Antitumor activity of some natural flavonoids and synthetic derivatives on various human and murine cancer cell lines

The effect of various natural flavonoids, cinnamic acid derivatives, and a series of synthetic flavones on cell proliferation was evaluated in vitro in a panel of established human and murine tumor cell lines. The most potent antiproliferative agents were caffeic acid n-butyl ester (12) > 2'-nitroflavone (26) > caffeic acid ethyl ester (11) approximately = 2',6-dinitroflavone (27) > apigenin (3) > 3'-bromoflavone (20) approximately = 2'-fluoro-6-bromoflavone (31). Some compounds showed a moderate effect, the order of cytotoxic activities being chrysin (2) > 2'-fluoro-6-chloroflavone (30) approximately = 2'-chlorochrysin (32) > alpha-naphthoflavone (7) > beta-naphthoflavone (8) approximately = 6-chloroflavone (14) approximately = 6-bromoflavone (15) approximately = 4'-nitroflavone (23). A structure-activity relationship analysis of each group of compounds was performed. None of the natural or synthetic compounds tested affected the proliferation of epithelial cells derived from normal mammary gland of mice or fibroblastic cells from mouse embryo, suggesting a selective action against tumor cells.

Crosstalk between oxidative stress-induced apoptotic and autophagic signaling pathways in Zn(II) phthalocyanine photodynamic therapy of melanoma

Melanoma is the most aggressive type of skin cancer, highly resistant to conventional therapies. Photodynamic therapy (PDT) is a minimally invasive treatment modality that combines the use of a photosensitizer, visible light and molecular oxygen, leading to oxidative stress in the specific site of irradiation. The cationic zinc(II) phthalocyanine Pc13 has shown to be a potent photosensitizer in different melanoma cell lines. In this study, we explored the intracellular signaling pathways triggered by Pc13 PDT and the role of these cascades in the phototoxic action of Pc13 in human melanoma A375 cells. Activation of MAPKs p38, ERK, JNK and PI3K-I/AKT was observed after treatment and prevented by using the antioxidant trolox. Inhibition of p38 reduced Pc13 phototoxicity, whereas blockage of JNK potentiated cell death. Results obtained indicate that p38 is involved in the cleavage of PARP-1, an important mediator of apoptosis. On the other hand, Pc13 irradiation induced the activation of an autophagic program, as evidenced by enhanced levels of Beclin-1, LC3-II and GFP-LC3 punctate staining. We also demonstrated that this autophagic response is promoted by JNK and negatively regulated by PI3K-I/AKT pathway. The blockage of autophagy increased Pc13 phototoxicity and enhanced PARP-1 cleavage, revealing a protective role of this mechanism, which tends to prevent apoptotic cell death. Furthermore, reduced susceptibility to treatment and increased activation of autophagy were detected in A375 cells submitted to repeated cycles of Pc13 PDT, indicating that autophagy could represent a mechanism of resistance to PDT. The efficacy of Pc13 PDT and an improved phototoxic action in combination with chloroquine were also demonstrated in tumor spheroids. In conclusion, we showed the interplay between apoptotic and autophagic signaling pathways triggered by Pc13 PDT-induced oxidative stress. Thus, autophagy modulation represents a promising therapeutic strategy to potentiate the efficacy of PDT in melanoma.

Photodynamic effects of zinc(II) phthalocyanine-loaded polymeric micelles in human nasopharynx KB carcinoma cells

A major difficulty in photodynamic therapy is the poor solubility of the photosensitizer (PS) under physiological conditions which correlates with low bioavailability. PS aggregation leads to a decrease in the photodynamic efficiency and a more limited activity in vitro and in vivo. To improve the aqueous solubility and reduce the aggregation of 2,9(10),16(17),23(24)-tetrakis[(2-dimethylamino)ethylsulfanyl]phthal-ocyaninatozinc(II) (Pc9), the encapsulation into four poloxamine polymeric micelles (T304, T904, T1107 and T1307) displaying a broad spectrum of molecular weight and hydrophilic-lipophilic balance was investigated. The aqueous solubility of Pc9 was increased up to 30 times. Morphological evaluation showed the formation of Pc9-loaded spherical micelles in the nanosize range. UV/Vis and fluorescence studies indicated that Pc9 is less aggregated upon encapsulation in comparison with Pc9 in water-DMSO 2% and remained photostable. Pc9-loaded micelles generated singlet molecular oxygen in high yields. Photocytotoxicity assays using human nasopharynx KB carcinoma cells confirmed that the encapsulation of Pc9 in T1107 and T1307 increases its photocytotoxicity by 10 times in comparison with the free form in water-DMSO. In addition, Pc9 incorporated into cells was mainly localized in lysosomes.

