Ameloblastoma Phenotypes Reflected in Distinct Transcriptome Profiles

A Retrospective Analysis of 129 Ameloblastoma Cases: Clinical and Demographical Trends from a Single Institution

Ameloblastomas are benign neoplasms of the jaw, but frequently require extensive surgery. The aim of the study was to analyze the demographic and clinicopathological features of ameloblastoma cases at a single Oral and Maxillofacial Surgery group in the United States.

STUDY DESIGN

A retrospective chart review of patients evaluated for ameloblastoma between 2010 and 2020 at a single tertiary care center. Age, race, sex, tumor size, tumor location, and histological subtypes were recorded.

RESULTS

A total of 129 cases of ameloblastoma were recorded with a mean patient age of 42 ± 18.6 years (range 9-91 years old), male to female ratio 1.08:1. Ameloblastoma presenting in the mandible outnumbered maxilla in primary (118 to 8, respectively) and recurrent cases (8 to 1, respectively). There was a higher prevalence of ameloblastoma in Black patients (61.3%) with mean age of Black patients occurring at 40.5 years and the mean age of White patients occurring at 47.8 years and mean tumor size trended larger in the Black patients (15.7 cm2) compared to White patients (11.8 cm2).

CONCLUSION

Data suggests a strong influence of racial factors on the incidence of ameloblastoma, with regards to size, Black patients with ameloblastoma trended higher and more data is needed to clearly elucidate any relationship between the tumor size and race, as other factors may influence the size (such as time to discovery).

Trends in Research of Odontogenic Keratocyst and Ameloblastoma

Odontogenic keratocyst (OKC) and ameloblastoma (AM) are common jaw lesions with high bone-destructive potential and recurrence rates. Recent advancements in technology led to significant progress in understanding these conditions. Single-cell and spatial omics have improved insights into the tumor microenvironment and cellular heterogeneity in OKC and AM. Fibroblast subsets in OKC and tumor cell subsets in AM have been analyzed, revealing mechanisms behind their biological behaviors, including OKC's osteolytic features and AM's recurrence tendencies. Spatial transcriptomics studies of AM have identified engineered fibroblasts and osteoblasts contributing to matrix remodeling gene and oncogene expression at the invasion frontier, driving AM progression. Three-dimensional culture technologies such as organoid models have refined analysis of AM subtypes; uncovered the role of AM fibroblasts in promoting tumor cell proliferation and invasion; and identified signaling pathways such as FOSL1, BRD4, EZH2, and Wnt as potential therapeutic targets. Organoid models also served as preclinical platforms for testing potential therapies. Although preclinical models for AM exist, reliable in vitro and in vivo models for OKC remain scarce. Promising mimic models, including human embryonic stem cells-derived epithelial cells, human oral keratinocytes, human immortalized oral epithelial cells, and HaCaT keratinocytes, show promise, but the advancements in 3-dimensional culture technology are expected to lead to further breakthroughs in this area. Artificial intelligence, including machine learning and deep learning, has enhanced radiomics-based diagnostic accuracy, distinguishing OKC and AM beyond clinician capability. Pathomics-based models further predict OKC prognosis and differentiate AM from ameloblastic carcinoma. Clinical studies have shown positive outcomes with targeted therapies. In a study investigating SMO-targeted treatments for nevoid basal cell carcinoma syndrome, nearly all OKC lesions resolved in 3 patients. A recent clinical trial with neoadjuvant BRAF-targeted therapy for AM demonstrated promising radiologic responses, potentially enabling organ preservation. This review highlights recent advancements and trends in OKC and AM research, aiming to inspire further exploration and progress in these fields.

Differences in BRAF V600E mutation between the epithelium and mesenchyme in classic ameloblastoma

OBJECTIVE

Laser capture microdissection (LCM) was used to pinpoint the mutated tissue in ameloblastoma and investigate whether B-Raf proto-oncogene, serine/threonine kinase (BRAF) mutation is the main pathogenic gene in classic ameloblastoma.

