Enanta Pharmaceuticals Inc (ENTA)

Don’t think ENTA’s lawyer sounded ‘very nervous’. Her presentation was adequate. This appeal will be decided on the facts of the case, the law, and the testimony / record to date.

As DD pointed out the question of whether PFE infringed has never been adjudicated this is all about whether the patent is valid.
Exactly. But the claims in the awarded patent cover C1 to C12. PFE could have raised with the PTO that they had disclosed C1, and if that was accepted by the PTO the claims in the awarded patent would have been limited to what is in the provisional, i.e., C2 to C12.
My understanding is that paxlovid infringes on C1 but not C2 to C12, but that has not been litigated.

re stat 6

This blurb discusses the stat6 space a bit, but notably absent is PFE's drug which is not far behind KYMR and also in phase 2:

https://drughunter.com/commentary/stat6-why-the-once-undruggable-is-now-the-hottest-target-in-immunology

https://clinicaltrials.gov/study/NCT07216027?term=PF-08049820&viewType=Card&aggFilters=phase:2,status:not%20rec&rank=1

The size of the study was decreased, 2 arms were dropped, and the completion date was pushed out by 8 months - all fairly recently

As DD pointed out the question of whether PFE infringed has never been adjudicated this is all about whether the patent is valid. The fact the provisional patent had these inconsistencies that was corrected post hoc was never something I honestly knew about until the case came to a head. Europe is another shot on goal for sure

I think the appeals court will decide based on the merits. I think she made the best argument for why there is a question of fact that should be decided by a jury. Personally reading the transcript slightly raised my hopes.

Either way someone screwed up big at ENTA (whether they didn't catch a typo in the provisional or they failed to list the full range of compounds). PFE also had a (smaller) screw up here. They should have caught this when the ENTA application was published and asked the PTO to limit the scope of the claims to what was in the provisional, since PFE had disclosed the C1 compound in the meanwhile. This would have put them in a stronger position.

Agreed. She sounded very nervous. I would not have done any better but she also didn’t give a great answer when she was asked to provide examples of cases. She only named one case and said out loud that there was another case but then she couldn’t recall it, which is not a great look. I never thought much of the merits but am interested to see what happens in Europe.

Lost her train of thought at one point (her words)
didn't have answers at the ready like PFE's lawyers, stammered a bit
the rebuttal time was limited to one precedent in case law - not a lawyer but seems to have been an opportunity to do more
Hopefully the briefs were solid though I mean It's much harder to write subscripts so it is very plausible in fact incredibly likely that C2-C12 was cut and pasted
Also the judges focused a bit on their expert having said the repeated typos were "likely" due to cut and paste in the original arguments before the court. You had an opportunity to prep the witness - could have guided them to avoid such language back when this was first argued. I mean the fact it said C one to twelve when the invention was written out, then a discrepancy occurred during the shorthand C2-12 and repeated18 times (when there would be no reason to narrow the scope of the invention by one carbon IMO) seems to have risen higher than a "likely" cut and paste error
also just compared to PFE's lawyers just seemed less sure of herself

...not impressed by ENTA’s lawyer... Can you elaborate?

PFE must be comfortable with their original argument, or they would not have chosen to stand on that ground. PFE hasn't actually risked anything yet; the question of whether PFE infringed on ENTA's patent has not yet been considered by any court.

We know most of this. However, great interpretations by AI if Enanta wins the suits Vs. Phizer in the U.S. and Europe. I see a large settlement in the works.

The May 11, 2026, hearing in the U.S. Court of Appeals for the Federal Circuit featured oral arguments rather than a final ruling. Therefore, the appeal was neither a win nor a loss for Enanta yet, as the three-judge panel took the case under advisement.The high-stakes legal battle involves Enanta’s U.S. Patent No. 11,358,953 ('953), which covers protease inhibitors that Enanta claims Pfizer infringed upon to create the COVID-19 antiviral Paxlovid.

The May 2026 Appeal: Enanta went to the Federal Circuit attempting to overturn the district court's invalidity and infringement rulings.Upcoming Decision: The Federal Circuit is expected to deliver its ruling by the end of September 2026.

The European Front: Meanwhile, Enanta is simultaneously pursuing Pfizer over the same infringement through a parallel lawsuit in the Unified Patent Court (UPC) of the European Union, which has a hearing scheduled for late September 2026..

The parallel European lawsuit represents a critical strategic pivot for Enanta following its lower court setbacks in the United States. By utilizing the relatively new European legal framework, Enanta is aiming for a complete turnaround in its multi-billion-dollar dispute over Paxlovid.The Core of the European DisputeEnanta initiated this enforcement action in August 2025. The lawsuit directly targets Pfizer's manufacturing, distribution, and sales of Paxlovid.

