Generation of the tumor-suppressive secretome from tumor cells

Diverse roles of aldolase enzymes in cancer development, drug resistance and therapeutic approaches as moonlighting enzymes

Aldolase enzymes, particularly ALDOA, ALDOB, and ALDOC, play a crucial role in the development and progression of cancer. While the aldolase family is mainly known for its involvement in the glycolysis pathway, these enzymes also have various pathological and physiological functions through distinct signaling pathways such as Wnt/β-catenin, EGFR/MAPK, Akt, and HIF-1α. This has garnered increased attention in recent years and shed light on other sides of this enzyme. Potential therapeutic strategies targeting aldolases include using siRNA, inhibitors like naphthol AS-E phosphate and TX-2098, and natural compounds such as HDPS-4II and L-carnosine. Additionally, anticancer peptides derived from ALDOA, like P04, can potentially increase cancer cells' sensitivity to chemotherapy. Aldolases also affect cancer drug resistance by different approaches, making them good therapeutic targets. In this review, we extensively explore the role of aldolase enzymes in various types of cancers in proliferation, invasion, migration, and drug resistance; we also significantly explore the possible treatment considering aldolase function.

Enhancing anti-tumor potential: low-intensity vibration suppresses osteosarcoma progression and augments MSCs' tumor-suppressive abilities

Rationale: Osteosarcoma (OS), a common malignant bone tumor, calls for the investigation of novel treatment strategies. Low-intensity vibration (LIV) presents itself as a promising option, given its potential to enhance bone health and decrease cancer susceptibility. This research delves into the effects of LIV on OS cells and mesenchymal stem cells (MSCs), with a primary focus on generating induced tumor-suppressing cells (iTSCs) and tumor-suppressive conditioned medium (CM). Methods: To ascertain the influence of vibration frequency, we employed numerical simulations and conducted experiments to determine the most effective LIV conditions. Subsequently, we generated iTSCs and CM through LIV exposure and assessed the impact of CM on OS cells. We also explored the underlying mechanisms of the tumor-suppressive effects of LIV-treated MSC CM, with a specific focus on vinculin (VCL). We employed cytokine array, RNA sequencing, and Western blot techniques to investigate alterations in cytokine profiles, transcriptomes, and tumor suppressor proteins. Results: Numerical simulations validated LIV frequencies within the 10-100 Hz range. LIV induced notable morphological changes in OS cells and MSCs, confirming its dual role in inhibiting OS cell progression and promoting MSC conversion into iTSCs. Upregulated VCL expression enhanced MSC responsiveness to LIV, significantly bolstering CM's efficacy. Notably, we identified tumor suppressor proteins in LIV-treated CM, including procollagen C endopeptidase enhancer (PCOLCE), histone H4 (H4), peptidylprolyl isomerase B (PPIB), and aldolase A (ALDOA). Consistently, cytokine levels decreased significantly in LIV-treated mouse femurs, and oncogenic transcript levels were downregulated in LIV-treated OS cells. Moreover, our study demonstrated that combining LIV-treated MSC CM with chemotherapy drugs yielded additive anti-tumor effects. Conclusions: LIV effectively impeded the progression of OS cells and facilitated the transformation of MSCs into iTSCs. Notably, iTSC-derived CM demonstrated robust anti-tumor properties and the augmentation of MSC responsiveness to LIV via VCL. Furthermore, the enrichment of tumor suppressor proteins within LIV-treated MSC CM and the reduction of cytokines within LIV-treated isolated bone underscore the pivotal tumor-suppressive role of LIV within the bone tumor microenvironment.

