Design and Synthesis of Tesirine, a Clinical Antibody–Drug Conjugate Pyrrolobenzodiazepine Dimer Payload

Pyrrolobenzodiazepine dimers are an emerging class of warhead in the field of antibody–drug conjugates (ADCs). Tesirine (SG3249) was designed to combine potent antitumor activity with desirable physicochemical properties such as favorable hydrophobicity and improved conjugation characteristics. One of the reactive imines was capped with a cathepsin B-cleavable valine-alanine linker. A robust synthetic route was developed to allow the production of tesirine on clinical scale, employing a flexible, convergent strategy. Tesirine was evaluated <i>in vitro</i> both in stochastic and engineered ADC constructs and was confirmed as a potent and versatile payload. The conjugation of tesirine to anti-DLL3 rovalpituzumab has resulted in rovalpituzumab-tesirine (Rova-T), currently under evaluation for the treatment of small cell lung cancer

GC-Targeted C8-Linked Pyrrolobenzodiazepine–Biaryl Conjugates with Femtomolar in Vitro Cytotoxicity and in Vivo Antitumor Activity in Mouse Models

DNA binding 4-(1-methyl-1<i>H</i>-pyrrol-3-yl)­benzenamine (MPB) building blocks have been developed that span two DNA base pairs with a strong preference for GC-rich DNA. They have been conjugated to a pyrrolo­[2,1-<i>c</i>]­[1,4]­benzodiazepine (PBD) molecule to produce C8-linked PBD–MPB hybrids that can stabilize GC-rich DNA by up to 13-fold compared to AT-rich DNA. Some have subpicomolar IC₅₀ values in human tumor cell lines and in primary chronic lymphocytic leukemia cells, while being up to 6 orders less cytotoxic in the non-tumor cell line WI38, suggesting that key DNA sequences may be relevant targets in these ultrasensitive cancer cell lines. One conjugate, <b>7h</b> (KMR-28-39), which has femtomolar activity in the breast cancer cell line MDA-MB-231, has significant dose-dependent antitumor activity in MDA-MB-231 (breast) and MIA PaCa-2 (pancreatic) human tumor xenograft mouse models with insignificant toxicity at therapeutic doses. Preliminary studies suggest that <b>7h</b> may sterically inhibit interaction of the transcription factor NF-κB with its cognate DNA binding sequence

A Potent Anti-CD70 Antibody–Drug Conjugate Combining a Dimeric Pyrrolobenzodiazepine Drug with Site-Specific Conjugation Technology

A highly cytotoxic DNA cross-linking pyrrolobenzodiazepine (PBD) dimer with a valine-alanine dipeptide linker was conjugated to the anti-CD70 h1F6 mAb either through endogenous interchain cysteines or, site-specifically, through engineered cysteines at position 239 of the heavy chains. The h1F6_239C-PBD conjugation strategy proved to be superior to interchain cysteine conjugation, affording an antibody–drug conjugate (ADC) with high uniformity in drug-loading and low levels of aggregation. In vitro cytotoxicity experiments demonstrated that the h1F6_239C-PBD was potent and immunologically specific on CD70-positive renal cell carcinoma (RCC) and non-Hodgkin lymphoma (NHL) cell lines. The conjugate was resistant to drug loss in plasma and in circulation, and had a pharmacokinetic profile closely matching that of the parental h1F6_239C antibody capped with N-ethylmaleimide (NEM). Evaluation in CD70-positive RCC and NHL mouse xenograft models showed pronounced antitumor activities at single or weekly doses as low as 0.1 mg/kg of ADC. The ADC was tolerated at 2.5 mg/kg. These results demonstrate that PBDs can be effectively used for antibody-targeted therapy

Pyrrolobenzodiazepine Dimer Antibody–Drug Conjugates: Synthesis and Evaluation of Noncleavable Drug-Linkers

Three rationally designed pyrrolobenzodiazepine (PBD) drug-linkers have been synthesized via intermediate <b>19</b> for use in antibody–drug conjugates (ADCs). They lack a cleavable trigger in the linker and consist of a maleimide for cysteine antibody conjugation, a hydrophilic spacer, and either an alkyne (<b>6</b>), triazole (<b>7</b>), or piperazine (<b>8</b>) link to the PBD. In vitro IC₅₀ values were 11–48 ng/mL in HER2 3+ SK-BR-3 and KPL-4 (<b>7</b> inactive) for the anti-HER2 ADCs (HER2 0 MCF7, all inactive) and 0.10–1.73 μg/mL (<b>7</b> inactive) in CD22 3+ BJAB and WSU-DLCL2 for anti-CD22 ADCs (CD22 0 Jurkat, all inactive at low doses). In vivo antitumor efficacy for the anti-HER2 ADCs in Founder 5 was observed with tumor stasis at 0.5–1 mg/kg, 1 mg/kg, and 3–6 mg/kg for <b>6</b>, <b>8</b>, and <b>7</b>, respectively. Tumor stasis at 2 mg/kg was observed for anti-CD22 <b>6</b> in WSU-DLCL2. In summary, noncleavable PBD-ADCs exhibit potent activity, particularly in HER2 models