{"id":62694,"date":"2024-12-30T11:34:10","date_gmt":"2024-12-30T11:34:10","guid":{"rendered":"https:\/\/biomedpharmajournal.org\/?p=62694"},"modified":"2025-01-06T18:16:45","modified_gmt":"2025-01-06T18:16:45","slug":"targeting-the-tumor-microenvironment-in-osteosarcoma-a-pathway-to-overcome-therapeutic-resistance","status":"publish","type":"post","link":"https:\/\/biomedpharmajournal.org\/staging\/vol17no4\/targeting-the-tumor-microenvironment-in-osteosarcoma-a-pathway-to-overcome-therapeutic-resistance\/","title":{"rendered":"Targeting the Tumor Microenvironment in Osteosarcoma: A Pathway to Overcome Therapeutic Resistance"},"content":{"rendered":"\n

Introduction<\/strong><\/p>\n\n\n\n

Around\n9.8 million fatalities worldwide are attributed to cancer, making it the second\nmost common cause of death for both men and women1<\/sup>. Osteosarcoma (OS) is a\nrelatively rare tumor of bone with a worldwide incidence of 3.4 cases per\nmillion people per year. For most of the 20th<\/sup> century, 5-year\nsurvival rates of 56.31% for classic OS were very low2<\/sup>.This cancer\ntype accounts for approximately 2.4% of all childhood malignancies, with the\nhighest incidence occurring between the ages of 10 and 30. In\ncomparison to the White population, OS is more common in African Americans,\nAsian\/Pacific Islanders, and Hispanics and has a small male predominance. While\nthe precise aetiology of osteosarcoma remains unclear, certain epidemiological\nrisk factors have been associated with an increased likelihood of contracting\nthe illness. Notably, an elevated incidence of osteosarcoma has been associated\nwith Li-Fraumeni syndrome, Rothmund-Tompson syndrome, hereditary\nretinoblastoma, and Bloom and Werner syndrome. Osteosarcoma is the most prevalent, primary\nmalignant bone pathology and is known for its aggressive nature. Particularly\nin older populations, other predisposing factors such fibrous dysplasia,\nPaget’s disease of the bone, and radiation exposure are also associated with an\nelevated risk 3,4<\/sup>. It’s interesting to note that, compared to the\ngeneral population, osteosarcoma is more commonly recorded in taller people 5<\/sup>.\nThere are several subtypes of osteosarcoma, the majority of which are\nhigh-grade and have aggressive biological behaviour 6<\/sup>. Results are\nstill not ideal despite advancements in OS treatment 7<\/sup>. In recent\ndecades, our understanding of cancer has significantly evolved. Cancer is now\nrecognized not merely as a genetic disease but as a complex ecosystem\ncomprising various non-cancerous cells and their extensive interactions within\nthe tumor. While genetic alterations are critical in cancer development and\nmetastasis, they alone are insufficient for the full progression of the\ndisease. The tumor microenvironment (TME) is a highly organized ecosystem where\ncancer cells are surrounded by diverse non-malignant cell types within a\nremodeled, vascularized extracellular matrix. This illustrates the intricate\ncomplexity of cancer that can be revealed by microscopic analysis of solid\ntumours. The TME is composed of numerous cell types, including neurones,\nadipocytes, immunological cells, endothelial cells (ECs), and cancer-associated\nfibroblasts (CAFs) (Table 1). Initially, host cells within the tumor\nmicroenvironment (TME) were considered passive observers of malignancy.\nHowever, mechanistic studies, particularly in preclinical tumor models, now\nsuggest that TME cells and the substances they secrete play crucial roles in\ncancer development, offering promising therapeutic targets8<\/sup>. The\ncellular makeup and functional condition of the TME will be influenced by the\norgan from which the tumour originates, the inherent traits of cancer cells,\nthe tumor’s stage, and the patient’s features. Different cells within the TME\ncan either be tumour supportive or tumour suppressing.  Osteosarcoma progression, metastasis,\nangiogenesis, hypoxia-induced resistance, and treatment resistance are all\nsignificantly influenced by the tumour microenvironment (TME). The TME is made\nup of many cell types that interact intricately with cancer cells, such as\nimmune cells, fibroblasts, endothelial cells, and components of the\nextracellular matrix. These interactions present a number of difficulties for\nexisting treatments, including radiation, chemotherapy, and newer forms of therapy\nlike immunotherapy. Due to its role in drug resistance, immunosuppression, and\ntumour heterogeneity, the TME presents serious treatment-related problems. For\nthe purpose of creating novel treatment approaches, such as combination\ntherapies that target both the tumour cells and the surrounding\nmicroenvironment, a deeper comprehension of the TME’s function in cancer\nbiology is vital. Getting beyond these obstacles will be essential to enhancing\ntreatment results and stopping the spread of cancer. This review examines\nstrategies to target the tumor microenvironment (TME) in osteosarcoma to\novercome therapeutic resistance and enhance treatment efficacy. The TME\ncomprising immune cells, blood vessels, fibroblasts, and metabolic factors\nsupports tumor growth and resistance to therapy. By focusing on approaches like\nimmune checkpoint inhibitors, anti-angiogenic agents, fibroblast disruptors,\nand exosome-based delivery, this review outlines a multi-faceted approach to\nimprove osteosarcoma treatment outcomes. Hence proved, previous studies\ntargeting the tumor microenvironment (TME) in osteosarcoma have shown promising\nresults. Immune checkpoint inhibitors like anti-PD-1 have enhanced immune\nresponses , while anti-angiogenic agents (e.g., bevacizumab) and  multi-kinase inhibitors (e.g., sorafenib)\nhave reduced tumor vascularization . Drugs targeting cancer-associated\nfibroblasts, like trabectedin, have improved chemotherapy sensitivity.\nAdditionally, hypoxia-activated drugs and exosome inhibitors have helped  reduce metastasis and increase drug delivery\nprecision. This review seeks to explore the relationships between osteosarcoma\ncells and the TME that lead to cancer growth, metastasis, and treatment failure\nin addition to identifying promising therapeutic targets and innovative\nstrategies to improve treatment outcomes9<\/sup>.<\/p>\n\n\n\n

