Effect of an NGR Peptide on the Efficacy of the Doxorubicin Phospholipid Delivery System

This study is a continuation of an investigation into the effect of a targeted component, a peptide with an NGR, on the properties of the previously developed doxorubicin phospholipid delivery system. The NGR peptide has an affinity for aminopeptidase N (known as the CD13 marker on the membrane surface of tumor cells) and has been extensively used to target drug delivery systems. This article presents the results of a study investigating the physical properties of the phospholipid composition with and without the peptide chain: particle size, zeta potential, stability in fluids, and dependence of doxorubicin release from nanoparticles at different pH levels (5.0, 6.5, 7.4). The cytotoxic effect of the compositions has also been shown to depend on the dose of the drug used for incubation, the presence of the targeted component in the composition, and the time of incubation time of the substances. There was a significant difference in the cytotoxic effect on HT-1080 (CD13-positive) and MCF-7 (CD13-negative) cells. Cell death pathway analysis has shown that death occurred mainly by apoptosis. We also present data on the effect of doxorubicin embedded in phospholipid nanoparticles with the targeted peptide on DNA assessed by differential pulse voltammetry, the mechanism of action being electrostatic interactions. The interactions of native dsDNA with doxorubicin encapsulated in phospholipid nanoparticles with the targeted peptide were studied electrochemically by differential pulse voltammetry. Here, we have highlighted that the targeted peptide in the doxorubicin composition moved specific interaction of the drug with dsDNA from intercalative mode to electrostatic interactions.

The effect of renalase-derived peptides on viability of HepG₂ and PC3 cells

Renalase (RNLS) is a recently discovered protein, which plays different roles inside and outside cells. Intracellular RNLS is a FAD-dependent oxidoreductase (EC 1.6.3.5), while extracellular RNLS lacks its N-terminal peptide, FAD cofactor, and exhibits various protective effects in a non-catalytic manner. Certain evidence exists, that plasma/serum RNLS is not an intact protein secreted into the extracellular space, and exogenous recombinant RNLS is effectively degraded during short-term incubation with human plasma samples. Some synthetic analogues of the RNLS sequence (e.g. the Desir's peptide RP-220, a 20-mer peptide corresponding to the RNLS sequence 220-239) have effects on cell survival. This suggests that RNLS-derived peptides, formed during proteolytic processing, may have own biological activity. Based on results of a recent bioinformatics analysis of potential cleavage sites of RNLS (Fedchenko et al., Medical Hypotheses, 2022) we have investigated the effect of four RNLS-derived peptides as well as RP-220 and its fragment (RP-224) on the viability of two cancer cell lines: HepG₂ (human hepatoma) and PC3 (prostate cancer). Two RNLS-derived peptides (RP-207 and RP-220) decreased the viability of HepG₂ cells in a concentration dependent manner. The most pronounced and statistically significant effect (30-40% inhibition of cell growth) was observed at 50 μM concentration of each peptide. In the experiments with PC3 cells five of six RNLS-derived peptides had a significant impact on the cell viability. RP-220 and RP-224 decreased cell viability; however, no concentration dependence of this effect was observed in the range of concentrations studied (1-50 μM). Three other RNLS-derived peptides (RP-207, RP-233, and RP-265) increased viability of PC3 cells by 20-30%, but no concentration-dependence of this effect was found. Data obtained suggest that some RNLS-derived peptides may influence the viability of various cells and manifestation and direction of the effect (increase of decrease of the cell viability) is cell-type-specific.

Implication of integrin α5β1 in senescence of SK-Mel-147 human melanoma cells

Downregulation of α5β1 integrin in the SK-Mel-147 human melanoma culture model sharply inhibits the phenotypic manifestations of tumor progression: cell proliferation and clonal activity. This was accompanied by a 2-3-fold increase in the content of SA-β-Gal positive cells thus indicating an increase in the cellular senescence phenotype. These changes were accompanied by a significant increase in the activity of p53 and p21 tumor suppressors and components of the PI3K/Akt/mTOR/p70 signaling pathway. Pharmacological inhibition of mTORC1 reduced the content of SA-β-Gal positive cells in the population of α5β1-deficient SK-Mel-147 cells. A similar effect was observed with pharmacological and genetic inhibition of the activity of Akt1, one of the three Akt protein kinase isoenzymes; suppression of other Akt isozymes did not affect melanoma cell senescence. The results presented in this work and previously obtained indicate that α5β1 shares with other integrins of the β1 family the function of cell protection from senescence. This function is realized via regulation of the PI3K/Akt1/mTOR signaling pathway, in which Akt1 exhibits a non-canonical activity.

Oxazolinyl derivatives of androst-16-ene as inhibitors of CYP17A1 activity and prostate carcinoma cells proliferation: Effects of substituents in oxazolinyl moiety

Steroid derivatives modified with nitrogen containing heterocycles are known to inhibit activity of steroidogenic enzymes, decrease proliferation of cancer cells and attract attention as promising anticancer agents. Specifically, 2'-(3β-hydroxyandrosta-5,16-dien-17-yl)-4',5'-dihydro-1',3'-oxazole 1a potently inhibited proliferation of prostate carcinoma cells. In this study we synthesized and investigated five new derivatives of 3β-hydroxyandrosta-5,16-diene comprising 4'-methyl or 4'-phenyl substituted oxazolinyl cycle 1 (b-f). Docking of compounds 1 (a-f) to CYP17A1 active site revealed that the presence of substitutents at C4' atom in oxazoline cycle, as well as C4' atom configuration, significantly affect docking poses of compounds in the complexes with enzyme. Testing of compounds 1 (a-f) as CYP17A1 inhibitors revealed that the only compound 1a, comprising unsubstituted oxazolinyl moiety, demonstrated strong inhibitory activity, while other compounds 1 (b-f) were slightly active or non active. Compounds 1 (a-f) efficiently decreased growth and proliferation of prostate carcinoma LNCaP and PC-3 cells at 96 h incubation; the effect of compound 1a was the most powerful. Compound 1a efficiently stimulated apoptosis and caused PC-3 cells death, that was demonstrated by a direct comparison of pro-apoptotic effects of compound 1a and abiraterone.