Monoclonal Antibodies Inducing Conformational Changes on the Antigen Molecule

Monoclonal antibodies (MoAbs) are extensively used as biological tools because of their invariable specificity. However, the interpretation of results can be misled by the behaviour of MoAb displaying allosteric effects, i.e. long-range conformational changes on the antigen (Ag). It has been shown that some MoAbs are able to modify the spatial structure of the corresponding protein Ag, affecting in this way its biological activity as well as its binding to a second MoAb. Thus, a researcher using a MoAb as a tool to investigate some features of an antigenic molecule must be aware of the possible positive or negative allosteric properties of the antibody.

Antiproliferative activity of various flavonoids and related compounds: additive effect of interferon-α2b

The antiproliferative activity of several natural and synthetic flavonoids and some related compounds was evaluated in vitro against a cell line derived from a human cervical carcinoma (WISH cells). According to their activities, the most potent derivatives were 2'-nitroflavone (14), 2',6-dinitroflavone (15) and the n-buthyl ester of caffeic acid (29). When these compounds were tested in the presence of recombinant human interferon-alpha2b (rhIFN-alpha2b), a cytokine exhibiting an antimitogenic action on WISH cells, an additive effect on cell growth inhibition was observed. Time course studies of the antiproliferative action exerted by the active derivatives or the rhIFN-alpha2b suggested that these compounds induced cell death.

Nanoclusters of crystallographically aligned nanoparticles for magnetic thermotherapy: aqueous ferrofluid, agarose phantoms and ex vivo melanoma tumour assessment

Magnetic hyperthermia is an oncological therapy where magnetic nanostructures, under a radiofrequency field, act as heat transducers increasing tumour temperature and killing cancerous cells. Nanostructure heating efficiency depends both on the field conditions and on the nanostructure properties and mobility inside the tumour. Such nanostructures are often incorrectly bench-marketed in the colloidal state and using field settings far off from the recommended therapeutic values. Here, we prepared nanoclusters composed of iron oxide magnetite nanoparticles crystallographically aligned and their specific absorption rate (SAR) values were calorimetrically determined in physiological fluids, agarose-gel-phantoms and ex vivo tumours extracted from mice challenged with B16-F0 melanoma cells. A portable, multipurpose applicator using medical field settings; 100 kHz and 9.3 kA m^-1, was developed and the results were fully analysed in terms of nanoclusters' structural and magnetic properties. A careful evaluation of the nanoclusters' heating capacity in the three milieus clearly indicates that the SAR values of fluid suspensions or agarose-gel-phantoms are not adequate to predict the real tissue temperature increase or the dosage needed to heat a tumour. Our results show that besides nanostructure mobility, perfusion and local thermoregulation, the nanostructure distribution inside the tumour plays a key role in effective heating. A suppression of the magnetic material effective heating efficiency appears in tumour tissue. In fact, dosage had to be increased considerably, from the SAR values predicted from fluid or agarose, to achieve the desired temperature increase. These results represent an important contribution towards the design of more efficient nanostructures and towards the clinical translation of hyperthermia.

