Melanoma-specific ferrocene esters of the fungal cytotoxin illudin M

Discovery and characterisation of a broderol-like illudin, omphaderol in the mycelial extracts of Omphalotus mexicanus (Omphalotaceae) using UPLC-QTOF-MS and NMR spectroscopy

INTRODUCTION

The genus Omphalotus, in particular the "Jack-O'Lantern mushrooms" Omphalotus illudens and Omphalotus olearius, are famous for the production of the DNA-alkylating illudins. A lesser-known species, Omphalotus mexicanus, native to Central America, also produces cytotoxic illudins S and M, but its minor secondary metabolites are yet to be investigated.

OBJECTIVE

To identify, isolate, and elucidate the structure of novel secondary metabolites of the illudin family in mycelial extracts of O. mexicanus from submerse cultivation.

METHODOLOGY

A fermentation of the fungus in 15 L stirred tank bioreactors is described. Mycelial extracts were separated using a combination of flash chromatography with preparative RP-C18 high-performance liquid chromatography (HPLC). Analysis of metabolites was done using an ultrahigh-performance liquid chromatography ultraviolet diode array detector (UPLC-UV-DAD) system coupled to an electrospray ionisation quadrupole time-of-flight (ESI-QTOF) mass spectrometer. Structures were elucidated using one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance spectroscopy (NMR) techniques followed by comparison of experimental and simulated electronic circular dichroism (ECD) spectra to determine absolute configurations.

RESULTS

Two novel illudin derivatives, for which we propose the names omphaderol (1) and illudaneol B (2), as well as illudaneol (3) and the unusual cyclobutylcyclopentane illudosin (4), were isolated from the mycelia and characterised.

CONCLUSION

Particularly the illudaneol derivatives with their high titers may be potential building blocks for an alternative semisynthetic route to new illudin derivatives with improved medical properties. Additionally, the findings improve the knowledge of minor illudin compounds in the mycelial extract of this fungus and may be of significance for future biosynthetic studies of the illudins.

Ferrocene-Based Drugs, Delivery Nanomaterials and Fenton Mechanism: State of the Art, Recent Developments and Prospects

Ferrocene has been the most used organometallic moiety introduced in organic and bioinorganic drugs to cure cancers and various other diseases. Following several pioneering studies, two real breakthroughs occurred in 1996 and 1997. In 1996, Jaouen et al. reported ferrocifens, ferrocene analogs of tamoxifen, the chemotherapeutic for hormone-dependent breast cancer. Several ferrocifens are now in preclinical evaluation. Independently, in 1997, ferroquine, an analog of the antimalarial drug chloroquine upon the introduction of a ferrocenyl substituent in the carbon chain, was reported by the Biot-Brocard group and found to be active against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Ferroquine, in combination with artefenomel, completed phase IIb clinical evaluation in 2019. More than 1000 studies have been published on ferrocenyl-containing pharmacophores against infectious diseases, including parasitic, bacterial, fungal, and viral infections, but the relationship between structure and biological activity has been scarcely demonstrated, unlike for ferrocifens and ferroquines. In a majority of ferrocene-containing drugs, however, the production of reactive oxygen species (ROS), in particular the OH. radical, produced by Fenton catalysis, plays a key role and is scrutinized in this mini-review, together with the supramolecular approach utilizing drug delivery nanosystems, such as micelles, metal-organic frameworks (MOFs), polymers, and dendrimers.

Palladium and Platinum Complexes of the Antimetabolite Fludarabine with Vastly Enhanced Selectivity for Tumour over Non-Malignant Cells

The purine derivative fludarabine is part of frontline therapy for chronic lymphocytic leukaemia (CLL). It has shown positive effects on solid tumours such as melanoma, breast, and colon carcinoma in clinical phase I studies. As the treatment of CLL cells with combinations of fludarabine and metal complexes of antitumoural natural products, e.g., illudin M ferrocene, has led to synergistically enhanced apoptosis, in this research study different complexes of fludarabine itself. Four complexes bearing a trans-[Br(PPh₃)₂]Pt/Pd fragment attached to atom C-8 via formal η¹-sigma or η²-carbene bonds were synthesised in two or three steps without protecting polar groups on the arabinose or adenine. The platinum complexes were more cytotoxic than their palladium analogues, with low single-digit micromolar IC₅₀ values against cells of various solid tumour entities, including cisplatin-resistant ones and certain B-cell lymphoma and CLL, presumably due to the ten-fold higher cellular uptake of the platinum complexes. However, the palladium complexes interacted more readily with isolated Calf thymus DNA. Interestingly, the platinum complexes showed vastly greater selectivity for cancer over non-malignant cells when compared with fludarabine.

