ACT-1 Peptide (DB18201): A Comprehensive Report on a Modulator of Cellular Communication for Tissue Repair and Regeneration

1. Introduction

ACT-1 peptide (DrugBank ID: DB18201) is an investigational biotech therapeutic agent designed to modulate cellular communication and promote tissue repair. This report provides a comprehensive analysis of ACT-1 peptide, encompassing its identity, originator and developer information, detailed mechanism of action, pharmacological properties, non-clinical development, extensive clinical trial program, current therapeutic indications, pipeline status, and regulatory and intellectual property landscape. The focus is on its development for various dermatological and ophthalmological conditions, leveraging its unique interactions with key junctional proteins.

2. Drug Identity and Basic Information

ACT-1 peptide, also known by synonyms such as α-Connexin carboxyl-Terminal 1 peptide, Granexin, Granexin Peptide, iNexin, Zifogaptide, and PEPTIDE 328967, is classified as a biotech drug, specifically a peptide-based therapeutic.[1] It is a synthetic 25-amino acid peptide.[4] Its chemical formula and average protein weight are not definitively available in all databases, characteristic of complex biologic entities.[1] The peptide's design incorporates a cell internalization sequence linked to a domain mimicking the C-terminus of Connexin43 (Cx43).[4] Pharmacologically, it functions as a modulator of gap junction and tight junction proteins, primarily targeting Connexin 43 and Zonula Occludens Protein 1 (ZO-1).[2] Its therapeutic class includes skin disorder therapies, eye disorder therapies, and potentially antineoplastics based on early research.[2]

3. Originator and Developer Information

The development of ACT-1 peptide began with foundational research at the Medical University of South Carolina (MUSC), where scientist Robert Gourdie and his laboratory developed the peptide while studying electrical conduction in the heart.[2] This academic discovery led to the formation of FirstString Research, Inc., co-founded by Gourdie and Gautam Ghatnekar (a former postdoctoral associate in Gourdie's lab), to translate these findings into therapeutic applications.[7] FirstString Research held the initial Investigational New Drug (IND) applications (including IND #074836 and #154394) and sponsored the early to mid-stage clinical trials for ACT-1, marketed under names like Granexin™ Gel.[4]

Subsequently, Xequel Bio, Inc. has taken over the development of the aCT1 technology platform, including Granexin® Gel and iNexin™ Ophthalmic Solution, and currently manages the INDs.[2] This progression from academic research to a focused startup and then to another biotech entity is a common pathway for translating university-originated innovations into clinical candidates. Such a trajectory often involves licensing agreements or acquisitions, reflecting the different expertise and resources required at each stage of the long and complex drug development process. The continued involvement of key figures like Gautam Ghatnekar, an inventor listed on crucial patents [17] and associated with FirstString Research, across various development phases, can provide valuable continuity in expertise and strategic vision for the therapeutic's advancement.

4. Mechanism of Action

The ACT-1 peptide exerts its therapeutic effects through a sophisticated and multifactorial mechanism of action, primarily centered on the modulation of Connexin43 (Cx43) and its interacting partner, Zonula Occludens 1 (ZO-1). This interaction influences both gap junction intercellular communication (GJIC) and tight junction integrity, ultimately promoting a regenerative healing response rather than merely suppressing inflammation.[4]

Cx43 is a transmembrane protein fundamental to the formation of gap junctions, which allow direct intercellular exchange of ions and small molecules, and hemichannels, which mediate communication between the cytoplasm and the extracellular milieu.[4] ZO-1 is a scaffolding protein crucial for tight junction assembly and also interacts with the C-terminus of Cx43 via its PDZ2 domain, regulating gap junction size and stability.[4] ACT-1, a 25-amino acid peptide, incorporates an antennapedia cell internalization sequence and the nine C-terminal amino acids of Cx43 (RPRPDDLEI).[4] It is designed to competitively bind the PDZ2 motif on ZO-1, thereby disrupting the native Cx43-ZO-1 interaction.[4] Additionally, evidence suggests ACT-1 can directly interact with the Cx43 C-terminal domain itself.[4]

This primary interaction initiates a cascade of cellular events. In injured tissues, Cx43 hemichannels tend to open excessively, releasing pro-inflammatory mediators like ATP into the extracellular space.[4] By disrupting the Cx43/ZO-1 binding and potentially interacting directly with Cx43, ACT-1 promotes the translocation of Cx43 from non-junctional hemichannels into gap junction plaques.[4] This shift has two critical consequences:

