Prostate cancer cells of increasing metastatic potential exhibit diverse contractile forces, cell stiffness, and motility in a microenvironment stiffness-dependent manner

Glyoxal-methyl-ethylene sulfonic acid fixative enhances the fixation of cytoskeletal structures for Förster resonance energy transfer measurements

Förster resonance energy transfer (FRET) serves as a tool for measuring protein-protein interactions using various sensor molecules. The tension sensor module relies on FRET technology. In our study, this module was inserted within the actinin molecule to measure the surface tension of the cells. Given that the decay curve of FRET efficiency correlates with surface tension increase, precise and accurate efficiency measurement becomes crucial. Among the methods of FRET measurements, FRET efficiency remains the most accurate if sample fixation is successful. However, when cells were fixed with 4% paraformaldehyde (PFA), the actinin-FRET sensor diffused across the cytoplasm; this prompted us to explore fixation method enhancements. Glyoxal fixative has been reported to improve cytoskeletal morphologies compared to PFA. However, it was not known whether glyoxal fits FRET measurements. Glyoxal necessitates an acetic acid solution for fixation; however, acidic conditions could compromise fluorescence stability. We observed that the pH working range of glyoxal fixative aligns closely with MES (methyl-ethylene sulfonic acid) Good's buffer. Initially, we switched the acidic solution for MES buffer and optimized the fixation procedure for in vitro and in vivo FRET imaging. By comparing FRET measurements on hydrogels with known stiffness to tumor nodules in mouse lung, we estimated in vivo stiffness. The estimated stiffness of cancerous tissue was harder than the reported stiffness of smooth muscle. This discovery shed lights on how cancer cells perceive environmental stiffness during metastasis.

Shi-pi-xiao-ji formula suppresses hepatocellular carcinoma by reducing cellular stiffness through upregulation of acetyl-coA acetyltransferase 1

BACKGROUND

Previous studies have shown that the Shi-pi-xiao-ji (SPXJ) herbal decoction formula is effective in suppressing hepatocellular carcinoma (HCC), but the underlying mechanisms are not known. Therefore, this study investigated whether the antitumor effects of the SPXJ formula in treating HCC were mediated by acetyl-coA acetyltransferase 1 (ACAT1)-regulated cellular stiffness. Through a series of experiments, we concluded that SPXJ inhibits the progression of HCC by upregulating the expression level of ACAT1, lowering the level of cholesterol in the cell membrane, and altering the cellular stiffness, which provides a new idea for the research of traditional Chinese medicine against HCC.

AIM

To investigate the anti-tumor effects of the SPXJ formula on the malignant progression of HCC.

METHODS

HCC cells were cultured in vitro with SPXJ-containing serum prepared by injecting SPXJ formula into wild-type mice. The apoptotic rate and proliferative, invasive, and migratory abilities of control and SPXJ-treated HCC cells were compared. Atomic force microscopy was used to determine the cell surface morphology and the Young’s modulus values of the control and SPXJ-treated HCC cells. Plasma membrane cholesterol levels in HCC cells were detected using the Amplex Red cholesterol detection kit. ACAT1 protein levels were estimated using western blotting.

RESULTS

Compared with the vehicle group, SPXJ serum considerably reduced proliferation of HCC cells, increased stiffness and apoptosis of HCC cells, inhibited migration and invasion of HCC cells, decreased plasma membrane cholesterol levels, and upregulated ACAT1 protein levels. However, treatment of HCC cells with the water-soluble cholesterol promoted proliferation, migration, and invasion of HCC cells as well as decreased cell stiffness and plasma membrane cholesterol levels, but did not alter the apoptotic rate and ACAT1 protein expression levels compared with the vehicle control.

CONCLUSION

SPXJ formula inhibited proliferation, invasion, and migration of HCC cells by decreasing plasma membrane cholesterol levels and altering cellular stiffness through upregulation of ACAT1 protein expression.