Chlorin e6 Phospholipid Delivery System Featuring APN/CD13 Targeting Peptides: Cell Death Pathways, Cell Localization, In Vivo Biodistribution

We have previously designed a phospholipid delivery system for chlorin e6 to increase the efficacy of photodynamic therapy involving a second-generation photosensitizer. Further research into the matter led to double modification of the obtained nanoparticles with ligands exhibiting targeting and cell-penetrating effects: an NGR-containing peptide and heptaarginine (R7), respectively. This study investigated the cell death pathway on HT-1080 tumor cells after treatment with the proposed compositions: the chlorin e6 phospholipid composition and the two-peptide chlorin e6 phospholipid composition. It was demonstrated that most of the cells died by apoptosis. Colocalization analysis of chlorin e6 in the phospholipid composition with two peptides showed mitochondria are one of the targets of the photosensitizer. An HT-1080 tumor-bearing mouse model was used to evaluate the biodistribution of the drug in tumor, liver, and kidney tissues after administration of the study compositions in comparison with free chlorin e6. The photosensitizer mostly accumulated in the tumor tissue of mice administered the phospholipid compositions, and accumulation was increased 2-fold with the peptide-containing composition and approximately 1.5-fold with the unenhanced composition, as compared with free chlorin e6. The enhancement of the chlorin e6 phospholipid composition with targeting and cell-penetrating peptides was found to be effective both in vitro and in vivo.

Chondroitin Sulfate and Fucosylated Chondroitin Sulfate as Stimulators of Hematopoiesis in Cyclophosphamide-Induced Mice

The immunosuppression and inhibition of hematopoiesis are considered to be reasons for the development of complications after intensive chemotherapy and allogeneic hematopoietic stem cell transplantation. Chondroitin sulfate (CS), isolated from the fish Salmo salar, and fucosylated chondroitin sulfate (FCS), isolated from the sea cucumber Apostichopus japonicus, were studied for their roles as stimulators of hematopoiesis in a model of cyclophosphamide-induced immunosuppression in mice. The recombinant protein r G-CSF was applied as a reference. The studied polysaccharides were shown to stimulate the release of white and red blood cells, as well as platelets from bone marrow in immunosuppressed mice, while r G-CSF was only responsible for the significant increase in the level of leucocytes. The analysis of different populations of leucocytes in blood indicated that r G-CSF mainly stimulated the production of neutrophils, whereas in the cases of the studied saccharides, increases in the levels of monocytes, lymphocytes and neutrophils were observed. The normalization of the level of the pro-inflammatory cytokine IL-6 in the serum and the recovery of cell populations in the spleen were observed in immunosuppressed mice following treatment with the polysaccharides. An increase in the proliferative activity of hematopoietic cells CD34(+)CD45(+) was observed following ex vivo polysaccharide exposure. Further study on related oligosaccharides regarding their potential as promising drugs in the complex prophylaxis and therapy of hematopoiesis inhibition after intensive chemotherapy and allogeneic hematopoietic stem cell transplantation seems to be warranted.

Composite phospholipid-gold nanoparticles with targeted fragment for tumor imaging

Gold nanoparticles and their conjugates have significant potential in the field of diagnosis of various diseases due to their SPR, which enhances light scattering and absorption. Conjugates of gold nanoparticles with various ligands can be used for imaging biomolecules or detecting malignant neoplasms at an early stage. This study focuses on the construction of composite (or hybrid) phospholipid-gold nanoparticles using soy phosphatidylcholine and a targeted ligand (folic acid derivative) to attach specific targeting properties. According to the method of dynamic light scattering, the diameter of the obtained nanoparticles was less than 100 nm, the results of the MTT test indicated their moderate cytotoxicity. In vitro and in vivo experiments showed a significant increase in the accumulation of phospholipid-gold nanoparticles with a targeted fragment compared to those without a targeted fragment both in HeLa cells and in a tumor (in BDF mice with an injected LLC tumor). The resulting nanoparticles are suitable for specific delivery into tumor cells and visualization of various malignant neoplasms, including at early stages, due to the increased expression of the folate receptor characteristic of cells of a wide range of tumors.

High-density lipoprotein remodeling by phospholipid nanoparticles improves cholesterol efflux capacity and protects from atherosclerosis

The efficiency of cholesterol efflux from cells promoted by high-density lipoproteins (HDLs) depends on HDL concentration and functional properties. The term "dysfunctional HDL" describes HDLs with impaired protective properties. Cholesterol efflux capacity (CEC) of HDL is reduced in patients with atherosclerosis, but the exact mechanisms underlying this impairment are not well characterized. Enriching HDLs with phospholipids (PLs) improves CEC. Herein, we assessed the potential of PL nanoparticles in improving HDL functionality. We lipidated HDL subfractions by incubating with PL nanoparticles containing soybean polyunsaturated phosphatidylcholine. Incubating blood plasma with PL nanoparticles resulted in the dose-dependent lipidation of all HDL subfractions. Changes in apolipoprotein A1 (apoA-1) and PL concentrations were the most prominent in the HDL₂ fraction. Concentrations of PL in the HDL₃ fraction and the fraction with a density > 1.21 g/mL increased by 30-50%, whereas apoA-1 levels decreased. We hypothesized that PL nanoparticles may cause HDL remodeling that can improve their functions. The CECs of lipidated HDLs were analyzed by incubating apolipoprotein B (apoB)-depleted plasma with ³H-cholesterol-labeled THP-1 macrophages. The findings revealed a two-fold increase in cholesterol efflux compared with native apoB-depleted plasma. Moreover, intravenous administration of PL nanoparticles restored lipid profiles and effectively protected blood vessels from atherosclerosis progression in cholesterol-fed rabbits compared with that of fenofibrate and atorvastatin. PL nanoparticles also protected against atherosclerosis and decreased the atherogenic index. Altogether, these results indicate that PL nanoparticles can be used to correct the lipid composition and CEC of HDLs. DATA AVAILABILITY: Additional data can be provided upon reasonable request from the date of publication of this article within 5 years. The request should be sent to the author-correspondent at the address cd95@mail.ru.

