Efficacy and safety of mitomycin C as an agent to treat corneal scarring in horses using an in vitro model

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

The TGM2 inhibitor cysteamine hydrochloride does not impact corneal epithelial and stromal wound healing in vitro and in vivo

Corneal wound healing is integral for resolution of corneal disease or for post-operative healing. However, corneal scarring that may occur secondary to this process can significantly impair vision. Tissue transglutaminase 2 (TGM2) inhibition has shown promising antifibrotic effects and thus holds promise to prevent or treat corneal scarring. The commercially available ocular solution for treatment of ocular manifestations of Cystinosis, Cystaran®, contains the TGM2 inhibitor cysteamine hydrochloride (CH). The purpose of this study is to assess the safety of CH on corneal epithelial and stromal wounds, its effects on corneal wound healing, and its efficacy against corneal scarring following wounding. Quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were first used to quantify and localize TGM2 expression in the cornea. Subsequently, (i) the in vitro effects of CH at 0.163, 1.63, and 16.3 mM on corneal epithelial cell migration was assessed with an epithelial cell migration assay, and (ii) the in vivo effects of application of 1.63 mM CH on epithelial and stromal wounds was assessed in a rabbit model with ophthalmic examinations, inflammation scoring, color and fluorescein imaging, optical coherence tomography (OCT), and confocal biomicroscopy. Post-mortem assessment of corneal tissue post-stromal wounding included biomechanical characterization (atomic force microscopy (AFM)), histology (H&E staining), and determining incidence of myofibroblasts (immunostaining against α-SMA) in wounded corneal tissue. TGM2 expression was highest in corneal epithelial cells. Application of the TGM2 inhibitor CH did not affect in vitro epithelial cell migration at the two lower concentrations tested. At 16.3 mM, decreased cell migration was observed. In vivo application of CH at 57 mM was well tolerated and did not adversely affect wound healing. No difference in corneal scarring was found between CH treated and vehicle control eyes. This study shows that the TGM2 inhibitor CH, at the FDA-approved dose, is well tolerated in a rabbit model of corneal wound healing and does not adversely affect epithelial or stromal wound healing. This supports the safe use of this medication in Cystinosis patients with open corneal wounds. CH did not have an effect on corneal scarring in this study, suggesting that Cystaran® administration to patients with corneal wounds is unlikely to decrease corneal fibrosis.

Evaluation of a novel combination of TRAM-34 and ascorbic acid for the treatment of corneal fibrosis in vivo

Corneal injury and aberrant wound healing commonly result in corneal fibrosis and subsequent vision loss. Intermediate-conductance calmodulin/calcium-activated K+ channels (KCa3.1) have been shown to promote fibrosis in non-ocular and ocular tissues via upregulation of transforming growth factor beta (TGFβ). TRAM-34 is a selective inhibitor of KCa3.1 and reduces fibrosis by downregulation of TGFβ-induced transdifferentiation of stromal fibroblasts to myofibroblasts. Ascorbic acid has been demonstrated to be effective in promoting corneal re-epithelialization and reduction of neovascularization via anti-VEGF and anti-MMP mechanisms. This study evaluates tolerability and efficacy of a novel combination of TRAM-34 (25μM) and ascorbic acid (10%) topical treatment for corneal fibrosis using an established in vivo rabbit model and conducting clinical eye examinations. Markers of corneal fibrosis were evaluated in all corneas at study endpoint via histopathology, immunofluorescence, and quantitative real-time PCR. The eyedrop treated eyes showed significantly improved clinical outcomes based on modified McDonald Shadduck scores, reduction of clinical haze on Fantes scores, and reduction of central corneal thickness (CCT). At cellular and molecular levels, eyedrop treatment also significantly reduced expression of alpha smooth muscle actin (α-SMA) mRNA and protein, collagen III mRNA, and fibronectin mRNA compared to non-treated eyes. Our study suggests that a tested new bimodal eyedrop is well tolerated and effectively reduces corneal fibrosis/haze in rabbits in vivo.