The Patent: Enanta is asserting European Patent No. EP 4 051 265 (the '265 patent). This patent is the direct European counterpart to the U.S. patent ('953) that was invalidated by the Massachusetts District Court.The Invention: The '265 patent covers coronavirus protease inhibitors developed by Enanta scientists in July 2020 to prevent viral replication. Enanta claims Pfizer's main antiviral molecule in Paxlovid, nirmatrelvir, copies this formulation.Enanta’s Strategic Advantages in the UPCShifting the battleground to the Unified Patent Court (UPC) gives Enanta several distinct structural advantages over traditional U.S. litigation:Pan-European Reach: Instead of suing Pfizer in separate European countries, a single favorable ruling from the UPC will instantly apply across all 18 participating EU member states.

Aggressive Speed: The UPC operates with unprecedented procedural velocity, strictly enforcing a 12-month target timeline from filing to a first-instance trial hearing.Independence from the U.S. Case: Because European patent law evaluates priority dates, claim corrections, and validity under different statutory rules than U.S. courts, the prior loss in Massachusetts has no legal binding power over the European judges.The September 2026 Trial HearingBecause Enanta filed the case in August 2025, the UPC's rapid schedule dictates that the oral trial hearing will occur by late August or September 2026.

The Judgment: A binding verdict is expected within weeks of the hearing concluding.Next Steps for Damages: If the UPC rules that Pfizer infringed Enanta's patent, the court will schedule separate, subsequent proceedings to calculate the financial damages and royalties owed from Paxlovid sales.

Enanta has not requested a specific, fixed cash amount in its lawsuit at the Unified Patent Court (UPC); instead, it is seeking a "reasonable royalty" on all Paxlovid sales across the 18 participating European Union nations.Because Paxlovid generated tens of billions of dollars globally during its peak pandemic years, a successful judgment could yield Enanta hundreds of millions to over $1 billion in retroactive and ongoing damages. The Financial Formula for DamagesUnder the UPC framework, if the court rules that Pfizer infringed on Enanta's '265 patent, financial damages will be calculated using a bifurcated two-step process:

Step 1:
The Liability Trial (Sept 2026): The upcoming trial strictly handles whether Pfizer is legally responsible for patent infringement. No dollar figures will be officially awarded during this stage.
Step 2:
Separate Damages Proceedings: If Enanta wins Step 1, the court will launch subsequent accounting proceedings. Enanta will demand access to Pfizer’s books to calculate exact Paxlovid revenues within the 18 European member states.Valuation Models and ProjectionsPharmaceutical Wall Street analysts project the potential financial payout based on standard industry metrics:The Industry-Standard Royalty Rate: Financial analysts at firms like RBC Capital Markets note that a typical baseline court-awarded royalty rate for a foundational drug compound patent sits at roughly 6% of gross sales.Peak vs. Post-Pandemic Sales Pools: At Paxlovid's global peak, when it brought in roughly $22 billion annually, a 6% global royalty would have been worth over $1.3 billion per year. While European post-pandemic sales have significantly stabilized, the retroactive payout covering EU sales from the drug's launch up through 2026 still represents a massive financial liability for Pfizer.What Enanta Is NOT ClaimingTo protect itself from public backlash and ensure its strategy focuses entirely on monetization, Enanta has explicitly stated that it will not seek an injunction. It is not trying to halt the production, distribution, or sales of Paxlovid in Europe. The legal strategy is entirely designed to secure a permanent, lucrative revenue share of Pfizer’s blockbuster product.

The judges probed both lawyers and didn’t tip their hat much from what I could tell. This is not a slam dunk for Pfizer at all IMO

PFE must be comfortable with their original argument, or they would not have chosen to stand on that ground. 

Thanks for the DD and link. Seems to me there’s a chance in favor of ENTA I.e. this is a question for a jury to decide.
It’s also clear ENTA’s provisional application was sloppy. I’m also not impressed by ENTA’s lawyer

If ENTA wins this appeal, then the invalidation of the patent would go to a jury trial. Am I correct to conclude that since the patent was invalidated by the District Court and since patent suits require unanimous jury verdicts to succeed, ENTA would need to convince a single juror to avoid patent invalidation? This is different than if the patent had been reexamined and revoked by the USPTO, in which case ENTA would need a unanimous jury in its favor to reinstate the patent.

I still think it is a long shot to win this appeal, but if above is correct, in that case PFE would be taking a significant risk by letting it go to a jury, so will probably settle or just buy ENTA...

Thanks, flo, and go_seek. I was able to listen after I disabled my ad-blocking utility.

GO SEEK is correct. Do NOT use the MP3 File download. Instead hit the PLAY arrow & follow along with the complete transcript that lights up as you proceed.

ENTA's attorney had v.g. responses from the 2 judges re: a JURY TRIAL. I have always been an OPTIMIST. Although a long shot, there have been several decisions in favor of the plaintiff on appeal. September.will be the reality.

