Fractionated Dosing Improves Preclinical Therapeutic Index of Pyrrolobenzodiazepine-Containing Antibody Drug Conjugates

Abstract

To use preclinical models to identify a dosing schedule that improves tolerability of highly potent pyrrolobenzodiazepine dimers (PBDs) antibody drug conjugates (ADCs) without compromising antitumor activity. A series of dose-fractionation studies were conducted to investigate the pharmacokinetic drivers of safety and efficacy of PBD ADCs in animal models. The exposure-activity relationship was investigated in mouse xenograft models of human prostate cancer, breast cancer, and gastric cancer by comparing antitumor activity after single and fractionated dosing with tumor-targeting ADCs conjugated to SG3249, a potent PBD dimer. The exposure-tolerability relationship was similarly investigated in rat and monkey toxicology studies by comparing tolerability, as assessed by survival, body weight, and organ-specific toxicities, after single and fractionated dosing with ADCs conjugated to SG3249 (rats) or SG3400, a structurally related PBD (monkeys). Observations of similar antitumor activity in mice treated with single or fractionated dosing suggests that antitumor activity of PBD ADCs is more closely related to total exposure (AUC) than peak drug concentrations (). In contrast, improved survival and reduced toxicity in rats and monkeys treated with a fractionated dosing schedule suggests that tolerability of PBD ADCs is more closely associated with than AUC. We provide the first evidence that fractionated dosing can improve preclinical tolerability of at least some PBD ADCs without compromising efficacy. These findings suggest that preclinical exploration of dosing schedule could be an important clinical strategy to improve the therapeutic window of highly potent ADCs and should be investigated further. .

Design and characterization of homogenous antibody-drug conjugates with a drug-to-antibody ratio of one prepared using an engineered antibody and a dual-maleimide pyrrolobenzodiazepine dimer

“…In general, the predominant toxicity in rats treated with PBD ADCs is dose-dependent bone marrow suppression. 19 Similarly, in this study, we observed dosedependent decreases in white blood cell and platelet counts that peaked on day 15 post-dose. Importantly, the degree of bone marrow suppression was similar in animals treated with 2 mg/kg of trastuzumab-C239i-SG3249 and those treated with 4 mg/kg of trastuzumab-Flexmab-SG3710 ( Figure S9).…”

“…Hinrichs and colleagues have further elucidated the importance of balancing anti-tumor activity with tolerability when advancing PBD-based ADCs through the preclinical pipeline. 19 After previous fractionated dosing regimens of ADCs based on tubulininhibitors, the authors used fractionated dosing with the PBDbased ADC 1C1-C239i-SG3249 (anti-EphA2, DAR = 2) at 0.5 mg/ kg and compared the anti-tumor effects to those of single-dose administrations of 1C1-C239i-SG3249 ADC at 1 mg/kg in preclinical models of breast, gastric, and pancreatic cancer. 19 They observed that, although dose-fractionation effectively lowers the highest peak serum drug concentrations, equivalent total exposure was maintained, which improved the tolerability of the PBD-based ADCs while maintaining their anti-tumor activity.…”

“…19 After previous fractionated dosing regimens of ADCs based on tubulininhibitors, the authors used fractionated dosing with the PBDbased ADC 1C1-C239i-SG3249 (anti-EphA2, DAR = 2) at 0.5 mg/ kg and compared the anti-tumor effects to those of single-dose administrations of 1C1-C239i-SG3249 ADC at 1 mg/kg in preclinical models of breast, gastric, and pancreatic cancer. 19 They observed that, although dose-fractionation effectively lowers the highest peak serum drug concentrations, equivalent total exposure was maintained, which improved the tolerability of the PBD-based ADCs while maintaining their anti-tumor activity. Fractionated dosing could further enhance the tolerability of trastuzumab-Flexmab-SG3710 by reducing organ-specific toxicities observed with PBDs, such as lower peripheral blood counts and bone marrow suppression.…”

“…The SG3199 warhead was subsequently linked to a maleimidocaproyl-polyethylene glycol (PEG 8 ) linker via a self-immolative valine-alanine dipeptide at the N10 position to generate the SG3249 payload, which was used to prepare ADCs. [19][20][21][22][23][24] Drawing upon the success of SG3249 as an ADC payload, we hypothesized that functionalization of the symmetrical N10 nitrogen with an additional cathepsin-B cleavable valine-alanine dipeptide and PEG 8 -maleimide linker would result in a symmetrical dual-maleimide PBD dimer, SG3710 (Figure 1), which could be used to re-bridge two adjacent cysteines, such as the ones at the immunoglobulin G1 (IgG1) hinge. The symmetrical nature of the SG3710 payload offers several key structural features that not only expand the applicability of PBD dimers, but also offer enhancement of the biochemical properties of previous versions of PBD dimers, such as SG3249, which is composed of a single chemical linker (Figure 1).…”

Antibody–Drug Conjugates: Future Directions in Clinical and Translational Strategies to Improve the Therapeutic Index

“…Furthermore, the success of fractionated dosing schedules with gemtuzumab ozogamicin or inotuzumab ozogamicin suggests that the same approach can be used with other ADCs. Indeed, a preclinical study of ADCs with pyrrolobenzodiazepine (PBD) warheads demonstrated that the in vivo efficacy and area under the concen-tration curve were similar regardless of whether the ADC was delivered as a single dose or as fractionated weekly doses, but that fractionated dosing reduced the plasma concentration of the drug and therefore reduced maximum serum concentration-driven toxicities (38).…”