Anticancer Peptides Derived from Aldolase A and Induced Tumor-Suppressing Cells Inhibit Pancreatic Ductal Adenocarcinoma Cells

PDAC (pancreatic ductal adenocarcinoma) is a highly aggressive malignant tumor. We have previously developed induced tumor-suppressing cells (iTSCs) that secrete a group of tumor-suppressing proteins. Here, we examined a unique procedure to identify anticancer peptides (ACPs), using trypsin-digested iTSCs-derived protein fragments. Among the 10 ACP candidates, P04 (IGEHTPSALAIMENANVLAR) presented the most efficient anti-PDAC activities. P04 was derived from aldolase A (ALDOA), a glycolytic enzyme. Extracellular ALDOA, as well as P04, was predicted to interact with epidermal growth factor receptor (EGFR), and P04 downregulated oncoproteins such as Snail and Src. Importantly, P04 has no inhibitory effect on mesenchymal stem cells (MSCs). We also generated iTSCs by overexpressing ALDOA in MSCs and peripheral blood mononuclear cells (PBMCs). iTSC-derived conditioned medium (CM) inhibited the progression of PDAC cells as well as PDAC tissue fragments. The inhibitory effect of P04 was additive to that of CM and chemotherapeutic drugs such as 5-Flu and gemcitabine. Notably, applying mechanical vibration to PBMCs elevated ALDOA and converted PBMCs into iTSCs. Collectively, this study presented a unique procedure for selecting anticancer P04 from ALDOA in an iTSCs-derived proteome for the treatment of PDAC.

Exploring the Tumor-Suppressing Potential of PSCA in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with low survival rates. We explored an innovative therapeutic approach by leveraging prognostic oncogenic markers. Instead of inhibiting these marker genes, we harnessed their tumor-modifying potential in the extracellular domain. Surprisingly, many of the proteins highly expressed in PDAC, which is linked to poor survival, exhibited tumor-suppressing qualities in the extracellular environment. For instance, prostate stem cell antigens (PSCA), associated with reduced survival, acted as tumor suppressors when introduced extracellularly. We performed in vitro assays to assess the proliferation and migration and evaluated the tumor-modifying capacity of extracellular factors from peripheral blood mononuclear cells (PBMCs) in PDAC tissues. Molecular docking analysis, immunoprecipitation, Western blotting, and RNA interference were employed to study the regulatory mechanism. Extracellular PSCA recombinant protein notably curtailed the viability, motility, and transwell invasion of PDAC cells. Its anti-PDAC effects were partially mediated by Mesothelin (MSLN), another highly expressed tumor-associated antigen in PDAC. The anti-tumor effects of extracellular PSCA complemented those of chemotherapeutic agents like Irinotecan, 5-Fluorouracil, and Oxaliplatin. PSCA expression increased in a conditioned medium derived from PBMCs and T lymphocytes. This study unveils the paradoxical anti-PDAC potential of PSCA, hinting at the dual roles of oncoproteins like PSCA in PDAC suppression.

Emerging roles of plasmacytoid dendritic cell crosstalk in tumor immunity

Plasmacytoid dendritic cells (pDCs) are a pioneer cell type that produces type I interferon (IFN-I) and promotes antiviral immune responses. However, they are tolerogenic and, when recruited to the tumor microenvironment (TME), play complex roles that have long been a research focus. The interactions between pDCs and other components of the TME, whether direct or indirect, can either promote or hinder tumor development; consequently, pDCs are an intriguing target for therapeutic intervention. This review provides a comprehensive overview of pDC crosstalk in the TME, including crosstalk with various cell types, biochemical factors, and microorganisms. An in-depth understanding of pDC crosstalk in TME should facilitate the development of novel pDC-based therapeutic methods.

Anticancer peptides from induced tumor-suppressing cells for inhibiting osteosarcoma cells

Osteosarcoma (OS) is the most frequent primary bone cancer, which is mainly suffered by children and young adults. While the current surgical treatment combined with chemotherapy is effective for the early stage of OS, advanced OS preferentially metastasizes to the lung and is difficult to treat. Here, we examined the efficacy of ten anti-OS peptide candidates from a trypsin-digested conditioned medium that was derived from the secretome of induced tumor-suppressing cells (iTSCs). Using OS cell lines, the antitumor capabilities of the peptide candidates were evaluated by assaying the alterations in metabolic activities, proliferation, motility, and invasion of OS cells. Among ten candidates, peptide P05 (ADDGRPFPQVIK), a fragment of aldolase A (ALDOA), presented the most potent OS-suppressing capabilities. Its efficacy was additive with standard-of-care chemotherapeutic agents such as cisplatin and doxorubicin, and it downregulated oncoproteins such as epidermal growth factor receptor (EGFR), Snail, and Src in OS cells. Interestingly, P05 did not present inhibitory effects on non-OS skeletal cells such as mesenchymal stem cells and osteoblast cells. Collectively, this study demonstrated that iTSC-derived secretomes may provide a source for identifying anticancer peptides, and P05 may warrant further evaluations for the treatment of OS.

