Microenvironment drives cell state, plasticity, and drug response in pancreatic cancer

Prognostically relevant RNA expression states exist in pancreatic ductal adenocarcinoma (PDAC), but our understanding of their drivers, stability, and relationship to therapeutic response is limited. To examine these attributes systematically, we profiled metastatic biopsies and matched organoid models at single-cell resolution. In vivo, we identify a new intermediate PDAC transcriptional cell state and uncover distinct site- and state-specific tumor microenvironments (TMEs). Benchmarking models against this reference map, we reveal strong culture-specific biases in cancer cell transcriptional state representation driven by altered TME signals. We restore expression state heterogeneity by adding back in vivo-relevant factors and show plasticity in culture models. Further, we prove that non-genetic modulation of cell state can strongly influence drug responses, uncovering state-specific vulnerabilities. This work provides a broadly applicable framework for aligning cell states across in vivo and ex vivo settings, identifying drivers of transcriptional plasticity and manipulating cell state to target associated vulnerabilities.

Abstract PO-058: Transcriptional subtype-specific microenvironmental crosstalk and tumor cell plasticity in metastatic pancreatic cancer

Metastatic pancreatic ductal adenocarcinoma (PDAC) is an aggressive and lethal malignancy with few therapeutic options. Tumor transcriptional state is a strong predictor of clinical outcome in PDAC, with two primary cell states, basal-like and classical, identified by bulk transcriptional profiling. Basal-like tumors carry a worse prognosis, but the mechanisms underlying this survival difference, the degree of cellular heterogeneity within a given tumor, and the subtype-specific contributions from the local immune microenvironment are not well understood. In addition, there are ongoing efforts to use patient-derived organoid models as functional surrogates for an individual patient’s disease, but the degree to which patient transcriptional phenotypes are preserved in their matched organoid models remains unclear. Here, we describe a pipeline that enables both direct characterization of the liver metastatic niche via single-cell RNA-sequencing and functional assessment of PDAC tumor biology in patient-matched organoid models. Starting from core needle biopsies of metastatic PDAC lesions, we applied this approach to profile 22 patient samples and their matched organoid models using single-cell RNA-sequencing with Seq-Well. We demonstrate significant heterogeneity at the single-cell level across the basal-like to classical transcriptional spectrum. Basal-like cells expressed more mesenchymal and stem-like features, while classical cells expressed features of epithelial and pancreatic progenitor transcriptional programs. A population of “hybrid” malignant cells co-expressed markers of both basal-like and classical states, suggesting that these phenotypes lie on a continuum rather than as discrete entities. Microenvironmental composition also differed by subtype across T/NK and macrophage populations. Specifically, basal-like tumors exhibited tumor cell crosstalk with specific macrophage subsets, while classical tumors harbored greater immune infiltration and a relatively pro-angiogenic microenvironment, raising important considerations for subtype-specific microenvironmental directed therapy. Finally, we found that matched organoids exhibited transcriptional drift along the basal-like to classical axis relative to their parent tumors, with evidence for selection against basal-like phenotypes in vitro. However, tumor cells in organoid culture exhibited remarkable plasticity and could recover in vivo basal-like phenotypes in response to changes in their growth conditions. Taken together, our work provides a framework for the analysis of human cancers and their matched models using single-cell methods to dissect tumor-intrinsic and extrinsic contributions, and reveals novel insights into the transcriptional heterogeneity and plasticity of PDAC.

Citation Format: Srivatsan Raghavan, Peter S. Winter, Andrew W. Navia, Hannah L. Williams, Alan DenAdel, Radha L. Kalekar, Jennyfer Galvez-Reyes, Kristen E. Lowder, Nolawit Mulugeta, Manisha S. Raghavan, Ashir A. Borah, Sara A. Vayrynen, Andressa Dias Costa, Junning Wang, Emma Reilly, Dorisanne Y. Ragon, Lauren K. Brais, Alex M. Jaeger, James M. Cleary, Lorin Crawford, Jonathan A. Nowak, Brian M. Wolpin, William C. Hahn, Andrew J. Aguirre, Alex K. Shalek. Transcriptional subtype-specific microenvironmental crosstalk and tumor cell plasticity in metastatic pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-058.

Oxidative stress in haemodialysis--intradialytic changes

Oxidative stress is likely to be involved in the development of complications due to haemodialysis. Though there is evidence for production of oxygen free radicals during haemodialysis, reports on net oxidative imbalance due to a single dialysis session are conflicting. Hence, a time-course analysis of changes in lipid peroxides (LPO) along with antioxidant enzymes and vitamins was carried out. Hourly changes in LPO and antioxidants were studied during a first-use cuprophan membrane and acetate dialysis in 20 patients on regular haemodialysis treatment. Data were corrected for haemoconcentration and standardised to measure the rate of change before statistical evaluation using analysis of variance for repeated measures. The results of the study showed a net oxidative stress due to a single dialysis session in the form of increased plasma and erythrocyte lipid peroxidation, decrease in plasma vitamin E, slight increase in plasma superoxide dismutase and erythrocyte glutathione peroxidase and no change in plasma glutathione peroxidase. erythrocyte superoxide dismutase and plasma vitamin A levels. The oxygen radical production was found to be maximum in the first hour of dialysis.

In vitro reducing abilities towards chromate of various hydroxy-containing compounds, including saccharides and their derivatives

The reduction of potassium chromate has been carried out with a variety of OH-containing compounds as reductants, which include pentoses, polyols, glycols, and sugar derivatives. The corresponding reactions were followed using UV-vis and EPR spectroscopies and electrochemistry. The progress of the chromate reduction reactions has been monitored by measuring UV-vis and EPR spectra as a function of time. The observed pseudo first-order reaction rate constants are derived based on the changes in the intensities of the Cr(VI), Cr(V), and Cr(III) signals. Cyclic voltammograms of the simple reductants and their final Cr(III) products formed from the reactions of chromate have also been measured. The reductive abilities of all these reductants have been derived from the spectral data and are discussed on a comparative basis. Based on the results, the aspects that makes a particular reductant more efficient has been addressed. The results obtained from UV-vis, EPR, and cyclic voltammetry are found to be mutually dependent and exhibit among themselves a linear correlation, suggesting that both the reducing and complexing nature of these molecules play important roles in the chromate reduction.