Optimization of the production process for the anticancer lead compound illudin M: downstream processing

Background

Secondary metabolites have played a key role as starting points for drug development programs due to their often unique features compared with synthetically derived molecules. However, limitations related to the discovery and supply of these molecules by biotechnological means led to the retraction of big pharmaceutical companies from this field. The reasons included problems associated with strain culturing, screening, re-discovery, purification and characterization of novel molecules from natural sources. Nevertheless, recent reports have described technical developments that tackle such issues. While many of these reports focus on the identification and characterization of such molecules to enable subsequent chemical synthesis, a biotechnological supply strategy is rarely reported. This may be because production processes usually fall under proprietary research and/or few processes may meet the requirements of a pharmaceutical development campaign. We aimed to bridge this gap for illudin M—a fungal sesquiterpene used for the development of anticancer agents—with the intention to show that biotechnology can be a vital alternative to synthetic processes dealing with small molecules.

Results

We used µL-scale models to develop an adsorption and extraction strategy for illudin M recovery from culture supernatant of Omphalotus nidiformis and these findings were successfully transferred into lab-scale. By adsorbing and eluting the product using a fixed resin-bed we reduced the working volume by ~ 90% and removed the aqueous phase from the process. After a washing step, a highly concentrated illudin M fraction was obtained by isocratic elution with 80% methanol. The fraction was dried and extracted using a water/heptane mixture, enriching illudin M in the heptane phase. From heptane illudin M could be instantly crystalized by concentrating the solution, achieving a final purity > 95%.

Conclusion

We have developed a robust, scalable and low-cost downstream process to obtain highly pure illudin M. By using solid phase extraction we reduced the production of solvent waste. Heptane from the final purification step could be recycled. The reduced amounts of solvents required, and the short purification time render this method a very economic and ecologic alternative to published processes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01886-2.

Optimization of the production process for the anticancer lead compound illudin M: process development in stirred tank bioreactors

Background

The fungal natural products illudin S and M have been investigated as precursors for the development of semisynthetic anticancer agents such as Irofulven (illudin S derivative) which is currently in phase II clinical trials. Recently, illudin M derivatives have shown improved in vitro selectivity towards cancer cells encouraging further investigation. This requires a stable supply of the precursor which is produced by Basidiomycota of the genus Omphalotus. We have recently reported a robust shake flask process for the production of gram quantities of illudin M from Omphalotus nidiformis aiming to transfer that process into stirred tank bioreactors, which can be used in a commercial production set-up. However, process transfer across different systems is not straightforward and particularly challenging when the producer is morphologically complex. There are only a few reports that address the development of bioprocesses for the production of compounds from Basidiomycota as these organisms have not been extensively studied because of their complex life cycles and often are difficult to cultivate under laboratory conditions.

Results

The recently developed shake flask process delivering stable titers of ~ 940 mg L⁻¹ of illudin M was investigated using off-gas analysis to identify critical parameters which facilitated the transfer from shaken into stirred tank bioreactors. Comparable titers to the shake flask process were achieved in 2 L stirred tank bioreactors (1.5 L working volume) by controlling growth of biomass with a carefully timed pH-shift combined with an improved precursor-feeding strategy. A scale-up experiment in a 15 L bioreactor (10 L working volume), resembling the process at 1.5 L resulted in 523 mg L⁻¹ and is the starting point for optimization of the identified parameters at that scale.

Conclusion

By identifying and controlling key process parameters, the production process for illudin M was transferred from shake flasks into 2 L stirred tank bioreactors reaching a comparable titer (> 900 mg L⁻¹), which is significantly higher than any previously reported. The insights obtained from 10 L scale pave the way towards further scale-up studies that will enable a sustainable supply of illudin M to support preclinical and clinical development programs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01870-w.