Allosteric effects of monoclonal antibodies on human growth hormone

We have previously shown that a monoclonal antibody (MAb) recognizing the human growth hormone (hGH) antigenic domain left exposed after binding to lactogenic receptors enhanced hGH binding probably through allosteric effects on the hormone binding site. Since receptors displaying different specificities would not recognize exactly the same hGH region, we explored whether some of our MAb could affect hGH binding to somatogenic receptors from rabbit liver and to human liver hGH-specific receptors. The effect of MAbAE5,AC8 and F11 on hGH binding was measured by determining the formation of 125I-MAb:hGH:receptor complexes using two different experimental approaches. Results from procedure A, which involved the previous binding of the hormone to microsomes before adding 125I-MAb, indicated that the hGH domain defined by epitopes AE5, AC8 and F11 is uncovered in the various hormone:receptor complexes. Procedure B was devised to reveal any alteration in the hGH molecule induced by the MAb. In this case performed 125I-MAb:hGH complexes were added to microsomes. Data showed that 125I-MAb AE5:hGH complexes bound better to the various receptors than 125I-MAb AE5 to hGH:receptor complexes. On the contrary, hGH previously bound to 125I-MAb AC8 or 125I-MAb F11 was less recognized by the receptors than the free hormone. Furthermore, binding of MAb AE5 or MAb F11 to hGH 20 K (a natural hGH variant lacking residues 32-46) also enhanced its affinity to the various receptors whereas MAb AC8 did not inhibit hGH 20 K binding. Results indicated that MAb recognizing the hGH antigenic area that remains unmasked after binding to different membrane-bound receptors are able to affect hormone binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibodies to human growth hormone modulate its biological properties

Previous results indicated that monoclonal antibodies (mAbs) termed mAb AE5, mAb AC8 and mAb F11, recognizing the human growth hormone (hGH) region left exposed after binding to lactogenic, somatogenic and hGH-specific receptors, produce allosteric changes in the hormone which modify its binding properties. To study whether these mAbs could also influence hGH biological activity, experiments were carried out with Nb2 cells, a rat lymphoma cell line which proliferates in the presence of lactogenic hormones. Experiments involving previous binding of the hormone to receptors before adding 125I-mAbs indicated that the hGH domain defined by overlapped epitopes AE5, AC8 and F11 is uncovered in hGH when it is bound to the cell membranes. To reveal any alteration in the hGH molecule induced by the mAbs, preformed 125I-mAb:hGH complexes were added to the cell membranes. Data showed that 125I-mAb AE5:hGH complexes bound better to the receptors than free hormone. On the contrary, hGH previously bound to 125I-mAb AC8 or 125I-mAb F11 was poorly recognized by Nb2 receptors. Furthermore, both mAbs AC8 and F11 strongly inhibited 125I-hGH binding to Nb2 cell membranes and hGH-induced Nb2 cell proliferation whereas mAb AE5 enhanced both hormone binding and hGH mitogenic effect. Additionally, since mAb AC8 is directed towards an epitope shared by hGH and human placental lactogen (hPL), it was also shown that this mAb could impair hPL biological activity even though it recognizes the hPL region left exposed in hPL:Nb2 cell receptor complexes. Data presented in this work suggest that mAbs directed to the hGH or hPL regions unmasked after binding to Nb2 cell receptors produce allosteric alterations in the binding properties of these hormones leading to either enhancement or decrease of their biological activities.

2'-Nitroflavone induces cell cycle arrest and apoptosis in HeLa human cervical carcinoma cells

The mechanism of antitumor action of a synthetic nitroflavone derivative, 2'-nitroflavone, was evaluated in vitro in HeLa human cervix adenocarcinoma cells. We showed that the nitroflavone derivative slowed down the cell cycle at the S phase and increase the population of cells at the G2/M phase after 24h of incubation. The treatment with 2'-nitroflavone also induced an apoptotic response, characterized by an increase of the sub-G1 fraction of cells, by cells with chromatin condensation and membrane blebbing, by a typical ladder of DNA fragmentation and by detection of apoptotic cells stained with Annexin V. The observed apoptosis was regulated by caspase-8 and -9, both contributing to the activation of the effector caspase-3. In addition, inhibitors of caspase-8 or -9 partially protected HeLa cells from 2'-nitroflavone-induced cell death. We also found that 2'-nitroflavone did not affect the total amount of Bax and Bcl-2 proteins, although a translocation of Bax from cytosol to mitochondria was evident after 6h of exposure. Furthermore, 2'-nitroflavone decreased the expression of the anti-apoptotic Bcl-XL protein, induced the release of cytochrome C to cytosol and increased the levels of Fas and Fas-L. Our results indicated that both death receptor and mitochondria-dependent pathways are involved in the apoptotic cell death triggered by 2'-nitroflavone and suggest that this derivative could be a potentially useful agent for the treatment of certain malignancies.

