DeBouganin Diabody Fusion Protein Overcomes Drug Resistance to ADCs Comprised of Anti-Microtubule Agents

Abstract

Antibody drug conjugates (ADC), comprised of highly potent small molecule payloads chemically conjugated to a full-length antibody, represent a growing class of therapeutic agents. The targeting of cytotoxic payloads via the specificity and selectivity of the antibody has led to substantial clinical benefits. However, ADC potency can be altered by mechanisms of resistance such as overexpression of efflux pumps or anti-apoptotic proteins. DeBouganin is a de-immunized variant of bouganin, a ribosome-inactivating protein (RIP) that blocks protein synthesis, thereby leading to apoptosis. When conjugated to trastuzumab (T-deB), deBouganin was more potent than ado-trastuzumab-emtansine (T-DM1) and unaffected by resistance mechanisms to which DM1 is susceptible. To further highlight the differentiating mechanism of action of deBouganin, HCC1419 and BT-474 tumor cells that survived T-DM1 or trastuzumab-MMAE (T-MMAE) treatment were treated with an anti-HER2 C6.5 diabody-deBouganin fusion protein or T-deB. C6.5 diabody-deBouganin and T-deB were potent against HCC1419 and BT-474 cells that were resistant to T-DM1 or T-MMAE killing. The resistant phenotype involved MDR pumps, Bcl-2 family members, and the presence of additional unknown pathways. Overall, the data suggest that deBouganin is effective against tumor cell resistance mechanisms selected in response to ADCs composed of anti-microtubule payloads.

Acquired Resistance to Antibody-Drug Conjugates

“…Obviously, the less two agents have in common, the less likely cross-resistance will occur. A recombinant immunotoxin consisting of the anti-HER2 diabody C6.5 fused to a de-immunized form of the plant toxin bouganin has been shown to overcome cross-resistance to both T-DM1 and a trastuzumab-MMAE conjugate due to its completely different mode of action [63]. Although the auristatin-based ADCs, as well as the immunotoxin both target HER2, the epitope of the C6.5 diabody does not overlap with that of trastuzumab, thereby allowing simultaneous treatment without competition for target binding.…”

Bouganin, an Attractive Weapon for Immunotoxins

“…In the same year, Chooniedass and co-workers described the engineering and biological activity of de-bouganin genetically linked to an anti-HER2 C6.5 diabody (deB-C6.5-diab). On breast cancer cell lines, the DeB-C6.5-diab and de-bouganin-trastuzumab conjugates showed greater cytotoxic activity than auristatin E- and emtansine-trastuzumab conjugates, demonstrating that de-bouganin is effective against tumor cell resistance mechanisms selected in response to immunoconjugates composed by anti-microtubule agents [ 49 ]. Main results obtained in preclinical experiments are summarized in Table 2 .…”

Special Issue: Ribosome-Inactivating Proteins—Commemorative Issue in Honor of Professor Fiorenzo Stirpe

“…In view of applications as anti-cancer agents, it is important that the selectivity, immunogenicity, half-life and toxicity of RIP-based conjugates are investigated. Therefore Chooniedass et al [ 5 ] studied the engineering and biological activity of different conjugates containing the plant toxin deBouganin for their interaction with a panel of breast cancer cell lines. In an attempt to adapt ribosome-inactivating proteins for clinical use, Sun et al [ 6 ] investigated the production, identification and anti-tumour activity of mono-pegylated ribosome-inactivating proteins from Momordica charantia .…”