Pre-clinical studies of EC2629, a highly potent folate- receptor-targeted DNA crosslinking agent

Abstract

Folate receptor (FR)-targeted small molecule drug conjugates (SMDCs) have shown promising results in early stage clinical trials with microtubule destabilizing agents, such as vintafolide and EC1456. In our effort to develop FR-targeted SMDCs with varying mechanisms of action, we synthesized EC2629, a folate conjugate of a DNA crosslinking agent based on a novel DNA-alkylating moiety. This agent was found to be extremely potent with an in vitro IC50 ~ 100× lower than folate SMDCs constructed with various microtubule inhibitors. EC2629 treatment of nude mice bearing FR-positive KB human xenografts led to cures in 100% of the test animals with very low dose levels (300 nmol/ kg) following a convenient once a week schedule. The observed activity was not accompanied by any noticeable weight loss (up to 20 weeks post end of dosing). Complete responses were also observed against FR-positive paclitaxel (KB-PR) and cisplatin (KB-CR) resistant models. When evaluated against FR-positive patient derived xenograft (PDX) models of ovarian (ST070), endometrial (ST040) and triple negative breast cancers (ST502, ST738), EC2629 showed significantly greater anti-tumor activity compared to their corresponding standard of care treatments. Taken together, these studies thus demonstrated that EC2629, with its distinct DNA reacting mechanism, may be useful in treating FR-positive tumors, including those that are classified as drug resistant. The folate receptor (FR) is a cell surface receptor that is overexpressed by many primary and metastatic cancers, including ovarian, lung and breast cancers 1-4. Covalent conjugation of the vitamin folic acid to various therapeutic-and imaging-based agents has enabled their specific delivery to tumors that express the FR protein 5-7. Therefore, we have been developing folate-targeted small molecule drug conjugates (SMDC's) to potentially enhance the safety and efficacy of anti-cancer agents 8-16. Pyrrolobenzodiazepine (PBD) dimers are a relatively new class of anticancer agents which bind to the minor groove of DNA, where they form covalent aminal crosslinks between the guanine residues with the two imine groups of the PBD 17. The resulting PBD-DNA crosslinks halt progression of replication forks and arrest tumor cells at the G2-M boundary, leading to cellular apoptosis. The unusually high potency of PBD dimers is due to their cell cycle-independent activity and to their minimal distortion of DNA, increasing the chances of evasion of DNA damage repair mechanisms 18. PBD compounds have been tested against a variety of tumors including ovarian cancer, SCLC (small cell lung cancer), and AML (acute myeloid leukemia). The investigational molecule, SJG136, was the first form of PBD dimer tested in clinical studies 19 , and this untargeted agent was found to be associated with dose-limiting hepatotoxicity and vascular leak syndrome. In an attempt to reduce toxicity, antibody drug conjugates (ADCs) of PBD's have been designed, thus combining the potent antitumor activity of the PBD dimer with the targeting...

Therapeutic strategies targeting folate receptor α for ovarian cancer

“…EC2629 is a folate conjugate of a DNA crosslinking agent pyrrolobenzodiazepine (PBD) linked by a novel DNA-alkylating moiety. Preclinical studies demonstrate that EC2629 has antitumor activity in ovarian, endometrial, and triple negative breast cancers ( 112 ). Notably, most ADCs using PBD as the payload are now halted due to excessive toxicity of PBD.…”

Carborane-Containing Folic Acid bis-Amides: Synthesis and In Vitro Evaluation of Novel Promising Agents for Boron Delivery to Tumour Cells

“…Cells of various types of tumours are characterized by active expression of folate receptors (FRs) and are able to accumulate folic acid and its derivatives [26][27][28][29]. Modification of xenobiotics [30][31][32][33][34][35], liposomes [36][37][38][39][40], and nanoparticles [41][42][43][44][45][46] using folic acid is a common way to obtain targeted agents for the tumour treatment and imaging.…”

Optimizing the enzymatic release of MMAE from isoDGR-based small molecule drug conjugate by incorporation of a GPLG-PABC enzymatically cleavable linker

“…Their easier synthesis, the accurate toxin to ligand ratio (compared to the drug to antibody ratio, DAR) and the lower molecular weight that increases cell permeability and decreases accumulation in healthy organs, are the main features that make SMDCs an attractive research field. Folic acid derivatives are considered the first small molecule ligands used for the selective delivery of cytotoxic payloads to tumors overexpressing folate receptor ( Reddy et al, 2020 ). In particular, the compound known as vintafolide (or EC145), in which the folic acid ligand is connected to desacetylvinblastine through a disulfide bond, is in phase III clinical trials (ID: NCT01170650).…”