Formation of complexes between 125I-labelled human or bovine somatotropins and binding proteins in vivo in rat liver and kidney

At 5 min after intravenous injection, both 125I-labelled human somatotropin and 125I-labelled bovine somatotropin were concentrated in rat liver and kidney. When the labelled hormones were administered along with an excess of the corresponding unlabelled hormone, a significant decrease of the uptake was observed in the liver, but not in the kidney. Study of the subcellular distribution of radioiodinated somatotropins in liver revealed that most of the radioactivity was specifically concentrated in the microsomal fraction. In contrast, the kidney fraction that accounted for most of the radioactivity was the 100 000 g supernatant. After solubilization, with 1% (w/v) Triton X-100, of the microsomal fractions obtained from both organs, the radioactive material was analysed by gel filtration on Sepharose CL-6B. By using this approach, it was demonstrated that both 125I-labelled human somatotropin and 125I-labelled bovine somatotropin bind in vivo to proteins present in liver. A small proportion of 125I-labelled human somatotropin was also shown to form complexes with proteins present in kidney. The present results demonstrate that the liver uptake is mainly due to binding of somatotropins to specific proteins, in contrast with the kidney, in which binding to specific sites contributes minimally to the overall uptake.

Monoclonal antibodies as probes to study the human growth hormone-binding domain to lactogenic rat liver receptors

A set of monoclonal antibodies (MAb) to human GH (hGH) was used to study the hormone binding orientation to its receptors (R) from female rat liver. The hGH antigenic region left exposed after its binding to liver microsomes was detected by measuring the ability of various [125I]MAb to bind to the preformed hGH-R complexes. Results indicated that a cluster of epitopes defined by the MAb, termed AE5, AC8, and AE12, remains accessible in the hGH-R complex whereas overlapping epitopes 3C11 and HG3 would define a hGH region involved in the binding site. Supporting these findings, solubilization and HPLC gel filtration of [125I]MAb-hGH-R complexes showed a radioactive peak of about 450,000 mol wt for MAb AE5 or AC8, but not for MAb 3C11 or HG3. [125I]MAb AE12 behaved differently, suggesting that epitope AE12 may be masked or altered in hGH-R-solubilized complexes. MAb directed to the putative hGH-binding site (MAb 3C11, HG3, and the closely related MAb 10C1 and NA71) failed to inhibit binding of the preformed [125I]MAb AE5-hGH complex to the receptors, suggesting a hormone modification after MAb AE5 binding. Accordingly competition experiments indicated an increase in the affinity of hGH for its receptors induced by this MAb. A higher hGH concentration was required to obtain 50% [125I]hGH binding to liver microsomes in the presence of MAb AE5 than in its absence. As the MAb used define epitopes that were previously correlated with the hGH structure, we concluded that a high flexible region (sequences 134-150) is exposed in the hGH-R complex. Furthermore, some MAb directed to this region enhance the hormone affinity for its rat liver receptors, probably through an induced conformational change.

A Penicillin Derivative Exerts an Anti-Metastatic Activity in Melanoma Cells Through the Downregulation of Integrin αvβ3 and Wnt/β-Catenin Pathway

The synthetic triazolylpeptidyl penicillin derivative, named TAP7f, has been previously characterized as an effective antitumor agent in vitro and in vivo against B16-F0 melanoma cells. In this study, we investigated the anti-metastatic potential of this compound on highly metastatic murine B16-F10 and human A375 melanoma cells. We found that TAP7f inhibited cell adhesion, migration and invasion in a dose-dependent manner. Additionally, we demonstrated that TAP7f downregulated integrin αvβ3 expression and Wnt/β-catenin pathway, a signaling cascade commonly related to tumor invasion and metastasis. Thus, TAP7f reduced both the enzymatic activity and the expression levels of matrix-metalloproteinases-2 and -9 in a time dependent manner. Moreover, TAP7f inhibited the expression of the transcription factor Snail and the mesenchymal markers vimentin, and N-cadherin, and up-regulated the expression of the epithelial marker E-cadherin, suggesting that the penicillin derivative affects epithelial-mesenchymal transition. Results obtained in vitro were supported by those obtained in a B16-F10-bearing mice metastatic model, that showed a significant TAP7f inhibition of lung metastasis. These findings suggest the potential of TAP7f as a chemotherapeutic agent for the treatment of metastatic melanoma.

