Respiratory complex I regulates dendritic cell maturation in explant model of human tumor immune microenvironment

BACKGROUND

Combining cytotoxic chemotherapy or novel anticancer drugs with T-cell modulators holds great promise in treating advanced cancers. However, the response varies depending on the tumor immune microenvironment (TIME). Therefore, there is a clear need for pharmacologically tractable models of the TIME to dissect its influence on mono- and combination treatment response at the individual level.

METHODS

Here we establish a patient-derived explant culture (PDEC) model of breast cancer, which retains the immune contexture of the primary tumor, recapitulating cytokine profiles and CD8+T cell cytotoxic activity.

RESULTS

We explored the immunomodulatory action of a synthetic lethal BCL2 inhibitor venetoclax+metformin drug combination ex vivo, discovering metformin cannot overcome the lymphocyte-depleting action of venetoclax. Instead, metformin promotes dendritic cell maturation through inhibition of mitochondrial complex I, increasing their capacity to co-stimulate CD4+T cells and thus facilitating antitumor immunity.

CONCLUSIONS

Our results establish PDECs as a feasible model to identify immunomodulatory functions of anticancer drugs in the context of patient-specific TIME.

Fibrin Stiffness Regulates Phenotypic Plasticity of Metastatic Breast Cancer Cells

The extracellular matrix (ECM)-regulated phenotypic plasticity is crucial for metastatic progression of triple negative breast cancer (TNBC). While ECM faithful cell-based models are available for in situ and invasive tumors, such as cell aggregate cultures in reconstituted basement membrane and in collagenous gels, there are no ECM faithful models for metastatic circulating tumor cells (CTCs). Such models are essential to represent the stage of metastasis where clinical relevance and therapeutic opportunities are significant. Here, CTC-like DU4475 TNBC cells are cultured in mechanically tunable 3D fibrin hydrogels. This is motivated, as in circulation fibrin aids CTC survival by forming a protective coating reducing shear stress and immune cell-mediated cytotoxicity and promotes several stages of late metastatic processes at the interface between circulation and tissue. This work shows that fibrin hydrogels support DU4475 cell growth, resulting in spheroid formation. Furthermore, increasing fibrin stiffness from 57 to 175 Pa leads to highly motile, actin and tubulin containing cellular protrusions, which are associated with specific cell morphology and gene expression patterns that markedly differ from basement membrane or suspension cultures. Thus, mechanically tunable fibrin gels reveal specific matrix-based regulation of TNBC cell phenotype and offer scaffolds for CTC-like cells with better mechano-biological properties than liquid.

Compressive stress-mediated p38 activation required for ERα + phenotype in breast cancer

Breast cancer is now globally the most frequent cancer and leading cause of women's death. Two thirds of breast cancers express the luminal estrogen receptor-positive (ERα + ) phenotype that is initially responsive to antihormonal therapies, but drug resistance emerges. A major barrier to the understanding of the ERα-pathway biology and therapeutic discoveries is the restricted repertoire of luminal ERα + breast cancer models. The ERα + phenotype is not stable in cultured cells for reasons not fully understood. We examine 400 patient-derived breast epithelial and breast cancer explant cultures (PDECs) grown in various three-dimensional matrix scaffolds, finding that ERα is primarily regulated by the matrix stiffness. Matrix stiffness upregulates the ERα signaling via stress-mediated p38 activation and H3K27me3-mediated epigenetic regulation. The finding that the matrix stiffness is a central cue to the ERα phenotype reveals a mechanobiological component in breast tissue hormonal signaling and enables the development of novel therapeutic interventions. Subject terms: ER-positive (ER + ), breast cancer, ex vivo model, preclinical model, PDEC, stiffness, p38 SAPK.

Sortilin-related receptor is a druggable therapeutic target in breast cancer

In breast cancer, the currently approved anti‐receptor tyrosine‐protein kinase erbB‐2 (HER2) therapies do not fully meet the expected clinical goals due to therapy resistance. Identifying alternative HER2‐related therapeutic targets could offer a means to overcome these resistance mechanisms. We have previously demonstrated that an endosomal sorting protein, sortilin‐related receptor (SorLA), regulates the traffic and signaling of HER2 and HER3, thus promoting resistance to HER2‐targeted therapy in breast cancer. This study aims to assess the feasibility of targeting SorLA using a monoclonal antibody. Our results demonstrate that anti‐SorLA antibody (SorLA ab) alters the resistance of breast cancer cells to HER2 monoclonal antibody trastuzumab in vitro and in ovo. We found that SorLA ab and trastuzumab combination therapy also inhibits tumor cell proliferation and tumor cell density in a mouse xenograft model of HER2‐positive breast cancer. In addition, SorLA ab inhibits the proliferation of breast cancer patient‐derived explant three‐dimensional cultures. These results provide, for the first time, proof of principle that SorLA is a druggable target in breast cancer.