Shi-pi-xiao-ji formula suppresses hepatocellular carcinoma by reducing cellular stiffness through upregulation of acetyl-coA acetyltransferase 1

BACKGROUND

Previous studies have shown that the Shi-pi-xiao-ji (SPXJ) herbal decoction formula is effective in suppressing hepatocellular carcinoma (HCC), but the underlying mechanisms are not known. Therefore, this study investigated whether the antitumor effects of the SPXJ formula in treating HCC were mediated by acetyl-coA acetyltransferase 1 (ACAT1)-regulated cellular stiffness. Through a series of experiments, we concluded that SPXJ inhibits the progression of HCC by upregulating the expression level of ACAT1, lowering the level of cholesterol in the cell membrane, and altering the cellular stiffness, which provides a new idea for the research of traditional Chinese medicine against HCC.

AIM

To investigate the anti-tumor effects of the SPXJ formula on the malignant progression of HCC.

METHODS

HCC cells were cultured in vitro with SPXJ-containing serum prepared by injecting SPXJ formula into wild-type mice. The apoptotic rate and proliferative, invasive, and migratory abilities of control and SPXJ-treated HCC cells were compared. Atomic force microscopy was used to determine the cell surface morphology and the Young’s modulus values of the control and SPXJ-treated HCC cells. Plasma membrane cholesterol levels in HCC cells were detected using the Amplex Red cholesterol detection kit. ACAT1 protein levels were estimated using western blotting.

RESULTS

Compared with the vehicle group, SPXJ serum considerably reduced proliferation of HCC cells, increased stiffness and apoptosis of HCC cells, inhibited migration and invasion of HCC cells, decreased plasma membrane cholesterol levels, and upregulated ACAT1 protein levels. However, treatment of HCC cells with the water-soluble cholesterol promoted proliferation, migration, and invasion of HCC cells as well as decreased cell stiffness and plasma membrane cholesterol levels, but did not alter the apoptotic rate and ACAT1 protein expression levels compared with the vehicle control.

CONCLUSION

SPXJ formula inhibited proliferation, invasion, and migration of HCC cells by decreasing plasma membrane cholesterol levels and altering cellular stiffness through upregulation of ACAT1 protein expression.

Differential modulation of cell morphology, migration, and Neuropilin-1 expression in cancer and non-cancer cell lines by substrate stiffness

Physical changes in the tumor microenvironment, such as increased stiffness, regulate cancer hallmarks and play an essential role in gene expression, cell morphology, migration, and malignancy. However, the response of cancer cells to stiffness is not homogeneous and varies depending on the cell type and its mechanosensitivity. In this study, we investigated the differential responses of cervical (HeLa) and prostate (PC-3) cancer cell lines, as well as non-tumoral cell lines (HEK293 and HPrEC), to stiffness using polyacrylamide hydrogels mimicking normal and tumoral tissues. We analyzed cell morphology, migration, and the expression of neuropilin 1 (NRP1), a receptor involved in angiogenesis, cell migration, and extracellular matrix remodeling, known to be associated with cancer progression and poor prognosis. Our findings reveal that NRP1 expression increases on substrates mimicking the high stiffness characteristic of tumoral tissue in the non-tumoral cell lines HPrEC and HEK293. Conversely, in tumoral PC-3 cells, stiffness resembling normal prostate tissue induces an earlier and more sustained expression of NRP1. Furthermore, we observed that stiffness influences cell spreading, pseudopodia formation, and the mode of cell protrusion during migration. Soft substrates predominantly trigger bleb cell protrusion, while pseudopodia protrusions increase on substrates mimicking normal and tumor-like stiffnesses in HPrEC cells compared to PC-3 cells. Stiffer substrates also enhance the percentage of migratory cells, as well as their velocity and total displacement, in both non-tumoral and tumoral prostate cells. However, they only improve the persistence of migration in tumoral PC-3 cells. Moreover, we found that NRP1 co-localizes with actin, and its suppression impairs tumoral PC-3 spreading while decreasing pseudopodia protrusion mode. Our results suggest that the modulation of NRP1 expression by the stiffness can be a feedback loop to promote malignancy in non-tumoral and cancer cells, contingent upon the mechanosensitivity of the cells.

