Role of platelets in tumor cell metastases

Platelet Physiology

Platelets are the smallest blood cells, numbering 150 to 350 × 109/L in healthy individuals. The ability of activated platelets to adhere to an injured vessel wall and form aggregates was first described in the 19th century. Besides their long-established roles in thrombosis and hemostasis, platelets are increasingly recognized as pivotal players in numerous other pathophysiological processes including inflammation and atherogenesis, antimicrobial host defense, and tumor growth and metastasis. Consequently, profound knowledge of platelet structure and function is becoming more important in research and in many fields of modern medicine. This review provides an overview of platelet physiology focusing particularly on the structure, granules, surface glycoproteins, and activation pathways of platelets.

Advancement and Applications of Platelet-inspired Nanoparticles: A Paradigm for Cancer Targeting

Platelet-inspired nanoparticles have ignited the possibility of new opportunities for producing similar biological particulates, such as structural cellular and vesicular components, as well as various viral forms, to improve biocompatible features that could improve the nature of biocompatible elements and enhance therapeutic efficacy. The simplicity and more effortless adaptability of such biomimetic techniques uplift the delivery of the carriers laden with cellular structures, which has created varied opportunities and scope of merits like; prolongation in circulation and alleviating immunogenicity improvement of the site-specific active targeting. Platelet-inspired nanoparticles or medicines are the most recent nanotechnology-based drug targeting systems used mainly to treat blood-related disorders, tumors, and cancer. The present review encompasses the current approach of platelet-inspired nanoparticles or medicines that have boosted the scientific community from versatile fields to advance biomedical sciences. Surprisingly, this knowledge has streamlined to development of newer diagnostic methods, imaging techniques, and novel nanocarriers, which might further help in the treatment protocol of the various diseased conditions. The review primarily focuses on the novel advancements and recent patents in nanoscience and nanomedicine that could be streamlined in the future for the management of progressive cancers and tumor targeting. Rigorous technological advancements like biomimetic stem cells, pH-sensitive drug delivery of nanoparticles, DNA origami devices, virosomes, nano cells like exosomes mimicking nanovesicles, DNA nanorobots, microbots, etc., can be implemented effectively for target-specific drug delivery.

Mean Platelet Volume Has Prognostic Value in Chronic Lymphocytic Leukemia

PURPOSE

Mean platelet volume (MPV) is a readily accessible and commonly tested hematological indicator. Recent studies revealed a significant impact of MPV on the course and prognosis of many diseases, including some types of cancer, as well as on the incidence of atrial fibrillation and bleeding. The study aimed to perform a retrospective analysis of MPV in terms of time to first treatment (TTFT) and to determine its prognostic value in the group of patients with chronic lymphocytic leukemia (CLL). Moreover, the study includes a retrospective analysis of platelet parameters in patients treated with ibrutinib concerning bleeding and atrial fibrillation.

PATIENTS AND METHODS

The study included 523 patients with CLL, for 344 the most important cytogenetic aberrations were reported. The Mann-Whitney, Kruskal-Wallis, Kaplan-Meier, chi-squared, log‑rank tests and multivariate Cox proportional hazard regression model were used to analyze collected data.

RESULTS

The receiver operating characteristic curve analysis was performed to identify optimal cut-off value for MPV. The analysis of survival curves showed that in the group of patients with higher values of MPV TTFT was significantly longer than in the group with lower MPV (17.9 vs 36 months, p=0.0015, cut-off value for MPV= 10.4 fl). In multivariate Cox proportional hazard regression model low MPV, the presence of del11q and del13q provided independent prognostic value for TTFT (HR=0.69, 95%-CI, 0.5293 to 0.9081; p=0.0078; HR=1.76, 95%-CI, 1.3000 to 2.3882, p=0.0003, HR=0.74, 95%-Cl, 0.5674 to 0.9588, p=0.0229, respectively). In the group treated with ibrutinib, 59 patients had no significant correlation between MPV level and the incidence of therapy complications, although in the group of patients with low MPV there was a tendency for more frequent occurrence of atrial fibrillation (p=0.259).

CONCLUSION

Low MPV values are associated with unfavorable prognosis and might represent a novel, independent prognostic factor in CLL.

The Emerging Role of Platelets in the Formation of the Micrometastatic Niche: Current Evidence and Future Perspectives

Accumulating evidence suggests that platelets play a key role in cancer metastatic dissemination through their multilevel interaction with tumor cells. Most crucial is the contribution of platelets to the formation and expansion of the early metastatic niche, a protective microenvironment that nurtures the first metastatic cells and is necessary for the establishment of overt metastatic disease. A multitude of mechanisms have been proposed toward this effect. The current review examines the implication of platelets in the three most well-studied mechanisms: (a) the initial preparation of the metastatic microenvironment by the formation of the extracellular matrix (ECM) and the recruitment of granulocytes, (b) the creation of the neovasculature (important for providing the developing tumor with oxygen and nutrients and clearing away the metabolic waste), and (c) the evasion of the immune response by the creation of an immune-suppressive environment around the developing metastases. Finally, the review provides current perspectives on the potential clinical relevance of platelets in cancer progression and their consequent role in cancer therapeutics.

