The comparison of adipose-derived stromal cells (ADSCs) delivery method in a murine model of hindlimb ischemia

BACKGROUND

Adipose-derived stromal cells (ADSCs) demonstrate ability to promote tissue healing and down-regulate excessive inflammation. ADSCs have been used to treat critical limb ischemia in preclinical and clinical trials, but still, there is little known about their optimal delivery strategy. To date, no direct analysis of different methods of ADSCs delivery has been performed in the hindlimb ischemia model. Therefore, in this study we focused on the therapeutic efficacy of different ADSCs delivery methods in a murine model of hindlimb ischemia.

METHODS

For the hADSCs isolation, we used the subcutaneous adipose tissue collected during the surgery. The murine hindlimb ischemia was used as a model. The unilateral femoral artery ligation was performed on 10-12-week-old male C57BL/6. ADSCs were delivered directly into ischemic muscle, into the contralateral muscle or intravenously. 7 and 14 days after the surgery, the gastrocnemius and quadriceps muscles were collected for the immunohistochemical analysis. The results were analyzed with relevant tests using the Statistica software.

RESULTS

Our research revealed that muscle regeneration, angiogenesis, arteriogenesis and macrophage infiltration in murine model of hindlimb ischemia differ depending on ADSCs delivery method. We have demonstrated that intramuscular method (directly into ischemic limb) of ADSCs delivery is more efficient in functional recovery after critical limb ischemia than intravenous or contralateral route.

CONCLUSIONS

We have noticed that injection of ADSCs directly into ischemic limb is the optimal delivery strategy because it increases: (1) muscle fiber regeneration, (2) the number of capillaries and (3) the influx of macrophages F4/80+/CD206+.

Antitumor effect of anti-vascular therapy with STING agonist depends on the tumor microenvironment context

Introduction

Targeting tumor vasculature is an efficient weapon to fight against cancer; however, activation of alternative pathways to rebuild the disrupted vasculature leads to rapid tumor regrowth. Immunotherapy that exploits host immune cells to elicit and sustain potent antitumor response has emerged as one of the most promising tools for cancer treatment, yet many treatments fail due to developed resistance mechanisms. Therefore, our aim was to examine whether combination of immunotherapy and anti-vascular treatment will succeed in poorly immunogenic, difficult-to-treat melanoma and triple-negative breast tumor models.

Methods

Our study was performed on B16-F10 melanoma and 4T1 breast tumor murine models. Mice were treated with the stimulator of interferon genes (STING) pathway agonist (cGAMP) and vascular disrupting agent combretastatin A4 phosphate (CA4P). Tumor growth was monitored. The tumor microenvironment (TME) was comprehensively investigated using multiplex immunofluorescence and flow cytometry. We also examined if such designed therapy sensitizes investigated tumor models to an immune checkpoint inhibitor (anti-PD-1).

Results

The use of STING agonist cGAMP as monotherapy was insufficient to effectively inhibit tumor growth due to low levels of STING protein in 4T1 tumors. However, when additionally combined with an anti-vascular agent, a significant therapeutic effect was obtained. In this model, the obtained effect was related to the TME polarization and the stimulation of the innate immune response, especially activation of NK cells. Combination therapy was unable to activate CD8+ T cells. Due to the lack of PD-1 upregulation, no improved therapeutic effect was observed when additionally combined with the anti-PD-1 inhibitor. In B16-F10 tumors, highly abundant in STING protein, cGAMP as monotherapy was sufficient to induce potent antitumor response. In this model, the therapeutic effect was due to the infiltration of the TME with activated NK cells. cGAMP also caused the infiltration of CD8+PD-1+ T cells into the TME; hence, additional benefits of using the PD-1 inhibitor were observed.

Conclusion

The study provides preclinical evidence for a great influence of the TME on the outcome of applied therapy, including immune cell contribution and ICI responsiveness. We pointed the need of careful TME screening prior to antitumor treatments to achieve satisfactory results.

The Effect of Radiotherapy on Cell Survival and Inflammatory Cytokine and Chemokine Secretion in a Co-Culture Model of Head and Neck Squamous Cell Carcinoma and Normal Cells

Radiotherapy (RT) is one of the main treatments for head and neck squamous cell carcinomas (HNSCCs). Unfortunately, radioresistance is observed in many cases of HNSCCs. The effectiveness of RT depends on both the direct effect inducing cell death and the indirect effect of changing the tumor microenvironment (TME). Knowledge of interactions between TME components after RT may help to design a new combined treatment with RT. In the study, we investigated the effect of RT on cell survival and cell secretion in a co-culture model of HNSCCs in vitro. We examined changes in cell proliferation, colony formation, cell cycle phases, type of cell death, cell migration and secretion after irradiation. The obtained results suggest that the presence of fibroblasts and endothelial cells in co-culture with HNSCCs inhibits the function of cell cycle checkpoints G₁/S and G₂/M and allows cells to enter the next phase of the cell cycle. We showed an anti-apoptotic effect in co-culture of HNSCCs with fibroblasts or endothelial cells in relation to the execution phase of apoptosis, although we initially observed increased activation of the early phase of apoptosis in the co-cultures after irradiation. We hypothesize that the anti-apoptotic effect depends on increased secretion of IL-6 and MCP-1.