The inhibition of pancreatic cancer progression by K-Ras-overexpressing mesenchymal stem cell-derived secretomes

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with poor survival. To explore an uncharted function of K-Ras proto-oncogene, K-Ras was activated in mesenchymal stem cells (MSCs) and the effects of MSC conditioned medium (CM) on PDAC were examined. Overexpression of K-Ras elevated PI3K signaling in MSCs, and K-Ras/PI3K-activated MSC-derived CM reduced the proliferation and migration of tumor cells, as well as the growth of ex vivo freshly isolated human PDAC cultures. CM's anti-tumor capability was additive with Gemcitabine, a commonly used chemotherapeutic drug in the treatment of PDAC. The systemic administration of CM in a mouse model suppressed the colonization of PDAC in the lung. MSC CM was enriched with Moesin (MSN), which acted as an extracellular tumor-suppressing protein by interacting with CD44. Tumor-suppressive CM was also generated by PKA-activated peripheral blood mononuclear cells. Collectively, this study demonstrated that MSC CM can be engineered to act as a tumor-suppressive agent by activating K-Ras and PI3K, and the MSN-CD44 regulatory axis is in part responsible for this potential unconventional option in the treatment of PDAC.

Osteosarcoma-enriched transcripts paradoxically generate osteosarcoma-suppressing extracellular proteins

Osteosarcoma (OS) is the common primary bone cancer that affects mostly children and young adults. To augment the standard-of-care chemotherapy, we examined the possibility of protein-based therapy using mesenchymal stem cells (MSCs)-derived proteomes and OS-elevated proteins. While a conditioned medium (CM), collected from MSCs, did not present tumor-suppressing ability, the activation of PKA converted MSCs into induced tumor-suppressing cells (iTSCs). In a mouse model, the direct and hydrogel-assisted administration of CM inhibited tumor-induced bone destruction, and its effect was additive with cisplatin. CM was enriched with proteins such as calreticulin, which acted as an extracellular tumor suppressor by interacting with CD47. Notably, the level of CALR transcripts was elevated in OS tissues, together with other tumor-suppressing proteins, including histone H4, and PCOLCE. PCOLCE acted as an extracellular tumor-suppressing protein by interacting with amyloid precursor protein, a prognostic OS marker with poor survival. The results supported the possibility of employing a paradoxical strategy of utilizing OS transcriptomes for the treatment of OS.

Association of Enolase-1 with Prognosis and Immune Infiltration in Breast Cancer by Clinical Stage

Purpose

Enolase-1 (ENO1) plays a key role in malignancies. Previous studies on the association between ENO1 expression and breast cancer prognosis had yielded inconsistent results. In the present study, we assessed the prognostic effect of ENO1 in breast cancer using Guangzhou Breast Cancer Study (GZBCS) cohort with full consideration of the potential confounders and the modification effects. The results were further validated in the TCGA-BRCA cohort and explained by tumor immunity.

Methods

ENO1 protein expressions were evaluated by immunohistochemistry in tissue microarrays from 961 patients with primary invasive breast cancer. Chi-square tests were used to assess the association of ENO1 levels with the patient's characteristics. Cox regression models were applied to assess the prognostic effects. The TCGA-BRCA cohort was utilized to validate the results and explore the potential mechanisms. The immune infiltration was determined using the CIBERSORT and ssGSEA algorithms; the correlation between ENO1 expression and the abundance of tumor-infiltrating immune cells (TIICs) and scores of immune-related functions was evaluated by Wilcoxon signed-rank tests and Spearman's rank test.