Anti-tumoral effects of low molecular weight heparins: A focus on the treatment of esophageal cancer

Esophageal cancer is one of the most prevalent types of cancer globally. With current treatment options, the survival is poor, and there are ongoing efforts to find new and more efficient therapeutic approaches. There are several reports on the anti-tumoral effects of low-molecular-weight heparins (LMWH). We have assessed the possible survival benefits and underlying mechanisms of LMWHs in malignancies with a focus on esophageal cancer. We conclude that the effects of LMWHs on survival of cancer patients is probably due to a combination of direct anti-tumoral, anti-angiogenic, and immunomodulatory effects and indirect effects on the coagulation system.

Antiplatelet agents for cancer treatment: a real perspective or just an echo from the past?

The association between coagulation and cancer development has been observed for centuries. However, the connection between inflammation and malignancy is also well-recognized. The plethora of evidence indicates that among multiple hemostasis components, platelets play major roles in cancer progression by providing surface and granular contents for several interactions as well as behaving like immune cells. Therefore, the anticancer potential of anti-platelet therapy has been intensively investigated for many years. Anti-platelet agents may prevent cancer, decrease tumor growth, and metastatic potential, as well as improve survival of cancer patients. On the other hand, there are suggestions that antiplatelet treatment may promote solid tumor development in a phenomenon described as "cancers follow bleeding." The controversies around antiplatelet agents justify insight into the subject to establish what, if any, role platelet-directed therapy has in the continuum of anticancer management.

Decreased platelet reactivity in patients with cancer is associated with high risk of venous thromboembolism and poor prognosis

Platelets are suggested to play a crucial role in cancer progression and the prothrombotic state of cancer patients. Here, we aimed to examine the activation status of platelets in cancer patients and investigate their association with risk of death and occurrence of venous thromboembolism (VTE) in a prospective observational cohort study. We measured platelet surface P-selectin, activated glycoprotein (GP) IIb/IIIa and monocyte-platelet aggregate (MPA) formation in vivo and platelet response to ex vivo stimulation with agonists of protease-activated receptor (PAR) -1, -4, and GPVI, by whole blood flow cytometry, before beginning of chemotherapy and repeatedly during the first six months thereafter (total number of samples analysed: 230). Endpoints of the study were occurrence of death or VTE during a two-year follow-up, respectively. Of 62 patients (median age [interquartile range, IQR]: 63 [54-70] years, 48 % female), 32 (51.6 %) died and nine (14.5 %) developed VTE. Association with a higher risk of death was found for lower platelet surface expression of P-selectin and activated GPIIb/IIIa in vivo and in response to PAR-1, -4 and GPVI activation, but not for MPA formation. Furthermore, reduced platelet responsiveness to PAR-1 and GPVI agonists was associated with higher risk of VTE (hazard ratio per decile increase of percentage P-selectin positive platelets: 0.73 [0.56-0.92, p=0.007] and 0.77 [0.59-0.98, p=0.034], respectively). In conclusion, cancer patients with a poor prognosis showed decreased platelet reactivity, presumably as a consequence of continuous activation. Our data suggest that decreased platelet reactivity is associated with increased mortality and VTE in cancer.

Clinical significance of preoperative thrombocytosis in patients who underwent radical nephrectomy for nonmetastatic renal cell carcinoma

Purpose

The aim of this study was to examine the association of preoperative thrombocytosis with the prognosis of patients with nonmetastatic renal cell carcinoma (RCC).

Materials and Methods

We conducted a retrospective analysis of 187 patients who underwent a radical nephrectomy for nonmetastatic RCC between July 1997 and June 2009. Thrombocytosis was defined as a platelet count≥400,000 µL, and patients were divided into 2 groups according to presence of preoperative thrombocytosis, and the cancer-specific survival rates and overall survival rates of the 2 groups after radical nephrectomy were compared.

Results

The mean age of the patients was 56.0±11.7 years and the mean follow-up period was 59.3±42.1 months; there were 20 patients with preoperative thrombocytosis. Thirty patients developed metastases and 9 patients died during the follow-up period. In Kaplan-Meier analysis using a univariate log-rank test, both cancer-specific survival rate (p=0.013) and overall survival rate (p=0.012) showed significant association with preoperative thrombocytosis. Controlling for pathological TNM stage, Fuhrman grade and tumor diameter, the Cox proportional hazards model for cancer-specific survival rates showed that preoperative thrombocytosis was an independent prognostic factor (p=0.025).

Conclusions

Preoperative thrombocytosis was associated with poorer prognosis in patients with nonmetastatic RCC. Thus, preoperative platelet count may be clinically useful for risk stratification of patients undergoing surgery for nonmetastatic RCC.

