Human relevance of NRAS/BRAF mouse melanoma models

Intertumoral Genetic Heterogeneity Generates Distinct Tumor Microenvironments in a Novel Murine Synchronous Melanoma Model

Simple Summary

Metastatic melanoma patients may present with multiple, simultaneous metastases that are genetically different. This intertumoral heterogeneity can cause these tumors to respond differently to the same systemic therapy. Progression of any one tumor, even when others regress, eventually leads to therapy termination. The mechanism underlying these mixed responses remains unknown due to a lack of clinically representative animal models. In a novel murine model of synchronous melanoma that recapitulates human intertumoral heterogeneity, we show that intertumoral genetic heterogeneity leads to the simultaneous generation of distinct tumor immune microenvironments within the same mouse. Furthermore, each tumor can independently regulate local PD-1 (programmed cell death protein 1) and PD-L1 (PD-1 ligand) expressions, an immunosuppressive axis targeted by popular checkpoint immunotherapies. This model is useful for furthering the study of intertumoral heterogeneity and of lesion-specific therapeutic responses.

Abstract

Metastatic melanoma portends a poor prognosis and patients may present with multiple, simultaneous tumors. Despite recent advances in systemic immunotherapy, a majority of patients fail to respond, or exhibit lesion-specific responses wherein some metastases respond as others progress within the same patient. While intertumoral heterogeneity has been clinically associated with these mixed lesion-specific therapeutic responses, no clear mechanism has been identified, largely due to the scarcity of preclinical models. We developed a novel murine synchronous melanoma model that recapitulates this intertumoral genetic and microenvironmental heterogeneity. We show that genetic differences between tumors are sufficient to generate distinct tumor immune microenvironments (TIME) simultaneously in the same mouse. Furthermore, these TIMEs lead to the independent regulation of PD-1/PD-L1 (programmed cell death protein 1/PD-1 ligand), a popular axis targeted by immune checkpoint therapy, in response to ongoing anti-tumor immunity and the presence of interferon-gamma. Currently, therapeutic selection for metastatic melanoma patients is guided by a single biopsy, which may not represent the immune status of all tumors. As a result, patients can display heterogeneous lesion-specific responses. Further investigations into this synchronous melanoma model will provide mechanistic insight into the effects of intertumoral heterogeneity and guide therapeutic selection in this challenging patient population.

Melanoma models for the next generation of therapies

There is a lack of appropriate melanoma models that can be used to evaluate the efficacy of novel therapeutic modalities. Here, we discuss the current state of the art of melanoma models including genetically engineered mouse, patient-derived xenograft, zebrafish, and ex vivo and in vitro models. We also identify five major challenges that can be addressed using such models, including metastasis and tumor dormancy, drug resistance, the melanoma immune response, and the impact of aging and environmental exposures on melanoma progression and drug resistance. Additionally, we discuss the opportunity for building models for rare subtypes of melanomas, which represent an unmet critical need. Finally, we identify key recommendations for melanoma models that may improve accuracy of preclinical testing and predict efficacy in clinical trials, to help usher in the next generation of melanoma therapies.

Adoptive T Cell Therapy for Solid Tumors: Pathway to Personalized Standard of Care

Adoptive cell therapy (ACT) with tumor-infiltrating T cells (TILs) has emerged as a promising therapy for the treatment of unresectable or metastatic solid tumors. One challenge to finding a universal anticancer treatment is the heterogeneity present between different tumors as a result of genetic instability associated with tumorigenesis. As the epitome of personalized medicine, TIL-ACT bypasses the issue of intertumoral heterogeneity by utilizing the patient’s existing antitumor immune response. Despite being one of the few therapies capable of inducing durable, complete tumor regression, many patients fail to respond. Recent research has focused on increasing therapeutic efficacy by refining various aspects of the TIL protocol, which includes the isolation, ex vivo expansion, and subsequent infusion of tumor specific lymphocytes. This review will explore how the therapy has evolved with time by highlighting various resistance mechanisms to TIL therapy and the novel strategies to overcome them.