[Targeted drug delivery system for doxorubicin based on a specific peptide and phospholipid nanoparticles]

Doxorubicin is one of the widely known and frequently used chemotherapy drugs for the treatment of various types of cancer, the use of which is difficult due to its high cardiotoxicity. Targeted drug delivery systems are being developed to reduce side effects. One of the promising components as vector molecules (ligands) are NGR-containing peptides that are affinity for the CD13 receptor, which is expressed on the surface of many tumor cells and tumor blood vessels. Previously, a method was developed for preparing a composition of doxorubicin embedded in phospholipid nanoparticles with a targeted fragment in the form of an ultrafine emulsion. The resulting composition was characterized by a small particle size (less than 40 nm) and a high degree of incorporation of doxorubicin (about 93%) into transport nanoparticles. When assessing the penetrating ability and the degree of binding to the surface of fibrosarcoma cells (HT-1080), it was shown that when the composition with the targeted fragment was added to the cells, the level of doxorubicin was almost 2 times higher than that of the liposomal form of doxorubicin, i.e. the drug in the system with the targeted peptide penetrated the cell better. At the same time, on the control line of breast adenocarcinoma cells (MCF-7), which do not express the CD13 receptor on the surface, there was not significant difference in the level of doxorubicin in the cells. The data obtained allow us to draw preliminary conclusions about the prospects of targeted delivery of doxorubicin to tumor cells when using a peptide conjugate containing an NGR motif and the further need for its comprehensive study.

Implication of integrins α3β1 and α5β1 in invasion and anoikis of SK-Mel-147 human melanoma cells: non-canonical functions of protein kinase Akt

Downregulation of integrins α3β1 and α5β1 strongly decreased cell colony formation and in vitro invasion and markedly enhanced anoikis in SK-Mel-147 human melanoma cells. These modifications were accompanied by a marked increase in the levels of active Akt protein kinase, which indicated it played a non-canonical function in the melanoma cells. Pharmacological inhibition of Akt1, an Akt isozyme, in cells depleted of α3β1 or α5β1 restored their invasive activity, while inhibition of the Akt 2 isoform did not cause a visible effect. Similar to our previous results with the α2β1 integrin, this finding suggested that in signaling pathways initiated by α3β1 and α5β1, the Akt1 isoform performs a non-canonical function in regulating invasive phenotype of melanoma cells. In contrast, when the effects of Akt inhibitors on anoikis of the melanoma cells were compared, the Akt2 isoform demonstrated a non-canonical activity in which Akt2 suppression led to a significant attenuation of apoptosis in cells with downregulated α3β1 or α5β1. Our results were the first evidence that, in the same tumor cells, different integrins can control various manifestations of tumor progression through distinct signaling pathways that are both common to various integrins and specific to a particular receptor.

New steroidal oxazolines, benzoxazoles and benzimidazoles related to abiraterone and galeterone

Seven new oxazoline, benzoxazole and benzimidazole derivatives were synthesized from 3β-acetoxyandrosta-5,16-dien-17-carboxylic, 3β-acetoxyandrost-5-en-17β-carboxylic and 3β-acetoxypregn-5-en-21-oic acids. Docking to active site of human 17α-hydroxylase/17,20-lyase revealed that all oxazolines, as well as benzoxazoles and benzimidazoles comprising Δ¹⁶ could form stable complexes with enzyme, in which steroid moiety is positioned similarly to that of abiraterone and galeterone, and nitrogen atom coordinates heme iron, while 16,17-saturated benzoxazoles and benzimidazoles could only bind in a position where heterocycle is located nearly parallel to heme plane. Modeling of the interaction of new benzoxazole and benzimidazole derivatives with androgen receptor revealed the destabilization of helix 12, constituting activation function 2 (AF2) site, by mentioned compounds, similar to one induced by known antagonist galeterone. The synthesized compounds inhibited growth of prostate carcinoma LNCaP and PC-3 cells at 96 h incubation; the potency of 2'-(3β-hydroxyandrosta-5,16-dien-17-yl)-4',5'-dihydro-1',3'-oxazole and 2'-(3β-hydroxyandrosta-5,16-dien-17-yl)-benzimidazole was superior and could inspire further investigations of these compounds as potential anti-cancer agents.

New azole derivatives of [17(20)E]-21-norpregnene: Synthesis and inhibition of prostate carcinoma cell growth

A number of isoxazole, 1,2,3-triazole, tetrazole, and 1,2,4-oxadiazole derivatives of [17(20)E]-21-norpregnene comprising 3β-hydroxy-5-ene and 3-oxo-4-ene fragments were prepared. Among the key steps for the synthesis of isoxazoles, 1,2,3-triazoles, and tetrazoles were (i) 1,3-dipolar cycloaddition of nitrile oxides or azides to acetylenes or nitriles and ii) dehydration of 17β-hydroxy-17α-methylene-azoles to [17(20)E]-21-norpregnene derivatives. 1,2,4-Oxadiazoles were prepared through the formation of acetimidamides. Potency of the synthesized compounds to inhibit CYP17A1 and to suppress growth of prostate carcinoma cells was investigated. Among the new azole derivatives, four compounds were found possessing high anti-proliferative activity.

Implication of integrin α2β1 in anoikis of SK-Mel-147 human melanoma cells: a non-canonical function of Akt protein kinase

Suppression of anoikis, a kind of apoptosis caused by disruption of contacts between cell and extracellular matrix, is an important prerequisite for cancer cell metastasis. In this communication, we demonstrate that shRNA-mediated depletion of α2 integrin subunit induces anoikis and substantially decreases colony-forming potential in SK-Mel-147 human melanoma cells. Suppression of α2β1 upregulates the levels of pro-apoptotic protein p53 and cyclin-dependent kinase inhibitors p21 and p27. Concomitantly, we detected decrease in the levels of anti-apoptotic protein Bcl-2 and cell cycle regulator c-Myc. Moreover, depletion of α2β1 reduces the activity of protein kinase Erk, while increases activity of Akt kinase. Pharmacological inhibition of P3IK kinase, an upstream activator of Akt, greatly enhanced anoikis in control cells while reduced that in cells with decreased levels of α2β1. Of three isoforms of Akt, down-regulation of Akt1 greatly diminished anoikis of cells depleted of α2β1, while down-regulation of Akt2 and Akt3 sharply increased anoikis in these cells. These findings were supported by the data of pharmacological inhibition of the Akt isoforms. Our results demonstrate for the first time that anoikis induced by α2β1 integrin knockdown can be attenuated by Akt1 inhibition.

