Molecular targets in the inhibition of angiogenesis

Stabilized tetraether lipids based particles guided prophyrins photodynamic therapy

Photodynamic therapy (PDT) that involves ergonomically delivered light in the presence of archetypical photosensitizer such as Protoporphyrin IX (PpIX) is a time-honored missile strategy in cancer therapeutics. Yet, the premature release of PpIX is one of the most abundant dilemma encounters the therapeutic outcomes of PDT due to associated toxicity and redistribution to serum proteins. In this study, ultrastable tetraether lipids (TELs) based liposomes were developed. PpIX molecules were identified to reside physically in the monolayer; thereby the inherent π-π stacking that leads to aggregation of PpIX in aqueous milieu was dramatically improved. TEL29.9 mol% and TEL62mol% based liposomes revealed PpIX sustained release diffusion pattern from spherical particles as confirmed by converged fitting to Baker & Lonsdale model. Stability in presence of human serum albumins, a key element for PDT accomplishment was emphasized. The epitome candidates were selected for vascular photodynamic (vPDT) in in-Ovo chick chorioallantoic membrane. Profoundly, TEL62mol% based liposomes proved to be the most effective liposomes that demonstrated localized effect within the irradiated area without eliciting quiescent vasculatures damages. Cellular photodynamic therapy (cPDT) revealed that various radiant exposure doses of 134, 202, 403 or 672 mJ.cm-2 could deliberately modulate the photo-responses of PpIX in TEL-liposomes.

Oxaliplatin targeting to angiogenic vessels by PEGylated cationic liposomes suppresses the angiogenesis in a dorsal air sac mouse model

Oxaliplatin (trans-l-diaminocyclohexane oxalatoplatinum, l-OHP) is a third-generation platinum analogue with proven anti-tumor activity against many tumor cell lines, however it does not show sufficient anti-tumor activity in vivo when used alone. In order to overcome this problem and to achieve an anti-angiogenic therapy with l-OHP, the drug was encapsulated into PEG-coated cationic liposomes, which were designed to target the newly formed vessels, and its anti-angiogenic activity was evaluated in an in vivo mouse dorsal air sac (DAS) assay. For the DAS assay, chambers filled with tumor cells were implanted underneath the dorsal skin. l-OHP encapsulated in PEG-coated cationic liposomes (5 mg/kg mice) was intravenously injected once on day 1, 2, 3 or 4 after chamber implantation. On the fifth day after chamber implantation, animals were sacrificed and tumor-angiogenesis was evaluated. Liposome-encapsulated l-OHP completely suppressed angiogenesis in the skin when it was administered day 3 after chamber implantation. Under similar experimental conditions, neither l-OHP encapsulated in PEG-coated neutral liposomes, nor free l-OHP, nor "empty" (no drug containing) PEG-coated cationic liposomes showed such strong suppressive effect. The present study suggests that the liposomal formulation of l-OHP, which targeted to angiogenic vessels, has a remarkable in vivo anti-angiogenic activity and the formulation may become a promising novel approach to achieve anti-angiogenic therapy.

Sanguinarine inhibits VEGF-induced angiogenesis in a fibrin gel matrix

BACKGROUND

The identification of possible ways to block blood vessels formation has become a major scientific objective of the last decade and several phytochemicals are currently being exploited to target tumour angiogenesis.

AIM

The effects of Sanguinarine (SA), an alkaloid from the root of Sanguinaria Canadensis, were evaluated in an in vitro angiogenesis model; moreover the effects on Akt phosphorylation in porcine aortic endothelial cell line (AOC) were also examined.

METHODS

SA (300 nM) was tested in the presence or absence of VEGF (100 ng/ml) in a three dimensional angiogenesis bioassay obtained pipetting a suspension of AOC on microcarrier beads in a fibrinogen solution before the addition of thrombine. Endothelial cell proliferation was measured at 48, 96, 144, 192 h. The phosphorylation of Akt was measured by ELISA in 2 x 10(5) AOC treated as described above.

RESULTS

The addition of SA abolished (p< 0.001) VEGF stimulatory effect on AOC growth at all the examined times. In addition, the stimulatory effect induced by VEGF on Akt phosphorylation was significantly (p< 0.001) inhibited by SA.