Results

ENO1 protein expression exerted a protective effect on OS in stage I/II patients (HR=0.58, 95% CI: 0.35-0.96) but not in stage III patients (HR=1.42, 95% CI: 0.81-2.49, P _interaction=0.04) in GZBCS; consistent results were obtained at mRNA levels in TCGA cohort. Immune infiltration analyses revealed that ENO1 was positively correlated with multiple antitumor TIICs (including M1 macrophages, B cells, CD8 T cells, T helper 2 cells, and NK cells) only in stage I/II but not stage III patients.

Conclusion

A higher expression of ENO1 was associated with a better prognosis only in early-stage breast cancer, which may be related to the different effects of ENO1 on immune infiltration, suggesting that ENO1 may be a promising target for precision immunotherapy in breast cancer.

The Double-Edged Proteins in Cancer Proteomes and the Generation of Induced Tumor-Suppressing Cells (iTSCs)

Unlike a prevalent expectation that tumor cells secrete tumor-promoting proteins and stimulate the progression of neighboring tumor cells, accumulating evidence indicates that the role of tumor-secreted proteins is double-edged and context-dependent. Some of the oncogenic proteins in the cytoplasm and cell membranes, which are considered to promote the proliferation and migration of tumor cells, may inversely act as tumor-suppressing proteins in the extracellular domain. Furthermore, the action of tumor-secreted proteins by aggressive "super-fit" tumor cells can be different from those derived from "less-fit" tumor cells. Tumor cells that are exposed to chemotherapeutic agents could alter their secretory proteomes. Super-fit tumor cells tend to secrete tumor-suppressing proteins, while less-fit or chemotherapeutic agent-treated tumor cells may secrete tumor-promotive proteomes. Interestingly, proteomes derived from nontumor cells such as mesenchymal stem cells and peripheral blood mononuclear cells mostly share common features with tumor cell-derived proteomes in response to certain signals. This review introduces the double-sided functions of tumor-secreted proteins and describes the proposed underlying mechanism, which would possibly be based on cell competition.

A drug screening to identify novel combinatorial strategies for boosting cancer immunotherapy efficacy

BACKGROUND

Chimeric antigen receptor (CAR) T cells and immune checkpoint blockades (ICBs) have made remarkable breakthroughs in cancer treatment, but the efficacy is still limited for solid tumors due to tumor antigen heterogeneity and the tumor immune microenvironment. The restrained treatment efficacy prompted us to seek new potential therapeutic methods.

METHODS

In this study, we conducted a small molecule compound library screen in a human BC cell line to identify whether certain drugs contribute to CAR T cell killing. Signaling pathways of tumor cells and T cells affected by the screened drugs were predicted via RNA sequencing. Among them, the antitumor activities of JK184 in combination with CAR T cells or ICBs were evaluated in vitro and in vivo.

RESULTS

We selected three small molecule drugs from a compound library, among which JK184 directly induces tumor cell apoptosis by inhibiting the Hedgehog signaling pathway, modulates B7-H3 CAR T cells to an effector memory phenotype, and promotes B7-H3 CAR T cells cytokine secretion in vitro. In addition, our data suggested that JK184 exerts antitumor activities and strongly synergizes with B7-H3 CAR T cells or ICBs in vivo. Mechanistically, JK184 enhances B7-H3 CAR T cells infiltrating in xenograft mouse models. Moreover, JK184 combined with ICB markedly reshaped the tumor immune microenvironment by increasing effector T cells infiltration and inflammation cytokine secretion, inhibiting the recruitment of MDSCs and the transition of M2-type macrophages in an immunocompetent mouse model.

CONCLUSION

These data show that JK184 may be a potential adjutant in combination with CAR T cells or ICB therapy.