Table 1: Major cellular and non-cellular components of the TME ( Original )<\/strong><\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\n

Type of Cell<\/strong><\/p>\n<\/td>\n

\n

TME Function<\/strong><\/p>\n<\/td>\n

\n

Ref<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Adaptive immune cells<\/em><\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

CD4+<\/sup>\u00a0T\u00a0cells<\/p>\n<\/td>\n

\n

CD4+ helper T cells primarily influence CD8+ T cell responses and other immune cells. In cancer, CD4+ T cells play dual roles: The subtype exhibits anti-tumor activity by producing IFN\u03b3 and TNF-\u03b1, directly killing cancer cells and supporting CD8+ T cells and B cells, while the the subtype secretes pro-tumoral and anti-inflammatory mediators. Emerging evidence suggests that CD4+ T cells are crucial for the effectiveness of Immune Checkpoint Blockade (ICB).<\/p>\n<\/td>\n

\n

10<\/p>\n<\/td>\n<\/tr>\n

\n

CD8+<\/sup>\u00a0T\u00a0cells<\/p>\n<\/td>\n

\n

CD8+ T cells are key effectors in tumor immune response, recognizing cancer cells via TCR binding to MHC-peptide complexes. After engagement, they induce apoptosis through granzyme, perforin, or FASL-FAS pathways. In tumors, CD8+ T cells often appear exhausted or dysfunctional. Immune checkpoint inhibition aims to reactivate these CD8+ T cells to fight cancer.<\/p>\n<\/td>\n

\n

11<\/p>\n<\/td>\n<\/tr>\n

\n

Myeloid immune cells<\/em><\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Macrophages<\/p>\n<\/td>\n

\n

Tumor-Associated Macrophages (TAMs) are versatile, with both pro- and anti-tumorigenic roles. Derived from bone marrow or yolk sac, TAMs exist in various subtypes within tumors. While they can directly phagocytose cancer cells and stimulate anti-tumor immunity, TAMs also promote angiogenesis, immunosuppression, metastasis, and treatment resistance.<\/p>\n<\/td>\n

\n

12<\/p>\n<\/td>\n<\/tr>\n

\n

Immune cells bridging the gap between innate and adaptive immunity<\/em><\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

NK cells<\/p>\n<\/td>\n

\n

Natural Killer (NK) cells are cytotoxic innate lymphoid cells that detect and destroy stressed cells lacking MHC class I. Higher levels of circulating and intratumoral NK cells are associated with better cancer survival. While NK cells have strong anti-tumor activity, tumors evade them through immune-suppressive myeloid cells, Tregs, and inhibitory receptor overexpression. NK cell-based therapies or activation of endogenous NK cells are emerging as promising immunotherapeutic strategies.<\/p>\n<\/td>\n

\n

13<\/p>\n<\/td>\n<\/tr>\n

\n

Stromal cells and matrix<\/em><\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Cancer-associated fibroblasts<\/p>\n<\/td>\n

\n

Cancer-associated fibroblasts (CAFs) are key components of the tumor stroma, consisting of diverse, functionally flexible subtypes. In the tumor microenvironment (TME), CAFs play complex roles, synthesizing and remodeling the ECM, affecting its mechanical properties and influencing cancer cell behavior. They promote angiogenesis, modulate the immune response, and aid in immune evasion by tumors.<\/p>\n<\/td>\n

\n

14<\/p>\n<\/td>\n<\/tr>\n

\n

Vascular cells<\/em><\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Blood vascular endothelial cells<\/p>\n<\/td>\n

\n

Endothelial cells (ECs) line all blood vessels, but tumor ECs differ from normal ones. Tumor ECs are highly diverse, with reduced adhesion molecules that weaken barrier function and increased inhibitory immune checkpoint molecules, promoting immunosuppression. They regulate fluid, oxygen, protein, and cell flow in the tumor environment.<\/p>\n<\/td>\n

\n

15<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u00a0<\/p>\n\n\n

Materials and Methods<\/strong><\/p>\n\n\n\n

A\ncomprehensive literature search was conducted using PubMed, Scopus, and Web of\nScience to identify peer-reviewed articles on targeting the tumor\nmicroenvironment (TME) in osteosarcoma. Included studies were preclinical and\nclinical research addressing TME-related therapeutic resistance mechanisms or\ntherapies targeting TME components, such as immune cells, cytokines, or the\nextracellular matrix. Articles on other cancers, studies with inadequate data,\nor review articles lacking original evidence were excluded. Key findings were categorised by TME\ncomponents, such as immune suppression, angiogenesis, and ECM remodelling, and\ntheir effects on treatment outcomes were examined by data synthesis.<\/p>\n\n\n\n