Efficacy of Targeted Radionuclide Therapy Using [131I]ICF01012 in 3D Pigmented BRAF- and NRAS-Mutant Melanoma Models and In Vivo NRAS-Mutant Melanoma

Simple Summary

Targeted radionuclide therapy (TRT) aims to selectively deliver radioactive molecules to tumor cells. For this purpose, we deliver iodine-131 ([¹³¹I]) to melanoma cells by using our laboratory-developed melanin specific radiotracer, the ICF01012. Approximately 50% and 20%–30% of human melanomas have activating mutation in BRAF or NRAS genes, respectively. These mutations lead to a constitutive activation of the MAPK/ERK pathway, which is known to be involved in tumor cells’ radioresistance. In this work, we showed using 3D in vitro tumor models, an additive efficiency of combining [¹³¹I]ICF01012-TRT and MAPK/ERK inhibitors in BRAF- and NRAS-mutant melanoma cells. In mice bearing NRAS^Q61K-mutated melanoma, TRT induced an impressive decrease in tumor growth, as well as a highly extended survival. Additionally, we showed that TRT reduces the metastatic capacity of melanoma, especially through lymph-node dissemination. These results are therefore of great interest, especially for patients with NRAS-mutant metastatic melanoma who currently lack specific efficient therapies.

Abstract

Purpose: To assess the efficiency of targeted radionuclide therapy (TRT), alone or in combination with MEK inhibitors (MEKi), in melanomas harboring constitutive MAPK/ERK activation responsible for tumor radioresistance. Methods: For TRT, we used a melanin radiotracer ([¹³¹I]ICF01012) currently in phase 1 clinical trial (NCT03784625). TRT alone or combined with MEKi was evaluated in three-dimensional melanoma spheroid models of human BRAF^V600E SK-MEL-3, murine NRAS^Q61K 1007, and WT B16F10 melanomas. TRT in vivo biodistribution, dosimetry, efficiency, and molecular mechanisms were studied using the C57BL/6J-NRAS^Q61K 1007 syngeneic model. Results: TRT cooperated with MEKi to increase apoptosis in both BRAF- and NRAS-mutant spheroids. NRAS^Q61K spheroids were highly radiosensitive towards [¹³¹I]ICF01012-TRT. In mice bearing NRAS^Q61K 1007 melanoma, [¹³¹I]ICF01012 induced a significant extended survival (92 vs. 44 days, p < 0.0001), associated with a 93-Gy tumor deposit, and reduced lymph-node metastases. Comparative transcriptomic analyses confirmed a decrease in mitosis, proliferation, and metastasis signatures in TRT-treated vs. control tumors and suggest that TRT acts through an increase in oxidation and inflammation and P53 activation. Conclusion: Our data suggest that [¹³¹I]ICF01012-TRT and MEKi combination could be of benefit for advanced pigmented BRAF-mutant melanoma care and that [¹³¹I]ICF01012 alone could constitute a new potential NRAS-mutant melanoma treatment.

Classification and Grading of Melanocytic Lesions in a Mouse Model of NRAS-driven Melanomagenesis

The mouse line carrying the Tg(Tyr-NRAS*Q61K)1Bee transgene is widely used to model in vivo NRAS-driven melanomagenesis. Although the pathological features of this model are well described, classification and interpretation of the resulting proliferative lesions-including their origin, evolution, grading, and pathobiological significance-are still unclear and not supported by molecular and biological evidence. Focusing on their classification and grading, this work combines histopathology and expression analysis (using both immunohistochemistry [IHC] and quantitative PCR) of selected biomarkers to study the full spectrum of cutaneous and lymph nodal melanocytic proliferations in the Tg(Tyr-NRAS*Q61K)1Bee mouse. The analysis of cutaneous and lymph nodal melanocytic proliferations has demonstrated that a linear correlation exists between tumor grade and Ki-67, microphthalmia-associated transcription factor (MITF), gp100, and nestin IHC, with a significantly increased expression in high-grade lesions compared with low-grade lesions. The accuracy of the assessment of MITF IHC in melanomas was also confirmed by quantitative PCR analysis. In conclusion, we believe the incorporation of MITF, Ki-67, gp100, and nestin analysis into the histopathological classification/grading scheme of melanocytic proliferations described for this model will help to assess with accuracy the nature and evolution of the phenotype, monitor disease progression, and predict response to experimental treatment or other preclinical manipulations.

Cutaneous Melanoma-A Long Road from Experimental Models to Clinical Outcome: A Review

Cutaneous melanoma is a complex disorder characterized by an elevated degree of heterogeneity, features that place it among the most aggressive types of cancer. Although significant progress was recorded in both the understanding of melanoma biology and genetics, and in therapeutic approaches, this malignancy still represents a major problem worldwide due to its high incidence and the lack of a curative treatment for advanced stages. This review offers a survey of the most recent information available regarding the melanoma epidemiology, etiology, and genetic profile. Also discussed was the topic of cutaneous melanoma murine models outlining the role of these models in understanding the molecular pathways involved in melanoma initiation, progression, and metastasis.

