RARE DISEASE
Amoebic keratitis
Amoebic keratitis
Amoebic keratitis
Drug discovery
6
drugs
With orphan designations
Overview
Acanthamoeba keratitis (AK) is a rare, sight-threatening corneal infection caused by Acanthamoeba protozoa. Predominantly affecting contact lens wearers, it arises from exposure to contaminated water or poor lens hygiene. Early symptoms mimic bacterial/viral keratitis, delaying diagnosis. Treatment involves dual topical therapy (chlorhexidine/polyhexamethylene biguanide + propamidine) targeting trophozoites and cysts, often requiring months of therapy. Severe cases may necessitate corneal transplant. Prognosis depends on early intervention but carries risks of permanent vision loss [1][3][12].
Burden
Global incidence: ~2.34 cases/million population, rising steadily due to contact lens misuse [2][7][12].
High morbidity: 41% risk of legal blindness in advanced cases; prolonged treatment (6–12 months) common [3][16][17].
Economic cost: $175M/year in U.S. healthcare expenditures, including antimicrobial prescriptions and surgical interventions [4][9][17].
Therapies
First-line: Dual topical therapy with biguanides (chlorhexidine 0.02%, PHMB 0.02–0.06%) and diamidines (propamidine 0.1%) hourly initially, tapered over months [1][3][8].
Adjunctive: Epithelial debridement, oral miltefosine for refractory cases, and cautious steroid use for inflammation [3][8][12].
Surgical: Penetrating keratoplasty reserved for perforation or scarring post-infection control [1][8].
Categories: rare infectious diseases, rare ophthalmic disorders
Research Papers
1,046 drug discovery papers about Amoebic keratitis, with 4 first-in-class and 9 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
1,046 drug discovery papers about Amoebic keratitis, with 4 first-in-class and 9 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
2026-08-04 | Enhanced antiamoebic efficacy of PHMB via methyltransferase inhibition to maintain drug sensitivity and block encystation
Abstract Background Acanthamoeba keratitis (AK) is a severe ocular infection. The primary treatment is polyhexamethylene biguanide (PHMB), but its efficacy is limited due to cyst resistance. This study investigated the role of DNA methylation in Acanthamoeba encystation and the potential efficacy of combining 5-azacytidine (5-AzaC; a methyltransferase inhibitor) with PHMB treatment. Methods Encystation was induced in Acanthamoeba castellanii using encystation buffer, followed by calcofluor white staining. Gene expression levels of virulence genes and the methyltransferase gene were assessed by quantitative PCR. The cell viability assay of A. castellanii on Statens Seruminstitut Rabbit Cornea (SIRC) cells was evaluated to determine functional virulence. Overexpression of methyltransferase via electroporation was established to further investigate its function. Results qPCR results revealed upregulated methyltransferase expression during encystation. Calcofluor white staining showed significantly reduced cyst formation in A. castellanii treated with 5-AzaC. This treatment also induced significant transcriptional reduction in virulence genes. Consistently, 5-AzaC-treated A. castellanii did not exhibit increased cytotoxicity against SIRC cells. Overexpression of the methyltransferase increases the encystation ratio. Combination treatment with PHMB and 5-AzaC significantly decreased A. castellanii survival. Conclusions Inhibiting DNA methylation enhances the antiamoebic effects of PHMB, offering a potential AK treatment strategy. DNA methylation may serve as a critical regulatory switch in A. castellanii , governing both morphological transformation and virulence genes expression. This work expands our understanding of epigenetic regulation in protozoa.
2026-07-31 | In Vitro Study of Carbonyl Thiourea Derivatives’ Cytotoxicity on Human Corneal Epithelial Cells
Introduction: The global rise of Acanthamoeba keratitis infections has highlighted the shortcomings in the current treatments and prevention approaches for the disease. Therefore, this study is a continuation of our prior work and is intended to investigate the possible adverse effects of using carbonyl thiourea derivatives as alternative ocular drugs for amoebic keratitis on non-targeted human corneal epithelial cells (HCEC) in vitro. Methods: The efficacy and safety profiles of two carbonyl thiourea derivatives, 2-(3-benzoylthioureido)-3-mercaptopropanoic acid (M1) and 2-(3-benzoylthioureido-4-(methylthio)butanoic acid (M2), were tested on HCEC lines using the cytotoxicity assay and microscopic analysis. Results and Discussion: The carbonyl thiourea compounds were found to be non-toxic on HCEC with IC50 of 37.73 µg.mL-1 and 30.68 µg.mL-1 on M1 and M2, respectively. These compounds have selectivity indices (SI) of 14.74 (M1) and 11.38 (M2), indicating moderate selectivity for the targeted Acanthamoeba cells. HCEC-treated cells continued to proliferate in a time-dependent manner without significantly altering the cell population by retaining 90% viability. However, the microscopic examination revealed that HCECs were poorly differentiated and disintegrated, with irregular forms after the compound treatment, as opposed to their original hexagonal morphology of the healthy viable cells. The AO/PI staining indicated that the thiourea compounds impaired HCEC membrane integrity. Conclusions: This study's findings are critical in providing relevant information on carbonyl thiourea compounds if they were to be proposed as anti-amoebic agents in treating or preventing Acanthamoeba keratitis infection.
