T 279/07 – Deadly Prodrugs

Following a refusal of its application by the Examining Division, the applicant filed an appeal as well as a new set of claims. Claim 1 of this set read:

1. Use of androst—5—ene—3ß,17ß—diol or prodrug thereof, for the manufacture of a pharmaceutical composition for treating or reducing the likelihood of acquiring, in a female patient in need thereof or benefitting therefrom, an indication where an estrogenic effect is desired to a greater extent than is an androgenic effect and in which lower androgenic activity than provided by DHEA is desired, the indication selected from the group consisting of hypogonadism, skin atrophy, skin dryness, vaginal atrophy, and urinary incontinence.

The Board came to the conclusion that this claim was unclear:

[2.1] Under A 84 the claim(s) shall define the matter for which protection is sought.

Thus, the question to be answered with respect to clarity under A 84 EPC is whether it is possible to determine if an embodiment falls within the scope of the claims or not.

In the present case, the chemical structures in independent claim 1 are mainly defined by a functional feature, namely “androst-5-ene—3ß,17ß-diol or prodrug thereof” (emphasis added).

According to the description, “prodrugs” of 5-Diol are defined as compounds “converted thereto in vivo”, and two specific structures, i.e. the 3-acetylated derivative of 5-Diol and a 3,17-succinic ester of 5-Diol, and 5-Diol fatty acids are disclosed […].

The Board has no doubt that the skilled person is perfectly able in most cases to decide whether or not a steroid derivative will be converted to 5-diol in vivo, in particular when the chemical entity differs from the 5-diol skeleton merely by the presence of usual hydrolysable hydroxyl protecting groups such as esters, carbonate esters, phosphate esters, acyloxyalkyl ethers a.s.o..

However, the Board is also convinced that, in order to establish whether a structurally more remote steroid derivative constitutes a prodrug of 5—diol, in other words in order to clearly establish the scope of protection of the claims, the skilled person would sometimes have no other choice than to synthesize a labeled sample of the steroid to be tested and to follow its biochemical transformations in vivo to determine whether or not the chemical structure under consideration is a biological precursor of 5-diol. In addition, toxicological studies might also be necessary.

According to the Case Law of the Boards of Appeal (e.g. T 68/85), clarity demands not only that a skilled person be able to understand the teaching of the claim but also that he be able to implement it. In other words, the feature must provide instructions which are sufficiently clear for the expert to reduce them to practice without unreasonable burden, if necessary with routine experiments.

The clarity requirement is therefore not met in the present case since, as shown above, the skilled person would have to find out in some cases merely by trial and error whether a steroid derivative meets the functional requirement set out in the claim, i.e. by making his own investigations, similar to a research programme.

Under these circumstances, the Board concludes that claim 1 of the main request does not fulfill the requirement of A 84.

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