cell lines and PDXs. PDXs were implanted into 5 to 10 NOD-Scid mice per group and treated with control ADC, saline, cisplatin or ABT-806 ADCs and followed longitudinally with caliper measurements. Comparative statistics were performed in Graphpad prism. Results: Three PDX models were selected according to their 806 IHC statuses (2 epithelioid 806 IHC positive, 1 biphasic histology 806 IHC negative). In one epithelioid PDX model, ABBV-321 resulted in significantly reduced tumor growth on day 27 post therapy with median tumor volumes of 180 mm3 (ADC control) compared with 78mm3 (ABBV-321; p = 0.0159 two-sided). Moreover, the median survival was also significantly longer in ABBV-321 treated models (p = 0.018). In the other epithelioid PDX model, ABBV-321 also resulted in significant responses (median 428mm3 (ADC control) vs 167mm3 (ABBV-321, p = 0.0201). In the 806 IHC negative PDX model, the differences in tumor volumes between all groups were found to be non-statistically significant (ADC control vs ABT-414, ADC control vs ABBV-221, ADC-control vs ABBV-321 groups) with p = 0.0597 for one-way ANOVA. MSTO211H cell line xenograft model also demonstrated significant anti-tumor response to both ABT-414 and ABBV-221 (p < 0.01). Conclusions: In a disease with limited therapies, ABT-806 targeting ADCs in MM demonstrated significant responses in 806+ PDX and cell lines. These data support clinical expansion of these compounds in 806+ MM patients.

Abstract 1145: Humanized immune-PDX mouse models for 10 different tumor entities in translational immuno-oncology research

Abstract We established humanized mouse models by transplantation of human hematopoietic (stem) cells to immunodeficient mice. Engraftment results in the development of a functional human immune system. By co-transplantation of human patient-derived xenografts (PDX) we successfully generated a fully human tumor-immune-cell (TIC) model in mice. These humanized TIC-PDX models for melanoma and lung cancer were further characterized by treatment with immune therapy drugs like the CTLA4 inhibitor ipilimumab (Ipi) and the PD-1 inhibitor nivolumab (Nivo). In our current studies we monitored the effects of the human immune cells and evaluated concepts for combination therapies i.e. with chemotherapy or radiation. We further established new human TIC-PDX models from other tumor entities like lymphoma, pancreatic or breast cancer. Hematopoietic stem cell engraftment was monitored by regular FACS analysis for human immune cells in the blood. PD-L1 expression on tumors as a target for immunotherapy was determined by FACS and immunohistochemistry. PD-L1 positive and negative PDX from 10 different entities were transplanted on humanized mice and treated with Nivo or Ipi alone or in combination therapy with radiation. Blood and tumor samples were analysed by FACS and immunohistochemistry for immune cell infiltration and activation. The transplanted stem cells showed engraftment in immunodeficient mice with proliferation and differentiation and established a functional human immune system with T-cells, B-cells, NK-cells, monocytes, and dendritic cells. So far, we have transplanted more than 40 different PDX from 10 different tumor entities on humanized mice. Most of investigated PDX (>70%) successfully engrafted on humanized mice and showed no difference in tumor growth compared to growth on non-humanized mice. However, for a few PDX we observed a delayed tumor growth or a complete rejection. These results suggest an immune reaction of the engrafted human immune cells against the PDX. The tumor engraftment or rejection in the humanized mice seems to be independent from the tumor entity. To evaluate whether engraftment of the PDX in mice with a human immune system is in part enabled by checkpoint mediated immune-tolerance, we have treated over 30 PDX models with Ipi or Nivo alone or in combination. Significant tumor growth delay, observed in most models, accompanied by an increased number of T-cells in the blood and in the tumor, has functionally validated our immune-PDX model. Response to the checkpoint inhibitors seems to correlate with innate immune responsiveness and PD-L1 expression and can be further increased by combination with radiotherapy. Our humanized immune-PDX models enable appropriate preclinical translational research in tumor immune biology and the evaluation of new therapies and combinations, as well as the identification and validation of biomarkers for immune therapy. Citation Format: Maria Stecklum, Annika Wulf-Goldenberg, Magdalena Paterka, Bernadette Brzezicha, Iduna Fichtner, Jens Hoffmann. Humanized immune-PDX mouse models for 10 different tumor entities in translational immuno-oncology research [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1145.