Role of platelets in cancer and cancer-associated thrombosis: Experimental and clinical evidences

The primary hemostatic function of platelets has been recognized for more than a century, but increasing experimental and clinical evidences suggest that platelets are also important mediators of cancer. Cancer indeed influences platelet physiology, and activated platelets participate in each step of cancer development by promoting tumor growth, angiogenesis, metastasis, and cancer-associated thrombosis. Based on both the results of numerous experimental models addressing the involvement of platelets in cancer progression and the results of epidemiologic studies on the use of anti-platelet drugs to prevent cancer, platelets have been proposed as a potential target to reduce the short-term risk of cancer, cancer dissemination and cancer mortality. However, the cancer-associated thrombosis and the risk of bleeding due to anti-platelet drugs are not enough evaluated in experimental models. Therefore, the interesting contribution of platelets to cancer and cancer-associated thrombosis requires the standardization of preclinical and clinical models.

Differential platelet levels affect response to taxane-based therapy in ovarian cancer

PURPOSE

We hypothesized that platelet levels during therapy could serve as a biomarker for response to therapy and that manipulation of platelet levels could impact responsiveness to chemotherapy.

EXPERIMENTAL DESIGN

The medical records of patients with recurrent or progressive ovarian cancer were retrospectively queried for changes in platelet and CA-125 levels during primary therapy. In vitro coculture experiments and in vivo orthotopic models of human ovarian cancer in mice were used to test the effect of modulating platelet levels on tumor growth and responsiveness to docetaxel.

RESULTS

Thrombocytosis at the diagnosis of ovarian cancer was correlated with decreased interval to progression (P = 0.05) and median overall survival (P = 0.007). Mean platelet levels corrected during primary therapy and rose at recurrence. Contrary to treatment-responsive patients, in a cohort of patients refractory to primary therapy, platelet levels did not normalize during therapy. In A2780, HeyA8, and SKOV3-ip1 ovarian cancer cell lines, platelet coculture protected against apoptosis (P < 0.05). In orthotopic models of human ovarian cancer, platelet depletion resulted in 70% reduced mean tumor weight (P < 0.05). Compared with mice treated with docetaxel, mice treated with both docetaxel and platelet-depleting antibody had a 62% decrease in mean tumor weight (P = 0.04). Platelet transfusion increased mean aggregate tumor weight 2.4-fold (P < 0.05), blocked the effect of docetaxel on tumor growth (P = 0.55) and decreased tumor cell apoptosis. Pretransfusion aspirinization of the platelets blocked the growth-promoting effects of transfusion.

CONCLUSIONS

Platelet-driven effects of chemotherapy response may explain clinical observations.

Levels of angiogenic proteins in plasma and platelets are not different between patients with hepatitis B/C-related cirrhosis and patients with cirrhosis and hepatocellular carcinoma

Increasing evidence suggests that levels of angiogenic proteins within blood platelets change at the earliest stages of cancer development and may thus provide a promising diagnostic and prognostic tool. Patients with cirrhosis have increased risk of developing hepatocellular carcinoma (HCC). We aimed to study whether development of HCC in hepatitis-related cirrhosis results in changes in platelet levels of angiogenic proteins. We studied the intraplatelet levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), hepatocyte growth factor (HGF), endostatin, platelet factor 4 (PF4) and thrombospondin type 1 (TSP-1) in 38 consecutive patients with hepatitis B- or C-related liver cirrhosis with or without HCC in addition to plasma levels of the same proteins. Twenty healthy volunteers were included to establish reference values for the various tests. Intraplatelet levels of VEGF, bFGF, HGF and endostatin were significantly higher in patients compared to controls. Intraplatelet levels of PDGF, PF4 and TSP-1 were comparable between patients and controls. Plasma levels of VEGF, bFGF and endostatin were comparable between patients and controls. Plasma levels of PDGF, PF4 and TSP-1 were decreased in patients, but this difference disappeared when levels were corrected for platelet count. Intraplatelet and plasma levels of all proteins assessed were comparable between patients with and without HCC. In conclusion, the intraplatelet levels of some angiogenic proteins are elevated in cirrhosis, but do not discriminate between patients with and without HCC. Thus, intraplatelet levels of angiogenic proteins do not seem useful as diagnostic or prognostic biomarker of HCC in cirrhotic patients.

