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The CH2 Domain Scaffold – ABDURINS™

RCT is developing a new biologics platform based on engineered CH2 domains (CH2D) called ABDURINS™. CH2Ds are small and durable protein scaffolds derived from monoclonal IgG antibodies, as seen below.

CH2 Domain Scaffold - IgG Antibodies

More than 30 monoclonal antibodies, three antibody-derived fragments and two antibody-drug conjugates have been approved in the United States and Europe for the treatment of various diseases. Although these products demonstrate significant clinical benefit in certain indications, such large molecules are limited by their poor penetration into tissues (e.g. solid tumors) and poor or absent binding to epitopes on the surface of some molecules that are accessible only by molecules of smaller size. Therefore, small and stable protein scaffolds may have distinct advantages as targeted therapeutic binders over antibodies against certain targets. In addition, small scaffolds may be better suited as scaffold-drug conjugates for the delivery of various warheads.

Antibody-like fragments are attractive as protein scaffolds for developing novel therapeutics due to their smaller size (12-50 kDa) compared with full-sized antibodies (150 kDa). The small size leads to greater and more rapid tissue accumulation, and to the ability to better recognize epitopes on protein targets. A major disadvantage of the existing smaller antibody-like scaffolds (less than 50kDa in size) is their short circulating half-life due to rapid renal clearance. Antibody-like scaffolds smaller than 50kDa typically have serum half-lives of less than one hour. A number of approaches are used to increase the serum half-life of the various scaffolds, including fusion to albumin or an Fc and the addition of half-life extension peptides or pegylation. The size advantages, however, are lost because such modifications increase the molecule’s size to avoid renal clearance.

To address the short half-life disadvantage of small antibody-like scaffolds, RCT is developing ABDURINS™ based on variants of the CH2 domain (CH2D). ABDURINS™ are small (12.5kDa) immunoglobulin-derived proteins amenable to loop and beta sheet modifications that enable binding to a target of interest. ABDURINS™ are stable, produced in Pichia or E. coli, and can be used to generate multifunctional molecules or carry toxic warheads. Published data demonstrate that the CH2D has a longer serum half-life (8-16 hrs.) compared to other scaffolds of a similar molecular weight (30 min.) as shown below.


Antibody-drug conjugates (ADCs) have demonstrated impressive clinical results in oncology; however, the extremely long half-life of the antibody (7-21 days) and short half-life of the linkers and drugs (hours) potentially limit the effectiveness of current ADC technology and increase unnecessary toxic side effects. ABDURINS™ have a half-life better suited to linker and drug half-life, and the small size should deliver more of the cytotoxic drug to the tumor than with a conventional ADC. ABDURINS™-Drug Conjugates or Abdurin immunotoxins may represent the next generation of ADC therapeutics with improved efficacy and reduced toxicity.

RCT’s ABDURINS™ platform includes proprietary DNA libraries containing ~1014binding members. These novel libraries are formatted for both phage display and CIS DNA display screening. Through RCT’s partnership with Isogenica (www.isogenica.com), users can access CIS DNA display either by partnering with RCT to perform library screening against a target of interest, or by acquiring the CIS DNA libraries and CIS display technology under a license for in-house screening. CIS DNA display is a powerful system which can screen significantly larger libraries and isolate and optimized binders in a fraction of the time it takes using phage display. RCT also has a partnership with IRBM (www.irbm.it) that allows partners and licensees access to broad ABDURIN™ product discovery and development program through early nonclinical testing.

RCT’s ABDURINS™ Platform licenses provide access to RCT’s libraries and intellectual property, to the NIH’s intellectual property relating to Dr. Dimitri Dimitrov’s CH2D inventions, and to Isogenica’s CIS DNA display screening system. If potential licensees would rather outsource the screening and discovery of high affinity binders to a therapeutic target of interest, Isogenica and IRBM are available to perform these services for partners.

CH2 Domain Scaffold - Advantages