Conjugates of 17-substituted testosterone and epitestosterone with pyropheophorbide a differing in the length of linkers

Conjugates of 17α-substituted testosterone (1 and 2) and 17β-substituted epitestosterone (3 and 4) with pyropheophorbide a were synthesized. The scheme consisted of synthesis of 17α-hydroxy-3-oxopregn-4-en-21-oic and 17β-hydroxy-3-oxopregn-4-en-21-oic acids, and their coupling with pyropheophorbide a by means of either ethylene diamine, or 1,5-diamino pentane linkers. Mutual influence of steroidal and macrocyclic fragments in conjugates molecules was dependent on configuration of C17 and length of linker, that was established by analysis of ¹H NMR spectra and molecular models of conjugates. Studies of interaction of conjugates with prostate carcinoma cells revealed that their uptake and internalization were independent on the androgen receptor activity, but dependent on the structure of conjugates, decreasing in the following row: 3 > 4 ≥ 1 > 2. Conjugates significantly decreased the LNCaP and PC-3 cells growth at 96 h incubation. Epitestosterone derivatives 3 and 4 also showed superior anti-proliferative activity versus testosterone ones. Conformationally more rigid conjugates 1 and 3, comprising short linkers, were more active than those with long linkers; conjugate 3 was the most potent.

Implication of Integrin α2β1 in Proliferation and Invasion of Human Breast Carcinoma and Melanoma Cells: Noncanonical Function of Akt Protein Kinase

Blocking the expression of integrin α2β1, which was accomplished by transduction of α2-specific shRNA, resulted in significant inhibition of proliferation and clonal activity in human MCF-7 breast carcinoma and SK-Mel-147 melanoma cells. Along with these changes, deprivation of α2β1 caused a sharp decrease in melanoma cell invasion in vitro. Analysis of integrin-mediating signal pathways that control cell behavior revealed a significant increase in activity of Akt protein kinase in response to depletion of α2β1. The increase in Akt activity that accompanies a suppressive effect on cell invasion contradicts well-known Akt function aimed at stimulation of tumor progression. This contradiction could be explained by the "reversed" (noncanonical) role played by Akt in some cells that consists in suppression rather than promotion of invasive phenotype. To test this suggestion, the effects of Akt inhibitors on invasive activity of SK-Mel-147 cells were investigated. If the above suggestion is true, then inhibition of Akt in cells depleted of α2β1 should result in the restoration of their invasive activity. It appeared that treatment with LY294002, which inhibits all Akt isoforms (Akt1, Akt2, Akt3), not only failed to restore the invasive phenotype of melanoma cells but further attenuated their invasive activity. However, treatment of the cells with an Akt1-specific inhibitor significantly increased their invasion. Thus, the stimulating effect of α2β1 integrin on invasion of melanoma cells is realized through a mechanism based on inhibition of one of the Akt isoforms, which in these cells exhibits a noncanonical function consisting in suppression of invasion.

FOXQ1 controls the induced differentiation of melanocytic cells

Oncogenic transcription factor FOXQ1 has been implicated in promotion of multiple transformed phenotypes in carcinoma cells. Recently, we have characterized FOXQ1 as a melanoma tumor suppressor that acts via repression of N-cadherin gene, and invasion and metastasis. Here we report that FOXQ1 induces differentiation in normal and transformed melanocytic cells at least partially via direct transcriptional activation of MITF gene, melanocytic lineage-specific regulator of differentiation. Importantly, we demonstrate that pigmentation induced in cultured melanocytic cells and in mice by activation of cAMP/CREB1 pathway depends in large part on FOXQ1. Moreover, our data reveal that FOXQ1 acts as a critical mediator of BRAF^V600E-dependent regulation of MITF levels, thus providing a novel link between two major signal transduction pathways controlling MITF and differentiation in melanocytic cells.

Comparison of [17(20)E]-21-Norpregnene oxazolinyl and benzoxazolyl derivatives as inhibitors of CYP17A1 activity and prostate carcinoma cells growth

Four new 4,5-dihydro-1,3-oxazole, and four new benzo-[d]-oxazole derivatives of [17(20)E]-21-norpregnene, differing in the structure of steroid moiety, were synthesized and evaluated for their potency to inhibit 17α-hydroxylase/17,20-lyase (CYP17A1) activity. Among new compounds, the only oxazolinyl derivative comprising 5-oxo-4,5-seco-3-yn- moiety potently inhibited CYP17A1. Binding modes of the oxazolinyl derivatives of [17(20)E]-21-norpregnene were analyzed by molecular dynamics simulations, and model of alternate, water-bridged type II interaction was proposed for these compounds. Eight new compounds, together with two CYP17A1-inhibiting oxazolinyl derivatives synthesized earlier, abiraterone and galeterone were evaluated for their potency to inhibit prostate carcinoma PC-3 and LNCaP cells growth. Oxazolinyl and benzoxazolyl derivatives comprising 3β-hydroxy-5-ene moieties potently inhibited prostate carcinoma cell growth; inhibitory potencies of 3-oxo-4-en- and 5-oxo-4,5-seco-3-yn- derivatives were significantly lower.

Hyperexpression of Integrin α5β1 Promotes Resistance of MCF-7 Human Breast Carcinoma Cells to Doxorubicin via ERK Protein Kinase Down-regulation

In MCF-7 human breast carcinoma cells, α5β1 integrin hyperexpression, which was accomplished by transduction of a full-length α5 integrin cDNA, increased by about 50-70% the number of cells, survived during 48-72 h cell treatment with doxorubicin. Up-regulation of α5β1 reduced the level of the apoptogenic p53 protein and p21 cell cycle inhibitor, but enhanced the activity of Akt and mTOR protein kinases. In addition to these findings, we observed a significant decrease in the activity of both isoforms of phosphokinase Erk1/2, which is known to play a key role in cell viability pathways, including pathways alleviating stress damages caused by distinct antitumor drugs. Diminished Erk activity accompanying the rise of drug resistance can be explained by an "atypical" function of this kinase, which, in the cells studied, promotes an enhanced rather than reduced sensitivity to doxorubicin. To verify this suggestion, the effect of a specific Erk inhibitor, PD98059, on the resistance to doxorubicin of control and α5 cDNA-transduced MCF-7 cells was investigated. The data showed that suppression of Erk activity increased the resistance of control cells (transduced with an "empty" vector) to a level higher than that demonstrated by the α5 cDNA-transduced cells. The highest level of resistance was observed in α5β1-trancduced cells treated with PD98059. Akt and mTOR kinase inhibitors had little if any effect on doxorubicin resistance of α5 cDNA-transduced MCF-7 cells. The data show for the first time that integrin α5β1 can stimulate drug resistance of tumor cells through a mechanism based on the inhibition of protein kinase Erk. From a more general view, the results of this investigation suggest that signal protein kinases can perform in tumor cells "non-canonical" functions, opposite to those, which are the basis for using kinase inhibitors in targeted cancer therapy. It follows that if a protein kinase is supposed to be used as a target for such therapy, it is important to explore its features in the particular tumor prior to the onset of treatment.