Novel Local "Off-the-Shelf" Immunotherapy for the Treatment of Myeloma Bone Disease

Myeloma bone disease (MBD) is one of the major complications in multiple myeloma (MM)-the second most frequent hematologic malignancy. It is characterized by the formation of bone lesions due to the local action of proliferating MM cells, and to date, no effective therapy has been developed. In this study, we propose a novel approach for the local treatment of MBD with a combination of natural killer cells (NKs) and mesenchymal stem cells (MSCs) within a fibrin scaffold, altogether known as FINM. The unique biological properties of the NKs and MSCs, joined to the injectable biocompatible fibrin, permitted to obtain an efficient "off-the-shelf" ready-to-use composite for the local treatment of MBD. Our in vitro analyses demonstrate that NKs within FINM exert a robust anti-tumor activity against MM cell lines and primary cells, with the capacity to suppress osteoclast activity (~60%) within in vitro 3D model of MBD. Furthermore, NKs' post-thawing cytotoxic activity is significantly enhanced (~75%) in the presence of MSCs, which circumvents the decrease of NKs cytotoxicity after thawing, a well-known issue in the cryopreservation of NKs. To reduce the tumor escape, we combined FINM with other therapeutic agents (bortezomib (BZ), and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)), observing a clear therapeutic synergistic effect in vitro. Finally, the therapeutic efficacy of FINM in combination with BZ and TRAIL was assessed in a mouse model of MM, achieving 16-fold smaller tumors compared to the control group without treatment. These results suggest the potential of FINM to serve as an allogeneic "off-the-shelf" approach to improve the outcomes of patients suffering from MBD.

Mesenchymal stromal cells as carriers of IL-12 reduce primary and metastatic tumors of murine melanoma

Due to immunosuppressive properties and confirmed tropism towards cancer cells mesenchymal stromal cells (MSC) have been used in many trials. In our study we used these cells as carriers of IL-12 in the treatment of mice with primary and metastatic B16-F10 melanomas. IL-12 has confirmed anti-cancer activity, induces a strong immune response against cancer cells and acts as an anti-angiogenic agent. A major limitation of the use of IL-12 in therapy is its systemic toxicity. The aim of the work was to develop a system in which cytokine may be administered intravenously without toxic side effects. In this study MSC were used as carriers of the IL-12. We confirmed antitumor effectiveness of the cells secreting IL-12 (MSC/IL-12) in primary and metastatic murine melanoma models. We observed inhibition of tumor growth and a significant reduction in the number of metastases in mice after MSC/IL-12 administration. MSC/IL-12 decreased vascular density and increased the number of anticancer M1 macrophages and CD8⁺ cytotoxic T lymphocytes in tumors of treated mice. To summarize, we showed that MSC are an effective, safe carrier of IL-12 cytokine. Administered systemically they exert therapeutic properties of IL-12 cytokine without toxicity. Therapeutic effect may be a result of pleiotropic (proinflammatory and anti-angiogenic) properties of IL-12 released by modified MSC.

Vascular disrupting agents in cancer therapy

Tumor blood vessel formation is a key process for tumor expansion. Tumor vessels are abnormal and differ from normal vessels in architecture and components. Besides oxygen and nutrients supply, the tumor vessels system, due to its abnormality, is responsible for: hypoxia formation, and metastatic routes. Tumor blood vessels can be a target of anti-cancer therapies. There are two types of therapies that target tumor vessels. The first one is the inhibition of the angiogenesis process. However, the inhibition is often ineffective because of alternative angiogenesis mechanism activation. The second type is a specific targeting of existing tumor blood vessels by vascular disruptive agents (VDAs). There are three groups of VDAs: microtubule destabilizing drugs, flavonoids with anti-vascular functions, and tumor vascular targeted drugs based on endothelial cell receptors. However, VDAs possess some limitations. They may be cardiotoxic and their application in therapy may leave viable residual, so called, rim cells on the edge of the tumor. However, it seems that a well-designed combination of VDAs with other anti-cancer drugs may bring a significant therapeutic effect. In this article, we describe three groups of vascular disruptive agents with their advantages and disadvantages. We mention VDAs clinical trials. Finally, we present the current possibilities of VDAs combination with other anti-cancer drugs.

Adipose tissue-derived stromal cells stimulated macrophages-endothelial cells interactions promote effective ischemic muscle neovascularization

Neovascularization, the process of new blood vessels formation in response to hypoxia induced signals, is an essential step during wound healing or ischemia repair. It follows as a cascade of consecutive events leading to new blood vessels formation and their subsequent remodeling to a mature and functional state, enabling tissue regeneration. Any disruption in consecutive stages of neovascularization can lead to chronic wounds or impairment of tissue repair. In the study we try to explain the biological basis of accelerated blood vessels formation in ischemic tissue after adipose tissue-derived stromal cells (ADSCs) administration. Experiments were performed on mouse models of hindlimb ischemia. We have evaluated the level of immune cells (neutrophils, macrophages) infiltration. The novelty of our work was the assessment of bone marrow-derived stem/progenitor cells (BMDCs) infiltration and their contribution to the neovascularization process in ischemic tissue. We have noticed that ADSCs regulated immune response and affected the kinetics and ratio of macrophages population infiltrating ischemic tissue. Our research revealed that ADSCs promoted changes in the morphology of infiltrating macrophages and their tight association with forming blood vessels. We assume that recruited macrophages may take over the role of pericytes and stabilize the new blood vessel or even differentiate into endothelial cells, which in consequence can accelerate vascular formation upon ADSCs administration. Our findings indicate that administration of ADSCs into ischemic muscle influence spatio-temporal distribution of infiltrating cells (macrophages, neutrophils and BMDCs), which are involved in each step of vascular formation, promoting effective ischemic tissue neovascularization.