Characterization of hydrogen sulfide toxicity to human corneal stromal fibroblasts

Hydrogen sulfide gas (H2 S) is a chemical weapon and a common environmental pollutant. H2 S intoxication is lethal to humans and animals. H2 S contact to the eye can cause vision loss. However, the molecular mechanisms associated with H2 S toxicity to the cornea remain unclear, and no specific therapy exists to mitigate ocular damage from H2 S. Here, we report H2 S-induced cytotoxicity and the parameters contributing to the molecular mechanisms associated with corneal toxicity using primary human corneal stromal fibroblasts (hCSFs) in vitro. Sodium hydrosulfide (NaSH) was used as a source of H2 S, and the cytotoxicity of H2 S was determined by treating hCSF cells with varying concentrations of NaSH (0-10 mM) for 0-72 hours. Changes in cell proliferation, oxidative stress factors, and the expression of inflammatory and fibrotic genes were studied using standard commercial kits and qRT-PCR. NaSH exposure to hCSFs showed dose- and time-dependent cytotoxicity. The IC50 of NaSH was determined to be 5.35 mM. NaSH 5.35 mM exposure led to significantly decreased cytochrome c oxidase activity, increased ROS production, and increased expression of inflammatory and fibrotic genes in hCSF cells. H2 S/NaSH exposure alters normal mitochondrial function, oxidative stress, and inflammatory and fibrotic gene responses in corneal stromal fibroblasts in vitro.

Efficacy of BCG vaccine and Mitomycin C for the treatment of ocular squamous cell carcinoma in bovines

Bovine ocular squamous cell carcinoma (BOSCC) also called cancer eye, represents the most economically important neoplasm in large animals. Hereditary factors, environmental factors, lack of eyelid pigmentation, age and dietary habits have all been reported to play a role in the etiopathogenesis of bovine ocular squamous cell carcinoma. In group I, six animals with small, localized eye cancer where vision was not affected were included and subjected to intralesional injection of Bacillus Calmette- Guerin (BCG) vaccine at 0, 14, 35, and 56 days interval. In group II (six animals), surgical excision and Mitomycin C 0.04% topically on alternate weeks for two months as adjunctive therapy. All the animals recovered completely with no recurrence for a follow up period of one year.

Systematic Review on Therapeutic Strategies to Minimize Corneal Stromal Scarring After Injury

OBJECTIVES

To evaluate recent studies on available and experimental therapies in preventing or minimizing corneal stromal scarring after injury.

METHODS

We performed an Entrez PubMed literature search using keywords "cornea," "scarring," "haze," "opacity," "ulcer," "treatments," "therapies," "treatment complications," and "pathophysiology" resulting in 390 articles of which 12 were analyzed after filtering, based on English language and publication within 8 years, and curation for relevance by the authors.

RESULTS

The 12 articles selected included four randomized control trials (RCTs) (two were double-blinded placebo-controlled RCTs, one was a prospective partially masked RCT, and one was an open-label RCT), two retrospective observational studies, and six laboratory-based studies including two studies having in vivo and in vitro experiments, one was in vivo study, one was ex vivo study, and the last two were in vitro studies. The current mainstay for preventing or minimizing corneal scarring involves the use of topical corticosteroids and local application of mitomycin C. However, supportive evidence for their use in clinical practice from well-designed RCTs is lacking. Laboratory studies on topical rosiglitazone therapy, vitamin C prophylaxis, gene therapy, and stem cell therapy have shown promising results but have yet to be translated to clinical research.

CONCLUSION

There is a need for more robust randomized controlled trials to support treatments using topical corticosteroids and mitomycin C. Furthermore, their clinical efficacy and safety profile should be compared with new treatments that have shown promising results in the laboratory setting. Ultimately, the goal should be to personalize cornea scarring treatment according to the most effective treatment for the specific underlying pathology.