1. Reduced Hemichannel Activity: This leads to a decrease in the release of ATP and other pro-inflammatory molecules, thereby tempering the inflammatory cascade. This is a key aspect of ACT-1's anti-inflammatory effect, observed as reduced infiltration of inflammatory cells (e.g., neutrophils) and diminished levels of inflammatory signaling molecules such as IL-6, IL-1β, and TNFα in various injury models.[4]
2. Enhanced Gap Junction Intercellular Communication (GJIC): The formation of more stable and functional gap junctions improves direct cell-to-cell communication, which is vital for coordinating cellular responses during tissue repair and maintaining homeostasis.[4]

Beyond gap junctions, ACT-1 also reinforces tight junction integrity. ZO-1 is instrumental in organizing claudins and occludin into functional tight junction strands that form a paracellular barrier.[4] By binding to ZO-1, ACT-1 is thought to stabilize ZO-1 at the plasma membrane, facilitating claudin oligomerization and preventing tight junction degradation following injury. This action helps to accelerate the re-establishment of cellular barrier function and can reduce tissue edema.[4]

The combined effects on inflammation, GJIC, and tight junction stability contribute to ACT-1's ability to promote re-epithelialization and accelerate wound healing.[4] Furthermore, ACT-1 influences the behavior of fibroblasts and the deposition of collagen. It has been shown to decrease the directionality of fibroblast movement and promote a more organized, less aligned collagen matrix that resembles unwounded skin, which is correlated with improved scar appearance and a more regenerative healing outcome.[8] This suggests a qualitative improvement in the healing process, moving beyond simple repair towards regeneration.

The mechanism of ACT-1 represents an approach that targets the cellular infrastructure regulating the injury response, rather than focusing on individual inflammatory mediators. This "upstream" intervention point may allow for a more comprehensive and coordinated modulation of the healing process. The dual influence on both gap junctions (via Cx43) and tight junctions (via ZO-1) likely provides a synergistic benefit to tissue barrier function and intercellular communication, critical for resolving injury. Moreover, the direct interaction of ACT-1 with the Cx43 C-terminus, as suggested by some studies [12], hints at a potentially more complex regulatory role than solely disrupting Cx43-ZO-1 binding, possibly involving allosteric modulation of Cx43 channels or their phosphorylation state, adding further depth to its mechanism.

Exploratory research has also touched upon ACT-1's potential in cancer, where it was found to promote GJIC in refractory HER2+ breast cancer cells and, in combination with BBI, decrease viability and increase Cx43 expression in canine oral mucosal melanoma cells, suggesting a role in sensitizing cancer cells to other therapies.[20]

5. Pharmacology

5.1. Pharmacokinetics (PK)

The pharmacokinetic profile of ACT-1 peptide is significantly influenced by its peptide nature, particularly its susceptibility to degradation, which has largely dictated its development for local and topical applications.

Routes of Administration and Formulations:

ACT-1 has been primarily developed for topical administration to target specific sites of injury or disease.

• Granexin® Gel: A topical gel formulation designed for dermal applications, including diabetic foot ulcers (DFUs), venous leg ulcers (VLUs), surgical scars, and cutaneous radiation injury.[1] Patent US9161984B2 details a formulation containing ACT-1 peptide (SEQ ID NO: 9), hydroxyethylcellulose as a stabilizer, buffering agents to maintain pH 5-7, and other excipients like parabens, glycerin, and EDTA.[18]
• iNexin™ Ophthalmic Solution: An ophthalmic solution for treating eye conditions such as corneal injuries and Persistent Corneal Epithelial Defects (PCED).[2]
• Aerosolized aCT1: Under preclinical investigation for pulmonary indications like Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS).[13]

Absorption and Cellular Uptake:

A critical design feature of ACT-1 is the inclusion of an N-terminal antennapedia cell internalization sequence (e.g., RQPKIWFPNRRKPWKK).4 This cell-penetrating peptide (CPP) motif is essential for facilitating the peptide's uptake across cellular membranes, enabling it to reach its intracellular and intercellular targets (Cx43 and ZO-1) when applied topically to tissues like skin or cornea.23 Without this CPP, the barrier function of epithelial layers would likely prevent effective penetration and therapeutic activity.