Properties of human growth hormone binding sites solubilized from female rabbit kidney

Human growth hormone binding sites from female rabbit kidney microsomes were solubilized by treatment with the nonionic detergent Triton X-100. The binding of 125I-labelled human growth hormone to the solubilized sites retains many of the properties observed in the particulate fraction, such as saturability, reversibility, high affinity and structural specificity. The association and the dissociation process are time- and temperature-dependent. The association rate constant, k1, is 1.6 . 10(7) mol-1 . 1 . min-1 at 25 degrees C, and the dissociation rate constant, k-1, is 2.8 . 10(-4) min-1 at 25 degrees C. Solubilization causes an increase in affinity as well as in binding capacity. Scatchard plots from saturation curves suggest the presence of a single class of binding sites with a dissociation equilibrium constant, Kd, of 1.3 . 10(-11) M and a binding capacity of 133 fmol/mg of protein. Similar results were obtained from competition experiments. Specificity studies revealed the lactogenic characteristics of the solubilized sites. The Stokes radii of the free binding sites and of the 125I-labelled human growth hormone-binding site complex, determined on a Sepharose CL-6B column, are 57 and 53 A, respectively.

Conformational and sequential epitopes on the human granulocyte-colony stimulating factor molecule (hG-CSF) and their role in binding to human placenta receptors

Monoclonal antibodies (mAbs) named 8C2 and 6E3, directed against the recombinant human granulocyte colony-stimulating factor (hG-CSF), were used as probes to study the cytokine orientation on its binding to receptors from human placenta. Competition enzyme linked immunoabsorbent assays (ELISA) revealed that mAb 8C2 would be directed to a linear epitope, whereas mAb 6E3 would delimit a more assembled epitope. Gel-filtration high performance liquid chromatography (HPLC) of the immune complexes formed by incubating [(125)I]hG-CSF with each mAb showed that epitope 8C2, but not 6E3, was altered after cytokine iodination. In addition, mAb 6E3 completely inhibited [(125)I]hG-CSF binding to human placental microsomes. Although [(125)I]mAb 6E3 was unable to bind to preformed hG-CSF-receptor complexes, [(125)I]mAb 8C2 did recognize hG-CSF previously bound to receptors, suggesting that epitope 8C2 would remain accessible in the hG-CSF-receptor complex. To identify the cytokine region defined by mAbs, hG-CSF was digested with different proteolytic enzymes: Arg-C, Glu-C, trypsin and alpha chymotrypsin. Immunoreactivity of the resulting peptides was examined by Western blot and their sequences were established by Edman degradation. Results showed that mAb 6E3 would be directed to a conformation-dependent epitope located close to the hG-CSF binding domain and included into the sequence 1-122/123, whereas mAb 8C2 recognized the region 41-58, which represents a linear epitope left exposed after cytokine binding to receptors from human placenta.

Identification of a linear epitope of interferon-alpha2b recognized by neutralizing monoclonal antibodies

Four monoclonal antibodies (mAbs) directed against the recombinant human interferon-alpha2b (IFN-alpha2b) were used as probes to study the interaction of the IFN molecule to its receptors. The [125I]IFN-alpha2b binding to immobilized mAbs was completely inhibited by IFN-alpha2b and IFN-alpha2a but neither IFNbeta nor IFNgamma showed any effect. Gel-filtration HPLC of the immune complexes formed by incubating [125I]IFN-alpha2b with paired mAbs revealed the lack of simultaneous binding of two different antibodies to the tracer, suggesting that all mAbs recognize the same IFN antigenic domain. Furthermore, the mAbs were also able to neutralize the IFN-alpha2b anti-viral and anti-proliferative activities as well as [125I]IFN-alpha2b binding to WISH cell-membranes. As [125I]mAbs did not recognize IFN exposed epitopes in the IFN:receptor complexes, mAb induction of a conformational change in the IFN binding domain impairing its binding to receptors was considered unlikely. In order to identify the IFN region recognized by mAbs, IFN-alpha2b was digested with different proteolytic enzymes. Immunoreactivity of the resulting peptides was examined by Western blot and their sequences were established by Edman degradation after blotting to poly(vinylidene difluoride) membranes. Data obtained indicated that the smallest immunoreactive region recognized by mAbs consisted of residues 107-132 or 107-146. As this zone includes the sequence 123-140, which has been involved in the binding to receptors, and our mAbs did not show an allosteric behaviour, it is concluded that they are directed to overlapping epitopes located close to or even included in the IFN binding domain.