Abstract 2966: Novel ex vivo model for ERα positive breast cancer

Three-dimensional ex vivo cultures from patient-derived tumor tissue offer new opportunities for drug development and personalized treatment of cancer. However, one of the main challenges in establishing a tumor type faithful ex vivo tissue culture system is in optimization of biochemical and physical microenvironment to preserve desired phenotypic features. A collaboration with the Helsinki University Hospital enables us to receive live patient-derived breast cancer tissue samples from most breast cancer surgeries performed in the Southern Finland, typically samples arriving twice a week. Together with a group of materials scientists from Aalto Technical University we have explored seven different 3D culture matrices and defined their biomechanical properties and stiffness values with rheological measurements. Four investigated matrices preserved the luminal CK8+ cell phenotype of the luminal cancers they derived from, whereas rest of the matrices that included commonly used Matrigel and collagen scaffolds promoted a switch in the cell identity from luminal CK8+ to basal CK14+ phenotype. Furthermore, the genetic expression profiles examined with NGS corresponded to observed phenotypic switch. We noticed significant species-specific differences between mouse mammary and human breast samples in their morphology, phenotypic responses and ERα+ preservation to microenvironmental matrix stiffness. Furthermore, a combination of scaffold stiffness and composition of biochemical matrix constituency is required for long-term maintenance of ERα+ luminal tumour phenotype. Therefore, both physical properties and composition of the microenvironment need to be optimized for maintenance of breast tumor type specific phenotype and genetic profiles of ex vivo tumor explant cultures.

Citation Format: Pauliina M. Munne, Lahja Martikainen, Iiris Räty, Kia Bertula, Nonappa Nonappa, Aino Peura, Minna Mutka, Marjut Leidenius, Tuomo Meretoja, Panu Kovanen, Johanna Mattson, Paivi Heikkila, Heikki Joensuu, Olli Ikkala, Juha T. Klefstrom. Novel ex vivo model for ERα positive breast cancer [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 2966.

Analysis of tissue interactions in ectodermal organ culture

The morphogenesis of ectodermal organs is regulated by epithelial mesenchymal interactions mediated by conserved signaling molecules. Analyzing the roles of these molecules will increase our understanding of mechanisms regulating organogenesis, and organ culture methods provide powerful tools in this context. Here we present two organ culture methods for skin and tooth development: the hanging drop method for the short-term culture of small explants and the Trowell-type method for the long-term cultures of variable size explants. The latter allows manipulations such as combining separated epithelial and mesenchymal tissues and the use of signal-releasing beads. The effects of signaling molecules on morphogenesis can be observed during culture by using tissues from GFP-reporter mice. After culture, the effects of signals on gene expression can be analyzed by in situ hybridization or quantitative RT-PCR.

Splitting placodes: effects of bone morphogenetic protein and Activin on the patterning and identity of mouse incisors

The single large rodent incisor in each jaw quadrant is evolutionarily derived from a mammalian ancestor with many small incisors. The embryonic placode giving rise to the mouse incisor is considerably larger than the molar placode, and the question remains whether this large incisor placode is a developmental requisite to make a thick incisor. Here we used in vitro culture system to experiment with the molecular mechanism regulating tooth placode development and how mice have thick incisors. We found that large placodes are prone to disintegration and formation of two to three small incisor placodes. The balance between one large or multiple small placodes was altered through the regulation of bone morphogenetic protein (BMP) and Activin signaling. Exogenous Noggin, which inhibits BMP signaling, or exogenous Activin cause the development of two to three incisors. These incisors were more slender than normal incisors. Additionally, two inhibitor molecules, Sostdc1 and Follistatin, which regulate the effects of BMPs and Activin and have opposite expression patterns, are likely to be involved in the incisor placode regulation in vivo. Furthermore, inhibition of BMPs by recombinant Noggin has been previously suggested to cause a change in the tooth identity from the incisor to the molar. This evidence has been used to support a homeobox code in determining tooth identity. Our work provides an alternative interpretation, where the inhibition of BMP signaling can lead to splitting of the large incisor placode and the formation of partly separate incisors, thereby acquiring molar-like morphology without a change in tooth identity.

Tinkering with the inductive mesenchyme: Sostdc1 uncovers the role of dental mesenchyme in limiting tooth induction

Like epithelial organs in general, tooth development involves inductive crosstalk between the epithelium and the mesenchyme. Classically, the inductive potential for tooth formation is considered to reside in the mesenchyme during the visible morphogenesis of teeth, and dental mesenchyme can induce tooth formation even when combined with non-dental epithelium. Here, we have investigated induction of mouse incisors using Sostdc1 (ectodin), a putative antagonist of BMP signaling in the mesenchymal induction of teeth. Deletion of Sostdc1 leads to the full development of single extra incisors adjacent to the main incisors. We show that initially, Sostdc1 expression is limited to the mesenchyme, suggesting that dental mesenchyme may limit supernumerary tooth induction. We test this in wild-type incisors by minimizing the amount of mesenchymal tissue surrounding the incisor tooth germs prior to culture in vitro. The cultured teeth phenocopy the extra incisors phenotype of the Sostdc1-deficient mice. Furthermore, we show that minimizing the amount of dental mesenchyme in cultured Sostdc1-deficient incisors causes the formation of additional de novo incisors that resemble the successional incisor development that results from activated Wnt signaling. Finally, Noggin and Dkk1 prevent individually the formation of extra incisors, and we therefore suggest that inhibition of both BMP and Wnt signaling contributes to the inhibitory role of the dental mesenchyme. Considering the role of mesenchyme in tooth induction and the design of tissue engineering protocols, our work may have uncovered how delicate control of tissue quantities alone influences the outcome between induction and inhibition.