I listened to all 41 minutes. Suggest that you don’t download the file. Rather use the recording play dialogue box that pops up with the link.

https://share.google/24rVZUrvElJPa0PFI

I listened to the arguments… fascinating dialogue. Thanks flo. It would be a victory if the Appeals Court would put the case to a jury. At that point there would probably be a settlement.

https://share.google/24rVZUrvElJPa0PFI

I downloaded the mp3 file, but the audio shut off after a few minutes. When I tried to download the file again, I got a message saying that I had used up too many of the website’s resources!

Research was done to see if there was a written record on the May 11th appeal.

Enanta Pharmaceuticals, Inc. v. Pfizer Inc.
Court of Appeals for the Federal Circuit

Date Argued: May 11th, 2026

Duration: 35:41

Docket Number: 25-1427

Kindly listen to the AUDIO which corresponds to the written record:

https://www.courtlistener.com/audio/104819/enanta-pharmaceuticals-inc-v-pfizer-inc/

Watertown-based biotech Enanta is represented by the Boston law firm Foley Hoag LLP. Pfizer is represented primarily by Williams & Connolly LLP

Barbara A. Fiacco et al represent Enanta
https://foleyhoag.com/people/fiacco-barbara/

Comments?

LOL. Perhaps ENTA temporarily removed materials from these shelves that they didn’t want the visiting students to see. Some of the students could conceivably have been moonlighting as corporate spies.

Trying not to judge the empty shelf space on the left. Been in many labs, industry and academic, never seen empty shelves like that.

Got it. The peds phase 2 will read out well before the adult phase 3 is completed. It already has a CT.gov entry and is 1/4 the size. So it’s possible they start the adult trial then partner both once peds data is in hand while the adult trial is still ongoing.
One thing I’m confident about is they have a program with value but a clear line of sight in the peds indication as well as adult if the resolve p tool pans out in a second phase 2 will increase the value of the program substantially

Just to clarify I didn't mean to say go it alone for adults and partner peds. I think they will fine one partner for both - they are in no position to commercialize so have to partner the adult indication at some point and I think it will be the same time as peds (they may retain profit sharing or something like that in the US rather than straight royalty)

I was only talking about running the phase 3 trial for high risk adults not ENTA commercializing it on their own.

From Jeffries -

ENTA: RSV program shows strong efficacy and regulatory momentum, with flexible development strategies
Jun 4, 2026, 13:09 GMT-4 Less than 1 min read

ENTA
+6.49%
The discussion highlighted progress in RSV drug development, with strong efficacy signals and ongoing FDA engagement for a novel registration path. Strategic flexibility includes both internal and partnership-driven trial execution, while preclinical data support robust target engagement for pipeline assets.

https://www.tradingview.com/news/urn:summary_document_transcript:quartr.com:3479812:0-enta-rsv-program-shows-strong-efficacy-and-regulatory-momentum-with-flexible-development-strategies/

I was pleased that we didn’t get the boiler plate description of the company at the start of today’s chat. Good exchange on RSV and STAT6.

Ya - that’s my point. Jay should have waited until after issuing the 8K then, if it is good news, start the dog and pony shows

Not totally sure why Jay agreed to this because he spent a good part of the session saying everyone needs to wait on the path with FDA (before end of June).You don't speak publicly about what the FDA will say when they haven't said it yet. This is SOP for all drug/biotech companies.

Re: Jefferies webcast

The most notable snippet from today’s webcast occurred when the Jefferies analyst asked Jay about KYMR's STAT6 degrader* and Jay responded with the rhetorical question, “Why use a degrader when the target is now druggable?” I.e., the STAT6 target has been well known for a few decades (and Jay even worked on STAT6 when he was a scientist at ABT), but nobody knew how to drug the target until fairly recently.

*See #msg-177596554 for background info. Note that KMYR's lead STAT6 compound is KT-621 (not KT-601).

Anyone watch today’s fireside with Jeffries? Not totally sure why Jay agreed to this because he spent a good part of the session saying everyone needs to wait on the path with FDA (before end of June). On the positive side side, Jay continues to gush about Zeli. I very much appreciated the back and forth with Akash, who clearly knows the subject matter. He really made Jay squirm.

Just to clarify I didn't mean to say go it alone for adults and partner peds. I think they will fine one partner for both - they are in no position to commercialize so have to partner the adult indication at some point and I think it will be the same time as peds (they may retain profit sharing or something like that in the US rather than straight royalty)
What I meant to say is they may wait on peds phase 2 data expected end of the year to partner both as that is a larger indication and would be important data to have to know the ultimate value of the program

Kaivamei,

Obviously we want to see FDA approval ASAP. However, successful phase 3 for high risk adults will drive the ENTA price higher well before FDA approval. I think dewophile hit the nail on the head with the go it alone for high risk adults and partnering for the pediatric indication, even if it means a phase 2 for the latter.

