High-Content Screening Comparison of Cancer Drug Accumulation and Distribution in Two-Dimensional and Three-Dimensional Culture Models of Head and Neck Cancer

Spatiotemporal analysis of ratiometric biosensors in live multicellular spheroids using SPoRTS

Here, we describe SPoRTS, an open-source workflow for high-throughput spatiotemporal image analysis of fluorescence-based ratiometric biosensors in living spheroids. To achieve this, we have implemented a fully automated algorithm for the acquisition of line intensity profile data, ultimately enabling semi-quantitative measurement of biosensor activity as a function of distance from the center of the spheroid. We demonstrate the functionality of SPoRTS via spatial analysis of live spheroids expressing a ratiometric biosensor based on the fluorescent, ubiquitin-based cell-cycle indicator (FUCCI) system, which identifies mitotic cells. We compare this FUCCI-based SPoRTS analysis with spatially quantified immunostaining for proliferation markers, finding that the results are strongly correlated.

Miniaturization and characterization of patient derived hepatocellular carcinoma tumor organoid cultures for cancer drug discovery applications

Patient derived tumor organoid (PDTO) models retain the structural, morphological, genetic, and clonal heterogeneity of the original tumors. The ability to efficiently generate, expand, and biobank PDTOs has the potential to make the clinical diversity of cancer accessible for personalized medicine assay guided therapeutic drug selection and drug discovery. We describe the miniaturization and growth in 96- and 384-well formats of a single non-tumor liver and two Hepatocellular carcinoma (HCC) organoids derived from cryopreserved PDTO cells and the application of high content imaging (HCI) to characterize the models and enhance drug sensitivity testing. Non-invasive sequentially acquired transmitted light images showed that seeding cryopreserved cells from non-tumoral and HCC PDTOs into 96- or 384-well plates in reduced growth factor Matrigel (rgf-MG) that were fed with growth medium every 3 days supported organoid growth up to 15 days. The number and sizes of organoids increased with longer times in culture. HCC PDTO's had more heterogeneous morphologies than non-tumor organoids with respect to size, shape, and optical density. Organoids cultured in rgf-MG could be stained in situ with HCI reagents without mechanical, chemical or enzymatic disruption of the hydrogel matrices and quantitative data extracted by image analysis. Hoechst and live/dead reagents provided organoid numbers and viability comparisons. HCC PDTO's stained with phalloidin or immuno-stained with α-tubulin antibodies revealed F-actin and microtubule cytoskeleton organization. HCC PDTO's stained with antibodies to signaling pathway proteins and their phosphorylation status allowed comparisons of relative expression levels and inference of pathway activation. Images of HCC PDTO's exposed to ellipticine showed that drugs penetrate Matrigel hydrogels and accumulate in organoid cells. 9-day 384-well HCC organoid cultures exhibited robust and reproducible growth signals suitable for cancer drug testing. Complimenting cell viability readouts with multiple HCI parameters including morphological features and dead cell staining improved the analysis of drug impact and enhanced the value that could be extracted from these more physiologically relevant three-dimensional HCC organoid cultures.

Cancer Stem Cells in Oral Squamous Cell Carcinoma: A Narrative Review on Experimental Characteristics and Methodological Challenges

Cancer stem cells (CSCs) represent a subpopulation of cancer cells that are believed to initiate and drive cancer progression. In animal models, xenotransplanted CSCs have demonstrated the ability to produce tumors. Since their initial isolation in blood cancers, CSCs have been identified in various solid human cancers, including oral squamous cell carcinoma (OSCC). In addition to their tumorigenic properties, dysregulated stem-cell-related signaling pathways-Wnt family member (Wnt), neurogenic locus notch homolog protein (Notch), and hedgehog-have been shown to endow CSCs with characteristics like self-renewal, phenotypic plasticity, and chemoresistance, contributing to recurrence and treatment failure. Consequently, CSCs have become targets for new therapeutic agents, with some currently in different phases of clinical trials. Notably, small molecule inhibitors of the hedgehog signaling pathway, such as vismodegib and glasdegib, have been approved for the treatment of basal cell carcinoma and acute myeloid leukemia, respectively. Other strategies for eradicating CSCs include natural compounds, nano-drug delivery systems, targeting mitochondria and the CSC microenvironment, autophagy, hyperthermia, and immunotherapy. Despite the extensive documentation of CSCs in OSCC since its first demonstration in head and neck (HN) SCC in 2007, none of these novel pharmacological approaches have yet entered clinical trials for OSCC patients. This narrative review summarizes the in vivo and in vitro evidence of CSCs and CSC-related signaling pathways in OSCC, highlighting their role in promoting chemoresistance and immunotherapy resistance. Additionally, it addresses methodological challenges and discusses future research directions to improve experimental systems and advance CSC studies.

