Antibody-Drug Conjugates (ADCs) Derived from Interchain Cysteine Cross-Linking Demonstrate Improved Homogeneity and Other Pharmacological Properties over Conventional Heterogeneous ADCs.

Conventional antibody-drug conjugates (ADCs) are heterogeneous mixtures of chemically distinct molecules that vary in both drugs/antibody (DAR) and conjugation sites. Suboptimal properties of heterogeneous ADCs have led to new site-specific conjugation methods for improving ADC homogeneity. Most site-specific methods require extensive antibody engineering to identify optimal conjugation sites and introduce unique functional groups for conjugation with appropriately modified linkers. Alternative nonrecombinant methods have emerged in which bifunctional linkers are utilized to cross-link antibody interchain cysteines and afford ADCs containing four drugs/antibody. Although these methods have been shown to improve ADC homogeneity and stability in vitro, their effect on the pharmacological properties of ADCs in vivo is unknown. In order to determine the relative impact of interchain cysteine cross-linking on the therapeutic window and other properties of ADCs in vivo, we synthesized a derivative of the known ADC payload, MC-MMAF, that contains a bifunctional dibromomaleimide (DBM) linker instead of a conventional maleimide (MC) linker. The DBM-MMAF derivative was conjugated to trastuzumab and a novel anti-CD98 antibody to afford ADCs containing predominantly four drugs/antibody. The pharmacological properties of the resulting cross-linked ADCs were compared with analogous heterogeneous ADCs derived from conventional linkers. The results demonstrate that DBM linkers can be applied directly to native antibodies, without antibody engineering, to yield highly homogeneous ADCs via cysteine cross-linking. The resulting ADCs demonstrate improved pharmacokinetics, superior efficacy, and reduced toxicity in vivo compared to analogous conventional heterogeneous ADCs.

DLL4 blockade inhibits tumor growth and reduces tumor-initiating cell frequency.

Previous studies have shown that blocking DLL4 signaling reduced tumor growth by disrupting productive angiogenesis. We developed selective anti-human and anti-mouse DLL4 antibodies to dissect the mechanisms involved by analyzing the contributions of selectively targeting DLL4 in the tumor or in the host vasculature and stroma in xenograft models derived from primary human tumors. We found that each antibody inhibited tumor growth and that the combination of the two antibodies was more effective than either alone. Treatment with anti-human DLL4 inhibited the expression of Notch target genes and reduced proliferation of tumor cells. Furthermore, we found that specifically inhibiting human DLL4 in the tumor, either alone or in combination with the chemotherapeutic agent irinotecan, reduced cancer stem cell frequency, as shown by flow cytometric and in vivo tumorigenicity studies.