Ingenol Disoxate: A Novel 4-Isoxazolecarboxylate Ester of Ingenol with Improved Properties for Treatment of Actinic Keratosis and Other Non-Melanoma Skin Cancers

Ingenol mebutate in cancer therapy: mechanisms, clinical applications and future directions

Ingenol mebutate (IM), a diterpene ester derived from Euphorbia species, has demonstrated promising anticancer properties through direct cytotoxicity and immune modulation. Despite initial clinical success, its therapeutic use has been curtailed due to safety concerns, including potential links to increased skin cancer risk. This review evaluates the mechanisms of action, preclinical and clinical efficacy, safety, and limitations of IM as an anticancer agent, identifying areas for further development. A comprehensive literature review was performed using Google Scholar to identify English-language articles published from 2010 to 2023. Keywords included "Ingenol mebutate," "PEP005," and "cancer therapy." Articles focusing on IM's pharmacological properties, therapeutic mechanisms, clinical studies, and safety profile were included. IM exerts anticancer effects through dual mechanisms: mitochondrial dysfunction leading to necrosis and immune-mediated cytotoxicity via protein kinase C activation. Preclinical studies show efficacy against pancreatic, colorectal, and epithelial cancers and clinical studies have reported success in treating actinic keratosis and nonmelanoma skin cancers. Challenges include intense local skin reactions and safety concerns, particularly its potential association with increased skin malignancy risk. IM represents a promising therapeutic agent due to its rapid and potent anticancer effects. However, optimizing its safety profile and exploring advanced delivery methods are critical to expanding its clinical applications. Further studies are required to establish its long-term efficacy and potential for broader use in oncology.

Construction of a Secondary Enclosure for UVB Irradiation of Mice

UV irradiation is commonly used in murine models of skin cancers. Despite the popularity of using UVB rays to model photocarcinogenesis in animals, there is a lack of standardization in the secondary enclosures used to administer radiation. An appraisal of the literature also shows a general lack of details regarding the materials and procedures utilized in the fabrication of such enclosures. We present in this study a detailed overview of the construction of a UVB exposure chamber that successfully induces lesions in hairless mice. A standardized protocol for producing a UVB enclosure may reduce methodological variation in future studies seeking to investigate photocarcinogenesis in animals.

Mouse models for actinic keratoses

Actinic keratoses (AKs) represent a premalignant skin condition due to chronic sun damage that dramatically increases in prevalence in the aging population. Currently, animal models of AKs utilize photocarcinogenesis, chemical carcinogens, or targeted gene modulation, and each method possesses unique strengths and weaknesses. Models using photodamage most comprehensively describe methods for preferentially selecting AK lesions, while replicating the pathogenesis of AKs with greater fidelity than models utilizing other carcinogenic methods. The following review of current murine models of AKs will aid in the selection of mouse models appropriate for future in vivo studies to test the efficacy of novel therapeutic agents for the treatment of AKs.

Total Synthesis as a Vehicle for Collaboration

"Collaboration" is not the first word most would associate with the field of total synthesis. In fact, the spirit of total synthesis is all-too-often reputed as being more competitive, rather than collaborative, sometimes even within individual laboratories. However, recent studies in total synthesis have inspired a number of collaborative efforts that strategically blend synthetic methodology, biocatalysis, biosynthesis, computational chemistry, and drug discovery with complex molecule synthesis. This Perspective highlights select recent advances in these areas, including collaborative syntheses of chlorolissoclimide, nigelladine A, artemisinin, ingenol, hippolachnin A, communesin A, and citrinalin B. The legendary Woodward-Eschenmoser collaboration that led to the total synthesis of vitamin B₁₂ is also discussed.

Updates on Treatment Approaches for Cutaneous Field Cancerization

Purpose of Review

Field cancerization describes the phenomenon that multiple heterogenous mutations may arise in an area exposed to chronic carcinogenic stimuli. Advances in the understanding of cutaneous field cancerization have led to novel therapeutic approaches to the management of actinic keratoses (AKs). Herein, we review the literature on the pathophysiology and emerging research of field cancerization in dermatology.

Recent Findings

The classification systems for grading AK lesions are being refined with investigations focusing on their clinical utility. There is a growing shift towards field-directed treatment for AKs as the importance of field cancerization becomes clearer. Current field-directed therapies are being optimized and novel therapeutic modalities are being studied.