Oral squamous cell carcinoma cancer stem cells have different drug sensitive to pharmacological NFκB and histone deacetylation inhibition

Despite many progresses in the development of new systemic therapies for oral squamous cell carcinoma (OSCC), the five-year survival rate of OSCC is low. The traditional chemotherapies approach (cisplatin - CDDP) shows some limitations like drug toxicity, limited efficacy, and drug resistance. Promising studies suggested OSCC cancer stem cells (CSC) presented resistance to CDDP. We have previously studied many targets, and we extensively showed the efficacy of the NFκB signaling and the role of histones acetylation, on different malignant tumors, including adenoid cystic carcinoma and mucoepidermoid carcinoma, but until then the effects of the NFkB inhibitor and histone deacetylase (HDAC) inhibitor on the biology of OSCC were not evaluated. Here we assessed the pharmacological inhibitor of NFκB emetine and HDAC inhibitor SAHA on the behavior of CSC derived from OSCC. Our data suggested that CDDP administration resulted in reduced viability of bulk OSCC cells and increased CSC. A single and isolated shot of emetine and SAHA were able to disrupt CSC by inhibiting the NFκB pathway and increasing the histone acetylation levels, respectively. Further, the combined administration of emetine and SAHA presented the same CSC disruption as seen in emetine alone.

WITHDRAWN: Detection and impact of hypoxic regions in multicellular tumor spheroid cultures formed by head and neck squamous cell carcinoma cells lines

The Publisher regrets that this article is an accidental duplication of an article previously published at http://dx.doi.org/10.1016/j.slasd.2021.10.008. This duplication was due to an error in the publishing workflow and was not the responsibility of the authors or editors. As a result, the duplicate article has been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

In Vitro Models of Head and Neck Cancer: From Primitive to Most Advanced

For several decades now, researchers have been trying to answer the demand of clinical oncologists to create an ideal preclinical model of head and neck squamous cell carcinoma (HNSCC) that is accessible, reproducible, and relevant. Over the past years, the development of cellular technologies has naturally allowed us to move from primitive short-lived primary 2D cell cultures to complex patient-derived 3D models that reproduce the cellular composition, architecture, mutational, or viral load of native tumor tissue. Depending on the tasks and capabilities, a scientific laboratory can choose from several types of models: primary cell cultures, immortalized cell lines, spheroids or heterospheroids, tissue engineering models, bioprinted models, organoids, tumor explants, and histocultures. HNSCC in vitro models make it possible to screen agents with potential antitumor activity, study the contribution of the tumor microenvironment to its progression and metastasis, determine the prognostic significance of individual biomarkers (including using genetic engineering methods), study the effect of viral infection on the pathogenesis of the disease, and adjust treatment tactics for a specific patient or groups of patients. Promising experimental results have created a scientific basis for the registration of several clinical studies using HNSCC in vitro models.

Metal-Organic Framework Mediated Radio-Enhancement Assessed in High-Throughput-Compatible 3D Tumor Spheroid Co-Cultures

Inorganic nanomaterials have gained increasing attention in radiation oncology, owing to their radiation therapy enhancing properties. To accelerate candidate material selection and overcome the disconnect between conventional 2D cell culture and in vivo findings, screening platforms unifying high-throughput with physiologically relevant endpoint analysis based on 3D in vitro models are promising. Here, a 3D tumor spheroid co-culture model based on cancerous and healthy human cells is presented for the concurrent assessment of radio-enhancement efficacy, toxicity, and intratissural biodistribution with full ultrastructural context of radioenhancer candidate materials. Its potential for rapid candidate materials screening is showcased based on the example of nano-sized metal-organic frameworks (nMOFs) and direct benchmarking against gold nanoparticles (the current "gold standard"). Dose enhancement factors (DEFs) ranging between 1.4 and 1.8 are measured for Hf-, Ti-, TiZr-, and Au-based materials in 3D tissues and are overall lower than in 2D cell cultures, where DEF values exceeding 2 are found. In summary, the presented co-cultured tumor spheroid-healthy fibroblast model with tissue-like characteristics may serve as high-throughput platform enabling rapid, cell line-specific endpoint analysis for therapeutic efficacy and toxicity assessment, as well as accelerated radio-enhancer candidate screening.