Proteomes from AMPK-inhibited peripheral blood mononuclear cells suppress the progression of breast cancer and bone metastasis

Background: During a developmental process, embryos employ varying tactics to remove unwanted cells. Using a procedure analogous to some of the embryonic cells, we generated a tumor-eliminating conditioned medium (CM) from AMPK-inhibited lymphocytes and monocytes in peripheral blood mononuclear cells (PBMCs). Methods: AMPK signaling was inhibited by the application of a pharmacological agent, Dorsomorphin, and the therapeutic effects of their conditioned medium (CM) were evaluated using in vitro cell cultures, ex vivo breast cancer tissues, and a mouse model of mammary tumors and tumor-induced osteolysis. The regulatory mechanism was evaluated using mass spectrometry-based proteomics, Western blotting, immunoprecipitation, gene overexpression, and RNA interference. Results: While AMPK signaling acted mostly anti-tumorigenic, we paradoxically inhibited it to build induced tumor-suppressing cells and their tumor-eliminating CM. In a mouse model of breast cancer, the application of AMPK-inhibited lymphocyte-derived CM reduced mammary tumors additively to a chemotherapeutic agent, Taxol. It also prevented bone loss in the tumor-bearing tibia. Furthermore, the application of CM from the patient-derived peripheral blood diminished ex vivo breast cancer tissues isolated from the same patients. Notably, proteins enriched in CM included Moesin (MSN), Enolase 1 (ENO1), and polyA-binding protein 1 (PABPC1), which are considered tumorigenic in many types of cancer. The tumor-suppressing actions of MSN and ENO1 were at least in part mediated by Metadherin (Mtdh), which is known to promote metastatic seeding. Conclusion: We demonstrated that PBMCs can be used to generate tumor-suppressive proteomes, and extracellular tumor-suppressing proteins such as MSN, ENO1, and PABPC1 are converted from tumor-promoting factors inside cancer cells. The results support the possibility of developing autologous blood-based therapy, in which tumor-suppressing proteins are enriched in engineered PBMC-derived CM by the inhibition of AMPK signaling.

Prostate cancer-associated urinary proteomes differ before and after prostatectomy

BACKGROUND

A wide range of disorders can be detected in the urine. Tumor-modifying proteins in the urine may serve as a diagnostic tool for cancer patients and the alterations in their profiles may indicate efficacies of chemotherapy, radiotherapy, and surgery.

METHODS

We focused on urinary proteomes of patients with prostate cancer and identified tumor-modifying proteins in the samples before and after prostatectomy. Protein array analysis was conducted to evaluate a differential profile of tumor-promoting cytokines, while mass spectrometry-based global proteomics was conducted to identify tumor-suppressing proteins.

RESULTS

The result revealed striking differences by prostatectomy. Notably, the urine from the post-prostatectomy significantly decreased the tumorigenic behaviors of prostate tumor cells as well as breast cancer cells. We observed that angiogenin, a stimulator of blood vessel formation, was reduced in the post-prostatectomy urine. By contrast, the levels of three cell-membrane proteins such as prostasin (PRSS8), nectin 2 (PVRL2), and nidogen 1 (NID1) were elevated and they acted as extracellular tumor-suppressing proteins. These three proteins, given extracellularly, downregulated tumorigenic genes such as Runx2, Snail, and transforming growth factor beta and induced apoptosis of tumor cells. However, the role of NID1 differed depending on the location, and intracellular NID1 was tumorigenic and reduced the percent survival.

CONCLUSIONS

This study demonstrated that prostatectomy remarkably altered the profile of urinary proteomes, and the post-prostatectomy urine provided tumor-suppressive proteomes. The result sheds novel light on the dynamic nature of the urinary proteomes and a unique strategy for predicting tumor suppressors.

PI3K-activated MSC proteomes inhibit mammary tumors via Hsp90ab1 and Myh9

Despite the advance in medications in the past decade, aggressive breast cancer such as triple-negative breast cancer is difficult to treat. Here, we examined a counter-intuitive approach to converting human bone marrow-derived mesenchymal stem cells (MSCs) into induced tumor-suppressing cells by administering YS49, a PI3K/Akt activator. Notably, PI3K-activated MSCs generated tumor-suppressive proteomes, while PI3K-inactivated MSCs tumor-promotive proteomes. In a mouse model, the daily administration of YS49-treated MSC-derived CM decreased the progression of primary mammary tumors as well as the colonization of tumor cells in the lung. In the ex vivo assay, the size of freshly isolated human breast cancer tissues, including estrogen receptor positive and negative as well as human epidermal growth factor receptor 2 (HER2) positive and negative, was decreased by YS49-treated MSC-derived CM. Hsp90ab1 was enriched in CM as an atypical tumor-suppressing protein and immunoprecipitated a non-muscle myosin, Myh9. Extracellular Hsp90ab1 and Myh9 exerted the anti-tumor action and inhibited the maturation of bone-resorbing osteoclasts. Collectively, this study demonstrated that the activation of PI3K generated tumor-suppressive proteomes in MSCs and supported the possibility of using patient-derived MSCs for the treatment of breast cancer and bone metastasis.

