CytomX Therapeutics said today it will receive a $15 milestone payment from AbbVie for advancing a cancer-fighting Probody™–drug conjugate (PDC) being developed by the companies into Good Laboratory Practice (GLP) toxicology studies toward filing an Investigational New Drug (IND) application next year.

CX-2029 is a PDC designed to target CD71, also known as transferrin receptor 1 (TfR1), on tumor cells while sparing healthy cells by localizing the drug candidate’s activity primarily to cancer tissue.

CD71 is highly and homogeneously expressed on many solid and blood tumor types. While that would make CD71 an ideal target for antibody–drug conjugate strategies, the target is present on most normal cells—a challenge the companies say can be addressed by developing a therapeutic based on CytomX’s Probody platform.

Probody therapeutics are designed to remain inactive until they are activated by proteases in the tumor microenvironment. According to CytomX, the therapeutics bind selectively to tumors and avoid binding to healthy tissue, thus minimizing toxicity and potentially create safer, more effective therapies.

CX-2029 is being developed to treat a range of cancers through an up-to-$500 million collaboration the companies launched in April 2016. Also that year, CytomX presented proof-of-concept data at the American Association for Cancer Research (AACR)’s annual meeting demonstrating the creation of a therapeutic window for a CD-71-targeting PDC.

CytomX is leading preclinical and early clinical development, while AbbVie has agreed to lead later development and commercialization, with global late-stage development costs shared between the two companies

AbbVie agreed to pay CytomX $30 million upfront and up to $470 million in payments tied to achieving development, regulatory, and commercial milestones. CytomX is also eligible to receive a share of U.S. profits, as well as tiered double-digit royalties on net product sales outside of the U.S.

CytomX also retains a co-promotion option in the U.S.

“Rapid progression of the CX-2029 program to this important milestone has been enabled by our close collaboration with AbbVie, and we look forward to advancing this first-in-class molecule into the clinic,” CytomX President and CEO Sean McCarthy, D.Phil., said in a statement.

The collaboration also gives AbbVie exclusive worldwide rights to develop and commercialize PDCs against up to two additional undisclosed targets. One of those targets was selected in March, CytomX disclosed in its Form 10-Q quarterly filing for the first quarter of this year.

Should AbbVie exercise those rights, CytomX could receive additional milestone and royalty payments per target on any resulting products.