Summary

Field cancerization underlies the transformation of photodamaged skin into AKs and potentially cutaneous SCC (cSCC). Clinically meaningful classification systems for AKs are needed to better inform decisions regarding treatment. As we learn more about the role of field characterization in photodamage, AKs and cSCCs, therapeutic strategies are becoming more field-directed rather than lesion-directed.

A Computational Investigation of the Uncatalysed and Water-Catalysed Acyl Rearrangements in Ingenol Esters

Ingenol esters have been identified as potent anticancer and HIV latency reversing agents. Ingenol-3-angelate was recently approved as a topical treatment for precancerous actinic keratosis skin lesions. It was found, however, that ingenol esters can undergo a series of acyl rearrangements, which may affect their biological potency and the shelf-life of drug formulations. We use double-hybrid density functional theory to explore the mechanisms for the uncatalysed and water-catalysed acyl migrations in a model ingenol ester. The uncatalysed reaction may proceed either via a concerted mechanism or via a stepwise mechanism that involves a chiral orthoester intermediate. We find that the stepwise pathway is kinetically preferred by a significant amount of ΔΔH‡298 = 44.5 kJ mol−1. The uncatalysed 3-O-acyl to 5-O-acyl and 5-O-acyl to 20-O-acyl stepwise rearrangements involve cyclisation and ring-opening steps, both concomitant with a proton transfer. We find that the ring-opening step is the rate-determining step for both rearrangements, with reaction barrier heights of ΔH‡298 = 251.6 and 177.1 kJ mol−1 respectively. The proton transfers in the cyclisation and ring-opening steps may be catalysed by a water molecule. The water catalyst reduces the reaction barrier heights of these steps by over 90 kJ mol−1.

Chemical Proteomics Identifies SLC25A20 as a Functional Target of the Ingenol Class of Actinic Keratosis Drugs

The diterpenoid ester ingenol mebutate (IngMeb) is the active ingredient in the topical drug Picato, a first-in-class treatment for the precancerous skin condition actinic keratosis. IngMeb is proposed to exert its therapeutic effects through a dual mode of action involving (i) induction of cell death that is associated with mitochondrial dysfunction followed by (ii) stimulation of a local inflammatory response, at least partially driven by protein kinase C (PKC) activation. Although this therapeutic model has been well characterized, the complete set of molecular targets responsible for mediating IngMeb activity remains ill-defined. Here, we have synthesized a photoreactive, clickable analogue of IngMeb and used this probe in quantitative proteomic experiments to map several protein targets of IngMeb in human cancer cell lines and primary human keratinocytes. Prominent among these targets was the mitochondrial carnitine-acylcarnitine translocase SLC25A20, which we show is inhibited in cells by IngMeb and the more stable analogue ingenol disoxate (IngDsx), but not by the canonical PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA). SLC25A20 blockade by IngMeb and IngDsx leads to a buildup of cellular acylcarnitines and blockade of fatty acid oxidation (FAO), pointing to a possible mechanism for IngMeb-mediated perturbations in mitochondrial function.

Pharmacokinetics and Safety of Ingenol Disoxate Gel Administered Under Maximum-Use Conditions to Patients With Actinic Keratosis

BACKGROUND AND OBJECTIVES

Ingenol disoxate (LEO 43204) is a field therapy in development for the treatment of actinic keratosis (AK) on areas between 25 and 250 cm². We evaluated the systemic exposure and safety of ingenol disoxate under maximum-use conditions.

METHODS

This was a phase I, open-label, non-randomized, multicenter trial. Patients ≥ 18 years of age with ≥ 15 clinically typical, visible, discrete AK lesions in a treatment area on the full face or approximately 250 cm² on the arm or scalp were treated once-daily for 3 consecutive days with ingenol disoxate 0.018, 0.1, or 0.037% gel, respectively.

RESULTS

The trial included 58 patients. Median age (range) of patients was 68 years (42-89) [face, N = 18], 66 years (43-88) [arm, N = 21], and 67 years (37-83) [scalp, N = 19]. The highest quantifiable ingenol disoxate level was observed in the arm group (0.33 nM, area under the concentration-time curve from time zero to the last data point [AUC_tlast] 3.12 nM·h). Mean composite local skin response scores peaked at Day 4 and declined towards baseline by Day 15 in all treatment groups. Most adverse events (AEs) were of mild or moderate intensity; the most common treatment-related AEs were application-site pain (face, 88.9%; arm, 57.1%; scalp, 100.0%) and application-site pruritus (face, 50.0%; arm, 52.4%; scalp, 42.1%).