CONCLUSION

SA appear to be an antiangiogenic natural product by directly suppressing the proliferative effect of VEGF on endothelial cell line: this effect could be mediated by blocking the VEGF-induced Akt activation.

Effects of recombinant human canstatin protein in the treatment of pancreatic cancer

AIM: To examine the effect of canstatin, a newly discovered endogenous inhibitor of angiogenesis, in the treatment of pancreatic cancer in vivo.

METHODS: The canstatin cDNA fragment was synthesized and amplified from the total RNA extracted from human placenta tissues by RT-PCR. The resulting product was firstly cloned into pUCm-T vector, then into plasmid pET-22b (+) and transformed into E. coli BL21. Isopropyl-1-thio-b-Dgalactopyran-oside (IPTG) was used to induce the expression of canstatin protein and affinity chromatography was used to purify the protein. To determine the activity of purified recombinant human canstatin (rhCanstatin), orthotopic xenograft human pancreatic cancer models were established. Human pancreatic cancer cells (SW1990) were injected into the pancreas of BALB/c nude mice. Twenty-four nude mice with orthotopic xenograft tumor were randomly divided into 3 groups 10 d after the inoculation, and were treated with PBS 0.3 mL, or canstatin 5 mg/kg, or 10 mg/kg per day for 3 wk intraperitoneally. When the experiment was over, all tumors were resected and the effects of rhCanstatin on tumor growth, microvessel density (MVD) were analyzed.

RESULTS: After IPTG induction, SDS-PAGE showed a new monomeric 24 kDa protein band. This protein was purified through affinity chromatography and refolded through dialysis with a final concentration of 60 mg/L. In orthotopic pancreatic cancer models, the final tumor volume in groups treated with PBS, canstatin 5 mg/kg, 10 mg/kg were 355.21 ± 39.54 mm³, 112.73 ± 10.47 mm³, and 61.75 ± 6.99 mm³ respectively. The immunohistochemical examination showed that the MVD in tumors treated with canstatin was significantly less than that in other group.

CONCLUSION: These findings demonstrate that the rhCanstatin effectively retards the growth of pancreatic cancer in a dose-dependent manner through inhibiting angiogenesis and may be a promising therapeutic agent for pancreatic cancer treatment in the clinic.

Fusion expression and purification of human endostatin gene and its activity analysis

AIM: To procure human endostatin fusion protein with biological activity.

METHODS: The total RNA was extracted from fetal liver and amplified to acquire human endostatin gene by reverse transcription polymerase chain reaction (RT-PCR). Then the obtained gene was cloned into expression vector pTRX and transformed into E.coli BL21 (DE3). Endostatin was expressed in the E.coli by IPTG inducement, and then purified. MTT assay was used to detect the inhibitory activity of endostatin on human umbilical vein endothelial cells (ECV304).

RESULTS: One band with a length of 573 bp was showed after electrophoresis of RT-PCR product. After the obtained gene was transformed into E.coli DH5a, the positive clone was identified by KpnI and NotI digestion and its sequence was identified by sequencing. The pTRX-endo expression vector was successfully constructed and expressed in E.coli BL21 (DE3). SDS-PAGE analysis showed that the expressed endostatin was the right one. It had good biological activity after purification. The growth of ECV304 cells was markedly inhibited by endostatin in a dose-dependent manner, and ED50 was 550 μg/L.

CONCLUSION: Human endostatin gene is successfully expressed in the prokaryotic expressing vector pTRX, and human endostatin protein can inhibit the proliferation of ECV 304 cells.

Antiangiogenic photodynamic therapy (PDT) by using long-circulating liposomes modified with peptide specific to angiogenic vessels

