The US Food and Drug Administration (FDA) should clarify certain aspects and revise certain sections of a draft guidance on developing bispecific antibodies, AstraZeneca, Regeneron, Novartis, Janssen, Pfizer and Eli Lilly said in comments submitted to the agency this week.
The draft guidance, released in April
, discusses the promise behind bispecific antibodies and the development challenges.
Examples of bispecific antibodies marketed in the US include Amgen’s Blincyto (blinatumomab), which brought in $230 million in worldwide sales in 2018, up 31% from 2017, and Roche’s hemophilia medicine Hemlibra (emicizumab-kxwh), which is expected to be a blockbuster. But more than a dozen others are coming, and recent safety concerns, such as a partial clinical hold initiated by FDA after Xencor reported
two patient deaths from a Phase 1 study of a bispecific antibody in February (the hold has since been lifted
), may have triggered the need for more FDA guidance.
But drugmakers pushed back on FDA’s assertion that one of the challenges in developing bispecific antibodies is “significant immunogenicity caused by novel epitopes.”
Pfizer, which called on FDA to delete that line in the guidance, noted, “Emerging clinical data suggest that the risk of immunogenicity of bispecific antibodies are likely to be similar, to that of monoclonal antibodies against one antigen.” Pfizer noted that blinatumomab anti-drug antibody “was reported in very few subjects through the entire program (<1%).”
Similarly, Janssen wrote: “Please clarify why reference is made to ‘significant immunogenicity caused by novel epitopes’ as this issue is not considered particularly pertinent to developing bispecific antibodies.”
Novartis called on FDA to provide a dedicated paragraph in the guidance on “specific immunogenicity assay considerations (e.g. epitope specific assay, type of neutralizing assays required).”
Lilly also sought clarification from FDA on “whether multiple confirmatory assays would satisfy this recommendation and whether they should be run in Phase 1 as well, given the potential higher risk associated with these molecules.”
Regeneron, meanwhile, called on FDA to be more specific about which recommendations apply to which bispecific antibodies.
“The guidance does not specify as to which bispecific category the different recommendations relate and suggests that all recommendations are applicable to all types of bispecifics, which is not appropriate based on experience in this space,” Regeneron said.
Regeneron also suggested creating two subcategories: “a) bispecifics that bridge two target cells and/or considered to be immune activating, and b)- bispecifics not considered to be agonistic and that do not bridge two target cells (e.g. Hemlibra).”
And AstraZeneca recommended that FDA better clarify cases when FDA may request a comparison of the bispecific antibody to an approved monospecific product directed against the same antigenic target to inform the risk-benefit assessment of the bispecific antibody. The firm also sought reassurances that such a comparison request would be made early in a development program and would be applicable only to an FDA-approved monoclonal antibody acting against one of the same targets of the bispecific.