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Introduction: 3D cellular models have become of increasing interest in anti-cancer drug discovery as a bridge between clinical models and traditional in vitro methods. An important component of this research is the comparison of drug-to-cell interactions and morphological characteristics between cells in mono-layer culture and the cells in 3D spheroids. Materials and Methods:The ResCu system is a novel long term, physiologically relevant culture system that avoids the need for passaging. It propagates tumoroids in a microenvironment that resembleshuman tissue. Cells with KRAS G12C mutation were cultured in the ResCu system for three months, during which they were constantly exposed to G12C inhibitors (G12Ci) for the evolution of resistant cell populations. Cells were also cultured in traditional 2D cultures and exposed to G12Ci. Transcriptomics was performed to determine resistant networks and identify different resistant subclones in each group. Results: We applied the ResCu system to model clinical resistance. We captured 95% of clinically identified on-target and pathway bypass resistance changes, and in the 2D system, only a fraction of mechanisms were discovered. Additionally, we noticed certain cell populations could tolerate higher doses of the G12Ci after resistance evolution in ResCu compared to 2D. A few had similar responses suggesting that the origin of the cell line plays a role in the microenvironment's impact on cellular response. Conclusion: By comparatively analyzing resistance evolution data for KRAS G12Ci in traditional 2D and ResCu, we were able to collect physiologically relevant data that can more confidently be applied to clinical studies than mono-layer cell culture data alone. Citation Format: Manasa Gadde, Elizabeth Schwabe, Kshithija Mulam, Lindsay Hill, Christopher Bulow. Bridging gaps in treatment resistance 2D models with the incorporation of 3D models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1682.

Introduction: Inflammatory breast cancer (IBC) is an aggressive and rare disease with poor prognosis, accounting for 10% of breast cancer mortality [1]. A primary factor contributing to the bleak prognosis is the lack of IBC specific treatments. There are currently no IBC specific therapies due to a lack of IBC specific diagnostic and targeting markers. Efforts focused on identifying driver mutations and tumor targets have implicated tumor stroma including stromal cells such as macrophages in mediating IBC-like symptoms. This highlights the significance of understanding the interactions of tumor cells with the tumor stroma in greater detail and the knowledge would enable determination of targetable biology from these interactions which would facilitate development of IBC specific treatments and therapeutics. What is needed is a model to capture the complexity of IBC, identify critical spatial hetero-cellular interactions and target them successfully in a physiologically relevant and high-throughput manner. Approach: To address this need, we developed a 3D IBC microfluidic platform, unique in its simultaneous integration of functional blood vessels, tumor cells, macrophages, and type I collagen whose density, stiffness, and porosity mimics cancerous breast stroma. The platform will be used to study the influence of macrophage-tumor-endothelial interactions on 2 key critical features of IBC: vascular sprouting and formation of IBC emboli surrounded by vascular sprouts. Results: The 3D IBC microfluidic platform composed of MDA-IBC3 cells and a functional endothelial blood vessel demonstrated both vascular sprouting and emboli formation, key features of IBC tumors seen in IBC patient derived xenograft (PDX) models. Additionally, we observed vascular nesting of MDA-IBC3 emboli, recreating a characteristic IBC phenomenon observed in Mary-X PDX models. Incorporation of macrophages significantly increased the number of new vascular sprouts, sprouting rate and resulted in sprouts forming at earlier time points. Additionally, the presence of macrophages resulted in the formation of a significantly more porous collagen matrix (p Conclusion: IBC is an aggressive and invasive breast cancer with a poor prognosis linked to tumor-stroma interactions. Current preclinical to study IBC consist primarily of PDX models where determining the influence of specific signaling pathways and microenvironmental stimuli on tumor progression is challenging. Here we present a novel 3D microfluidic IBC platform to study tumor stromal interactions in a controlled manner. The MDA-IBC3 breast tumor platform demonstrated both vascular sprouting and emboli formation, key features of IBC seen in PDX models and the presence of macrophages increased both angiogenic sprouting and remodeling of the collagen matrix. The stark differences in the tumor platform response associated with macrophage presence strengthens the hypothesis of tumor stroma as a key player driving the aggressive nature of IBC and reveals a potential target for IBC therapeutics. [1] Fernandez, S.V., et al., Breast cancer research and treatment, 140(1): p. 23-33, 2013 Citation Format: Manasa Gadde, Caleb Phillips, Omar Rahal, Wendy Woodward, Marissa Rylander, Thomas Yankeelov. An in vitro microfluidic tumor platform for modeling and investigating tumor stromal interactions in inflammatory breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-06-02.