Author Correction: Combination of anti-vascular agent - DMXAA and HIF-1α inhibitor - digoxin inhibits the growth of melanoma tumors

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Monitoring of diffusion properties and transverse relaxation time of mouse ischaemic muscle after administration of human mesenchymal stromal cells derived from adipose tissue

Objectives

Application of non‐invasive imaging methods plays an important role in the assessment of cellular therapy effects in peripheral artery disease. The purpose of this work was to evaluate the kinetics of MRI‐derived parameters characterizing ischaemic hindlimb muscle after administration of human mesenchymal stromal cells derived from adipose tissue (hADSC) in mice.

Materials and methods

MRI experiments were performed on a 9.4T Bruker system. The measurement protocol included transverse relaxation time mapping and diffusion tensor imaging. The monitoring period encompassed 14 days after femoral artery ligation and subsequent cell administration. The effect of hADSC transplantation was compared with the effect of normal human dermal fibroblasts (NHDFs) and phosphate‐buffered saline injection.

Results

The most significant differences between the hADSC group and the remaining ones were observed around day 3 after ischaemia induction (increased transverse relaxation time in the hADSC group in comparison with the control group) and around day 7 (increased transverse relaxation time and decreased third eigenvalue of the diffusion tensor in the hADSC group in comparison with the control and NHDF groups) at the site of hADSC injection. Histologically, it was associated with increased macrophage infiltration at days 3‐7 and with the presence of small regenerating fibres in the ischaemic tissue at day 7.

Conclusions

Our results underscore the important role of macrophages in mediating the therapeutic effects of hADSCs and confirm the huge potential of magnetic resonance imaging in monitoring of cellular therapy effects.

Human ADSC xenograft through IL-6 secretion activates M2 macrophages responsible for the repair of damaged muscle tissue

BACKGROUND

Adipose-derived mesenchymal stromal cells (ADSCs) are multipotent stromal cells. The cells secrete a number of cytokines and growth factors and show immunoregulatory and proangiogenic properties. Their properties may be used to repair damaged tissues. The aim of our work is to explain the muscle damage repair mechanism with the utilization of the human adipose-derived mesenchymal stromal cells (hADSCs).

METHODS

For the hADSCs isolation, we used the subcutaneous adipose tissue collected during the surgery. The murine hind limb ischemia was used as a model. The unilateral femoral artery ligation was performed on 10-12-week-old male C57BL/6NCrl and NOD SCID mice. The mice received PBS^- (controls) or 1 × 10⁶ hADSCs. One, 3, 7, 14 and 21 days after the surgery, we collected the gastrocnemius muscles for the immunohistochemical analysis. The results were analyzed with relevant tests using the Statistica software.

RESULTS

The retention time of hADSCs in the limb lasted about 14 days. In the mice receiving hADSCs, the improvement in the functionality of the damaged limb occurred faster than in the control mice. More new blood vessels were formed in the limbs of the mice receiving hADSCs than in limbs of the control mice. hADSCs also increased the infiltration of the macrophages with the M2 phenotype (7-AAD^-/CD45⁺/F4/80⁺/CD206⁺) into the ischemic limbs. hADSCs introduced into the limb of mice secreted interleukin-6. This cytokine stimulates the emergence of the proangiogenic M2 macrophages, involved, among others, in the repair of a damaged tissue. Both macrophage depletion and IL-6 blockage suppressed the therapeutic effect of hADSCs. In the mice treated with hADSCs and liposomes with clodronate (macrophages depletion), the number of capillaries formed was lower than in the mice treated with hADSCs alone. Administration of hADSCs to the mice that received siltuximab (human IL-6 blocker) did not cause an influx of the M2 macrophages, and the number of capillaries formed was at the level of the control group, as in contrast to the mice that received only the hADSCs.

CONCLUSIONS

The proposed mechanism for the repair of the damaged muscle using hADSCs is based on the activity of IL-6. In our opinion, the cytokine, secreted by the hADSCs, stimulates the M2 macrophages responsible for repairing damaged muscle and forming new blood vessels.

Combined Tumor Cell-Based Vaccination and Interleukin-12 Gene Therapy Polarizes the Tumor Microenvironment in Mice

Tumor progression depends on tumor milieu, which influences neovasculature formation and immunosuppression. Combining immunotherapy with antiangiogenic/antivascular therapy might be an effective therapeutic approach. The aim of our study was to elaborate an anticancer therapeutic strategy based on the induction of immune response which leads to polarization of tumor milieu. To achieve this, we developed a tumor cell-based vaccine. CAMEL peptide was used as a B16-F10 cell death-inducing agent. The lysates were used as a vaccine to immunize mice bearing B16-F10 melanoma tumors. To further improve the therapeutic effect of the vaccine, we combined it with interleukin (IL)-12 gene therapy. IL-12, a cytokine with antiangiogenic properties, activates nonspecific and specific immune responses. We observed that combined therapy is significantly more effective (as compared with monotherapies) in inhibiting tumor growth. Furthermore, the tested combination polarizes the tumor microenvironment, which results in a switch from a proangiogenic/immunosuppressive to an antiangiogenic/immunostimulatory one. The switch manifests itself as a decreased number of tumor blood vessels, increased levels of tumor-infiltrating CD4⁺, CD8⁺ and NK cells, as well as lower level of suppressor lymphocytes (Treg). Our results suggest that polarizing tumor milieu by such combined therapy does inhibit tumor growth and seems to be a promising therapeutic strategy.

