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United States securities and exchange commission logo
October 28, 2020
Laura Shawver
Chief Executive Officer
Silverback Therapeutics, Inc.
500 Fairview Ave N, Suite 600
Seattle, Washington 98109
Re: Silverback
Therapeutics, Inc.
Draft Registration
Statement on Form S-1
Submitted October
2, 2020
CIK No. 0001671858
Dear Dr. Shawver:
We have reviewed your draft registration statement and have the
following comments. In
some of our comments, we may ask you to provide us with information so
we may better
understand your disclosure.
Please respond to this letter by providing the requested
information and either submitting
an amended draft registration statement or publicly filing your
registration statement on
EDGAR. If you do not believe our comments apply to your facts and
circumstances or do not
believe an amendment is appropriate, please tell us why in your
response.
After reviewing the information you provide in response to these
comments and your
amended draft registration statement or filed registration statement, we
may have additional
comments.
Draft Registration Statement on Form S-1, Submitted October 2, 2020
Prospectus Summary, page 1
1. Balance your disclosure
in the first sentence on page 1 by clarifying that you have only
one product candidate
in early clinical stage. In addition, please revise your statement on
page 4 that a key
element to your business strategy is to [a]dvance SBT6050 through
development and seek
expedited approval, as well as any similar references, including on
page 110, to avoid any
implication that you have the ability to accelerate FDA approvals
and commercialization
of your product. Please also revise to explain the meaning of your
statement on page 110
that you are pursuing clinical development strategies that
demonstrate
proof-of-concept early. We note that it is not clear from your Business
discussion how you
intend to seek accelerated approval for your product candidates.
Laura Shawver
FirstName
Silverback LastNameLaura Shawver
Therapeutics, Inc.
Comapany
October 28,NameSilverback
2020 Therapeutics, Inc.
October
Page 2 28, 2020 Page 2
FirstName LastName
2. In the pipeline table on page 2, which also appears on pages 90 and
108, please tell us
why you believe you should include two arrows for SBT6050 given that
your narrative
description of the Phase 1 trial in the Business section indicates
that there is only one
Phase 1 trial, and so the two arrows merely represent different parts
of the same trial. We
also note that the combination with PD-1 inhibitor aspect of the
SBT6050 program is not
described in the Summary, nor is PD-1 defined in the Summary. Please
also tell us why
you believe the TLR8 agonist program and ASGR1-TGF agonist program
should be
included in the pipeline table given they are in the early
pre-clinical phase, the selected
targets remain undisclosed, and your narrative disclosure only briefly
discusses these
programs.
3. You state that SBT6050 is intended to target tumors such as certain
breast, gastric and
non-small cell lung cancers, "among others." However, your pipeline
table shows that the
targeted indications are breast, gastric, and NSCLC. Please revise
your disclosures here,
and elsewhere in your prospectus as appropriate, to clarify the
intended target indications
for this product candidate.
4. Please expand your statement on page 3 that Nectin4 has been
clinically validated by
Seattle Genetics to explain that another product targeting Nectin4 was
approved, and state
the product's intended indication, as you more clearly explain on page
126.
5. We note the following statements that appear on pages 1 and 3 and
elsewhere referring to
[s]ingle agent pharmacological activity" in the first
dose-escalation cohort of your Phase
1 trial. Please remove these statements from the Summary as your
discussions of trials in
the Summary should be limited to endpoints and serious adverse events.
In addition, in the
Business section on page 125, please clarify what type of
pharmacological activity
consistent with the potential mechanism of action has been observed,
and also
disclose how many patients are referenced by the statement, how many
doses were
received by those presenting such activity, the dosage amounts
received by those patients,
and the meaning of where data are available.
6. Please incorporate the definition of functional cure from page 129 on
page 4.
7. Balance your statement in the second bullet on page 4 that you intend
to advance
SBT6050 into "earlier lines of therapy" by also disclosing that you do
not expect to
initially seek approval of your product candidates as a first line
therapy, as you indicate on
page 27, or advise.
