Anticancer drugs. II. Synthesis and biological evaluation of spin labeled derivatives of podophyllotoxin

Biosynthesis, total synthesis, and pharmacological activities of aryltetralin-type lignan podophyllotoxin and its derivatives

Covering: up to 2022Podophyllotoxin (PTOX, 1), a kind of aryltetralin-type lignan, was first discovered in the plant Podophyllum peltatum and its structure was clarified by W. Borsche and J. Niemann in 1932. Due to its potent anti-cancer and anti-viral activities, it is considered one of the molecules most likely to be developed into modern drugs. With the increasing market demand and insufficient storage of natural resources, it is crucial to expand the sources of PTOXs. The original extraction method from plants has gradually failed to meet the requirements, and the biosynthesis and total synthesis have become the forward-looking alternatives. As key enzymes in the biosynthetic pathway of PTOXs and their catalytic mechanisms being constantly revealed, it is possible to realize the heterogeneous biosynthesis of PTOXs in the future. Chemical and chemoenzymatic synthesis also provide schemes for strictly controlling the asymmetric configuration of the tetracyclic core. Currently, the pharmacological activities of some PTOX derivatives have been extensively studied, laying the foundation for clinical candidate drugs. This review focuses primarily on the latest research progress in the biosynthesis, total synthesis, and pharmacological activities of PTOX and its derivatives, providing a more comprehensive understanding of these widely used compounds and supporting the future search for clinical applications.

Recent progress on C-4-modified podophyllotoxin analogs as potent antitumor agents

Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water-soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C-4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure-activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL-331, TOP-53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide-related drugs and provides detailed coverage of the current status and recent development of C-4-modified PPT analogs as anticancer clinical trial candidates.

Toward synthesis of third-generation spin-labeled podophyllotoxin derivatives using isocyanide multicomponent reactions

Spin-labeled podophyllotoxins have elicited widespread interest due to their far superior antitumor activity compared to podophyllotoxin. To extend our prior studies in this research area, we synthesized a new generation of spin-labeled podophyllotoxin analogs via isocyanide multicomponent reactions and evaluated their cytotoxicity against four human cancer cell lines (A-549, DU-145, KB and KBvin). Most of the compounds exhibited potent cytotoxic activity against all four cell lines, notably against the drug resistant KBvin cancer cell line. Among the new analogs, compounds 12e (IC50: 0.60-0.75 μM) and 12h (IC50: 1.12-2.03 μM) showed superior potency to etoposide (IC50: 2.03 to >20 μM), a clinically available anticancer drug. With a concise efficient synthesis and potent cytotoxic profiles, compounds 12e and 12h merit further development as a new generation of epipodophyllotoxin-derived antitumor clinical trial candidates.

Synthesis of novel derivatives of bispodophyllotoxin as potential antineoplastic agents--part XVI

Podophyllotoxin and related analogs present numerous challenges associated with optimal antitumor activity and severe unpredictable toxicity. In an attempt to find biorational podophyllotoxin-related drug, two moieties of podophyllotoxin have been linked at C4-position by a simple modification of the carbodiimide procedure to provide novel bispodophyllotoxin analogs (4a-4e) and their structural information was extensively characterized by using 1H-NMR, IR, and HRMS.

Design, synthesis, and biological evaluation of novel spin-labeled derivatives of podophyllotoxin as potential antineoplastic agents. Part XII

Five novel nitroxyl spin-labeled ester derivatives of podophyllotoxin (11a-11e) have been prepared and their structural information on these nitroxyl spin-labeled ester derivatives of podophyllotoxin (11a-11e) using (1)HNMR spectroscopy was efficiently obtained by application of the in situ reduction of representative nitroxyl spin-labeled ester derivative of podophyllotoxin 11e with phenylhydrazine for the preparation of N-hydroxylamine 12 in the NMR tube. These novel derivatives were further evaluated for their in vitro cytotoxic activity against five neoplastic cell lines (K562, HL-60, SPCA-1, Lewis, and L-1210) using MTT assay. Most of the target compounds (except for all these compounds against SPCA-1) exhibited more pronounced cytotoxicity against several neoplastic cell lines than that of the prototypical inhibitor etoposide.

The absolute configuration of a nitroxide spin labeled derivative of podophyllotoxin determined by the crystal structure

The crystal structure of the nitroxide spin labeled derivative of podophyllotoxin was first reported. X-ray analysis demonstrated that four contiguous chiral centers in the molecule, C1, C2, C3, and C4, adopt cis- (1:2), trans- (2:3), and cis- (3:4) arrangement.Key words: crystal structure, synthesis, nitroxyl radical, podophyllotoxin.