A Method for the In Vitro Cytotoxicity Assessment of Anti-cancer Compounds and Materials Using High Content Screening Analysis

To date, there is a large bottleneck associated with cancer drug design and development: a lack of appropriate methodologies for screening their potential toxicity. This issue not only causes a high attrition rate for these compounds but also slows down the drug discovery process in general. To overcome this problem, robust, accurate, and reproducible methodologies for assessing anti-cancer compounds are essential. Multiparametric technique and high-throughput analysis, in particular, are favored due to the time- and cost-effective way in which they assess large panels of materials, and due to their large informational output. Following extensive work within our group, we have developed a protocol for assessing the toxicity of anti-cancer compounds using a high-content screening and analysis (HCSA) platform, which is both time-effective and reproducible.

Targeting Several Biologically Reported Targets of Glioblastoma Multiforme by Assaying 2D and 3D Cultured Cells

Glioblastoma multiforme (GBM) is account for 70% of all primary malignancies of the central nervous system. The median survival of human patients after treatment is around 15 months. There are several biological targets which have been reported that can be pursued using ligands with varied structures to treat this disease. In our group, we have developed several ligands that target a wide range of proteins involved in anticancer effects, such as histone deacetylase (HDACs), G protein-coupled estrogen receptor 1 (GPER), estrogen receptor-beta (ERβ) and NADPH oxidase (NOX), that were screened on bidimensional (2D) and tridimensional (3D) GBM stem cells like (GSC). Our results show that some HDAC inhibitors show antiproliferative properties at 21-32 µM. These results suggest that in this 3D culture, HDACs could be the most relevant targets that are modulated to induce the antiproliferative effects that require in the future further experimental studies.

Detection and impact of hypoxic regions in multicellular tumor spheroid cultures formed by head and neck squamous cell carcinoma cells lines

In solid tumors like head and neck cancer (HNC), chronic and acute hypoxia have serious adverse clinical consequences including poorer overall patient prognosis, enhanced metastasis, increased genomic instability, and resistance to radiation-, chemo-, or immuno-therapies. However, cells in the two-dimensional monolayer cultures typically used for cancer drug discovery experience 20%-21% O₂ levels (normoxic) which are 4-fold higher than O₂ levels in normal tissues and ≥10-fold higher than in the hypoxic regions of solid tumors. The oxygen electrodes, exogenous bio-reductive markers, and increased expression of endogenous hypoxia-regulated proteins like HIF-1α generally used to mark hypoxic regions in solid tumors are impractical in large sample numbers and longitudinal studies. We used a novel homogeneous live-cell permeant HypoxiTRAK™ (HPTK) molecular probe compatible with high content imaging detection, analysis, and throughput to identify and quantify hypoxia levels in live HNC multicellular tumor spheroid (MCTS) cultures over time. Accumulation of fluorescence HPTK metabolite in live normoxic HNC MCTS cultures correlated with hypoxia detection by both pimonidazole and HIF-1α staining. In HNC MCTSs, hypoxic cytotoxicity ratios for the hypoxia activated prodrugs (HAP) evofosfamide and tirapazamine were much smaller than have been reported for uniformly hypoxic 2D monolayers in gas chambers, and many viable cells remained after HAP exposure. Cells in solid tumors and MCTSs experience three distinct O₂ microenvironments dictated by their distances from blood vessels or MCTS surfaces, respectively; oxic, hypoxic, or intermediate levels of hypoxia. These studies support the application of more physiologically relevant in vitro 3D models that recapitulate the heterogeneous microenvironments of solid tumors for preclinical cancer drug discovery.

Modeling Prostate Cancer Treatment Responses in the Organoid Era: 3D Environment Impacts Drug Testing

Organoid-based studies have revolutionized in vitro preclinical research and hold great promise for the cancer research field, including prostate cancer (PCa). However, experimental variability in organoid drug testing complicates reproducibility. For example, we observed PCa organoids to be less affected by cabazitaxel, abiraterone and enzalutamide as compared to corresponding single cells prior to organoid assembly. We hypothesized that three-dimensional (3D) organoid organization and the use of various 3D scaffolds impact treatment efficacy. Live-cell imaging of androgen-induced androgen receptor (AR) nuclear translocation and taxane-induced tubulin stabilization was used to investigate the impact of 3D scaffolds, spatial organoid distribution and organoid size on treatment effect. Scaffolds delayed AR translocation and tubulin stabilization, with Matrigel causing a more pronounced delay than synthetic hydrogel as well as incomplete tubulin stabilization. Drug effect was further attenuated the more centrally organoids were located in the scaffold dome. Moreover, cells in the organoid core revealed a delayed treatment effect compared to cells in the organoid periphery, underscoring the impact of organoid size. These findings indicate that analysis of organoid drug responses needs careful interpretation and requires dedicated read-outs with consideration of underlying technical aspects.

