Synthesis and biological evaluation of novel pyrrolo[2,1-c][1,4]benzodiazepine prodrugs for use in antibody-directed enzyme prodrug therapy

Glucarpidase (carboxypeptidase G2): Biotechnological production, clinical application as a methotrexate antidote, and placement in targeted cancer therapy

Patients receiving high-dose methotrexate (HDMTX) for malignancies are exposed to diverse complications, including nephrotoxicity, hepatotoxicity, mucositis, myelotoxicity, neurological symptoms, and death. Glucarpidase is a recombinant carboxypeptidase G2 (CPG2) that converts MTX into nontoxic metabolites. In this study, the role of vector type, gene optimization, orientation, and host on the expression of CPG2 is investigated. The effectiveness of various therapeutic regimens containing glucarpidase is classified and perspectives on the dose adjustment based on precision medicine are provided. Conjugation with cell-penetrating peptides, human serum albumin, and polymers such as PEG and dextran for delivery, higher stability, and production of the biobetter variants of CPG2 is highlighted. Conjugation of CPG2 to F(ab՜)2 or scFv antibody fragments against tumor-specific antigens and the corresponding prodrugs for tumor-targeted drug delivery using the antibody-directed enzyme prodrug therapy (ADEPT) is communicated. Trials to reduce the off-target effects and the possibility of repeated ADEPT cycles by adding pro-domains sensitive to tumor-overexpressed proteases, antiCPG2 antibodies, CPG2 mutants with immune-system-unrecognizable epitopes, and protective polymers are reported. Intracellular cpg2 gene expression by gene-directed enzyme prodrug therapy (GDEPT) and the concerns regarding the safety and transfection efficacy of the GDEPT vectors are described. A novel bifunctional platform using engineered CAR-T cell micropharmacies, known as Synthetic Enzyme-Armed KillER (SEAKER) cells, expressing CPG2 to activate prodrugs at the tumor niche is introduced. Taken together, integrated data in this review and recruiting combinatorial strategies in novel drug delivery systems define the future directions of ADEPT, GDEPT, and SEAKER cell therapy and the placement of CPG2 therein.

Antibody-drug conjugates (ADCs) delivering pyrrolobenzodiazepine (PBD) dimers for cancer therapy

INTRODUCTION

The rationally designed pyrrolobenzodiazepine (PBD) dimers emerged around ten years ago as a new class of drug component for antibody-drug conjugates (ADC). They produce highly cytotoxic DNA cross-links, exploiting a completely different cellular target to the auristatin and maytansinoid tubulin inhibitor classes and a different mode of DNA damage to other DNA interacting warheads such as calicheamicin.

AREAS COVERED

The properties which make the PBD dimers suitable warheads for ADCs, and the development of the two main payload structures talirine and tesirine, are discussed. The clinical experience with the twenty PBD dimer-containing ADCs to enter the clinic is reviewed, with a focus on vadastuximab talirine and rovalpituzumab tesirine, both of which were discontinued following pivotal studies, and loncastuximab tesirine and camidanlumab tesirine which are progressing towards approval.

EXPERT OPINION

Reviewing the clinical efficacy and safety data from almost forty clinical trials of PBD dimer-containing ADCs highlights the complexities and challenges of ADC early clinical development. It enables some conclusions to be made about reasons for failure and suggests strategies to optimise the future clinical development of this promising class of ADCs in a rapidly expanding field.

1,4-Diazepines: A Review on Synthesis, Reactions and Biological Significance

Background:

1,4-Diazepines are two nitrogen containing seven membered heterocyclic compounds and associated with a wide range of biological activities. Due to its medicinal importance, scientists are actively involved in the synthesis, reactions and biological evaluation of 1,4-diazepines since number of decades.

Objective:

The primary purpose of this review is to discuss the synthetic schemes and reactivity of 1,4- diazepines. This article also describes biological aspects of 1,4-diazepine derivatives, that can be usefully exploited for the pharmaceutical sector.

Conclusion:

This review summarizes the abundant literature on synthetic routes, chemical reactions and biological attributes of 1,4-diazepine derivatives. We concluded that 1,4-diazepines have significant importance due to their biological activities like antipsychotic, anxiolytic, anthelmintic, anticonvulsant, antibacterial, antifungal and anticancer. 1,4-diazepine derivatives with significant biological activities could be explored for potential use in the pharmaceutical industries.