Distribution:

ACT-1 is intended for local action at the site of application, minimizing systemic exposure.4 A clinical trial (NCT02652572) was designed to assess systemic exposure following topical application of Granexin® gel to venous leg ulcers, though specific results from this PK study are not detailed in the available information.39

Metabolism and Elimination:

Systemic administration of ACT-1 peptide and its variants faces significant challenges due to rapid plasma degradation. Studies involving αCT11, a 9-amino acid variant of αCT1, revealed that the peptide was virtually undetectable in rat blood plasma within approximately 10 minutes following intravenous injection.40 Similar rapid degradation was observed ex vivo in isolated plasma, with the peptide being nearly undetectable within 30-60 minutes. This degradation is primarily mediated by plasma proteases and phosphatases, as their inhibition significantly reduced peptide breakdown.40 This inherent plasma instability is a defining pharmacokinetic characteristic that has steered the development strategy towards local delivery. Earlier work also noted rapid metabolism of the full ACT-1 peptide.24

Bioavailability:

For topical and local applications, the key pharmacokinetic goal is achieving and maintaining therapeutic concentrations at the target tissue rather than systemic bioavailability. The antennapedia sequence aids local tissue penetration.5 Formulation strategies, such as the hydroxyethylcellulose gel for Granexin® 18 and the investigation of sustained-release microcapsules for corneal delivery 23, are crucial for optimizing local bioavailability, stability, and retention at the site of action. The effectiveness of αCT1 in sustained-release microcapsules in a corneal wound model underscores the importance of formulation in overcoming local clearance or degradation.23

The profound plasma instability of ACT-1 is a pivotal factor that has shaped its entire development trajectory, making systemic administration largely unfeasible without substantial modifications or sophisticated delivery systems, thus mandating the focus on topical/local routes.

5.2. Pharmacodynamics (PD)

The pharmacodynamic effects of ACT-1 are linked to its concentration at the target site and the duration of its interaction with cellular components.

Dose-Response Relationships:

Clinical trials have investigated various concentrations of ACT-1. For instance, Granexin® Gel has typically been studied at a concentration of 100μM ACT1.9 The iNexin™ ophthalmic solution was tested in a Phase 1b trial at concentrations of 0.08%, 0.4%, and 2.0% aCT1.15 Preclinical studies also support dose-dependent activity; for example, aCT1 at 200 μM, when combined with BBI, demonstrated effects on canine melanoma cells.20

Onset and Duration of Action:

The onset and duration of ACT-1's pharmacodynamic effects vary by indication and endpoint.

• Improvements in wound healing parameters, such as accelerated closure and reduced inflammation, have been observed within days to weeks in both preclinical models and clinical trials, depending on the specific wound type and assessment metric.[7]
• For scar improvement, which involves tissue remodeling, efficacy is assessed over longer durations, typically several months (e.g., 9 months post-surgery).[10] The rapid plasma degradation implies a very short systemic duration of action if the peptide were administered intravenously without protection. For its intended topical applications, the local tissue retention, governed by the formulation and local clearance mechanisms, determines the effective duration of action at the target site. The pharmacodynamic outcomes, such as wound closure or scar modulation, are the result of a cascade of biological events initiated by ACT-1's interaction with junctional proteins, rather than a simple, direct effect with a clearly defined plasma concentration-effect relationship typical of systemically acting drugs.

6. Non-Clinical Development

The non-clinical development of ACT-1 peptide has provided substantial evidence for its efficacy across a range of injury models and has elucidated key aspects of its mechanism and safety.

