Antibody-guided localized activation of bioorthogonal protodrugs via click chemistry

Abstract Shasqi is developing a platform to activate drugs at a specific site in the body, thus enhancing their efficacy while minimizing systemic toxicity and adverse drug events (ADEs). Most drugs are administered systemically and spread throughout the body. Due to lack of specificity for the pathological site, high doses are required to achieve

effective therapeutic concentrations, causing toxicity and ADEs at sites of the body where they are not needed. Each year, there are approximately 1.2 million reports of ADEs in the U.S. alone, representing over 5% of all hospitalized patients. The overall costs of ADE-related morbidity and mortality are thought to exceed $177 billion.

ADEs also contribute to the 90% failure rate of drug candidates due to the inability to achieve therapeutic concentrations at the target site or intolerable side effects. To overcome these critical limitations, Shasqi designed the Click Activated Protodrugs (CAP) platform to achieve higher concentrations of active drugs at

specific pathological sites while minimizing systemic toxicity. CAP consists of an activating agent that is targeted to a disease site and a protodrug that is administered systematically. At the target site, the activating agent selectively and rapidly captures the protodrug via a bioorthogonal click chemistry reaction, followed by local

release of active drug. The first-generation CAP system used an injectable sodium hyaluronate (NaHA) biopolymer as the activating agent and doxorubicin (Dox) for the protodrug. This system is now being tested in a Phase 2a trial in patients with injectable solid tumors. Over 8 dose escalation cohorts, a dose-limiting toxicity

has not been observed, even at doses up to 12-times the molar equivalent of conventional Dox per cycle. This demonstrates the striking effectiveness of the CAP platform at limiting drug-related toxicities. Shasqi now seeks to develop a second-generation (Gen2) platform with an antigen-targeted version of the activating agent to

enable local activation of the protodrug at multiple sites, including locations not reachable by injection. As a proof of concept of this technology, Shasqi has demonstrated through conducting Phase I-equivalent studies the dose- dependent tumor regression in a HER+ gastric cancer model through HER2-targeting of a protodrug of the

chemotherapeutic monomethyl auristatin E (MMAE). For this Direct to Phase II project Shasqi will further advance this system by undertaking four specific aims: 1) developing and testing novel HER2-targeted activating agent conjugates in vivo, 2) confirming efficacy of selected conjugate with TCO-MMAE in a syngeneic HER2+

breast cancer model, 3) performing pharmacokinetic (PK) studies and dosing optimization, and 4) GLP manufacturing of protodrug and cell line development for HER2 Fab-Tz to enable toxicology studies. These aims will identify novel antigen-targeted structures for use in Shasqi’s Gen2 CAP and will advance an initial product

toward the clinic. This will provide a better understanding of the antigen-targeted activating agents in the platform, which could be used in the future to develop site-directed treatments for other indications, including antibiotics for site-specific infections, autoimmunity, and localized anti-inflammatory and pain management.