Patient-derived Xenograft Cancer Models Research Articles

107 (PB097) - Preclinical characterization of TOS-358, a potent and selective covalent inhibitor of wild-type and mutant PI3Kα with superior anticancer activity

Phosphoinositide 3-kinase alpha (PI3Kα) is the most frequently mutated oncogene in cancer, inferring a critical role for this protein in neoplasia. The molecular biology of PI3Kα reveals it to be a protein that integrates a large and diverse set of cellular signals. In the development of small molecule inhibitors of this target protein it has been demonstrated that deep but also durable inhibition is critical to potent anti-cancer activity, an area traditionally challenging for reversible competitive and allosteric inhibitors. TOS-358 was developed to inhibit covalently both wild-type and mutant PI3Kα with observed IC50 s of 2.2 nM for WT PI3Kα and 4.1 nM for mutant PI3Ka (H1047R). TOS-358 is highly selective in a kinome-wide screen and selective for PI3Kα over other isoforms. We confirmed covalent binding to PI3Kα by NanoBRET in washout experiments, where it was observed that TOS-358 maintained 90% binding at 100 nM 6 hours after washout; in contrast, binding of Alpelisib at 100 nM was completely lost over the same time frame. Irreversible binding was further established using TR-FRET assay in which Kinact/KI was found to be 5.6 × 107 M−1s−1. Importantly, we also noted that TOS-358 produced sustained inhibition of phosphorylated AKT(S473) to 48 hours while allosteric inhibitors lose >60% inhibition. TOS-358 mediated cell growth inhibition has been evaluated in a panel of 120 cell lines and compared with Alpelisib in the same panel. This analysis revealed approximately 50% more cell lines to be responsive to TOS-358 compared with Alpelisib. There was no strong association of response and PI3Kα mutation status, and in fact for both TOS-358 and Alpelisib there was a higher frequency of WT PI3Kα cell lines responding to either treatment. TOS-358 activity has been tested in multiple different cell-derived and patient-derived xenograft cancer models and was found to produce reproducible and substantial tumor growth inhibition. Indeed, in several PDX models, TOS-358 induced tumor regressions while the clinical stage molecules Alpelisib and Inavolisib were unable to generate similar tumor regressions despite pharmacokinetic exposures comparable to, or in excess of, TOS-358. Finally, TOS-358 generated little or no glucose impact in mice and dogs at exposures that produced superior efficacy in these cancer models. Taken together, our in vitro and in vivo data reveal TOS-358 to be a potent, selective covalent inhibitor of PI3Kα with superior anticancer activity to comparator molecules. Conflict of interest: Ownership: The authors are employees of and may hold equity in Totus Medicines.

Feasibility and sensitivity study of radiomic features in photoacoustic imaging of patient-derived xenografts

Photoacoustic imaging is an increasingly popular method of exploring the tumour microenvironment, which can provide insight into tumour oxygenation status and potentially treatment response assessment. Currently, the measurements most commonly performed on such images are the mean and median of the pixel values of the tumour volumes of interest. We investigated expanding the set of measurements that can be extracted from these images by adding radiomic features. In particular, we found that Skewness was sensitive to differences between basal and luminal patient derived xenograft cancer models with an eta ^2 of 0.86, and that it was robust to variations in confounding factors such as reconstruction type and wavelength. We also built discriminant models with radiomic features that were correlated with the underlying tumour model and were independent from each other. We then ranked features by their importance in the model. Skewness was again found to be an important feature, as were 10th Percentile, Root Mean Squared, and several other texture-based features. In summary, this paper proposes a methodology to select radiomic features extracted from photoacoustic images that are robust to changes in acquisition and reconstruction parameters, and discusses features found to have discriminating power between the underlying tumour models in a pre-clinical dataset.

Abstract 327: Antitumor efficacy of trastuzumab deruxtecan in combination with adavosertib in HER2-expressing Cyclin E amplified gastroesophageal cancers

Abstract Purpose: Trastuzumab deruxtecan (T-DXd) is a HER2-directed antibody-drug conjugate approved for patients with HER2-positive gastric/gastroesophageal junction (GEJ) cancers. Amplification of CCNE1, which encodes cyclin E, has been proposed as a mechanism of resistance to HER2-targeted therapies. The Wee1 kinase inhibitor adavosertib (AZD1775) has demonstrated enhanced antitumor activity in the setting of cyclin E overexpression. We investigated the efficacy of T-DXd in combination with adavosertib in HER2-expressing cancers with and without co-amplification of CCNE1. Methods: Frequency of CCNE1 amplification was determined among patients with ERBB2 amplification in a clinical genomic database at the MD Anderson Cancer Center (MDACC) and within The Cancer Genome Atlas (TCGA). Sulforhodamine B assay, western blotting, and Annexin V staining were used to determine the effects of T-DXd and DXd in combination with adavosertib in vitro. Four HER2-expressing gastric/GEJ patient-derived xenograft (PDX) models with or without co-amplification of CCNE1 were tested with T-DXd in combination with adavosertib in vivo. Tumor volume and body weights were measured twice weekly and treatment responses were assessed by the relative treatment-to-control ratio, waterfall plots, and event-free survival (event defined as the day which tumors doubled in size from baseline). Results: Of 515 patients identified at MDACC with ERBB2 amplification, 60 (11.6%) had co-amplification of CCNE1. Of the 405 patients identified within the TCGA with ERBB2 amplification, 43 (10.6%) had co-amplification of CCNE1. Tumor types with the highest frequency of ERBB2/CCNE1 co-amplification were gastric/GEJ (38.1% MDACC, 31.0% TCGA), endometrial (25.0% MDACC, 29.6% TCGA), and ovarian (15.4% MDACC, 15.4% TCGA). Adavosertib was synergistic in combination with DXd in four cell lines with ERBB2 amplification, CCNE1 amplification, or ERBB2/CCNE1 co-amplification. Both DXd and T-DXd upregulated cyclin E and γH2AX protein expression at 24 and 96 hours, and the combination of DXd or T-DXd with adavosertib enhanced apoptosis. T-DXd induced durable tumor regression in two HER2 amplified and HER2 overexpressing gastroesophageal PDX cancer models with HER2 amplification/3+ overexpression and concomitant cyclin E amplification/expression. Adavosertib enhanced the antitumor activity of T-DXd in two HER2 low, cyclin E amplified gastroesophageal cancer PDX models (one with an ERBB2 G778A mutation). Conclusions: ERBB2 and CCNE1 are frequently co-amplified. Our findings provide supporting rationale for combining T-DXd with adavosertib in HER2-expressing cancers with CCNE1 co-amplification. Further study is needed to determine if therapeutic induction of cyclin E with DXd may sensitize to Wee1 kinase inhibition in patients without cyclin E amplification as well. Citation Format: Timothy P. DiPeri, Kurt W. Evans, Gabriela Raso, Yasmeen Q. Rizvi, Xiaofeng Zheng, Bryce Kirby, Kathleen Kong, Khandan Keyomarsi, Jaffer A. Ajani, Timothy A. Yap, Funda Meric-Bernstam. Antitumor efficacy of trastuzumab deruxtecan in combination with adavosertib in HER2-expressing Cyclin E amplified gastroesophageal cancers [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 327.

