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Page 2 of 9 Wickremesekera et al. J Cancer Metastasis Treat 2019;5:62 I http://dx.doi.org/10.20517/2394-4722.2019.09

Results: DAB IHC staining showed the presence of PRR, ACE, ATIIR1 and ATIIR2 in all ten samples of MM to the
brain. IF IHC staining showed that the CSC subpopulations in MM to the brain expressed PRR, ATIIR1 and ATIIR2;
and a CSC subpopulation on the endothelium of the microvessels expressed ACE. Western blotting and NanoString
mRNA analysis confirmed protein and mRNA expression of these components of the RAS, respectively.

Conclusion: CSCs in MM to the brain expressed components of the RAS. Targeting the CSCs using modulators of
the RAS may be a novel therapeutic approach for treating this aggressive cancer.

Keywords: Malignant melanoma, metastatic, cancer stem cells, renin-angiotensin system, cancer, brain

INTRODUCTION
Metastatic melanoma (MM) to the brain occurs in 30% of melanoma patients and accounts for 5%-8% of all
[1]
brain tumors . For many years, the median survival of MM to the brain is 6-9 months following mainstay
[2-5]
treatments including surgical excision, stereotactic radiosurgery and external beam radiotherapy .
Investigations into MM to the brain have identified real time preferential hematogenous dissemination
[6]
of tumor cells , with survival of these cells within brain capillaries, migration to breach the blood brain
[7]
barrier, angiogenesis and intraparenchymal proliferation .
Although immunotherapies that enhance T-lymphocyte activity such as Ipilimumab, anti-cytotoxic
T-lymphocyte associated antigen-4 and anti-programmed cell death-1 inhibitors can improve the median
[8,9]
survival, some cause significant toxicities . Up to 50%-60% of MM patients harbor the BRAF V600
[10]
somatic mutation . Vemurafenib, a BRAF inhibitor, increases the median survival to 16 months [11]
but despite an initially good response, progression-free survival remains poor, at seven months . Used
[5]
together, kinase inhibitors, BRAF-targeted and MEK-targeted small molecule drugs relieve intracranial
symptoms and induces remission but cessation due to toxicity causes rapid intracranial and/or
[12]
extracranial disease progression . The short period of remission after neuro-mimicry and individualized
tumor targets has been attributed to the initiation, propagation and differentiation of cancer stem cells
[13]
[14]
(CSCs) .

The CSC concept proposes that cancer is caused by CSCs that possess the ability for uncontrolled
growth and propagation . CSCs have been demonstrated in many types of cancer including breast
[15]
[17]
[16]
carcinoma , glioblastoma and oral cavity squamous cell carcinoma (OCSCC) [18-20] . We have recently
identified and characterized three CSC subpopulations within MM to the brain: a Melan-A subpopulation
+
-
and a Melan-A subpopulations that express embryonic stem cell (ESC) markers OCT4, SALL4, SOX2
and NANOG within the tumor, and a pSTAT3 subpopulation localized to the CD34 endothelium of
+
+
[21]
microvessels within the tumor .
[22]
The RAS has been linked to carcinogenesis for some time . In the classical RAS, angiotensinogen (ANG)
is converted to angiotensin I (ATI) by renin. ATI is then converted to angiotensin II (ATII) by angiotensin
converting enzyme (ACE). The RAS is implicated in central nervous system disorders such as Parkinson’s
disease and dementia with neuroprotective and neurotoxic features although its role in carcinogenesis is
[23]
not discussed in a recent review . GB cells in culture express ANG, pro-renin, ACE, ATII, angiotensin
II receptor 1 (ATIIR1) and angiotensin II receptor 2 (ATIIR2); and renin inhibitors decrease DNA
[24]
synthesis, induce apoptosis and reduce viable cell numbers . Renin and its precursor pro-renin bind
to pro-renin receptor (PRR) to activate the MAPK signaling cascades. PRR is associated with increased
[25]
cell proliferation, decreased apoptosis and highly expressed in pancreatic ductal adenocarcinoma . CSC
[26]
subpopulations in GB and OCSCC of different subsites [27-29] express components of RAS.