Botulinum toxin Type A has been widely used to improve the appearance of glabellar lines since its first approval in Canada in 2001 and the United States in 2002. Three injectable formulations are now approved in the United States and Canada for this indication—onabotulinumtoxinA, abobotulinumtoxinA, and incobotulinumtoxinA. Injectable daxibotulinumtoxinA is in clinical development.
Injectable daxibotulinumtoxinA is composed of a purified 150 kDa botulinum toxin Type A (RTT150) formulated without additives in a lyophilized powder containing a proprietary peptide (RTP004).1 The peptide is a single straight-chain peptide consisting of a backbone and 2 protein transduction domains. The backbone is a sequence of consecutive lysines, which carry a positive charge and form an electrostatic bond with daxibotulinumtoxinA. This results in the peptide binding to the neurotoxin with high avidity. The botulinum toxin is produced without using any animal or human blood derivatives and contains no inactive proteins.
Injectable daxibotulinumtoxinA has been observed to prolong the duration of response in both the preclinical and clinical settings. Results from animal studies have confirmed that injectable daxibotulinumtoxinA exhibits less diffusion than onabotulinumtoxinA2 and suggest that it may offer a relatively greater degree and duration of response at target sites.2 In a dose-escalation study, 98% of subjects treated with injectable daxibotulinumtoxinA attained a reduction in glabellar line severity at maximum frown at Week 4.3 The median duration of response was evaluated in the group who had received the highest dose (64U using the current potency method or 100U with the method in use at the time) and found to be 29.4 weeks.3 Injectable daxibotulinumtoxinA was generally well tolerated and there was no evidence of spread beyond the treatment area.
A Phase 2 study has now been performed to further evaluate the efficacy, duration of response, and safety and tolerability of injectable daxibotulinumtoxinA in comparison with placebo and with onabotulinumtoxinA.
The study was a randomized, dose-ranging, parallel-group, double-blind, multicenter evaluation of injectable daxibotulinumtoxinA (20U, 40U, or 60U) compared with onabotulinumtoxinA 20U and placebo. The protocol was approved by the relevant institutional review boards and conformed to the ethical guidelines of the Declaration of Helsinki. All subjects provided written informed consent.
Subjects eligible to enroll in the study were required to have moderate or severe glabellar lines during maximum frown according to both the Investigator Global Assessment—Facial Wrinkle Severity (IGA-FWS) scale and the Patient Facial Wrinkle Severity (PFWS) scale. The subjects were also required to be 30 to 65 years of age and to be willing to refrain from treatment with facial fillers, lasers, and products that could affect skin remodeling or cause an active dermal response in the treatment area. They were not allowed to have a history of a topical steroid on the treatment area, or any immunosuppressants, in the previous 30 days; a prescription retinoid in the treatment area during the previous 3 months; botulinum toxin Type A in the face in the previous 6 months; or chemical peels of at least medium depth during the previous 9 months. They were also not allowed to have undergone any procedure that may affect the glabellar region during the previous 12 months.
Subjects were randomly assigned in an equal ratio to 5 groups: 20U, 40U, or 60U injectable daxibotulinumtoxinA (RT002; Revance Therapeutics, Inc., Newark, CA), 20U onabotulinumtoxinA (BOTOX Cosmetic, Allergan, Inc., Irvine, CA), or placebo. All treatments consisted of five 0.1 mL injections, 2 in each corrugator muscle and one in the procerus muscle.
An independent statistician provided a randomization scheme of treatment assignments for each study site and subjects eligible for randomization were given the next available subject number. The assigned product was reconstituted by an unblinded preparer and the masked product was provided to the investigator in a syringe. The subjects, investigators, and other site staff remained blinded to the treatment assignments.
The onabotulinumtoxinA 20U dose was prepared from a 100U vial and reconstituted with 2.5 mL of preservative free saline as per label, so that 0.5 mL of product was present in the prepared syringe for injection enabling a dose of 4U per 0.1 mL to be administered per injection site. A serial dilution technique using preservative free saline was used to prepare the RT002 study treatments from a 160U stock vial of lyophilized RT002, to arrive at 20U, 40U, or 60U per 0.5 mL in the prepared syringe for injection.