Human somatotropin binding to rabbit kidney microsomal fraction

Specific binding of 125I-labelled human somatotropin was demonstrated in microsomal membranes (microsomes) from rat and rabbit kidneys. Female rabbit kidney microsomes showed the highest binding activity and were used for further study. The association of 125I-labelled human somatotropin was time- and temperature-dependent and the binding reaction was reversible. Scatchard analysis of saturation data indicated a dissociation equilibrium constant, KD, of 56 pM and a binding capacity of 37 fmol per mg of protein. Similar results were obtained from competition experiments. Binding of 125I-labelled human somatotropin to the microsomes was specifically inhibited by hormones with lactogenic activity. The binding sites, as well as 125I-labelled human somatotropin, were not inactivated on incubation. Treatment of the microsomes with trypsin and chymotrypsin decreased the specific binding by over 90%. Preheating of the microsomes at 55 degrees C for 15 min abolished 50% of the specific binding activity.

Lysosomal permeabilization and endoplasmic reticulum stress mediate the apoptotic response induced after photoactivation of a lipophilic zinc(II) phthalocyanine

We have previously reported that the phototoxic action of the lipophilic phthalocyanine Pc9 (2,9(10),16(17),23(24) tetrakis[(2-dimethylamino)ethylsulfanyl]phthalocyaninatozinc(II)) encapsulated into poloxamine micelles is related to the induction of an apoptotic response in murine colon CT26 carcinoma cells. In the present study, we explored the intracellular signals contributing to the resulting apoptotic death. We found that Pc9-T1107 arrests cell cycle progression immediately after irradiation promoting then an apoptotic response. Thus, 3 h after irradiation the percentage of hypodiploid cells increased from 5.9 ± 0.6% to 23.1 ± 0.1%; activation of caspases 8 and 9 was evident; the population of cells with loss of mitochondrial membrane potential increased from 1.1 ± 0.4% to 44.0 ± 9.3%; the full-length forms of Bid and PARP-1 were cleaved; and a 50% decrease of the expression levels of the anti-apoptotic proteins Bcl-2 and Bcl-X_L was detected. We also found that the photosensitizer, mainly retained in lysosomes and endoplasmic reticulum (ER), promotes the permeabilization of lysosomal membranes and induces ER stress. Lysosomal membrane permeabilization was demonstrated by the reduction of acridine orange lysosome fluorescence, the release of Cathepsin D into the cytosol and ∼50% decrease of Hsp70, a chaperone recognized as a lysosomal stabilizer. Cathepsin D also contributed to Bid cleavage and caspase 8 activation. The oxidative damage to the ER induced an unfolded protein response characterized, 3 h after irradiation, by a 3-fold increase in cytosolic Ca²⁺ levels and 3-4 times higher expression of ER chaperones GRP78/BIP, calnexin, Hsp90 and Hsp110. The cell death signaling promoted by cytosolic Ca²⁺, calpains and lysosomal proteases was partially abolished by the Ca²⁺ chelator BAPTA-AM, the calpain inhibitor PD 150606 and proteases inhibitors. Furthermore, Bax down-regulation observed in Pc9-treated cells was undetectable in the presence of PD 150606, indicating that calpains contribute to Bax proteolytic damage. In summary, our results indicate that photoactivation of Pc9-T1107 led to lysosomal membrane permeabilization, induction of ER stress and activation of a caspase-dependent apoptotic cell death.

Relative localization of the prolactin receptor binding sites for lactogenic hormones

A monoclonal antibody termed MAb R7B4, directed to an epitope present in prolactin receptors (PRLRs), was used as a tool to map the receptor binding sites for human growth hormone (hGH), ovine prolactin (oPRL) and human placental lactogen (hPL). Although the three hormones completely inhibited the binding of each other to Nb2 cells or rat liver receptors, MAb R7B4 behaviour was different depending on the hormone tested and the receptor source. According to the MAb effects, PRLR from Nb2 cells would locate both hGH and oPRL close to R7B4 epitope, whereas hPL would bind far from the MAb binding site. On the other hand, PRLR from rat liver should bind hGH close to the R7B4 epitope but oPRL and hPL would be recognized by a separate region of the same receptor. Thus, results presented in this paper suggest that PRLR binding sites for hGH, oPRL and hPL do not exactly overlap in spite of full competition between ligands.

