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EXPERT OPINION
ON DRUG DISCOVERY
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/iedc20
How good are the current models of adrenocortical carcinoma for novel drug discovery?
Carmen Ruggiero, Mabrouka Doghman-Bouguerra & Enzo Lalli
To cite this article: Carmen Ruggiero, Mabrouka Doghman-Bouguerra & Enzo Lalli (2022) How good are the current models of adrenocortical carcinoma for novel drug discovery?, Expert Opinion on Drug Discovery, 17:3, 211-213, DOI: 10.1080/17460441.2022.1993817
To link to this article: https://doi.org/10.1080/17460441.2022.1993817
Published online: 20 Oct 2021.
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EDITORIAL
How good are the current models of adrenocortical carcinoma for novel drug discovery?
Carmen Ruggieroa,b,*, Mabrouka Doghman-Bouguerraa,b* and Enzo Lalli (Da,b,c
aInstitut de Pharmacologie Moléculaire et Cellulaire CNRS UMR, Valbonne, France; bUniversité Côte d’Azur, Valbonne, France; ‘Inserm, Valbonne, France
ARTICLE HISTORY Received 9 September 2021; Accepted 12 October 2021
1. Introduction
During the last decade, significant advances have been made in the definition of the molecular mechanisms underlying the onset and progression of adrenocortical carcinoma (ACC). A better understanding of ACC tumorigenesis has come from the identification of several genetic and molecular drivers of this malignancy thanks to an extensive profiling analysis of ACC tumors. Unfortunately, the development of novel therapeutic options has been hampered by the relative lack of in vitro and in vivo preclinical models recapitulating the entire spectrum of ACC heterogeneity, molecular features, tumor microenviron- ment and sensitivity to the available treatments. The recent establishment and implementation of novel ACC cell lines, genetically engineered mouse models, patient-derived ACC xenografts (PDX) in mice and emerging preclinical in vivo mod- els offer novel experimental possibilities for drug discovery.
2. Preclinical research models
2.1. In vitro cell lines
Until recently, NCI-H295 and its H295R subclone were the only differentiated human ACC cell line available [1]. Their ability to produce steroids from different zones of the adrenal cortex after stimulation with effective agonists made them important models for ACC research. Those cell lines were thoroughly exploited to dissect the molecular mechanisms underlying adrenocortical tumorigenesis, whose understanding is neces- sary for novel drug discovery.
In 2016, Hantel and coworkers successfully established an adult ACC PDX model (see section 2.2) and also explanted xenografts pieces for in vitro culturing. The established MUC- 1 cells expressed adrenocortical markers and maintained in vitro hormonal activity [2]. MUC-1 displayed drug resistance against the clinical gold standard therapy etoposide, doxoru- bicin, cisplatin and mitotane (EDP-M), which was not observed for the NCI-H295R model [2].
In 2018, two new PDX-derived ACC cell lines, CU-ACC1 and CU-ACC2, have been established [3]. CU-ACC1 derived from
a sporadic ACC metastasis to the perinephric region, whereas CU-ACC2 originated from an ACC liver metastasis in a patient with Lynch syndrome. CU-ACC1 cells secreted cortisol but not aldosterone, while CU-ACC2 were not secretory and exhibited a loss of MSH2 (consistent with the known germline mutation of the patient causing Lynch syndrome) [3]. They have both already been used to explore novel targeted therapies for ACC.
The latest ACC cell line developed is JIL-2266. Of note, those cells have been transferred directly to the cell culture, without a previous passage as xenograft in nude mice nor the presence of feeder cells [4]. Compared to NCI-H295R, JIL-2266 cells revealed a low steroid secretion and are significantly less sensi- tive to mitotane [4]. They present a high mutational burden associated with a germline mutation in the MUTYH gene, encoding a protein involved in DNA glycosylase-initiating base- excision repair. JIL-2266 cells thus represent a novel pre-clinical ACC model to study oxidative DNA damage.
2.2. In vivo models
The early genetically engineered mouse models used in mod- eling ACC were generated with either activation of Wnt/B catenin signaling cascade or overexpression of IGF2, two important pathways activated in ACC [5-7]. However, in all those models the genetic alterations in both pathways failed to trigger malignant adrenocortical tumorigenesis. More recently, Batisse-Lignier et al. have developed a transgenic mice model with adrenocortical-specific expression of the SV40 large T-antigen (AdTAg mice) to evaluate the oncogenic potential of p53/Rb inhibition in the adrenal gland [8]. All mice developed large adrenal carcinomas with metastasis to the liver and lungs. This model has allowed to prove the efficacy of mTORC1 inhibition by rapamycin on tumor development. Recently, Borges et al. developed another ACC mouse model with simultaneous ß-catenin activation combined with Trp53 deletion and observed ACC development with metastases [9].
NCI-H295R xenografts have been established and solid tumors were locally measurable, however no development of metastasis was observed in those tumor-bearing mice. Of
note, subcutaneous NCI-H295R xenografts have been employed upon genetic modification for preclinical testing of existing therapies and to implement new pharmacological approaches. Recently, a mouse xenograft model of metastatic ACC established by intrasplenic injection of NCI-H295R cells followed by splenectomy has been shown to produce liver metastasis, representing a new preclinical model for drug screening in advanced-stage disease [10].