In an effort to standardize the rating of wrinkle severity across investigators, a set of training photographs exhibiting the grades of wrinkle severity was used to train investigators how to assess the force of muscular contraction using the IGA-FWS scale that classifies wrinkle severity to be none (0), mild (1), moderate (2), or severe (3). A photograph guide was provided showing examples of none (no wrinkles), mild (very shallow wrinkles), moderate (moderate wrinkles), and severe (deep and furrowed wrinkles). Subjects were evaluated for IGA-FWS score at least every 4 weeks and if the score at maximum frown had not yet returned to baseline at Week 24, evaluations were continued every 4 weeks until this had occurred (up to Week 36). One of the primary outcome measures was the proportion of responders at Week 24 (a responder being a subject with at least a 1-point improvement from baseline in glabellar severity at maximum frown according to the IGA-FWS scale). The median duration of response (time since injection for at least a 1-point improvement in IGA-FWS score to revert to baseline levels) was another primary outcome measure.
Glabellar line severity was also evaluated by the subjects at maximum frown using the PFWS. The PFWS is similar to the IGA-FWS scale, with the following descriptions for clarification: none = no wrinkles; mild = very shallow wrinkles; moderate = moderate wrinkles; and severe = deep wrinkles.
Investigators and subjects evaluated the global improvement in aesthetics at each postbaseline visit using the Global Aesthetic Improvement Scale (GAIS) (Table 1).
A sample size of 50 in each group was planned to be sufficient to detect statistical trending for the difference between each active treatment group and placebo in duration of response through 36 weeks of follow-up. The study was not powered to detect statistically significant differences between active treatment groups. All statistical analyses were performed using Statistical Analysis System (SAS) software, version 9.3 or higher, with all comparisons assessed at an alpha level of 0.05 without adjusting for multiplicity.
Between-group differences in the proportion of subjects showing improvements from baseline or attaining glabellar line severity of none or mild were evaluated using the Cochran–Mantel–Haenszel test. The median duration of response and 95% confidence intervals were calculated using the Kaplan–Meier method. The mean duration of response was estimated using the area under the Kaplan–Meier curve. If no response was attained by Week 4, the duration of response was considered zero. Between-group differences in the duration of response were evaluated using the log-rank test.
A total of 268 subjects were enrolled in 9 private practice settings (experienced university-affiliated clinical trial centers) in Canada and included in the safety analyses. The first treatment was on December 23, 2014 and the last visit was on December 1, 2015.
Overall, 98% of subjects completed the study (3 discontinued from the placebo group and 2 from the 20U daxibotulinumtoxinA group due to subject withdrawals or loss to follow-up). Per protocol analyses required the exclusion of 77 subjects, most of these (57/77) being attributable to the Week 24 visit being more than 5 days off schedule (Table 2).
Across the treatment groups, most subjects were Caucasian (89%–95%) and women (76%–92%), and their mean age ranged from 47 to 50 years. Baseline characteristics were generally similar in each group, although it should be noted that the 60U daxibotulinumtoxinA group had a relatively greater proportion of men and glabellar lines that investigators rated as severe (Table 3).
All botulinum toxin groups were highly effective—at Week 4, the proportion of subjects with at least a 1-point improvement in the IGA-FWS score at maximum frown was 100%, 100%, and 100% with daxibotulinumtoxinA (20U, 40U, and 60U, respectively), 95% with onabotulinumtoxinA, and 3% with placebo (p < .001 for all botulinum toxin groups vs placebo) (Figure 1 and Table 4). At Week 24, the corresponding percentages were 18%, 36%, and 29% with daxibotulinumtoxinA (20U, 40U, and 60U, respectively), 19% with onabotulinumtoxinA, and 3% with placebo (p < .05 for all botulinum toxin groups vs placebo).
For both investigator and subject ratings of wrinkle severity, greater efficacy was achieved with 60U, and especially 40U, daxibotulinumtoxinA than with 20U onabotulinumtoxinA—with statistical superiority achieved at several time points (Figures 1 and 2; p < .05). Thus, for investigator ratings, 40U daxibotulinumtoxinA showed statistically significantly greater efficacy than 20U onabotulinumtoxinA at Weeks 8, 16, and 20 (Figure 1). And for subject ratings, 40U daxibotulinumtoxinA showed statistically significantly greater efficacy than 20U onabotulinumtoxinA at Weeks 12 and 16 (Figure 2). The 20U daxibotulinumtoxinA group showed a smaller trend toward greater efficacy relative to 20U onabotulinumtoxinA.