Optimization of the production process for the anticancer lead compound illudin M: improving titers in shake-flasks

BACKGROUND

The fungal sesquiterpenes Illudin M and S are important base molecules for the development of new anticancer agents due to their strong activity against some resistant tumor cell lines. Due to nonspecific toxicity of the natural compounds, improvement of the pharmacophore is required. A semisynthetic derivative of illudin S (Irofulven) entered phase II clinical trials for the treatment of castration-resistant metastatic prostate cancer. Several semisynthetic illudin M derivatives showed increased in vitro selectivity and improved therapeutic index against certain tumor cell lines, encouraging further investigation. This requires a sustainable supply of the natural compound, which is produced by Basidiomycota of the genus Omphalotus. We aimed to develop a robust biotechnological process to deliver illudin M in quantities sufficient to support medicinal chemistry studies and future preclinical and clinical development. In this study, we report the initial steps towards this goal.

RESULTS

After establishing analytical workflows, different culture media and commercially available Omphalotus strains were screened for the production of illudin M.Omphalotus nidiformis cultivated in a medium containing corn steep solids reached ~ 38 mg L-1 setting the starting point for optimization. Improved seed preparation in combination with a simplified medium (glucose 13.5 g L-1; corn steep solids 7.0 g L- 1; Dox broth modified 35 mL), reduced cultivation time and enhanced titers significantly (~ 400 mg L-1). Based on a reproducible cultivation method, a feeding strategy was developed considering potential biosynthetic bottlenecks. Acetate and glucose were fed at 96 h (8.0 g L-1) and 120 h (6.0 g L-1) respectively, which resulted in final illudin M titer of ~ 940 mg L-1 after eight days. This is a 25 fold increase compared to the initial titer.

CONCLUSION

After strict standardization of seed-preparation and cultivation parameters, a combination of experimental design, empirical trials and additional supply of limiting biosynthetic precursors, led to a highly reproducible process in shake flasks with high titers of illudin M. These findings are the base for further work towards a scalable biotechnological process for a stable illudin M supply.

Has Ferrocene Really Delivered Its Role in Accentuating the Bioactivity of Organic Scaffolds?

Ferrocene is an important structural core in bioorganometallic chemistry because of its inherent stability, excellent redox properties, and low toxicity. Ferroquine and ferrocifen are two of the most notable contributions of ferrocene to medicinal chemistry with remarkable antimalarial and anticancer properties. The improved medicinal properties of these drug candidates highlight the impact that ferrocene can have on the molecular and biological properties of the bioactive compounds. In this Perspective, we investigate the scope and limitations of ferrocene incorporation into organic compounds/natural products on their mode of action and biological activities. We have also discussed the detailed role of ferrocene modifications in influencing the anticancer, antimalarial, and antimicrobial properties of various bioactive moieties to design safer and promising ferrocene-based drugs.

Synthesis and In Vitro Anticancer Activity of 6-Ferrocenylpyrimidin-4(3H)-one Derivatives

AIM AND OBJECTIVE

Some ferrocenyl derivatives are active in vitro and in vivo against cancer. Generally, ferrocenyl derivatives for cancer research have three key components: a ferrocene moiety, a conjugated linker that lowers the oxidation potential and some derivative (peptide, nucleobase and others) that can interact with biomolecules. Since the pyrimidine fragment can easily pass through the membrane into the cells and become involved in metabolism; it appears to be promising. Furthermore, this fragment is an electron-acceptor group, so a spacer can be excluded. Therefore, the synthesis of 6-ferrocenylpyrimidin-4(3H)-one derivatives and the study of their anticancer activity have scientific and practical interest.

METHODS

The syntheses of 6-ferrocenylpyrimidin-4(3H)-one derivatives were performed by the condensation of ethyl 3-ferrocenyl-3-oxopropionate with thiourea or acetamidine or guanidine. The cytotoxicity of four 6- ferrocenylpyrimidin-4(3H)-one derivatives was evaluated by using the MTT assay in vitro against Human breast adenocarcinoma MCF-7 and normal human skin fibroblast HSF cells. The tested derivatives induced a concentration-dependent cytotoxic response in cell lines.

RESULTS

A study of the cytotoxic activity of 6-ferrocenylpyrimidin-4(3H)-one derivatives by the MTT test has found that all compounds have a dose-dependent toxic effect on the lines of breast cancer cells (MCF-7) and normal human fibroblast cells (HSF). The most pronounced cytotoxic effect is exhibited by 2-methyl-6-ferrocenylpyrimidin- 4(3H)-one (MCF-7, IC50 17 ± 1 µM).