PDX models in athymic mice that reflected the diversity and heterogeneity of ACC patients’ tumors have been recently described. The first PDX of pediatric ACC (SJ-ACC3) has been developed by Pinto et al. [11] via the implantation in immu- nocompromised mice of an adrenal mass incidentally found and resected from an 11-year-old boy bearing a germline TP53 mutation. Screening of this xenograft for drug responsiveness showed that cisplatin had a potent antitumor effect, whereas etoposide, doxorubicin and a panel of commonly employed chemotherapeutics had little or no antitumor activity. Of note, the topoisomerase inhibitor topotecan showed cytostatic effects with tumor growth impairment, indicating this drug as a potential new treatment for pediatric ACC [11]. Unfortunately, it was not possible to establish a cell line for complementary in vitro experiments from this xenograft.
MUC-1, the first adult ACC PDX model along with the corresponding cell line (see 2.1) was derived from a metastatic ACC neck lesion of an adult patient [2]. MUC-1 tumor analysis revealed highly vascularized, proliferating and SF-1 positive xenografts [2].
Two further PDX models, CU-ACC1 and CU-ACC2 and the corresponding cell lines (see 2.1) have been recently estab- lished via subcutaneous implantation of patient tumor tissues in nude mice [3]. Their adrenocortical origin has been con- firmed and the immunohistological features of the derived tumor tissues matched those of the patients’ tumors [3].
Recently, Lang et al. described the first humanized CU-ACC2- M2B ACC PDX mouse model to examine the in vivo effects of the PD-1 inhibitor pembrolizumab on tumor growth as well as the changes in infiltrating lymphocytes and immune cells in periph- eral lymphatic organs [12]. Mice treatment with pembrolizumab showed a significant tumor inhibition respect to the controls, which correlated with an increased tumor-infiltrating lympho- cyte activity [12]. Those effects were paralleled by a remarkable response of the CU-ACC2 patient to the treatment, with a reduction in the size of target lesions and no new metastases. Overall, these data suggest that humanized ACC PDXs represent a useful model to define mechanisms and biomarkers involved in the response and the resistance to immunotherapy.
New non-mammalian models have also emerged as novel preclinical tools in ACC research. Chicken embryo chorioallan- toic membrane (CAM) models have been used for the evalua- tion of the metastatic potential of NCI-H295R cells overexpressing SF-1 in a doxycycline-dependent fashion [13]. Moreover, zebrafish (Danio rerio) embryos xenografted with ACC cells have been recently exploited to study the in vivo cytotoxicity of abiraterone acetate against ACC cell xenografts, showing the potential of this vertebrate model as a useful tool for drug screening in ACC [14].
3. Expert opinion
ACC is a rare disease with heterogeneous clinical phenotypes and molecular genotypes with a poor survival rate at five years. Unfortunately, the paucity of preclinical research models has severely limited the development of targeted therapies for patients with ACC. The disappointing results concerning the clinical translation of novel therapeutic approaches for ACC patients have highlighted the inadequacy of the currently employed tumor models, which poorly represent ACC hetero- geneity, being thus non-predictive of the clinical suitability of novel pharmacological strategies.
Recent studies have given deeper insight into the genomic and the genetic landscape of ACC, revealing specific molecular subtypes of ACC tumors with high mutational rates, which are predictive of a particularly poor prognosis [15]. With the enlarged classification of ACC tumor subtypes and the recog- nition of the disease heterogeneity, the need of models to shed light on the molecular pathways leading to malignant transformation and to test the efficacy of novel drugs has become more urgent.
Indeed, thanks to novel in vitro techniques based on the use of ROCK inhibitors and feeder cells and the growing experience in establishing PDXs, novel ACC cell lines and matched PDX models have been developed providing new tools to investigate the molecular mechanisms underlying ACC pathogenesis and to evaluate patient-specific therapeutic options.
The development of improved preclinical models that encompass the full spectrum of the heterogeneity of patients’ tumors, defined at an ‘omics’ or at a ‘multi-omics’ single-cell level, represents a challenge for the future of personalized ACC therapies. Moreover, further advances in ACC PDX huma- nized mouse models will allow to better understand the role of the tumor microenvironment to infuence the response to immunotherapy and to guide more personalized clinical treat- ment decisions. The functional analysis of tumor drug responses will need a fine interconnection between the choice of the so-called cancer ‘avatar’ models and the time, scale and cost of drug screening to lay the foundations for a precision therapy for ACC patients. The availability of multiple preclini- cal models such as ACC tumor cell lines, genetically modified mice, PDXs in mice and zebrafish and so far unexplored patient-derived organoid models are likely to offer in the future valuable tools for in vitro screening and in vivo testing of novel drugs to treat ACC.
Funding
This manuscript was not funded.
Declaration of interest
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
ORCID
Enzo Lalli D http://orcid.org/0000-0002-0584-5681
References
Papers of special note have been highlighted as either of interest (.) or of considerable interest ( .. ) to readers.
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