Similar results were obtained with the other efficacy measures (Figures 3–5). The proportion of subjects with at least a 2-point improvement in IGA-FWS score was higher with all doses of daxibotulinumtoxinA than with onabotulinumtoxinA at all visits from Weeks 2 to 24 except for the 20U dose group at Weeks 4 and 8 (Figure 3 and Table 4). The 40U dose of daxibotulinumtoxinA achieved the most sustained efficacy and the proportion of subjects in this group achieving at least a 2-point improvement in IGA-FWS score was significantly higher than with 20U onabotulinumtoxinA at Weeks 8, 12, 16, and 20 (p < .05). The proportion of subjects with glabellar lines of none or mild severity on the IGA-FWS scale was greater with all doses of daxibotulinumtoxinA than with 20U onabotulinumtoxinA at almost all visits from Weeks 2 to 24 (excepting only the 20U daxibotulinumtoxinA group at Week 24, where it was equivalent)—and for the 40U daxibotulinumtoxinA group, the proportion was significantly higher at Weeks 8, 16, 20, and 24 (p < .05) (Figure 4 and Table 4).
Duration of Response
The median duration of response (i.e., duration of at least a 1-point improvement from baseline in IGA-FWS score at maximum frown) was longer with daxibotulinumtoxinA (20.0, 23.6, and 20.9 weeks for 20U, 40U, and 60U doses, respectively) than with 20U onabotulinumtoxinA (18.8 weeks) or placebo (0.0 weeks) (p < .001 for all botulinum toxin groups vs placebo and p = .030 for daxibotulinumtoxinA 40U vs onabotulinumtoxinA) (Table 5 and Figure 6). Photographic documentation of examples of durable responses is shown in Figures 7 and 8.
Safety and Tolerability
DaxibotulinumtoxinA was generally well tolerated at all 3 doses evaluated. Adverse events were predominantly localized, transient, and mild, and there were no serious adverse events. The only severe adverse event that was at least possibly related to treatment was a migraine in 1 subject in the 20U daxibotulinumtoxinA dose group.
Adverse events considered at least possibly related to treatment and occurring in more than 1 subject in any group are shown in Table 6. The incidence of headache and injection site erythema was lower in all daxibotulinumtoxinA dose groups than in the onabotulinumtoxinA group. Eyelid ptosis occurred in 5 subjects (notably, none of these were men) and only with onabotulinumtoxinA and the highest dose of daxibotulinumtoxinA (60U). These cases of eyelid ptosis were mild in severity with onabotulinumtoxinA (1) and mild (1) or moderate (3) with daxibotulinumtoxinA, and lasted 51 days with onabotulinumtoxinA and an average of 47 days with daxibotulinumtoxinA. Facial asymmetry occurred in 4 subjects who were treated with daxibotulinumtoxinA. This was also transient, with all cases resolved within 2 to 11 days. Three of the cases were considered to be mild and the fourth did not have severity reported.
A sizeable number of subjects were excluded from the per protocol analyses because of their Week 24 visits being at least 5 days off schedule. Even though this occurred with a similar frequency in all cohorts, the per protocol population was used for all efficacy analyses because accurately comparing the duration of response between groups was an important goal of the study.
All botulinum toxin groups showed considerably greater efficacy than placebo, and 40U daxibotulinumtoxinA offered greater efficacy than 20U daxibotulinumtoxinA. The 60U dose did not generally enhance efficacy further, which could be attributable to a “ceiling effect” or the relatively greater proportion of severe glabellar lines and men in this group at baseline (it is known that men require a higher dose of botulinum toxin Type A than women to achieve a similar effect4,5).
Statistical and clinical superiority were observed for 40U daxibotulinumtoxinA over 20U onabotulinumtoxinA for a range of efficacy outcomes (improvements in IGA-FWS, PFWS, and GAIS scores; proportion of subjects achieving glabellar lines of none or mild severity; and duration of response) even though the study was not powered to detect statistically significant differences between active treatment groups. For example, the proportion of subjects with glabellar line severity rated by investigators as none or mild with 40U daxibotulinumtoxinA was more than double—and significantly greater than—that with 20U onabotulinumtoxinA at Weeks 16, 20, and 24 (67% vs 32% at Week 16 [p = .002] and 31% vs 12% at Week 24 [p = .041]). The last time point at which onabotulinumtoxinA was able to match the 31% responder rate achieved with daxibotulinumtoxinA at Week 24 was Week 16—that is 8 weeks earlier than with daxibotulinumtoxinA.