Characteristic of c-Kit+ progenitor cells in explanted human hearts

According to literature data, self-renewing, multipotent, and clonogenic cardiac c-Kit⁺ progenitor cells occur within human myocardium. The aim of this study was to isolate and characterize c-Kit⁺ progenitor cells from explanted human hearts. Experimental material was obtained from 19 adult and 7 pediatric patients. Successful isolation and culture was achieved for 95 samples (84.1 %) derived from five different regions of the heart: right and left ventricles, atrium, intraventricular septum, and apex. The average percentage of c-Kit⁺ cells, as assessed by FACS, ranged between 0.7 and 0.9 %. In contrast to published data we do not observed statistically significant differences in the number of c-Kit⁺ cells between disease-specific groups, parts of the heart or sexes. Nevertheless, c-Kit⁺ cells were present in significant numbers (11–24 %) in samples derived from three explanted pediatric hearts. c-Kit⁺ cells were also positive for CD105 and a majority of them was positive for CD31 and CD34 (83.7 ± 8.6 and 75.7 ± 11.4 %, respectively). Immunohistochemical analysis of the heart tissue revealed that most cells possessing the c-Kit antigen were also positive for tryptase, a specific mast cell marker. However, flow cytometry analysis has shown cultured c-Kit⁺ cells to be negative for hematopoietic marker CD45 and mast cell marker CD33. Isolated c-Kit⁺ cells display mesenchymal stem cell features and are thought to differentiate into endothelial cells.

D-K6L 9 peptide combination with IL-12 inhibits the recurrence of tumors in mice

D-K6L9 peptide is bound by phosphatidylserine and induces necrosis in cancer cells. In our therapeutic experience, this peptide, when administered directly into B16-F10 murine melanoma tumors, inhibited their growth. Cessation of therapy results, however, in tumor relapse. We aimed at developing a combined therapy involving D-K6L9 and additional factors that would yield complete elimination of tumor cells in experimental animals. To this purpose, we employed glycyrrhizin, an inhibitor of HMGB1 protein, BP1 peptide and interleukin (IL)-12. Glycyrrhizin or BP1, when combined with D-K6L9, inhibits growth of primary tumors only during the period of their administration. A long-term tumor growth inhibitory effect was obtained only in combining D-K6L9 with IL-12. At 2 months following therapy cessation, 60 % of animals were alive. Prolonged survival was noted in mice bearing B16-F10 tumors as well as in mice bearing C26 colon carcinoma tumors.

[HMGB1--its role in tumor progression and anticancer therapy]

HMGB1 is an evolutionarily conserved protein with a wide spectrum of action. Its main receptors are RAGE and TLR found on the surface of immune system cells as well as endothelial cells. Although signaling pathways for both receptor groups are different, ultimately they both activate NFκB transcription factor which, in turn, activates genes encoding adhesion proteins, proinflammatory cytokines and proangiogenic factors. Inside cells, HMGB1 is found mainly in the cell nucleus, where it participates in replication, recombination, transcription and DNA repair processes. Following release into the extracellular space, HMGB1 becomes a proinflammatory cytokine which stimulates formation of new blood microvessels, enhances cell migration, activates the inflammatory condition and affects cell proliferation. HMGB1 protein also takes part in regeneration of damaged tissues and stimulates autophagy. HMGB1 plays a potential role in anticancer therapy. Increased amounts of HMGB1 in cancer cells and elevated levels in the bloodstream are noted among patients afflicted with various cancers. HMGB1 protects cells from apoptosis, as it affects telomere stability. HMGB1 also stimulates a number of proteins involved in proliferation of cancer cells and inhibits signals that control cell growth. Ability to arrest HMGB1 release from cells or to inhibit its activity appears to be a promising therapeutic approach. At present, several inhibitors of HMGB1 are known and can be used in anticancer therapy.  

["Vicious circles" of glioblastoma tumors: vascularization and invasiveness]

Glioblastoma multiforme is the most common and a particularly aggressive form of glial primary brain tumors. This malignancy accounts for ca. 70% of all diagnosed cases. Unfortunately, average survival of glioma patients does not exceed one year from diagnosis. Specific vascularization pattern (presence of numerous microvessels and glomerular vessels) and exceptional invasiveness are characteristic features of glioblastoma tumors. Both of these features reflect complex underlying processes forming two vicious circles. Common to both of these circles is the state of tumor underoxygenation. Hypoxia that occurs in the vicinity of abnormal tumor blood vessels stimulates formation of novel microvessels and invasiveness of tumor cells. In their essence, both of the vicious circles are processes allowing tumor cells to adapt to an underoxygenated tumor milieu. These processes play an important role in tumor progression, which reflects a specific type of evolution of cancer cells. Late effects of this evolution include appearance of highly aggressive, chemo- and radiotherapy resistant neoplastic cells. Increased adaptation capabilities of such cancer cells have a negative influence on the therapeutic process. Effective therapeutic strategies should not be directed against single cancer cell markers; instead, they should be targeted so as to break both vicious cycles. Herein we discuss several such strategies. In our opinion, effective therapeutic approaches must include a combination of several agents that recognize and simultaneously break both vicious cycles, i.e. vascularization and invasiveness. Also, agents that decrease hypoxia in cancer cells, for example drugs inhibiting activity of HIF-1α, might also prove therapeutically effective in such approaches. 

