Pre-clinical pharmacology and mechanism of action of SG3199, the pyrrolobenzodiazepine (PBD) dimer warhead component of antibody-drug conjugate (ADC) payload tesirine

Abstract

Synthetic pyrrolobenzodiazepine (PBD) dimers, where two PBD monomers are linked through their aromatic A-ring phenolic C8-positions via a flexible propyldioxy tether, are highly efficient DNA minor groove cross-linking agents with potent cytotoxicity. PBD dimer SG3199 is the released warhead component of the antibody-drug conjugate (ADC) payload tesirine (SG3249), currently being evaluated in several ADC clinical trials. SG3199 was potently cytotoxic against a panel of human solid tumour and haematological cancer cell lines with a mean GI50 of 151.5 pM. Cells defective in DNA repair protein ERCC1 or homologous recombination repair showed increased sensitivity to SG3199 and the drug was only moderately susceptible to multidrug resistance mechanisms. SG3199 was highly efficient at producing DNA interstrand cross-links in naked linear plasmid DNA and dose-dependent cross-linking was observed in cells. Cross-links formed rapidly in cells and persisted over 36 hours. Following intravenous (iv) administration to rats SG3199 showed a very rapid clearance with a half life as short as 8 minutes. These combined properties of cytotoxic potency, rapid formation and persistence of DNA interstrand cross-links and very short half-life contribute to the emerging success of SG3199 as a warhead in clinical stage ADCs.

Characterization of Disulfide Bond Rebridged Fab–Drug Conjugates Prepared Using a Dual Maleimide Pyrrolobenzodiazepine Cytotoxic Payload

“…SG3710 contains two maleimide‐(polyethylene glycol) 8 ‐valine‐alanine‐ para ‐aminobenzoic acid linkers at each of the two symmetrical N10 positions of the PBD (Figure b). The warhead (i.e., the sequence‐selective DNA minor‐groove cross‐linker) of SG3710 is SG3199 (depicted in blue in Figure ), which is also the warhead of tesirine (SG3249). SG3199 is released from SG3710, and from SG3249, in the lysosomal compartment upon cleavage by cathepsin B.…”

“…SG3199 is released from SG3710, and from SG3249, in the lysosomal compartment upon cleavage by cathepsin B. After translocation to the nucleus and insertion in the DNA minor groove, an aminal bond is formed through nucleophilic attack of the N2 of a guanine base at the electrophilic C11 position on the SG3199 …”

Bispecific Antibodies and Antibody–Drug Conjugates for Cancer Therapy: Technological Considerations

“…Other common ADC payloads such as MMAE [126] and maytansinoids [107] are also substrates for MDR1 and induce upregulation of drug transporters in cancer cells upon ADC treatment. In contrast, PBD dimers [118] and exatecan [127] are not efficiently pumped out by this mechanism, which may in part explain the sensitivity of T-DM1-resistant cancer cells to trastuzumab deruxtecan [128] and the increased interest in these classes of ADC payloads.…”

“…PBDs are a class of antitumor/antibiotic natural compounds produced by actinomycetes [116] and capable of selectively binding to the minor groove of the DNA double helix at a 5 -(A/G)G(A/G)-3 sequence to form a covalent bond to the amino group of guanine base [117]. Synthetically produced PBD dimers exhibit potent cytotoxicity by crosslinking DNA strands, and a PBD dimer, SG3199 (Figure 2c), could inhibit the growth of various human cancer cell lines with subnanomolar GI 50 (drug concentration at 50% growth inhibition) [118]. The cytotoxicity of PBD dimer depends on the structure of PBD core and exocyclic substituents, as well as the structure and length of the dimerization linker [119].…”

“…The cytotoxicity of PBD dimer depends on the structure of PBD core and exocyclic substituents, as well as the structure and length of the dimerization linker [119]. Rovalpituzumab tesirine (Rova-T; an anti-DLL3 ADC) is an example of an ADC with PBD dimer payload; once internalized, the linker of its tesirine payload is cleaved and the cytotoxic drug SG3199 is released into the cytosol [118]. Although Rova-T was withdrawn from phase 3 trials due to the lack of survival benefit, many PBD dimer-conjugated ADCs are in earlier phases of clinical trials to exploit the exceptionally potent cytotoxicity of this class of payload molecules [119].…”