Key In Vitro Efficacy Studies:

In vitro studies have been instrumental in characterizing ACT-1's effects at a cellular level. The peptide has been shown to enhance gap junction intercellular communication (GJIC) in diverse cell types, including restoring communication in refractory HER2+ breast cancer cells.22 It also promotes the stabilization of Cx43 protein within cells.22 In scratch wound assays using mouse NIH 3T3 fibroblasts and primary human dermal fibroblasts, αCT1 treatment accelerated wound closure and modified cell migration patterns, specifically by decreasing directional persistence.25 In models of ocular corneal injury, ACT-1 reduced the levels of key inflammatory signaling molecules, including IL-6, IL-1β, TNFα, Cox-2, MMP-9, and VEGF.4 Studies on canine oral mucosal melanoma (OMM) cells (TLM1 line) indicated that while ACT-1 (200 μM) alone did not significantly impact cell viability, its combination with Bowman-Birk protease inhibitor (BBI) led to a significant decrease in viability and an increase in Cx43 expression at the cell membrane.20

Key In Vivo Efficacy Studies (Animal Models):

In vivo studies have further substantiated ACT-1's therapeutic potential:

• Dermal Wound Healing and Scarring: Across various animal models (mouse, rat, pig, and guinea pig), topical application of ACT-1 to excisional or incisional wounds consistently resulted in accelerated wound closure, diminished inflammation, reduced granulation tissue formation, and notably, an improved scar appearance characterized by a less aligned collagen fiber matrix that more closely resembles that of unwounded skin.[6] This latter finding suggests a true regenerative effect rather than merely accelerated repair.
• Corneal Wound Healing: In a rat corneal burn model, ACT-1 enhanced wound healing, leading to faster re-epithelialization and reduced inflammation. Efficacy was particularly noted when ACT-1 was delivered via a sustained-release system using A-PLO microcapsules, highlighting the importance of formulation for local delivery.[23]
• Cardiac Injury (Ischemia-Reperfusion): Ex vivo studies on mouse hearts subjected to ischemia-reperfusion (I/R) injury demonstrated beneficial effects of αCT1 and its shorter variant αCT11.[40] Furthermore, αCT1 released from cardiac patches in a mouse model of cryo-induced ventricular injury reduced Cx43 remodeling, decreased arrhythmias, and helped maintain cardiac conduction.[40] However, these positive findings in cardiac models were contrasted by the lack of efficacy when αCT11 was administered intravenously in an in vivo rat I/R model. This discrepancy was attributed to the rapid degradation of the peptide in plasma, preventing it from reaching the cardiac tissue in sufficient concentrations.[40] This set of cardiac studies critically underscores the pharmacokinetic limitations of systemic peptide delivery and reinforces the rationale for local administration strategies.
• Age-Related Macular Degeneration (AMD): In a mouse model of laser-induced choroidal neovascularization (CNV), a hallmark of wet AMD, topically administered aCT1 eye drops were as effective as systemic anti-VEGF therapy in reducing CNV lesion and fluid dome size. This suggests that ACT-1 can ameliorate RPE dysfunction and holds potential as a non-invasive treatment for neovascular AMD.[28]

The breadth of these positive preclinical results across diverse tissues (skin, cornea, heart ex vivo) and injury types supports the fundamental role of Cx43/ZO-1 modulation in the biological response to damage, indicating a broadly applicable mechanism of action for ACT-1.

Preclinical Safety and Toxicology Overview:

Throughout preclinical testing, ACT-1 has generally been reported as well-tolerated, especially with local application.4 For instance, cell toxicity analyses in corneal studies showed minimal cell loss with microcapsule-delivered ACT-1.23 The peptide's relatively low molecular weight (approximately 3.6 kDa) is also anticipated to reduce the risk of an immunogenic response.4

7. Clinical Development Program

The clinical development of ACT-1 peptide, under various product names such as Granexin® Gel and iNexin™ Ophthalmic Solution, has spanned Phase 1 to Phase 3 trials across multiple dermatological and ophthalmological indications. Over 450 patients have received aCT1 under INDs #074836 and #154394, demonstrating a commitment to evaluating its therapeutic potential.[4]