Platelets promote osteosarcoma cell growth through activation of the platelet-derived growth factor receptor-Akt signaling axis

The interactions of tumor cells with platelets contribute to the progression of tumor malignancy, and the expression levels of platelet aggregation-inducing factors positively correlate with the metastatic potential of osteosarcoma cells. However, it is unclear how tumor-platelet interaction contributes to the proliferation of osteosarcomas. We report here that osteosarcoma-platelet interactions induce the release of platelet-derived growth factor (PDGF) from platelets, which promotes the proliferation of osteosarcomas. Co-culture of platelets with MG63 or HOS osteosarcoma cells, which could induce platelet aggregation, enhanced the proliferation of each cell line in vitro. Analysis of phospho-antibody arrays revealed that co-culture of MG63 cells with platelets induced the phosphorylation of platelet derived growth factor receptor (PDGFR) and Akt. The addition of supernatants of osteosarcoma-platelet reactants also increased the growth of MG63 and HOS cells as well as the level of phosphorylated-PDGFR and -Akt. Sunitinib or LY294002, but not erlotinib, significantly inhibited the platelet-induced proliferation of osteosarcoma cells, indicating that PDGF released from platelets plays an important role in the proliferation of osteosarcomas by activating the PDGFR and then Akt. Our results suggest that inhibitors that specifically target osteosarcoma-platelet interactions may eradicate osteosarcomas.

Expression of Aggrus/podoplanin in bladder cancer and its role in pulmonary metastasis

Platelet aggregation-inducing factor Aggrus, also known as podoplanin, is associated with tumor malignancy by promoting hematogenous metastasis. Aggrus overexpression has been reported in some tumor tissues including lung, esophagus, head and neck and brain. We here found the frequent upregulation of aggrus mRNA in urinary bladder cancers using cancer tissue panels from various organs. Immunohistochemical analysis confirmed Aggrus protein expression in urinary bladder cancers and suggested a positive correlation between Aggrus expression and metastatic tendency in bladder cancers. Endogenous expression of Aggrus protein on the cell surface was found in the mouse bladder cancer MBT-2 cell line and human bladder cancer SCaBER cell lines. Knockdown of Aggrus expression in MBT-2 cells decreased their ability to induce platelet aggregation and form pulmonary metastasis in syngeneic mouse models. Knockdown of Aggrus expression in the human bladder cancer SCaBER cells also attenuated their ability to induce platelet aggregation and form pulmonary metastasis in mice. Moreover, pulmonary metastasis of SCaBER cells was prevented by prior administration of our generated anti-Aggrus neutralizing monoclonal antibodies by attenuating their retention in lung. These results indicate that Aggrus plays an important role in bladder cancer metastasis. Thus, anti-Aggrus neutralizing antibodies would be useful for the prevention of hematogenous metastasis of Aggrus-positive bladder cancer.

A novel and essential role for FcγRIIa in cancer cell-induced platelet activation

Platelets play a role in cancer by acting as a dynamic reservoir of effectors that facilitate tumor vascularization, growth, and metastasis. However, little information is available about the mechanism of tumor cell-induced platelet secretion (TCIPS) or the molecular machinery by which effector molecules are released from platelets. Here we demonstrate that tumor cells directly induce platelet secretion. Preincubation of platelets with human colon cancer (Caco-2), prostate cancer (PC3M-luc), or breast cancer cells (MDA-MB-231;MCF-7) resulted in a marked dose-dependent secretion of dense granules. Importantly, TCIPS preceded aggregation which always displayed a characteristic lag time. We investigated the role of platelet receptors and downstream molecules in TCIPS. The most potent modulators of TCIPS were the pharmacologic antagonists of Syk kinase, phospholipase C and protein kinase C, all downstream mediators of the immunoreceptor tyrosine-based activation motif (ITAM) cascade in platelets. Supporting this, we demonstrated a central role for the immune Fcγ receptor IIa (FcγRIIa) in mediating platelet-tumor cell cross-talk. In conclusion, we demonstrate that cancer cells can promote platelet dense-granule secretion, which is required to augment platelet aggregation. In addition, we show a novel essential role for FcγRIIa in prostate cancer cell-induced platelet activation opening the opportunity to develop novel antimetastatic therapies.

Platelet P2Y12 is involved in murine pulmonary metastasis

The involvement of platelets in tumor progression is well recognized. The depletion of circulating platelets or pharmacologic inhibitors of platelet activation decreases the metastatic potential of circulating tumor cells in metastasis mouse models. The platelet ADP receptor P2Y12 amplifies the initial hemostatic responses activated by a variety of platelet agonists and stabilizes platelet aggregation, playing a crucial role in granule secretion, integrin activation and thrombus formation. However, the relationship between P2Y12 and tumor progression is not clear. In our study, the Lewis Lung Carcinoma (LLC) spontaneous metastatic mouse model was used to evaluate the role of P2Y12 in metastasis. The results demonstrated that P2Y12 deficiency significantly reduced pulmonary metastasis. Further studies indicated that P2Y12 deficiency diminished the ability of LLC cells to induce platelet shape change and release of active TGFβ1 by a non-contact dependent mechanism resulting in a diminished, platelet-induced EMT-like transformation of the LLC cells, and that transformation probably is a prerequisite of LLC cell metastasis. Immunohistochemical analyses indicated an obvious P2Y12 deficiency related attenuation of recruitment of VEGFR1+ bone marrow derived cell clusters, and extracellular matrix fibronectin deposition in lungs, which presumably are required for pre-metastatic niche formation. In contrast to the LLC cells, non-epithelial melanoma B16 cells induced platelet aggregation in a cell number and P2Y12-dependent manner. Also, a platelet induced EMT-like transformation of B16 cells is dependent on P2Y12. In agreement with the LLC cell model, platelet P2Y12 deficiency also results in significantly less lung metastasis in the B16 melanoma experimental metastasis model. These results demonstrate that P2Y12 is a safe drug target for anti-thrombotic therapy, and that P2Y12 may serve as a new target for inhibition of tumor metastasis.