Altering equine corneal fibroblast differentiation through Smad gene transfer

OBJECTIVE

To explore the impact of equine corneal fibroblast (ECF) to myofibroblast (ECM) differentiation by altering the expression of the Smad genes either individually or in combination. Specifically, we sought to examine the ECF differentiation after (a) silencing of Smad2, 3, and 4 profibrotic genes individually and (b) overexpression of antifibrotic Smad7 gene and in a combination with pro- and antifibrotic Smad genes.

METHODS

Equine corneal fibroblast primary cultures were generated as previously described. ECFs were transfected with individual plasmids which silenced gene expression of either Smad2, 3, or 4 or in combination with a plasmid overexpressing Smad7 using Lipofectamine 2000™ or Lipofectamine BLOCK-iT™. Smad-transfected clones were then exposed to TGF-β1 to induce differentiation to myofibroblasts. Immunofluorescence and qRT-PCR techniques quantified levels of ECF differentiation to ECM by measuring alpha smooth muscle actin, a known marker of ECM transdifferentiation.

RESULTS

Silencing of individual Smad2, 3, or 4 genes or overexpression of Smad7 showed significant inhibition of ECF transdifferentiation (73-83% reduction). Silencing of Smad2 showed the greatest inhibition of ECF transdifferentiation in (a) and was therefore utilized for the combination gene transfer testing. The combination gene transfer consisting of Smad7 overexpression and Smad2 silencing attenuated ECF differentiation significantly; however, the level was not significant compared to the overexpression of Smad7 individually.

CONCLUSIONS

Using gene transfer technology involving profibrotic Smad silencing, antifibrotic Smad overexpression or its combination is a novel strategy to control TGF-β1-mediated fibrosis in equine fibroblasts. Combination gene therapy was not better than single gene therapy in this study.

Development of a novel ex vivo equine corneal model

OBJECTIVE

To develop an ex vivo equine corneal organ culture model. Specifically, to assess the equine cornea's extracellular matrix and cellularity after 7 days using two different culture techniques: either (i) immersion system or (ii) air/liquid interface system, to determine the best ex vivo equine corneal model.

ANIMALS STUDIED

Fourteen healthy equine corneas of various breeds.

PROCEDURES

Equine corneas with 2 mm of perilimbal sclera were freshly harvested from 7 horses undergoing humane euthanasia. One corneal-scleral ring (CSR) from each horse was randomly placed in the (i) immersion condition organ culture system (IC), with the contralateral CSR being placed in the (ii) air/liquid interface organ culture system (ALC) for 7 days. All corneas were evaluated using serial daily gross photography, histology, qPCR, and TUNEL assay.

RESULTS

corneal-scleral rings placed in the IC (i) had complete loss of corneal transparency on gross photography by 7 days, showed a significant level of corneal stromal disorganization, significantly increased α-SMA levels on qPCR, and apoptosis on TUNEL assay compared to controls. The ALC (ii) had weak stromal disorganization on histopathologic examination and was not significantly different from normal equine corneal controls on all other evaluated parameters.

CONCLUSIONS

The air-liquid interface organ culture system maintains the equine cornea's extracellular matrix and preserves corneal transparency, while the immersion condition results in near complete degradation of normal equine corneal architecture after 7 days in culture. The air-liquid organ culture is a viable option to maintain a healthy equine cornea in an ex vivo setting for wound healing studies.

Therapeutic potential of Pirfenidone for treating equine corneal scarring

OBJECTIVE

To evaluate the safety and efficacy of Pirfenidone (PFD) in the treatment of equine corneal fibrosis using an in vitro model.