Synthesis and biological evaluation of new spin-labeled derivatives of podophyllotoxin

In order to find compounds with superior bioactivity and less toxicity, a series of spin-labeled podophyllotoxin derivatives were synthesized and tested for the partition coefficients and cytotoxicity against P-388 and A-549. Furthermore, we also determined antioxidant activities of target molecular in tissues of SD rats by the TBA method. Results revealed that most synthesized compounds showed more significant cytotoxicity against P-388 and A-549 in vitro than VP-16. Among them, 9d exhibited most potent cytotoxicity against P-388 and A-549 cells (IC50 is <0.01 and 0.13 microM, respectively). Also, the antioxidative activities showed that the modified compounds of 4'-demethylepipodophyllotoxin (9a-d and 10a-c) are higher than those of podophyllotoxin series (8a-d). The relationship between the cytotoxicity and antioxidative activity discussed.

Antitumor and antioxidant activity of spin labeled derivatives of podophyllotoxin (GP-1) and congeners

The spin labeled derivative of podophyllotoxin, i.e. podophyllic acid-[4-(2,2,6,6,-tetramethyl-1-piperidyloxy)] hydrazone (GP-1,2) and its congeners (GP-1-OH,3, GP-1-H, 4) were synthesized. The inhibition activity to the transplanted tumor S180 and HepA and the LD50 values of these compounds in mice were tested. Their partition coefficients and pKa values were measured. The results showed that the anticancer activity of these compounds followed the order GP-1 >GP-1-OH> GP-1-H. It can be attributed to the influence of their partition coefficients and ionization constants to the compounds properties. Meanwhile, the antilipoperoxidative activities of GP-1, GP-1-OH and GP-1-H to MDA formation of liver homogenate of rat induced by Fe2+-ascorbic acid were measured. Electrochemical studies were carried out to measure the redox midpoint potentials. The relationship between the redox midpoint potentials and the antilipoperoxidative activity followed the same order as the antitumor activity. The EPR (Electron Paramagnetic Resonance) spectroscopy of the blood from carotid artery of anesthetized Wistar rat in vivo was measured. The results indicated that there is an equilibration between GP-1 and GP-1-OH, furthermore, GP-1-H can be oxidized partly to GP-1 and equilibrated with GP-1-OH in vivo. The EPR signal intensity of GP-1 is stronger than GP-1-OH and GP-1-H. It can be concluded that the oxidative state of nitroxide in compounds play a key role to the antioxidant activity.

New spin labeled analogues of podophyllotoxin as potential antitumor agents

Four new nitroxyl labeled derivatives of podophyllotoxin, 4-(2, 2, 6, 6-tetramethyl-1-oxyl-4-piperidyl)oxy-epipodophyllotoxin (4), 4-(2, 2, 6, 6-tetramethyl-1-oxyl-4-piperidyl)oxy-4'-demethylepipodophyllotoxin (5), 4-(2, 2, 5, 5-tetramethyl-1-oxyl-3-pyrrolinyl)formyloxy-epipodophyllotox in (6) and 4-(2, 2, 5, 5-tetramethyl-1-oxyl-3-pyrrolinyl)formyloxy-4'-demethylep ipodophyllotoxin (7), have been synthesized and evaluated for their antitumor activity in vitro. Compounds 5 and 7 showed superior activity to clinically used etoposide (VP-16,2) in their inhibition of leukemia P388, lung cancer A549 and stomach carcinoma SGC-7901 cells. 4'-Demethyl-epipodophyllotoxins 5 and 7 was found to be more active than eipodophyllotoxins 4 and 6 lacking a free phenolic hydroxyl group at C-4'.

Synthesis and antitumor activity of spin labeled derivatives of podophyllotoxin

Three new nitroxyl labeled derivatives of podophyllotoxin 4-6 have been synthesized and evaluated for their antitumor activity in vitro. Compounds 4-6 showed significant inhibitory activity against human nasopharyngeal carcinoma KB,lung cancer A549 and stomach carcinoma SGC-7901 cells, as well as mouse leukemia L1210 and P388 cells. Compounds 4 and 5 exhibited comparable or superior activity to clinically used etoposide (VP-16,2) in their inhibition of these cell lines.