Components of the Tumor Microenvironment in\nOsteosarcoma<\/strong><\/p>\n\n\n\n

Cancer-Associated Fibroblasts (CAFs)<\/strong><\/p>\n\n\n\n

Cancer-associated fibroblasts (CAFs) have a variety of protumorigenic roles in the tumour microenvironment. Clinical translation of these preclinical findings which point to the possibility of reducing, eliminating, or reprogramming CAFs has not yet taken place. Undoubtedly, a deeper comprehension of these cells and their roles will enhance cancer therapies. Nearly every organ and healthy tissue contains fibroblasts, which aid in wound healing by promoting fibrosis and inflammation. CAFs are mesenchymal-lineage activated fibroblasts linked to cancer that promote inflammation and fibrosis around tumours. The lack of lineage markers for haematopoietic, endothelial, and epithelial cells, as well as their shape and correlation with cancer cells, characterize CAFs 14<\/sup>. In addition to playing important roles in immune modulation, angiogenesis, and extracellular matrix remodelling of the tumour, CAFs also generate and maintain cancer stem cells, which in turn promotes therapy resistance. Numerous cell progenitors, which can differ between tissues, can give rise to CAFs. Not all CAFs have their origins clearly and completely explained. Although the CAF phenotype differs within and between tumour types, the change to CAF, regardless of its cause, is almost invariably irreversible.Although they can also evolve into CAFs, mesenchymal stromal cells, also known as mesenchymal stem cells, are mostly derived from local resident fibroblast populations.MSCs can differentiate into osteoblasts, chondrocytes, and adipocytes and display a similar, less abundant set of surface markers 16<\/sup>. CAFs and resting fibroblasts from normal tissues differ significantly in a few key ways. CAFs have a spindle-shaped morphology, branching cytoplasm, and indented nuclei. Often, they are bigger than fibroblasts that are at rest. This, however, is the main functional distinction between the two. The ability of CAFs to secrete, migrate, and proliferate has enhanced. CAFs produce more extracellular matrix components, such as tenascin, periostin (POSTN), and secreted protein rich in cysteine (SPARC), than untransformed fibroblasts because of their increased metabolic activity. Increased synthesis and frequently a more rigid and contractile pattern of collagen deposition are characteristics of aberrant collagen production by CAFs 17<\/sup>. Tumours are diverse ecosystems that vary in both function and geography.The variety of origins that might give rise to CAFs complicates their phenotypic, gene expression, and functions. While numerous investigations have also looked at these cells in other human tumour types, the majority of research on different CAF subpopulations at the single cell level has been carried out in the context of pancreatic cancer in humans.  In human pancreatic cancer, the expression of \u03b1-SMA and IL-6 defines at least two primary CAF phenotypes, which are examples of some of these classes. iCAFs, a myofibroblastic Cancer \u2013 Associated Fibroblasts (myCAF) population with low \u03b1-SMA expression and high levels of IL-6 and IL-11 secretion, are more inflammatory in nature, matrix-secreting, TGF-\u03b2 sensitive, high in \u03b1-SMA and low in cytokines (e.g.,IL-6,IL-11)18<\/sup>.<\/p>\n\n\n\n

Immune Cells<\/strong><\/p>\n\n\n\n

Myeloid-derived\nsuppressor cells (MDSCs), T-regulatory cells (Tregs), and tumor-associated\nmacrophages (TAMs) collaborate to produce an immunosuppressive tumour\nmicroenvironment (TME) that aids in the survival and dissemination of cancer.\nTAMs secrete cytokines, like IL-10 and TGF-\u03b2, that promote Treg growth, inhibit\nT cell activity, and contribute in the growth of tumours. By secreting immunosuppressive\ncytokines, consuming IL-2, and blocking effector T cells with the help of\nmolecules like CTLA-4, tregs impair anti-tumor immune responses. By generating\nreactive oxygen species, consuming less essential nutrients, and upregulating\nimmunological checkpoints such as PD-L1, MDSCs further inhibit T cell activity.\nCollectively, these cells facilitate tumour immune evasion, reduce the immune\nresponse, and increase resistance to treatments like chemotherapy and\nimmunotherapy 19<\/sup>.<\/p>\n\n\n\n

Extracellular Matrix (ECM)<\/strong><\/p>\n\n\n\n

The\nextracellular matrix (ECM) facilitates the motility, invasion, and metastasis\nof osteosarcoma cells by providing structural support and biochemical cues that\nstimulate cancer growth. Extracellular matrix (ECM) compositional changes and\nremodelling enzymes, such as matrix metalloproteinases (MMPs), degrade the ECM\nin osteosarcoma, allowing cancer cells to proliferate. In addition, the ECM\nstimulates signalling pathways that enhance cell invasion, motility, and\nsurvival through interactions with integrins and other cell surface\nreceptors.  Furthermore, the\nextracellular matrix (ECM) hardens and rearranges to promote cancer cell\ninfiltration into neighbouring tissues, permitting metastasis to far-off organs\nlike the lungs. The aggressiveness and treatment resistance of osteosarcoma are\ninfluenced by these ECM alterations20<\/sup>.<\/p>\n\n\n\n

Hypoxia and Its Impact on Osteosarcoma\nProgression<\/strong><\/p>\n\n\n\n

One histological feature that is\nfrequently observed on biopsies is that bone cancer is a highly necrotic tumour\neven at the time of diagnosis.The\nrapid and uncontrolled expanding proliferation of cancer cells, which are\nskilled at producing an aberrant neo angiogenesis 21<\/sup> and hypoxic\nmicroenvironment 22<\/sup>, may be the cause of this necrosis. OTS is\ndistinguished by the assessment of the necrotic rate upon surgical tumour\nresection following a neo adjuvant multi chemotherapy approach, in addition to\nthe discovery of tumour necrosis during biopsy. The endpoint of extreme\npersistent hypoxia is thought to be tumour necrosis. Because it induces\nhypoxia-related indicators, this necrosis can alter metabolic responses and\nexacerbate oxidative stress. On the other hand, hypoxia may also cause\napoptosis and necrosis to be inhibited during the course of cancer treatment\nand progression 23<\/sup>. Hypoxia has the ability to cause necrosis in the\ntumor’s core. Thus, the hypoxia-specific tumour microenvironment may be\nsignificant for the development, oncogenesis, and treatment of OTS.\nConsequently, in order to comprehend their function and determine their druggability\nin OTS, we attempt to unravel the normoxic\/hypoxic pathways in healthy tissues,\nbones, and osteosarcomas. <\/p>\n\n\n\n

Results<\/strong><\/p>\n\n\n\n

Hypoxic regions within the tumor microenvironment promote osteosarcoma survival and metastasis by inducing Hypoxia Inducible Factors (HIFs)<\/strong><\/p>\n\n\n\n