Platelets promote tumor growth and metastasis via direct interaction between Aggrus/podoplanin and CLEC-2

The platelet aggregation-inducing factor Aggrus, also known as podoplanin, is frequently upregulated in several types of tumors and enhances hematogenous metastasis by interacting with and activating the platelet receptor CLEC-2. Thus, Aggrus-CLEC-2 binding could be a therapeutic molecular mechanism for cancer therapy. We generated a new anti-human Aggrus monoclonal antibody, MS-1, that suppressed Aggrus-CLEC-2 binding, Aggrus-induced platelet aggregation, and Aggrus-mediated tumor metastasis. Interestingly, the MS-1 monoclonal antibody attenuated the growth of Aggrus-positive tumors in vivo. Moreover, the humanized chimeric MS-1 antibody, ChMS-1, also exhibited strong antitumor activity against Aggrus-positive lung squamous cell carcinoma xenografted into NOD-SCID mice compromising antibody-dependent cellular cytotoxic and complement-dependent cytotoxic activities. Because Aggrus knockdown suppressed platelet-induced proliferation in vitro and tumor growth of the lung squamous cell carcinoma in vivo, Aggrus may be involved in not only tumor metastasis but also tumor growth by promoting platelet-tumor interaction, platelet activation, and secretion of platelet-derived factors in vivo. Our results indicate that molecular target drugs inhibiting specific platelet-tumor interactions can be developed as antitumor drugs that suppress both metastasis and proliferation of tumors such as lung squamous cell carcinoma.

A humanized single-chain antibody against beta 3 integrin inhibits pulmonary metastasis by preferentially fragmenting activated platelets in the tumor microenvironment

Platelets play a supportive role in tumor metastasis. Impairment of platelet function within the tumor microenvironment may provide a clinically useful approach to inhibit metastasis. We developed a novel humanized single-chain antibody (scFv Ab) against integrin GPIIIa49-66 (named A11) capable of lysing activated platelets. In this study, we investigate the effect of A11 on the development of pulmonary metastases. In the Lewis lung carcinoma (LLC) metastatic model, A11 decreases the mean number of surface nodules and mean volume of pulmonary nodules. It protects against lung metastases in a time window that extended 4 hours before and 4 hours after the IV injection of LLCs. Coinjection of GPIIIa49-66 albumin reverses the antimetastatic activity of A11 in the B16 melanoma model, consistent with the pathophysiologic relevance of the platelet GPIIIa49-66 epitope. Significantly, A11 had no effect on angiogenesis using both in vitro and in vivo assays. The underlying molecular mechanisms are a combination of inhibition of each of the following interactions: between activated platelets and tumor cells, platelets and endothelial cells, and platelets and monocytes, as well as disaggregation of an existing platelet/tumor thrombus. Our observations may provide a novel antimetastatic strategy through lysing activated platelets in the tumor microenvironment using humanized anti-GPIIIa49-66 scFv Ab.

A case report of primary breast angiosarcoma with fatal pulmonary hemorrhage due to thrombocytopenia

Primary angiosarcomas of the breast are rare malignancy that account for fewer than 0.04% of all malignant breast tumors. The prognosis is poor. Surgery is the first line of treatment for angiosarcoma. Adjuvant chemotherapy and radiotherapy have been tried, but their efficacy remains controversial. Here we present the case of a 47-year-old woman with a palpable left breast mass that was diagnosed as a primary angiosarcoma. The patient underwent modified radical mastectomy with adjuvant chemotherapy and radiotherapy. Postoperatively, eighteen months later, the angiosarcoma recurred. The patient returned complaining of dyspnea and hemoptysis and was found to have a large pleural effusion. She developed a gradual onset of thrombocytopenia that persisted despite platelet transfusions. Finally, the patient died of respiratory failure secondary to pulmonary hemorrhage.

