Cancer Metastasis and Treatment Resistance: Mechanistic Insights and Therapeutic Targeting of Cancer Stem Cells and the Tumor Microenvironment.

Cancer metastasis and treatment resistance are the main causes of treatment failure and cancer-related deaths. Their underlying mechanisms remain to be fully elucidated and have been attributed to the presence of cancer stem cells (CSCs)-a small population of highly tumorigenic cancer cells with pluripotency and self-renewal properties, at the apex of a cellular hierarchy. CSCs drive metastasis and treatment resistance and are sustained by a dynamic tumor microenvironment (TME). Numerous pathways mediate communication between CSCs and/or the surrounding TME. These include a paracrine renin-angiotensin system and its convergent signaling pathways, the immune system, and other signaling pathways including the Notch, Wnt/ß-catenin, and Sonic Hedgehog pathways. Appreciation of the mechanisms underlying metastasis and treatment resistance, and the pathways that regulate CSCs and the TME, is essential for developing a durable treatment for cancer. Pre-clinical and clinical studies exploring single-point modulation of the pathways regulating CSCs and the surrounding TME, have yielded partial and sometimes negative results. This may be explained by the presence of uninhibited alternative signaling pathways. An effective treatment of cancer may require a multi-target strategy with multi-step inhibition of signaling pathways that regulate CSCs and the TME, in lieu of the long-standing pursuit of a 'silver-bullet' single-target approach.

Insights Into Vascular Anomalies, Cancer, and Fibroproliferative Conditions: The Role of Stem Cells and the Renin-Angiotensin System.

Cells exhibiting embryonic stem cell (ESC) characteristics have been demonstrated in vascular anomalies (VAs), cancer, and fibroproliferative conditions, which are commonly managed by plastic surgeons and remain largely unsolved. The efficacy of the mTOR inhibitor sirolimus, and targeted therapies that block the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways in many types of cancer and VAs, further supports the critical role of ESC-like cells in the pathogenesis of these conditions. ESC-like cells in VAs, cancer, and fibroproliferative conditions express components of the renin-angiotensin system (RAS) - a homeostatic endocrine signaling cascade that regulates cells with ESC characteristics. ESC-like cells are influenced by the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways, which directly regulate cellular proliferation and stemness, and interact with the RAS at multiple points. Gain-of-function mutations affecting these pathways have been identified in many types of cancer and VAs, that have been treated with targeted therapies with some success. In cancer, the RAS promotes tumor progression, treatment resistance, recurrence, and metastasis. The RAS modulates cellular invasion, migration, proliferation, and angiogenesis. It also indirectly regulates ESC-like cells via its direct influence on the tissue microenvironment and by its interaction with the immune system. In vitro studies show that RAS inhibition suppresses the hallmarks of cancer in different experimental models. Numerous epidemiological studies show a reduced incidence of cancer and improved survival outcomes in patients taking RAS inhibitors, although some studies have shown no such effect. The discovery of ESC-like cells that express RAS components in infantile hemangioma (IH) underscores the paradigm shift in the understanding of its programmed biologic behavior and accelerated involution induced by ß-blockers and angiotensin-converting enzyme inhibitors. The findings of SOX18 inhibition by R-propranolol suggests the possibility of targeting ESC-like cells in IH without ß-adrenergic blockade, and its associated side effects. This article provides an overview of the current knowledge of ESC-like cells and the RAS in VAs, cancer, and fibroproliferative conditions. It also highlights new lines of research and potential novel therapeutic approaches for these unsolved problems in plastic surgery, by targeting the ESC-like cells through manipulation of the RAS, its bypass loops and converging signaling pathways using existing low-cost, commonly available, and safe oral medications.

Image-guided transthoracic transpedicular microdiscectomy for a giant thoracic disc herniation: patient series.

