Sebetralstat: A Rapidly Acting Oral Plasma Kallikrein Inhibitor for the On-Demand Treatment of Hereditary Angioedema

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This Review article is of great interest as it discussess the pathogenetic mechanisms which occur during angioedema attacks in patients with Hereditary angioedema disease (HAE). This is a rare genetic disease characterized by almost always impredictable angioedema attacks which can occur in the face, extremities, abdomen, genitalia, oropharyngeal tissues and larynx. The latter localization of angioedema can be life-threatening.

In this Review the Authors discuss about the pathogenesis of HAE and available treatments, highlighting the pathogenetic role of plasma kallikrein (Pka).

After discussing the pros and cons of already available treatments they present the innovative oral on demand treatment of HAE attacks with Pka inhibitor, Sebetralstas.

The description  of this new treatment for HAE attacks  is very clear and rich of details reporting Phase 1 Trials results.

The role of Sebetralstas inhibiting both Pka-mediated cleavage of the kallicrein kinin system and activation of Factor XII is reported.

Poinit to point review:

Please check caption of Figure 8 as "the" is reported twice.

The present review  underlines the unmet needs in the treatment of patients with HAE and presents the new treatment updates. 

 

Author Response

Reply: The authors thank reviewer 1 for the thoughtful review of this manuscript and their positive feedback.

Point to point review:

Please check caption of Figure 8 as "the" is reported twice.

Reply: This has been corrected

Reviewer 2 Report

Comments and Suggestions for Authors

- Section 2.2 (Selectivity and Safety Profiling) is a bit confusing due to the repeated use of “selectivity against. For example, in the sentence “Of note, sebetralstat has high selectivity against tissue kallikrein and thus would not be expected to interfere with the generation of Lys-bradykinin… (lines 201-202). Multiples examples can be found in the literature that use “selectivity against X” to express either that “significant binding of the molecule occurs exclusively with X” or that “the molecule does not bind X significantly”. However, it is my impression that the former use is by far more common and better understood specially by non-native English speakers. The same comment applies for lines 208-210 and line 215. I recommend the authors to consider rephrasing these sentences for impoved clarity.       

- In the In Vitro Pharmacology section (lines 264-267), the authors point to technical differences in the measurements of PKa inhibition and HK protection (enzyme kinetics vs. endpoint protection assays) to explain the large disagreement in the obtained IC50 values. In any case, I consider that a ~4-fold discrepancy requires further comments, specially for those not knowledgeable about these biochemical assays. Which one of the values offered (47.5-54.4nM for PKa inhibition vs 200nM for HK protection) better represents the in vivo effects of Sebetralstat?  

- Figure 5. Effects of sebetralstat on PKa activity and HK cleavage in healthy volunteers. In figure 5B the proportion of native and cleaved HK after sebetralstat administration are shown and according to reference #44, in these experiments the relative concentration of HK (%) after DXS stimulation was compared to the amount of HK observed in the absence of DXS stimulation in reference control plasma. In my view, this comparison probably overstimates HKc%. Why was not done to DXS-stimulated control plasmas instead?

- Figure 7 presents results from a study by Aygören-Pürsün et al. The footnote is too concise and some parts of the figure are not explained (for example, It goes without saying that “Number at Risk” seems to refer to Number of patients, but it is not specified). Moreover, what criteria are used to designate a patient as being “at risk”? Please expand the footnote properly.

Comments on the Quality of English Language

No further comments

Author Response

- Section 2.2 (Selectivity and Safety Profiling) is a bit confusing due

to the repeated use of “selectivity against. For example, in the

sentence “Of note, sebetralstat has high selectivity against

tissue kallikrein and thus would not be expected to interfere

with the generation of Lys-bradykinin… (lines 201-202).

Multiples examples can be found in the literature that use

“selectivity against X” to express either that “significant binding of

the molecule occurs exclusively with X” or that “the molecule does

not bind X significantly”. However, it is my impression that the

former use is by far more common and better understood specially

by non-native English speakers. The same comment applies for

lines 208-210 and line 215. I recommend the authors to consider

rephrasing these sentences for improved clarity.

Reply: The selectivity information in this review article is based on the publication by Davie et al (ref # 46) on sebetralstat and the terminology used to express selectivity are based on this report.  While we agree multiple methods can be used to establish selectivity, the evaluation of sebetralstat selectivity was based on functional assessments of catalytic activity and are quantified as IC₅₀s (table 2 from reference 46). This report did not provide binding data to describe selectivity.

