Mitomycin C induces multidrug resistance in glaucoma surgery

[Anti-scarring effect of rapamycin in rabbits following glaucoma filtering surgery]

OBJECTIVE

To study the anti- scarring effect of rapamycin in rabbits receiving glaucoma filtering surgery.

METHODS

Ninety-six Chinchilla rabbits were randomized equally into 3 rapamycin treatment groups and one control group. All the rabbits underwent trabeculectomy, after which the rabbits in the 3 rapamycin groups were treated with eye drops containing 1%, 3%, or 5% rapamycin in the operated eyes, and those in the control groups were given castor oil 4 times a day. The intraocular pressure (IOP) and inflammatory reaction in the treated eyes were observed, and the PCNA-positive cells in the filtering bleb were detected using immunohistochemistry. RTFs isolated from the Tenon's capsule of the rabbits were cultured in vitro, and the expressions of caspase-3, caspase-8, and caspase-9 in the fibroblasts were detected after treatment with different concentrations of rapamycin.

RESULTS

The IOP was significantly lower in rapamycin-treated group than in the control group after the surgery (P < 0.05). The counts of the PCNA-positive cells were significantly lower in rapamycin-treated rabbits than in the control group (P < 0.05). Rapamycin treatment dose-dependently increased the expressions of caspase-3 and caspase- 9 at both the mRNA (P < 0.001) and protein (P < 0.001) levels without causing significant changes in the expressions of caspase-8.

CONCLUSIONS

Rapamycin can inhibit excessive proliferation of the fibroblasts in the filtering bleb to reduce scar formation after glaucoma filtration surgery in rabbits. Rapamycin also increases the expressions of caspase-3 and caspase-9 to induce apoptosis of the RTFs.

Targeted therapy for the post-operative conjunctiva: SPARC silencing reduces collagen deposition

BACKGROUND

To develop targeted antifibrotic therapy for glaucoma filtration surgery; this study determines the effectiveness of small interfering RNA (siRNA) to reduce in vivo secreted protein acidic and rich in cysteine (SPARC) expression using the mouse model of conjunctival scarring.

METHODS

Experimental surgery was performed as described for the mouse model of conjunctival scarring. Scrambled (siScram) or Sparc (siSparc) siRNAs, loaded on layer-by-layer (LbL) nanoparticles, were injected into the conjunctiva immediately after surgery. Expression of Sparc, Col1a1, Fn1 and Mmp14 was measured by real-time PCR and immunoblotting on days 7 and 14 postsurgery. Live imaging of the operated eyes was performed using slit lamp, anterior segment-optical coherence tomography and confocal microscopy. Tissue pathology was evaluated by histochemical and immunofluorescent analyses of operated conjunctival cryosections. Tissue apoptosis was quantitated by annexin V assay. RESULTS : siSparc, delivered via expanded LbL nanoparticles, significantly inhibited Sparc transcription in both day 7 (2.04-fold) and day 14 (1.39-fold) treated tissues. Sparc suppression on day 7 was associated with a significant reduction of Col1a1 (2.52-fold), Fn1 (2.89-fold) and Mmp14 (2.23-fold) mRNAs. At the protein level, both SPARC and collagen 1A1 (COL1A1) were significantly reduced at both time points with siSparc treatment. Nanoparticles were visualised within cell-like structures by confocal microscopy, while overt tissue response or apoptosis was not observed. CONCLUSIONS : SPARC targeted therapy effectively reduced both SPARC and collagen production in the operated mouse conjunctiva. This proof-of-concept study suggests that targeted treatment of fibrosis in glaucoma surgery is safe and feasible, with the potential to extend to a range of potential genes associated with fibrosis.

Interferon-alpha and interferon-gamma modulate Fas-mediated apoptosis in mitomycin-C-resistant human Tenon's fibroblasts

BACKGROUND

The aim of the study was to investigate, using a native mitomycin-C-resistant human Tenon's fibroblast cell line, the possibility that interferon-alpha and gamma could be used with Fas agonists as an alternative anti-fibrotic strategy to mitomycin-C in trabeculectomy.