Carboplatin response in preclinical models for ovarian cancer: comparison of 2D monolayers, spheroids, ex vivo tumors and in vivo models

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. Among the key challenges in developing effective therapeutics is the poor translation of preclinical models used in the drug discovery pipeline. This leaves drug attrition rates and costs at an unacceptably high level. Previous work has highlighted the discrepancies in therapeutic response between current in vitro and in vivo models. To address this, we conducted a comparison study to differentiate the carboplatin chemotherapy response across four different model systems including 2D monolayers, 3D spheroids, 3D ex vivo tumors and mouse xenograft models. We used six previously characterized EOC cell lines of varying chemosensitivity and performed viability assays for each model. In vivo results from the mouse model correlated with 2D response in 3/6 cell lines while they correlated with 3D spheroids and the ex vivo model in 4/6 and 5/5 cell lines, respectively. Our results emphasize the variability in therapeutic response across models and demonstrate that the carboplatin response in EOC cell lines cultured in a 3D ex vivo model correlates best with the in vivo response. These results highlight a more feasible, reliable, and cost-effective preclinical model with the highest translational potential for drug screening and prediction studies in EOC.

Isoginkgetin leads to decreased protein synthesis and activates an ATF4-dependent transcriptional response

Isoginkgetin (IGG) is a small molecule inhibitor of pre-mRNA splicing. Failure to accurately remove introns could lead to the production of aberrant mRNAs and proteins. The cellular responses to splicing stress are not well defined. Here, we used oligonucleotide microarrays to assess genome wide changes in gene expression associated with exposure to IGG. Two of the 3 enriched pathways identified using PANTHER analysis of differentially expressed transcripts are linked to the ATF4 transcription factor. We confirmed that ATF4 was selectively translated and upregulated in response IGG despite an almost complete block to total protein synthesis. Importantly, partial disruption of the ATF4 gene using CRISPR-mediated gene editing prevented IGG-induced changes in gene expression. Remarkably, another spliceosome inhibitor, pladienolide B, did not inhibit translation, activate ATF4 or increase ATF4-dependent gene expression. Taken together, IGG activates ATF4 and an ATF4-dependent transcriptional response but these effects are not common to all spliceosome inhibitors.

3D Bioprinting for In Vitro Models of Oral Cancer: Toward Development and Validation

The tumor microenvironment (TME) of oral carcinomas has highly complex contents and a dynamic nature which is difficult to study using oversimplified two-dimensional (2D) cell culture systems. By contrast, three dimensional (3D) in vitro models such as spheroids, organoids, and scaffold-based constructs have been able to replicate tumors three-dimensionality and have allowed a better understanding of the role of various microenvironmental cues in the initiation and progression of cancer. However, the heterogeneity of TME cannot be fully reproduced by these traditional tissue engineering strategies since they are unable to control the organization of multiple cell types in a complex architecture. 3D bioprinting is an emerging field that can be leveraged to produce biomimetic and complex tissue structures. Bioprinting allows for controllable and precise placement of multicomponent bioinks composed of multiple biomaterials, different types of cells, and soluble factors according to the natural compartments of the target tissue, aiming to reproduce the equivalent of the complex tissue. As such, 3D bioprinting provides a unique opportunity to fabricate in vitro tumor models with a complexity similar to that of the in vivo oral carcinoma. This will facilitate a thorough investigation of cellular physiology, cancer progression, and anti-cancer drug screening with unprecedented control and reproducibility. In this review, we discuss the role of 3D bioprinting in reconstituting oral cancer, the prospects of application to fill the literature gap, and the challenges that need to be addressed in order to exploit this emerging technology for future work in oral cancer research.

Academic collaborative models fostering the translation of physiological in vitro systems from basic research into drug discovery

The success of preclinical drug discovery strongly relies on the ability of experimental models to resemble human pathophysiology. The number of compounds receiving approval for clinical use is limited, and this has led to the development of more physiologically relevant cellular models aimed at making preclinical results more prone to be successfully translated into clinical use. In this review, we summarize the technologies available in the field of high-throughput screening (HTS) using complex cellular models, and describe collaborative initiatives, such as EU-OPENSCREEN, which can efficiently support researchers to easily access state-of-the-art chemical biology platforms for improving the drug discovery process.

