Authored by: Jeremy J. Gustrowsky
In a recent decision, the Federal Circuit affirmed that ImmunoGen, Inc. was not entitled to a patent for a specific dosing regimen of its cancer drug, IMGN853 (mirvetuximab soravtansine), used to treat ovarian and peritoneal cancers. The case centered on U.S. Patent Application No. 14/509,809, which claimed a method of administering IMGN853 at a dose of 6 mg per kilogram of adjusted ideal body weight (AIBW). ImmunoGen argued that this dosing method reduced harmful side effects, particularly ocular toxicity, but the court found the claims unpatentable as obvious in light of existing prior art.
The court’s analysis focused on whether a person skilled in the field would have been motivated to try AIBW dosing at the claimed amount and whether there was a reasonable expectation of success. Prior art already disclosed dosing IMGN853 at around 6 mg/kg based on total body weight (TBW), and AIBW dosing was a known method for reducing drug toxicity in other contexts. The court determined that, even though AIBW dosing had not previously been used for antibody drug conjugates like IMGN853, it was a logical step for someone trying to address toxicity issues, especially since the drug’s toxic payload (DM4) was known to cause ocular side effects.
ImmunoGen contended that the specific problem of ocular toxicity with IMGN853 was not known at the time, so there would have been no motivation to use AIBW dosing. However, the court clarified that patent law does not require the inventor’s specific motivation to be known in the prior art—what matters is whether the claimed invention would have been an obvious solution to any known problem in the field. Because the prior art taught both the use of AIBW dosing to reduce toxicity and the use of 6 mg/kg dosing for IMGN853, the court found that the claimed method was not inventive.
Ultimately, the Federal Circuit upheld the district court’s decision, finding no clear error in the conclusion that ImmunoGen’s dosing regimen was obvious and therefore unpatentable. This case highlights the importance of demonstrating a true inventive step beyond what is already known or suggested in the field, especially when adjusting well-known dosing methods for new drugs.