2 additional -

They are still functioning!

On Monday, we had the pleasure of hosting AP Chemistry students from #WatertownHighSchool for a special visit to our laboratories. Students learned about the drug discovery process, toured our facilities and enjoyed lunch, while attending a panel discussion featuring Enanta employees who shared their career experiences in the biotech industry. A big thank you to those involved for sharing your time and insights, and a special shoutout to everyone who organized the event. #STEMCareers #EnantaCares #GreatChemistryCures

No leak… daily trade volumes are not high. Conclusions regarding the likelihood of a partnership have been drawn by investors based on the news flow (or lack thereof) to date.
ENTA stock can be moved up or down by a determined seller or buyer. Better days are ahead.

“How many here still think a partnership before the phase 3 trial is more likely than not?”

I think it’s more likely at this point they partner after phase 3 bc clearly don’t like the terms (if any) on the table now.
however your point about waiting for more Pediatric data (the larger indication ) may well be the case in which case they may end up starting the adult pivotal and partner after more peds phase 2 data before any phase 3 reads out

I would love for FDA approval of Zelicapavir to come within a year, but the Phase 3 trial will take a year at least, possibly longer, and then another year to approval is realistic. 
Proximate catalysts may be the company reporting about its meeting with the FDA, expected this quarter, or the RSV partnership which we are all hoping for. 
In principle the partnership could come at any time, but I suspect the company first wants trial data using their proprietary Resolve-p tool for evaluating zeli in peds, so that would mean partnering most likely after the end of this year or early next year. 
How many here still think a partnership before the phase 3 trial is more likely than not?

the suit in the EU probably has a better chance than the appeal in the US


As I posted earlier -

From AI:

Enanta Pharmaceuticals' patent suit in the European Unified Patent Court (UPC) against Pfizer over Paxlovid could indeed produce substantial rewards. While a European victory could yield meaningful damages from European sales, a U.S. loss is legally independent and would not prevent European recovery.A quick look at the details:The European Strategy: Enanta filed a lawsuit in the EU's Unified Patent Court (UPC) alleging that Pfizer's COVID-19 pill Paxlovid infringes upon its European Patent No. EP 4 051 265. Because UPC rulings apply across 18 participating EU nations, a victory here could allow Enanta to secure significant royalties or damages from massive European sales.

I don’t know enough to venture a guess but the suit in the EU probably has a better chance than the appeal in the US. Most of the litigation costs were incurred already the appeal and EU costs are much less so at this point makes sense to see it through.

From what my gut tells me, there is a LEAK. Our company will be bringing Zelicapavir trial 3 by themselves. This is causing a dramatic stock dump due to the large financial means necessary to pay for this trial.
Remember, this is the McDonald generation - no patience needed. IMHO - some are now throwing away a huge windfall once the FDA approves our RSV drug within a year.

You are probably right I was overly optimistic about the chance of receiving a reversal.
I’m afraid Jay is going to play the high risk/ high reward game. Stock traders who are making what appears to be easy money on chips on a daily basis don’t want to put money that may be stagnant for six months.
I guess time will tell…..

PFE might ask for their defense costs to be covered by Enanta. Regarding credibility, the company has claimed a best in class performance on all of their candidates and touted the possibility of efficacy in adjacent categories of disease/infection when it wasn't yet supported. One of the COVID assets was supposed th have efficacy as a pan antiviral. That projection mirrored their strategy in communicating the potential of many of their previous concepts. When they revealed the lab move, their reality as a pre proof of concept venture became salient.

If the probability of success in the PFE litigation was 15-20% I would completely agree. IMHO it is well under 5%, maybe as low as 1%. I hope I am underestimating, and we can always hit the jackpot. I think ENTA should have settled for something nominal (like $10-20M, what PFE will probably spend on this litigation).

15-20% for a few hundred million windfall seems like a worthwhile pursuit. There is clarity in the legal timelines now so perhaps they are waiting on this resolution and if it doesn’t go their way they may be more flexible on partnering terms if that is the holdup. They also will have kit data eoy so that too will let them know where they want to put their investment dollars and partnering efforts.

Understood… the lack of clarity on the partnership strategy does not help IMO. I expect he’ll continue to say, if the right deal comes… they’ll act. The downturn lately is overdone. Trading volumes remain low… the way ENTA trades, there’s a Good chance we’ll be above $13 in a week. 🍀

From my perspective Jay has lost some credibility with share holders. For the last few years it’s the same old story, “we are searching for a partner”. He would have been better off to say we are going to fund the next phase ourselves months ago.
In addition wasting money on litigation where you chances of winning are less than maybe 15-20% is not helping.
Over promise and under deliver is becoming the theme here.

If ENTA drops to single digits I may buy a bit more.