Factors to consider when interrogating 3D culture models with plate readers or automated microscopes

Along with the increased use of more physiologically relevant three-dimensional cell culture models comes the responsibility of researchers to validate new assay methods that measure events in structures that are physically larger and more complex compared to monolayers of cells. It should not be assumed that assays designed using monolayers of cells will work for cells cultured as larger three-dimensional masses. The size and barriers for penetration of molecules through the layers of cells result in a different microenvironment for the cells in the outer layer compared to the center of three-dimensional structures. Diffusion rates for nutrients and oxygen may limit metabolic activity which is often measured as a marker for cell viability. For assays that lyse cells, the penetration of reagents to achieve uniform cell lysis must be considered. For live cell fluorescent imaging assays, the diffusion of fluorescent probes and penetration of photons of light for probe excitation and fluorescent emission must be considered. This review will provide an overview of factors to consider when implementing assays to interrogate three dimensional cell culture models.

Advanced Multi-Dimensional Cellular Models as Emerging Reality to Reproduce In Vitro the Human Body Complexity

A hot topic in biomedical science is the implementation of more predictive in vitro models of human tissues to significantly improve the knowledge of physiological or pathological process, drugs discovery and screening. Bidimensional (2D) culture systems still represent good high-throughput options for basic research. Unfortunately, these systems are not able to recapitulate the in vivo three-dimensional (3D) environment of native tissues, resulting in a poor in vitro–in vivo translation. In addition, intra-species differences limited the use of animal data for predicting human responses, increasing in vivo preclinical failures and ethical concerns. Dealing with these challenges, in vitro 3D technological approaches were recently bioengineered as promising platforms able to closely capture the complexity of in vivo normal/pathological tissues. Potentially, such systems could resemble tissue-specific extracellular matrix (ECM), cell–cell and cell–ECM interactions and specific cell biological responses to mechanical and physical/chemical properties of the matrix. In this context, this review presents the state of the art of the most advanced progresses of the last years. A special attention to the emerging technologies for the development of human 3D disease-relevant and physiological models, varying from cell self-assembly (i.e., multicellular spheroids and organoids) to the use of biomaterials and microfluidic devices has been given.

Head and Neck Cancer Stem Cell-Enriched Spheroid Model for Anticancer Compound Screening

Cancer stem cells (CSCs), a rare cell population in tumors, are resistant to conventional chemotherapy and thus responsible for tumor recurrence. To screen for active compounds targeting CSCs, a good CSC-enriched model compatible with high-throughput screening (HTS) is needed. Here, we describe a new head and neck cancer stem cell-enriched spheroid model (SCESM) suitable for HTS analyses of anti-CSC compounds. We used FaDu cells, round-bottom ultra-low adherent (ULA) microplates, and stem medium. The formed spheroids displayed increased expression of all stem markers tested (qRT-PCR and protein analysis) in comparison to the FaDu cells grown in a standard adherent culture or in a well-known HTS-compatible multi-cellular tumor spheroid model (MCTS). Consistent with increased stemness of the cells in the spheroid, confocal microscopy detected fast proliferating cells only at the outer rim of the SCESM spheroids, with poorly/non-proliferating cells deeper in. To confirm the sensitivity of our model, we used ATRA treatment, which strongly reduced the expression of selected stem markers. Altogether, we developed a CSC-enriched spheroid model with a simple protocol, a microplate format compatible with multimodal detection systems, and a high detection signal, making it suitable for anti-CSC compounds' HTS.

Uptake, distribution and radio-enhancement effects of gold nanoparticles in tumor microtissues

Radiotherapy is an integral and highly effective part of cancer therapy, applicable in over 50% of patients affected by cancer. Due to the low specificity of the X-ray irradiation, the maximal radiation dose is greatly limited in order to avoid damage to surrounding healthy tissue. The limitations in applicable dose oftentimes result in the survival of a subpopulation of radio-resistant cells that then cause cancer reoccurence. Approaches based on tumor-targeted high atomic number inorganic nanoparticles have been proposed to locally increase the photoelectric absorption cross-section of tumors relative to healthy tissue. However, the complex interplay between the nanoparticle radio-enhancers and the tumor tissue has led to poor translation of in vitro findings to (pre)clinics. Here, we report the development of a tumor microtissue model along with analytical imaging for the quantitative assessment of nanoparticle-based radio-enhancement as a function of nanoparticle size, uptake and intratissural distribution. The advanced in vitro model exhibits key features of cancerous tissues, including diminished susceptibility to drugs and attenuated response to nanoparticle treatment compared to corresponding conventional 2D cell cultures. Whereas radio-enhancement effects between 2D and 3D cell cultures were comparable for 5 nm gold particles, the limited penetration of 50 nm gold nanoparticles into 3D microtissues led to a significantly reduced radio-enhancement effect in 3D compared to 2D. Taken together, tumor microtissues, which in stark contrast to 2D cell culture exhibit tissue-like features, may provide a valuable high-throughput intermediate pre-selection step in the preclinical translation of nanoparticle-based radio-enhancement therapy designs.

