Producers of biopharmaceuticals are finding that the assessment of critical quality attributes is increasingly a matter of evaluating post-translational modifications (PTMs), especially glycosylation.
One such producer, the contract manufacturer Fujifilm Diosynth Biotechnologies, treats PTMs as indicators of process and product consistency. In fact, Min Zhang, Ph.D., the company’s principal scientist for upstream process development, uses the terms “quality” and “PTM” nearly interchangeably.
Bioprocessors and contractors such as Fujifilm have a wealth of experience with PTMs, at least in certain contexts—late in development and through manufacturing. Data, however, is scarce in other contexts—preclinical and early clinical trials.
“In many cases, we are limited to using knowledge of PTMs from a generic antibody as the standard,” admits Dr. Zhang. One example consists of high-mannose glycans, which are associated with very short clearance. As experience accumulates, desirable molecular attributes are based more on the specific molecule and its performance in studies.
The focus on PTMs throughout development underscores the iterative nature
of process development. Developers know which PTMs, particularly glycosylations, are associated with desirable and undesirable attributes, and appropriately try to overexpress or eliminate them.
Dr. Zhang counts protein folding/misfolding and aggregation as independently significant PTMs, even though process conditions and not the usual cell-derived post-translational factors may be responsible. Immunogenicity caused by aggregation is one of the major factors influencing late clinical-stage failures.
Upstream processing, including culture conditions, media, and feed, are known to influence PTMs, but no formula exists for dialing in quality attributes. Process interventions are, as Dr. Zhang puts it, “the million dollar question,” as almost any upstream factor affects quality.
“That includes molecule design, cell line, and process conditions.” Even such pedestrian values as dissolved oxygen and pH are relevant. There is no single way to guarantee quality attributes within spec, but Dr. Zhang assures that “we have many different tools available.”