Advantages of integrating Brillouin microscopy in multimodal mechanical mapping of cells and tissues

Recent research has highlighted the growing significance of the mechanical properties of cells and tissues in the proper execution of physiological functions within an organism; alterations to these properties can potentially result in various diseases. These mechanical properties can be assessed using various techniques that vary in spatial and temporal resolutions as well as applications. Due to the wide range of mechanical behaviors exhibited by cells and tissues, a singular mapping technique may be insufficient in capturing their complexity and nuance. Consequently, by utilizing a combination of methods-multimodal mechanical mapping-researchers can achieve a more comprehensive characterization of mechanical properties, encompassing factors such as stiffness, modulus, viscoelasticity, and forces. Furthermore, different mapping techniques can provide complementary information and enable the exploration of spatial and temporal variations to enhance our understanding of cellular dynamics and tissue mechanics. By capitalizing on the unique strengths of each method while mitigating their respective limitations, a more precise and holistic understanding of cellular and tissue mechanics can be obtained. Here, we spotlight Brillouin microscopy (BM) as a noncontact, noninvasive, and label-free mechanical mapping modality to be coutilized alongside established mechanical probing methods. This review summarizes some of the most widely adopted individual mechanical mapping techniques and highlights several recent multimodal approaches demonstrating their utility. We envision that future studies aim to adopt multimodal techniques to drive advancements in the broader realm of mechanobiology.

Assessment of Anti-Prostate Cancer Activity among Four Seaweeds, with Focus on Caulerpa lentillifera J.Agardh

In response to a global shift towards health-conscious and environmentally sustainable food choices, seaweed has emerged as a focus for researchers due to its large-scale cultivation potential and the development of bioactive substances. This research explores the potential anticancer properties of seaweed extracts, focusing on analyzing the impact of four common edible seaweeds in Taiwan on prostate cancer (PCa) cells' activity. The study used bioassay-guided fractionation to extract Cl80 from various seaweeds with androgen receptor (AR)-inhibitory activity. Cl80 demonstrated effective suppression of 5α-dihydrotestosterone (DHT)-induced AR activity in 103E cells and attenuated the growth and prostate-specific antigen (PSA) protein expression in LNCaP and 22Rv1 cells. Additionally, Cl80 exhibited differential effects on various PCa cell lines. Concentrations above 5 μg/mL significantly inhibited LNCaP cell proliferation, while 22Rv1 cells were more resistant to Cl80. PC-3 cell proliferation was inhibited at 5 μg/mL but not completely at 50 μg/mL. A clonogenic assay showed that at a concentration of 0.5 μg/mL, the colony formation in LNCaP and PC-3 cells was significantly reduced, with a dose-dependent effect. Cl80 induced apoptosis in all PCa cell types, especially in LNCaP cells, with increased apoptotic cells observed at higher concentrations. Cl80 also decreased the mitochondrial membrane potential (ΔΨm) in a dose-dependent manner in all PCa cell lines. Furthermore, Cl80 suppressed the migration ability of PCa cells, with significant reductions observed in LNCaP, 22Rv1, and PC-3 cells at various concentrations. These compelling findings highlight the promising therapeutic potential of C. lentillifera J.Agardh and its isolated compound Cl80 in the treatment of PCa.

Linking cell mechanical memory and cancer metastasis

Metastasis causes most cancer-related deaths; however, the efficacy of anti-metastatic drugs is limited by incomplete understanding of the biological mechanisms that drive metastasis. Focusing on the mechanics of metastasis, we propose that the ability of tumour cells to survive the metastatic process is enhanced by mechanical stresses in the primary tumour microenvironment that select for well-adapted cells. In this Perspective, we suggest that biophysical adaptations favourable for metastasis are retained via mechanical memory, such that the extent of memory is influenced by both the magnitude and duration of the mechanical stress. Among the mechanical cues present in the primary tumour microenvironment, we focus on high matrix stiffness to illustrate how it alters tumour cell proliferation, survival, secretion of molecular factors, force generation, deformability, migration and invasion. We particularly centre our discussion on potential mechanisms of mechanical memory formation and retention via mechanotransduction and persistent epigenetic changes. Indeed, we propose that the biophysical adaptations that are induced by this process are retained throughout the metastatic process to improve tumour cell extravasation, survival and colonization in the distant organ. Deciphering mechanical memory mechanisms will be key to discovering a new class of anti-metastatic drugs.