Risks Associated with Our Business, page 5
8. Expand on the penultimate bullet to discuss specifics of how the
COVID-19 pandemic has
already affected your trials. For example, you state on page 39 that
some of your trial sites
have slowed down or stopped further enrollment of new patients and
denied access to site
monitors. Please also similarly revise to provide specifics in your
disclosures on pages 91-
92.
Laura Shawver
FirstName
Silverback LastNameLaura Shawver
Therapeutics, Inc.
Comapany
October 28,NameSilverback
2020 Therapeutics, Inc.
October
Page 3 28, 2020 Page 3
FirstName LastName
Implications of Being an Emerging Growth Company and Smaller Reporting Company,
page 6
9. Please supplementally provide us with copies of all written
communications, as defined
in Rule 405 under the Securities Act, that you, or anyone authorized
to do so on your
behalf, present to potential investors in reliance on Section 5(d) of
the Securities Act,
whether or not they retain copies of the communications.
Risk Factors
If we are required by the FDA to obtain approval of a companion diagnostic
test, page 25
10. You state that separate FDA approval may be needed for a companion
diagnostic test.
Please explain whether there are currently any existing companion
diagnostic tests
available to be used in connection with your product candidate, and if
there are not, please
revise to clarify that separate approval would be required, or advise.
Please also add a
bullet to your summary risks disclosure on page 5 to explain that your
product
candidates will need companion diagnostic assays, and if there are
currently no such
existing tests, disclose that these diagnostic tests will need to be
separately developed and
approved.
Our principal stockholders and management own a significant percentage of our
stock. . ., page
65
11. We note your statement that a significant percentage of your voting
stock will be owned
by directors, officers and five percent stockholders and their
affiliates upon closing of the
offering. Please revise this risk factor to clarify whether the
percentage ownership
disclosed assumes the purchase of any shares in the directed share
program. In addition,
please add risk factor disclosure where appropriate that several of
your directors were
appointed by your significant shareholders, as you discuss on page
166.
Business
Lead Product Candidate SBT6050: TLR8 Agonist Conjugated to a HER2 Antibody,
page 111
12. On page 114 you state that HER2 expression is "prevalent in
meaningfully large patient
sub-populations in a wide variety of tumor types including breast,
gastric, non-small cell
lung, colorectal, bladder, uterine, pancreatic, head and neck,
ovarian, esophageal, and
gallbladder cancers, providing the potential to address a large
HER2-expressing tumor
agnostic market estimated to be more than 160,000 newly-diagnosed
patients annually in
the United States based in part on estimated prevalence rates.
Please provide the basis for
this conclusion, including the estimated prevalence percentage rates,
and such rates in
breast, gastric and NSCLC patients, as your pipeline table indicates
that your SBT6050
product candidate is intended for these indications.
13. In your description of SBT6050-S in vitro studies in mice starting on
page 118, please
include the number of mice in the study and explain the meaning of
"complete response
rate" and mice being cured on page 121.
Laura Shawver
FirstName
Silverback LastNameLaura Shawver
Therapeutics, Inc.
Comapany
October 28,NameSilverback
2020 Therapeutics, Inc.
October
Page 4 28, 2020 Page 4
FirstName LastName
14. Although your narrative lead-in to the figure at the bottom of page
119 references
functional results of SBT6050 in human and SBT6050-S in mice, the line
graph appears to
show only results for mice. Please revise the graphic to display the
human comparison or
advise.
15. Please revise the disclosure to provide the number of subjects for the
mouse study results
described on pages 120-121, explain whether the studies were powered
to show statistical
significance, and describe how they relate to the FDA's standards of
efficacy. Please also
provide similar information for your SBT6290 study discussed on page
128.
16. Please provide further details concerning the primate studies
mentioned on page 122,
including the number of subjects and duration.
17. In the description of your Phase 1/1b trial for SBT6050 on page 124,
please clearly state
the total anticipated number of participants for each of Part 1 and
Part 3.
18. We note your statements on page 124 that the purpose of parts 2 and 4
of your Phase 1/1b
trial is to confirm the safety of the RP2D for SBT6050. Please
revise these and
any similar statements throughout your prospectus that state or imply
that your product
candidates are safe or effective as these determinations are solely
within the authority of
the FDA and comparable regulatory bodies.
