Molecular characteristics and potential therapeutic targets in Merkel cell carcinoma

The Role of Citrate Homeostasis in Merkel Cell Carcinoma Pathogenesis

Simple Summary

Merkel cell carcinoma (MCC) is a rare but highly aggressive skin cancer. Despite important progress, overall understanding of the events that drive MCC carcinogenesis remains incomplete. We discovered that the plasma membrane citrate transporter (pmCiC) is upregulated in Merkel cell carcinoma cell lines. Cancer cells import extracellular citrate via pmCiC to support their metabolism, which is critical to support proliferation and metastatic spread. In this study, we show that inhibition of pmCiC can decrease the growth rate of Merkel cell carcinoma cell lines. Targeting pmCiC and thereby the tumor metabolism should be considered further as a potential anti-cancer therapy.

Abstract

Merkel cell carcinoma (MCC) is a rare but highly aggressive tumor of the skin with a poor prognosis. The factors driving this cancer must be better understood in order to discover novel targets for more effective therapies. In the search for targets, we followed our interest in citrate as a central and critical metabolite linked to fatty acid synthesis in cancer development. A key to citrate uptake in cancer cells is the high expression of the plasma membrane citrate transporter (pmCiC), which is upregulated in the different adenocarcinoma types tested so far. In this study, we show that the pmCiC is also highly expressed in Merkel cell carcinoma cell lines by western blot and human tissues by immunohistochemistry staining. In the presence of extracellular citrate, MCC cells show an increased proliferation rate in vitro; a specific pmCiC inhibitor (Na⁺-gluconate) blocks this citrate-induced proliferation. Furthermore, the 3D in vivo Chick Chorioallantoic Membrane (CAM) model showed that the application of Na⁺-gluconate also decreases Merkel cell carcinoma growth. Based on our results, we conclude that pmCiC and extracellular citrate uptake should be considered further as a potential novel target for the treatment of Merkel cell carcinoma.

Quantitative proteome analysis of Merkel cell carcinoma cell lines using SILAC

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumour of the skin with growing incidence. To better understand the biology of this malignant disease, immortalized cell lines are used in research for in vitro experiments. However, a comprehensive quantitative proteome analysis of these cell lines has not been performed so far.

METHODS

Stable isotope labelling by amino acids in cell culture (SILAC) was applied to six MCC cell lines (BroLi, MKL-1, MKL-2, PeTa, WaGa, and MCC13). Following tryptic digest of labelled proteins, peptides were analysed by mass spectrometry. Proteome patterns of MCC cell lines were compared to the proteome profile of an immortalized keratinocyte cell line (HaCaT).

RESULTS

In total, 142 proteins were upregulated and 43 proteins were downregulated. Altered proteins included mitoferrin-1, histone H2A type 1-H, protein-arginine deiminase type-6, heterogeneous nuclear ribonucleoproteins A2/B1, protein SLX4IP and clathrin light chain B. Furthermore, several proteins of the histone family and their variants were highly abundant in MCC cell lines.

CONCLUSIONS

The results of this study present a new protein map of MCC and provide deeper insights in the biology of MCC. Data are available via ProteomeXchange with identifier PXD008181.

Treatment of Advanced Merkel Cell Carcinoma: Current Therapeutic Options and Novel Immunotherapy Approaches

Advanced Merkel cell carcinoma (MCC) is a very aggressive, rare neuroendocrine tumor of the skin with a high frequency of locoregional recurrence and metastasis, and a high mortality rate. Surgical resection, sentinel lymph node biopsy, and radiotherapy represent the gold standard of treatment in patients with localized disease, while chemotherapy has a significant role in the treatment of advanced disease. However, no definitive evidence on the survival impact of radiotherapy in the advanced stages has been provided to date, and response to chemotherapy remains brief in the majority of cases, indicating an urgent need for alternative approaches. Biological and genome sequencing studies have implicated multiple molecular pathways in MCC, thus leading to the development of new agents that target angiogenic factors, anti-apoptosis molecules, poly-ADP ribose polymerase, intracellular signal proteins such as the PI3K/AKT/mTOR pathway, and peptide receptors such as somatostatin receptors. More recently, immunotherapy agents such as avelumab, pembrolizumab, and nivolumab, which act by blocking the programmed cell-death (PD)-1/PD-L1 immune checkpoint, have shown promising results, especially in the advanced setting, and should now be considered standard of care for metastatic MCC. Current research is focusing on developing new immunotherapeutic strategies, identifying predictive biomarker to aid in the selection of patients responsive to immunotherapy, and defining combination approaches to increase efficacy in refractory patients.

Cancer-testis antigens as biomarkers for Merkel cell carcinoma: Pitfalls and opportunities

BACKGROUND

The prognosis and treatment options for metastatic Merkel cell carcinoma (MCC) are poor. The immune-privileged status of cancer-testis (CT) antigens imparts tumor specificity, making them ideal candidates for targeted immunotherapy. We investigate the usefulness of the CT antigens SPA17 (sperm protein-17 [SP-17]), IGF2BP3 (insulin-like growth factor-II mRNA-binding protein 3 [IMP-3]), and transmembrane protein with epidermal growth factor (EGF)-like and two follistatin-like domains 1 (TMEFF1) as potential MCC biomarkers and evaluate their possible utility in immunotherapy and molecularly targeted image-guided treatment.

METHODS

The CT antigens SP-17, IMP-3, and TMEFF1 were selected using transcriptome profiling to identify CT antigens expressed in MCC tumors. Antibodies directed against these CT antigens were stained. Twelve normal skin tissue samples were used as a control. The average percentage of positive cells in each tumor was computed.