 The\nmarrow milieu surrounding bone contains growth factors, cytokines, blood\nsupplies, and tumor-supporting cells such as T cells, stromal cells, and\nmacrophages. In the growth and remodelling of the skeleton, osteoblasts and\nosteoclasts are essential. Two distinct processes intra membranous or\nendochondral ossification can result in the formation of bone. Flat bones are\nthe exclusive domain of the intra membranous bone development. It starts off as\nmesenchymal cells, which go on to become osteoblasts for the skull. It originates from a chondrocyte\nanlage, which is replaced by bones in other parts of the flat skeleton 24<\/sup>.Endochondral bone production occurs in\nthree stages, with physioxia and hypoxia playing crucial roles. In the first\nstage, mesenchymal cells condense and differentiate into chondrocytes, which\nultimately form growth plates. These chondrocytes proliferate significantly in\nthe growth plates, creating columnar layers.At the distal end of these layers,\ncells cease proliferation, exit the cell cycle, and develop into hypertrophic\nchondrocytes associated with mineralization.24,25<\/sup>.The growth plate itself is a specialized form\nof mesenchymal tissue containing hypoxic and avascular regions26<\/sup>.\nTo overcome this challenging environment, chondrocytes need to synthesise\nVEGF-A and produce HIF-1\u03b1 in order to initiate the angiogenic switch, which\npermits cartilage to be replaced by bone 25<\/sup>. The stabilisation of\nHIF-2\u03b1, which counteracts HIF-1\u03b1 activity, and the production of pVHL, which is\ncontrolled by HIF-1\u03b1, are connected to this overexpression 27<\/sup>. In\nactuality, throughout the endochondral process, the HIF signalling system is\ncrucial for controlling the vascular and osteoblastic niches. It is thought\nthat osteoblast activity, quantity, and bone formation are positively regulated\nby HIF-1\u03b1. It hastens bone macrophage senescence by encouraging non-oxidative\nglycolysis in osteoblasts and postponing osteoclastogenesis 25<\/sup>.\nThus, it may be inferred that HIF-1\u03b1 primarily influences osteoclast-mediated\nbone resorption while having minimal impact on osteoclast differentiation 28<\/sup>.\nTo give the macrophages adaptive support during bone resorption, it speeds up\nglycolytic and mitochondrial metabolism and upregulates the expression of\ncytokines that may regulate the process of differentiation 29,30<\/sup>. On\nthe other hand, HIF-2\u03b1 could be seen as a negative regulator of the formation\nof bone mass that influences the osteoblast lineage directly 25<\/sup>. Similarly, MIF (Macrophage Migration\nInhibitory Factor) appears to be p53-dependent in its regulation of HIF-1\u03b1\nactivity.The pathological\nhypoxia and physiological oxygen tension that arise during cancer processes may\npresent a favourable environment for the homing, initiation, and proliferation\nof tumour cells in the context of a hypoxic growth plate.  <\/p>\n\n\n\n

The role of hypoxia in mediating resistance to chemotherapy and radiotherapy<\/strong><\/p>\n\n\n\n

It\nseems that hypoxia plays a critical role in both local and remote OTS\nscenarios. As was already known, the local environment of growth plates, which\nis permissive to fluctuations in oxygen levels, is where osteosarcoma cells\noften develop. The onset and progression of osteosarcoma appear to be\ncorrelated with changes in the hypoxia biomarkers. Numerous studies have\ndemonstrated correlations between the poor prognosis of OTS and certain\nbiomarkers, such as mTOR, HIFs, or CA IX (Carbonic Anhydrase IX) 26-28<\/sup>.\nThey are emphasizing how hypoxia is the primary factor causing OTS cancer\ngrowth, treatment resistance, and propensity for metastasis. Using both tumour\ncollections and in vitro<\/em> or in vivo<\/em> preclinical models, it was\npossible to illustrate the concept of hypoxia in osteosarcomas through an\nexamination of the study materials. But the primary hypoxia-related marker\nassociated with OTS has been HIF-1\u03b1, which is often overexpressed in locally\naggressive and metastatic OTS 28<\/sup>. It is possible to explain the\nrelationship between the overexpression of GLUT-1 (Glucose Transporter 1), CA\nIX, or VEGF\/VEGFR and the overall enhancement of hypoxic pathways from the\nmembrane to the nucleus as well as the rise in intra-tumor microvessel density 29<\/sup>.\nAt that time, HIF-1\u03b1 was primarily identified as a key factor in the\nmodification of the tumour microenvironment. Although HIF-2\u03b1 has not received\nas much research as its homologues, it appears to have a role in OTS stemness\ncharacteristics promotion and apoptosis 30<\/sup>. Consequently, it was\ndiscovered that HIF-2\u03b1 was primarily a significant driver in OTS cells that\nexperienced a certain metabolic change. An OTS cell and cancer microenvironment\neffect was combined by mTOR, which was generally directly associated to\nautophagic processes and linked to Pi3K\/AKT upstream signalling induced by\ndistinct tyrosine kinase receptors 31<\/sup>. However, since hypoxia is\npresent from the beginning of OTS cells, it is still unclear, for example, how\nprecisely all those indicators interact during OTS progression and metastatic\npropension. While more research on OTS is required, it is now understood that\nthe sporadically involved hypoxia signalling pathways in various cancer types\ncan be explained by a balanced HIF-1\u03b1\/HIF-2\u03b1 and variations in both markers’\nexpression 19<\/sup>. Recent research has linked increased genomic\ninstability in cancer cells, particularly in osteosarcomas, to intra-tumor\nhypoxia. Osteosarcomas often display elevated levels of chromosomal breakage\nand chromothripsis, a phenomenon involving extensive chromosome rearrangement\nand fragmentation within the tumor.32<\/sup>. A poor prognosis is\nassociated with this genomic instability and complexity, which are often\naccompanied in these tumour types with a high dysregulation of microRNAs\nfollowing hypoxia. It has likely been demonstrated that miRNA-133a contributes\nto chromosomal dysregulation and the advancement of osteosarcoma in OTS 33<\/sup>.<\/p>\n\n\n\n

Interaction Between the Tumor\nMicroenvironment and Osteosarcoma Cells<\/strong><\/p>\n\n\n\n