Pharmacological targeting of guanosine monophosphate synthase suppresses melanoma cell invasion and tumorigenicity

Malignant melanoma possesses one of the highest metastatic potentials among human cancers. Acquisition of invasive phenotypes is a prerequisite for melanoma metastases. Elucidation of the molecular mechanisms underlying melanoma invasion will greatly enhance the design of novel agents for melanoma therapeutic intervention. Here, we report that guanosine monophosphate synthase (GMPS), an enzyme required for the de novo biosynthesis of GMP, has a major role in invasion and tumorigenicity of cells derived from either BRAF(V600E) or NRAS(Q61R) human metastatic melanomas. Moreover, GMPS levels are increased in metastatic human melanoma specimens compared with primary melanomas arguing that GMPS is an attractive candidate for anti-melanoma therapy. Accordingly, for the first time we demonstrate that angustmycin A, a nucleoside-analog inhibitor of GMPS produced by Streptomyces hygroscopius efficiently suppresses melanoma cell invasion in vitro and tumorigenicity in immunocompromised mice. Our data identify GMPS as a powerful driver of melanoma cell invasion and warrant further investigation of angustmycin A as a novel anti-melanoma agent.

Implication of α2β1 integrin in anoikis of MCF-7 human breast carcinoma cells

Silencing of α2β1 integrin expression significantly promoted anchorage-dependent apoptosis (anoikis) and drastically reduced clonal activity of MCF-7 human breast carcinoma cells. Depletion of α2β1 enhanced the production of apoptotic protein p53 and of inhibitor of cyclin-dependent protein kinases, p27, while downregulating antiapoptotic protein Bcl-2 and multifunctional protein cMyc. Blocking the expression of α2β1 had no effect on activity of protein kinase Akt, but it sharply increased the kinase activity of Erk1/2. Pharmacological inhibition of Erk1/2 had a minor effect on anoikis of control cells, while it reduced anoikis of cells with downregulated α2β1 to the level of control cells. The data show for the first time that integrin α2β1 is implicated in the protection of tumor cells from anoikis through a mechanism based on the inhibition of protein kinase Erk.

[Molecular modeling of interaction of 17(20)Z- and 17(20)E-pregna-5,17(20)-dien-21-oyl amides with the nuclear receptor LXRbeta]

Aiming the search of novel regulators of lipid metabolism and their potential targets, in this study we performed molecular modeling of eight isomeric 17(20)Z- and 17(20)E-pregna-5,17(20)-dien-21-oyl amides differing in structure of the amide moiety. Analysis of the low energy conformers revealed that all 17(20)E-isomers had three main energy minima (corresponding to values of the dihedral angle theta20,21 (C17 = C20-C21 = 0) to approximately 0 degrees, to approximately 120 degrees and to approximately 240 degrees), the most occupied minimum was found to correspond to theta20,21 to approximately 0 degrees; while 17(20)Z-isomers had either one or two pools of low energy conformations. Molecular docking of these compounds to the ligand-binding site of the nuclear receptor LXRbeta (a potential target) indicates high probability of binding for E-isomers and the absence of that for Z-isomers. Results of the molecular modeling were confirmed by an experiment in which stimulation of triglyceride biosynthesis in Hep G2 cells in the presence of 17(20)E-3beta-hydroxypregna-5,17(20)-dien-21-oyl (hydroxyethyl)amide was demonstrated.

[Integrins as a potential target for targeted anticancer therapy]

The review briefly summarizes information of structure of integrins and their involvement in the development and malignant progression of tumors. Special attention is paid to approaches based on modification of functional properties of integrins that prevent/antagonize tumor growth and progression; these approaches developed in modem experimental biology have certain perspective in clinical application.

Integrin α5β1 simultaneously controls EGFR-dependent proliferation and Akt-dependent pro-survival signaling in epidermoid carcinoma cells

To delineate distinctive role of the components of α5β1 integrin-EGFR axis in control of epidermoid carcinoma cell proliferation, we performed individual inhibition of α5β1 and EGFR via genetic and phamacological methods, respectively. We demonstrated that pharmacological inhibition of epidermal growth factor receptor (EGFR) significantly affected proliferation of A431 human cells by inducing the G0/G1 cell cycle arrest, whereas shRNA-mediated depletion of α5 subunit of α5β1 integrin led to a similar type of cell cycle arrest followed by significant apoptosis. Both treatments resulted in suppression of activated (phosphorylated) forms of focal adhesion kinase (FAK) and Erk. However, unlike EGFR inhibition, depletion of α5 led to substantial suppression of AKT activity. Accordingly, pharmacological inhibition of EGFR and AKT recapitulated detrimental effects caused by shRNA-mediated depletion of α5. Moreover, depletion of α5 led to a severe drop in the amounts of active EGFR. Thus, for the first time, we demonstrated that α5β1 integrin simultaneously maintains pro-survival signaling via continuous activation of AKT and up-regulates proliferation via activation of EGFR.

[Implication of integrin alpha5beta1 in human breast carcinoma apoptosis and drug resistance]

Doxorubicin-resistant MCF-7Dox line, which is a derivative of the drug-sensitive MCF-7 human breast carcinoma line, differs from the latter by a strongly reduced expression of the alpha2beta1 integrin and a highly increased expression of the alpha5beta1 receptor. Silencing of this integrin in the MCF-7Dox cells by transfection with alpha5-specific siRNA markedly stimulated anoikis and increased sensitivity of the cells to doxorubicin. Alpha5beta1 silencing also leads to significant inhibition of the activity of kinases Akt and Erk2 in MCF-7Dox cells. Our results suggest that integrins alpha5beta1-induced signals, controlling distinct aspects of cell behavior, are conducted through the common signal pathways.