Table 1: Summary of Key Clinical Trials for ACT-1 Peptide

NCT ID	Product Name(s)	Phase	Indication(s)	Sponsor(s)	Est. Enrollment	Status	Key Efficacy Highlights (from snippets)	Key Safety Highlights (from snippets)
NCT04331080	Granexin® Gel	2b/3	Scar Formation (Bilateral Anchor Incision Breast Surgery)	Xequel Bio, Inc.	184	Completed 16	Primary endpoint: Scarring score. Results not yet detailed in snippets, but builds on prior scar data.	Expected to be well-tolerated based on previous studies.
NCT02667327	Granexin® Gel (aCT1 peptide)	3	Diabetic Foot Ulcer (DFU)	FirstString Research, Inc.	552 (planned)	Terminated.39 (Previously noted as ongoing/Phase 3 testing underway 9)	Primary outcome: Incidence of complete wound closure at week 12. Earlier Phase 2 DFU trial showed 72.1% vs 57.1% (SOC) reduction in ulcer area at 12 weeks (p=0.03); greater % achieving 100% closure.42 Phase 2 met primary endpoints.10	Phase 2 DFU trial: No treatment-related AEs; not immunogenic.42 Generally well-tolerated in Phase 2.10
N/A (Phase 2)	Granexin™ Gel (ACT1)	2	Venous Leg Ulcers (VLU)	FirstString Research, Inc.	N/A	Completed 7	79% ulcer closure with ACT1 + compression vs. 36% with compression alone at 12 weeks.7 Met primary endpoints with significant improvements in wound closure.10	No side effects reported by patients.7 No drug-related systemic or local AEs.10
N/A (Phase 1b)	iNexin™ (aCT1 ophthalmic solution)	1b	Corneal Injury in Dry Eye Disease	Xequel Bio, Inc.	36	Completed 15	Early efficacy signals: improvements in corneal staining and ocular discomfort within 2 weeks.15	Safe and well-tolerated at doses tested. No serious AEs or dose-limiting toxicities.15
N/A (Phase 2)	αCT1 gel	2	Scar Reduction (Laparoscopic Surgery)	FirstString Research, Inc. (Implied)	N/A	Completed 26	At 9 months, 47% improvement in scar scores (Vancouver Scar Scale; P=0.0045) vs. control. Higher Global Assessment Scale score (P=0.0009). Improvements in pigmentation, thickness, surface roughness, suppleness.26	Adverse events similar in both groups. Well-tolerated.10
NCT03049910	Granexin® Gel	2	Partial Thickness Burns	FirstString Research, Inc.	N/A	Withdrawn 45	N/A	N/A

Note: N/A indicates data not available in the provided snippets or trial was withdrawn before generating such data.

Efficacy Findings by Therapeutic Area:

• Dermatology:
• Chronic Wounds (DFUs and VLUs): Early to mid-stage clinical trials demonstrated that Granexin® Gel (ACT1) significantly accelerated the healing of chronic DFUs and VLUs compared to standard of care (SOC). For DFUs, a Phase 2 trial reported a 72.1% reduction in mean ulcer area at 12 weeks with ACT1 versus 57.1% for SOC, along with a higher incidence of complete wound closure and a shorter median time to closure.[42] Similar positive outcomes were seen in Phase 2 trials for VLUs, with one study showing 79% ulcer closure with ACT1 plus compression versus 36% with compression alone.[7] These results indicated a strong potential for ACT-1 in these challenging wound types. However, the subsequent Phase 3 trial for DFUs (GAIT 1, NCT02667327) was terminated.[39] The reasons for this termination are not provided in the available information, creating an information gap regarding its future in this specific indication. The termination of a pivotal Phase 3 trial, if not due to overwhelming positive efficacy leading to early stoppage or clear safety concerns, often suggests challenges in meeting predefined endpoints against an optimized standard of care, recruitment difficulties, or strategic or financial decisions by the sponsor. This event is significant given the promising earlier data.
• Scar Management: ACT-1 has shown considerable promise in improving the appearance of surgical scars. A Phase 2 trial involving patients with laparoscopic surgery incisions found that αCT1 gel, applied acutely, resulted in a 47% improvement in scar scores (Vancouver Scar Scale) at 9 months post-surgery compared to control-treated incisions within the same participant.[26] Improvements were also noted in scar pigmentation, thickness, surface roughness, and mechanical suppleness. This effect on scar quality, likely linked to its influence on fibroblast behavior and collagen organization, is a key differentiator. The recently completed Phase 2b/3 trial (NCT04331080) evaluating Granexin® Gel for scar reduction following bilateral anchor incision breast surgery suggests this remains a high-priority area for Xequel Bio.[16]
• Radiation-Induced Skin Injuries (CRI, RD) and Burns: ACT-1 is in development for these indications, with Granexin® Gel reportedly in Phase 2/3 for radiodermatitis and Phase 3 for radiation injuries, and Phase 2 for burns.[2] An Orphan Drug Designation has been granted for CRI.[13] Specific clinical trial results for these indications are not detailed in the provided information. A Phase 2 trial for partial thickness burns (NCT03049910) was withdrawn.[45]
• Ophthalmology (iNexin™ Ophthalmic Solution / aCT1):
• Corneal Injuries and Epithelial Defects: A Phase 1b study of iNexin™ for corneal injury in patients with dry eye disease demonstrated that the ophthalmic solution was safe and well-tolerated, with early efficacy signals including improvements in corneal staining and ocular discomfort observed within two weeks.[15] iNexin™ is in Phase 2 development for Persistent Corneal Epithelial Defects (PCED) and Recurrent Corneal Erosions (RCE).[2] An Orphan Drug Designation is pending or has been granted for PCED.[13]

