Antibody-Mediated Delivery of Chimeric BRD4 Degraders. Part 2: Improvement of In Vitro Antiproliferation Activity and In Vivo Antitumor Efficacy

Abstract

Heterobifunctional compounds that direct the ubiquitination of intracellular proteins in a targeted manner via coopted ubiquitin ligases have enormous potential to transform the field of medicinal chemistry. These chimeric molecules, often termed proteolysis-targeting chimeras (PROTACs) in the chemical literature, enable the controlled degradation of specific proteins via their direction to the cellular proteasome. In this report, we describe the second phase of our research focused on exploring antibody−drug conjugates (ADCs), which incorporate BRD4-targeting chimeric degrader entities. We employ a new BRD4-binding fragment in the construction of the chimeric ADC payloads that is significantly more potent than the corresponding entity utilized in our initial studies. The resulting BRD4-degrader antibody conjugates exhibit potent and antigen-dependent BRD4 degradation and antiproliferation activities in cell-based experiments. Multiple ADCs bearing chimeric BRD4-degrader payloads also exhibit strong, antigen-dependent antitumor efficacy in mouse xenograft assessments that employ several different tumor models.

Light-Controllable PROTACs for Temporospatial Control of Protein Degradation

“…One way to achieve targeted degradation of protein is to specifically deliver PROTACs into cancer cells, by taking advantage of the receptors expressed on the membrane of cancer cells, but not of normal cells. Recently, the antibody drug-conjugate (ADC) approach has been adopted for delivering PROTACs into cancer cells that expressing cancer-specific membrane-anchored receptors, such as HER2 ( Dragovich et al, 2020 , 2021a , b ; Maneiro et al, 2020 ; Pillow et al, 2020 ). A major disadvantage of antibody-conjugated PROTAC is its relatively high molecule weight and weak stability.…”

“…An alternative approach for controllable action of PROTACs in cancer cells could be taking advantage of cancer-specific receptors or transporters, such as HER2 and FOLR1 ( Scaranti et al, 2020 ) for the guided delivery of PROTACs into cancer, but not normal cells. To this end, other types of third generation PROTACs, including antibody-conjugated PROTACs ( Dragovich et al, 2020 , 2021a , b ; Maneiro et al, 2020 ; Pillow et al, 2020 ) and folate-PROTAC ( Liu et al, 2021 ), have been recently developed, which specifically deliver PROTAC to cancer cells, thus avoiding potential toxicity to normal cells. Compared with the light-controllable PROTACs, folate-PROTAC ( Liu et al, 2021 ) have relatively higher molecule weight of over 1,000 Da, and antibody-conjugated PROTACs ( Dragovich et al, 2020 , 2021a , b ; Maneiro et al, 2020 ; Pillow et al, 2020 ) are macromolecule drug that could only be administrated by injection.…”

“…To this end, other types of third generation PROTACs, including antibody-conjugated PROTACs ( Dragovich et al, 2020 , 2021a , b ; Maneiro et al, 2020 ; Pillow et al, 2020 ) and folate-PROTAC ( Liu et al, 2021 ), have been recently developed, which specifically deliver PROTAC to cancer cells, thus avoiding potential toxicity to normal cells. Compared with the light-controllable PROTACs, folate-PROTAC ( Liu et al, 2021 ) have relatively higher molecule weight of over 1,000 Da, and antibody-conjugated PROTACs ( Dragovich et al, 2020 , 2021a , b ; Maneiro et al, 2020 ; Pillow et al, 2020 ) are macromolecule drug that could only be administrated by injection. Taken together, further studies are needed to make these third generation PROTACs (light-controllable PROTACs, antibody-conjugated PROTACs and folate-PROTAC) more practical in clinic.…”

Site-Specific Antibody Conjugation to Engineered Double Cysteine Residues

“…Although highly-potent cytotoxins allow ADCs with a DAR of two, higher DAR conjugates may broaden the range of the efficacy towards cancer cells expressing low level of tumor-specific antigens [ 8 ]. There are also needs for antibody conjugates with high DAR when they are coupled with payloads other than cytotoxins [ 24 , 25 , 26 ].…”

In Silico Modeling and Scoring of PROTAC-Mediated Ternary Complex Poses

“…Results of HAPOD scoring within the same ternary system and across different systems indicated that the four crystal ternary poses all show an occupancy score of >70 and T score >380 K, while non-native poses generally did not. Looking further into this finding, we applied HAPOD to measure occupancy and T scores for all the available VHL and CRBN-containing ternary crystal structures 35.…”