Fucans, but not fucomannoglucuronans, determine the biological activities of sulfated polysaccharides from Laminaria saccharina brown seaweed

Sulfated polysaccharides from Laminaria saccharina (new name: Saccharina latissima) brown seaweed show promising activity for the treatment of inflammation, thrombosis, and cancer; yet the molecular mechanisms underlying these properties remain poorly understood. The aim of this work was to characterize, using in vitro and in vivo strategies, the anti-inflammatory, anti-coagulant, anti-angiogenic, and anti-tumor activities of two main sulfated polysaccharide fractions obtained from L. saccharina: a) L.s.-1.0 fraction mainly consisting of O-sulfated mannoglucuronofucans and b) L.s.-1.25 fraction mainly composed of sulfated fucans. Both fractions inhibited leukocyte recruitment in a model of inflammation in rats, although L.s.-1.25 appeared to be more active than L.s.-1.0. Also, these fractions inhibited neutrophil adhesion to platelets under flow. Only fraction L.s.-1.25, but not L.s.-1.0, displayed anticoagulant activity as measured by the activated partial thromboplastin time. Investigation of these fractions in angiogenesis settings revealed that only L.s.-1.25 strongly inhibited fetal bovine serum (FBS) induced in vitro tubulogenesis. This effect correlated with a reduction in plasminogen activator inhibitor-1 (PAI-1) levels in L.s.-1.25-treated endothelial cells. Furthermore, only parent sulfated polysaccharides from L. saccharina (L.s.-P) and its fraction L.s.-1.25 were powerful inhibitors of basic fibroblast growth factor (bFGF) induced pathways. Consistently, the L.s.-1.25 fraction as well as L.s.-P successfully interfered with fibroblast binding to human bFGF. The incorporation of L.s.-P or L.s.-1.25, but not L.s.-1.0 into Matrigel plugs containing melanoma cells induced a significant reduction in hemoglobin content as well in the frequency of tumor-associated blood vessels. Moreover, i.p. administrations of L.s.-1.25, as well as L.s.-P, but not L.s.-1.0, resulted in a significant reduction of tumor growth when inoculated into syngeneic mice. Finally, L.s.-1.25 markedly inhibited breast cancer cell adhesion to human platelet-coated surfaces. Thus, sulfated fucans are mainly responsible for the anti-inflammatory, anticoagulant, antiangiogenic, and antitumor activities of sulfated polysaccharides from L. saccharina brown seaweed.

[Anticoagulant activity of fucoidans from brown algae]

The anticoagulant activity of polysaccharide fucoidans from 11 species of brown algae was studied. The anticoagulant activity was measured by the activated partial thromboplastin time (APTT), prothrombin time and thrombin time. Inhibitory action of fucoidans varied significantly from one species to another. Fucoidans from Laminaria saccharina and Fucus distichus showed high anticoagulant activities, while fucoidans from Cladosiphon okamuranus and Analipus japonicus were almost inactive. The fucoidan inhibitory effect on thrombin and factor Xa in the presence or in the absence of natural thrombin inhibitor, antithrombin III (AT III), was also studied. In contrast to the best studied anticoagulant heparin the most of the fucoidans inhibited thrombin in the absence of AT III. In the presence of AT III inhibitory effect of fucoidans was increased considerably. Unlike heparin, the effect of fucoidans on factor Xa was very weak in the presence of AT III and was not observed in the absence of AT III. The correlation between the anticoagulant activities of this series of fucoidans and their anti-inflammatory action, studied by us earlier, was not found. It is expected that two these types of fucoidan activities depend on different structural features of fucoidans. These findings show the possibility to obtain fucoidans with high anti-inflammatory action and with low anticoagulant activity. Anticoagulant activity of the fucoidans did not depend on the content of fucose, the other neutral sugars and sulfates in the preparations, and also on the structure of the backbone of molecule. Taken together, these results indicate on prospects of fucoidan study as potential therapeutic agents.

Synthesis and cytotoxicity evaluation of 22,23-oxygenated stigmastane derivatives

Starting from (22E)-3alpha,5alpha-cyclo-6beta-methoxystigmast-22-ene eighteen derivatives of (22S,23S)-22,23-oxidostigmastane, (22R,23R)-22,23-oxidostigmastane, and (22R,23R)-22,23-dihydroxystigmastane were synthesized and screened for cytotoxicity in human hepatoma Hep G2 cells and human breast carcinoma MCF-7 cells using MTT assay. Four compounds of this series exhibited high cytotoxicity in both cells; three compounds were selectively toxic in MCF-7 cells, one compound was toxic in Hep G2 cells, rather than in MCF-7 cells; four compounds at low concentrations increased MTT test values over the control.

Cytotoxic derivatives of (22R,23R)-dihydroxystigmastane

(22R,23R)-22,23-dihydroxystigmast-4-en-3-one, (22R,23R)-22,23-dihydroxystigmast-4-en-3,6-dione, (22R,23R)-3beta,5alpha,6beta,22,23-pentahydroxystigmastane, (22R,23R)-5alpha,6alpha-oxido-3beta,22,23-trihydroxystigmastane, (22R,23R)-5beta,6beta-oxido-3beta,22,23-trihydroxystigmastane, and (22R,23R)-3beta,6beta,22,23-tetrahydroxystigmast-4-ene were synthesized. Their cytotoxicities were comparatively studied using the MCF-7 line of carcinoma cells of human mammary gland and cells of human hepatoma of the Hep G2 line.

A comparative study of the anti-inflammatory, anticoagulant, antiangiogenic, and antiadhesive activities of nine different fucoidans from brown seaweeds

The anti-inflammatory, antiangiogenic, anticoagulant, and antiadhesive properties of fucoidans obtained from nine species of brown algae were studied in order to examine the influence of fucoidan origin and composition on their biological activities. All fucoidans inhibited leucocyte recruitment in an inflammation model in rats, and neither the content of fucose and sulfate nor other structural features of their polysaccharide backbones significantly affected the efficacy of fucoidans in this model. In vitro evaluation of P-selectin-mediated neutrophil adhesion to platelets under flow conditions revealed that only polysaccharides from Laminaria saccharina, L. digitata, Fucus evanescens, F. serratus, F. distichus, F. spiralis, and Ascophyllum nodosum could serve as P-selectin inhibitors. All fucoidans, except that from Cladosiphon okamuranus carrying substantial levels of 2-O-alpha-D-glucuronopyranosyl branches in the linear (1-->3)-linked poly-alpha-fucopyranoside chain, exhibited anticoagulant activity as measured by activated partial thromboplastin time whereas only fucoidans from L. saccharina, L. digitata, F. serratus, F. distichus, and F. evanescens displayed strong antithrombin activity in a platelet aggregation test. The last fucoidans potently inhibited human umbilical vein endothelial cell (HUVEC) tubulogenesis in vitro and this property correlated with decreased levels of plasminogen-activator inhibitor-1 in HUVEC supernatants, suggesting a possible mechanism of fucoidan-induced inhibition of tubulogenesis. Finally, fucoidans from L. saccharina, L. digitata, F. serratus, F. distichus, and F. vesiculosus strongly blocked MDA-MB-231 breast carcinoma cell adhesion to platelets, an effect which might have critical implications in tumor metastasis. The data presented herein provide a new rationale for the development of potential drugs for thrombosis, inflammation, and tumor progression.