STUDY DESIGN

A total of 24 patients with ameloblastoma scheduled to undergo surgery between 2000 and 2024 were included in the study. LCM was used to isolate tumor cells. Oxford nanopore technology (ONT) was used to analyze the collected cells. GO and KEGG enrichment analyses were then performed on the 300 most highly expressed genes in the epithelial tissue and mesenchyme.

RESULTS

Mandibular follicular ameloblastoma showed BRAF V600E mutations in all epithelial cells but not in the mesenchyme. The mutation rate was significantly higher in mandibular ameloblastomas compared to the maxilla (P < .05). RNA-seq showed that traditional follicular ameloblastoma epithelium was enriched in "growth factor receptor binding" and "angiogenesis regulation," while the mesenchyme was enriched in "ECM receptor interaction." KEGG enrichment analysis showed differential gene expression, mainly in MAPK and PI3K-AKT pathways.

CONCLUSION

Classical follicular ameloblastoma shows the presence of BRAF V600E mutation in epithelial tissue, with a higher mutation rate in the mandible than in the maxilla. The signaling pathways of MAPK and PI3K may be significantly involved in epithelial signal transduction.

Molecular pathogenesis of ameloblastoma

Ameloblastoma (AM) is a benign, although aggressive, epithelial odontogenic tumour originating from tooth-forming tissues or remnants. Its aetiopathogenesis remains unclear; however, molecular analysis techniques have allowed researchers to progress in understanding its genetic basis. The high frequency of BRAF p.V600E as a main driver mutation in AM is well established; nevertheless, it is insufficient to explain its tumourigenesis. In this review, we aimed to integrate the current knowledge about the biology of AM and to describe the main genetic alterations reported, focusing on the findings of large-scale sequencing and gene expression profiling techniques. Current evidence shows that besides BRAF mutation and activation of the MAPK pathway, alterations in Hedgehog and Wnt/β-catenin pathway-related genes are also involved in AM pathogenesis. Recently, a tumour suppressor gene, KMT2D, has been reported as mutated by different research groups. The biological impact of these mutations in the pathogenesis of AM has yet to be elucidated. Further studies are needed to clarify the impact of these findings in the identification of novel biomarkers that could be useful for diagnosing, classifying, and molecular targeting this neoplasm.

LRP5, SLC6A3, and SOX10 Expression in Conventional Ameloblastoma

Cell proliferation and invasion are characteristic of many tumors, including ameloblastoma, and are important features to target in possible future therapeutic applications.

OBJECTIVE

The objective of this study was the identification of key genes and inhibitory drugs related to the cell proliferation and invasion of ameloblastoma using bioinformatic analysis.

METHODS

The H10KA_07_38 gene profile database was analyzed by Rstudio and ShinyGO Gene Ontology enrichment. String, Cytoscape-MCODE, and Kaplan-Meier plots were generated, which were subsequently validated by RT-qPCR relative expression and immunoexpression analyses. To propose specific inhibitory drugs, a bioinformatic search using Drug Gene Budger and DrugBank was performed.

RESULTS

A total of 204 significantly upregulated genes were identified. Gene ontology enrichment analysis identified four pathways related to cell proliferation and cell invasion. A total of 37 genes were involved in these pathways, and 11 genes showed an MCODE score of ≥0.4; however, only SLC6A3, SOX10, and LRP5 were negatively associated with overall survival (HR = 1.49 (p = 0.0072), HR = 1.55 (p = 0.0018), and HR = 1.38 (p = 0.025), respectively). The RT-qPCR results confirmed the significant differences in expression, with overexpression of >2 for SLC6A3 and SOX10. The immunoexpression analysis indicated positive LRP5 and SLC6A3 expression. The inhibitory drugs bioinformatically obtained for the above three genes were parthenolide and vorinostat.

CONCLUSIONS

We identify LRP5, SLC6A3, and SOX10 as potentially important genes related to cell proliferation and invasion in the pathogenesis of ameloblastomas, along with both parthenolide and vorinostat as inhibitory drugs that could be further investigated for the development of novel therapeutic approaches against ameloblastoma.

