Synthesis and evaluation of highly releasable and structurally stable antibody-SN-38-conjugates

Abstract

Camptothecins, traditional chemotherapy drugs, have been clinically used in antibody-drug conjugates (ADCs), which refreshes the recognition that ADCs preferably incorporate highly potent payloads. However, SN-38, active metabolite of irinotecan from camptothecins, tended to be incorporated into ADCs with an unstable acid sensitive bond, not with the widely used Cathepsin B (CTSB) sensitive bond, which may pose the risk of off-target. Herein, we reported a novel strategy to construct highly releasable and structurally stable SN-38-conjugates, in which CTSB linkers directly connected to the 10-OH group through ether bond, not to the common 20-OH group of lactones of SN-38. In this paper, rapid release of SN-38 was skillfully demonstrated by utilizing the fluorescence properties of SN-38. The SN-38-ether-ADC displayed highly stable serum stability with the half-life over 10 days. Moreover, the drug-antibody-ratio (DAR) of ADC could be elevated to 7.1 through the introduction of polyethylene glycol (PEG) moieties without aggregation. The optimized ADC exhibited potent in vitro activities up to 5.5 nM, comparable to SN-38. Moreover, this ADC group significantly delayed tumor growth in vivo . In conclusion, the novel strategy has the potential to promote the development of SN38-ADCs and enrich the conjugation approaches for hydroxyl-bearing payloads.

Development of a Targeted SN-38-Conjugate for the Treatment of Glioblastoma

“…In the context of an SN-38 ether-based drug delivery system, data from stability studies at pH 7.4 show that the structural integrity of the conjugate is maintained within the period evaluated. This is similar to literature reports. , These data suggest that the conjugate could be stable to degradation while in circulation. This stability is essential to prevent premature drug release, which could lead to unintended toxic effects on healthy cells.…”

“…This is similar to literature reports. 47,62 These data suggest that the conjugate could be stable to degradation while in circulation. This stability is essential to prevent premature drug release, which could lead to unintended toxic effects on healthy cells.…”

“…To a solution of Boc-Ala-PABA ( 3 ) (3.5 g, 11.8 mmol) in dry THF (20 mL) on an ice bath was slowly added phosphorus tribromide (PBr 3 ) (3.2 g, 11.8 mmol) in anhydrous DCM (20 mL). 47 The progress of the reaction was monitored by TLC. After 3 h, the reaction was complete, and the solution was transferred into cold water (250 mL).…”

“…Boc-Ala-PAB-SN-38 (4) (0.45 g, 0.672 mmol) was dissolved in 20% TFA in dichloromethane to initiate Boc deprotection. 47 The mixture was stirred at room temperature for 2 h and monitored via TLC ( Scheme 1 ). The crude product was obtained by evaporation.…”

Research Progress of SN38 Drug Delivery System in Cancer Treatment

“…At present, this type of toxin has been approved as an SN38-based ADC, IMMU-132. 70 In addition, IMMU-130, IMMU-140, and others are currently in the development stage ( Table S3 ).…”