Vasostatin increases oxygenation of B16-F10 melanoma tumors and raises therapeutic efficacy of cyclophosphamide

One of the preconditions of effective anticancer therapy is efficient transfer of the therapeutic agent (chemotherapeutic) to tumor cells. Fundamental barriers making drug delivery and action difficult include underoxygenation, elevated interstitial pressure, poor and abnormal tumor blood vascular network and acidic tumor milieu. In this study we aimed at developing an optimized scheme of administering a combination of an angiogenesis-inhibiting drug (vasostatin) and a chemotherapeutic (cyclophosphamide) in the therapeutic treatment of mice bearing experimental B16-F10 melanoma tumors. We report that the strongest tumor growth inhibition was observed in mice that received two, three or four vasostatin doses in combination with one injection of cyclophosphamide (i.e., V2 + CTX, V3 + CTX or V4 + CTX schemes). Double administration of vasostatin increases oxygenation of B16-F10 tumors. On the other hand, its five-fold administration lowers tumor oxygenation, breaks down tumor vascular network (increasing hypoxia) and leads in consequence to death of cancer cells and appearance of necrotic areas in the tumor. A decreased cyclophosphamide dose in combination with two doses of vasostatin (V2 + CTX scheme) inhibits tumor growth similarly to a larger dose of cyclophosphamide alone.

Vasostatin increases oxygenation of B16-F10 melanoma tumors and raises therapeutic efficacy of cyclophosphamide

One of the preconditions of effective anticancer therapy is efficient transfer of the therapeutic agent (chemotherapeutic) to tumor cells. Fundamental barriers making drug delivery and action difficult include underoxygenation, elevated interstitial pressure, poor and abnormal tumor blood vascular network and acidic tumor milieu. In this study we aimed at developing an optimized scheme of administering a combination of an angiogenesis-inhibiting drug (vasostatin) and a chemotherapeutic (cyclophosphamide) in the therapeutic treatment of mice bearing experimental B16-F10 melanoma tumors. We report that the strongest tumor growth inhibition was observed in mice that received two, three or four vasostatin doses in combination with one injection of cyclophosphamide (i.e., V2 + CTX, V3 + CTX or V4 + CTX schemes). Double administration of vasostatin increases oxygenation of B16-F10 tumors. On the other hand, its five-fold administration lowers tumor oxygenation, breaks down tumor vascular network (increasing hypoxia) and leads in consequence to death of cancer cells and appearance of necrotic areas in the tumor. A decreased cyclophosphamide dose in combination with two doses of vasostatin (V2 + CTX scheme) inhibits tumor growth similarly to a larger dose of cyclophosphamide alone.

Therapeutic antitumor potential of endoglin-based DNA vaccine combined with immunomodulatory agents

Therapy targeting tumor blood vessels ought to inhibit tumor growth. However, tumors become refractory to antiangiogenic drugs. Therefore, therapeutic solutions should be sought to address cellular resistance to antiangiogenic therapy. In this regard, reversal of the proangiogenic and immunosuppressive phenotype of cancer cells, and the shift of the tumor microenvironment towards more antiangiogenic and immune-stimulating phenotype may hold some promise. In our study, we sought to validate the effects of a combination therapy aimed at reducing tumor blood vessels, coupled with the abrogation of the immunosuppressive state. To achieve this, we developed an oral DNA vaccine against endoglin. This antigen was carried by an attenuated Salmonella Typhimurium and applied before or after tumor cell inoculation into immunocompetent mice. Our results show that this DNA vaccine effectively inhibited tumor growth, in both the prophylactic and therapeutic settings. It also activated both specific and nonspecific immune responses in immunized mice. Activated cytotoxic T-lymphocytes were directed specifically against endothelial and tumor cells overexpressing endoglin. The DNA vaccine inhibited angiogenesis but did not affect wound healing. In combination with interleukin-12-mediated gene therapy, or with cyclophosphamide administration, the DNA vaccine resulted in reduced microvessel density and lowered the level of Treg lymphocytes in the experimental tumors. This effectively inhibited tumor growth and prolonged survival of the treated animals. Polarization of tumor milieu, from proangiogenic and immunosuppressive, towards an immunostimulatory and antiangiogenic profile represents a promising avenue in anticancer therapy.

[Peptides: a new class of anticancer drugs]

Peptides are a novel class of anticancer agents embracing two distinct categories: natural antibacterial peptides, which are preferentially bound by cancer cells, and chemically synthesized peptides, which bind specifically to precise molecular targets located on the surface of tumor cells. Antibacterial peptides bind to both cell and mitochondrial membranes. Some of these peptides attach to the cell membrane, resulting in its disorganization. Other antibacterial peptides penetrate cancer cells without causing cell membrane damage, but they disrupt mitochondrial membranes. Thanks to phage and aptamer libraries, it has become possible to obtain synthetic peptides blocking or activating some target proteins found in cancer cells as well as in cells forming the tumor environment. These synthetic peptides can feature anti-angiogenic properties, block enzymes indispensable for sustained tumor growth, and reduce tumor ability to metastasize. In this review the properties of peptides belonging to both categories are discussed and attempts of their application for therapeutic purposes are outlined.