Wnt signaling: a double-edged sword in protecting bone from cancer

Wnt signaling plays a critical role in loading-driven bone formation and bone homeostasis, whereas its activation in cancer cells promotes their progression. Currently, major research efforts in cancer treatment have been directed to the development of Wnt inhibitors. Recent studies on tumor-bone interactions, however, presented multiple lines of evidence that support a tumor-suppressive role of Lrp5, a Wnt co-receptor, and β-catenin, in Wnt signaling. This review describes the action of Wnt signaling as a double-edged sword in the bone microenvironment and suggests the possibility of a novel option for protecting bone from cancer.

Generation of the Chondroprotective Proteomes by Activating PI3K and TNFα Signaling

Simple Summary

Chondrosarcoma and inflammatory arthritis are two joint-damaging diseases. Here, we examined whether a counterintuitive approach of activating tumorigenic and inflammatory signaling may generate joint-protective proteomes in mesenchymal stem cells and chondrocytes for the treatment of chondrosarcoma and inflammatory arthritis. While activating PI3K signaling and the administration of TNFα to chondrosarcoma cells and chondrocytes promoted tumor progression and inflammatory responses, those cells paradoxically generated a chondroprotective conditioned medium. Notably, the chondroprotective conditioned medium was enriched with Hsp90ab1 that interacted with GAPDH. Extracellular GAPDH interacted with L1CAM, an oncogenic transmembrane protein, and inhibited tumorigenic behaviors, whereas intracellular GAPDH downregulated p38 in chondrocytes and exerted anti-inflammatory effects. The result supports the unconventional approach of generating chondroprotective proteomes.

Abstract

Purpose: To develop a novel treatment option for Chondrosarcoma (CS) and inflammatory arthritis, we evaluated a counterintuitive approach of activating tumorigenic and inflammatory signaling for generating joint-protective proteomes. Methods: We employed mesenchymal stem cells and chondrocytes to generate chondroprotective proteomes by activating PI3K signaling and the administration of TNFα. The efficacy of the proteomes was examined using human and mouse cell lines as well as a mouse model of CS. The regulatory mechanism was analyzed using mass spectrometry-based whole-genome proteomics. Results: While tumor progression and inflammatory responses were promoted by activating PI3K signaling and the administration of TNFα to CS cells and chondrocytes, those cells paradoxically generated a chondroprotective conditioned medium (CM). The application of CM downregulated tumorigenic genes in CS cells and TNFα and MMP13 in chondrocytes. Mechanistically, Hsp90ab1 was enriched in the chondroprotective CM, and it immunoprecipitated GAPDH. Extracellular GAPDH interacted with L1CAM and inhibited tumorigenic behaviors, whereas intracellular GAPDH downregulated p38 and exerted anti-inflammatory effects. Conclusions: We demonstrated that the unconventional approach of activating oncogenic and inflammatory signaling can generate chondroprotective proteomes. The role of Hsp90ab1 and GAPDH differed in their locations and they acted as the uncommon protectors of the joint tissue from tumor and inflammatory responses.

Suppression of breast cancer-associated bone loss with osteoblast proteomes via Hsp90ab1/moesin-mediated inhibition of TGFβ/FN1/CD44 signaling