A histopathological classification system of Tyr::NRASQ61K murine melanocytic lesions: A reproducible simplified classification

Genetically engineered mouse models offer essential opportunities to investigate the mechanisms of initiation and progression in melanoma. Here, we report a new simplified histopathology classification of mouse melanocytic lesions in Tyr::NRAS^Q61K derived models, using an interactive decision tree that produces homogeneous categories. Reproducibility for this classification system was evaluated on a panel of representative cases of murine melanocytic lesions by pathologists and basic scientists. Reproducibility, measured as inter-rater agreement between evaluators using a modified Fleiss' kappa statistic, revealed a very good agreement between observers. Should this new simplified classification be adopted, it would create a robust system of communication between researchers in the field of mouse melanoma models.

Oncogenic BRAF mutations and p16 expression in melanocytic nevi and melanoma in the Polish population

Introduction

Twenty-five - fifty percent of skin melanomas arise from nevi. Melanocyte proliferation is activated by BRAF^V600E, then is arrested, but single nevi transform to melanomas. p16 controls arrest, and p16 loss may promote transformation.

Aim

To analyze BRAF^V600E, p16 expression and melanocyte proliferation in dermal, compound and dysplastic nevi, cells of primary and metastatic melanoma in the Polish population.

Material and methods

One hundred and thirty-two nevi (dermal, compound, dysplastic) and 41 melanomas (in situ, primary, metastatic) were studied. BRAF was assessed by cobas^® 4800 BRAF^V600 Mutation Test, High Resolution Melting Assay validated with: pyrosequencing and immunohistochemistry. p16 and Ki67 expression was analyzed by IHC.

Results

Eighty-two percent of nevi and 57% of melanomas display BRAF^V600E expression. Most dermal and compound nevi had > 50% of p16(+) cells. BRAF^V600E dysplastic nevi had a low number of p16(+) cells. Nevi without BRAF^V600E (WT), had 90% of cells p16(+). In 60% of in situ and primary melanomas, there was a low number of cells of p16(+). Fifty percent of WT metastatic melanoma and 33% of BRAF^V600E showed a high level of p16. The number of Ki67(+) cells in dysplastic nevi was very low. In 25% of BRAF^V600E melanomas in situ and 55% of WT, > 10% cells were Ki67(+). All BRAF^V600E primary melanomas and 66% of WT had > 10% Ki67(+) cells. Twenty percent of BRAF^V600E and WT metastases had > 10% of Ki67(+), however, 62% of BRAF^V600E and 32% of WT samples had > 50% of Ki67(+) cells.

Conclusions

BRAF^V600E and p16 are more frequent in nevi than in melanoma in vivo. A significantly higher p16 expression was observed in mutated nevi than in WT, while in melanoma it was just the opposite. The proliferation rate of melanoma cells negatively correlated with p16 expression.

Molecular Biology and Genetic Mechanisms in the Progression of the Malignant Skin Melanoma

Malignant skin melanoma is a tumor deriving from transformed skin melanocytes as a result of complex interactions between genetic and environmental factors. This melanoma has a potential to metastasize early and very often it is resistant to the existing modalities of the systemic therapy. As in any other neoplasms, certain types of melanoma may skip certain stages of progression. The progression from one stage to another is accompanied by specific biological changes. Several key changes in the melanoma tumorogenesis influence the regulation of the cell proliferation and vitality, including the RAS-RAF-ERK, PI3K-AKT, and p16INK4/CDK4/RB pathways. A key role in the dissreguarity of the RAS-RAF-ERK (MAPK) pathway in the malignant melanoma development have been demonstrated by many studies. To date, the molecular genetic alterations during melanoma development have been partially known. In the pathogenesis of the malignant melanoma, there are mutations of various genes such as NRAS, BRAF, and PTEN and mutations and deletions of CDKN2A. In the past years, great advance has been made in the insights of the molecular aspects of the melanoma pathogenesis. However, this field yet poses a challenge to discover new details about the melanoma molecular characteristics. The research results are focused towards the improvement of the melanoma patients prognosis by introducing personalized targeted therapy.

