Background: There is a significant, unmet medical need for effective treatments that reduce scarring, with patients indicating that they value any improvement in scarring. Transforming growth factor beta 1 (TGFb₁) has been shown in numerous studies to play a key role in promoting scarring and fibrosis, and we have previously reported that TGFb₃ demonstrates an isoform specific difference from TGFb₁ and reduces scarring in pre-clinical models. We present here the translation of these pre-clinical data to the clinic with the results of a phase II randomized, placebo-controlled human clinical trial investigating the optimal concentration of a single intradermal application of avotermin (TGFb₃) for the improvement of scarring, when administered to incisional wounds with approximated margins. We also report data from preclinical studies which elucidate the molecular, cellular and tissue mechanisms of action of avotermin that underlie its effects.
Methods: In the clinical study (RN1001-0050), healthy volunteers received a total of eight standardized, 1cm, full-thickness incisions, four on the inner aspect of each arm. After wound closure, both margins of each site received an intradermal injection of study treatment, with sites randomized to one of four doses of avotermin (5, 50, 200 or 500ng/100µL/linear cm wound margin) or placebo.  The study was powered to show treatment differences (avotermin vs placebo) in the total scar score (ToScar), a summary measure of how closely scars resemble normal skin over time. ToScar was calculated by summing scores assigned to standardized photographs of scars at Week 6 and Months 3, 4, 5, 6 and 7 post-surgery by an Independent External Scar Assessment Panel (IESAP, Lay Panel) using a 100mm visual analogue scale (VAS). Assessments were also conducted by investigators and an IESAP (Clinical Panel; a facial plastic surgeon, five aesthetic dermatologists). All assessors were blinded to treatment. In pre-clinical studies a range of relevant in vitro and in vivo models were utilized to evaluate the isoform specific effects and mechanism of action of avotermin at the intracellular signalling, gene expression, cellular function and tissue level, including in vivo temporal and spatial analysis of key molecular and cellular processes in a rat full thickness cutaneous incisional wound model following avotermin treatment.    
Results: The clinical trial included 39 subjects (97% Caucasians, 64% males, median age 34 years), who received 312 incisions overall. The primary objective was met with avotermin achieving statistically significant improvements in ToScar versus placebo, with the 200ng/100µL/linear cm dose achieving the greatest magnitude of scar improvement (p<0.0001). VAS scores from the IESAP (Lay Panel) and IESAP (Clinical Panel) also showed that avotermin achieved statistically significant improvements in scars at Month 7 (p<0.02 versus placebo). All avotermin doses showed a favorable safety profile and there was no evidence of systemic absorption. Mechanism of action studies demonstrated that avotermin (TGFb₃) elicits isoform specific effects on: signal transduction; regulation of extracellular matrix/remodelling genes; attenuated inflammation; increased cell migration and an earlier resolution of wound myofibroblasts resulting in the regeneration of a collagen architecture within the scar that is more similar to normal surrounding skin.
Conclusions: In this phase II clinical trial intradermal administration of avotermin at the time of surgery resulted in statistically significant improvements in scar appearance compared with placebo, with the data demonstrating that the optimal dose of avotermin was 200ng/100µL/linear cm of wound margin. The molecular and cellular mechanism of action of avotermin identified to date provides a clear scientific rationale to underpin its scar reduction effect. These clinical data demonstrate avotermin, a new class of prophylactic medicine, improved scar appearance and indicates the potential of avotermin to add to good surgical technique for the improvement of scar appearance.