Safety and Tolerability Profile:

Across numerous clinical trials involving topical or local administration, ACT-1 peptide has demonstrated a favorable safety and tolerability profile.4

• In trials for chronic wounds (DFUs, VLUs) and scar reduction, no drug-related systemic or local adverse events were commonly reported, and adverse event rates were often similar between ACT-1 and control groups.[7]
• The Phase 1b trial of iNexin™ ophthalmic solution reported no serious adverse events or dose-limiting toxicities.[15]
• In a DFU trial, ACT-1 was not found to be immunogenic.[42] The peptide's low molecular weight is also considered to reduce immunogenic risk.[4]

The consistent efficacy signals in promoting healing and improving tissue quality, particularly with local application, alongside a robust safety profile, underscore the therapeutic potential of ACT-1.

8. Therapeutic Indications and Pipeline Status

Xequel Bio is advancing the aCT1 peptide technology platform across several therapeutic areas, primarily focusing on dermatology, ophthalmology, and exploring pulmonology. The pipeline leverages the peptide's unique mechanism of action for conditions where local delivery is feasible and addresses significant unmet medical needs.

Table 2: ACT-1 Peptide Product Pipeline and Regulatory Designations (Xequel Bio)

Product Name	Formulation	Therapeutic Area	Specific Indication	Highest Development Phase (Xequel Bio / AdisInsight )	Orphan Drug Designation (FDA)
Granexin® Gel	Topical Gel	Dermatology	Cutaneous Radiation Injury (CRI)	Phase 2 / Phase 3	Granted (08/03/2017 for "treatment of CRI due to radiation disaster") 13
			Radiation Dermatitis (RD)	Phase 2 / Phase 2/3	Not explicitly mentioned
			Scars (e.g., post-surgical)	Phase 2b/3 (NCT04331080 completed) / Phase 3	Not explicitly mentioned
			Burns	Phase 2 (NCT03049910 Withdrawn)	Not explicitly mentioned
			Diabetic Foot Ulcers (DFU)	Previously Phase 3 (NCT02667327 Terminated - FirstString) / Phase 3	Not explicitly mentioned
			Leg Ulcers (Venous)	Previously Phase 2 (FirstString) / Phase 3	Not explicitly mentioned
iNexin™ Ophthalmic Solution	Ophthalmic Solution	Ophthalmology	Persistent Corneal Epithelial Defects (PCED)	Phase 2 / Phase 2	Pending 13 (Previous ODD for Nexagon for PED 46)
			Recurrent Corneal Erosions (RCE)	Phase 2 / Phase 2	Not explicitly mentioned
			Corneal Injuries (incl. in Dry Eye Disease)	Phase 1b completed / Phase 2	Not explicitly mentioned
			Fuchs' Dystrophy	Preclinical / Preclinical	Not explicitly mentioned
			Diabetic Retinopathy	Preclinical / Preclinical	Not explicitly mentioned
Aerosolized aCT1	Aerosol	Pulmonology	Acute Lung Injury (ALI)	Preclinical / Preclinical	Not explicitly mentioned
			Acute Respiratory Distress Syndrome (ARDS)	Preclinical / Preclinical	Not explicitly mentioned

Note: Discrepancies in phase reflect differing information sources; Xequel Bio's website is generally prioritized for their current pipeline view.