Engagement of αIIbβ3 (GPIIb/IIIa) with ανβ3 integrin mediates interaction of melanoma cells with platelets: a connection to hematogenous metastasis

A mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remain poorly understood. Here, we used murine B16 melanoma cells to observe functional aspects of how platelets contribute to the process of hematogenous metastasis. We found that platelets interfere with a distinct step of the metastasis cascade, as they promote adhesion of melanoma cells to the endothelium in vitro under shear conditions. Constitutively active platelet receptor GPIIb/IIIa (integrin αIIbβ3) expressed on Chinese hamster ovary cells promoted melanoma cell adhesion in the presence of fibrinogen, whereas blocking antibodies to aνβ3 integrin on melanoma cells or to GPIIb/IIIa significantly reduced melanoma cell adhesion to platelets. Furthermore, using intravital microscopy, we observed functional platelet-melanoma cell interactions, as platelet depletion resulted in significantly reduced melanoma cell adhesion to the injured vascular wall in vivo. Using a mouse model of hematogenous metastasis to the lung, we observed decreased metastasis of B16 melanoma cells to the lung by treatment with a mAb blocking the aν subunit of aνβ3 integrin. This effect was significantly reduced when platelets were depleted in vivo. Thus, the engagement of GPIIb/IIIa with aνβ3 integrin interaction mediates tumor cell-platelet interactions and highlights how this interaction is involved in hematogenous tumor metastasis.

Do all roads lead to Rome? Routes to metastasis development

Metastasis, the life-threatening aspect of cancer, is a systemic disease process. Considerable progress has been made in recent years regarding how tumor cells circulating in the blood and lymphatic systems interact with and extravasate into secondary sites, and what determines whether these disseminated tumors cells survive, remain dormant or go on to form macrometastases. New insights into the routes that tumor cells take once leaving the primary tumor have emerged. Novel concepts regarding early seeding of metastases coupled to parallel progression, self-seeding of primary tumors by circulating tumor cells and the induction of premetastatic niches in distant organs by primary tumors have come to the fore. The perceived role of the lymphatic system in determining patterns of metastasis formation in distant organs has been reassessed. Together these new insights have the potential to offer new therapeutic options. In particular, the regulation of tumor cell dormancy emerges as a key event in metastasis formation, and therapeutic control of dormancy holds the promise of rendering cancer a chronic rather than life-threatening disease.

Antimetastatic efficacy of silibinin: molecular mechanisms and therapeutic potential against cancer

Cancer is a major health problem around the world. Research efforts in the last few decades have been successful in providing better and effective treatments against both early stage and localized cancer, but clinical options against advanced metastatic stage/s of cancer remain limited. The high morbidity and mortality in most of the cancers are attributed to their metastatic spread to distant organs. Due to its extreme clinical relevance, metastasis has been extensively studied and is now understood as a highly complex biological event that involves multiple steps including acquisition of invasiveness by cancer cells, intravasation into circulatory system, survival in the circulation, arrest in microvasculature, extravasation, and growth at distant organs. The increasing understanding of molecular underpinnings of these events has provided excellent opportunity to target metastasis especially through nontoxic and biologically effective nutraceuticals. Silibinin, a popular dietary supplement isolated from milk thistle seed extracts, is one such natural agent that has shown biological efficacy through pleiotropic mechanisms against a variety of cancers and is currently in clinical trials. Recent preclinical studies have also shown strong efficacy of silibinin to target cancer cell's migratory and invasive characteristics as well as their ability to metastasize to distant organs. Detailed mechanistic analyses revealed that silibinin targets signaling molecules involved in the regulation of epithelial-to-mesenchymal transition, proteases activation, adhesion, motility, invasiveness as well as the supportive tumor-microenvironment components, thereby inhibiting metastasis. Overall, the long history of human use, remarkable nontoxicity, and preclinical efficacy strongly favor the clinical use of silibinin against advanced metastatic cancers.

Platelets: guardians of tumor vasculature

Solid tumors generate a prothrombotic environment capable of platelet activation. Recent findings indicate that the activated platelets are crucial regulators of tumor vascular homeostasis in that they prevent tumor hemorrhage. Surprisingly, this effect is independent of platelets' capacity to form thrombi and instead relies on the secretion of their granule content. Thus, targeting platelet secretory activities may represent a new approach to specifically destabilize tumor vasculature.

Osteotropic cancers: from primary tumor to bone

It has long been recognized that primary cancers spread to distant organs with characteristic preference. Bone metastases occur in approximately 70% of patients with advanced breast and prostate cancer, causing severe morbidity and hospitalization. In the last decade, we have gained a better understanding of the mechanisms by which certain tumor types tend to metastasize specifically to bone. It appears that the interaction between the organ microenvironment and cancer cells is fundamental for establishing metastatic growth. Accordingly, Stephen Paget's 'seed and soil' hypothesis - stating that circulating cancer cells (the 'seeds') disperse in all directions, but can accomplish metastases only in organs where the microenvironment (the 'soil') is permissive for their growth - still holds forth today. For this reason, this review uses the 'seed and soil' hypothesis as a template to discuss novel insight and developments in the bone metastasis field.

