Avacta (AIM: AVCT) opens AVA6103 Phase 1: Can sustained-release engineering salvage exatecan’s clinical legacy?

Avacta Therapeutics (AIM: AVCT), the London-headquartered clinical-stage biopharmaceutical company, has opened enrollment for the Phase 1 trial of FAP-Exd (AVA6103), its second pipeline asset and the first sustained-release peptide drug conjugate built on the company’s proprietary pre|CISION tumor-activation platform. Two specialist oncology centers in Virginia and Texas are now accepting patients, with the first enrollment anticipated before the end of March 2026. The development marks a decisive expansion of Avacta’s clinical footprint, moving the platform beyond its lead program, faridoxorubicin (AVA6000), and into a structurally distinct drug class with a substantially larger addressable patient population. AVCT shares were trading near 63p to 68p in early March 2026, within a 52-week range of 26p to 84p, having recovered sharply from their 2025 lows.

What is the pre|CISION platform and why does the FAP-cleavage mechanism matter for cancer drug delivery?

The pre|CISION platform is built around fibroblast activation protein alpha, a protease that is consistently overexpressed in the tumor microenvironment of most solid tumors but is present at negligible levels in healthy tissue. Avacta’s peptide drug conjugates exploit this selectivity: the conjugate circulates in the bloodstream in an inactivated form, and the cytotoxic payload is released only when the linker peptide is cleaved by FAP at the tumor site. The clinical value of this architecture lies in what it avoids. Conventional chemotherapy, and to a significant degree even the newer generation of antibody-drug conjugates, delivers toxic payloads throughout the body, generating systemic side effects that limit the doses patients can tolerate and therefore cap efficacy. Pre|CISION effectively reframes the delivery problem as a selectivity problem, and Avacta’s Phase 1 data from AVA6000 validated the mechanism in humans, with tumor-to-plasma doxorubicin ratios reaching a median of 100:1 at 24 hours post-dose.

AVA6103 extends this logic to exatecan, a topoisomerase I inhibitor significantly more potent than the doxorubicin payload in AVA6000. Exatecan was tested in the clinic two decades ago but its development as a monotherapy was discontinued because of severe and dose-limiting toxicities, including neutropenia that made tolerability unworkable at therapeutically relevant doses. The pre|CISION engineering is therefore not just about incremental refinement; it is an attempt to resurrect a clinical-grade mechanism that previously failed due to a delivery problem rather than a biological one.

How does AVA6103 differ from AVA6000 and what does the sustained-release mechanism add to the clinical thesis?

The most technically significant distinction between AVA6103 and its predecessor is the sustained-release mechanism. AVA6000 delivers doxorubicin to the tumor, but the free drug’s half-life at the tumor site limits the duration of exposure. AVA6103 is engineered to release exatecan progressively within the tumor over an extended window. Preclinical pharmacokinetic modeling demonstrated tumor exatecan concentrations persisting for more than 60 hours following a single dose, despite the free drug having a plasma half-life of approximately nine hours. In murine patient-derived xenograft models, that sustained intratumoral concentration produced durable complete responses, including in tumors that were resistant to topoisomerase I inhibition by other agents.

The therapeutic index improvement is substantial on paper. Preclinical data presented at the 2024 EORTC-NCI-AACR symposium showed that the maximum tolerated dose of AVA6103 in daily dosing regimens was 75 times higher than that of conventional exatecan, with intratumoral concentrations running up to 50-fold higher than systemic plasma levels. Critically, AVA6103 also exhibits a bystander effect: exatecan released from FAP-positive cancer-associated fibroblasts can diffuse into adjacent FAP-negative cancer cells, extending cytotoxic reach beyond the immediate site of FAP cleavage. Whether these preclinical numbers hold in humans is the central question the Phase 1 trial must answer, but the mechanistic rationale for expecting improved tolerability is grounded in validated platform data from AVA6000’s first-in-human experience.

Which tumor types will be studied in the Phase 1a dose escalation and why were these indications selected?

The Phase 1a dose escalation will enrol patients with four advanced solid tumor types: pancreatic cancer, cervical and vulvar cancer, gastric and gastroesophageal junction cancers, and small cell lung cancer. The selection reflects a deliberate combination of unmet need and biological rationale. All four indications are characterized by high FAP expression in the tumor microenvironment, which is the fundamental prerequisite for pre|CISION activation. Pancreatic cancer, in particular, is a notoriously dense, fibroblast-rich tumor stroma environment where FAP activity is among the highest observed across solid tumors, making it a logical entry point.