Oxidation of carbidopa by tyrosinase and its effect on murine melanoma

Oxidation of the anti-Parkinsonian agent carbidopa by tyrosinase was investigated. The products of this reaction were identified as 3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid and 6,7-dihydroxy-3-methylcinnoline. These results demonstrate that after oxidation of the catechol moiety to an o-quinone either a redox exchange with the hydrazine group or a cyclization reaction occur. The cyclization product underwent additional oxidation reactions leading to aromatization. The cyclization reaction is undesired in the case of hydrazine-containing anti-melanoma prodrugs and will have to be taken into account in designing such compounds. Carbidopa was tested against B16(F10) melanoma cells in culture and showed cytotoxicity significantly higher than either of its oxidation products and l-dopa. This effect, however, was not specific to this cell line.

Combination of combretastatin A4 phosphate and doxorubicin-containing liposomes affects growth of B16-F10 tumors

The study aimed to check the effectiveness of anticancer therapy combining a vascular-disruptive drug (combretastatin phosphate, CA4P) and a liposomal formulation of a chemotherapeutic (doxorubicin). CA4P was synthesized in our laboratory according to a previously described procedure. The antivascular drug and long-circulating doxorubicin-loaded liposomes were used to treat B16-F10 murine melanoma experimental tumors. Seventy-four hours after drug administration, a decrease in the number of tumor blood vessels was apparent and necrotic areas within tumors were visible. Combination therapy consisting of alternate administrations of CA4P and liposomal doxorubicin yielded greater inhibition of tumor growth than monotherapies alone. The best therapeutic results were obtained with the antivascular drug administered intratumorally every second day at 50 mg/kg body mass. In the case of combined therapy, the best results were obtained when the vascular-disruptive agent (CA4P) and the antineoplastic agent (liposomal doxorubicin) were administered in alternation.

Combination of combretastatin A4 phosphate and doxorubicin-containing liposomes affects growth of B16-F10 tumors

The study aimed to check the effectiveness of anticancer therapy combining a vascular-disruptive drug (combretastatin phosphate, CA4P) and a liposomal formulation of a chemotherapeutic (doxorubicin). CA4P was synthesized in our laboratory according to a previously described procedure. The antivascular drug and long-circulating doxorubicin-loaded liposomes were used to treat B16-F10 murine melanoma experimental tumors. Seventy-four hours after drug administration, a decrease in the number of tumor blood vessels was apparent and necrotic areas within tumors were visible. Combination therapy consisting of alternate administrations of CA4P and liposomal doxorubicin yielded greater inhibition of tumor growth than monotherapies alone. The best therapeutic results were obtained with the antivascular drug administered intratumorally every second day at 50 mg/kg body mass. In the case of combined therapy, the best results were obtained when the vascular-disruptive agent (CA4P) and the antineoplastic agent (liposomal doxorubicin) were administered in alternation.

Chimeric protein ABRaA-VEGF121 is cytotoxic towards VEGFR-2-expressing PAE cells and inhibits B16-F10 melanoma growth

It has been known that VEGF(121) isoform can serve as a carrier of therapeutic agents targeting tumor endothelial cells. We designed and constructed synthetic cDNA that encodes a chimeric protein comprising abrin-a (ABRaA) toxin A-chain and human VEGF(121). Expression of the ABRaA-VEGF(121) chimeric protein was carried out in E. coli strain BL21(DE3). ABRaA-VEGF(121) preparations were isolated from inclusion bodies, solubilized and purified by affinity and ion-exchanged chromatography (Ni-agarose and Q-Sepharose). Finaly, bacterial endotoxin was removed from the recombinant protein. Under non-reducing conditions, the recombinant protein migrates in polyacrylamide gel as two bands (about 84 kDa homodimer and about 42 kDa monomer). ABRaA-VEGF(121) is strongly cytotoxic towards PAE cells expressing VEGFR-2, as opposed to VEGFR-1 expressing or parental PAE cells. The latter are about 400 times less sensitive to the action of this fusion protein. The biological activity of the ABRaA domain forming part of the chimeric protein was assessed in vitro: ABRaA-VEGF(121) inhibited protein biosynthesis in a cell-free translation system. Preincubation of ABRaA-VEGF(121) with antibody neutralizing the biological activity of human VEGF abolished the cytotoxic effect of the chimeric protein in PAE/KDR cells. Experiments in vivo demonstrated that ABRaA-VEGF(121) inhibits growth of B16-F10 murine melanoma tumors.

Chimeric protein ABRaA-VEGF121 is cytotoxic towards VEGFR-2-expressing PAE cells and inhibits B16-F10 melanoma growth

It has been known that VEGF(121) isoform can serve as a carrier of therapeutic agents targeting tumor endothelial cells. We designed and constructed synthetic cDNA that encodes a chimeric protein comprising abrin-a (ABRaA) toxin A-chain and human VEGF(121). Expression of the ABRaA-VEGF(121) chimeric protein was carried out in E. coli strain BL21(DE3). ABRaA-VEGF(121) preparations were isolated from inclusion bodies, solubilized and purified by affinity and ion-exchanged chromatography (Ni-agarose and Q-Sepharose). Finaly, bacterial endotoxin was removed from the recombinant protein. Under non-reducing conditions, the recombinant protein migrates in polyacrylamide gel as two bands (about 84 kDa homodimer and about 42 kDa monomer). ABRaA-VEGF(121) is strongly cytotoxic towards PAE cells expressing VEGFR-2, as opposed to VEGFR-1 expressing or parental PAE cells. The latter are about 400 times less sensitive to the action of this fusion protein. The biological activity of the ABRaA domain forming part of the chimeric protein was assessed in vitro: ABRaA-VEGF(121) inhibited protein biosynthesis in a cell-free translation system. Preincubation of ABRaA-VEGF(121) with antibody neutralizing the biological activity of human VEGF abolished the cytotoxic effect of the chimeric protein in PAE/KDR cells. Experiments in vivo demonstrated that ABRaA-VEGF(121) inhibits growth of B16-F10 murine melanoma tumors.