Conventional Ameloblastoma. A Case Report with Microarray and Bioinformatic Analysis

Ameloblastoma is a rare benign epithelial odontogenic neoplasm, but with great clinical implications, as despite its benignity and slow growth, most cases are locally aggressive with a significant recurrence rate. Histological, cellular, or molecular analyses of its pathogenesis have confirmed the complexity of this neoplasm. We present the case of a 20-year-old patient with a suggestive clinical and radiographic diagnosis of ameloblastoma. An incisional biopsy was obtained confirming the diagnosis of conventional ameloblastoma. Left hemimandibulectomy and plate reconstruction were performed. Histopathological analysis of the surgical specimen confirmed the conventional ameloblastoma with a plexiform pattern and significant areas of cystic degeneration and amyloid-like-like deposits. Additionally, a microarray was carried out with bioinformatic analysis for the enrichment, protein interaction, and determination of eight hub genes (CRP, BCHE, APP, AKT1, AGT, ACTC1, ADAM10, and APOA2) related to their pathogenesis.

Genetic Profile of Adenomatoid Odontogenic Tumor and Ameloblastoma. A Systematic Review

Purpose: To perform a comprehensive and systematic critical appraisal of the genetic alterations reported to be present in adenomatoid odontogenic tumor (AOT) compared to ameloblastoma (AM), to aid in the understanding in their development and different behavior.

Methods: An electronic search was conducted in PubMed, Scopus, and Web of Science during March 2021. Eligibility criteria included publications on humans which included genetic analysis of AOT or AM.

Results: A total of 43 articles reporting 59 AOTs and 680 AMs were included. Different genomic techniques were used, including whole-exome sequencing, direct sequencing, targeted next-generation sequencing panels and TaqMan allele-specific qPCR. Somatic mutations affecting KRAS were identified in 75.9% of all AOTs, mainly G12V; whereas a 71% of the AMs harbored BRAF mutations, mainly V600E.

Conclusions: The available genetic data reports that AOTs and AM harbor somatic mutations in well-known oncogenes, being KRAS G12V/R and BRAFV600E mutations the most common, respectively. The relatively high frequency of ameloblastoma compared to other odontogenic tumors, such as AOT, has facilitated the performance of different sequencing techniques, allowing the discovery of different mutational signatures. On the contrary, the low frequency of AOTs is an important limitation for this. The number of studies that have a assessed the genetic landscape of AOT is still very limited, not providing enough evidence to draw a conclusion regarding the relationship between the genomic alterations and its clinical behavior. Thus, the presence of other mutational signatures with clinical impact, co-occurring with background KRAS mutations or in wild-type KRAS cases, cannot be ruled out. Since BRAF and RAS are in the same MAPK pathway, it is interesting that ameloblastomas, frequently associated with BRAFV600E mutation have aggressive clinical behavior, but in contrast, AOTs, frequently associated with RAS mutations have indolent behavior. Functional studies might be required to solve this question.

Whole exome sequencing and system biology analysis support the "two-hit" mechanism in the onset of Ameloblastoma

BACKGROUND

Ameloblastoma is the most frequent odontogenic tumor. Various evidence has highlighted the role of somatic mutations, including recurrent mutation BRAF V600E, in the tumorigenesis of Ameloblastoma, but the intact genetic pathology remains unknown.

MATERIAL AND METHODS

We sequenced the whole exome of both tumor tissue and healthy bone tissue from four mandibular ameloblastoma patients. The identified somatic mutations were integrated into Weighted Gene Co-expression Network Analysis on publicly available expression data of odontoblast, ameloblast, and Ameloblastoma.

RESULTS

We identified a total of 70 rare and severe somatic mutations. We found BRAF V600E on all four patients, supporting previous discovery. HSAP4 was also hit by two missense mutations on two different patients. By applying Weighted Gene Co-expression Network Analysis on expression data of odontoblast, ameloblast, and Ameloblastoma, we found a proliferation-associated gene module that was significantly disrupted in tumor tissues. Each patient carried at least two rare, severe somatic mutations affecting genes within this module, including HSPA4, GNAS, CLTC, NES, and KMT2D. All these mutations had a ratio of variant-support reads lower than BRAF V600E, indicating that they occurred later than BRAF V600E.

