CXCR4-CXCL12 axis: Pivotal role as a metastatic mediator in small cell sarcoma

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Background: The chemokine CXCL12, and its receptor CXCR4, are expressed in over 23 different types of cancers, and have been associated with the metastatic phenotype and inferior clinical outcomes. Given the poor prognosis after failure of front-line therapy for patients with metastatic Ewing's sarcoma (EWS) and rhabdomyosarcoma (RMS), we examined the functional role of CXCR4 in these small cell sarcoma in vitro. Methods: Human EWS and RMS cell lines and tissue were used to study CXCR4 expression and activation. Immunoblotting techniques were used to evaluate CXCR4 activation and inhibition. Cell viability, cell cycle, apoptosis, chemosensitivity, migration, and invasion assays were utilized to assess the effects of the small peptide CXCR4 antagonist, CTCE-9908 (Chemokine Therapeutics) on cultured cells. Results: CXCR4 was highly expressed on 46 % of human RMS tumor samples. CXCR4 underwent phosphorylation after stimulation with CXCL12 in EWS and RMS cell lines with downstream activation of Akt, p42/44 MAPK, JAK2 and PLCγ1 in select cell lines. CTCE-9908 was able to specifically inhibit downstream signaling of Akt, p42/44 MAPK and JAK2. Decrease in cell proliferation (20–30%, p < .05), increase in cell apoptosis (20–40 %, p < .05) and cell cycle arrest was also observed with CXCR4 blockade. CTCE-9908 significantly inhibited migration and invasion (68–93 %, p < .05) in our cell lines. Conclusions: CXCR4-CXCL12 axis may be important in EWS and RMS metastasis. These results provide evidence that CTCE-9908 may be a novel therapy for these sarcomas.

No significant financial relationships to disclose.

Bilirubin as an inhibitor of cartilage metabolism: effect on avian chondrocyte proliferation in cell culture

Elevated levels of bilirubin and other tetrapyrroles are common to a number of chronic hematologic and liver diseases that can result in growth failure. This report establishes a cellular model system for the study of these endogenous growth inhibitors. Primary chondrocyte cultures were prepared from embryonic chick cartilage; cells were incubated (0.3 X 10(5) cells per plate) in tissue culture medium containing 10% fetal bovine serum (FBS) with or without added bilirubin, 0.01-0.10 mM. Bilirubin caused profound, dose-dependent inhibition of chondrocyte proliferation: after 7 days, control incubations contained 11.45 +/- 2.0 X 10(5) cells per plate versus 4.92 +/- 0.55 X 10(5) cells per plate for wells with added 0.01 mM bilirubin and 1.76 +/- 0.30 X 10(5) for cultures with added 0.05 mM bilirubin. In chondrocytes cultured for 3 days, the addition of 0.05 mM bilirubin was associated with inhibition of [3H]thymidine incorporation into DNA (47 +/- 5% of control), [3H]uridine incorporation into RNA (11 +/- 0.05% of control), and [14C]leucine incorporation into proteins (16 +/- 1% of control). The inhibition of chondrocyte proliferation induced by a range of bilirubin concentrations (0.01-0.10 mM) was in no way attenuated by the addition of physiologic concentrations of albumin (4 g/dl). After 3 days in media containing bilirubin or heme (at equimolar concentrations), chondrocytes were subsequently incubated in FBS alone for an additional 3 days; only partial reversal of the bilirubin (or heme)-induced inhibition was then observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilirubin and heme as growth inhibitors of chicken embryos in ovo

The increased morbidity during pregnancies complicated by hematologic or liver disease has generally been attributed to the metabolic abnormalities of the illness itself. Because tetrapyrrole concentrations are elevated in these conditions, we introduced bilirubin or heme (prepared as 10 mM solutions) into the air sac of fertilized chicken eggs to study their effect on the growth of normal chicken embryos. In 9-d eggs, the injection of 0.06 mL heme resulted in significant embryo growth inhibition as indicated by overall wt (91 +/- 3% versus control), tibia length (84 +/- 2%), tibia wt (81 +/- 3%), femur length (88 +/- 1%), and femur wt (78 +/- 3%); doses greater than 0.10 mL resulted in substantial fetal losses. The injection of 0.06 mL bilirubin into the same-age eggs also resulted in less than normal tibia length (87 +/- 2% versus control), tibia wt (75 +/- 4%), femur length (91 +/- 2%), and femur wt (81 +/- 3%); larger doses resulted in more pronounced growth inhibition, but fetal losses were less common than with heme. Older chick embryos (12-d) appeared more resistant to the effects of bilirubin: 0.15 mL bilirubin inhibited only tibia and femur wt; larger doses were required to significantly suppress the other growth parameters. The same-age chicken embryos, however, remained exquisitely sensitive to heme; 0.05 mL resulted in less than normal whole embryo wt (88 +/- 2% versus control), tibia length (80 +/- 1%), tibia wt (76 +/- 1%), femur length (78 +/- 1%), and femur wt (77 +/- 1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Hematoporphyrin can inhibit the metabolism and growth of embryonic chicken cartilage in vitro