Pyrazine ring-based Na+/H+ exchanger (NHE) inhibitors potently inhibit cancer cell growth in 3D culture, independent of NHE1

The Na+/H+ exchanger-1 (NHE1) supports tumour growth, making NHE1 inhibitors of interest in anticancer therapy, yet their molecular effects are incompletely characterized. Here, we demonstrate that widely used pyrazinoylguanidine-type NHE1 inhibitors potently inhibit growth and survival of cancer cell spheroids, in a manner unrelated to NHE1 inhibition. Cancer and non-cancer cells were grown as 3-dimensional (3D) spheroids and treated with pyrazinoylguanidine-type (amiloride, 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), 5-(N,N-dimethyl)-amiloride (DMA), and 5-(N,N-hexamethylene)-amiloride (HMA)) or benzoylguanidine-type (eniporide, cariporide) NHE1 inhibitors for 2-7 days, followed by analyses of viability, compound accumulation, and stress- and death-associated signalling. EIPA, DMA and HMA dose-dependently reduced breast cancer spheroid viability while cariporide and eniporide had no effect. Although both compound types inhibited NHE1, the toxic effects were NHE1-independent, as inhibitor-induced viability loss was unaffected by NHE1 CRISPR/Cas9 knockout. EIPA and HMA accumulated extensively in spheroids, and this was associated with marked vacuolization, apparent autophagic arrest, ER stress, mitochondrial- and DNA damage and poly-ADP-ribose-polymerase (PARP) cleavage, indicative of severe stress and paraptosis-like cell death. Pyrazinoylguanidine-induced cell death was partially additive to that induced by conventional anticancer therapies and strongly additive to extracellular-signal-regulated-kinase (ERK) pathway inhibition. Thus, in addition to inhibiting NHE1, pyrazinoylguanidines exert potent, NHE1-independent cancer cell death, pointing to a novel relevance for these compounds in anticancer therapy.

Maximizing the Value of Cancer Drug Screening in Multicellular Tumor Spheroid Cultures: A Case Study in Five Head and Neck Squamous Cell Carcinoma Cell Lines

With approval rates <5% and the probability of success in oncology clinical trials of 3.4%, more physiologically relevant in vitro three-dimensional models are being deployed during lead generation to select better drug candidates for solid tumors. Multicellular tumor spheroids (MCTSs) resemble avascular tumor nodules, micrometastases, or the intervascular regions of large solid tumors with respect to morphology, cell-cell and cell-extracellular matrix contacts, and volume growth kinetics. MCTSs develop gradients of nutrient and oxygen concentration resulting in diverse microenvironments with differential proliferation and drug distribution zones. We produced head and neck squamous cell carcinoma (HNSCC) MCTSs in 384-well U-bottom ultra-low-attachment microtiter plates and used metabolic viability and imaging methods to measure morphologies, growth phenotypes and the effects of 19 anticancer drugs. We showed that cell viability measurements underestimated the impact of drug exposure in HNSCC MCTS cultures, but that incorporating morphology and dead-cell staining analyses increased the number of drugs judged to have substantially impacted MCTS cultures. A cumulative multiparameter drug impact score enabled us to stratify MCTS drug responses into high-, intermediate-, and low-impact tiers, and maximized the value of these more physiologically relevant tumor cultures. It is conceivable that the viable cells present in MCTS cultures after drug exposure arise from drug-resistant populations that could represent a source of drug failure and recurrence. Long-term monitoring of treated MCTS cultures could provide a strategy to determine whether these drug-resistant populations represent circumstances where tumor growth is delayed and may ultimately give rise to regrowth.