BACKGROUND: This case series reports on five consecutive patients who underwent image-guided transpedicular transthoracic microdiscectomy. The authors retrospectively reviewed five patients who had undergone Stealth image-guided transpedicular transthoracic microdiscectomy between 2015 and 2021. OBSERVATIONS: Image guidance with O-arm verified critical anatomical landmarks in the setting of large central calcified and/or soft tissue disc prolapse. This allowed limited rib head resection, pedicle removal, and corpectomy to give adequate access and not require interbody fusion. The authors performed a partial posterior corpectomy anterior to the affected disc prolapse and microsurgical delivery of the affected disc anteriorly into the corpectomy cave away from the thecal sac. Electronic and radiographic records were analyzed at their initial presentation and at follow-up. The median patient age was 51 years (range, 44-56 years), with 80% of the patients being males. Four of five patients had significant improvement of their presenting clinical symptoms. One patient had a complicated postoperative recovery with a pneumothorax and subsequent bilateral pneumonia requiring intensive care. Another patient developed delayed postoperative worsening of paraparesis. LESSONS: The use of Stealth image guidance with O-arm for transthoracic microdiscectomy for complex calcified thoracic disc herniation is an effective operative technical adjunct to verify anatomical landmarks and limit the microsurgical procedure.

Cell Populations Expressing Stemness-Associated Markers in Lung Adenocarcinoma.

The stemness-associated markers OCT4, NANOG, SOX2, KLF4 and c-MYC are expressed in numerous cancer types suggesting the presence of cancer stem cells (CSCs). Immunohistochemical (IHC) staining performed on 12 lung adenocarcinoma (LA) tissue samples showed protein expression of OCT4, NANOG, SOX2, KLF4 and c-MYC, and the CSC marker CD44. In situ hybridization (ISH) performed on six of the LA tissue samples showed mRNA expression of OCT4, NANOG, SOX2, KLF4 and c-MYC. Immunofluorescence staining performed on three of the tissue samples showed co-expression of OCT4 and c-MYC with NANOG, SOX2 and KLF4 by tumor gland cells, and expression of OCT4 and c-MYC exclusively by cells within the stroma. RT-qPCR performed on five LA-derived primary cell lines showed mRNA expression of all the markers except SOX2. Western blotting performed on four LA-derived primary cell lines demonstrated protein expression of all the markers except SOX2 and NANOG. Initial tumorsphere assays performed on four LA-derived primary cell lines demonstrated 0-80% of tumorspheres surpassing the 50 µm threshold. The expression of the stemness-associated markers OCT4, SOX2, NANOG, KFL4 and c-MYC by LA at the mRNA and protein level, and the unique expression patterns suggest a putative presence of CSC subpopulations within LA, which may be a novel therapeutic target for this cancer. Further functional studies are required to investigate the possession of stemness traits.

The renin-angiotensin system in central nervous system tumors and degenerative diseases.