Hematoporphyrin (HP) derivatives have been recognized chiefly as growth inhibitors of neoplastic tissues within the context of tumor phototherapy. We investigated the possibility that HP may also modify the growth potential of rapidly growing nonneoplastic tissues and describe the effect of HP on the metabolism and growth of embryonic chick cartilage in vitro. In the embryonic chick pelvic rudiment prolonged organ-culture bioassay, pelvic rudiment growth was significantly inhibited when HP 0.01 mmol/L was added to the culture medium (after 5 days in organ culture, weight increment in presence of serum + 136% +/- 12% v + 90% +/- 8% in presence of serum plus HP 0.01 mmol/L and + 43% +/- 10% in presence of serum plus HP 0.025 mmol/L, P less than .001). Inhibition of cartilage growth was irreversible if HP was added to the culture medium without serum for 2 days, but partial reversibility was observed when hypophysectomized rat serum was present during that period. Therefore, the protective effect of serum was apparently unrelated to pituitary-dependent growth factors. Binding of HP to albumin did not eliminate its inhibitory effects. Uridine incorporation into RNA and, to a lesser extent, sulfate incorporation into proteoglycans were reduced in cartilage incubated overnight with HP. Our study shows that HP can exert partially reversible inhibition of cartilage metabolism and growth suggesting potentially novel tissue actions for this compound.

Bilirubin inhibits cartilage metabolism and growth in vitro

The potential effect of bilirubin on cartilage metabolism and growth in vitro was studied using embryonic chick and hypophysectomized rat cartilage bioassays, both very sensitive to cartilage growth factors and growth inhibitors. In chick cartilage, 0.25 mmol/L bilirubin caused significant but reversible inhibition of growth. Growth inhibition was due, at least in part, to bilirubin-induced inhibition of [35S]sulfate incorporation into proteoglycans by as little as 0.05 mmol/L bilirubin and to a lesser extent by inhibition of [14C]leucine incorporation into proteins and [3H]uridine incorporation into RNA. The addition of albumin or serum had no effect on bilirubin bioactivity. Thus, bilirubin may have a novel role in the pathophysiology of skeletal growth ratardation associated with some chronic diseases.

Heme inhibits cartilage metabolism and growth in vitro

The present study was designed to investigate the potential role of heme as a direct inhibitor of cartilage metabolism and growth. We used the embryonic chick pelvic rudiment bioassays and the hypophysectomized rat cartilage sulfation bioassay, both sensitive to growth factors and growth inhibitors. In the chick bioassay pelvic rudiment growth was inhibited when heme was added to the culture medium at 0.1 mmol/L (after five days in culture, cartilage weight 224% +/- 11% of initial with normal serum, but 141% +/- 3% of initial with serum plus heme 0.25 mmol/L); the heme-induced growth inhibition was promptly reversible when cartilages were placed in heme-free medium. This was due, at least in part, to heme-induced inhibition of (1) [35S] sulfate incorporation into proteoglycans by as little as 0.05 mmol/L heme (66% +/- 5% of assay buffer); (2) [14C] leucine incorporation into proteins by greater than or equal to 0.05 mmol/L heme (85% +/- 6% of assay buffer); and (3) [3H] uridine incorporation by greater than or equal to 0.10 mmol/L heme (50% +/- 4% of assay buffer). In the rat cartilage sulfation bioassay (the literature "standard" bioassay for skeletal growth studies) a dose-dependent inhibition of [35S] sulfate incorporation occurred with greater than or equal to 0.01 mmol/L added heme (82% +/- 3% of assay buffer). Heme caused a dose-dependent and reversible inhibition of cartilage metabolism and growth, and it may have a novel role in the pathophysiology of growth retardation associated with some chronic disease.