CONCLUSIONS

We suggest that a severe somatic mutation on the gene network of cell proliferation other than BRAF V600E, namely second hit, may contribute to the tumorigenesis of Ameloblastoma.

Conceptual changes in ameloblastoma: Suggested re-classification of a "veteran" tumor

OBJECTIVES

The merging of ameloblastoma (AM) with mural unicystic ameloblastoma (UAM-M) was suggested by the 2017 WHO based on similar treatment needs. In an international multicenter study, we investigated the characteristics of their merged product (merged-AM) and raised the possibility of unifying AM and UAM (total-AM).

MATERIALS AND METHODS

AM and UAM (luminal/intraluminal/mural), separate and combined, were analyzed for demographic/clinical/radiological features. ANOVA and chi-square tests were followed by univariate and multivariate analyses, and significance was set at p < .05.

RESULTS

The patients' mean age was 39.6 ± 20.3 years in merged-AM (147 AM, 76 UAM-M), 45.1 ± 19.4 years in AM (p = .009). Merged-AM comprised 51.3% multilocular/48.7% unilocular tumors, AM comprised 72.5%/27.5%, respectively (p < .001). Merged-AM was associated with impacted teeth in 30.8%, AM in 18% (p = .023). The probability of merged-AM for multilocularity increased by 2.4% per year of age (95%CI 0.6-4.2, p = .009). Association with impacted teeth decreased by 7.9% per year of age (95%CI 1.9-14.39, p = .009). Merged-AM did not differ from total-AM (p > .05).

CONCLUSIONS

Merged-AM partially differed from AM, but differences appeared to diminish in an age/time-wise manner. Merged-AM and total-AM were nearly indistinguishable. Therefore, AM and UAM may be considered a continuous spectrum of one type of tumor, further necessitating revision of the treatment approaches.

Ameloblastoma cell lines derived from different subtypes demonstrate distinct developmental patterns in a novel animal experimental model

Objective

Ameloblastoma is a representative odontogenic tumor comprising several characteristic invasive forms, and its pathophysiology has not been sufficiently elucidated. A stable animal experimental model using immortalized cell lines is crucial to explain the factors causing differences among the subtypes of ameloblastoma, but this model has not yet been disclosed. In this study, a novel animal experimental model has been established, using immortalized human ameloblastoma-derived cell lines.

Methodology

Ameloblastoma cells suspended in Matrigel were subcutaneously transplanted into the heads of immunodeficient mice. Two immortalized human ameloblastoma cell lines were used: AM-1 cells derived from the plexiform type and AM-3 cells derived from the follicular type. The tissues were evaluated histologically 30, 60, and 90 days after transplantation.

Results

Tumor masses formed in all transplanted mice. In addition, the tumors formed in each group transplanted with different ameloblastoma cells were histologically distinct: the tumors in the group transplanted with AM-1 cells were similar to the plexiform type, and those in the group transplanted with AM-3-cells were similar to the follicular type.

Conclusions

A novel, stable animal experimental model of ameloblastoma was established using two cell lines derived from different subtypes of the tumor. This model can help clarify its pathophysiology and hasten the development of new ameloblastoma treatment strategies.

A review of the molecular profile of benign and malignant odontogenic lesions

Odontogenic cysts and tumors are heterogeneous lesions, originating from elements or remnants of the odontogenic apparatus. Although the majority of these lesions are benign and never undergo malignant transformation, rare malignant tumors may arise de novo or from benign precursors. The molecular basis of these lesions is still poorly understood. This article summarizes and discusses studies using small, medium, and large-scale and/or "-omic" techniques to describe the molecular characteristics of benign and malignant odontogenic lesions and briefly debates strategies to increase the use of "-omic" and multi-omic approaches or integrative analyses in the research of these lesions. A comprehensive understanding of the molecular aspects of odontogenic lesions by using large-scale approaches will enable us to refine the classification of this heterogeneous group of disorders and provide more accurate biomarkers for precise diagnosis, prognosis, and development of molecular tools in the management of patients with these conditions.