Phenotypic Heterogeneity, Bidirectionality, Universal Cues, Plasticity, Mechanics, and the Tumor Microenvironment Drive Cancer Metastasis

Tumor diseases become a huge problem when they embark on a path that advances to malignancy, such as the process of metastasis. Cancer metastasis has been thoroughly investigated from a biological perspective in the past, whereas it has still been less explored from a physical perspective. Until now, the intraluminal pathway of cancer metastasis has received the most attention, while the interaction of cancer cells with macrophages has received little attention. Apart from the biochemical characteristics, tumor treatments also rely on the tumor microenvironment, which is recognized to be immunosuppressive and, as has recently been found, mechanically stimulates cancer cells and thus alters their functions. The review article highlights the interaction of cancer cells with other cells in the vascular metastatic route and discusses the impact of this intercellular interplay on the mechanical characteristics and subsequently on the functionality of cancer cells. For instance, macrophages can guide cancer cells on their intravascular route of cancer metastasis, whereby they can help to circumvent the adverse conditions within blood or lymphatic vessels. Macrophages induce microchannel tunneling that can possibly avoid mechanical forces during extra- and intravasation and reduce the forces within the vascular lumen due to vascular flow. The review article highlights the vascular route of cancer metastasis and discusses the key players in this traditional route. Moreover, the effects of flows during the process of metastasis are presented, and the effects of the microenvironment, such as mechanical influences, are characterized. Finally, the increased knowledge of cancer metastasis opens up new perspectives for cancer treatment.

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Correlation of Plasma Membrane Microviscosity and Cell Stiffness Revealed via Fluorescence-Lifetime Imaging and Atomic Force Microscopy

The biophysical properties of cells described at the level of whole cells or their membranes have many consequences for their biological behavior. However, our understanding of the relationships between mechanical parameters at the level of cell (stiffness, viscoelasticity) and at the level of the plasma membrane (fluidity) remains quite limited, especially in the context of pathologies, such as cancer. Here, we investigated the correlations between cells' stiffness and viscoelastic parameters, mainly determined via the actin cortex, and plasma membrane microviscosity, mainly determined via its lipid profile, in cancer cells, as these are the keys to their migratory capacity. The mechanical properties of cells were assessed using atomic force microscopy (AFM). The microviscosity of membranes was visualized using fluorescence-lifetime imaging microscopy (FLIM) with the viscosity-sensitive probe BODIPY 2. Measurements were performed for five human colorectal cancer cell lines that have different migratory activity (HT29, Caco-2, HCT116, SW 837, and SW 480) and their chemoresistant counterparts. The actin cytoskeleton and the membrane lipid composition were also analyzed to verify the results. The cell stiffness (Young's modulus), measured via AFM, correlated well (Pearson r = 0.93) with membrane microviscosity, measured via FLIM, and both metrics were elevated in more motile cells. The associations between stiffness and microviscosity were preserved upon acquisition of chemoresistance to one of two chemotherapeutic drugs. These data clearly indicate that mechanical parameters, determined by two different cellular structures, are interconnected in cells and play a role in their intrinsic migratory potential.

Measuring Melanoma Nanomechanical Properties in Relation to Metastatic Ability and Anti-Cancer Drug Treatment Using Scanning Ion Conductance Microscopy

A cell's mechanical properties have been linked to cancer development, motility and metastasis and are therefore an attractive target as a universal, reliable cancer marker. For example, it has been widely published that cancer cells show a lower Young's modulus than their non-cancerous counterparts. Furthermore, the effect of anti-cancer drugs on cellular mechanics may offer a new insight into secondary mechanisms of action and drug efficiency. Scanning ion conductance microscopy (SICM) offers a nanoscale resolution, non-contact method of nanomechanical data acquisition. In this study, we used SICM to measure the nanomechanical properties of melanoma cell lines from different stages with increasing metastatic ability. Young's modulus changes following treatment with the anti-cancer drugs paclitaxel, cisplatin and dacarbazine were also measured, offering a novel perspective through the use of continuous scan mode SICM. We found that Young's modulus was inversely correlated to metastatic ability in melanoma cell lines from radial growth, vertical growth and metastatic phases. However, Young's modulus was found to be highly variable between cells and cell lines. For example, the highly metastatic cell line A375M was found to have a significantly higher Young's modulus, and this was attributed to a higher level of F-actin. Furthermore, our data following nanomechanical changes after 24 hour anti-cancer drug treatment showed that paclitaxel and cisplatin treatment significantly increased Young's modulus, attributed to an increase in microtubules. Treatment with dacarbazine saw a decrease in Young's modulus with a significantly lower F-actin corrected total cell fluorescence. Our data offer a new perspective on nanomechanical changes following drug treatment, which may be an overlooked effect. This work also highlights variations in cell nanomechanical properties between previous studies, cancer cell lines and cancer types and questions the usefulness of using nanomechanics as a diagnostic or prognostic tool.