Pyrrolobenzodiazepine Dimers as Antibody–Drug Conjugate (ADC) Payloads

The pyrrolobenzodiazepine (PBD) ring system was first discovered in the 1960s and is found in several naturally occurring potent anti-tumour antibiotics. The mode of action of PBDs involves sequence-selective [purine–guanine–purine (PuGPu)] alkylation in the minor groove of DNA through covalent binding from guanine N2 to the PBD C11-position. Dimerization of the PBD ring system gives molecules that can cross-link DNA, which leads to a substantial increase in potency and DNA binding affinity and an extension of sequence-selectivity compared with monomers. PBD dimers feature as the cytotoxic component of numerous ADCs being evaluated in clinical trials. PBD-ADC clinical candidates loncastuximab tesirine, camidanlumab tesirine and rovalpituzumab tesirine employ a PBD N10 linkage while vadastuximab talirine uses a C2-linkage. The PBD dimer scaffold is versatile and offers many opportunities to diversify the ADC platform, with extensive research being performed worldwide to develop the next generation of PBD payload–linker molecules. The search for new PBD payload–linker molecules has mainly focused on changes in payload structure (e.g. PBD C2 modification and macrocyclisation), alternative conjugation strategies (e.g. haloacetamides, ‘click’ approaches and pyridyl disulphides), non-peptide triggers in the linker (e.g. disulphides) and non-cleavable derivatives (i.e. payload release through antibody degradation).

One-pot tandem cyclisation to pyrrolo[1,2-a][1,4]benzodiazepines: a modified approach to the Pictet-Spengler reaction

We have reported a one-pot two-step methodology for the synthesis of highly condensed heterocycles, pyrrolo[1,2-a][1,4]benzodiazepines, by a modified Pictet-Spengler reaction under mild conditions in a short time. Our approach has a few advantages over the conventional two components synthesis as it is step and atom economic, environmentally benign and a convergent synthetic method. We have discussed here the broad substrate scope of this novel methodology.

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 in vitro 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.

The development of pyrrolobenzodiazepines as antitumour agents

INTRODUCTION

DNA interacting agents play a major role in cancer chemotherapy, either as single agents, in combination drug regimens, or as components of novel targeted therapies. The search for more selective and efficacious drugs that can deliver critical DNA damage with minimal side effects continues.

AREAS COVERED

The development of the pyrrolobenzodiazepines (PBDs) from their discovery as natural products in the 1960s, through synthetic PBD monomers, PBD hybrids and conjugates, and PBD dimers is described. The latter molecules are capable of forming sequence selective, non-distorting and potently cytotoxic DNA interstrand cross-links in the minor groove of DNA. In particular, the development of PBD dimer SJG-136 (SG2000), currently in Phase II clinical trials, is presented. Potential future cancer therapeutic applications of PBDs, including their use as components of targeting strategies, are also discussed.

EXPERT OPINION

The culmination of over four decades of study on structure-activity relationships of PBDs has led to a detailed understanding of how to introduce structural modification to enhance biological activity and potency. The challenge for the next phase in the development of the PBDs is to harness this activity and potency in a new generation of cancer therapeutics.

Development of pyrrolo[2,1-c][1,4]benzodiazepine beta-galactoside prodrugs for selective therapy of cancer by ADEPT and PMT

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a class of well-studied DNA-interactive agents with a potential for use in the treatment of cancer. The clinical utility of these molecules is limited because of the lack of selectivity for tumor tissues, high reactivity of the pharmacophoric imine functionality, low water solubility, and stability. To address the shortcomings, especially the lack of selectivity, associated with the molecules, two new beta-galactoside prodrugs of PBDs have been synthesized and evaluated for their potential use in selective therapy of solid tumors by ADEPT and PMT protocols. The preliminary studies reveal the prodrugs to be much less toxic compared to the parent moieties. These prodrugs are activated by E. coli beta-galactosidase (EC 3.2.1.23) to form the active cytotoxic moiety signifying their utility in ADEPT of cancer. One of the significant outcomes of the present study is the toxification of the prodrug 1 a by the endogenous beta-galactosidase of human liver cancer cells (Hep G2) to form the cytotoxic moiety, enabling selective therapy of hepatocellular carcinoma. Another important property of these molecules is their enhanced water solubility and stability, which are essential for a molecule to be an effective drug.

Antibody-directed enzyme prodrug therapy (ADEPT) for cancer

Antibody-directed enzyme prodrug therapy was conceived as a means of restricting the action of cytotoxic drugs to tumor sites. Since antigenic targets were a central component of the approach, colonic cancer, with its virtually universal expression of carcinoembryonic antigen at the cellular level, presented an obvious starting point. The principle of antibody-directed enzyme prodrug therapy is to use an antibody directed at a tumor-associated antigen to vector an enzyme to tumor sites. The enzyme should be retained at tumor sites after it has cleared from blood and normal tissues. A nontoxic prodrug, a substrate for the enzyme, is then given and, by cleaving an inactivating component from the prodrug, a potent cytotoxic agent is generated. One of the potential advantages of such a system is that a small cytotoxic agent, generated within a tumor site, is much more diffusible than a large antibody molecule. Moreover, failure to express the target antigen by cancer cells does not protect them from the bystander action of the cytotoxic agent. This review will primarily consider the studies of the London group since this is the only group that has so far reported clinical trials and it is only through clinical trials that the requirements of a successful antibody-directed enzyme prodrug therapy system can be identified.