CONCLUSION

The experimental results confirm the importance of investigation and design of ferrocenylpyrimidin- 4(3H)-one derivatives as anticancer agents. Compounds where the pyrimidine derivatives are directly linked to the ferrocene unit rather than via a spacer group also may be of interest for antiproliferative drug design.

Biological and chemical diversity go hand in hand: Basidiomycota as source of new pharmaceuticals and agrochemicals

The Basidiomycota constitutes the second largest higher taxonomic group of the Fungi after the Ascomycota and comprises over 30.000 species. Mycelial cultures of Basidiomycota have already been studied since the 1950s for production of antibiotics and other beneficial secondary metabolites. Despite the fact that unique and selective compounds like pleuromutilin were obtained early on, it took several decades more until they were subjected to a systematic screening for antimicrobial and anticancer activities. These efforts led to the discovery of the strobilurins and several hundreds of further compounds that mainly constitute terpenoids. In parallel the traditional medicinal mushrooms of Asia were also studied intensively for metabolite production, aimed at finding new therapeutic agents for treatment of various diseases including metabolic disorders and the central nervous system. While the evaluation of this organism group has in general been more tedious as compared to the Ascomycota, the chances to discover new metabolites and to develop them further to candidates for drugs, agrochemicals and other products for the Life Science industry have substantially increased over the past decade. This is owing to the revolutionary developments in -OMICS techniques, bioinformatics, analytical chemistry and biotechnological process technology, which are steadily being developed further. On the other hand, the new developments in polythetic fungal taxonomy now also allow a more concise selection of previously untapped organisms. The current review is dedicated to summarize the state of the art and to give an outlook to further developments.

Metal Complexes of Natural Product Like-compounds with Antitumor Activity

Cancer continues to be one of the major causes of death worldwide. Despite many advances in the understanding of this complex disease, new approaches are needed to improve the efficacy of current therapeutic treatments against aggressive tumors. Natural products are one of the most consistently successful sources of drug leads. In recent decades, research activity into the clinical potential of this class of compounds in cancer has increased. Furthermore, a highly promising field is the use of metals and their complexes in the design and development of metal-based drugs for the treatment of cancer. Metal complexes offer unique opportunities due to their ability to alter pharmacology, improving the efficacy and/or reducing the negative side effects of drug molecules. In addition, transition metals as copper, iron, and manganese, among others, can interact with active sites of enzymes, playing important roles in multiple biological processes. Thus, these complexes not only possess higher activities but also reach their targets more efficiently. This review article highlights recent advances on the emerging and expanding field of metal-based drugs. The emphasis is on new therapeutic strategies consisting of metal complexes with natural product like-compounds as a starting point for the rational design of new antitumor agents.

Current State of Metal-Based Drugs for the Efficient Therapy of Lung Cancers and Lung Metastases

Lung cancer is the second most common cancer in both men and women and thus a leading cause of cancer-related deaths worldwide. New efficient treatments especially for its advanced stages and metastases are desperately needed, particularly with regard to overcoming the resistance which thwarts the efficacy of most clinically established drugs such as the platinum complexes. Glimpses of hope are new metal-based drugs that have emerged over the past decade which displayed efficacy in patients with platinum-resistant tumors and metastases. This chapter provides an overview of the latest developments of such metal-based drugs against lung cancer.

Ferrocene incorporated selenoureas as anticancer agents

For a compound to be a best chemopreventive agent it should be a descent DNA binder and at the same time should be active against any of the three stages of carcinogenesis i.e. cancer initiation, cancer propagation and tumor growth. Most of the problems associated with chemotherapy can be overcome if the chemopreventive agent is active against all the three stages of cancer development. Cancer may be initiated by higher concentration of free radicals, inflammating agents and phase I enzymes (Cytochrome P450) in the body. Cancer propagation can be very efficiently controlled by inducing the phase II enzymes (glutathione S-transferases (GSTs), UDP-glucuronosyl transferases, and quinone reductases) in the body and cancer termination depends on the killing of the faulty cells i.e. cytotoxic actions. This article reports comprehensively the comparative DNA binding studies (with, cyclic voltammetry, UV-vis spectroscopy and viscometry), antioxidant activities (DPPH scavenging), anti-inflammatory activities (nitrite inhibition), phase I enzyme inhibition activities (aromatase inhibition), phase II enzyme induction studies (quinone reductase induction) and cytotoxic studies against neuroblastoma (MYCN2 and SK-N-SH), liver cancer (Hepa 1c1c7) and breast cancer (MCF-7) of seventeen ferrocene incorporated selenoureas.