METHODS

Healthy donor equine corneas were collected and used to generate primary equine corneal fibroblasts (ECFs) by growing cultures in minimal essential medium supplemented with 10% fetal bovine serum. Equine corneal myofibroblasts (ECMs), used as a model of equine corneal fibrosis, were produced by growing ECF cultures in serum-free medium containing transforming growth factor β1 (1 ng/mL). Trypan blue viability assays and changes in ECF morphology were utilized to determine the optimal PFD dose for this in vitro model. Trypan blue viability, phase-contrast microscopy, and TUNEL assays were used to evaluate the cytotoxicity of PFD. Scratch and MTT assays were used to evaluate the effect of PFD on cellular migration and proliferation. Real-time PCR, immunoblot analysis, and immunocytochemistry were employed to determine the efficacy of PFD to inhibit ECM formation in vitro.

RESULTS

Topical PFD application at 200 μg/mL successfully decreased αSMA expression when compared to the TGFβ1 only treatment group (P < 0.01). PFD application ≤ 200 μg/mL did not affect ECF phenotype or cellular viability and did not result in significant cytotoxicity.

CONCLUSIONS

Pirfenidone safely and effectively inhibits TGFβ1-induced equine corneal fibrosis in vitro. In vivo studies are warranted.

Quiescent keratocytes fail to repair MMC induced DNA damage leading to the long-term inhibition of myofibroblast differentiation and wound healing

PURPOSE

The purpose of this study was to determine the acute and long-term effects of mitomycin C (MMC) on quiescent rabbit corneal keratocytes regarding cell proliferation, myofibroblast differentiation and DNA repair.

METHODS

Quiescent keratocytes cultured in serum-free media were exposed to various concentrations of MMC and then treated with transforming growth factor-β (TGFβ). DNA damage was evaluated in both cultured keratocytes and live rabbit eyes following treatment with MMC. The long-term ability of quiescent keratocytes to repair MMC induced damage in vivo was evaluated in rabbits treated with MMC 2 months before 100 μm deep lamellar keratectomy (LK) injury.

RESULTS

MMC significantly blocked TGFβ-induced cell proliferation and myofibroblast differentiation in cultured quiescent keratocytes and altered the transcriptional regulation of macrophage chemotactic protein-1 (MCP-1) and alpha smooth muscle actin (αSMA). MMC also induced phosphorylation of the nuclear histone marker of DNA damage, γH2AX (a member of the H2A histone family), without induction of cell cycle entry or immediate DNA repair measured by Comet assay. In live rabbits, 0.2 mg/ml MMC significantly induced γH2AX nuclear immunostaining (p<0.05) throughout the cornea and corneas receiving 0.2 mg/ml MMC treatment 2 months before LK injury showed complete absence of any corneal scarring.

CONCLUSIONS

MMC induces DNA damage to quiescent corneal keratocytes, which remains unrepaired, resulting in abnormal cell replication and gene transcription that leads to long-term effects on corneal repair. Overall these findings suggest that there may be long-term and perhaps permanent consequences to the application of MMC as an anti-fibrotic therapy.

Efficacy and safety of suberoylanilide hydroxamic acid (Vorinostat) in the treatment of canine corneal fibrosis

OBJECTIVE

Study aims were to evaluate the safety and efficacy of the Food and Drug Administration-approved drug Vorinostat [suberoylanilide hydroxamic acid (SAHA)] in the treatment of canine corneal fibrosis using an in vitro model.

METHODS

Healthy donor canine corneas were collected and used to generate primary canine corneal fibroblasts (CCFs) by growing cultures in minimal essential medium supplemented with 10% fetal bovine serum. Canine corneal myofibroblasts, used as a model for corneal fibrosis, were produced by growing CCF cultures in serum-free medium containing transforming growth factor β1 (1 ng/mL). Trypan blue exclusion assays were used to determine the optimal SAHA dose for this in vitro model. Four hour after culturing with TGFβ1, CCF cultures were treated with 0.06% SAHA for 5 min (group 1) and for 24 h (group 2), representing single and multiple dose treatment regimes, respectively. Cultures were then further incubated in the presence of TGFβ1 (1 ng/μL) under serum-free conditions until they reached 70% confluence. Trypan blue exclusion, immunocytochemistry, and TUNEL assays were used to evaluate the cytotoxicity of SAHA. Real-time PCR, western blot analysis, and immunocytochemistry were used to determine the efficacy of SAHA to inhibit canine corneal myofibroblast formation.