Unmet Medical Needs Addressed:

The ACT-1 peptide platform targets conditions with substantial unmet needs:

• Chronic Wounds (DFUs, VLUs): These are prevalent, difficult to treat, and can lead to severe complications, including amputation. Existing treatments often have limited efficacy.[7]
• Scar Management: Effective treatments to minimize and improve the appearance of surgical and traumatic scars are highly sought after, particularly where aesthetic outcomes are critical.[8]
• Corneal Injuries and Defects: These can cause pain, inflammation, and vision loss, with current treatments sometimes being inadequate for severe or persistent cases.[15]
• Radiation-Induced Skin Injuries: A significant concern for cancer patients undergoing radiotherapy and in scenarios of radiological incidents, with limited specific countermeasures available.[13]

The strategic focus on dermatological and ophthalmological indications is evident, aligning with the peptide's local delivery suitability and its mechanism of action related to tissue barrier integrity and inflammation modulation. The termination of the DFU Phase 3 trial may have led to a re-evaluation of priorities, with scar management and orphan indications like CRI and PCED appearing prominent.

9. Regulatory Affairs and Intellectual Property

Orphan Drug Designations (ODD):

ACT-1 peptide, under its various formulation names, has received Orphan Drug Designation from the U.S. Food and Drug Administration (FDA) for specific indications:

• Granexin® Gel (aCT1 peptide): Granted FDA ODD on August 3, 2017, for the "Treatment of cutaneous radiation injury due to radiation disaster." The sponsor listed is Xequel Bio, Inc..[13] This designation is significant as it positions Granexin gel as a potential medical countermeasure for radiological events, an area with specific governmental interest and potential fast-track or procurement pathways.
• Nexagon® Gel (earlier name/formulation for aCT1): Granted FDA ODD in 2009 for the "treatment of persistent epithelial defects of the eye." The sponsor at the time was CoDa Therapeutics.[46] This designation likely provides a foundation for the current development of iNexin™ for Persistent Corneal Epithelial Defects (PCED).
• iNexin™ Ophthalmic Solution (aCT1): FDA ODD is listed as "Pending" for PCED by Xequel Bio.[13] This could be a new application or related to the prior Nexagon ODD.

No specific Orphan Drug Designations by the European Medicines Agency (EMA) for ACT-1 peptide, Granexin, or iNexin were identified in the provided information.[32]

Investigational New Drug (IND) Status:

The ACT-1 peptide has been administered to over 450 patients under INDs #074836 and #154394, which cover the clinical development programs for its various formulations and indications.4

Regulatory Approval Status:

As of the latest available information, ACT-1 peptide, Granexin® Gel, or iNexin™ Ophthalmic Solution have not received full marketing approval from the FDA or EMA for any indication.14 The FDA ODD for CRI notes it is "Not FDA Approved for Orphan Indication".14

Intellectual Property:

The intellectual property surrounding ACT-1 peptide is a cornerstone of its development.

• U.S. Patent 9,161,984 B2: Titled "FORMULATIONS AND METHODS OF USE FOR ALPHA CONNEXIN C-TERMINAL (ACT) PEPTIDES," this patent is key. Gautam Ghatnekar is listed as the inventor, with FirstString Research, Inc. as the original assignee (now Xequel Bio Inc.). The patent, with a priority date of March 1, 2012, covers topical gel formulations of alpha connexin C-terminal peptides, specifically including the ACT-1 peptide sequence (SEQ ID NO: 9; RQPKIWFPNRRKPWKKRPRPDDLEI). It details formulations stabilized with hydroxyethylcellulose and their use in treating wounds (acute surgical, chronic ulcers like DFUs and VLUs), accelerating healing, and reducing scarring.[17] The claims emphasize the composition of the topical gel, including the peptide linked to a cellular internalization transporter (antennapedia sequence), and methods of its use.
• Numerous other patents related to connexin-derived peptides and their applications have been filed by the inventors and associated entities, indicating a robust patent estate.[17] The New Chemical Entity (NCE) status of ACT-1 [2], combined with ODDs and a strong patent portfolio focusing on formulations and methods of use, provides a framework for potential market exclusivity. The protection of specific topical formulations is particularly critical, given that the peptide's efficacy is highly dependent on stable and effective local delivery.

10. Discussion

ACT-1 peptide has emerged as a novel therapeutic candidate with a unique mechanism of action centered on modulating cellular communication and barrier function through its interaction with Cx43 and ZO-1. This approach distinguishes it from many conventional wound healing and anti-inflammatory agents.