RESULTS

Twelve of 14 (86%) MCC cases showed crisp nuclear staining for SP-17, with 2.06% of cells staining positive. IMP-3 showed crisp, perinuclear staining in all 14 MCC cases, with 52.93% MCC cells staining positive. TMEFF1 showed perinuclear staining in all 14 MCC cases, with 96.51% of tumor cells staining positive.

CONCLUSIONS

CT antigens were found to be expressed in both MCC and some control tissues. SP-17 was the most specific yet the least sensitive. IMP-3 and TMEFF1 were both sensitive but not specific. CT antigens may represent valuable treatment targets in MCC.

Update on eighth edition American Joint Committee on Cancer classification for Merkel cell carcinoma and histopathological parameters that determine prognosis

Merkel cell carcinoma (MCC) is a rare primary cutaneous neuroendocrine carcinoma. The annual incidence of MCC is increasing in the USA. Timely diagnosis and proper staging of this tumour are crucial as MCC has high rates of regional recurrence and lymph node and distant metastasis. In this review, we outline the key differences between the tumor node metastasis (TNM) staging criteria for MCC in the seventh and eighth editions of the AJCC Cancer Staging Manual We also discuss histopathological parameters that are not included in the eighth edition of the manual but have been shown in other studies to predict a worse prognosis in patients with MCC. Correct assessment and reporting of these clinically relevant histopathological parameters is of utmost importance for practising pathologists as management differs according to the stage of the tumour. This review aims to increase awareness of all these parameters, and proper recognition would guide the treating clinicians towards the most appropriate treatment options that can be given to patients.

Poly ADP-ribose polymerase-1 as a potential therapeutic target in Merkel cell carcinoma

BACKGROUND

Patients with metastatic Merkel cell carcinoma are treated similarly to small cell lung cancer (SCLC). Poly ADP-ribose polymerase-1 (PARP1) is overexpressed in SCLC and response to PARP inhibitors have been reported in patients with SCLC. Our study explores PARP as a therapeutic target in Merkel cell carcinoma.

METHODS

We evaluated PARP1 expression and Merkel cell polyomavirus (MCPyV) in 19 patients with Merkel cell carcinoma. Target exome-sequencing was performed in 14 samples. Sensitivity to olaparib was tested in 4 Merkel cell carcinoma cell lines.

RESULTS

Most Merkel cell carcinomas (74%) express PARP1 at high levels. Mutations in DNA-damage repair genes were identified in 9 samples (64%), occurred exclusively in head neck primaries, and correlated with TP53/RB1 mutations. The TP53/RB1 mutations were more frequent in MCPyV-negative tumors. Sensitivity to olaparib was seen in the Merkel cell carcinoma line with highest PARP1 expression.

CONCLUSION

Based on PARP1 overexpression, DNA-damage repair gene mutations, platinum sensitivity, and activity of olaparib in a Merkel cell carcinoma line, clinical trials with PARP inhibitors are warranted in Merkel cell carcinoma.

A rare case of Merkel cell carcinoma presenting as a giant intra-thoracic mass: A case report and review of the literature

RATIONALE

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine-derived cutaneous cancer. Ectopic or single metastatic MCC located in thorax is extremely rare; meanwhile, its definite management has not been elucidated yet.

PATIENT CONCERNS

A 64-year-old female patient with a giant mass located in her left thorax was presented for stuffy pain of left chest for 6 months and fever for half a month. She underwent radical resection of vulvar MCC 10 years ago.

DIAGNOSES

Computed tomography (CT)-guided biopsy of the intrathoracic mass revealed a diagnosis of MCC, without synchronous urogenital lesions on pelvic CT images.

INTERVENTIONS

This bulky tumor was completely resected via thoracotomy, along with the adjacent pulmonary lobe, pericardium, pleura, and diaphragm.

OUTCOMES

The patient survived without local-regional recurrence or distant metastasis during the follow-up of 1 year up to now.

LESSONS

Ectopic or single metastatic MCC should be considered in the differential diagnosis of intrathoracic tumors, especially in patients with a history of MCC. Besides, a timely surgery combined with chemotherapy is effective for this disease.

Intraepidermal Merkel cell carcinoma: A case series of a rare entity with clinical follow up

BACKGROUND

Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous carcinoma. MCC typically involves dermis and although epidermotropism has been reported, MCC strictly intraepidermal or in situ (MCCIS) is exceedingly rare. Most of the cases of MCCIS described so far have other associated lesions, such as squamous or basal cell carcinoma, actinic keratosis and so on. Herein, we describe 3 patients with MCC strictly in situ, without a dermal component.

METHODS

Our patients were elderly. 2 of the lesions involved the head and neck area and 1 was on a finger. All tumors were strictly intraepidermal in the diagnostic biopsies, and had histomorphologic features and an immunohistochemical profile supporting the diagnosis of MCC. Excisional biopsies were performed in 2 cases and failed to reveal dermal involvement by MCC or other associated malignancies.

RESULTS AND CONCLUSION

Our findings raise the awareness that MCC strictly in situ does exist and it should be included in the differential diagnosis of Paget's or extramammary Paget's disease, pagetoid squamous cell carcinoma, melanoma and other neoplasms that typically show histologically pagetoid extension of neoplastic cells. Considering the limited number of cases reported to date, the diagnosis of isolated MCCIS should not warrant a change in management from the typical MCC.