METHODS

A clinically resistant and in vitro verified mitomycin-C-resistant human Tenon's fibroblast cell line was pretreated with interferon-alpha and interferon-gamma for 48 h before stimulation with an agonistic Fas antibody (CH11) for 2 days to induce cell death. Cell death assays were undertaken. Changes in apoptosis-related proteins were determined by flow cytometry and Western blot.

RESULTS

Pretreatment with interferon-alpha or interferon-gamma for 48 h increased Fas, Fas-associated protein with death domain and caspase-8 expression. Protein expression was further increased by combined exposure to interferon-alpha and gamma. Pretreatment with cytokines had no effect on Fas-L and Bcl-2. Interferon-alpha alone did not change the rate of induced cell death. A combination of interferon-alpha and gamma synergistically increased the sensitivity of mitomycin-C-resistant human Tenon's fibroblast cell line to induced cell death. An antagonistic anti-Fas antibody (ZB4) completely blocked induced cell death. Broad caspase inhibitors specific for caspases-8 and -3 reduced induced deaths in interferon pretreated mitomycin-C-resistant human Tenon's fibroblast cell line in a dose-dependent manner.

CONCLUSIONS

Interferon-alpha and interferon-gamma render mitomycin-C-resistant human Tenon's fibroblast cell line sensitive to Fas-mediated apoptosis. The mechanism involves increased death-inducing signalling complex formation by upregulation of Fas, Fas-associated protein with death domain and caspase-8 expression.

P-glycoprotein Blockers Augment the Effect of Mitomycin C on Human Tenon's Fibroblasts

PURPOSE

Mitomycin C (MMC), which induces apoptosis in human Tenon's fibroblasts (HTF), is frequently used to retard wound healing after glaucoma surgery. The aim of this in vitro study was to examine whether adjunctive Verapamil and Cyclosporine could augment the cytotoxic effect of MMC on HTF.

METHODS

Fibroblast cell lines were established by explant culture from human tissue biopsy samples obtained during trabeculectomy procedures. Cells were exposed to MMC at varying concentrations (0.01-0.4 mg/ml) for 3 minutes, prior to washing in the presence or absence of the following drugs: Staurosporine (0.003mg/ml), Verapamil (2.5-0.25 mg/ml), or Cyclosporine (50-0.5 mg/ml). Following exposure, cells were cultured for 6 hours and surviving cells quantitated by haemocytometer counts.

RESULTS

Both Verapamil and Staurosporine exhibited mild toxic effects on their own, but greatly enhanced the apoptotic effect of MMC. Staurosporine is too toxic to be considered clinically, so its augmentive effect on the activity of MMC was not studied further here. Doses as low as 0.25 mg/ml of Verapamil continued to show significant augmentation of the apoptotic effect of MMC Cyclosporine at a clinically used concentration (5 mg/ml) exhibited modest augmentation of the effect of MMC.

CONCLUSIONS

Verapamil and Cyclosporine in clinically acceptable concentrations potentiate the effect of MMC and may obviate the need for high dose antimetabolites in trabeculectomy; however, further preclinical study is required.

TRANSLATIONAL RELEVANCE

Adjunctive Verapamil or Cyclosporine may allow lower dose MMC to be used in glaucoma filtration surgery while maintaining the same antifibrotic effects.

Effect of magnetic nanoparticles of Fe3O4 and wogonin on the reversal of multidrug resistance in K562/A02 cell line

BACKGROUND

Multidrug resistance is the main obstacle to the efficiency of systemic chemotherapy against hematologic malignancy. This study investigated the reversible effect of the copolymer wogonin and daunorubicin coloaded into Fe(3)O(4) magnetic nanoparticles, and the mechanism potentially involved.