Avacta’s clinical development team applied an AI-assisted approach to indication selection, querying large oncology datasets to identify cancers with co-expression of FAP and SLFN11, a gene that is a predictive biomarker for sensitivity to topoisomerase I inhibitor therapy. This co-expression signature narrows the patient population to those most likely to respond, which is a meaningful design choice in a dose-escalation study where early efficacy signals inform dose progression decisions. Whether SLFN11 expression becomes a formal patient selection criterion in later stages will depend on what the Phase 1a pharmacokinetic and tumor biopsy data show.

The trial is running two parallel dosing schedules simultaneously: a Q2W arm and a Q3W arm. This parallel design generates comparative pharmacokinetic and safety data across both schedules within the same Phase 1a framework, compressing the timeline to a dose recommendation and informing expansion cohort design without requiring a sequential scheduling study. First safety and pharmacokinetic data from the trial are expected in the second half of 2026.

How does AVA6103 sit within the broader antibody-drug conjugate and peptide drug conjugate competitive landscape?

The competitive landscape for tumor-targeted cytotoxic delivery has shifted considerably in the past three years. Trastuzumab deruxtecan, developed by AstraZeneca and Daiichi Sankyo, has demonstrated the commercial and clinical viability of topoisomerase I inhibitor payloads in an antibody-drug conjugate format, generating multi-billion dollar revenues and regulatory approvals across HER2-expressing cancers. That success has also exposed the limitations of antibody-based targeting: off-target tissue expression of delivery antigens, payload-driven interstitial lung disease, and the practical constraint that the antibody’s target antigen must be expressed on the cancer cell surface rather than in the surrounding stroma.

Avacta’s pre|CISION approach targets FAP in the tumor stroma rather than a surface antigen on cancer cells. FAP is not expressed on cancer cells directly in most solid tumors; it is expressed on the cancer-associated fibroblasts that form the tumor microenvironment. This is a meaningful architectural difference. It means pre|CISION conjugates do not require the cancer cell to express the target protein, which significantly broadens the eligible patient population. It also means the selectivity mechanism is protease activity rather than antibody-antigen binding, which offers a different risk profile for off-target release. The sustained-release mechanism adds a further differentiation from both conventional ADCs and from first-generation PDC designs, provided the human pharmacokinetic data confirm the preclinical profile.

The more direct competitive comparisons are with other FAP-targeting therapeutic platforms in oncology development. Several programs globally are exploring FAP as an oncological target, including FAP-targeted radionuclide therapies and bispecific T-cell engagers in early development. Avacta’s pre|CISION platform sits in the payload-delivery category rather than the immune-activation category, meaning it is competing on a different axis. The company’s structural moat, to the extent one exists at this stage, lies in the validated clinical pharmacology from AVA6000 demonstrating that FAP cleavage actually occurs in human tumors at the rates the preclinical models predict.

What are the execution risks in the Phase 1 trial and what would early readouts need to show to validate the AVA6103 thesis?

Phase 1 oncology trials are primarily designed to establish safety and determine the recommended Phase 2 dose, not to prove efficacy. For AVA6103, the critical unknowns are whether the sustained-release pharmacokinetic profile observed in mice translates into humans, whether systemic exatecan exposure remains suppressed at dose levels that achieve meaningful tumor concentrations, and whether the tolerability advantage over conventional exatecan materializes in a diverse patient population with different metabolic and performance status profiles than controlled preclinical models.

The dual Q2W and Q3W schedule design introduces a layer of operational complexity that, while scientifically valuable, requires careful site-level management to ensure dosing discipline and consistent pharmacokinetic sampling. Avacta has opened its first two sites at Virginia Cancer Specialists Research Institute in Fairfax, Virginia, and NEXT Oncology Specialists in Dallas, Texas. Both are experienced specialty oncology trial centers with established patient pipelines in the tumor types under study, which partially mitigates enrollment risk. However, the four-indication scope of the dose escalation means patient identification requires active screening across a range of disease types, and enrollment rates across early-phase oncology studies in these indications vary considerably.