The interaction between these cancer\ncells and the tumour microenvironment (TME) is essential for osteosarcoma\ngrowth, invasion, and treatment resistance.Pro-inflammatory cytokines, such IL-6 and IL-10, attract\ntumor-associated macrophages (TAMs) and T-regulatory cells (Tregs) into an\nimmunosuppressive environment and aid in immune evasion. Osteosarcoma cells\nrelease growth factors including VEGF and TGF-\u03b2, which promote angiogenesis and\ncancer survival. Furthermore, exosomes carrying proteins and microRNAs that\naffect stromal cells and encourage angiogenesis, metastasis, and ECM\nremodelling are released by osteosarcoma cells. Osteosarcoma cells and the TME\ninteract in a way that increases tumour aggressiveness and promotes treatment\nresistance 34<\/sup>. Tumour microenvironment (TME) composition and\nbehaviour are modified by osteosarcoma cells to facilitate tumour growth,\ninvasion, and resistance to treatment. In order to promote angiogenesis and\nguarantee a sufficient blood supply for oxygen and nourishment, they produce\ngrowth factors including VEGF and TGF-\u03b2. Additionally, the extracellular matrix\n(ECM) is broken down by matrix metalloproteinases (MMPs) secreted by\nosteosarcoma cells, which promotes cell migration and invasion of nearby\ntissues. They also produce cytokines like IL-6 and IL-10, which attract and\nactivate immune-suppressive cells, including T-regulatory cells (Tregs) and\ntumor-associated macrophages (TAMs), thereby reducing the tumor\u2019s ability to\nelicit an effective immune response. Osteosarcoma cells also communicate\nwith one another through exosomes, which carry proteins, microRNAs, and other\nsubstances that impact distant organs and surrounding stromal cells, promoting\nmetastasis and treatment resistance.Osteosarcoma cells modify the TME via these pathways in order to improve\ntheir chances of surviving, proliferating, and spreading 35<\/sup>.<\/p>\n\n\n\n

Influence of the Tumor Microenvironment on\nTherapeutic Resistance<\/strong><\/p>\n\n\n\n

TME contributes to chemotherapy and radiotherapy resistance in osteosarcoma<\/strong><\/p>\n\n\n\n

The TME is made up of different cell types (fibroblasts, endothelial cells, immune cells), extracellular elements (chemokines, cytokines, hormones, and extracellular matrix) that surround and are fed by the vasculature, and different physical and chemical elements (an acidic environment and hypoxia). The TME is necessary for metastasis, carcinogenesis, and tumour development. The tumour microenvironment (TME) has a major impact on the initiation and maintenance of cancer hallmarks, such as promoting angiogenesis, maintaining proliferative signalling, preventing cell death, and initiating invasion and metastasis 36<\/sup>. The effectiveness of treatment is also significantly impacted by the TME. The result of continuous interactions between the surrounding matrix and cancer cells is TME-reduced multidrug resistance. Compared to non-tumor cells in the TME, which are more genetically stable and responsive to stimulation, cancer cells are more likely to exhibit chemo resistance due to their genomic instability. The idea that efforts aimed at addressing TME elements or their signaling pathways could result in therapeutic breakthroughs for cancer patients is raised by the finding that cancer growth and treatment resistance are strongly associated with the TME. <\/p>\n\n\n\n

Hypoxic TME and chemoresistance in OS <\/strong><\/p>\n\n\n\n

Because of their hypermetabolism, aberrant\ngrowth, and excessive oxygen consumption, tumour cells usually exist in a\nhypoxic environment 37<\/sup>. There is now strong evidence linking\nhypoxia-inducible factors (HIFs) to medication resistance 38<\/sup>.\nNumerous genes involved in angiogenesis, glycolysis, and erythropoiesis can be\ninduced to express themselves during hypoxia by HIFs produced for hypoxic adaptation.\nThey can also bring back oxygen equilibrium through transcription and\nepigenetics 39<\/sup>. Hypoxia can, in fact, result in an acidic\nenvironment; the classic example of this is the Warburg effect, in which cancer\ncells favour using glycolysis as a fuel source. H+-ATPases, Na+-H+ exchangers,\nand HCO3-transporters are able to transfer the acidosis from an intracellular\nto an external environment 40<\/sup>.
\nMoreover, the rapid growth of tumour and their abnormal vascular patterns\naccelerate the build-up of acid, causing cancer cells to have an intracellular\npH greater than 7.4 and an exterior pH of 6.6-7.1. By contrast, normal cells\nhave an internal pH of 7.2 and an external pH of about 7.4 41<\/sup>.<\/p>\n\n\n\n

Tumor-associated macrophages modulate chemoresistance in OS <\/strong><\/p>\n\n\n\n

