Avacta Group (AIM:AVCT) said preclinical data show its experimental drug AVA6103 continued to shrink HER2-positive, FAP-positive gastric tumours in mice even after those tumours had progressed on Enhertu, the approved antibody-drug conjugate it is positioned to compete with.
The London-based, AIM-listed life sciences company develops targeted oncology drugs through its pre|CISION platform, which uses a tumour-specific protein, fibroblast activation protein (FAP), to release potent payloads directly in the tumour while limiting exposure to healthy tissue.
Avacta presented the findings alongside the design of its ongoing FOCUS-01 Phase 1 trial at the European Society for Medical Oncology (ESMO) Congress.
In the preclinical work, all animals previously treated with AVA6103 and then re-exposed to the drug after progressing on Enhertu achieved stable disease, while every animal retreated with Enhertu instead progressed further.
Tumour tissue analysis found rising FAP expression and growing recruitment of FAP-positive fibroblasts over the course of AVA6103 treatment, a mechanism the company says helps explain sustained drug delivery over time.
"AVA6103's continued ability to shrink HER2+ gastric tumors after progression on Enhertu® demonstrates the potential of pre|CISION® PDCs to deliver sustained antitumor activity in preclinical models, well beyond the time points achievable with ADCs," said Dave Liebowitz, Avacta's chief medical officer.
He added that the drug appears resistant to antigen loss, a limitation that has constrained Enhertu's efficacy over time in some patients.
AVA6103 is Avacta's first Next-Generation pre|CISION candidate, a FAP-activated version of the chemotherapy exatecan, the same class of payload used in Enhertu.
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The company reported clinical proof of mechanism for AVA6103 last month, when the first three dose levels in 19 FOCUS-01 patients showed a clean safety profile, including no cases of neutropenia, against rates of 22% on comparable Enhertu doses and 64% on equivalent doses of conventional exatecan.
Enrolment has since progressed to a fourth dose level, delivering a payload dose more than double the maximum tolerated dose of conventional exatecan and approaching the payload dose used in Enhertu's approved breast cancer regimen.
Liebowitz said the trial is "progressing well towards tumor PK in late Q4 2026 or early Q1 2027", with first efficacy data expected in the first half of 2027.