Hemoglobin as a direct inhibitor of cartilage growth in vitro

Growth retardation is a feature of several diseases associated with chronic hemolysis (i.e., uremia and the hemoglobinopathies). Although the growth failure is undoubtedly multifactorial, circulating hemoglobin (Hb) may inhibit cartilage growth directly. We tested this hypothesis using the hypophysectomized rat costal cartilage sulfation bioassay and the embryonic chicken pelvic rudiment bioassay, both very sensitive to growth factors and growth inhibitors. In the rat bioassay, Hb produced a dose-dependent inhibition of both basal and normal rat serum (NRS)-stimulated 35SO4 uptake. In the chick bioassay, NRS stimulated cartilage growth as expected, but Hb severely inhibited both basal and NRS-stimulated growth. However, after the cartilages were preincubated with Hb for 2 days, subsequent exposure to NRS allowed them to resume growth at the same rate as cartilage exposed to NRS for the entire 5 days. The growth inhibition could be accounted for by the heme contained in Hb. We conclude that Hb produces a dose-dependent and reversible inhibition of cartilage growth and may contribute to the growth retardation associated with chronic hemolytic conditions.

Tetrapyrroles as inhibitors of normal cartilage metabolism: relative potency of different compounds

The present study was designed to explore the role of different tetrapyrroles as inhibitors of cartilage metabolism. We studied the effects of tetrapyrroles on the incorporation of [35S]sulfate into proteoglycans, [14C]-leucine into protein, and [3H]uridine into the RNA of normal cartilage from two different vertebrate classes using the embryonic chicken pelvic rudiment bioassay and the hypophysectomized rat costal cartilage bioassay, both very sensitive to cartilage growth factors and growth inhibitors. We compared the relative potencies of the following compounds: both metalloporphyrins (heme and chlorophyllin), linear tetrapyrroles (bilirubin), and heme proteins (hemoglobin, myoglobin, and cytochrome c). Hemoglobin and heme were the most potent inhibitors of rat cartilage metabolism, and bilirubin was a far more potent inhibitor of embryonic chick cartilage metabolism. Chlorophyllin had moderate inhibitory activity, especially on chick cartilage, whereas cytochrome c was inactive in these bioassays. Surprisingly, myoglobin was relatively ineffective despite its close similarity to heme and hemoglobin. The bilirubin-induced inhibition of sulfate incorporation into chick cartilage was partially prevented when glutathione was included in the incubation medium, suggesting that a free-radical mechanism may be involved. There were significant differences in the sensitivity of the two cartilages studied, indicating there may be species-dependent sensitivity to different tetrapyrroles.

Cartilage sulfation inhibitor from rat liver: partial characterization of properties and biologic action

Cartilage sulfation (somatomedin) inhibitors (CSI) from rat liver produce reversible inhibition of cartilage growth. After gel filtration Sephadex G-200, CSI appear to have MW approximately 100,000 and they are urea- and trypsin-labile factors. To explore further the mechanism of CSI action, we used the chick pelvic rudiment bioassay and studied the effect of CSI on the incorporation on 35S-sulfate (proteoglycan synthesis), 14C-leucine (protein synthesis), 3H-uridine (RNA synthesis), and 3H-thymidine (DNA synthesis). Normal rat serum (NRS) significantly stimulated the incorporation of all four isotopes, as expected. After a 24-hour incubation, CSI significantly blunted cartilage stimulation by NRS regarding total isotope uptake (1), 35S-sulfate (NRS, 96 +/- 8 mcg/100 mg cartilage dry weight; NRS + CSI, 48 +/- 4, mean +/- SEM, n = 29, P less than .05); and (2) 14C-leucine (NRS, 2,089 +/- 172 cpm/mg dry weight; NRS + CSI, 1,102 +/- 141, n = 18, P less than .05); and (3) 3H-uridine (NRS, 6,711 +/- 832 cpm/mg; NRS + CSI, 3,227 +/- 425 cpm/mg, n = 18, P less than .05); but not (4) 3H-thymidine (NRS, 3,540 +/- 620 cpm/mg; NRS + CSI 3,249 +/- 285, n = 19). The inhibition of 35S-sulfate and 14C-leucine uptake by CSI was dose-dependent and reversible. For 35S-sulfate, uptake by cartilage incubated with CSI alone for 40 hours was 13 +/- 3 micrograms/100 mg; with CSI for 16 hours then fresh medium with NRS for 24 hours uptake was 39 +/- 12, P less than .05.(ABSTRACT TRUNCATED AT 250 WORDS)

Cartilage sulfation inhibitor from rat liver curtails growth of embryonic chicken cartilage in vitro

