Development

FDA clears Iksuda's CA242-targeted ADC for Phase I study in GI cancers

Edited by Robert McTiernan··3 min read
FDA clears Iksuda's CA242-targeted ADC for Phase I study in GI cancers

UK-based Iksuda Therapeutics has received US FDA clearance of its investigational new drug application for IKS04, a CA242-directed antibody-drug conjugate (ADC) carrying a pyrrolobenzodiazepine (PBD) prodrug payload, enabling Phase I evaluation in patients with gastrointestinal (GI) cancers. The clearance marks the third Iksuda asset to enter clinical development, following IKS014, a HER2-directed ADC, and IKS03, a CD19-directed ADC currently in Phase I for B-cell malignancies.

IKS04 pairs a humanised anti-CA242 antibody with a glucuronide-triggered PBD prodrug, incorporating platform technology from South Korea-based LigaChem Biosciences. Specific enrolment numbers, primary endpoints, and a trial completion date have not been disclosed. The programme will employ what Iksuda terms the "IKS04 Regimen" — co-administration of the ADC with unconjugated anti-CA242 antibody — a dosing strategy the company describes as a first in the ADC field.

Scientific and clinical context

CA242 is a tumour-specific sialylated carbohydrate glycotope highly expressed across multiple gastrointestinal malignancies, with limited expression in normal tissue. The expression profile has been characterised in peer-reviewed literature: a study in British Journal of Cancer reported CA242 sensitivity approximately three times higher than CA50 for colorectal cancer at equivalent specificity, and tissue immunohistochemistry confirmed differential expression between malignant and benign pancreatic lesions.

Despite this target rationale, two prior CA242-directed ADCs — cantuzumab mertansine (huC242-DM1) and cantuzumab ravtansine (IMGN242/huC242-DM4), both developed by ImmunoGen — failed in Phase I due to insufficient antitumour activity. Both used maytansinoid tubulin inhibitor payloads. Their limited clinical activity has generally been attributed to the combination of payload characteristics, tumor biology, and the inherent challenges of treating gastrointestinal malignancies, rather than clear failure of the CA242 target itself. IKS04's PBD prodrug payload operates through a mechanistically distinct route: minor-groove DNA crosslinking at picomolar concentrations, a mechanism that appears less susceptible to some multidrug resistance efflux mechanisms than tubulin inhibitors.

Earlier generations of PBD-based ADCs demonstrated exceptional potency but were often limited by systemic toxicity, driving development of newer prodrug strategies intended to improve the therapeutic window. CA242's glucuronide linker adds a further layer of selectivity. β-Glucuronidase, the enzyme required to cleave the prodrug and release active PBD, is elevated in the tumour microenvironment but absent from systemic circulation. LigaChem's platform employs a two-step activation sequence, requiring both enzymatic cleavage and a subsequent intracellular activation step before fully active PBD is generated.

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The IKS04 Regimen addresses a separate and well-documented limitation of solid tumour ADC therapy: the binding site barrier (BSB). High-affinity antibody binding near tumour vasculature traps ADC molecules before they can diffuse into deeper tumour parenchyma, particularly problematic for high-antigen-expressing targets such as CA242. A Nature Communications study demonstrated that co-administration of unconjugated antibody transiently saturates perivascular antigen-binding sites, enabling deeper ADC penetration. Iksuda's own preclinical data, published in Molecular Cancer Therapeutics, confirmed that co-administration of unconjugated anti-CA242 antibody enhanced ADC efficacy in GI cancer xenograft models.

GI cancers collectively represent one of oncology's most poorly served areas. Pancreatic ductal adenocarcinoma carries a five-year survival rate below 13% for metastatic disease, and no approved immunotherapy exists for unselected patients. Colorectal cancer has no approved ADC despite several attempts. Biliary tract cancer median overall survival remains approximately 12–15 months even with recently approved immunotherapy combinations such as durvalumab plus gemcitabine-cisplatin.

In the broader GI ADC landscape, the most advanced novel program is precemtabart tocentecan (M9140), a CEACAM5-directed ADC developed by Germany-based Merck KGaA, which reported a 31% objective response rate in heavily pre-treated metastatic colorectal cancer patients in Phase I and has since initiated a Phase III trial. TROP2-directed sacituzumab tirumotecan (SKB264/MK-2870), developed by Keystone Bio and MSD (Merck & Co.), is in Phase I/II evaluation across colorectal, pancreatic, and biliary tract cancers. Both programs employ topoisomerase I inhibitor payloads, representing the dominant ADC approach currently being explored in gastrointestinal tumours. IKS04's PBD-based DNA crosslinking mechanism and its novel co-dosing strategy represent a divergent approach, though clinical validation remains pending.

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