 

- In the In Vitro Pharmacology section (lines 264-267), the authors

point to technical differences in the measurements of PKa inhibition

and HK protection (enzyme kinetics vs. endpoint protection assays)

to explain the large disagreement in the obtained IC50 values. In

any case, I consider that a ~4-fold discrepancy requires further

comments, specially for those not knowledgeable about these

biochemical assays. Which one of the values offered (47.5-54.4nM

for PKa inhibition vs 200nM for HK protection) better represents the

in vivo effects of Sebetralstat?

Reply: Since both assays are performed in whole plasma in the presence of DXS, a strong activator of the KKS, we believe that both assays reflect the effects of sebetralstat in vivo. The IC₅₀ values of 54.4nM and 47.5nM for sebetralstat in healthy and HAE plasma, respectively, are not significantly different. In part 1 of the phase 2 trial, PKa inhibition >90% occurred from 30min post dose to 4 hrs (the last time point studied). Near complete HK protection also occurred during this period. The PK analysis showed that sebetralstat concentrations were greater than ~2000 ng/ml (~982 nM) during this time interval (Fig 6A). This period of high exposure and near complete inhibition corresponded to a period of rapid improvement in PGI-C shown in figure 7. While IC₅₀ data are useful in evaluating compounds, we believe that near complete inhibition of PKa activity mediated the in vivo clinical response of sebetralstat for the on-demand treatment of HAE attacks in the phase 2 trial.

 

- Figure 5. Effects of sebetralstat on PKa activity and HK cleavage

in healthy volunteers. In figure 5B the proportion of native and

cleaved HK after sebetralstat administration are shown and

according to reference #44, in these experiments the relative

concentration of HK (%) after DXS stimulation was compared to the

amount of HK observed in the absence of DXS stimulation in

reference control plasma. In my view, this comparison probably

overstimates HKc%. Why was not done to DXS-stimulated control

plasmas instead?

Reply: The authors agree that there are multiple ways to analyze HK cleavage and the levels of cHK. We have found that cHK is rapidly degraded in the presence of DXS. This is likely due to its further proteolysis that occurs concurrently with its generation. Thus, the level of cHK in DXS-stimulated control plasma is influenced by both its generation and its rate of degradation, which reduces its levels and ultimately the immunoreactivity of the cHK fragments. The mechanism of action of sebetralstat is the protection of HK from cleavage, which is why reference #44 measured the loss of HK immunoreactivity.

 

- Figure 7 presents results from a study by Aygören-Pürsün et al.

The footnote is too concise and some parts of the figure are not

explained (for example, It goes without saying that “Number at

Risk” seems to refer to Number of patients, but it is not specified).

Moreover, what criteria are used to designate a patient as being “at

risk”? Please expand the footnote properly.

Reply: The figure 7 legend has been expanded as suggested. “Number at Risk: The count of individuals who have not yet experienced the event and have not been censored.”

 

Reviewer 3 Report

Comments and Suggestions for Authors

I congtatulate with the Authors for providing a clear, comprehensive, well written review on a new therapeutic development for a rare clinical condition which, however, emergency physicians not unfrequently encounter and manage.

Although the paper is evidently focused on sebetralstrat for the on-demand treatment of HAE, a more detailed description of the clinical picture of the syndrome may help the reader to deal with the following paragraphs of the paper.

 

 

Author Response

I congtatulate with the Authors for providing a clear,

comprehensive, well written review on a new therapeutic

development for a rare clinical condition which, however,

emergency physicians not unfrequently encounter and manage.

Although the paper is evidently focused on sebetralstrat for the on-

demand treatment of HAE, a more detailed description of the

clinical picture of the syndrome may help the reader to deal with

the following paragraphs of the paper.

Reply: The authors thank reviewer 3 for their thoughtful review and helpful suggestion. The following information has been added to page 1, lines 31-36. “Criteria for the diagnosis of HAE includes the clinical presentation of recurrent subcutaneous or submucosal angioedema that last more than 12 hours and/or unexplained recurrent abdominal pain that spontaneously resolves in 24-72 hours, and laboratory measurements of C1 inhibitor demonstrating a <50% deficiency [1]. Additional supporting information includes a documented family history of HAE and the identification of C1 inhibitor gene mutations that affect its synthesis or function.”