ST Pharm has thrown down the gauntlet in the global AIDS (HIV) treatment market, worth 35 trillion won a year. The company has wrapped up phase 2a trials of its homegrown drug candidate "STP0404 (Pirmitegravir)" and plans to announce results in the second half of this year. The market is currently dominated by a handful of global big pharma companies, including Gilead, ViiV, and Merck (MSD).
STP0404 is the world's first ALLINI (allosteric integrase inhibitor) class candidate to enter phase 2 as an HIV treatment. Global drugmakers have attempted to study this class for more than a decade, but many projects were halted in preclinical stages due to toxicity and other issues, raising expectations that a successful development could significantly ripple through the market.
However, with MSD bringing a new‑mechanism HIV therapy to market first, a key task for out‑licensing will be how strongly STP0404 can demonstrate differentiation.
◇ ST Pharm nears "world's first" title as it finishes phase 2a of new HIV drug
ST Pharm said on the 6th (U.S. local time) that it completed the last patient's last visit (LPLV) for the STP0404 phase 2a trial. The company expects to receive top‑line results in the third quarter and the final clinical study report (CSR) in the fourth quarter.
STP0404 is cited as potentially effective in patients who have developed resistance to existing integrase strand transfer inhibitors (INSTIs). While existing INSTIs directly inhibit the active site of the viral replication enzyme, STP0404 binds to a different, allosteric site of the enzyme and disrupts its structure.
The phase 2a trial enrolled 36 adults with HIV‑1 infection who were treatment‑naive or had limited treatment experience, administering STP0404 or placebo once daily for 10 days.
In an interim analysis of 16 participants in cohorts 1 and 2 (200 mg and 400 mg), the amount of virus in the blood (HIV‑1 RNA) decreased significantly through day 11 in the treatment arms (p<0.0001). The mean reduction was about 15 to 36‑fold, well above the U.S. Food and Drug Administration threshold (a decrease of at least 0.5 log10 copies/mL). No serious adverse events (SAEs) requiring treatment discontinuation were observed.
These interim results were presented orally at IDWeek 2025, an infectious disease conference held in Atlanta last year. Out of more than 5,000 abstracts submitted annually, only about 5% to 10% are accepted for oral presentation. At the time, the industry interpreted this as a signal that the global academic community was paying attention to the STP0404 data.
◇ MSD's new HIV therapy launches in the U.S., shows noninferiority versus existing regimens
ST Pharm is prioritizing a strategy to build overseas partnerships through out‑licensing after phase 2a. It also signed material transfer agreements (MTAs), providing drug samples to multiple pharmaceutical companies for preliminary discussions.
A swing factor is MSD's new HIV therapy "Idvynso (IDVYNSO)." Idvynso won U.S. Food and Drug Administration approval last month, and sales began at U.S. pharmacies on the 11th.
Idvynso is a once‑daily two‑drug regimen combining doravirine and islatravir. It is the first fully oral two‑drug regimen that does not include tenofovir or an INSTI, which had been mainstays in HIV treatment, and is cited as potentially useful for older patients or those on long‑term therapy.
In phase 3, it achieved an 89% viral suppression maintenance rate at week 96, demonstrating noninferiority compared with maintenance arms on existing two‑ or three‑drug oral regimens, including Gilead's Biktarvy.
On safety, concerns about decreased kidney function that have been raised with tenofovir‑based therapies did not stand out, and changes in weight, blood glucose, and lipid levels were also deemed not clinically significant. A past concern about CD4 T‑cell declines during the development of islatravir was not observed with the low‑dose regimen used in the phase 3 trials.
The monthly wholesale price is about $4,455 (about 6.2 million won), similar to Biktarvy.
◇ "Not a direct competitor, but the bar for proof just got higher"
Idvynso and STP0404 are not easy to view as being in direct competition. Idvynso targets patients already on treatment with sufficiently suppressed virus (HIV‑1 RNA below 50 copies/mL), focusing on switching maintenance therapy from existing drugs, while STP0404 is cited as potentially supplementing patients with resistance to existing therapies or being developed as a combination therapy based on a new mechanism.
However, since both are oral HIV treatments, some market overlap is possible. In the industry, there is a view that if a first‑mover drug captures the market early, it could weigh on ST Pharm's negotiating power for technology transfer as a latecomer.
In the long run, a competitive landscape could still emerge. There are precedents where a new drug, like MSD's Isentress, started in resistant or limited patient groups and then, after accumulating clinical data, expanded its indications into maintenance or first‑line treatment markets.
Some also say that if clinical competitiveness is sufficiently demonstrated, ST Pharm could continue with subsequent development on its own. While global phase 3 trials and commercialization require substantial funding, the company is part of the Dong‑A Socio Group and is seen as having some capacity to support funding.
A ST Pharm official said, "It is difficult to disclose specific strategies," and noted, "We plan to set our course after securing the top‑line results."