Effects of various adjuvants and a viral infection on the antibody specificity toward native or cryptic epitopes of a protein antigen

An immunization protocol that induces antibodies (Abs) directed to cryptic epitopes of a protein antigen (Ag) reduces the efficacy of vaccines that ideally should induce Abs against native epitopes. We have shown earlier that viral infections concomitant with immunization against a protein tend to shift the Ab specificity toward cryptic epitopes and tend to induce the production of autoantibodies (autoAbs). Here, we show the effects of three adjuvants on the Ab specificity in the absence or presence of a viral infection (lactate dehydrogenase-elevating virus or LDV), with human growth hormone (hGH) being, as before, the protein Ag. Pathogen-free CBA/Ht and BALB/c mice were immunized with hGH in the presence of complete Freund's adjuvant (CFA), monophosphoryl lipid A (MPL) or alum, with the animals being either infected with LDV or not infected with LDV. Conventional and competition enzyme-linked immunosorbent assays (ELISAs) indicated that in noninfected mice, CFA induced higher titres of anti-hGH Ab than did MPL or alum, with the Ab being almost totally directed to cryptic hGH epitopes. Strikingly, CFA plus LDV infection in CBA/Ht mice shifted the specificity of the anti-hGH Ab toward native epitopes, whereas the virus decreased the Ab titre when MPL or alum was used. Our Western blot results showed that 70% of mice immunized with hGH in the presence of any adjuvant produced autoAbs against a variety of tissue Ags. The amount of autoAb and the concentration of Ab to hGH cryptic epitopes did correlate, suggesting a relationship between both kinds of Ab. Significant differences were observed in the various effects of adjuvants and the viral infection between the two mouse strains used in this work.

Binding in vitro to rat liver receptors does not correlate with activities in vivo of bovine somatotropin. Use of chemically modified derivatives as probes

Bovine somatotropin with an increasing number of its carboxylate groups modified by reaction with glycine methyl ester in the presence of a water-soluble carbodi-imide was tested for its activity in different bioassays. Only those derivatives which were known to be active in the body-weight-increase bioassay were able to compete with 125I-labelled bovine somatotropin for their specific binding sites in vivo. No difference was found in the rate of clearance of a poorly active derivative as compared with that of native somatotropin. In contrast, both active and inactive derivatives were found to be equally effective in displacing the tracer from its binding sites present in isolated cells and membrane preparations from rat liver. These results suggest that the liver somatogenic receptors studied in vitro are less discriminating than those detected in vivo.

In Vivo Photodynamic Therapy With a Lipophilic Zinc(II) Phthalocyanine Inhibits Colorectal Cancer and Induces a Th1/CD8 Antitumor Immune Response

BACKGROUND AND OBJECTIVES

Photodynamic therapy (PDT) is an antitumor procedure clinically approved for the treatment of different cancer types. Despite strong efforts and promising results in this field, PDT has not yet been approved by any regulatory authority for the treatment of colorectal cancer, one of the most prevalent gastrointestinal tumors. In the search of novel therapeutic strategies, we examined the in vivo effect of PDT with a lipophilic phthalocyanine (Pc9) encapsulated into polymeric poloxamine micelles (T1107) in a murine colon carcinoma model.

STUDY DESIGN/MATERIALS AND METHODS

In vivo assays were performed with BALB/c mice challenged with CT26 cells. Pc9 tumor uptake was evaluated with an in vivo imaging system. Immunofluorescence, western blot, and flow cytometry assays were carried out to characterize the activation of apoptosis and an antitumor immune response.

RESULTS

Pc9-T1107 effectively delayed tumor growth and prolonged mice survival, without generating systemic or tissue-specific toxicity. The induction of an apoptotic response was characterized by a decrease in the expression levels of Bcl-X_L , Bcl-2, procaspase 3, full length Bid, a significant increment in the amount of active caspase-3 and the detection of PARP-1 cleavage. Infiltration of CD8⁺ CD107a⁺ T cells and higher levels of interferon-γ and tumor necrosis factor-α were also found in PDT-treated tumors.

CONCLUSIONS

Pc9-T1107 PDT treatment reduced tumor growth, inducing an apoptotic cell death and activating an immune response. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.