Important elements of the tumour microenvironment (TME), Tumor-Associated Macrophages (TAMs) typically exhibit tumor-suppressive characteristics and regulate treatment response. Rather than being founded in resident macrophages that proliferate within tumours, TAMs in solid tumours are rooted in circulating monocytes. Bone marrow monocytes have the ability to penetrate tumours through the bloodstream and then develop into macrophages. Type M1 and type M2 macrophages are distinguished by the degree of polarisation. M2 macrophages are activated by cytokines like interleukin (IL)-4, IL-10, and IL-13, whereas M1 macrophages are driven to differentiate by cytokines like interferon-gamma (IFNg) 42<\/sup>. In a similar vein, M1 macrophages are typically thought to combat cancer, but M2 macrophages aid in the development of cancer 43<\/sup>. As a matter of fact, the TME regulates TAM functional polarisation in a significant way 44<\/sup>. Drug resistance in OS mediated by angiogenesis. Angiogenesis is a hallmark of cancer and a highly adaptable process that is essential to tumour growth, metastasis, and medication resistance. Many processes, including blood vessel development, smooth muscle cell recruitment, endothelial cell migration, differentiation, and proliferation, are associated with angiogenesis 45<\/sup>. A malignant vascular network that is marked by dilated, convoluted, and hyperpermeable vessels can arise from tumours that exhibit an unbalanced balance between pro- and anti-angiogenic signals. This can lead to spatiotemporal heterogeneity in the oxygenation and blood flow of the tumour or an increase in the interstitial fluid pressure of the tumour 46<\/sup>. Furthermore, abnormal bone homeostasis can be brought on by dysregulation of angiogenic and angiocrine processes 47<\/sup>. The compromised effectiveness of chemotherapy, radiation, and immunotherapy is a clear indication of the physiological effects of these vascular anomalies and the milieu that follows, which promotes tumour growth 46<\/sup>. Apart from its involvement in acidity, hypoxia, and increased IFP in drug resistance, angiogenesis also limits the absorption of anticancer drugs due to the abnormal vascular architecture of OS 48<\/sup>. Anticancer drug distribution is uneven because chemotherapeutics must penetrate tumour tissues and blood vessel walls in order to destroy cancer cells. As a result, some target tumour cells that are close to tumour blood arteries are exposed to a potentially fatal dose of the cytotoxic chemical 49<\/sup>. As a result, the drug’s killing power is restricted. The role of CAFs and immune cells in mediating drug resistance through signaling pathways. Adhesion, growth, proliferation, motility, and survival of cells are all regulated by PI3K\/Akt, one of the most important intracellular signal transduction pathways 50<\/sup>. A growing body of research 51<\/sup> has demonstrated that human cancer, including OS, is associated with aberrant expression of PI3K\/Akt signalling pathway components. Immuno staining study has revealed a substantial and significant correlation between PI3K\/Akt signalling and a poor prognosis in primary OS cases 52<\/sup>. Moreover, Akt activity has a substantial correlation with lung metastasis. Several investigations have exhibited how aberrant expression of proteins might trigger the PI3K\/Akt signalling pathway, contributing to the pathogenesis of OS 53-57<\/sup>. A glycoprotein on the surface called intracellular adhesion molecule-1 (ICAM-1) facilitates cell-ECM interaction and encourages metastasis in malignancies. The Fractalkine\/CX3CR1 axis can be used to increase ICAM-1 expression, which will help OS cell motility. The mechanism is mediated by the PI3K\/Akt\/NF-\u03baB signalling pathway. The Fractalkine\/CX3CR1 axis has the capacity to phosphorylate Akt through PI3K within the PI3K\/Akt\/NF-\u03baB cascade. NF-\u03baB may then be further activated as a result. In the end, NF-\u03baB plays the role of a transcription factor, helping to produce ICAM-1 53<\/sup>. The IL-8\/CXCR1 axis can directly activate Akt signalling to improve OS resistance to Anoikis 58<\/sup>. Tumor-suppressing STF cDNA 3 (TSSC3), an apoptosis-related imprinted gene and a prognostic marker for OS patients, can activate autophagy in OS and disrupt the src-dependent PI3K\/Akt\/mTOR signalling pathway to inhibit cell migration and invasion in vitro and in vivo 54<\/sup>. In addition to being essential for maintaining the extracellular matrix’s formation, overexpression of fibrin-4 initiates the PI3K\/Akt\/mTOR signalling pathway, which promotes OS cell invasion and metastasis 55<\/sup>. In the meantime, EMT, a critical biological process in cancer cell metastasis, is accelerated by Fibulin-4 overexpression 55<\/sup>. Increased expression of GPNMB stimulates the PI3K\/Akt\/mTOR signalling pathway and facilitates the development and metastasis of OS cells 56<\/sup>. Furthermore, transcription factors affect the activation of PI3K\/Akt. For instance, overexpression of the zinc finger transcription factor ZIC2 can promote OS cell motility, invasion, and survival by activating PI3K\/Akt57<\/sup>. <\/p>\n\n\n\n

Targeting the Tumor Microenvironment in Osteosarcoma Therapy<\/strong><\/p>\n\n\n\n

Anti-angiogenic Therapy<\/strong><\/p>\n\n\n\n

Over the past ten years, a number of Phase\nI\/II clinical trials have been carried out, mostly involving advanced-stage OS,\nto treat neo-vascularization in OS 59<\/sup>. Clinical trials involving\nanti-angiogenic drugs that target VEGFRs, like sorafenib alone 60<\/sup> or\nin combination with everolimus, a mTOR2 inhibitor 61<\/sup>, have shown the\ngreatest promise. Treatment advantages were observed in the Italian Sarcoma\nGroup trials on recurrent OS, with 46\u201347% of patients showing a 4-6 months\nincrease in progression free survival. However, in OS patients with resectable\nand localised OS, the combination of pre and post-operative chemotherapies with\nthe well-known anti-VEGF antibody bevacizumab did not improve patient outcomes\nor increase the proportion of patients who reacted favourably to neo-adjuvant\ntherapy.  However, the therapy may cause\nproblems with wound healing following surgery 62<\/sup>. In a spinal OS\ninstance, the combination of sorafenib and denosumab, an antibody that targets\nRANKL found in the osteoid matrix, led to a successful metabolic tumour\nregression 63<\/sup>. Preclinical research has recently investigated\ntargeting VEGFR-2, a VEGF receptor expressed mostly on angiogenic arteries but\nalso on OS cancer cells, as a potential anti-angiogenic treatment approach 64<\/sup>.\nAccording to findings, VEGFR2\/STAT3\/BCL2 signalling links the highly selective\nVEGFR-2 inhibitor apatinib to direct anti-tumoral efficaciousness 64<\/sup>.\nIt has also been demonstrated that using the monoclonal antibody ramucirumab to\ntarget VEGFR-2 has anti-angiogenic effect in vitro 65<\/sup>. Surprisingly, even with the addition\nof doxorubucin-based cytotoxic treatment, anti-mouse Vegfr-2 antibody infusion\ndid not change tumour growth in preclinical OS paediatric cancer models.This implies that, although it is\nchallenging to accomplish effectively, targeting both the tumour and the\nvascular microenvironment is essential in OS.<\/p>\n\n\n\n

Immune Modulation<\/strong><\/p>\n\n\n\n

The TME demonstrates a wide range of immune\ncell compositions found in various cancer types. Some cancers show very few\nindications of inflammation, while other tumours include a large number of\nimmune cells within or around them 66<\/sup>. Cells from both arms of the immune\nsystem make up the TME, and depending on the chemical cues it contains, the\nsame type of immune cell may either promote or hinder the growth of tumours 67<\/sup>.Cancer cells are surrounded by a\npersistent overexpression of inflammatory mediators, which makes it harder for\nthe immune system to recognise and eradicate aberrant cells i.e., immune cells\ndevelop a tolerance to cancer cells 68<\/sup>. Several tactics could be used\nto slow the growth of the tumour due to the immune system’s involvement in\ncancer: (1) focussing on chronic inflammation or pro-tumorigenic factors\nsupplied by adaptive immune cells (2) blocking macrophage differentiation into\nthe pro-tumoral phenotype (TAMs) (3) inhibiting macrophage recruitment into\ntumour tissues (4) inducing anti-tumoral activity to prevent the development of\ncancer or a poor prognosis for the patient in the event that a tumour has\nalready grown 69<\/sup>. <\/p>\n\n\n\n