Background: Bone is a frequent site of metastases from breast cancer, but existing therapeutic options are not satisfactory. Although osteoblasts have active roles in cancer progression by assisting the vicious bone-destructive cycle, we employed a counterintuitive approach of activating pro-tumorigenic Wnt signaling and examined the paradoxical possibility of developing osteoblast-derived tumor-suppressive, bone-protective secretomes. Methods: Wnt signaling was activated by the overexpression of Lrp5 and β-catenin in osteoblasts as well as a pharmacological agent (BML284), and the therapeutic effects of their conditioned medium (CM) were evaluated using in vitro cell cultures, ex vivo breast cancer tissues, and a mouse model of osteolysis. To explore the unconventional regulatory mechanism of the action of Wnt-activated osteoblasts, whole-genome proteomics analysis was conducted, followed by immunoprecipitation and gain- and loss-of-function assays. Results: While osteoblasts did not present any innate tumor-suppressing ability, we observed that the overexpression of Lrp5 and β-catenin in Wnt signaling made their CM tumor-suppressive and bone-protective. The growth of breast cancer cells and tissues was inhibited by Lrp5-overexpressing CM (Lrp5 CM), which suppressed mammary tumors and tumor-driven bone destruction in a mouse model. Lrp5 CM also inhibited the differentiation and maturation of bone-resorbing osteoclasts by downregulating NFATc1 and cathepsin K. The overexpression of Lrp5 upregulated osteopontin that enriched Hsp90ab1 (Hsp90 beta) and moesin (MSN) in Lrp5 CM. Hsp90ab1 and MSN are atypical tumor-suppressing proteins since they are multi-tasking, moonlighting proteins that promote tumorigenesis in tumor cells. Importantly, Hsp90ab1 immuno-precipitated latent TGFβ and inactivated TGFβ, whereas MSN interacted with CD44, a cancer stem-cell marker, as well as fibronectin 1, an ECM protein. Furthermore, Hsp90ab1 and MSN downregulated KDM3A that demethylated histones, together with PDL1 that inhibited immune responses. Conclusion: In contrast to inducing tumor-enhancing secretomes and chemoresistance in general by inhibiting varying oncogenic pathways in chemotherapy, this study presented the unexpected outcome of generation tumor-suppressive secretomes by activating the pro-tumorigenic Wnt pathway. The results shed light on the contrasting role of oncogenic signaling in tumor cells and osteoblast-derived secretomes, suggesting a counterintuitive option for the treatment of breast cancer-associated bone metastasis.

Conversion of Osteoclasts into Bone-Protective, Tumor-Suppressing Cells

Simple Summary

Osteoclasts are bone-resorbing cells and, together with bone-forming osteoblasts, they are responsible for maintaining healthy bones. When cancer cells invade into the bone, however, osteoclasts assist in cancer progression and stimulate bone loss. In this study, we converted the bone-destructive action of osteoclasts by activating their Wnt signaling and generated an osteoclast-derived, bone-protective, tumor-suppressive conditioned medium. The conditioned medium was able to suppress tumor growth and bone loss in a mouse model of mammary tumors and bone metastasis. The described approach is expected to add a novel strategy to treat primary breast cancer as well as bone metastasis.

Abstract

Osteoclasts are a driver of a vicious bone-destructive cycle with breast cancer cells. Here, we examined whether this vicious cycle can be altered into a beneficial one by activating Wnt signaling with its activating agent, BML284. The conditioned medium, derived from Wnt-activated RAW264.7 pre-osteoclast cells (BM CM), reduced the proliferation, migration, and invasion of EO771 mammary tumor cells. The same inhibitory effect was obtained with BML284-treated primary human macrophages. In a mouse model, BM CM reduced the progression of mammary tumors and tumor-induced osteolysis and suppressed the tumor invasion to the lung. It also inhibited the differentiation of RANKL-stimulated osteoclasts and enhanced osteoblast differentiation. BM CM was enriched with atypical tumor-suppressing proteins such as Hsp90ab1 and enolase 1 (Eno1). Immunoprecipitation revealed that extracellular Hsp90ab1 interacted with latent TGFβ (LAP-TGFβ) as an inhibitor of TGFβ activation, while Hsp90ab1 and Eno1 interacted and suppressed tumor progression via CD44, a cell-adhesion receptor and a cancer stem cell marker. This study demonstrated that osteoclast-derived CM can be converted into a bone-protective, tumor-suppressing agent by activating Wnt signaling. The results shed a novel insight on the unexplored function of osteoclasts as a potential bone protector that may develop an unconventional strategy to combat bone metastasis.