Mechanisms of Drug Resistance in Melanoma

Metastatic melanoma is associated with poor outcome and is largely refractory to the historic standard of care. In recent years, the development of targeted small-molecule inhibitors and immunotherapy has revolutionised the care and improved the overall survival of these patients. Therapies targeting BRAF and MEK to block the mitogen-activated protein kinase (MAPK) pathway were the first to show unprecedented clinical responses. Following these encouraging results, antibodies targeting immune checkpoint inhibition molecules cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death (PD)-1, and PD-ligand1(PD-L1) demonstrated sustained tumour regression in a significant subset of patients by enabling an anti-tumour immunologic response. Despite these landmark changes in practice, the majority of patients are either intrinsically resistant or rapidly acquire resistance to MAPK pathway inhibitors and immune checkpoint blockade treatment. The lack of response can be driven by mutations and non-mutational events in tumour cells, as well as by changes in the surrounding tumour microenvironment. Common resistance mechanisms bypass the dependence of tumour cells on initial MAPK pathway driver mutations during targeted therapy, and permit evasion of the host immune system to allow melanoma growth and survival following immunotherapy. This highlights the requirement for personalised treatment regimens that take into account patient-specific genetic and immunologic characteristics. Here we review the mechanisms by which melanomas display intrinsic resistance or acquire resistance to targeted therapy and immunotherapy.

Impact of oncogenic BRAF mutations and p16 expression on the growth rate of early melanomas and naevi in vivo

BACKGROUND

It is important to know what drives and arrests melanocytic growth in vivo but observations linking oncogenic mutations to growth rates of melanocytic neoplasms in vivo are sparse.

OBJECTIVES

To clarify the relationship between BRAF(V) (600E) mutations and p16 expression and the growth rate of melanocytic neoplasms in vivo.

METHODS

We measured the growth rate of 54 melanocytic lesions (26 melanomas, 28 naevi) in vivo with digital dermatoscopy and correlated it with BRAF(V) (600E) and p16 expression, and with dermatoscopic and histological patterns.

RESULTS

Melanomas grew faster than naevi (mean 2·7 vs. 0·8 mm(2) /year; P < 0·001) and the growth rate was faster in lesions with more nests (> 25% nests: 2·0 mm(2) /year vs. < 25% nests: 1·0 mm(2) /year; P = 0·036). Melanomas with the BRAF(V) (600E) mutation grew significantly faster than melanomas without the mutation (mean 3·36 vs. 1·60 mm(2) /year, P = 0·018). This effect of the BRAF(V) (600E) mutation on the growth rate was not observed in melanocytic naevi (mean 1·01 vs. 0·47 mm(2) /year, P = 0·274). Histopathologically, extensive nesting, larger nests and larger cell sizes were more common in melanocytic neoplasms with the BRAF(V) (600E) mutation than in those without the mutation. Melanomas expressing p16 had a slower growth rate than melanomas without p16 expression (2·27 vs. 4·34 mm(2) /year, P = 0·047). This effect was not observed in naevi (0·81 vs. 0·68 mm(2) /year, P = 0·836).

CONCLUSIONS

The expression of BRAF(V) (600E) and the loss of p16 accelerate the growth rate of early melanomas in vivo but not in melanocytic naevi. In comparison to melanocytic proliferations that lack the mutation, the epidermal melanocytes in lesions that harbour BRAF(V) (600E) mutations are larger and more frequently arranged in large nests.

Anti-tumor properties of cis-resveratrol methylated analogs in metastatic mouse melanoma cells

Resveratrol (E-3,5,4'-trihydroxystilbene) is a polyphenol found in red wine that has been shown to have multiple anti-cancer properties. Although cis-(Z)- and trans-(E)-isomers of resveratrol occur in nature, the cis form is not biologically active. However, methylation at key positions of the cis form results in more potent anti-cancer properties. This study determined that synthetic cis-polymethoxystilbenes (methylated analogs of cis-resveratrol) inhibited cancer-related phenotypes of metastatic B16 F10 and non-metastatic B16 F1 mouse melanoma cells. In contrast with cis- or trans-resveratrol and trans-polymethoxystilbene which were ineffective at 10 μM, cis-polymethoxystilbenes inhibited motility and proliferation of melanoma cells with low micromolar specificity (IC50 < 10 μM). Inhibitory effects by cis-polymethoxystilbenes were significantly stronger with B16 F10 cells and were accompanied by decreased expression of β-tubulin and pleckstrin homology domain-interacting protein, a marker of metastatic B16 cells. Thus, cis-polymethoxystilbenes have potential as chemotherapeutic agents for metastatic melanoma.