Despite their differences, central nervous system (CNS) tumors and degenerative diseases share important molecular mechanisms underlying their pathologies, due to their common anatomy. Here we review the role of the renin-angiotensin system (RAS) in CNS tumors and degenerative diseases, to highlight common molecular features and examine the potential merits in repurposing drugs that inhibit the RAS, its bypass loops, and converging signaling pathways. The RAS consists of key components, including angiotensinogen, (pro)renin receptor (PRR), angiotensin-converting enzyme 1 (ACE1), angiotensin-converting enzyme 2 (ACE2), angiotensin I (ATI), angiotensin II (ATII), ATII receptor 1 (AT1R), ATII receptor 2 (AT2R) and the Mas receptor (MasR). The RAS is integral to systemic and cellular pathways that regulate blood pressure and body fluid equilibrium and cellular homeostasis. The main effector of the RAS is ATII which exerts its effect by binding to AT1R and AT2R through two competitive arms: an ACE1/ATII/AT1R axis, which is involved in regulating oxidative stress and neuroinflammation pathways, and an ATII/AT2R and/or ATII/ACE2/Ang(1-7)/MasR axis that potentiates neuroprotection pathways. Alterations of these axes are associated with cellular dysfunction linked to CNS diseases. The generation of ATII is also influenced by proteases that constitute bypass loops of the RAS. These bypass loops include cathepsins B, D and G and chymase and aminopeptidases. The RAS is also influenced by converging pathways such as the Wnt/ß-catenin pathway which sits upstream of the RAS via PRR, a key component of the RAS. We also discuss the co-expression of components of the RAS and markers of pluripotency, such as OCT4 and SOX2, in Parkinson's disease and glioblastoma, and their potential influences on transduction pathways involving the Wnt/ß-catenin, MAPK/ERK, PI3K/AKT and vacuolar (H+) adenosine triphosphatase (V-ATPase) signaling cascades. Further research investigating modulation of the ACE1/ATII/AT1R and ACE2/Ang(1-7)/MasR axes with RAS inhibitors may lead to novel treatment of CNS tumors and degenerative diseases. The aim of this review article is to discuss and highlight experimental and epidemiological evidence for the role of the RAS, its bypass loops and convergent signaling pathways in the pathogenesis of CNS tumors and degenerative diseases, to direct research that may lead to the development of novel therapy.

The Renin-Angiotensin System in the Tumor Microenvironment of Glioblastoma.

Glioblastoma (GB) is an aggressive primary brain tumor. Despite intensive research over the past 50 years, little advance has been made to improve the poor outcome, with an overall median survival of 14.6 months following standard treatment. Local recurrence is inevitable due to the quiescent cancer stem cells (CSCs) in GB that co-express stemness-associated markers and components of the renin-angiotensin system (RAS). The dynamic and heterogeneous tumor microenvironment (TME) plays a fundamental role in tumor development, progression, invasiveness, and therapy resistance. There is increasing evidence showing the critical role of the RAS in the TME influencing CSCs via its upstream and downstream pathways. Drugs that alter the hallmarks of cancer by modulating the RAS present a potential new therapeutic alternative or adjunct to conventional treatment of GB. Cerebral and GB organoids may offer a cost-effective method for evaluating the efficacy of RAS-modulating drugs on GB. We review the nexus between the GB TME, CSC niche, and the RAS, and propose re-purposed RAS-modulating drugs as a potential therapeutic alternative or adjunct to current standard therapy for GB.

The Role of the Renin-Angiotensin System in the Cancer Stem Cell Niche.

Cancer stem cells (CSCs) drive metastasis, treatment resistance, and tumor recurrence. CSCs reside within a niche, an anatomically distinct site within the tumor microenvironment (TME) that consists of malignant and non-malignant cells, including immune cells. The renin-angiotensin system (RAS), a critical regulator of stem cells and key developmental processes, plays a vital role in the TME. Non-malignant cells within the CSC niche and stem cell signaling pathways such as the Wnt, Hedgehog, and Notch pathways influence CSCs. Components of the RAS and cathepsins B and D that constitute bypass loops of the RAS are expressed on CSCs in many cancer types. There is extensive in vitro and in vivo evidence showing that RAS inhibition reduces tumor growth, cell proliferation, invasion, and metastasis. However, there is inconsistent epidemiological data on the effect of RAS inhibitors on cancer incidence and survival outcomes, attributed to different patient characteristics and methodologies used between studies. Further mechanistic studies are warranted to investigate the precise effects of the RAS on CSCs directly and/or the CSC niche. Targeting the RAS, its bypass loops, and convergent signaling pathways participating in the TME and other key stem cell pathways that regulate CSCs may be a novel approach to cancer treatment.

Embryonic stem cell-like subpopulations are present within Schwannoma.