We studied the effect of high MW cartilage sulfation (somatomedin) inhibitors from rat liver on cartilage growth in vitro. Pelvic rudiments from 11-day-old chicken embryos (5.70 mg average weight) were incubated in an organ-culture system with defined tissue-culture medium; after two days (T0-2), media were changed and incubation continued for another three days (T2-5). Normal rat serum (10% vol/vol) stimulated cartilage growth (weight change + 1.33 +/- 0.16 mg, mean +/- SEM T0-2 and + 1.33 +/- 0.27 mg, T2-5). Partially purified cartilage sulfation inhibitors (CSI) caused a weight decrease (-1.09 +/- 0.17 mg T0-2 and -0.44 +/- 0.06 mg T2-5). Adding inhibitors to cartilage incubations containing normal serum abolished the growth-promoting effect of serum (-0.79 +/- 0.07 mg T0-2 and -0.40 +/- 0.08 mg T2-5). The growth-curtailing effect of CSI was reversible; after preincubating cartilage with CSI for two days (-0.62 +/- 0.11 mg T0-2), subsequently exposing it to normal serum allowed cartilage growth to resume (+1.02 +/- 0.21 mg T2-5). Cartilages incubated with normal serum and various concentrations of inhibitor exhibited a dose-dependent inhibition of serum-stimulated growth. Cartilage Length was not altered by the inhibitor; cartilage dry:wet weight ratio or protein concentration (microgram/mg wet weight) did not differ among groups. Triodothyronine (T3) stimulated cartilage growth in a dose-dependent manner as expected. Adding CSI to cartilage incubations containing T3 (1.5 nmol/l or 15 nmol/L) completely abolished the growth-stimulating effect of T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic regulation of somatomedin activity in rat liver

We have compared circulating and hepatic somatomedin (SM) activity in rats with diabetes or malnutrition of varying severity. Somatomedin activity was measured by the hypophysectomized rat costal cartilage bioassay. In both moderate diabetes and moderate malnutrition, mean serum SM activity was not significantly lower than normal (79 +/- 13% (S.E.M.) and 95 +/- 11% vs normal controls respectively). In contrast, liver perfusate SM activity was significantly reduced in both groups (51 +/- 12% for moderate diabetes and 44 +/- 12% for moderate malnutrition). Liver extract SM activity was also significantly decreased in both moderate diabetes and malnutrition (74 +/- 4% and 75 +/- 6% vs normal controls respectively). In severe diabetes and malnutrition, both liver and serum activities were low, consistent with previous reports. Our studies showed that liver SM activity fell in response to metabolic stress before a decrease in circulating levels occurred, supporting the concept that the liver regulates serum SM activity and growth in diabetes and malnutrition.

Extraction of cartilage sulfation inhibitors and somatomedins from rat liver

Both cartilage sulfation inhibitors and somatomedins were identified in extracts from rat liver. After extraction at pH 7.4 (neutral extract), cartilage inhibitors were found in neutral liver extracts from normal, diabetic, fasted, and hypophysectomized rats [61 +/- 4%, 68 +/- 3% 60 +/- 6%, and 62 +/- 7% below assay buffer (mean +/- SEM), respectively; all P less than 0.001 below buffer]. Exposure to 80 C or pH 2.4, inactivated the inhibitors in all samples. After gel filtration on Sephadex G-100, pH 7.4, cartilage inhibitors in the neutral extracts had molecular sizes similar to those of inhibitors in the diabetic rat serum (mol wt, greater than 45,000). After the inhibitors were removed with neutral buffer extraction, reextraction at pH 2.4 (neutral/acid extracts) revealed somatomedins only in the livers of normal rats. Cartilage stimulation by somatomedins in neutral/acid extracts was linear and parallel to stimulation by normal serum. After gel filtration on Sephadex G-75, pH 2.4, somatomedins in neutral/acid extracts from normal rat liver were found to have an apparent molecular weight larger than that of serum somatomedins (mol wt, approximately 25,000-45,000), consistent with recent findings for hepatic somatomedins. The data indicate that both somatomedins and inhibitors can be extracted from rat liver.

Somatomedin inhibitors in serum and liver of growth hormone-deficient diabetic rats

Diabetes of moderate severity was induced with streptozotocin in growth hormone (and therefore somatomedin)-deficient rats. Somatomedin inhibitors were identified in the serum and liver perfusate of these animals, as shown by the ability of samples to blunt basal cartilage sulfation and cartilage stimulation by added normal serum. The data suggest that the induction of somatomedin inhibitors is under the influence of insulin and nutrition rather than growth hormone, indicating that their regulation may differ from that of growth-promoting somatomedins. With this model, it is possible to obtain preparations that are relatively free of somatomedins in which to study the properties of somatomedin inhibitors.