Prostate cancer cells synergistically defend against CD8+ T cells by secreting exosomal PD-L1

BACKGROUND

Metastatic castration-resistant prostate cancer (mCRPC) remains fatal and incurable, despite a variety of treatments that can delay disease progression and prolong life. Immune checkpoint therapy is a promising treatment. However, emerging evidence suggests that exosomal programmed necrosis ligand 1 (PD-L1) directly binds to PD-1 on the surface of T cells in the drain lineage lymph nodes or neutralizes administered PD-L1 antibodies, resulting in poor response to anti-PD-L1 therapy in mCRPC.

MATERIALS AND METHODS

Western blotting and immunofluorescence were performed to compare PD-L1 levels in exosomes derived from different prostate cancer cells. PC3 cells were subcutaneously injected into nude mice, and then ELISA assay was used to detect human specific PD-L1 in exosomes purified from mouse serum. The function of CD8+ T cells was detected by T cell mediated tumor cell killing assay and FACS analysis. A subcutaneous xenograft model was established using mouse prostate cancer cell RM1, exosomes with or without PD-L1 were injected every 3 days, and then tumor size and weight were analyzed to evaluate the effect of exosomal PD-L1.

RESULTS

Herein, we found that exosomal-PD-L1 was taken up by tumor cells expressing low levels of PD-L1, thereby protecting them from T-cell killing. Higher levels of PD-L1 were detected in exosomes derived from the highly malignant prostate cancer PC3 and DU145 cell lines. Moreover, exosomal PD-L1 was taken up by the PD-L1-low-expressing LNCaP cell line and inhibited the killing function of CD8-T cells on tumor cells. The growth rate of RM1-derived subcutaneous tumors was decreased after knockdown of PD-L1 in tumor cells, whereas the growth rate recovered following exosomal PD-L1 tail vein injection. Furthermore, in the serum of mice with PCa subcutaneous tumors, PD-L1 was mainly present on exosomes.

CONCLUSION

In summary, tumor cells share PD-L1 synergistically against T cells through exosomes. Inhibition of exosome secretion or prevention of PD-L1 sorting into exosomes may improve the therapeutic response of prostate tumors to anti-PD-L1 therapy.

Membrane tension-mediated stiff and soft tumor subtypes closely associated with prognosis for prostate cancer patients

BACKGROUND

Prostate cancer (PCa) is usually considered as cold tumor. Malignancy is associated with cell mechanic changes that contribute to extensive cell deformation required for metastatic dissemination. Thus, we established stiff and soft tumor subtypes for PCa patients from perspective of membrane tension.

METHODS

Nonnegative matrix factorization algorithm was used to identify molecular subtypes. We completed analyses using software R 3.6.3 and its suitable packages.

RESULTS

We constructed stiff and soft tumor subtypes using eight membrane tension-related genes through lasso regression and nonnegative matrix factorization analyses. We found that patients in stiff subtype were more prone to biochemical recurrence than those in soft subtype (HR 16.18; p < 0.001), which was externally validated in other three cohorts. The top ten mutation genes between stiff and soft subtypes were DNAH, NYNRIN, PTCHD4, WNK1, ARFGEF1, HRAS, ARHGEF2, MYOM1, ITGB6 and CPS1. E2F targets, base excision repair and notch signaling pathway were highly enriched in stiff subtype. Stiff subtype had significantly higher TMB and T cells follicular helper levels than soft subtype, as well as CTLA4, CD276, CD47 and TNFRSF25.

CONCLUSIONS

From the perspective of cell membrane tension, we found that stiff and soft tumor subtypes were closely associated with BCR-free survival for PCa patients, which might be important for the future research in the field of PCa.