Novel side chain modified Delta8(14)-15-ketosterols

Synthesis of five novel Delta8(14)-15-ketosterols comprising modified side chains starting from ergosterol is described. Ergosteryl acetate was converted into (22E)-3beta-acetoxy-5alpha-ergosta-8(14),22-dien-15-one through three stages in 32% overall yield; further transformations of the product obtained led to (22E)-3beta-hydroxy-5alpha-ergosta-8(14),22-dien-15-one, (22S,23S)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one, (22R,23R)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one, (22R,23R)-5alpha-ergost-8(14)-en-15-on-3beta,22,23-triol and (22R,23R)-3beta-hydroxy-22,23-isopropylidenedioxy-5alpha-ergost-8(14)-en-15-one. New Delta8(14)-15-ketosterols were evaluated for their cytotoxicity and effects on sterol biosynthesis in human hepatoma Hep G2 cells in comparison with known 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. Among the compounds tested, (22R,23R)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one was found to be the most potent inhibitor of sterol biosynthesis (IC(50)=0.6+/-0.2microM), whereas (22R,23R)-5alpha-ergost-8(14)-en-15-on-3beta,22,23-triol exhibited the highest cytotoxicity (TC(50)=12+/-3microM at a 24h incubation).

Δ5-7-Ketosterols with modified side chain: The synthesis and the effects on viability and cholesterol biosynthesis in Hep G2 cells

(22E)-3beta-Hydroxysitosta-5,22-dien-7-one, (22R, 23R)-3beta,22,23-trihydroxysitost-5-en-7-one, and (22R, 23R)-3beta-hydroxy-22,23-isopropylidenedioxysitost-5-en-7-one were synthesized. The cytotoxicity and effects on cholesterol biosynthesis of the resulting 7-ketosterols, 7-ketocholesterol, and (22S,23S)-3beta-hydroxy-22,23-oxidositost-5-en-7-one were studied in hepatoblastoma Hep G2 cells.

The role of beta1 integrin subfamily in anchorage-dependent apoptosis of breast carcinoma cells differing in multidrug resistance

Integrin expression was investigated in MCF-7 human breast adenocarcinoma line and in the MCF-7Dox line, which was selected from MCF-7 by a resistance to multiple antitumor drugs (MDR). We have shown that acquisition of MDR was accompanied by a drastically reduced expression of some integrins of the beta1-subfamily (alpha2beta1, alpha3beta1, alpha6beta1) and of alpha vbeta5 intergin in the adenocarcinoma cells. In contrast, expression of alpha5beta1 integrin was markedly increased in the MDR cells. Along with multiple antitumor drug resistance, MCF-7Dox cells demonstrate elevated resistance to anchorage-dependent apoptosis (anoikis) and enhanced in vitro invasive activity. To elucidate the implication of beta1-integrins in the above phenotypic modifications, the effect of beta1-integrin signaling was assayed. Stimulation of beta1-mediated signaling was accomplished by treating of the cells with antibodies to the beta1-subunit common for members of the beta1-subfamily. These data show that activation of beta1-integrin signaling markedly upregulated anoikis of the adenocarcinoma cells.

Integrins: structure and signaling

Integrins are cell surface transmembrane glycoproteins that function as adhesion receptors in cell-extracellular matrix interactions and link the matrix proteins to the cytoskeleton. The family of human integrins comprises 24 members, each of which is a heterodimer consisting of 1 of 18 alpha- and 1 of 8 beta-subunits. Integrins play an important role in the cytoskeleton organization and in transduction of intracellular signals, regulating various processes such as proliferation, differentiation, apoptosis, and cell migration. This review summarizes current views on the structure of integrins, integrin associated proteins, and biochemical mechanisms underlying their signaling functions.

Expression and Role of Integrins in Invasive Activity of Oncotransformed Fibroblasts Differing in Spontaneous Metastasizing

Four closely related lines of RSV-transformed Syrian hamster fibroblasts differing drastically in their spontaneous metastatic capacity were investigated for the surface expression of integrins, in vitro invasion, and production of MMP-2 collagenase. The highly metastasizing HET-SR-2SC-LNM cells differ from the lowly metastasizing parental HET-SR cells in a high level of the surface expression of the collagen-specific alpha1beta1, alpha2beta1, and alphavbeta3 integrins, a high invasive activity, and an increased production of MMP-2. The same properties are characteristic for the actively metastasizing cells of the independent HET-SR-1 line. The lowly metastasizing fibroblasts that are derived from HET-SR-2SC-LNM retain a high level of the expression of the alpha1beta1 and alpha2beta1 integrins, but, unlike the parental line, they exhibit a decreased expression of the alphavbeta3 integrin, invasion in Matrigel, and MMP-2 production. Substrate stimulation of the signal function of the collagen-specific integrins increases the production of MMP-2 by the metastatically active fibroblasts. Inhibition of the signal activity of the integrins by RGD-containing pentapeptide or by genistein reduces markedly in vitro invasion in Matrigel and MMP-2 production. The role of specific properties of the extracellular matrix surrounding tumor cells and of specific surface integrins expressed in these cells in developing of the malignant phenotype is discussed.

Multidrug-resistant tumor cells with decreased malignancy: a role for integrin αvβ3

We studied whether acquisition of multidrug resistance (MDR) by tumor cells can alter their integrin profile and malignant behavior. Hamster fibroblast cell line HET-SR-2SC-LNM was selected for MDR, yielding the 2SC/20 subline. Compared with the parental cells, the 2SC/20 subline weakly adhered to denatured collagen (dCol) which correlated with decreased expression of alphavbeta3, a dCol receptor. Importantly, 2SC/20 subline demonstrated significantly decreased activity of collagenase MMP-2, lower ability to invade Matrigel, and attenuated metastasis in syngeneic animals. We provide evidence for the first time that selection for MDR can be associated with down-regulation of alphavbeta3 integrin, supporting our recent proof of the pro-apoptotic role of this integrin (Oncogene 20 (2001) 4710). Lack of alphavbeta3 expression may link cell survival under toxic conditions with decreased malignancy of the resulting drug resistant tumor.