Abstract A39: Patient-derived xenografts to test emerging therapies for triple negative breast cancer

Abstract Introduction: Patients with triple negative breast cancer (TNBC) that do not respond to cytotoxic neoadjuvant therapy have a poor prognosis, thus there is a pressing need to develop pre-clinical models of chemoresistant TNBC and identify optimal therapeutic targets. Patient-derived xenografts (PDX) are a simple, expandable approach to model TNBC in vivo. We have generated a collection of triple negative PDXs that have undergone molecular characterization at the DNA, RNA and protein levels and have initiated characterization of their therapeutic sensitivity to standard chemotherapeutics regimens as well as targeted therapies. Methods: Tumors from patients and matching PDXs have been characterized by cancer-specific targeted exome sequencing, RNA sequencing, and Reverse Phase Protein Arrays. We have established single agent sensitivities for a set of PDXs to standard TNBC therapies (paclitaxel, carboplatin, doxorubicin, eribulin, gemcitabine) and the following targeted therapies: talazoparib (PARP), MLN0128 (mTOR), buparlisib (PI3K), and trametinib (MEK1/2). Results: We have generated 25 hormone receptor-low/HER2- PDXs from 24 patients (1 primary-local recurrence pair) with an overall engraftment rate of 49% for this patient population. Exome sequencing found that the PDXs mostly maintain the somatic mutation profile of the originating tumor and exhibit alterations common to TNBC: 16 (73%) with TP53 mutations, 2 (9%) with PI3KCA mutations and 4 (18%) with PTEN deletions. RNA sequencing demonstrated that the PDXs maintain gene expression profiles similar to the originating tumor and that our panel is comprised of PDXs representative of five TNBC molecular subtypes. Treatment with standard therapies established differential sensitivity to paclitaxel and carboplatin between PDXs. The two models with PI3KCA alterations were responsive to mTOR/PI3K inhibition and unresponsive to trametinib and talazoparib, supporting heightened reliance on mTOR/PI3K signaling in PI3KCA mutant TNBC. Talazoparib was the only targeted agent tested that caused regression as a single agent in any model. All three models that regressed with talazoparib treatment had genetic alterations linked to DNA damage pathways (BRCA1 germline alteration, ATM deletion; PTEN deletion); these models also had low BRCA1 mRNA expression and were the only PDXs to regress when treated with carboplatin. Conclusions: PDXs of all TNBC subtypes can be generated from TNBC patients that are resistant to neoadjuvant chemotherapy. These PDXs maintain molecular alterations of TNBC, retain patient-specific gene expression, and display differential response to therapies enabling identification of associations between responses and molecular traits. Citation Format: Kurt W. Evans, Erkan Yuca, Stephen M. Scott, Natalia Arango Paez, Xiaofeng Zheng, Ken Chen, Laura Gonzales, Coya Tapia, Emily Tarco, Dalliah M. Black, Gordon B. Mills, Funda Meric-Bernstam. Patient-derived xenografts to test emerging therapies for triple negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr A39.

Abstract 4105: Dissecting the mechanisms of hepatocyte replacement in breast cancer liver metastases

