The influence of trauma, Dextran 1000, and Dextran 40 on the lodgement of circulating tumor cells

The role of calcium channels and serotonin (5-HT2) receptors for tumour cell lodgement in the liver

The effect of blockade of calcium channels and/or 5-HT receptors on the hepatic lodgement of intraportally injected fibrosarcoma cells was studied in rats. The calcium channel blocker verapamil and the 5-HT2 antagonist ketanserin each had a significant lodgement reducing effect. The pure 5-HT2 antagonist R 56413 was most effective and dose-dependent in its tumour cell lodgement reducing effect. At the highest dose tested (2.5 mg/kg body weight) R 56413 was as effective as thrombocytopenia, indicating that 5-HT is the most important platelet-released product that influences tumour cell lodgement.

Arterial occlusion reduces tumour cell lodgement in the rat liver

The lodgement of tumour cells (TCs) is a key event in the development of metastases in distant organs. Experimental and clinical studies have shown that ligation of the hepatic artery may reduce the mass of established metastases. In the present study the effect of hepatic artery or portal vein occlusion on the early phase of metastasis development, i.e. TC lodgement, was investigated. Occlusion of the hepatic artery immediately before intraportal TC infusion reduced TC lodgement, while a temporary occlusion of the portal vein directly after the TC infusion led to increased TC lodgement. It is speculated that the decrease in TC lodgement after arterial occlusion is due to local increase in blood flow, which might enhance the passage of the TCs through the liver, and to a decrease in pH causing an increased rate of TC destruction. The increased TC lodgement after portal vein occlusion, on the other hand, should mainly be due to flow reduction, promoting TC trapping in the liver microvasculature.

Involvement of platelet-released 5-HT in tumor cell lodgement

Adherence of circulating tumor cells in the microvasculature (lodgement) is a key event in metastasis formation, once cells released from a primary neoplasm have reached the bloodstream. Platelets appear to be involved in tumor cell lodgement, since thrombocytopenia significantly reduces the number of lodged tumor cells. Platelets activated by tumor cells are known to release 5-HT, and therefore the present study was focused on the influence of this amine on hepatic lodgement of intraportally injected fibrosarcoma cells in rats. Lodgement was quantified by labeling of tumor cells with [5-125I]iodo-2-deoxy-uridine. 5-HT levels were simultaneously determined using liquid chromatography with electrochemical detection (LCED) from hepatic areas with lodged tumor cells, as seen in vital microscopy. Injection of tumor cells increased hepatic 5-HT levels twofold (614 +/- 64 micrograms/g) compared with the levels found in rapidly killed (284 +/- 22 micrograms/g) or saline-injected animals (231 +/- 75 micrograms/g). In thrombocytopenia lodgement was reduced by 47% and hepatic 5-HT levels by 52% in comparison with tumor cell-injected controls. Peripheral blockade of 5-HT2 receptors with ketanserin (0.6 mg/kg sc) also reduced lodgement by 28% and hepatic 5-HT levels by 36%, strongly indicating involvement of platelet-released 5-HT in the lodgement process. Immunocytochemical studies of hepatic tissue in untreated rats demonstrated presence of 5-HT only in mast cells, while as early as 15 min after tumor cell injection 5-HT immunopositive nerves were also seen. This implies an active uptake of circulating 5-HT by neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

The importance of 5-HT for tumor cell lodgement in the liver

Arrest and lodgement of circulating tumor cells in the microvasculature is a prerequisite for metastasis formation. Aggregation of activated platelets and subsequent release of bioactive substances seem to influence the lodgement process. Since thrombocytopenia has been shown to reduce lodgement and since 5-HT is one of the compounds released from activated platelets, the present investigation was directed toward the influence of this amine on tumor cell lodgement in the liver after intraportal injection of fibrosarcoma cells. Lodgement was quantitated by an isotope technique with simultaneous measurements of 5-HT levels by a LCEC technique in rat liver biopsies from areas with lodged tumor cells as observed with vital fluorescence microscopy. To test the importance of 5-HT released from platelets, thrombocytopenia was induced with anti-platelet serum in one experimental group, while animals in another group were treated with ketanserin (a selective 5-HT2 receptor blocking agent). Animals given tumor cells alone showed a two-fold increase in 5-HT levels compared with animals injected with saline, indicating a relation between 5-HT release and tumor cell lodgement. In thrombocytopenic animals lodgement was reduced to 53% (5-HT levels reduced to 50%) of tumor-cell-injected controls. Ketanserin treatment reduced tumor cell lodgement to 72% (5-HT levels to 63%). The results indicate that 5-HT is one of the substances released from activated platelets and that 5-HT is involved in tumor cell lodgement.

