Led by strong demand for oncology drugs, high-potency manufacturing continues to be an active area of investment, particularly
for antibody drug conjugates (ADCs). ADCs, which consist of a monoclonal antibody (mAb) chemically linked to a small-molecule
therapeutic, are a promising modality for certain therapeutic areas. ADCs are attracting the interest of both small and large
pharmaceutical companies in their drug-development efforts as well as contract manufacturers specializing in high-potency
Patricia Van Arnum
The potential of ADCs was affirmed earlier this year when Roche's Genentech received FDA approval for Kadcyla (ado-trastuzumab
emtansine or T-DM1) for treating HER2-positive metastatic breast cancer (mBC). The drug combines trastuzumab (Herceptin),
which targets human epidermal growth factor receptor 2 (HER2) receptors with a maytansine derivative DM1, a small-molecule
cytotoxin that binds to tubulin to prevent microtubule formation, through a stable thioether linker (4-[N-maleimidomethyl] cyclohexane-1-carboxylate) (1–3). Roche/Genentech has more than 25 ADCs in development, with eight ADCs
in Phase I or Phase II studies for different types of cancer.
Kadcyla is the first FDA-approved ADC for treating HER2-positive mBC, and one of the few commercially approved ADCs. In August
2011, FDA approved Adcetris (brentuximab vedotin), codeveloped by Seattle Genetics and Millennium Pharmaceuticals (now part
of Takeda Pharmaceutical). Adcetris consists of three parts: the chimeric IgG1 antibody cAC10, specific for human CD30, the
microtubule-disrupting agent monomethyl auristatin E (MMAE), and a protease-cleavable linker that covalently attaches MMAE
to cAC10 (1, 2). Before the approval of Adcetris, the only other ADC approved by FDA was Mylotarg (gemtuzumab ozogamicin),
approved more than 10 years ago in 2000. The drug, an anti-CD33 mAb conjugated to the cytotoxin calicheamicin, was developed
by Wyeth (now part of Pfizer) and granted accelerated approval in 2000 but was voluntarily withdrawn by Pfizer in 2010 because
a required Phase III trial failed to demonstrate a survival advantage (1, 3).
Pfizer suffered another setback in its ADC development program earlier this year, when in May, it discontinued a Phase III
study for one of its investigational ADCs, inotuzumab ozogamicin, for treating non-Hodgkin lymphoma. The drug continues to
be evaluated as a treatment in adult acute lymphoblastic leukemia. Inotuzumab ozogamicin was originally developed by Celltech
(now UCB) before Pfizer acquired all manufacturing and development rights.
Pfizer, like other pharmaceutical companies, is partnering with smaller biopharmaceutical companies to advance ADCs. In June
2013, Pfizer formed a global strategic collaboration, worth up to $635 million, with CytomX to develop and commercialize multiple
CytomX Probody Drug Conjugates (PDCs), propertiary ADCs of CytomX. Pfizer has exclusive rights to pursue development and commercialization
of select PDCs. The companies will work together on preclinical research. Pfizer is responsible for development and potential
commercialization of any selected PDCs with CytomX eligible to receive upfront, research, and preclinical milestone payments
as well as potential tiered royalties.