Strengths and Unique Attributes:

The primary strength of ACT-1 lies in its multifactorial effects: it not only reduces inflammation but also actively promotes re-epithelialization, protects cellular barriers, and, significantly, appears to improve the quality of healed tissue by fostering a more regenerative healing process leading to better scar appearance.4 This potential for true tissue regeneration, particularly in scar management, is a notable attribute. The consistent and favorable safety and tolerability profile observed in numerous clinical trials with local and topical administration is another significant advantage, especially for chronic conditions or sensitive application sites like the eye.4 Its formulation versatility (gel, ophthalmic solution, potential for aerosolization) allows it to be adapted for various target tissues.13 Furthermore, ACT-1 addresses clear unmet medical needs in areas like chronic wounds, challenging scars, corneal injuries, and radiation-induced skin damage, underscored by the granting of Orphan Drug Designations.2

Current Challenges and Limitations:

The most significant limitation of ACT-1 is its profound plasma instability and rapid degradation when administered systemically.24 This has effectively restricted its development to local delivery routes, precluding its use for systemic diseases unless advanced (and currently undeveloped for ACT-1) delivery technologies can overcome this hurdle. The termination of the pivotal Phase 3 GAIT 1 trial (NCT02667327) for Diabetic Foot Ulcers is a major setback for one of its lead chronic wound indications.39 While the reasons are not publicly detailed in the provided information, such an event can impact investor confidence and may necessitate a re-evaluation of the strategy for DFU, a large and complex market. If not due to safety concerns (which seems unlikely given the overall safety profile), it might reflect difficulties in demonstrating superiority in a challenging patient population against an evolving standard of care, or other strategic/financial considerations. The drug development timeline has also been extensive, spanning over a decade from initial discovery to the current clinical stages.2

Competitive Landscape (Inferred):

In the chronic wound space (DFUs, VLUs), ACT-1 would compete against standard wound care, various advanced dressings, other biologics (e.g., growth factors), and emerging cell-based therapies. Its unique mechanism promoting regenerative healing could be a key differentiator. For scar reduction, the competitive field includes topical silicone products, intralesional corticosteroids, and laser therapies. An effective peptide that improves collagen organization and final scar quality would be a significant clinical advance. In ophthalmology, iNexin™ would compete with artificial tears, anti-inflammatory eye drops, autologous serum, and surgical options, depending on the specific corneal or retinal condition. Its ability to modulate barrier function and inflammation could offer advantages.

Future Research and Development Directions:

Key future steps include the public dissemination of results from completed late-stage trials, notably NCT04331080 for surgical scars. A clear strategy regarding the DFU and VLU indications, post-GAIT 1 termination, is needed. Further development of the aerosolized aCT1 for pulmonary conditions will depend on robust preclinical validation. Continued research into advanced formulations to enhance local peptide stability and retention, or even to explore niche systemic applications if stability can be markedly improved, would be beneficial. Deeper investigation into the full spectrum of molecular interactions and downstream signaling pathways modulated by ACT-1 could further refine the understanding of its pleiotropic effects and identify new therapeutic opportunities in conditions characterized by junctional protein dysregulation, provided local delivery is feasible. The long-term success will hinge not only on demonstrating definitive clinical efficacy in pivotal trials but also on establishing cost-effectiveness and ease of use compared to existing therapies, especially for chronic conditions.

11. Conclusion

ACT-1 peptide is an innovative investigational therapeutic that targets fundamental mechanisms of cellular communication and tissue response to injury by modulating Connexin43 and ZO-1. Its development has primarily focused on topical and local applications, where it has demonstrated a strong safety profile and promising efficacy in promoting wound healing, reducing inflammation, and notably, improving the quality of tissue repair, including scar appearance, across various dermatological and ophthalmological conditions. Orphan Drug Designations for cutaneous radiation injury and persistent corneal epithelial defects highlight its potential in addressing significant unmet medical needs.

While the peptide's systemic utility is constrained by rapid plasma degradation, its local efficacy, supported by a unique mechanism that fosters a regenerative healing environment, positions it as a potentially valuable addition to the therapeutic armamentarium for a range of challenging conditions. Successful completion and positive outcomes from ongoing and planned late-stage clinical trials, alongside a clear strategic path for its lead indications, will be crucial in realizing the full therapeutic promise of ACT-1 peptide.

12. References

[1]

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