Stroma-Rich Co-Culture Multicellular Tumor Spheroids as a Tool for Photoactive Drugs Screening

Conventional 3D multicellular tumor spheroids of head and neck squamous cell carcinoma (HNSCC) consisting exclusively of cancer cells have some limitations. They are compact cell aggregates that do not interact with their extracellular milieu, thus suffering from both insufficient extracellular matrix (ECM) deposition and absence of different types of stromal cells. In order to better mimic in vivo HNSCC tumor microenvironment, we have constructed a 3D stroma-rich in vitro model of HNSCC, using cancer-associated MeWo skin fibroblasts and FaDu pharynx squamous cell carcinoma. The expression of stromal components in heterospheroids was confirmed by immunochemical staining. The generated co-culture FaDu/MeWo spheroids were applied to study penetration, distribution and antitumor efficacy of photoactive drugs such as Temoporfin and Chlorin e6 used in the photodynamic therapy flow cytometry and fluorescence microscopy techniques. We also investigated the distribution of photodiagnostic agent Indocyanine Green. We demonstrated that the presence of stroma influences the behavior of photoactive drugs in different ways: (i) No effect on Indocyanine Green distribution; (ii) lower accumulation of Chlorin e6; (iii) better penetration and PDT efficiency of Temoporfin. Overall, the developed stroma-rich spheroids enlarge the arsenal of in vitro pre-clinical models for high-throughput screening of anti-cancer drugs.

Cellular Uptake and Efflux of Palbociclib In Vitro in Single Cell and Spheroid Models

Adequate drug distribution through tumors is essential for treatment to be effective. Palbociclib is a cyclin-dependent kinase 4/6 inhibitor approved for use in patients with hormone receptor positive, human epidermal growth factor receptor 2 negative metastatic breast cancer. It has unusual physicochemical properties, which may significantly influence its distribution in tumor tissue. We studied the penetration and distribution of palbociclib in vitro, including the use of multicellular three-dimensional models and mathematical modeling. MCF-7 and DLD-1 cell lines were grown as single cell suspensions (SCS) and spheroids; palbociclib uptake and efflux were studied using liquid chromatography-tandem mass spectrometry. Intracellular concentrations of palbociclib for MCF-7 SCS (C max 3.22 µM) and spheroids (C max 2.91 µM) were 32- and 29-fold higher and in DLD-1, 13- and 7-fold higher, respectively, than the media concentration (0.1 μM). Total palbociclib uptake was lower in DLD-1 cells than MCF-7 cells in both SCS and spheroids. Both uptake and efflux of palbociclib were slower in spheroids than SCS. These data were used to develop a mathematical model of palbociclib transport that quantifies key parameters determining drug penetration and distribution. The model reproduced qualitatively most features of the experimental data and distinguished between SCS and spheroids, providing additional support for hypotheses derived from the experimental data. Mathematical modeling has the potential for translating in vitro data into clinically relevant estimates of tumor drug concentrations. SIGNIFICANCE STATEMENT: This study explores palbociclib uptake and efflux in single cell suspension and spheroid models of cancer. Large intracellular concentrations of palbociclib are found after drug exposure. The data from this study may aid understanding of the intratumoural pharmacokinetics of palbociclib, which is useful in understanding how drug distributes within tumor tissue and optimizing drug efficacy. Biomathematical modelling has the potential to derive intratumoural drug concentrations from plasma pharmacokinetics in patients.

Confirmation of Selected Synergistic Cancer Drug Combinations Identified in an HTS Campaign and Exploration of Drug Efflux Transporter Contributions to the Mode of Synergy

Systematic unbiased high-throughput screening (HTS) of drug combinations (DCs) in well-characterized tumor cell lines is a data-driven strategy to identify novel DCs with potential to be developed into effective therapies. Four DCs from a DC HTS campaign were selected for confirmation; only one appears in clinicaltrials.gov and limited preclinical in vitro data indicates that the drug pairs interact synergistically. Nineteen DC-tumor cell line sets were confirmed to interact synergistically in three pharmacological interaction models. We developed an imaging assay to quantify accumulation of the ABCG2 efflux transporter substrate Hoechst. Gefitinib and raloxifene enhanced Hoechst accumulation in ABCG2 (BCRP)-expressing cells, consistent with inhibition of ABCG2 efflux. Both drugs also inhibit ABCB1 efflux. Mitoxantrone, daunorubicin, and vinorelbine are substrates of one or more of the ABCG2, ABCB1, or ABCC1 efflux transporters expressed to varying extents in the selected cell lines. Interactions between ABC drug efflux transporter inhibitors and substrates may have contributed to the observed synergy; however, other mechanisms may be involved. Novel synergistic DCs identified by HTS were confirmed in vitro, and plausible mechanisms of action studied. Similar approaches may justify the testing of novel HTS-derived DCs in mouse xenograft human cancer models and support the clinical evaluation of effective in vivo DCs in patients.