Data evaluating the duration of ≥1-point improvements in IGA-FWS score also show a significantly longer duration of response with 40U daxibotulinumtoxinA than with 20U onabotulinumtoxinA (median of 23.6 vs 18.8 weeks, p = .030). Perhaps somewhat surprisingly, the duration of response was also greater with 40U daxibotulinumtoxinA than 60U daxibotulinumtoxinA. A previous small open-label study3 reported an even longer median duration with a higher dose of daxibotulinumtoxinA (29 weeks with a corresponding dose of 64U calculated using a saline potency method).
In addition to its prolonged duration of efficacy, the data showing at least a 2-point improvement in IGA-FWS scores suggest that daxibotulinumtoxinA can also achieve greater initial efficacy—because, at Week 4, the proportion of subjects achieving such improvement was 76% with 20U onabotulinumtoxinA, 85% with 40U daxibotulinumtoxinA, and 95% with 60U daxibotulinumtoxinA.
Although the key findings summarized above focus on the 40U dose of daxibotulinumtoxinA (because this is the dose generally associated with the greatest clinical benefit), the 20U dose of daxibotulinumtoxinA also showed apparent clinical superiority over 20U onabotulinumtoxinA. This was most notable when comparing the proportion of subjects achieving at least a 1-point improvement in the investigator rating of glabellar line severity (Figure 1) and when comparing the proportion of subjects whose glabellar lines were rated as none or mild severity (Figure 4). The difference was even statistically significant at Week 16 for the proportion of subjects whose glabellar lines were rated as none or mild severity (despite the study not being powered to detect such differences). These results show that the overall superiority of the 40U dose of daxibotulinumtoxinA is not just an effect of the higher dose as there are also differences when the same number of units of each botulinum toxin are compared.
There was no apparent dose relationship in the incidence of adverse events with daxibotulinumtoxinA, with the probable exception of eyelid ptosis. The absence of eyelid ptosis with the 20U and 40U doses of daxibotulinumtoxinA is encouraging, and it is also reassuring that the cases with 60U of daxibotulinumtoxinA had a similar duration on average to the case with onabotulinumtoxinA, particularly in the context of a longer lasting treatment for glabellar lines. Overall, the efficacy and tolerability data suggest that 40U is the optimal dose to pursue in Phase 3 studies. Nevertheless, as no eyelid ptosis was observed in men, it is tempting to speculate that the 60U dose might also be appropriate for men.
The results of this study refer to the Revance injectable formulation of botulinum toxin Type A and cannot be generalized to any other formulations or serotypes of botulinum toxin Type A. The potency units of botulinum toxins are not interchangeable. As a result, units of daxibotulinumtoxinA should not be equated with the same number of units of onabotulinumtoxinA as the relative potencies of daxibotulinumtoxinA and onabotulinumtoxinA have not been established.
The 40U dose of daxibotulinumtoxinA has the most favorable risk:benefit profile and will be evaluated in Phase 3 studies. Compared with 20U onabotulinumtoxinA, it offers significantly greater efficacy and a significantly longer duration of response (median of 24 weeks vs 19 weeks; p = .030), and was well tolerated (unlike 20U onabotulinumtoxinA, no ptosis was observed with 40U daxibotulinumtoxinA). A more prolonged duration of response is a key unmet need in botulinum toxin therapy and reducing the frequency of injections would be a significant advantage that would likely enhance patient satisfaction.
Injectable daxibotulinumtoxinA could represent the first of a new generation of botulinum toxin treatments, offering an enhanced duration of response without compromising safety or tolerability. As a result, Phase 3 data are eagerly awaited. Although onabotulinumtoxinA—the gold standard neuromodulator—has been fully justified in developing an enviable reputation globally, daxibotulinumtoxinA deserves very careful study, as it is currently the only new neuromodulator to challenge both the quality and duration of response of onabotulinumtoxinA.