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

Advances with antibody-drug conjugates in breast cancer treatment

Antibody-drug conjugate-based therapy for treatment of cancer has attracted much attention because of its enhanced efficacy against numerous cancer types. Commonly, an ADC includes a mAb linked to a therapeutic payload. Antibody, linker and payload are the three main components of ADCs. The high specificity of antibodies is integrated with the strong potency of payloads in ADCs. ADCs with potential cytotoxic small molecules as payloads, generate antibody-mediated cancer therapy. Recently, ADCs with DNA-damaging agents have shown favor over microtubule-targeting agents as payloads. Although ADC resistance can be a barrier to effectiveness, several ADC therapies have been either approved or are in clinical trials for cancer treatment. The ADC-based treatments of breast cancers, particularly TNBC, MDR and metastatic breast cancers, have shown promise in recent years. This review discusses ADC drug designs, and developed for different types of breast cancer including TNBC, MDR and metastatic breast cancer.

Acquired Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) combine the tumor selectivity of antibodies with the potency of cytotoxic small molecules thereby constituting antibody-mediated chemotherapy. As this inherently limits the adverse effects of the chemotherapeutic, such approaches are heavily pursued by pharma and biotech companies and have resulted in four FDA (Food and Drug Administration)-approved ADCs. However, as with other cancer therapies, durable responses are limited by the fact that under cell stress exerted by these drugs, tumors can acquire mechanisms of escape. Resistance can develop against the antibody component of ADCs by down-regulation/mutation of the targeted cell surface antigen or against payload toxicity by up-regulation of drug efflux transporters. Unique resistance mechanisms specific for the mode of action of ADCs have also emerged, like altered internalization or cell surface recycling of the targeted tumor antigen, changes in the intracellular routing or processing of ADCs, and impaired release of the toxic payload into the cytosol. These evasive changes are tailored to the specific nature and interplay of the three ADC constituents: the antibody, the linker, and the payload. Hence, they do not necessarily endow broad resistance to ADC therapy. This review summarizes preclinical and clinical findings that shed light on the mechanisms of acquired resistance to ADC therapies.

Bouganin, an Attractive Weapon for Immunotoxins

Bougainvillea (Bougainvillea spectabilis Willd.) is a plant widely used in folk medicine and many extracts from different tissues of this plant have been employed against several pathologies. The observation that leaf extracts of Bougainvillea possess antiviral properties led to the purification and characterization of a protein, named bouganin, which exhibits typical characteristics of type 1 ribosome-inactivating proteins (RIPs). Beyond that, bouganin has some peculiarities, such as a higher activity on DNA with respect to ribosomal RNA, low systemic toxicity, and immunological properties quite different than other RIPs. The sequencing of bouganin and the knowledge of its three-dimensional structure allowed to obtain a not immunogenic mutant of bouganin. These features make bouganin a very attractive tool as a component of immunotoxins (ITs), chimeric proteins obtained by linking a toxin to a carrier molecule. Bouganin-containing ITs showed very promising results in the experimental treatment of both hematological and solid tumors, and one bouganin-containing IT has entered Phase I clinical trial. In this review, we summarize the milestones of the research on bouganin such as bouganin chemico-physical characteristics, the structural properties and de-immunization studies. In addition, the in vitro and in vivo results obtained with bouganin-containing ITs are summarized.

Enzymatic conjugation using branched linkers for constructing homogeneous antibody–drug conjugates with high potency

An efficient enzymatic method using branched linkers was developed for the construction of potent homogeneous antibody–drug conjugates.