Stromal Targeting<\/strong><\/p>\n\n\n\n

In the extracellular matrix (ECM),\nstromal cells must move, multiply, and produce in order for tissue inside an\norgan to function correctly 70<\/sup>.Mesenchymal stromal cells are a highly varied population of progenitor\ncells with a range of origins that are present in most adult human tissues and\nplay a significant role in the genesis of malignancies. The ECM remodelling\ncharacteristics of mesenchymal stromal cells include their capacity to develop\ninto non hematopoietic cells and take part in collagen turnover. Furthermore,\nthey have a role in immune response regulation, tissue regeneration, and repair\n70,71<\/sup>. Mesenchymal stromal cells are drawn to TME’s wound like\nstructure in an effort to repair injured tissue 70<\/sup>. The response of\nmesenchymal stromal cells to external stimuli can result in an inflammatory\nphenotype of macrophages that either promotes or prevents the growth of tumours\n70-72<\/sup>. For instance, proangiogenic and immune suppressive substances\n(e.g., EGF, PDGF, fibroblast growth factor 2, FGF-2, VEGF, IL-6, and IL-10) are\ncreated when TNF, IL-1, IFN-\u03b3, and hypoxic conditions are present in the TME,\nwhich promotes tumour growth 71<\/sup>. <\/p>\n\n\n\n

Emerging Therapies and Clinical Trials<\/strong><\/p>\n\n\n\n

Small molecule inhibitors, immunotherapies,\nand medications that interfere with the tumor stroma interaction are some of\nthe novel treatment strategies that target the TME. These strategies also\nconcentrate on interfering with important interactions that promote tumour\ngrowth and resistance. While VEGF inhibitors restrict angiogenesis and cut off\nthe tumor’s blood supply, small molecule inhibitors such as MMP inhibitors\ntarget matrix remodelling enzymes to prevent tumour invasion and metastasis.\nImmunotherapies, such as immune checkpoint inhibitors (anti-PD-1\/PD-L1),\nfunction to reawaken the immune system and break through the immunosuppressive\nTME, increasing the ability of T cells to fight cancer cells. Furthermore,\nmedications that interfere with the tumor-stroma interaction like TGF-\u03b2\nblockers or CAF inhibitors hinder the extracellular matrix’s components and\ncancer-associated fibroblasts’ ability to sustain the tumour, decreasing the\ntumor’s structural and biochemical support system. These therapies collectively target the TME\nto inhibit tumor progression and improve treatment outcomes. Several\ndrugs that target components of the tumour microenvironment (TME) in\nosteosarcoma are being studied in ongoing clinical studies in an effort to\nincrease therapeutic success. Immune checkpoint drugs, such nivolumab\n(anti-PD-1) and pembrolizumab, are being tested in order to reverse\nTME-mediated immunosuppression and reactivate T cells to combat tumours.\nClinical trials are also being conducted on angiogenesis inhibitors, which\ninclude sunitinib and bevacizumab (anti-VEGF), to stop the creation of new\nblood vessels that are necessary for the growth of tumours. Other strategies\ninvolve using MMP inhibitors to target cancer-associated fibroblasts (CAFs) and\nECM remodelling enzymes, as well as investigating TGF-\u03b2 blockers to sabotage\nthe tumor-stroma relationship. The TME is a crucial target for novel\nosteosarcoma treatments, as several trials are combining these medicines with\ntraditional chemotherapy to improve outcomes.<\/p>\n\n\n\n

 Future\nDirections and Challenges<\/strong><\/p>\n\n\n\n

Osteosarcoma may respond better to treatment\nif treatments are developed that alter the tumour microenvironment (TME).\nTargeting the Extra Cellular Matrix (ECM), Tumor-Associated Macrophages (TAMs),\nand Cancer-Associated Fibroblasts (CAFs) might disturb the milieu that promotes\ntumour growth, invasion, and immune evasion. Chemotherapy, immunotherapy, and\ntargeted therapies can be more effective when strategies such as switching TAMs\nfrom a pro-tumor (M2) to an anti-tumor (M1) phenotype, inhibiting MMPs to\nprevent ECM disintegration, and limiting TGF-\u03b2 to decrease stromal support are\ncombined. These strategies seek to modify the TME in order to decrease drug\nresistance, enhance immune system identification of cancer cells, and\nultimately make osteosarcoma more susceptible to conventional therapies.\nBecause the tumour microenvironment (TME) is complicated and overlaps with\nnormal physiological processes, developing medicines that specifically target\nthe TME without damaging healthy tissues presents substantial obstacles.\nBecause growth factors, cytokines, and extracellular matrix (ECM) proteins are\namong the components of the TME that are also present in normal tissues, it is\ndifficult to create therapeutics that specifically disrupt the relationships\nthat fuel tumour growth without compromising healthy cells. Targeting immune\ncells such as T-regulatory cells (Tregs) or tumor-associated macrophages (TAMs)\nmay also compromise immune function normally, perhaps resulting in autoimmune\nillness or inadvertent immune suppression. Furthermore, the dynamic and varied\ncharacter of the TME across different tumor kinds and stages hampers the\ndevelopment of universal therapeutics. Improved biomarkers and delivery methods\nare needed to achieve accurate targeting in order to reduce off-target effects\nand increase TME specificity. Tumour microenvironment (TME) research in\nosteosarcoma is undergoing a revolution thanks to the introduction of\nsophisticated models like as organoids and 3D tumour cultures, which provide\nmore physiologically realistic systems for understanding tumor stroma\ninteractions and treatment responses. Researchers can examine how osteosarcoma\ncells interact with their surroundings in a more realistic setting by using 3D\nmodels and organoids, which simulate the complex architecture, cellular\nvariety, and ECM composition of real tumours, in contrast to typical 2D cell\ncultures. These models aid in the investigation of tumour invasion, migration,\nand immune evasion. They also facilitate the assessment of the effects of\nTME-targeting medicines on the course of osteosarcoma. <\/p>\n\n\n\n

