Antibody-drug conjugates (ADCs) are a promising new therapeutic modality having demonstrated clinical efficacy in the treatment of cancer. While ADCs have better exposures than their constitutive chemotypes, it is important that they maintain the favorable pharmacokinetics of their antibody backbones. Previous work incorporating PEG into the drug-linker as a sidechain helped to mask the hydrophobicity of the chemotypes, resulting in improved ADC exposures in rats compared to ADCs with non-PEGylated drug-linkers. The current studies were aimed at understanding the effect of PEG chain length on ADC efficacy, tumor and tissue distribution in tumor bearing mice.

Efficacy and biodistribution of radiolabeled ADCs with 2, 4, 8, 12 and 24 PEG units in the drug-linker as a side chain were investigated in SCID mice bearing a subcutaneous xenograft of L540cy tumor cells. A non-PEGylated ADC was used as control. Antibody based radioactivity in plasma, tumor, liver, lung, kidney, spleen and brain were measured over 14 days. MMAE, the free drug released from the ADC, was measured by mass spectrometry. Reduction in tumor weight was determined as a measure of efficacy. Compartmental analysis of the plasma exposure data was conducted to understand the change in rate constants with change in PEG chain length.

ADCs with side chain PEGylated drug-linkers had greater plasma and tumor exposures than the non-PEGylated control ADC. Increasing PEG chain length in the linker led to increased plasma and tumor exposures, and lower plasma clearances. Tumor distribution was binary with ADCs with 2 and 4 PEG units in the linker showing similar tumor exposures while the ADCs with 8, 12 and 24 PEG units providing similar but significantly higher tumor exposures. ADCs with 8, 12 and 24 PEG units in the linker had significantly higher tumor to plasma exposure ratios than ADCs with 2 and 4-PEG units in the drug-linker. The reduction in tumor weights was also binary. ADCs with 2 and 4 PEG units provided a 35-45% decrease in tumor weights while ADCs with 8, 12 and 24 PEG units in the linker provided 75-85% reduction in tumor weights. The non-PEGylated control ADC decreased the tumor weights by 11%.

In general, PEGylated ADCs increased the extent of tissue distribution, but the tissue to plasma ratios remained the same indicating that the increased tissue exposures was a function of increased plasma exposures. However, PEGylated ADC tumor exposure increased beyond that expected based solely on the increase in plasma exposure.

Incorporation of PEG as a side chain into the drug-linker improved the tumor disposition of ADCs with little alteration in tissue disposition. ADCs with 8, 12 and 24 PEG units in the drug-

linker showed preferential uptake into tumor, but not the tissues as evidenced by tumor (or tissue) to plasma exposure ratios. Over all, the ADCs with 8, 12 and 24 PEG units in the linker provided the optimal combination of tumor distribution, efficacy and tissue distribution.

Citation Format: Nagendra V. Chemuturi, Martha Anderson, Julia Cochran, Thomas Pires, Josh Hunter, David Meyer, Jason Neale, Alice Chin, Paul Pittman, Cindy Balasubramanian, Francisco Zapata, Jessica Simmons, Robert Lyon, Steve Alley. Effect of PEG chain length on antibody-drug conjugate tumor and tissue distribution in tumor bearing xenograft mice [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 4075. doi:10.1158/1538-7445.AM2017-4075