Role of integrin alphavbeta3 in substrate-dependent apoptosis of human intestinal carcinoma cells

Incubation of human intestinal carcinoma Caco-2 cells in suspension (i.e., in the absence of substrate contacts) leads to massive cell death by apoptosis. Since this type of apoptosis has been referred to as anoikis, we designated these cells as anoikis-positive. However, a minor proportion of Caco-2 cells, designated as anoikis-negative, survived in suspension. Extended incubation of the cells in suspension resulted in the reduction of the number of viable cells. In comparison to the original Caco-2 cell population, the anoikis-negative cells demonstrated markedly decreased levels of expression of integrin alphavbeta3 on the cell surface and of transcription of the alphav subunit gene. Activation of the signaling function of alphavbeta3 in the original Caco-2 cells led to substantial stimulation of anoikis, while the inhibition of expression of this receptor resulted in better resistance of the cells to anoikis. The data provide the first evidence that alphavbeta3 integrin can generate apoptosis-stimulating signals.

[The role of alphavbeta3 integrin in changes of the invasive phenotype in CP-transformed fibroblasts with multiple drug resistance]

A line of Syrian hamster RSV-ransformed fibroblasts having resistance to a number of cytostatics was shown to differ from the parental drug-sensitive line by an extremaly low expression of the integrin alpha v beta 3. In vitro invasive activity of the drug-resistrant cells appeared to be lower than that of their drug-sensitive counterparts. The role of integrin alpha v beta 3 in malignant phenotype and multiple drug resistance of tumor cells is discussed.

Integrin alphavbeta3 promotes anchorage-dependent apoptosis in human intestinal carcinoma cells

A population of cells surviving during prolonged incubation in suspension (anoikis-negative cells) were selected from the original anoikis-positive human intestinal carcinoma cell line Caco-2. Anoikis-negative cells are characterized by a strong transcriptional downregulation of the alphav-integrin chain as detected by FACS analysis, RT-PCR and Northern blotting. This finding suggested that alphav-integrin generates a signal stimulating apoptosis of Caco-2 cells upon their detachment from the extracellular matrix. Two lines of evidence supporting this suggestion were provided. First, activation of the alphavbeta3 integrin on Caco-2 cells by their treatment with an alphavbeta3-specific monoclonal antibody resulted in marked stimulation of anoikis. Second, treatment of Caco-2 cells with alphav-specific antisense oligonucleotide resulted in downregulation of the expression of alphav chain and in elevated resistance of these cells to anoikis. Thus, for the first time, our data prove that alphavbeta3 integrin can be an active transducer of apoptosis-stimulating signals generated in response to disruption of the cell-matrix contacts.

Integrin expression and collagenase activity of RSV-transformed Syrian hamster fibroblasts, differing in spontaneous metastasizing

The expression of extracellular matrix (ECM) specific receptors, integrins, and the activities of type IV collagenase and interstitial collagenase were investigated in two strains of oncogenically transformed fibroblasts, drastically differing in spontaneous metastasizing. Both strains were shown to express quite limited patterns of integrins. Of those, alpha 5 beta 1 integrin is greatly reduced on highly metastatic (HM) cells, while the expression of alpha v beta 3 is strongly suppressed on lowly metastatic (LM) fibroblasts. No differences between the strains were found in either intracellular or secreted activities of type IV collagenase, while the activity of interstittial collagenase, secreted by HM cells, was twice as much as secreted by LM cells. The results imply the role of cooperated modifications of integrin-directed cell-ECM interaction and collagenase activity in establishing a metastatic phenotype.

[Determination of procollagen type III aminopropeptide by a solid phase method using antibodies conjugated with peroxidase or protein A labelled with radioactive iodine]

A solid-phase assay was developed for estimation of procollagen III aminopropeptide which involved both immunoenzymatic and radioimmune procedures. The assay did not require the iodine-labelled aminopropeptide, while content of the antigen was estimated using the conjugate of secondary antibodies and peroxidase or iodine-labelled protein A. Substitution of the protein A for the antibodies conjugate and peroxidase enabled to abolish the radioactive materials use.

Secretion and intracellular degradation of collagen in cultures of normal and SV-40-transformed human fibroblasts

With a pulse-chase technique, secretion and intracellular degradation of collagen were investigated in human cultured normal and SV-40-transformed fibroblasts. Normal cells at a proliferative phase of growth secreted collagen more actively than the stationary phase (resting) cells. Transformed fibroblasts secreted protein at a lower rate than both normal cell types. Resting and dividing normal cells displayed no differences in the rates of intracellular collagen degradation at the various stages of the chase period. Transformed cells did not differ from the normal ones in collagen degradation rates at the first hour of the chase period while at later times in the chase period, the total amount of degraded collagen was reduced by 20-30% in the transformed vs normal cultures. The data are discussed in the view of possible relations between the various mechanisms of intracellular transport and degradation of collagen.

[Biosynthesis and secretion of collagen in normal and SV-40 virus-transformed human embryonal fibroblasts]

The biosynthesis and secretion of collagen proteins was studied in cultures of normal human embryo fibroblasts at different passages and growth stages as well as in cultures of human embryo fibroblasts transformed by oncogenic virus SV-40. It was found that normal fibroblasts maintain at a constant level the collagen synthesis throughout 20 passages, which is typical of proliferating and resting cells. Virus-transformed cells produce 3-4 times less collagen proteins on a per cell count. Normal and transformed fibroblasts do not differ in terms of total protein synthesis. Secretion of collagen and non-collagen proteins in transformed cell cultures appeared to be much lower than in normal cell cultures. Study of synthesized proteins by polyacrylamide gel electrophoresis showed that both types of cells secrete collagen proteins predominantly as polymers containing interchain S-S bonds of 3-helix molecules. Study of the protein-synthesizing activity of two polysomal fractions, i.e. membrane bound and free polysomes, isolated from the cells of both types in a cell-free system showed that membrane-bound polysomes from transformed fibroblasts synthesize collagen much less actively in comparison with normal cells. However, in transformed cells free polysomes, in contrast with normal cells, are active participants of a cell-free collagen protein synthesis.

[Characteristics of collagen preparations labelled in vitro by 14C-acetic anhydrides. Their use for the determination of collagenase activity and as radioactive markers]

A modified procedure in developed for acetylation by means of 14C-acetic anhydride of highly purified collagen I preparations. The acetylated collagen exhibited high specific radioactivity and was effectively hydrolyzed by bacterial collagenase. The 14C-acetylated collagen was used as a radioactive marker in electrophoretic analysis of labelled proteins.