BACKGROUND: There is accumulating evidence of the presence of embryonic stem cell (ESC)-like cells in benign tumors. AIM: This study aimed to identify ESC-like cells in Schwannoma using the induced-pluripotent stem cell (iPSC) markers OCT4, SOX2, NANOG, KLF4 and c-MYC. METHODS: Immunohistochemical (IHC) staining (n = 20) and RT-qPCR (n = 6) were performed on Schwannoma tissue samples (STS) to investigate protein and mRNA expression of these iPSC markers, respectively. Immunofluorescence (IF) staining was performed to investigate co-localization of the iPSC markers with CD34, α-SMA and CD133. RESULTS: IHC staining and RT-qPCR demonstrated protein and mRNA expression of all five iPSC markers, respectively. IF staining showed expression of SOX2, KLF4 and c-MYC on the tumor cells and the endothelium of the tumor microvessels which also expressed OCT4, while NANOG was exclusively expressed on the endothelium of the tumor microvessels. The OCT4+/CD34+ endothelium expressed CD133. CONCLUSION: We have identified a putative OCT4+/SOX2+/NANOG+/KLF4+/c-MYC+/CD133+ ESC-like subpopulation on the endothelium of tumor microvessels and an OCT4-/SOX2+/NANOG-/KLF4+/c-MYC+/CD133+ ESC-like subpopulation, within Schwannoma.

Cancer Stem Cell Subpopulations Are Present Within Metastatic Head and Neck Cutaneous Squamous Cell Carcinoma.

Cancer stem cells (CSCs) have been identified in many cancer types including primary head and neck cutaneous squamous cell carcinoma (HNcSCC). This study aimed to identify and characterize CSCs in metastatic HNcSCC (mHNcSCC). Immunohistochemical staining performed on mHNcSCC samples from 15 patients demonstrated expression of the induced pluripotent stem cell (iPSC) markers OCT4, SOX2, NANOG, KLF4, and c-MYC in all 15 samples. In situ hybridization and RT-qPCR performed on four of these mHNcSCC tissue samples confirmed transcript expression of all five iPSC markers. Immunofluorescence staining performed on three of these mHNcSCC samples demonstrated expression of c-MYC on cells within the tumor nests (TNs) and the peri-tumoral stroma (PTS) that also expressed KLF4. OCT4 was expressed on the SOX2+/NANOG+/KLF4+ cells within the TNs, and the SOX2+/NANOG+/KLF4+ cells within the PTS. RT-qPCR demonstrated transcript expression of all five iPSC markers in all three mHNcSCC-derived primary cell lines, except for SOX2 in one cell line. Western blotting showed the presence of SOX2, KLF4, and c-MYC but not OCT4 and NANOG in the three mHNcSCC-derived primary cell lines. All three cell lines formed tumorspheres, at the first passage. We demonstrated an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ CSC subpopulation and an OCT4+/NANOG-/SOX2+/KLF4+/c-MYC+ subpopulation within the TNs, and an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ subpopulation within the PTS of mHNcSCC.

Cell Populations Expressing Stemness-Associated Markers in Vascular Anomalies.