The pharmacokinetic data expected in the second half of 2026 will be the first clinical test of whether Avacta’s sustained-release engineering delivers the tumor exposure profiles the preclinical modeling predicted. The AVA6000 Phase 1 trial established a high bar for the platform: 63 patients dosed, tumor-to-plasma ratios confirmed at 100:1 at 24 hours, and no maximum tolerated dose identified even at doses substantially above conventional doxorubicin equivalents. If AVA6103’s Phase 1a data show a comparable or superior plasma clearance profile alongside sustained intratumoral exatecan concentrations, the clinical case for advancing to Phase 1b expansion cohorts and eventually Phase 2 becomes substantially more compelling.

What does the AVCT share price trajectory suggest about market positioning ahead of the Phase 1 data readout?

Avacta Therapeutics shares were trading in the 63p to 68p range in early March 2026, having recovered meaningfully from a 52-week low of 26p touched in the prior year. The 52-week high stands at 84p, and analyst consensus price targets cluster around 80p to 83p, implying modest upside from current levels if clinical milestones proceed on schedule. The recovery from the 52-week low reflects a re-rating of the pipeline following FDA clearance of the AVA6103 IND application in January 2026 and the broader recognition of the platform’s dual-asset clinical status. The market capitalisation at current prices is approximately £280m to £300m, a valuation that for a clinical-stage oncology business with two assets in human testing and a proprietary platform with preclinical validation across multiple tumor types is not obviously stretched.

The key value inflection point is the second half of 2026 Phase 1a pharmacokinetic data release. Clinical-stage oncology companies at Avacta’s development stage typically show significant share price movement around early Phase 1 data, either in response to safety signals that compress the dose escalation window or, conversely, evidence of tumor-selective pharmacology that validates the dose-finding hypothesis. The asymmetry of potential outcomes is characteristic of early clinical oncology investment. At current trading levels, the market appears to be pricing in continued progression without assuming either a rapid efficacy signal or a safety setback.

Key takeaways: what the AVA6103 Phase 1 opening means for Avacta, its competitors, and the tumor-targeted drug delivery sector

• Avacta Therapeutics has formally opened clinical recruitment for AVA6103, its second pre|CISION peptide drug conjugate, at two US specialty oncology centers, with first patient enrollment targeted before end of March 2026.
• AVA6103 delivers exatecan, a potent topoisomerase I inhibitor previously discontinued as a monotherapy due to severe systemic toxicity, via tumor-selective FAP cleavage with a proprietary sustained-release mechanism.
• Preclinical data indicated a 75-fold increase in therapeutic index versus conventional exatecan and sustained intratumoral drug concentrations exceeding 60 hours from a single dose, metrics that have no human validation yet but set a high benchmark for clinical translation.
• The Phase 1a design covers four tumor indications with high FAP expression: pancreatic cancer, cervical and vulvar cancer, gastric and gastroesophageal junction cancers, and small cell lung cancer. Two parallel dosing schedules (Q2W and Q3W) run simultaneously.
• Indication selection was informed by AI-assisted co-expression analysis of FAP and SLFN11, a predictive biomarker for topoisomerase I sensitivity, giving the program a more defined patient enrichment hypothesis than broad pan-tumor trials.
• The validated clinical pharmacology from AVA6000 provides a meaningful advantage: the pre|CISION FAP cleavage mechanism has been confirmed in human tumors at 100:1 tumor-to-plasma ratios, reducing the platform-level proof-of-concept risk for AVA6103.
• Relative to the antibody-drug conjugate field, Avacta’s FAP-stromal targeting strategy reaches a broader patient population than antigen-surface approaches and offers a different toxicity mechanism compared to established ADC payloads like trastuzumab deruxtecan.
• Preliminary safety and pharmacokinetic data are expected in the second half of 2026, representing the primary value catalyst for AVCT shares from current trading levels around 63p to 68p.
• Execution risks include translation of the sustained-release pharmacokinetic profile from preclinical to human settings, enrollment complexity across four distinct tumor types, and the operational demands of running dual-schedule parallel arms simultaneously.
• The opening of AVA6103 confirms Avacta as a genuine multi-asset clinical platform rather than a single-program speculative play, which materially changes the risk profile for institutional investors evaluating the company’s 2026 and 2027 milestones.