Platinum(II) complexes with steroidal esters of l-methionine and l-histidine: Synthesis, characterization and cytotoxic activity

Advancements in steroidal Pt(II) & Pt(IV) derivatives for targeted chemotherapy (2000-2023)

One of the key strategies in chemotherapy involves crosslinking the DNA strands of cancer cells to impede their replication, with platinum (Pt) coordination compounds being a prominent class and cisplatin being its major representative. Steroidal ligands tethered to DNA interactive Pt core act as drug carriers for targeted therapy. While crosslinking of nuclear or mitochondrial DNA strands using coordination complexes has been studied for years, there remains a lack of comprehensive reviews addressing the advancements made in steroidal-Pt derivatives. This review specifically focuses on advancements made in steroid-tethered structural derivatives of Pt(II) or prodrug Pt(IV) for targeted chemotherapy, synthesized between 2000 and 2023. This period was deliberately chosen due to the widespread use of computational techniques for more accurate structure-based drug-design in last two decades. This review discusses the strategy behind tethering steroidal ligands such as testosterone, estrogen, bile acids, and cholesterol to the central DNA interactive Pt core through specific linker groups. The steroidal ligands function as drug delivery vehicles of DNA interactive Pt core and bind with their respective target receptors or proteins that are often overexpressed in cancer cells, thus enabling targeted delivery of Pt moiety to interact with DNA. We discussed structural features such as the location of the linker group on the steroid, the mono, bi, and tridentate configuration of the chelating arm in coordination with Pt, and the rigidity and flexibility of the linker group. The comparative in vitro, in vivo activities, and relative binding affinities of the designed compounds against standard Pt drugs are also discussed. We also provided a critique of observed trends and shortcomings. Our review will provide insights into future molecular designing of targeted DNA crosslinkers and their structural optimization to achieve desired drug properties. From this analysis, we proposed further research directions leading to the future of targeted chemotherapy.

Design, synthesis and biological evaluation of novel 2-alkylidene 19-norcalcitriol analogs

Continuing our studies aimed at A-ring modified vitamin D compounds, we designed novel 19-norcalcitriol derivatives bearing at C-2 pegylated chains of different lengths. The terminal fragments of these substituents contain hydroxyls or moieties possessing nitrogen and/or sulfur atoms capable of transition metal ions complexation. Also, two conjugate-type platinum(II) complexes of 19-norcalcitriol were obtained in which l-methionine served as chelating moiety. The convergent synthesis of the target 19-norcalcitriol analogs involved several steps with the crucial one being condensation of A-ring phosphine oxide and the known Grundmann ketone by Wittig-Horner reaction. Further elaboration of the 2-alkylidene substituent provided all final compounds which were then tested to determine their affinity for the vitamin D receptor and cytotoxic activity.

Synthesis of Gemini analogs of 19-norcalcitriol and their platinum(II) complexes

Hormonally active vitamin D₃ metabolite, calcitriol, plays an important role in calcium-phosphate homeostasis, immune system actions and cell differentiation. Although anticancer activity of calcitriol is well documented and thousands of its analogs have been synthesized, none has been approved as a potential drug against cancer. Therefore, we attempted to introduce the cytotoxic effect to the calcitriol molecule by its linking to cisplatin. Herein, we present the synthesis of vitamin D compounds, designed on the basis of molecular modeling and docking experiments to the vitamin D receptor, and characterized by the presence of significantly different two side chains attached to C-20. In this study, a new synthetic approach to Gemini analogs was developed. Preparation of the target 19-norcalcitriol compounds involved separate syntheses of several building blocks (the A-ring, C/D-rings and side-chain fragments). The convergent synthetic strategy was used to combine these components by the different coupling processes, the crucial one being Wittig-Horner reaction of the Grundmann ketone analog with the known 2-methylene A-ring phosphine oxide. Due to the nature of the constructed steroidal side chains (bidentate ligands), which allowed coordination of metal ions, the first conjugate-type platinum(II) complexes of the vitamin D analogs were also successfully prepared and characterized. The target vitamin D compounds, displaying significant affinity for a vitamin D receptor, were assessed in vitro for their anti-proliferative activities towards several cell lines.

Synthesis and anti-tumour, immunomodulating activity of diosgenin and tigogenin conjugates

A series of novel diosgenin (DSG) and tigogenin (TGG) derivatives with diosgenin or tigogenin steroid aglycons linked to levulinic and 3,4-dihydroxycinnamic acids, dipeptides and various amino acids by an ester bond at the C3-oxygen atom of the steroid skeleton has been synthesized. Diosgenyl esters have been prepared by an esterification reaction (DCC/DMAP) of diosgenin with the corresponding acids. All analogues have been evaluated in vitro for their antiproliferative profile against cancer cell lines (MCF-7, MDA-MB-231, PC-3) and human umbilical vein endothelial cells (HUVEC). Analogue2c (l-serine derivative of TGG), the best representative of the series showed IC₅₀ of 1.5 μM (MCF-7), and induced apoptosis in MCF-7 by activating caspase-3/7. The immunomodulatory properties of six synthesized analogues have been determined by examining their effects on the expression of cytokine genes essential for the functioning of the human immune system (IL-1, IL-4, IL-10, IL-12 and TNF-α). Biological evaluation has revealed that new compounds 4c and 16a do not induce the expression of pro-inflammatory cytokines in THP-1 cells after the lipopolysaccharide (LPS) stimulation. They also stimulate the expression of anti-inflammatory IL-10 that acts stronger than diosgenin itself. An in silico ADME properties(absorption, distribution, metabolism, excretion) study was also performed to predict the pharmacokinetic profile of the synthesized compounds. To shed light on the molecular interactions between the synthesized compounds and the glucocorticoid receptor and the estrogen receptor, 2c, 4c and 16a compounds were docked into the active binding sites of these receptors. The in silico and in vitro data suggested that this new group of compounds might be considered as a promising scaffold for further modification of more potent and selective anticancer and immunomodulatory agents.