2026-07-18 | Impact of cyst maturity on drug resistance assays in Acanthamoeba Genotype T4.
Therapeutic failure in Acanthamoeba Keratitis (AK) is largely driven by the high resistance of cysts to antimicrobial agents. However, the development of effective cysticidal drugs is hindered by the lack of standardized in vitro encystation protocols. Inconsistencies in induction methods can produce immature cells that lack the structural defenses of mature clinical walls, potentially leading to false-positive results in drug screening. This study aims to evaluate the impact of cyst maturity on drug resistance assays by systematically comparing two common liquid media-glucose-supplemented PBS (PBSEB) and alkaline encystation buffer (EB2)-within Acanthamoeba Genotype T4 backgrounds. We assessed morphological transitions, transcriptional profiles (EMSP, ATG8, and CS-I), ultrastructure (TEM), and functional resistance to sodium dodecyl sulfate (SDS) and chlorhexidine gluconate (CHG) using environmental reference and clinical isolates, including the stress-tolerant NCKU_D strain. Although both media induced morphological rounding and upregulated the autophagy marker ATG8, functional and molecular assays revealed distinct developmental outcomes. PBSEB-treated cells failed to significantly upregulate the critical early serine proteinase EMSP and exhibited insufficient CS-I expression, remaining highly susceptible to SDS lysis and lacking intact walls under TEM. Conversely, EB2 triggered a robust 11.8-fold increase in EMSP, yielding structurally mature, SDS-resistant cysts. Importantly, functional assays demonstrated that EB2-induced cysts exhibited significantly higher chemical resistance to CHG than the PBSEB group at 48 h, with this resistance advantage further widening by 72 h of induction. Based on these distinct profiles, we suggest that while PBSEB serves as a useful model for investigating cell detachment kinetics and early autophagic pathways, the EB2 protocol is more suitable for evaluating downstream therapeutic efficacy and product safety where functional, double-walled resistance is required to avoid false-positive outcomes in Genotype T4 drug screening.
2026-07-08 | Polihexanide 0.8 mg/mL to manage Acanthamoeba keratitis in clinical practice: a multicentre, retrospective study in Poland
Dataset of the manuscript: "Polihexanide 0.8 mg/mL to manage Acanthamoeba keratitis in clinical practice: a multicentre, retrospective study in Poland"
2026-07-01 | Carbon nanotubes based nano-materials against Acanthamoeba castellanii
Acanthamoeba castellanii is a free-living amoeba that causes diseases such as Acanthamoeba Keratitis (AK) and Acanthamoeba granulomatous encephalitis (AGE), both of which can result in irreversible harm or even death if left untreated. Treating A. castellanii infection is challenging due to its ability to transform into its resistant cysts form when it is in harsh conditions, making complete eradication difficult. Additionally, the sensitive nature of the site of infection requires the treatment to have a low cytotoxicity. Therefore, there is a pressing need to discover improved treatment options. This study evaluates the anti-amoebic properties of Tioconazole (TCZ) and Tioconazole chitosan oxidized multiwalled carbon nanotubes (TCO) and its cytotoxicity to human cells. Various assays were conducted against A. castellanii strain (ATCC 50492) T4 genotype at concentrations ranging from 10 to 100 µg/mL to determine its amoebicidal, amoebistatic, encystation, and excystation effects. The cytotoxicity of TCO against HaCaT cell lines was evaluated using MTT cytotoxicity assay. Both TCZ and TCO exhibited significant amoebicidal and amoebistatic effects at all concentrations tested. However, at the highest concentration tested TCZ lost amoebicidal effectiveness, while TCO maintained its effectiveness. Additionally, TCO showed greater amoebistatic effect then TCZ at 25 µg/mL. Although both TCZ and TCO exhibited inhibitory effect on encystation and excystation, TCO had a significantly weaker effect compared to TCZ. In the cytotoxic assay, both TCZ and TCO exhibited no significant cytotoxic effect. However, at the high concentration TCO displayed significantly lower cytotoxicity then TCZ. This study has shown the potential of TCO as a promising candidate for treating A. castellanii infections, offering effective amoebicidal and amoebistatic properties with lower cytotoxicity.