Antitumor effect of RGD-4C-GG-D(KLAKLAK)2 peptide in mouse B16(F10) melanoma model

Vasculature targeting agents have been tested as cancer therapeutics for the past few years. Such therapy could be accomplished using, for example, bifunctional (two-domain) peptides. RGD-4C-GG-D(KLAKLAK)2, a peptide designed by Ellerby and coworkers (1999) (full sequence: ACDCRGDCFCGGKLAKLAKKLAKLAK), binds selectively to alphaVbeta3 integrin receptors expressed in tumor neovasculature and, after internalization, effectively induces apoptosis of endothelial cells. The aim of this study was to examine if RGD-4C-GG-D(KLAKLAK)2 would efficiently target cells, among them B16(F10), that overexpress alphaVbeta3 receptors, and whether it would be suitable for therapeutic treatment of primary B16(F10) murine melanoma tumors. Thus, the peptide would target two distinct tumor compartments: that formed by endothelium of blood vessels and that made up of neoplastic cells. The therapeutic peptide was recognized and did induce apoptosis in B16(F10) cell line. Tumor growth inhibition was observed following direct intratumoral administration. However, cessation of peptide administration led to rapid tumor growth and death of the animals.

Antitumor effect of RGD-4C-GG-D(KLAKLAK)2 peptide in mouse B16(F10) melanoma model

Vasculature targeting agents have been tested as cancer therapeutics for the past few years. Such therapy could be accomplished using, for example, bifunctional (two-domain) peptides. RGD-4C-GG-D(KLAKLAK)2, a peptide designed by Ellerby and coworkers (1999) (full sequence: ACDCRGDCFCGGKLAKLAKKLAKLAK), binds selectively to alphaVbeta3 integrin receptors expressed in tumor neovasculature and, after internalization, effectively induces apoptosis of endothelial cells. The aim of this study was to examine if RGD-4C-GG-D(KLAKLAK)2 would efficiently target cells, among them B16(F10), that overexpress alphaVbeta3 receptors, and whether it would be suitable for therapeutic treatment of primary B16(F10) murine melanoma tumors. Thus, the peptide would target two distinct tumor compartments: that formed by endothelium of blood vessels and that made up of neoplastic cells. The therapeutic peptide was recognized and did induce apoptosis in B16(F10) cell line. Tumor growth inhibition was observed following direct intratumoral administration. However, cessation of peptide administration led to rapid tumor growth and death of the animals.

Negligible induction of IFN-gamma, IL-12 and TNF-alpha by DNA-PEI 750 kDa/albumin complexes

A 750 kDa polyethylenimine (PEI 750 kDa) combined with albumin has been found to mediate in vivo a highly efficient transfection of small amounts of plasmid DNA. Using this exceptional carrier system we evaluated the inflammatory responses triggered by CpG sequences found in plasmid DNA. Using as little as 1 mug DNA transferred in vivo caused an almost negligible response from pro-inflammatory cytokines (IFN-gamma, IL-12 and TNF-alpha), as assessed in serum with a commercially available kit. Administering 750 kDa PEI/albumin/plasmid DNA complexes every three days assured a high and prolonged in vivo expression of a reporter protein. A further increase in the level of such protein was obtained by administering the investigated complexes concurrently with dexamethasone. High gene transfer capability and a relatively low pro-inflammatory response of 750 kDa PEI/albumin/DNA complexes can be exploited for recurrent gene transfer into lungs to treat (via inhalation or instillation) cancer or genetic disorders such as cystic fibrosis.

In vivo gene transfer using cetylated polyethylenimine

This report describes gene transfer in vitro as well as in vivo using cetylated low-molecular mass (600 Da) polyethylenimine (28% of amine groups substituted with cetyl moieties), termed CT-PEI. This compound is hydrophobic and has to be incorporated into liposomes in order to be suitable for gene transfer studies. Serum-induced plasmid DNA degradation assay demonstrated that CT-PEI-containing liposomal carriers could protect complexed DNA (probably via condensation). In vitro luciferase gene expression achieved using medium supplemented with 10% serum was comparable to that achieved in serum-reduced medium and was highest for CT-PEI/cholesterol liposomes, followed by CT-PEI/dioleoylphosphatidylcholine liposomes and PEI 600 Da (uncetylated) carrier. In vivo systemic transfer into mice was most efficient when liposome formulations contained CT-PEI and cholesterol. Higher luciferase expression was then observed in lungs than in liver. liposomes containing cetylated polyethylenimine and cholesterol are a suitable vehicle for investigating systemic plasmid DNA transfer into lungs.