Peptidomimetics Based On Dehydroepiandrosterone Scaffold: Synthesis, Antiproliferation Activity, Structure-Activity Relationship, and Mechanisms

A series of novel peptidomimetics bearing dehydroepiandrosterone moiety were designed, synthesized, and evaluated for their inhibition activities against cell proliferation. According to the preliminary studies on inhibitory activities, some of the newly prepared compounds indicated significantly inhibition activities against human hepatoma cancer (HepG2), human lung cancer (A549), human melanoma (A875) cell lines compared with the control 5-fluorouracil. Especially, compounds Ii (IC₅₀ < 14 μM) and Ik (IC₅₀ < 13 μM) exhibited obvious inhibition activities against all tested cell lines. The highly potential compound Ik induced apoptosis in HepG2 cells were analyzed by flow cytometry, and the apoptotic effects of compound Ik were further evaluated using Annexin V-FITC/propidium iodide dual staining assay, which revealed these highly potential compounds induced cell death in HepG2 cells at least partly by apoptosis.

Distribution and effect of steroidal saponin derivative WRC3 in B16 melanoma cells

Steroidal saponins have recently attracted attention due to their structural diversity and significant biological activities, including anti‑hyperlipidemic, antibacterial, anti‑inflammatory, immunomodulatory and anti‑HIV activities. In the present study, it was demonstrated that WRC3, a novel saponin derivative, can inhibit B16 cancer cells by inducing apoptotic cell death with an IC50 value of 12.09 µM. The inhibitory effect of WRC3 on B16 cells appears to occur in a time‑ and concentration‑dependent manner. The fluorescence distribution observed by confocal microscopy revealed that WRC3 entered cells and acted in the cytoplasm without causing genetic toxicity. Following administration of WRC3 (2.5, 5.0 and 7.5 g/kg body weight) once a day for 7 days, no obvious abnormalities were observed in the organs of the mice as demonstrated by hematoxylin and eosin staining. Compared with the normal control group, aspartate transaminase (AST), alanine transaminase (ALT), creatine and urea levels in the serum of mice treated with WRC3 (2.5‑7.5 µM) remained unchanged. In conclusion, it was demonstrated that WRC3 can induce cancer cell death without causing genetic toxicity, hepatotoxicity or nephrotoxicity.

New platinum(II) complexes conjugated at position 7α of 17β-acetyl-testosterone as new combi-molecules against prostate cancer: design, synthesis, structure-activity relationships and biological evaluation

Prostate cancer is a major public health problem worldwide and, more specifically, new treatments for hormone-refractory cancers are highly sought by several research groups. Although platinum(II)-based chemotherapy and other strategies grow in interest to treat castration-resistant prostate cancer (CRPC), they still exhibit modest activity on CRPC and overall patient survival. In this study, we designed and prepared new combi-molecules using 17β-acetyl-testosterone and amino acid platinum(II) complexes linked at the position 7α to target and to improve the antiproliferative activity of platinum(II)-based chemotherapy on prostate cancer cells. Twelve chemical intermediates and six new combi-molecules were prepared and characterized. Structure-activity relationships studies show that the platinum complex moiety is essential for an optimal cytocidal activity. Moreover, stereochemistry of the amino acid involved in the platinum complexes had only minor effects on the antiproliferative activity whereas pyridinyl (10a and b) and thiazolyl (10f) complexes exhibited the highest cytocidal activities that are significantly superior to that of cisplatin used as control on human prostate adenocarcinoma LNCaP (AR+), PC3 (AR-) and DU145 (AR-). Compounds 10a, b and f arrested the cell cycle progression in S-phase and induced double strand breaks as confirmed by the phosphorylation of histone H2AX into γH2AX. Compounds 10a and f showed 33 and 30% inhibition, respectively of the growth of HT-1080 tumors grafted onto chick chorioallantoic membranes. Finally, compounds 10a and 10f exhibited low toxicity on the chick embryos (18 and 21% of death, respectively), indicating that these new combi-molecules might be a promising new class of anticancer agents for prostate cancer.

Synthesis, characterization and biological studies of diosgenyl analogues

A series of optical amino acid diosgenyl esters and diosgenyl salicylate conjugates were designed and synthesized to develop new anticancer and anti-inflammatory agents. The analogue 9c that contains an 6-aminohexanoic acid residue at C-3 of diosgenin exhibits higher potency against all three tumor cell lines with IC(50) values ranging from 4.7 μM in C26 cells to 14.6 μM in Hep G2 cells. In addition, seven of newly synthesized compounds significantly inhibit xylene-induced ear edema and exhibit comparable or better anti-inflammatory activities than those of diosgenin and aspirin. Furthermore, preliminary structure-activity relationship studies demonstrate that diosgenyl salicylate conjugates have stronger anti-inflammatory activities than amino acid diosgenyl esters.