Cell-surface nucleolin is a signal transducing P-selectin binding protein for human colon carcinoma cells

We have previously shown that P-selectin binding to Colo-320 human colon carcinoma cells induces specific activation of the alpha(5)beta(1) integrin with a concomitant increase of cell adhesion and spreading on fibronectin substrates in a phosphatidylinositol 3-kinase (PI3-K) and p38 MAPK-dependent manner. Here, we identified by affinity chromatography and characterized nucleolin as a P-selectin receptor on Colo-320 cells. Nucleolin mAb D3 significantly decreases the Colo-320 cell adhesion to immobilized P-selectin-IgG-Fc. Moreover, nucleolin becomes clustered at the external side of the plasma membrane of living, intact cells when bound to cross-linked P-selectin-IgG-Fc chimeric protein. We have also found P-selectin binding to Colo-320 cells induces tyrosine phosphorylation specifically of cell-surface nucleolin and formation of a signaling complex containing cell-surface nucleolin, PI3-K and p38 MAPK. Using siRNA approaches, we have found that both P-selectin binding to Colo-320 cells and formation of the P-selectin-mediated p38 MAPK/PI3-K signaling complex require nucleolin expression. These results show that nucleolin (or a nucleolin-like protein) is a signaling receptor for P-selectin on Colo-320 cells and suggest a mechanism for linkage of nucleolin to P-selectin-induced signal transduction pathways that regulate the adhesion and the spreading of Colo-320 on fibronectin substrates.

Clinical Significance of Platelet Count in Patients with Renal Cell Carcinoma

INTRODUCTION

During the last decades numerous prognostic factors have been studied for predicting survival of renal cell carcinoma (RCC). Platelet count has previously been reported to correlate with prognosis in RCC. The aim of the this study was to evaluate the significance of thrombocytosis in determining prognosis in patients with localized RCC who underwent radical nephrectomy.

PATIENTS AND METHODS

The study included 118 consecutive patients. Patients were divided into a normal platelet count group (group 1) and a thrombocytosis group (group 2) according to the preoperative platelet count. Thrombocytosis was defined as a platelet count greater than 400,000/microl. The data about stage distribution, grade, tumor size, histological subtype, hemoglobin level, Body Mass Index (BMI), age, ECOG score, gender, and survival rate of tumors between these two groups were compared. Survival estimates were compared with the Kaplan-Meier method and multivariate analysis was performed using a Cox model.

RESULTS

The mean age of the patients was 61.4 years (range 30-78), and the mean follow-up period was 52.7 +/- 19.6 months (range 9-96). Thrombocytosis was present in 23 patients (19.49%). Fourteen (60.86%) of 23 patients with thrombocytosis died of disease progression. Patients with thrombocytosis had a worse prognosis than patients without thrombocytosis (p = 0.001). Thrombocytosis was noted in 8 (10.81%) of 74 patients with stage pT1-pT2 disease and in 15 (34.09%) of 44 patients with stage pT3-pT4 disease (p = 0.004). In univariate analysis, platelet count was correlated with T stage, hemoglobin level, lymph node positivity, ECOG score, and tumor size. Controlling for established prognostic indicators of pathologic stage, tumor size, platelet count, and lymph positivity using Cox's regression test, the difference in survival between the groups remained significant (p < 0.05).

CONCLUSION

The platelet count can be considered a useful prognostic factor in patients with RCC who undergo radical nephrectomy.

P-selectin activates integrin-mediated colon carcinoma cell adhesion to fibronectin

During hematogenous cancer metastasis, tumor cells separate from a primary mass, enter the bloodstream, disperse throughout the body, migrate across vessel walls, and generate distant colonies. The later steps of metastasis superficially resemble leukocyte extravasation, a process initiated by selectin-mediated cell tethering to the blood vessel wall followed by integrin-mediated arrest and transendothelial migration. Some cancer cells express P-selectin ligands and attach to immobilized P-selectin, suggesting that these cells can arrest in blood vessels using sequential selectin- and integrin-mediated adhesion, as do leukocytes. We hypothesize that selectin binding may regulate subsequent integrin-mediated steps in metastasis. Using a model system of cultured Colo 320 human colon adenocarcinoma cells incubated with soluble P-selectin-IgG chimeric protein, we have found that P-selectin can stimulate activation of the alpha(5)beta(1) integrin resulting in a specific increase of adhesion and spreading of these cells on fibronectin substrates. P-selectin binding also induced activation of p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol 3-kinase (PI3-K). PI3-K inhibitors blocked P-selectin-mediated integrin activation, cell attachment, and cell spreading. Inhibition of p38 MAPK activation blocked cell spreading, but not cell attachment. P-selectin binding also resulted in formation of a signaling complex containing PI3-K and p38 MAPK. These results suggest that P-selectin binding to tumor cells can activate alpha(5)beta(1) integrin via PI3-K and p38 MAPK signaling pathways leading to increased cell adhesion. We propose that P-selectin ligands are important tumor cell signaling molecules that modulate integrin-mediated cell adhesion in the metastatic process.

Platelet--cancer interactions: mechanisms and pharmacology of tumour cell-induced platelet aggregation

During haematogenous metastasis, cancer cells migrate to the vasculature and interact with platelets resulting in tumour cell-induced platelet aggregation (TCIPA). We review: 1. The biological and clinical significance of TCIPA; 2. Molecular mechanisms involved in platelet aggregation by cancer cells; 3. Strategies for pharmacological regulation of these interactions. We conclude that pharmacological regulation of platelet-cancer cell interactions may reduce the impact of TCIPA on cancer biology.