In vivo gene transfer using cetylated polyethylenimine

This report describes gene transfer in vitro as well as in vivo using cetylated low-molecular mass (600 Da) polyethylenimine (28% of amine groups substituted with cetyl moieties), termed CT-PEI. This compound is hydrophobic and has to be incorporated into liposomes in order to be suitable for gene transfer studies. Serum-induced plasmid DNA degradation assay demonstrated that CT-PEI-containing liposomal carriers could protect complexed DNA (probably via condensation). In vitro luciferase gene expression achieved using medium supplemented with 10% serum was comparable to that achieved in serum-reduced medium and was highest for CT-PEI/cholesterol liposomes, followed by CT-PEI/dioleoylphosphatidylcholine liposomes and PEI 600 Da (uncetylated) carrier. In vivo systemic transfer into mice was most efficient when liposome formulations contained CT-PEI and cholesterol. Higher luciferase expression was then observed in lungs than in liver.

IN CONCLUSION

liposomes containing cetylated polyethylenimine and cholesterol are a suitable vehicle for investigating systemic plasmid DNA transfer into lungs.

Antiangiogenic gene therapy in inhibition of metastasis

This short review attempts to demonstrate the usefulness of antiangiogenic gene therapy in achieving inhibition of growth in experimentally-induced metastases. Certain normal tissues (for example skeletal muscle) may be used in vivo, after genetic modification, as a "bioreactor", able to produce and secrete into the bloodstream proteins known to exert antiangiogenic effects. By inhibiting neoangiogenesis these proteins would thus prevent the development of metastases. The review discusses also the perspectives of antimetastatic therapy based on certain types of allogenic cells (for example myoblasts and fibroblasts) that had been genetically modified and then microencapsulated. The strategy of encapsulation is aimed at protecting the modified cells secreting antiangiogenic factors from being eliminated by the immune system. Secretion of antiangiogenic proteins by these microencapsulated cells can be controlled with inducible promoters. Antiangiogenic genes remaining under the transcriptional control of such promoters may be switched on and off using antibiotics, such as tetracycline derivatives, or steroid hormones.

Electrotransfer of gene encoding endostatin into normal and neoplastic mouse tissues: inhibition of primary tumor growth and metastatic spread

Electroporation-mediated gene transfer relies upon direct delivery of plasmids into cells permeabilized by electric fields, a method more efficient than transfer using nonviral vectors, although neither approaches the transfer efficiency of viral vectors. Here we studied electrotransfer of a gene encoding an angiogenesis inhibitor (endostatin) into primary tumors and muscle tissues, which would serve as a site of synthesis and secretion into the bloodstream of a therapeutic antimetastatic protein with systemic effects. Optimum electroporation conditions (voltage, number and duration of impulses, separation of caliper electrodes) were first established to maximize expression of a reporter gene transferred into murine Renca kidney carcinoma, B16(F10) melanoma, or skeletal muscle tissues. In neoplastic tissues, electrotransfer of plasmid DNA was far more efficient than electroporation with lipoplexes, but no differences between naked DNA and lipoplexes were found in case of electroporated muscles. We then studied the electrotransfer of plasmid DNA carrying the endostatin gene into pre-established experimental Renca tumors. A significant inhibition of tumor growth was observed in animals electroporated with this construct. Electrotransfer of the endostatin gene into muscle tissues resulted in reduced numbers of experimental B16(F10) metastases in the lungs. This study clearly shows that electroporation may be used to efficiently transfer antiangiogenic genes into both normal and neoplastic tissues.

Direct in vivo transfer of plasmid DNA into murine tumors: effects of endotoxin presence and transgene localization

The purpose of this study was to investigate the effect of endotoxin presence in plasmid DNA preparations on the efficiency of transfection achieved in vivo with B16(F10) and Renca tumors and to determine transgene localization. Our data show that endotoxin markedly decreases the efficiency of transfection. Furthermore, the transgene transferred in vivo can be found in both neoplastic and normal (most likely myofibroblast) cells lying in proximity of the administration site.

Antiangiogenic gene therapy in inhibition of metastasis

This short review attempts to demonstrate the usefulness of antiangiogenic gene therapy in achieving inhibition of growth in experimentally-induced metastases. Certain normal tissues (for example skeletal muscle) may be used in vivo, after genetic modification, as a "bioreactor", able to produce and secrete into the bloodstream proteins known to exert antiangiogenic effects. By inhibiting neoangiogenesis these proteins would thus prevent the development of metastases. The review discusses also the perspectives of antimetastatic therapy based on certain types of allogenic cells (for example myoblasts and fibroblasts) that had been genetically modified and then microencapsulated. The strategy of encapsulation is aimed at protecting the modified cells secreting antiangiogenic factors from being eliminated by the immune system. Secretion of antiangiogenic proteins by these microencapsulated cells can be controlled with inducible promoters. Antiangiogenic genes remaining under the transcriptional control of such promoters may be switched on and off using antibiotics, such as tetracycline derivatives, or steroid hormones.

Direct in vivo transfer of plasmid DNA into murine tumors: effects of endotoxin presence and transgene localization

The purpose of this study was to investigate the effect of endotoxin presence in plasmid DNA preparations on the efficiency of transfection achieved in vivo with B16(F10) and Renca tumors and to determine transgene localization. Our data show that endotoxin markedly decreases the efficiency of transfection. Furthermore, the transgene transferred in vivo can be found in both neoplastic and normal (most likely myofibroblast) cells lying in proximity of the administration site.