2026-08-04 | Enhanced antiamoebic efficacy of PHMB via methyltransferase inhibition to maintain drug sensitivity and block encystation
Abstract Background Acanthamoeba keratitis (AK) is a severe ocular infection. The primary treatment is polyhexamethylene biguanide (PHMB), but its efficacy is limited due to cyst resistance. This study investigated the role of DNA methylation in Acanthamoeba encystation and the potential efficacy of combining 5-azacytidine (5-AzaC; a methyltransferase inhibitor) with PHMB treatment. Methods Encystation was induced in Acanthamoeba castellanii using encystation buffer, followed by calcofluor white staining. Gene expression levels of virulence genes and the methyltransferase gene were assessed by quantitative PCR. The cell viability assay of A. castellanii on Statens Seruminstitut Rabbit Cornea (SIRC) cells was evaluated to determine functional virulence. Overexpression of methyltransferase via electroporation was established to further investigate its function. Results qPCR results revealed upregulated methyltransferase expression during encystation. Calcofluor white staining showed significantly reduced cyst formation in A. castellanii treated with 5-AzaC. This treatment also induced significant transcriptional reduction in virulence genes. Consistently, 5-AzaC-treated A. castellanii did not exhibit increased cytotoxicity against SIRC cells. Overexpression of the methyltransferase increases the encystation ratio. Combination treatment with PHMB and 5-AzaC significantly decreased A. castellanii survival. Conclusions Inhibiting DNA methylation enhances the antiamoebic effects of PHMB, offering a potential AK treatment strategy. DNA methylation may serve as a critical regulatory switch in A. castellanii , governing both morphological transformation and virulence genes expression. This work expands our understanding of epigenetic regulation in protozoa.
2026-07-31 | In Vitro Study of Carbonyl Thiourea Derivatives’ Cytotoxicity on Human Corneal Epithelial Cells
Introduction: The global rise of Acanthamoeba keratitis infections has highlighted the shortcomings in the current treatments and prevention approaches for the disease. Therefore, this study is a continuation of our prior work and is intended to investigate the possible adverse effects of using carbonyl thiourea derivatives as alternative ocular drugs for amoebic keratitis on non-targeted human corneal epithelial cells (HCEC) in vitro. Methods: The efficacy and safety profiles of two carbonyl thiourea derivatives, 2-(3-benzoylthioureido)-3-mercaptopropanoic acid (M1) and 2-(3-benzoylthioureido-4-(methylthio)butanoic acid (M2), were tested on HCEC lines using the cytotoxicity assay and microscopic analysis. Results and Discussion: The carbonyl thiourea compounds were found to be non-toxic on HCEC with IC50 of 37.73 µg.mL-1 and 30.68 µg.mL-1 on M1 and M2, respectively. These compounds have selectivity indices (SI) of 14.74 (M1) and 11.38 (M2), indicating moderate selectivity for the targeted Acanthamoeba cells. HCEC-treated cells continued to proliferate in a time-dependent manner without significantly altering the cell population by retaining 90% viability. However, the microscopic examination revealed that HCECs were poorly differentiated and disintegrated, with irregular forms after the compound treatment, as opposed to their original hexagonal morphology of the healthy viable cells. The AO/PI staining indicated that the thiourea compounds impaired HCEC membrane integrity. Conclusions: This study's findings are critical in providing relevant information on carbonyl thiourea compounds if they were to be proposed as anti-amoebic agents in treating or preventing Acanthamoeba keratitis infection.
2026-07-18 | Impact of cyst maturity on drug resistance assays in Acanthamoeba Genotype T4.