The influence of antiserotonin treatment with ketanserin on the pulmonary lodgement of circulating tumour cells in normal and traumatized rats

As shown in earlier studies, the lodgement of circulating tumour cells in the lungs is reduced by thrombocytopenia in both normal and traumatized rats. Other experiments have shown that thrombocytopenia and antiserotonin treatment with ketanserin, which has a selective effect on 5-HT2 receptors, decrease the hepatic lodgement of intraportally injected tumour cells. The present studies show that treatment with ketanserin also reduces the lodgement of i.v.-injected tumour cells in the lungs in both normal and traumatized rats.

The arrest of circulating tumor cells in the liver microcirculation. A vital fluorescence microscopic, electron microscopic and isotope study in the rat

Previous studies have shown that thrombocytopenia reduces the lodgement of circulating tumor cells, thus indicating a role of platelets in tumor cell lodgement. In this study, a vital fluorescence microscopic technique, electron microscopy and isotope measurements were combined to analyse the very first phase (5 min) of tumor cell lodgement using a syngeneic, methylcholantrene induced fibrosarcoma. The mode of tumor cell arrest in the liver microvasculature of normal and thrombocytopenic rats was studied. In addition, tumor cell size and deformability were investigated in vitro. The in vitro experiments showed that the fibrosarcoma cells were very rigid. Both the vital microscopic and electron microscopic studies indicated that the tumor cells mainly became arrested by mechanical trapping in narrow liver sinusoids. Arrest of tumor cells by adherence to venular walls was a rare finding. Platelets did not seem to influence any of these initial phenomena of tumor cell lodgement. The isotope measurements, which showed no difference in the number of tumor cells lodged in the liver between normal and thrombocytopenic rats, further indicated that the initial arrest of the fibrosarcoma cells was not influenced by platelets.

The effect of thrombocytopenia and antiserotonin treatment on the lodgement of circulating tumor cells. A vital fluorescence microscopic, electron microscopic and isotope study in the rat

The hepatic lodgement of intraportally injected fibrosarcoma cells was analysed with a combination of vital fluorescence microscopic, electron microscopic and isotope techniques in normal, thrombocytopenic and antiserotonin treated (Ketanserin) rats. Ketanserin had no effect on the initial arrest of the tumor cells, as measured 5 min after tumor cell injection, which is in analogy with our previous results on thrombocytopenia. Three hours after injection, the number of lodged tumor cells was significantly reduced by both thrombocytopenia and Ketanserin treatment. Thrombocytopenia was more efficient in reducing tumor cell lodgement than antiserotonin treatment. The in vivo and electron microscopic observations indicated that the reduction of tumor cell lodgement was due to an increased destruction of tumor cells. The similar effects of Ketanserin and thrombocytopenia suggest that serotonin, when released from platelets activated in the presence of tumor cells, increases the survival of fibrosarcoma cells lodged in the liver.

Studies on mechanisms involved in metastasis formation from circulating tumor cells. Factors influencing tumor cell lodgement during normal and post-traumatic conditions

As shown in earlier studies the formation of metastases after i.v. tumor cell injection in rats is increased in the immediate post-traumatic period and treatment with heparin, thrombocytopenia, and defibrinogenation decreases the formation of metastases. Thrombocytopenia also inhibits the stimulating effect of trauma on metastasis formation. The results of the studies reported in this paper show that the changes of metastasis formation induced by the factors mentioned above with few exceptions are well correlated to the lodgement of the injected tumor cells. Thus, heparin treatment and thrombocytopenia decrease the pulmonary lodgement of i.v. injected tumor cells. Trauma increases the pulmonary lodgement of i.v. injected tumor cells but when trauma is combined with thrombocytopenia, the effect of thrombocytopenia dominates and the pulmonary lodgement of tumor cells decreases when compared to control conditions. Despite this, trauma still gives rise to increased tumor cell lodgement during thrombocytopenia.