Ferrocifen type anti cancer drugs

The mechanisms of action of ferrocifens depend on several features: chemical structures, used concentrations, nature of cancer cells.

Ferrocene and (arene)ruthenium(II) complexes of the natural anticancer naphthoquinone plumbagin with enhanced efficacy against resistant cancer cells and a genuine mode of action

A series of ferrocene and (arene)ruthenium(II) complexes attached to the naturally occurring anticancer naphthoquinones plumbagin and juglone was tested for efficacy against various cancer cell lines and for alterations in the mode of action. The plumbagin ferrocene and (p-cymene)Ru(II) conjugates 1c and 2a overcame the multi-drug drug resistance of KB-V1/Vbl cervix carcinoma cells and showed IC50 (72 h) values around 1 μM in growth inhibition assays using 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT). They were further investigated for their influence on the cell cycle of KB-V1/Vbl and HCT-116 colon carcinoma cells, on the generation of reactive oxygen species (ROS) by the latter cell line, for their substrate character for the P-glycoprotein drug eflux pump via the calcein-AM efflux assays, and for DNA affinity by the electrophoretic mobility shift assay (EMSA). The derivatives 1c and 2a increased the number of dead cancer cells (sub-G0/G1 fraction) in a dose- and time-dependent manner. ROS levels were significantly increased upon treatment with 1c and 2a. These compounds also showed a greater affinity to linear DNA than plumbagin. While plumbagin did not affect calcein-AM transport by P-glycoprotein the derivatives 1c and 2a exhibited a 50% or 80% inhibition of the P-glycoprotein-mediated calcein-AM efflux relative to the clinically established sensitizer verapamil.

Natural compounds' activity against cancer stem-like or fast-cycling melanoma cells

Background

Accumulating evidence supports the concept that melanoma is highly heterogeneous and sustained by a small subpopulation of melanoma stem-like cells. Those cells are considered as responsible for tumor resistance to therapies. Moreover, melanoma cells are characterized by their high phenotypic plasticity. Consequently, both melanoma stem-like cells and their more differentiated progeny must be eradicated to achieve durable cure. By reevaluating compounds in heterogeneous melanoma populations, it might be possible to select compounds with activity not only against fast-cycling cells but also against cancer stem-like cells. Natural compounds were the focus of the present study.

Methods

We analyzed 120 compounds from The Natural Products Set II to identify compounds active against melanoma populations grown in an anchorage-independent manner and enriched with cells exerting self-renewing capacity. Cell viability, cell cycle arrest, apoptosis, gene expression, clonogenic survival and label-retention were analyzed.

Findings

Several compounds efficiently eradicated cells with clonogenic capacity and nanaomycin A, streptonigrin and toyocamycin were effective at 0.1 µM. Other anti-clonogenic but not highly cytotoxic compounds such as bryostatin 1, siomycin A, illudin M, michellamine B and pentoxifylline markedly reduced the frequency of ABCB5 (ATP-binding cassette, sub-family B, member 5)-positive cells. On the contrary, treatment with maytansine and colchicine selected for cells expressing this transporter. Maytansine, streptonigrin, toyocamycin and colchicine, even if highly cytotoxic, left a small subpopulation of slow-dividing cells unaffected. Compounds selected in the present study differentially altered the expression of melanocyte/melanoma specific microphthalmia-associated transcription factor (MITF) and proto-oncogene c-MYC.

Conclusion

Selected anti-clonogenic compounds might be further investigated as potential adjuvants targeting melanoma stem-like cells in the combined anti-melanoma therapy, whereas selected cytotoxic but not anti-clonogenic compounds, which increased the frequency of ABCB5-positive cells and remained slow-cycling cells unaffected, might be considered as a tool to enrich cultures with cells exhibiting melanoma stem cell characteristics.