For the improvement of therapeutic efficacy in photodynamic therapy (PDT) by using a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA), we previously prepared polyethylene glycol (PEG)-modified liposomes encapsulating BPD-MA (PEG-Lip BPD-MA). PEGylation of liposomes enhanced the accumulation of BPD-MA in tumor tissue at 3 h after injection of it into Meth-A-sarcoma-bearing mice, but, unexpectedly, decreased the suitability of the drug for PDT when laser irradiation was performed at 3 h after the injection of the liposomal photosensitizer. To improve the bioavailability of PEG-Lip BPD-MA, we endowed the liposomes with active-targeting characteristics by using Ala-Pro-Arg-Pro-Gly (APRPG) pentapeptide, which had earlier been isolated as a peptide specific to angiogenic endothelial cells. APRPG-PEG-modified liposomal BPD-MA (APRPG-PEG-Lip BPD-MA) accumulated in tumor tissue similarly as PEG-Lip BPD-MA and to an approx. 4-fold higher degree than BPD-MA delivered with non-modified liposomes at 3 h after the injection of the drugs into tumor-bearing mice. On the contrary, unlike the treatment with PEG-Lip BPD-MA, APRPG-PEG-Lip BPD-MA treatment strongly suppressed tumor growth after laser irradiation at 3 h after injection. Finally, we observed vasculature damage in the dorsal air sac angiogenesis model by APRPG-PEG-Lip BPD-MA-mediated PDT. The present results suggest that antiangiogenic PDT is an efficient modality for tumor treatment and that tumor neovessel-targeted, long-circulating liposomes are a useful carrier for delivering photosensitizer to angiogenic endothelial cells.

Antineovascular therapy, a novel antiangiogenic approach

Angiogenesis is a crucial event in tumour growth, since the growth of tumour cells depends on the supply of essentials such as oxygen and nutrients. Therefore, suppression of angiogenesis is expected to show potent therapeutic effects on various cancers. Additionally, this 'antiangiogenic therapy' is thought not only to eradicate primary tumour cells, but also suppress tumour metastases through disruption of haematogenous metastatic pathways. Tumour dormancy therapy does not aim to disrupt newly formed angiogenic vessels but aims to inhibit further formation of neovessels through inhibiting certain processes of angiogenesis. This raises a question of whether or not these antiangiogenic agents bring complete cure of tumours as complete cut-off of oxygen and nutrients is not expected by the treatment with these agents. This paper will review a novel antiangiogenic therapy, antineovascular therapy (ANET). ANET is categorised in antiangiogenic therapy but is different from tumour dormancy therapy using conventional angiogenic inhibitors: ANET aims to disrupt neovessels rather than to inhibit neovessel formation. ANET is based on the fact that angiogenic endothelial cells are growing cells and would be effectively damaged by cytotoxic agents when the agents are effectively delivered to the neovessels. The complete eradication of angiogenic endothelial cells may cause complete cut-off of essential supplies to the tumour cells and lead to indirect but strong cytotoxicity instead of cytostasis caused by the inhibition of angiogenesis. For the purpose of ANET, an angiogenic vasculature-targeting probe has been developed, by which cytotoxic anticancer agents are actively delivered to the angiogenic endothelial cells by using drug delivery system (DDS) technology. Another way to damage newly formed vessels by cytotoxic agents is achieved by metronomic-dosing chemotherapy. This chemotherapy shifts the target of chemotherapeutic agents from tumour cells to angiogenic endothelial cells by selective dosing schedule. Similarly, the shift of target from tumour cells to angiogenic endothelial cells enhanced therapeutic efficacy of cancer photo-dynamic therapy (PDT): in this antiangiogenic PDT, photosensitizers are delivered more to neovessel endothelial cells than to tumour cells. These therapeutic strategies would be clinically applied in the future.

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Molecular cloning of human canstatin gene

AIM: To clone human canstatin gene and to detect and analyze its coding sequence.

METHODS: The total RNA was extracted from human placenta. The canstatin gene fragment was synthesized and amplified from the total RNA by RT-PCR. pUCm-T vector was cloned into the RT-PCR product to obtain recombinant pUCm-T/ canstatin. The pUCm-T/canstatin was then transformed into E.coli DH 5a, and sequence of the gene was detected.

RESULTS: The extracted total RNA was separated into three clear bands indicating 28 S, 18 S, and 5 S after electrop-horesis. The values of A₂₆₀ and A₂₈₀ were 0.879 and 0.410 respectively (A₂₆₀:A₂₈₀ = 2.095). The concentration of total RNA was 1.8 g/L. The PCR product was the same as target gene canstatin. BamH I and Hind III digestion proved the final product positive. The sequence of the cloned gene (684 bp) completely matched with that of canstatin gene in Genbank.

CONCLUSION: Human canstatin gene is successfully cloned, which establishes the foundation for further study of its anti-tumor activity.