The superior prognostic value of humoral factors compared with molecular proliferation markers in renal cell carcinoma

BACKGROUND

The American Joint Committee on Cancer and the Union Internationale Contre le Cancer have acknowledged routine laboratory parameters, such as serum calcium, alkaline phosphatase, hemoglobin, and the erythrocyte sedimentation rate (ESR), as predictors of survival in patients with renal cell carcinoma. The predictive value of these parameters compared with proliferation markers, such as Ki-67, proliferating cell nuclear antigen (PCNA), topoisomerase II-alpha, and p100, has not been determined.

METHODS

Forty-eight consecutive patients who underwent nephrectomy for nonmetastatic renal cell carcinoma between 1990 and 1994 were observed up to 120 months postoperatively. Ten of 48 patients developed tumor progression 6-69 months after surgery. Routine preoperative laboratory parameters as well as tumor-specific data were assessed. Findings were compared with tumor proliferation indices, which were obtained by immunohistochemical staining for nuclear antigens Ki-67, PCNA, topoisomerase II-alpha, and p100 in paraffin embedded tumor tissue.

RESULTS

Univariate and multivariate statistical analyses demonstrated superiority of routine laboratory values compared with tumor proliferation indices in predicting progression-free survival and disease-specific death. The best predictor after tumor size and symptomatic presentation was ESR (P < 0.0001), with ESR values > 70 mm at 2 hours indicating a significantly poorer prognosis. Only the proliferation marker Ki-67 reached univariate significance at a threshold of 7%.

CONCLUSIONS

Routine laboratory parameters, such as alkaline phosphatase, lactate dehydrogenase, thrombocyte count, and especially ESR, provided superior long-term prognostic information for patients with nonmetastatic renal cell carcinoma compared with the molecular tumor proliferation markers Ki-67, PCNA, topoisomerase II-alpha, and p100.

Cutaneous angiosarcoma with thrombocytopenia

Thrombocytopenia was observed in 3 patients with cutaneous angiosarcoma of the scalp and face. A sudden decrease in the platelet count occurred in association with rapid enlargement of primary or metastatic lesions. Neither antiplatelet antibody nor platelet-associated IgG was detected. Increased serum levels of beta-thromboglobulin and platelet factor 4 indicated that platelets were destroyed and consumed within the vascular bed of the tumor. Prominent PECAM-1 expression on tumor cells may be involved in intratumoral platelet aggregation and consumption. We suggest that the sudden development of profund thrombocytopenia in patients with angiosarcoma may suggest either rapid growth of the primary tumor or herald the development of metastatic disease.

An antithrombotic role for nutritional antioxidants: implications for tumor metastasis and other pathologies

Nutritional antioxidants support prostacyclin synthesis by preventing lipid hydroperoxide-mediated inhibition of prostacyclin synthetase. Recent preliminary clinical studies indicate that supplementary antioxidants exert antithrombotic effects in vivo that are most likely attributable to enhanced prostacyclin production. Optimal antioxidant nutrition may thus have preventive and therapeutic value for disorders in which inappropriate platelet aggregation plays an etiologic role, including MI, stroke, atherogenesis, pre-eclampsia, and the vascular complications of diabetes. In light of evidence that platelet aggregation encourages the implantation of hematogenous tumor metastases, supplemental antioxidants should also impede tumor dissemination--an effect which will be complemented by the immunostimulant actions of these nutrients. By exerting anticarcinogenic, immunostimulant and anti-metastatic effects, nutritional antioxidants should act to inhibit neoplasia at each stage of its development.

Intratumoral consumption of indium-111 labeled platelets in a patient with hemangiomatosis and intravascular coagulation (Kasabach-Merritt syndrome)

Previous studies regarding sites of platelet destruction in patients with the Kasabach-Merritt syndrome are conflicting. The authors recently studied an adult patient with multiple large hemangiomata, thrombocytopenia, and intravascular coagulation by external imaging following the injection of autologous Indium-111 labeled platelets. Sequential images showed prompt accumulation of platelet-associated radioactivity in areas within the right hemithorax which corresponded to certain tumors noted on the chest roentgenogram. Despite the presence of multiple other lesions in bone and soft tissues, platelet radioactivity was otherwise normally confined to liver and spleen. Using data obtained from serial images, it was shown that radioactivity within the thoracic masses actually increased over time. These data indicate that platelet consumption occurred as an active process and that localization was not a result of tumor vascularity. It is concluded that platelets are locally consumed within certain hemangiomata. However, within the same individual, there may exist considerable heterogeneity among these tumors with respect to platelet-trapping ability. In similar patients with multiple tumors, indium-platelet scanning might be used to direct local therapy to particular lesions in an effort to correct the thrombocytopenia.