19. You mention HER2 IHC 2+ and 3+ overexpression, amplifications, and
mutations in the
addressable market data on page 125. Please explain the relevance of
mutations to your
SBT6050 product candidate. We note, for instance, on page 124 you only
mention
expressions and amplifications in describing the eligible patients for
your Phase 1/1b trial.
Please also disclose on page 126 the basis for your belief that
SBT6050 may benefit more
than 48,000 patients annually, and if used in earlier lines of
treatment may benefit more
than 160,000 patients annually.
20. Please revise the disclosure to specifically explain the basis for
believing that you could
have product candidates for these applications shown in the graphic on
page 135.
Include descriptions of the pre-clinical trials conducted to date.
SBT6290: TLR8 Agonist Conjugated to a Nectin4 Antibody, page 126
21. On page 127 you state that Nectin4-expressing tumors as shown in the
referenced figure represents "over 80,000 patients annually in early
line settings and over
16,000 patients with relapsed or refractory cancer annually in the
United States. Please
revise your narrative disclosure to clarify how the figure on page 127
reflects early line
and relapsed or refractory cancer, given the legend states the figure
shows incidence of
Nectin4 expression and yearly deaths with Nectin4 expression in the
United States,
and the percentages in the graphic appear to mean that these amounts
should be further
reduced.
22. Please further explain your lead-in disclosure to the graphics on page
128, including the
significance of the vertical axis.
Laura Shawver
FirstName
Silverback LastNameLaura Shawver
Therapeutics, Inc.
Comapany
October 28,NameSilverback
2020 Therapeutics, Inc.
October
Page 5 28, 2020 Page 5
FirstName LastName
SBT8230: TLR8 Agonist Conjugated to an ASGR1 Antibody, page 129
23. Please label the vertical axis for the graphic at the top of page 131.
In addition, revise your
lead-in disclosures on page 133 to clarify the significance of the
three charts on page 133
and the top chart on page 134, including defining AAV-HBV and
explaining the vertical
axes. Also disclose the number of mice in the studies, and whether the
studies were
powered for statistical significance.
Intellectual Property, page 140
24. Please provide the foreign jurisdictions applicable to the patent and
patent applications
listed on pages 140-141.
Certain Relationships and Related Party Transactions, page 186
25. On page 189 you state that shares under the directed share program
will be offered to
"certain" of your directors and officers. Please clarify if all of
your directors and executive
officers are eligible to participate in the program.
Principal Stockholders, page 190
26. We note that the last row of the principal stockholder table on page
191 reflects a total of
3,962,094 for all current executive officers and directors as a group,
yet certain executive
officers and directors are shown in the table as individually owning
more than 3,962,094
shares. Please reconcile this discrepancy.
27. Please revise the disclosure to identify the natural person or persons
who have voting
and/or investment control of the shares held by each of your greater
than five percent
stockholders on page 191.
Financial Statements
Notes to Financial Statements
12. Licensing Agreement, page F-25
28. Please revise your disclosure regarding the WuXi license agreement to
disclose the
amount of upfront license fees paid. In addition, you state here "In
the event the Company
manufactures its commercial supplies of a product produced by the
Licensed Cell Line
using a manufacturer other than WuXi Bio or its affiliates, the
Company will become
obligated to pay WuXi Bio aggregate milestone payments, upon
achievement of certain
sales milestones, of up to the low eight figures." Since an amount
that is up to the low
eight figures would be material, please revise to disclose the amount
that may be paid.
Please provide corresponding disclosures in the Business section.
Laura Shawver
Silverback Therapeutics, Inc.
October 28, 2020
Page 6
You may contact Lisa Vanjoske at 202-551-3614 or Tracey McKoy at
202-551-3772 if
you have questions regarding comments on the financial statements and related
matters. Please
contact Margaret Schwartz at 202-551-7153 or Dorrie Yale at 202-551-8776 with
any other
questions.
Sincerely,
FirstName LastNameLaura Shawver
Division of
Corporation Finance
Comapany NameSilverback Therapeutics, Inc.
Office of Life
Sciences
October 28, 2020 Page 6
cc: Charles Kim, Esq.
FirstName LastName