RESULTS

Topical SAHA application in both treatment groups successfully decreased α-smooth muscle actin expression when compared to the TGFβ1 only treatment group (P < 0.05). Tested SAHA did not affect CCF phenotype or cellular viability and did not cause significant cell death.

CONCLUSIONS

Suberoylanilide hydroxamic acid safely and effectively inhibits TGFβ1-induced CCFs transformation to myofibroblast in vitro.

A retrospective comparison of surgical removal and subsequent CO2 laser ablation versus topical administration of mitomycin C as therapy for equine corneolimbal squamous cell carcinoma

OBJECTIVE

  To compare the complications and nonrecurrence rate following topical mitomycin C (MMC) therapy vs. CO(2) laser ablation for treating equine corneolimbal squamous cell carcinoma (SCC).

STUDY DESIGN

  Retrospective study.

SAMPLE POPULATION

  Twenty-five horses with corneolimbal SCC.

PROCEDURES

  Medical records of horses undergoing surgical tumor resection followed by either topical MMC therapy (0.04%) or CO(2) laser ablation between the years of 2004 and 2010 were reviewed. Recurrence and complications were compared between groups and within MMC subgroups defined by the time at which treatment was initiated relative to surgery.

RESULTS

  Therapy with topical MMC resulted in a nonrecurrence rate comparable to that achieved with CO(2) laser ablation (82.4% vs. 85.7%, respectively). Initiation of MMC following epithelialization of the surgical site a mean of 15 days postoperatively did not result in increased recurrence rates relative to treatment in the immediate postoperative period. Vision- or globe-threatening complications tended to occur with greater frequency in horses receiving topical MMC in the immediate postoperative period (5 of 6 major complications) relative to following epithelialization of the surgical site (1 of 6 major complications).

CONCLUSIONS

  Horses receiving adjunctive topical MMC therapy were no more likely to experience tumor recurrence than were horses undergoing CO(2) laser ablation in the horses in this study. Initiation of two to three rounds of MMC following epithelialization of the surgical site results in fewer major complications and achieves comparable disease resolution relative to treatment in the immediate postoperative period.

Mitomycin C: a promising agent for the treatment of canine corneal scarring

OBJECTIVE

To evaluate the safety and efficacy of mitomycin C (MMC) in prevention of canine corneal scarring.

METHODS

With an in vitro approach using healthy canine corneas, cultures of primary canine corneal fibroblasts or myofibroblasts were generated. Primary canine corneal fibroblasts were obtained by growing corneal buttons in minimal essential medium supplemented with 10% fetal bovine serum. Canine corneal myofibroblasts were produced by growing cultures in serum-free medium containing transforming growth factor β1 (1 ng/mL). Trypan blue assay and phase-contrast microscopy were used to evaluate the toxicity of three doses of MMC (0.002%, 0.02% and 0.04%). Real-time PCR, immunoblot, and immunocytochemistry techniques were used to determine MMC efficacy to inhibit markers of canine corneal scarring.

RESULTS

A single 2-min treatment of 0.02% or less MMC did not alter canine corneal fibroblast or keratocyte phenotype, viability, or growth. The 0.02% dose substantially reduced myofibroblast formation (up to 67%; P < 0.001), as measured by the change in RNA and protein expression of fibrosis biomarkers (α-smooth muscle actin and F-actin).

CONCLUSION

This in vitro study suggests that a single 2-min 0.02% MMC treatment to the canine corneal keratocytes is safe and may be useful in decreasing canine corneal fibrous metaplasia. In vivo studies are warranted.