PTAB Upholds Validity of Herceptin Patent

Today the Patent Trial and Appeal Board issued a unanimous decision in Phigenix, Inc. v. ImmunoGen, Inc., upholding the validity of Immunogen’s US Patent Number 8,337,856.  The petition for inter partes review (IPR) was filed by Phigenix, Inc..  Genentech is a real party-in-interest in the proceedings.

 The ’856 patent claims “[a]n immunoconjugate comprising an anti-ErbB2 antibody conjugated to a maytansinoid, wherein the antibody is [HERCEPTIN].”  Herceptin is a biologic developed by Genentech for the treatment of some forms of breast cancer and gastric cancer.

Phigenix cited several prior art references which allegedly rendered the claims obvious and thus invalid under 35 USC 103.  One of the primary references, Chari 1992, describes immunoconjugates comprising an anti-ErbB2 mouse monoclonal antibody chemically coupled to a maytansinoid toxin (DMI).  The other primary reference was the HERCEPTIN label itself.  A Phigenix expert (Rosenblum) submitted a declaration which, according to Phigenix, established that it would have been obvious to substitute HERCEPTIN for the mouse antibody described in Chari 1192 “based on the teachings of Chari 1992 and HERCEPTIN label, as well as the general knowledge in the art at the time.”

The PTAB rejected petitioner’s argument, however, finding that the patent owner had provided persuasive evidence that at the time the patent was filed “prior art indicated that HERCEPTIN®-maytansinoid immunoconjugates would have been expected to exhibit unacceptable levels of antigen-dependent toxicity in normal human liver tissue in patients.”  The PTAB went on to find persuasive evidence in support of patent owner’s argument that ordinary artisans would not have had a reasonable expectation that any immunoconjugate, much less the claimed Herceptin®-maytansinoid immunoconjugate in particular, would be useful to treat solid tumors in humans,” given that “[r]esearchers had targeted tumors with immunoconjugates for about 40 years before the ’856 patent” without success and in view of evidence “indicating that preparing any antibody-toxin immunoconjugate for use in the treatment of human tumors was difficult and unpredictable.”

Previously, the PTAB declined to Institute review in a separate case involving a related patent, US Patent Number 7,575,748.  Phigenix, Inc. v. Genentech, Inc. and ImmunoGen, Inc., Case IPR2014-00842 (PTAB Dec. 9, 2014) (Paper 10).