Treatment of vascular anomalies (VAs) is mostly empirical and, in many instances unsatisfactory, as the pathogeneses of these heterogeneous conditions remain largely unknown. There is emerging evidence of the presence of cell populations expressing stemness-associated markers within many types of vascular tumors and vascular malformations. The presence of these populations in VAs is supported, in part, by the observed clinical effect of the mTOR inhibitor, sirolimus, that regulates differentiation of embryonic stem cells (ESCs). The discovery of the central role of the renin-angiotensin system (RAS) in regulating stem cells in infantile hemangioma (IH) provides a plausible explanation for its spontaneous and accelerated involution induced by ß-blockers and ACE inhibitors. Recent work on targeting IH stem cells by inhibiting the transcription factor SOX18 using the stereoisomer R(+) propranolol, independent of ß-adrenergic blockade, opens up exciting opportunities for novel treatment of IH without the ß-adrenergic blockade-related side effects. Gene mutations have been identified in several VAs, involving mainly the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways. Existing cancer therapies that target these pathways engenders the exciting possibility of repurposing these agents for challenging VAs, with early results demonstrating clinical efficacy. However, there are several shortcomings with this approach, including the treatment cost, side effects, emergence of treatment resistance and unknown long-term effects in young patients. The presence of populations expressing stemness-associated markers, including transcription factors involved in the generation of induced pluripotent stem cells (iPSCs), in different types of VAs, suggests the possible role of stem cell pathways in their pathogenesis. Components of the RAS are expressed by cell populations expressing stemness-associated markers in different types of VAs. The gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways interact with different components of the RAS, which may influence cell populations expressing stemness-associated markers within VAs. The potential of targeting these populations by manipulating the RAS using repurposed, low-cost and commonly available oral medications, warrants further investigation. This review presents the accumulating evidence demonstrating the presence of stemness-associated markers in VAs, their expression of the RAS, and their interaction with gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways, in the pathogenesis of VAs.

Keloid-associated lymphoid tissues in keloid lesions express vitamin D receptor.

Objectives: Vitamin D receptor (VDR) may play a role in keloid disorder. This study investigated the expression of VDR by the embryonic stem cell (ESC)-like population within keloid-associated lymphoid tissues (KALTs) which expresses components of the renin-angiotensin system (RAS). Methods: 11 formalin-fixed paraffin-embedded sections of keloid lesions (KLs) underwent 3,3-diaminobenzidine (DAB) immunohistochemical (IHC) staining for VDR. Immunofluorescence (IF) dual IHC staining of CD34/VDR and OCT4/VDR was performed on two representative KLs. Transcriptional activation of VDR was investigated in four representative snap-frozen KLs using reverse-transcriptase-quantitative polymerase chain reaction (RT-qPCR). Results: DAB IHC staining demonstrated the presence of VDR on the KALTs within the keloid tissue samples. RT-qPCR confirmed transcriptional activation of VDR. IF IHC staining demonstrated expression of VDR on the CD34+ and the OCT4+ endothelium of the microvessels, and the OCT4+ perivascular cells, within the KALTs. Conclusions: This study demonstrated the expression of VDR by the ESC-like population within the KALTs in KLs. Further work is needed to elucidate the precise interaction between VDR and the RAS in regulating the primitive population within the KALTs.

The Role of the Renin-Angiotensin System and Vitamin D in Keloid Disorder-A Review.

Keloid disorder (KD) is a fibroproliferative condition characterized by excessive dermal collagen deposition in response to wounding and/or inflammation of the skin. Despite intensive research, treatment for KD remains empirical and unsatisfactory. Activation of the renin-angiotensin system (RAS) leads to fibrosis in various organs through its direct effect and the resultant hypertension, and activation of the immune system. The observation of an increased incidence of KD in dark-skinned individuals who are predisposed to vitamin D deficiency (VDD) and hypertension, and the association of KD with hypertension and VDD, all of which are associated with an elevated activity of the RAS, provides clues to the pathogenesis of KD. There is increasing evidence implicating embryonic-like stem (ESC) cells that express ESC markers within keloid-associated lymphoid tissues (KALTs) in keloid lesions. These primitive cells express components of the RAS, cathepsins B, D, and G that constitute bypass loops of the RAS, and vitamin D receptor (VDR). This suggests that the RAS directly, and through signaling pathways that converge on the RAS, including VDR-mediated mechanisms and the immune system, may play a critical role in regulating the primitive population within the KALTs. This review discusses the role of the RAS, its relationship with hypertension, vitamin D, VDR, VDD, and the immune system that provide a microenvironmental niche in regulating the ESC-like cells within the KALTs. These ESC-like cells may be a novel therapeutic target for the treatment of this enigmatic and challenging condition, by modulating the RAS using inhibitors of the RAS and its bypass loops and convergent signaling pathways.