SGN-CD228A Is an Investigational CD228-Directed Antibody-Drug Conjugate with Potent Antitumor Activity across a Wide Spectrum of Preclinical Solid Tumor Models.

SGN-CD228A is an investigational antibody-drug conjugate (ADC) directed to melanotransferrin (CD228, MELTF, MFI2, p97), a cell-surface protein first identified in melanoma. SGN-CD228A consists of a humanized antibody, hL49, with high specificity and affinity for CD228 that is stably conjugated to 8 molecules of the clinically validated microtubule-disrupting agent monomethyl auristatin E (MMAE) via a novel glucuronide linker. We performed comprehensive IHC studies, which corroborated published RNA sequencing data and confirmed low CD228 expression in normal tissues and high expression in several cancers, including melanoma, squamous non-small cell lung cancer (NSCLC), triple-negative breast cancer (TNBC), colorectal cancer, and pancreatic cancer. SGN-CD228A was efficiently internalized in various tumor cell types, and its cytotoxic activity was dependent on CD228 expression and internalization and intrinsic sensitivity to the MMAE payload. Compared with the valine-citrulline dipeptide linker, the novel glucuronide linker increased the cellular retention of MMAE in vitro and conferred improved antitumor activity against melanoma cell lines in vitro and in vivo. In addition, SGN-CD228A was active across melanoma, TNBC, and NSCLC cell line- and patient-derived xenograft models with heterogeneous antigen expression. In vivo, CD228 expression was important for response to SGN-CD228A but was not well correlated across all tumor types, suggesting that other factors associated with ADC activity are important. Overall, SGN-CD228A is a CD228-directed, investigational ADC that employs innovative technology and has compelling preclinical antitumor activity. SGN-CD228A is investigated in a Phase I clinical trial (NCT04042480) in patients with advanced solid tumors.

Novel Auristatins with High Bystander and Cytotoxic Activities in Drug Efflux-positive Tumor Models.

Auristatins, a class of clinically validated anti-tubulin agents utilized as payloads in antibody-drug conjugates, are generally classified by their membrane permeability and the extent of cytotoxic bystander activity on neighboring cells after targeted delivery. The drugs typically fall within two categories: membrane permeable monomethyl auristatin E-type molecules with high bystander activities and susceptibility to efflux pumps, or charged and less permeable monomethyl auristatin F (MMAF) analogs with low bystander activities and resistance to efflux pumps. Herein, we report the development of novel auristatins that combine the attributes of each class by having both bystander activity and cytotoxicity on multidrug-resistant (MDR+) cell lines. Structure-based design focused on the hydrophobic functionalization of the N-terminal N-methylvaline of the MMAF scaffold to increase cell permeability. The resulting structure-activity relationships of the new auristatins demonstrate that optimization of hydrophobicity and structure can lead to highly active free drugs and antibody-drug conjugates with in vivo bystander activities.

De novo design of potent and resilient hACE2 decoys to neutralize SARS-CoV-2.

We developed a de novo protein design strategy to swiftly engineer decoys for neutralizing pathogens that exploit extracellular host proteins to infect the cell. Our pipeline allowed the design, validation, and optimization of de novo human angiotensin-converting enzyme 2 (hACE2) decoys to neutralize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The best monovalent decoy, CTC-445.2, bound with low nanomolar affinity and high specificity to the receptor-binding domain (RBD) of the spike protein. Cryo-electron microscopy (cryo-EM) showed that the design is accurate and can simultaneously bind to all three RBDs of a single spike protein. Because the decoy replicates the spike protein target interface in hACE2, it is intrinsically resilient to viral mutational escape. A bivalent decoy, CTC-445.2d, showed ~10-fold improvement in binding. CTC-445.2d potently neutralized SARS-CoV-2 infection of cells in vitro, and a single intranasal prophylactic dose of decoy protected Syrian hamsters from a subsequent lethal SARS-CoV-2 challenge.

De novo design of ACE2 protein decoys to neutralize SARS-CoV-2.

There is an urgent need for the ability to rapidly develop effective countermeasures for emerging biological threats, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the ongoing coronavirus disease 2019 (COVID-19) pandemic. We have developed a generalized computational design strategy to rapidly engineer de novo proteins that precisely recapitulate the protein surface targeted by biological agents, like viruses, to gain entry into cells. The designed proteins act as decoys that block cellular entry and aim to be resilient to viral mutational escape. Using our novel platform, in less than ten weeks, we engineered, validated, and optimized de novo protein decoys of human angiotensin-converting enzyme 2 (hACE2), the membrane-associated protein that SARS-CoV-2 exploits to infect cells. Our optimized designs are hyperstable de novo proteins (∼18-37 kDa), have high affinity for the SARS-CoV-2 receptor binding domain (RBD) and can potently inhibit the virus infection and replication in vitro. Future refinements to our strategy can enable the rapid development of other therapeutic de novo protein decoys, not limited to neutralizing viruses, but to combat any agent that explicitly interacts with cell surface proteins to cause disease.