Why the Patent Court rejected the ‘prodrug strategy’

AstraZeneca wins second trial on ‘Forxiga’s substance patent’… Dong-A ST files an appeal

Patent Court has the same principle of action and effect…"is not difficult to develop the technology”

Last decision to be made by the Supreme Court… ‘strategy to overcome substance patents of original drugs’ at a crossroad

Dong-A ST is challenging the substance patent of AstraZeneca’s SGLT-2 inhibitor antidiabetic treatment ‘Forxiga (dapagliflozin).’ The industry’s eyes are focused on Dong-A ST’s challenge, with the expectation that Dong-A ST’s success would bring a new strategy that can overcome the substance patent of originals.

 

However, Dong-A ST’s attempt has been put to a stop by the Patent Court of Korea.

 

The final decision will be made by the Supreme Court, but attention is focused on why the Patent Court of Korea overturned the first instance court's ruling and ruled in favor of AstraZeneca in its appeal against Dong-A ST.

 

◆ "Clear difference between the original drug and prodrug” judged in both the first and second trials According to the ruling on the 28th, the Patent Court of Korea ruled in favor of AstraZeneca on the grounds that the principle of action between the original substance of Forxiga and Dong-A ST's prodrug was the same.

 

Pro-drug is a ‘pro’ drug that is considered a similar but different drug from the original drug.

 

Its chemical structure is partially different in the substituents with the original drug from its manufacture to immediately before administration.

 

However, once administered, the drug shows the same effect as the original By principle, it sounds similar to salt-modified drugs, but the difference Is clear.

 

The salt can be changed through simple ion bonding.

 

Its chemical structure itself does not change.

 

However, prodrugs change the substituents through a more difficult covalent binding method.

 

It has a different chemical structure to the original drug.

 

The first and the second court both made the same judgment on whether the prodrug could be considered a completely new substance.

 

Both the Intellectual Property Trial and Appeal Board (IPTAB) and the Patent Court of Korea interpreted Dong-A ST’s prodrug as a completely different substance to the original substance.

 

The IPTAB judged that the “difference in chemical structure is clear, therefore, Dong-A ST’s prodrug is outside the scope of rights held by Forxiga’s patented invention.” ◆ Patent Court of Korea “a skill that can be easily conceived by an ordinary skilled person" However, the two courts' rulings differed in the ‘ease of substitution issue.’ The courts made different judgments on whether an ordinary skilled person in the industry may easily produce Dong-A ST’s prodrug.

 

While the first court judged that developing the prodrug was not easy, the second instance court judged that it "was a substance anyone with ordinary skills in the industry could produce.” The evidence AstraZeneca submitted for the appeal played an important role in the ruling.

 

The Patent Court of Korea explained, “the specific form of ‘formate ester’ that Dong-A ST used to develop its Forxiga prodrug has been found in various literature.” ◆Deleted ‘produg’ in the patent registration process …Court decides it was “common practice" at the time Dong-A ST appealed using the fact that the term ‘prodrug’ was deleted in the process of AstraZeneca’s patent registration.

 

In fact, when AstraZeneca first filed the substance patent for Forxiga in 2006, it listed its scope as “compounds with chemical structural formula I, or other pharmaceutically acceptable salt or stereoisomer, or prodrug ester thereof.” However, the prodrug part was deleted after the first patent claim was rejected by the Korean Intellectual Property Office.

 

The final patent registered specifies the scope as “compounds with chemical structural formula I, or other pharmaceutically acceptable salt or stereoisomer,” without the prodrug part.

 

Dong-A ST claimed that the deletion of "prodrug esters" from the claim indicates the waiver of those rights on the company’s part.

 

However, the Patent Court of Korea turned down the claim.

 

The court judged “AstraZeneca did not consciously delete the part, and “it was KIPO's practice at the relevant time not to allow the term "prodrug" in patent claims for formal reasons.” ◆Up to the supreme court…’ strategy to overcome substance patents of original drugs’ at a crossroad Dong-A ST expressed dissent at the Court’s decision and filed an appeal.

 

The case will therefore be judged by the Supreme Court.

 

If the Supreme Court determines that there is a problem with the second trial ruling, the patent strategy of the entire domestic pharmaceutical industry may be revised.

 

Like Dong-A ST, other companies will opt to challenge the substance patent of original drugs using the prodrug strategy.

 

On the other hand, if the Supreme Court confirms the judgment of the second instance court, the substance patent of original drugs may continue to remain impenetrable.