Human iPS Cell-Derived Patient Tissues and 3D Cell Culture Part 2: Spheroids, Organoids, and Disease Modeling

Human induced pluripotent stem cells (HiPSCs) provide several advantages for drug discovery, but principally they provide a source of clinically relevant tissue. Furthermore, the use of HiPSCs cultured in three-dimensional (3D) systems, as opposed to traditional two-dimensional (2D) culture approaches, better represents the complex tissue architecture in vivo. The use of HiPSCs in 3D spheroid and organoid culture is now growing, but particularly when using myocardial, intestinal enteric nervous system, and retinal cell lines. However, organoid cell culture is perhaps making the most notable impact in research and drug discovery, in which 3D neuronal cell cultures allow direct modeling of cortical cell layering and neuronal circuit activity. Given the specific degeneration seen in discrete neuronal circuitry in Alzheimer’s disease (AD) and Parkinson’s disease (PD), HiPSC culture systems are proving to be a major advance. In the present review, the second part of a two-part review, we discuss novel methods in which 3D cell culture systems (principally organoids) are now being used to provide insights into disease mechanisms. (The use of HiPSCs in target identification was reviewed in detail in Part 1.)

High Content Screening Characterization of Head and Neck Squamous Cell Carcinoma Multicellular Tumor Spheroid Cultures Generated in 384-Well Ultra-Low Attachment Plates to Screen for Better Cancer Drug Leads

Multicellular tumor spheroid (MCTS) cultures represent more physiologically relevant in vitro cell tumor models that recapitulate the microenvironments and cell-cell or cell-extracellular matrix interactions which occur in solid tumors. We characterized the morphologies, viability, and growth behaviors of MCTSs produced by 11 different head and neck squamous cell carcinoma (HNSCC) cell lines seeded into and cultured in ultra-low attachment microtiter plates (ULA-plates) over extended periods of time. HNSCC MCTS cultures developed microenvironments, which resulted in differences in proliferation rates, metabolic activity, and mitochondrial functional activity between cells located in the outer layers of the MCTS and cells in the interior. HNSCC MCTS cultures exhibited drug penetration and distribution gradients and some developed necrotic cores. Perhaps the most profound effect of culturing HNSCC cell lines in MCTS cultures was their dramatically altered and varied growth phenotypes. Instead of the exponential growth that are characteristic of two-dimensional HNSCC growth inhibition assays, some MCTS cultures displayed linear growth rates, categorized as rapid, moderate, or slow, dormant MCTSs remained viable but did not grow, and some MCTSs exhibited death phenotypes that were either progressive and slow or rapid. The ability of MCTS cultures to develop microenvironments and to display a variety of different growth phenotypes provides in vitro models that are more closely aligned with solid tumors in vivo. We anticipate that the implementation MCTS models to screen for new cancer drugs for solid tumors like HNSCC will produce leads that will translate better in in vivo animal models and patients.

Implementation of the NCI-60 Human Tumor Cell Line Panel to Screen 2260 Cancer Drug Combinations to Generate >3 Million Data Points Used to Populate a Large Matrix of Anti-Neoplastic Agent Combinations (ALMANAC) Database

Animal and clinical studies demonstrate that cancer drug combinations (DCs) are more effective than single agents. However, it is difficult to predict which DCs will be more efficacious than individual drugs. Systematic DC high-throughput screening (HTS) of 100 approved drugs in the National Cancer Institute's panel of 60 cancer cell lines (NCI-60) produced data to help select DCs for further consideration. We miniaturized growth inhibition assays into 384-well format, increased the fetal bovine serum amount to 10%, lengthened compound exposure to 72 h, and used a homogeneous detection reagent. We determined the growth inhibition 50% values of individual drugs across 60 cell lines, selected drug concentrations for 4 × 4 DC matrices (DCMs), created DCM master and replica daughter plate sets, implemented the HTS, quality control reviewed the data, and analyzed the results. A total of 2620 DCMs were screened in 60 cancer cell lines to generate 3.04 million data points for the NCI ALMANAC (A Large Matrix of Anti-Neoplastic Agent Combinations) database. We confirmed in vitro a synergistic drug interaction flagged in the DC HTS between the vinca-alkaloid microtubule assembly inhibitor vinorelbine (Navelbine) tartrate and the epidermal growth factor-receptor tyrosine kinase inhibitor gefitinib (Iressa) in the SK-MEL-5 melanoma cell line. Seventy-five percent of the DCs examined in the screen are not currently in the clinical trials database. Selected synergistic drug interactions flagged in the DC HTS described herein were subsequently confirmed by the NCI in vitro, evaluated mechanistically, and were shown to have greater than single-agent efficacy in mouse xenograft human cancer models. Enrollment is open for two clinical trials for DCs that were identified in the DC HTS. The NCI ALMANAC database therefore constitutes a valuable resource for selecting promising DCs for confirmation, mechanistic studies, and clinical translation.