METHODS

The growth inhibition rate of K562/A02 cells was investigated by MTT assay, and apoptosis of cells and the intracellular daunorubicin concentration were detected by flow cytometry. Distribution of nanoparticles taken up by K562/A02 cells was observed under a transmission electron microscope and demonstrated by Prussian blue staining. The transcription level of MDR1 mRNA and expression of P-glycoprotein were determined by reverse transcriptase polymerase chain reaction and Western blotting assay, respectively.

RESULTS

The reversible effect of daunorubicin-wogonin magnetic nanoparticles was 8.87-fold that of daunorubicin + wogonin and of daunorubicin magnetic nanoparticles. Transmission electron microscopy and Prussian blue staining revealed that the nanoparticles were located in the endosome vesicles of cytoplasm. Also, the apoptosis rate and accumulation of intracellular daunorubicin in the daunorubicin-wogonin magnetic nanoparticle group were significantly higher than that in the daunorubicin, daunorubicin + wogonin, and daunorubicin magnetic nanoparticle groups. Furthermore, transcription of MDR1 mRNA and expression of P-glycoprotein in K562/A02 cells were significantly downregulated in the daunorubicin-wogonin magnetic nanoparticle group compared with the other groups.

CONCLUSION

These findings suggest that the remarkable effects of the novel daunorubicin-wogonin magnetic nanoparticle formulation on multidrug resistant K562/A02 leukemia cells would be a promising strategy for overcoming multidrug resistance.

A novel doxorubicin-mitomycin C co-encapsulated nanoparticle formulation exhibits anti-cancer synergy in multidrug resistant human breast cancer cells

Anthracycline-containing treatment regimens are currently the most widely employed regimens for the management of breast cancer. These drug combinations are often designed based on non-cross resistance and minimal overlapping toxicity rather than drug synergism. Moreover, aggressive doses are normally used in chemotherapy to achieve a greater therapeutic benefit at the cost of more acute and long-term toxic effects. To increase chemotherapeutic efficacy while decreasing toxic effects, rational design of drug synergy-based regimens is needed. Our previous work showed a synergistic effect of doxorubicin (DOX) and mitomycin C (MMC) on murine breast cancer cells in vitro and improved efficacy and reduced systemic toxicity of DOX-loaded solid polymer-lipid hybrid nanoparticles (PLN) in animal models of breast cancer. Herein we have demonstrated true anticancer synergy of concurrently applied DOX and MMC, and have rationally designed PLN to effectively deliver this combination to multidrug resistant (MDR) MDA435/LCC6 human breast cancer cells. DOX-MMC co-loaded PLN were effective in killing MDR cells at 20-30-fold lower doses than the free drugs. This synergistic cell killing was correlated with enhanced induction of DNA double strand breaks that preceded apoptosis. Importantly, co-encapsulation of dual agents into a nanoparticle formulation was much more effective than concurrent application of single agent-containing PLN, demonstrating the requirement of simultaneous uptake of both drugs by the same cells to enhance the drug synergy. The rationally designed combination chemotherapeutic PLN can overcome multidrug resistance at a significantly lower dose than free drugs, exhibiting the potential to enhance chemotherapy and reduce the therapeutic limitations imposed by systemic toxicity.

Modulation of wound healing during and after glaucoma surgery

Following all types of glaucoma filtration surgery (GFS), scarring still poses the major threat to long-term success. The healing and scarring determine the percentage of patients achieving low final intraocular pressures (IOPs) that are associated with virtually no glaucoma progression. The use of antifibrotic agents to inhibit scarring of trabeculectomy blebs is now a well-established clinical practice. Unfortunately, severe complications such as leakage, infection, hypotony, and endophthalmitis with complete loss of vision may occur. In addition, surgery still fails in some individuals despite maximal doses of current antifibrotics. Better therapeutic agents are needed. Many promising new agents are being evaluated clinically and in vitro. In this chapter, we will discuss our current understanding of the wound healing process after glaucoma surgery and promising new treatment modalities.