CONCLUSION

Very low systemic exposure to ingenol disoxate was observed when applied to the face, arm, or scalp in patients with AK under maximum-use conditions. No new safety signals were identified.

TRIAL REGISTRATION

NCT02424305.

Three-day Field Treatment with Ingenol Disoxate (LEO 43204) for Actinic Keratosis: A Phase II Trial

OBJECTIVE: The purpose of this study was to evaluate the safety and efficacy of ingenol disoxate gel using a once-daily, three-day field treatment regimen in patients with actinic keratosis. DESIGN: This was a Phase II, multicenter, open-label trial (clinicaltrials.gov: NCT02305888). SETTING: The study was conducted in 20 trial sites in the United States. PARTICIPANTS: Participants included patients with 5 to 20 clinically typical actinic keratosis lesions on the full face/chest (250cm²), scalp (25-250cm²), or the trunk/extremities (250cm²). MEASUREMENTS: We measured incidence of dose-limiting events based on local skin responses. Percentage reduction in actinic keratosis lesion count from baseline, complete clearance, and partial clearance (≥75%) of actinic keratosis lesions were assessed at Week 8. RESULTS: Nine of 63 (14.3%) patients in the face/chest group reported dose-limiting events; zero of 63 patients in the scalp group reported dose-limiting events; and 11 of 62 (17.7%) patients in the trunk/extremities group reported dose-limiting events. Mean composite local skin response scores peaked at Day 4, then rapidly declined, reaching or approaching baseline levels by Week 4. Less than five percent of patients reported severe adverse events; the most common treatment-related adverse events were application site pain and pruritus. The reduction in actinic keratosis lesion count was 78.9, 76.3, and 69.1 percent for the face/chest, scalp, and trunk/extremities groups, respectively. Complete clearance was achieved in 36.5, 39.7, and 22.6 percent of patients in the face/chest, scalp, and trunk/extremities groups, respectively. Partial clearance was achieved in 71.4, 65.1, and 50.0 percent of patients in the face/chest, scalp, and trunk/extremities groups, respectively. CONCLUSION: Ingenol disoxate demonstrated adverse events and local skin reaction profiles similar to results seen in trials evaluating shorter two-day regimens and was effective in patients with actinic keratosis. These data support the use of ingenol disoxate gel for actinic keratosis field treatment.

Three-Day Field Treatment with Ingenol Disoxate (LEO 43204) for Actinic Keratosis: Cosmetic Outcomes and Patient Satisfaction from a Phase II Trial

Objective: To report cosmetic outcomes and patient satisfaction with ingenol disoxate (LEO 43204) used in a once-daily, three-day field treatment regimen in patients with actinic keratosis. Design: This was a phase II, multicenter, open-label trial (ClinicalTrials.gov: NCT02305888) involving 20 trial sites in the United States. Participants: Patients with between five and 20 clinically typical actinic keratoses lesions on the full face/250cm² on the chest, 25cm² to 250cm² on the scalp, or 250cm² on the trunk/extremities were included. Measurements: The assessment methods in this study included the examination of global photo-damage at Week 8; a cosmetic outcome questionnaire to evaluate the overall appearance and feel of the skin following treatment at Week 8; and a treatment satisfaction questionnaire for medication (TSQM) to evaluate patient satisfaction with treatment at Week 8. Results: Treatment adherence was high, with 97 percent of patients overall applying the full three-day regimen. Global photo-damage improvement was seen in 66, 69, and 72 percent of patients in the face/chest, scalp, and trunk/extremities groups, respectively. Improved overall appearance of the treatment area was reported by 95, 97, and 80 percent of patients in the face/chest, scalp, and trunk/extremities groups, respectively. In addition, overall feel of the treatment area was reported as improved by 92, 95, and 70 percent of patients in the face/chest, scalp, and trunk/extremities groups, respectively. Overall, the mean scores for all four treatment satisfaction questionnaires for medication domains were high in each treatment group, ranging from 66.7/100 to 91.3/100. In particular, mean scores for global satisfaction were 73.9/100, 79.7/100, 66.7/100 for the face/chest, scalp, and trunk/extremities groups, respectively. Conclusion: Actinic keratosis field treatment with ingenol disoxate provided favorable cosmetic benefits and high treatment satisfaction.