Discussion<\/strong><\/p>\n\n\n\n

The reviewed studies reveal that the osteosarcoma Tumor MicroEnvironment (TME) is highly immunosuppressive, with Tumor-Associated Macrophages (TAMs), regulatory T cells (Tregs), and Myeloid-Derived Suppressor Cells (MDSCs) promoting immune evasion and resistance to therapy. Targeting these cells using CSF-1R inhibitors and anti-CTLA-4 therapies has shown promise in enhancing anti-tumor immunity and sensitizing cells to chemotherapy. Additionally, angiogenesis, driven by VEGF, contributes to resistance, but anti-VEGF therapies like bevacizumab show mixed results, suggesting the need for multi-pathway inhibition. The extracellular matrix (ECM) also acts as a barrier to drug penetration, and its disruption using MMP inhibitors or enzymatic approaches improves chemotherapy delivery. However, targeting the ECM selectively remains challenging. Future research should focus on combining immune checkpoint inhibitors, anti-angiogenic therapies, and ECM-targeting strategies, with nanotechnology-based drug delivery offering a potential solution to improve therapeutic efficacy in osteosarcoma.<\/p>\n\n\n\n

Conclusion<\/strong><\/p>\n\n\n\n

One important factor influencing the\ndevelopment, metastasis, and treatment resistance of osteosarcoma is the Tumour\nMicroEnvironment (TME). Growth factors, cytokines, and exosomes secreted by\nosteosarcoma cells interact with the TME to form a microenvironment that\nfacilitates tumour survival and immune evasion. The TME continues to be a major\nobstacle to effective therapy, despite advancements in conventional treatments,\nand it also plays a role in drug resistance and tumour recurrence. These\nobstacles may be addressed by employing cutting-edge treatment approaches that\ntarget certain TME constituents, such as immune cells, cancer-associated\nfibroblasts, and ECM remodelling enzymes. To find more efficient, focused\ntreatments, additional investigation into the processes of TME modulation and\nthe creation of sophisticated preclinical models, such as organoids and 3D\ncultures, are necessary. By addressing the supportive role of the TME, future treatments may\nimprove outcomes for osteosarcoma patients and reduce therapeutic resistance.<\/p>\n\n\n\n

Acknowledgement<\/strong><\/p>\n\n\n\n

The authors express their thanks to Saveetha College of Pharmacy \u2013 SIMATS for providing the necessary facilities to carry out this research work.<\/p>\n\n\n\n

Funding Sources <\/strong><\/p>\n\n\n\n

The author(s) received no financial support\nfor the research, authorship, and\/or publication of this article <\/p>\n\n\n\n

Conflict of Interest <\/strong><\/p>\n\n\n\n

The\nauthor(s) do not have any conflict of interest <\/p>\n\n\n\n

Data Availability Statement<\/strong><\/p>\n\n\n\n

This statement does not apply to this article.<\/p>\n\n\n\n

Ethics Statement<\/strong><\/p>\n\n\n\n

This research did not involve human participants, animal subjects, or any material that requires ethical approval.<\/p>\n\n\n\n

Informed Consent Statement<\/strong><\/p>\n\n\n\n

This study did not involve human participants, and therefore, informed consent was not required.<\/p>\n\n\n\n

Clinical Trial Registration<\/strong><\/p>\n\n\n\n

This research does not involve any clinical trials<\/p>\n\n\n\n

Author Contributions<\/strong><\/p>\n\n\n\n

Kaniga Pandi: Conceptualization, Methodology, Writing \u2013 Original Draft.<\/p>\n\n\n\n

Binoy Varghese Cheriyan: Visualization, Supervision, Project Administration.<\/p>\n\n\n\n

Rithika Sooriyaprakash: <\/sup>Data Collection.<\/p>\n\n\n\n

Pradhosh Sakthivel: <\/sup>Analysis.<\/p>\n\n\n\n

Rajeshkumar Thirupathi: Data Collection.<\/p>\n\n\n\n

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    Abbreviation<\/strong><\/p>\n\n\n\n

    TME – Tumor micro environment <\/p>\n\n\n\n

    CAF- Cancer associated fibroblasts<\/p>\n\n\n\n

    ECM- Extracellular matrix<\/p>\n\n\n\n

    OS- Osteosarcoma<\/p>\n\n\n\n

    EC-Endothelial cells<\/p>\n\n\n\n

    ICB- Immune checkpoint blockade<\/p>\n\n\n\n

    TAM- Tumor- associated macrophages <\/p>\n\n\n\n

    NK- Natural killer<\/p>\n\n\n\n

    MDSC- Myeloid derived suppressor cells<\/p>\n\n\n\n

    Tregs – T-regulatory cells<\/p>\n\n\n\n

    MMP- Matrix metalloproteinases<\/p>\n\n\n\n

    HIF- Hypoxia- inducible factors <\/p>\n\n\n\n

    MIF- Macrophage migration inhibitory factor<\/p>\n\n\n\n

    CA IX- Carbonic anhydrase IX<\/p>\n\n\n\n

    GLUT-1- Glucose transporter 1<\/p>\n\n\n\n

    STF- Tumor suppressing <\/p>\n\n\n\n

    OTS- Osteosarcoma<\/p>\n","protected":false},"excerpt":{"rendered":"

    Introduction Around 9.8 million fatalities worldwide are attributed to cancer, […]<\/p>\n","protected":false},"author":15,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[119],"tags":[],"class_list":["post-62694","post","type-post","status-publish","format-standard","hentry","category-vol17no4"],"_links":{"self":[{"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/posts\/62694","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/users\/15"}],"replies":[{"embeddable":true,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/comments?post=62694"}],"version-history":[{"count":5,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/posts\/62694\/revisions"}],"predecessor-version":[{"id":63523,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/posts\/62694\/revisions\/63523"}],"wp:attachment":[{"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/media?parent=62694"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/categories?post=62694"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/biomedpharmajournal.org\/staging\/wp-json\/wp\/v2\/tags?post=62694"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}