Therapeutic failure in Acanthamoeba Keratitis (AK) is largely driven by the high resistance of cysts to antimicrobial agents. However, the development of effective cysticidal drugs is hindered by the lack of standardized in vitro encystation protocols. Inconsistencies in induction methods can produce immature cells that lack the structural defenses of mature clinical walls, potentially leading to false-positive results in drug screening. This study aims to evaluate the impact of cyst maturity on drug resistance assays by systematically comparing two common liquid media-glucose-supplemented PBS (PBSEB) and alkaline encystation buffer (EB2)-within Acanthamoeba Genotype T4 backgrounds. We assessed morphological transitions, transcriptional profiles (EMSP, ATG8, and CS-I), ultrastructure (TEM), and functional resistance to sodium dodecyl sulfate (SDS) and chlorhexidine gluconate (CHG) using environmental reference and clinical isolates, including the stress-tolerant NCKU_D strain. Although both media induced morphological rounding and upregulated the autophagy marker ATG8, functional and molecular assays revealed distinct developmental outcomes. PBSEB-treated cells failed to significantly upregulate the critical early serine proteinase EMSP and exhibited insufficient CS-I expression, remaining highly susceptible to SDS lysis and lacking intact walls under TEM. Conversely, EB2 triggered a robust 11.8-fold increase in EMSP, yielding structurally mature, SDS-resistant cysts. Importantly, functional assays demonstrated that EB2-induced cysts exhibited significantly higher chemical resistance to CHG than the PBSEB group at 48 h, with this resistance advantage further widening by 72 h of induction. Based on these distinct profiles, we suggest that while PBSEB serves as a useful model for investigating cell detachment kinetics and early autophagic pathways, the EB2 protocol is more suitable for evaluating downstream therapeutic efficacy and product safety where functional, double-walled resistance is required to avoid false-positive outcomes in Genotype T4 drug screening.
2026-07-08 | Polihexanide 0.8 mg/mL to manage Acanthamoeba keratitis in clinical practice: a multicentre, retrospective study in Poland
Dataset of the manuscript: "Polihexanide 0.8 mg/mL to manage Acanthamoeba keratitis in clinical practice: a multicentre, retrospective study in Poland"
2026-07-01 | Carbon nanotubes based nano-materials against Acanthamoeba castellanii
Acanthamoeba castellanii is a free-living amoeba that causes diseases such as Acanthamoeba Keratitis (AK) and Acanthamoeba granulomatous encephalitis (AGE), both of which can result in irreversible harm or even death if left untreated. Treating A. castellanii infection is challenging due to its ability to transform into its resistant cysts form when it is in harsh conditions, making complete eradication difficult. Additionally, the sensitive nature of the site of infection requires the treatment to have a low cytotoxicity. Therefore, there is a pressing need to discover improved treatment options. This study evaluates the anti-amoebic properties of Tioconazole (TCZ) and Tioconazole chitosan oxidized multiwalled carbon nanotubes (TCO) and its cytotoxicity to human cells. Various assays were conducted against A. castellanii strain (ATCC 50492) T4 genotype at concentrations ranging from 10 to 100 µg/mL to determine its amoebicidal, amoebistatic, encystation, and excystation effects. The cytotoxicity of TCO against HaCaT cell lines was evaluated using MTT cytotoxicity assay. Both TCZ and TCO exhibited significant amoebicidal and amoebistatic effects at all concentrations tested. However, at the highest concentration tested TCZ lost amoebicidal effectiveness, while TCO maintained its effectiveness. Additionally, TCO showed greater amoebistatic effect then TCZ at 25 µg/mL. Although both TCZ and TCO exhibited inhibitory effect on encystation and excystation, TCO had a significantly weaker effect compared to TCZ. In the cytotoxic assay, both TCZ and TCO exhibited no significant cytotoxic effect. However, at the high concentration TCO displayed significantly lower cytotoxicity then TCZ. This study has shown the potential of TCO as a promising candidate for treating A. castellanii infections, offering effective amoebicidal and amoebistatic properties with lower cytotoxicity.
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Drug Discovery Landscape
6 orphan drug designations for Amoebic keratitis, including 1 approved therapy.
6 orphan drug designations for Amoebic keratitis, including 1 approved therapy.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
polyhexanide | small molecules | FDA | 2017-11-06 | — | Società Industria Farmaceutica Italiana S.p.A. |
povidone-iodine 0.5% (w/w) in dimethylsulfoxide 44% (w/w) | small molecules | FDA | 2017-05-11 | — | Veloce BioPharma, LLC |
miltefosine | small molecules | FDA | 2016-12-06 | — | Profounda, Inc. |
Polihexanide [AKANTIOR] | small molecules | EMA | 2007-11-14 | 2024-08-23 | S.I.F.I. Società Industria Farmaceutica Italiana S.p.A. |
Miltefosine | small molecules | EMA | 2005-05-27 | — | Orpha-Devel Handels und Vertriebs GmbH |
Propamidine isethionate 0.1% ophthalmic solution | small molecules | FDA | 1988-03-10 | — | Bausch & Lomb |
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