Kevin J. Hamblett

Effects of drug loading on the antitumor activity of a monoclonal antibody drug conjugate.

Purpose: An antibody-drug conjugate consisting of monomethyl auristatin E (MMAE) conjugated to the anti-CD30 monoclonal antibody (mAb) cAC10, with eight drug moieties per mAb, was previously shown to have potent cytotoxic activity against CD30+ malignant cells. To determine the effect of drug loading on antibody-drug conjugate therapeutic potential, we assessed cAC10 antibody-drug conjugates containing different drug-mAb ratios in vitro and in vivo. Experimental Design: Coupling MMAE to the cysteines that comprise the interchain disulfides of cAC10 created an antibody-drug conjugate population, which was purified using hydrophobic interaction chromatography to yield antibody-drug conjugates with two, four, and eight drugs per antibody (E2, E4, and E8, respectively). Antibody-drug conjugate potency was tested in vitro against CD30+ lines followed by in vivo xenograft models. The maximum-tolerated dose and pharmacokinetic profiles of the antibody-drug conjugates were investigated in mice. Results: Although antibody-drug conjugate potency in vitro was directly dependent on drug loading (IC50 values E8<E4<E2), the in vivo antitumor activity of E4 was comparable with E8 at equal mAb doses, although the E4 contained half the amount of MMAE per mAb. E2 was also an active antitumor agent but required higher doses. The maximum-tolerated dose of E2 in mice was at least double that of E4, which in turn was twice that of E8. MMAE loading affected plasma clearance, as E8 cleared 3-fold faster than E4 and 5-fold faster than E2. Conclusions: By decreasing drug loading per antibody, the therapeutic index was increased demonstrating that drug loading is a key design parameter for antibody-drug conjugates.

Abstract 61: Zymelink drug conjugate platform: redefining the therapeutic window for ADCs

Antibody drug conjugates (ADCs) combine the specificity of monoclonal antibodies with potent antineoplastic small molecules, and promise efficacy without the systemic toxicity of chemotherapy. Despite this tremendous potential, most clinical ADCs have failed to provide sufficient therapeutic benefit before the onset of off-target dose-limiting platform toxicities. Here we report the development of proprietary protease cleavable N-acyl sulfonamide linked hemiasterlin and auristatin payloads, Zymelink, that allow the generation of an efficacious ADC platform with improved tolerability. Both Zymelink drug-linkers were conjugated via maleimides to endogenous cysteines. As Zymelink drug-linkers are more polar than maleimide valine citrulline monomethyl auristatin E drug-linker, the resulting ADCs can be produced with potential advantages in PK, efficacy and safety. The resulting ADCs exhibit potent in vitro cytotoxicity. A trastuzumab-based ADC prepared with Zymelink drug-linker and demonstrated at least equivalent efficacy compared to a trastuzumab-based ADC prepared with MMAE, promoting durable complete regressions in a patient-derived xenograft model. Zymelink hemiasterlin and auristatin ADCs were tolerated at 5-6 fold higher doses compared to a MMAE ADC in cynomolgus monkeys. The maximum tolerated dose of the MMAE ADC was just 3 mg/kg based on severe neutropenia. Zymelink hemiasterlin ADC was tolerated at 15 mg/kg with no evidence of neutropenia or elevations in transaminases. Zymelink auristatin ADC was tolerated at 18 mg/kg based on increased levels of transaminases at 24 mg/kg. Moreover, Zymelink ADCs exhibited greater serum exposure at equivalent doses. These results suggest Zymelink ADCs have a greatly expanded therapeutic window compared to MMAE conjugates. Citation Format: Stuart Barnscher, John Babcook, Jamie Rich, Geoff Winters, Graham Garnett, Andrea Hernandez, Vincent Fung, Kevin Yin, Kevin Hamblett, Rupert Davies. Zymelink drug conjugate platform: redefining the therapeutic window for ADCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 61. doi:10.1158/1538-7445.AM2017-61