用于体外和体内治疗实体瘤的海葱苷A糖基类似物的临床前发现

Cancer persists as one of the leading causes of mortality in the US, accounting for over 2 million new cases and 611,000 deaths in 2024. In parallel, several small-molecule drugs are currently in development for the treatment of malignancies. Within those, natural products, their synthetic analogs, or other derivatives, account for about 50% of all FDA-approved anticancer small molecules. Several naturally-derived cardiac glycosides, including digoxin, digitoxin, and proscillaridin A, have been originally identified as cardiomyocyte modulators and are currently being investigated for their anti-cancer properties. These cardiac glycosides are generally classified into cardenolides and bufadienolides, which bear butenolide and pyrone D-ring functionality, respectively, and have exhibited remarkable in vitro toxicity in various cancerous cell lines. As simple modifications on steroidal small molecules have demonstrated success in augmenting bioavailability or enhancing downstream biological activities, we sought to prepare synthetic analogs of proscillaridin A, a bufadienolide isolated from the genus Scilla. We synthesized five analogs of proscillaridin A bearing acetate esters, silyl ethers, or dimethyl ketals to investigate how ketalization, acetylation, and/or silylation of the A-ring allylic glycoside might alter its anti-cancer properties. The antiproliferative activity of these compounds was evaluated alongside proscillaridin A and two model cardiac glycosides - digoxin and digitoxin - across several breast, colorectal, liver, and ovarian cancer cell lines. Through a diverse panel of cell viability and cytotoxicity experiments, reporter assays, and cell cycle and protein marker analysis by flow cytometry, we find that ketalization of the glycan of proscillaridin A provides similar, and in some cases enhanced, in vitro potency. Subsequently, to evaluate the preclinical applicability of these compounds in inhibiting solid tumor growth, we found that direct, intraperitoneal injection of proscillaridin A and its analogs demonstrated reasonably potent antitumor activity in a murine mammary cancer model, albeit with dose-limiting ADMET properties. This study establishes the foundation for further in vitro and in vivo evaluations of cardiac glycosides for the treatment of cancer.