Abstract The liver is a common site of metastasis in metastatic breast cancer and is associated with significant mortality. Histopathological examination of human breast cancer liver metastases (BCLMs) reveals that the majority of these tumours present with a ‘replacement growth pattern.’ In this growth pattern, the breast cancer cells freely invade the liver parenchyma and replace the resident hepatocytes. In advanced BCLMs, breast cancer cells can eventually replace a significant volume of the liver parenchyma which, ultimately, leads to organ failure and death. However, the mechanism through which breast cancer cells replace the resident hepatocytes is unknown. Here we set out to establish how this replacement of hepatocytes by breast cancer cells occurs in BCLMs. To do so, we established two in vivo models of advanced BCLM: (a) an ER+PR+HER2- model using the MCF7 cell line, and (b) a triple negative patient-derived xenograft model using breast cancer cells isolated from a pleural effusion. We have also established an in vitro co-culture system, where MCF7 cells are co-cultured with HepG2 cells, which is designed to mimic the breast cancer cell-hepatocyte interaction observed in vivo. Both in vivo models exhibit a histology that closely mimics the replacement growth pattern of human BCLMs, where breast cancer cells replace hepatocytes at the tumour-liver interface. To address whether hepatocytes are killed by adjacent breast cancer cells in vivo, we evaluated hepatocyte death by apoptosis using appropriate markers (cleaved-PARP and cleaved-caspase-3). Surprisingly, although extensive apoptotic death of breast cancer cells in the tumour mass could be observed, no evidence for apoptotic death of hepatocytes could be found. However, we observed extensive cell-in-cell invasion at the tumour-liver interface, where live breast cancer cells enter the cytoplasm of adjacent hepatocytes. We also observe a similar process of cell-in-cell invasion within in vitro cultures of MCF-7 cells with HepG2 cells. Although cell-in-cell invasion has been described as a mechanism of non-apoptotic cell death in breast cancer cells, the role of cell-in-cell invasion between breast cancer cells and hepatocytes in BCLMs has not been investigated. Our current studies are focused in two areas: (a) we are using intra-vital microscopy and time-lapse microscopy to investigate whether cell-in-cell invasion between breast cancer cells and hepatocytes mediates non-apoptotic death of hepatocytes both in vivo and in vitro, and (b) we are investigating the molecular mechanisms that mediate cell-in-cell invasion between breast cancer cells and hepatocytes. In conclusion, we present preliminary evidence for a novel mechanism via which breast cancer cells could replace hepatocytes in BCLMs. Further studies aimed at elucidating the molecular basis of this mechanism may reveal novel targets for preventing the replacement of the liver parenchyma by metastatic breast cancer cells. Citation Format: Mark R. Nathan, Lefteris Kostaras, Victoria Bridgeman, Shane Foo, Peter Vermeulen, Andrew Reynolds. Dissecting the mechanisms of hepatocyte replacement in breast cancer liver metastases. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4105.

Abstract 924: Predictive biomarker identification for combined anti-mTOR and anti-IGF-1R treatment in luminal B breast cancer

Abstract Luminal B breast cancer is one of the most aggressive subtypes of breast cancer for which effective treatments are needed. Recently, a phase I clinical study revealed that blockade of mTOR and IGF-1R has potential clinical activity in this cancer subtype. However, biomarkers to predict patient's response to the combination are still needed. Previous exploratory studies in ovarian cancer have associated low RAS-pathway activity, as determined by a RAS gene expression signature score, and high levels of IGF-1R axis genes with response to this combination therapy. In the present study we evaluated low RAS signature/high IGF-1/high IGF-1R as potential predictive biomarkers for anti-mTOR and anti-IGF-1R combination therapy in luminal B breast cancer patient-derived xenografts (PDX) treated with the allosteric mTOR inhibitor ridaforolimus and the monoclonal antibody against IGF-1R, dalotuzumab. Expression array analysis revealed that our 6 luminal B PDXs exhibited a low RAS signature score, compared to 6 HER2 and triple negative PDXs. Overall, luminal B PDXs expressed higher IGF-1R as compared to the other breast cancer subtypes with some variability among the different luminal models. Low expression of human IGF-pathway ligands IGF-1 and IGF-2 among the luminal PDXs, compared to luminal B breast cancers, suggested to us the need of exogenous IGF-1 ligand supplementation to derive IGF-1R feedback activation and combinatorial antitumor response. Accordingly, three high IGF-1R-PDXs treated with the anti-mTOR and anti-IGF-1R combination therapy supplemented with recombinant human IGF-1 exhibited statistically significant anti-tumor response as compared to single agents, whereas two low IGF-1R-expressing PDXs did not. As anticipated, ridaforolimus induced the IGF-1R-axis by increasing the levels of the adapter protein IRS-1, which potentiated Akt signaling. Hence, in vitro knockdown of IRS-1 promoted the antiproliferative activity of ridaforolimus in patient-derived tumor cells. In conclusion, our results demonstrate that baseline IGF-pathway expression, namely IGF-1, IGF-1R and IRS-1, predict benefit to combined anti-mTOR and anti-IGF-1R treatment in breast cancer and supports further exploration in luminal B breast cancers that derived benefit from this combination. Citation Format: Martin A. Rivas, Yasir H. Ibrahim, Olga Rodríguez, Pilar Antón, Patricia Cozar, Patricia Gómez-Pardo, Claudia Aura, Brian B. Haines, Sriram Sathyanarayanan, Theresa Zhang, Violeta Serra, José Baselga. Predictive biomarker identification for combined anti-mTOR and anti-IGF-1R treatment in luminal B breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 924. doi:10.1158/1538-7445.AM2014-924