Pentacyclic triterpenoids with nitrogen- and sulfur-containing heterocycles: synthesis and medicinal significance.

Triterpenoids are natural compounds with a variety of biological activities and are usually produced by plants as secondary metabolites. In recent decades, scientists focused on the properties of triterpenoids have discovered many activities, such as antitumor, antiviral, antimicrobial, anti-inflammatory and others. Thousands of new triterpenoids with various skeletal modifications have now been synthesized. One of the most important modifications is the formation of a new heterocyclic ring. The simple fact that the vast majority of currently used drugs are heterocyclic compounds has encouraged a lot of researches to synthesize analogous triterpenoid derivatives in order to find new molecules with higher activities and consequently optimize their pharmacological profile. The biological properties of triterpenoid heterocycles are very promising and many of them have been studied, especially as antitumor agents. This review is mainly focused on the synthesis of various types of nitrogen and occasionally sulfur-containing heterocyclic triterpenoids for their potential use as future drugs in medicine and in addition discusses their overall biological activities.

Preparation of Conjugates of Cytotoxic Lupane Triterpenes with Biotin.

To better understand the mechanism of action of antitumor triterpenes, we are developing methods to identify their molecular targets. A promising method is based on combination of quantitative proteomics with SILAC and uses active compounds anchored to magnetic beads via biotin-streptavidin interaction. We developed a simple and fast solid-phase synthetic technique to connect terpenes to biotin through a linker. Betulinic acid was biotinylated from three different conjugation sites for use as a standard validation tool since many molecular targets of this triterpene are already known. Then, a set of four other cytotoxic triterpenoids was biotinylated. Biotinylated terpenes were similarly cytotoxic to their nonbiotinylated parents, which suggests that the target identification should not be influenced by linker or biotin. The developed solid-phase synthetic approach is the first attempt to use solid-phase synthesis to connect active triterpenes to biotin and is applicable as a general procedure for routine conjugation of triterpenes with other molecules of choice.

Design and Preclinical Evaluation of a Novel B7-H4-Directed Antibody-Drug Conjugate, AZD8205, Alone and in Combination with the PARP1-Selective Inhibitor AZD5305.

PURPOSE: We evaluated the activity of AZD8205, a B7-H4-directed antibody-drug conjugate (ADC) bearing a novel topoisomerase I inhibitor (TOP1i) payload, alone and in combination with the PARP1-selective inhibitor AZD5305, in preclinical models. EXPERIMENTAL DESIGN: IHC and deep-learning-based image analysis algorithms were used to assess prevalence and intratumoral heterogeneity of B7-H4 expression in human tumors. Several TOP1i-ADCs, prepared with Val-Ala or Gly-Gly-Phe-Gly peptide linkers, with or without a PEG8 spacer, were compared in biophysical, in vivo efficacy, and rat toxicology studies. AZD8205 mechanism of action and efficacy studies were conducted in human cancer cell line and patient-derived xenograft (PDX) models. RESULTS: Evaluation of IHC-staining density on a per-cell basis revealed a range of heterogeneous B7-H4 expression across patient tumors. This informed selection of bystander-capable Val-Ala-PEG8-TOP1i payload AZ14170133 and development of AZD8205, which demonstrated improved stability, efficacy, and safety compared with other linker-payload ADCs. In a study of 26 PDX tumors, single administration of 3.5 mg/kg AZD8205 provided a 69% overall response rate, according to modified RECIST criteria, which correlated with homologous recombination repair (HRR) deficiency (HRD) and elevated levels of B7-H4 in HRR-proficient models. Addition of AZD5305 sensitized very low B7-H4-expressing tumors to AZD8205 treatment, independent of HRD status and in models representing clinically relevant mechanisms of PARPi resistance. CONCLUSIONS: These data provide evidence for the potential utility of AZD8205 for treatment of B7-H4-expressing tumors and support the rationale for an ongoing phase 1 clinical study (NCT05123482). See related commentary by Pommier and Thomas, p. 991.

Evaluation of Pyrrolobenzodiazepine-Loaded Nanoparticles: A Targeted Drug Delivery Approach.

We describe the development and evaluation of pyrrolobenzodiazepines (PBDs) in poly(dl-lactide-co-glycolide) and lipid nanoparticle drug delivery systems. We have established that the partition coefficient (LogP) of PBD is a key influencer of the encapsulation efficiency in nanoparticle systems, with higher LogP values associated with higher encapsulation efficiencies toward increased drug payload delivery and better antitumor efficacy. Cytotoxicity assays demonstrated that compounds with higher LogP values demonstrated higher 50% inhibitory concentration values than the free drug. In vivo efficacy studies in mice demonstrated that a single injection of nanoparticle PBD formulations could inhibit tumor growth for nearly 3 weeks, whereas the free drug failed to inhibit growth. Importantly, mice treated with PBD-loaded nanoparticles did not experience significant loss of body weight. These data demonstrate that nanoparticles containing PBD molecules can be used as an alternative to the widely used antibody drug conjugate approach in delivering cytotoxic PBDs.

Synthesis of cytotoxic 2,2-difluoroderivatives of dihydrobetulinic acid and allobetulin and study of their impact on cancer cells.

In this article, we describe the preparation and cytotoxic properties of a small focused library of lupane and 18α-oleanane triterpenoids that contain a combination of two structural motifs known to enhance the biological activities. First, we introduced two fluorine atoms to position 2 of the skeleton. Second, we synthesized a set of hemiester prodrugs, which were intended to increase the solubility and activity. Starting from betulin, we obtained two hydroxyketones (derivatives of dihydrobetulinic acid and allobetulin) and their fluorination using DAST provided 2,2-difluoro-3-oxo-compounds as the main products. Then the 3-oxo group in each derivative was reduced by NaBH4 to obtain 3ß-hydroxy compounds suitable for modifying by various hemiesters. We prepared 21 compounds, 11 of them new, their cytotoxicity was tested on T lymphoblastic leukemia CCRF-CEM cells first and the most active derivatives were selected for screening on another six tumor and two non-tumor cell lines. All of them showed selectivity against cancer lines with therapeutic index between 2 and 8. All hemiesters had activity in the same range as the free hydroxyl derivatives and they would be suitable prodrugs for future in vivo experiments. Interestingly, all hemiesters of 2,2-difluorodihydrobetulonic acid had higher activity against p53 knock-out p53-/- cancer cell line than against the non-mutated analog. In active derivatives, the cell cycle was analyzed by flow cytometry and several compounds slowed down cell cycle progression through G0/G1 or S-phase.