Abstract 3042: Anti-cancer efficacy of an anti-ErbB3 antibody, ISU104, against the cancers with NRG1-overexpression, NRG1-fusion, or oncogenic ErbB3 mutations

Abstract ErbB3, a heterodimeric partner of EGFR or ErbB2, plays important roles in the survival and growth of cancer cells through activation of PI3K/AKT pathway. ErbB3 can be activated by NRG1 expressed either by cancer cells or adjacent mesenchymal cells, or NRG1-fusion proteins produced by genetic alterations in cancer cells. Oncogenic driver mutations in ErbB3 also induce its activation. Previously, we have demonstrated preclinical anti-cancer efficacy of a monoclonal anti-ErbB3 antibody, ISU104 as a monotherapy or in combination with anti-EGFR antibody in various preclinical models. Biomarker analysis of the models demonstrated that there is a significant positive correlation between tumor growth inhibition by ISU104 and NRG1 mRNA/pERBB3 protein expression levels. Based on this analysis, anti-cancer efficacy of ISU104 was further explored in cancer cells and cell line- or patient-derived xenograft cancer models with high NRG1 expression, NRG1-fusion or oncogenic ErbB3 mutations. ISU104 potently inhibited phosphorylation of ERBB3 and AKT, cell proliferation and tumor growth of such models. Potential impacts of other genetic alterations on the anti-cancer efficacy of ISU104 were also investigated. Overall, the presented data suggest that ISU104, an anti-ErbB3 agent in the early stage of clinical development, can be applied for the treatment of the solid tumors expressing high level of NRG1 or harboring genetic alterations such as NRG1-fusion or oncogenic ErbB3 mutations. Citation Format: Seung-Beom Hong, Mirim Hong, Tae-Eun Kim, Ju Yeon Kim, Jung Won Kim, Jeongin Cho, Bongseok Shin, Donggoo Bae. Anti-cancer efficacy of an anti-ErbB3 antibody, ISU104, against the cancers with NRG1-overexpression, NRG1-fusion, or oncogenic ErbB3 mutations [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3042.

Abstract 1660: Humanization of patient derived xenograft (PDX) cancer model mice with peripheral blood mononuclear cells (PBMCs)

Abstract Immunocompetent transgenic mouse models have for decades served as valuable tools to address the effect of oncogenes and tumor suppressors. Immunodeficient mice have been used to establish patient derived xenograft (PDX) models harboring human tumors. These types of models have been used to study cancer initiation and progression as well as preclinical evaluation of anticancer drugs. One major limiting factor for both these model systems is the immune system; the PDX models lack an immune system and the immune system in immunocompetent mouse models display differences compared to the human immune system. Thus, in cancer research there is a need for preclinical models to study the influence of human immune cells on tumor progression and response to cancer therapies. We have established and optimized protocols for intravenous (IV) or intraperitoneal (IP) injections of isolated human PBMCs, to generate humanized mice harboring human immune cells. Our protocols do not require irradiation or busulfan pretreatment of the animals. Flow cytometry analyses showed that mainly T helper cells, CD4+, and cytotoxic T cells, CD8+, were present in the humanized mice. Immunohistochemistry (IHC) analyses of humanized PDX cancer model mice showed that human lymphocytes were present in the tumor periphery and some very few cells within the tumor, in addition to the human leukocytes in the liver and spleen. The growth rates of the PDX tumors were not affected by the humanization. Our protocols require minimal preparations of the animals and generate humanized PDX mice harboring human lymphocytes locating in close proximity of, as well as inside the PDX tumors. The model systems are suitable for preclinical studies of human, adaptive immune responses in tumor progression and cancer therapies. Citation Format: Jens Henrik Norum, Dag Josefsen, Gunnar Kvalheim, Olav Engebråten, Therese Sørlie, Gunhild M. Mælandsmo. Humanization of patient derived xenograft (PDX) cancer model mice with peripheral blood mononuclear cells (PBMCs) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1660. doi:10.1158/1538-7445.AM2017-1660