Relationships between the aqueous chemistry and the in vitro cytotoxic activities of mixed-amine cisplatin analogues

Steroids from the South China Sea Gorgonian Subergorgia suberosa

From the South China sea gorgonian Subergorgia suberosa, two new steroids, (22E)-14α-hydroxy-cholesta-1,4,22-trien-3-one (1) and 3-(1′,2′-ethandiol)-cholest-3β,5α,6α, 11α-tetraol (2) were obtained, in addition to six known steroids. The structures of compounds 1 and 2 were determined by spectroscopic methods. Cytotoxicity of the six known steroids against human cancer cell lines A549, HONE1, and HeLa was evaluated by MTT methods, and their anti-larval activity was evaluated in settlement inhibition assays with laboratory-reared Balanus amphitrite and Bugular neritina larvae.

Purine alkaloids from the South China Sea gorgonian Subergorgia suberosa

Four new purine alkaloids, namely, 6-(1'-purine-6',8'-dionyl)suberosanone ( 1), 3,9-(2-imino-1-methyl-4-imidazolidinone-5-yl)isopropenylpurine-6,8-dione ( 2), 1-(3'-carbonylbutyl)purine-6,8-dione ( 3), and 9-(3'-carbonylbutyl)purine-6,8-dione ( 4), together with three known compounds, guanosine ( 5), thymidine ( 6), and adenosine ( 7), were isolated from the EtOH/CH 2Cl 2 extracts of the South China Sea gorgonian Subergorgia suberosa. The structures of 1- 4 were determined on the basis of extensive spectroscopic analysis, including 1D and 2D NMR data. Compounds 1- 4 all showed weak cytotoxicity toward human cancer cell lines MDA-MB-231 and A435.

5-Alkynyl-2'-deoxyuridines: chromatography-free synthesis and cytotoxicity evaluation against human breast cancer cells

Starting with 5-iodo-2'-deoxyuridine, a series of 5-alkynyl-2'-deoxyuridines (with n-propyl, cyclopropyl, 1-hydroxycyclohexyl, p-tolyl, p-tert-butylphenyl, p-pentylphenyl, and trimethylsilyl alkyne substituents) have been synthesized via the palladium-catalyzed (Sonogashira) coupling reaction followed by a simplified isolation protocol (76-94% yield). The cytotoxic activity of modified nucleosides against MCF-7 and MDA-MB-231 human breast cancer cells has been determined in vitro. 5-Ethynyl-2'-deoxyuridine, the only nucleoside in the series containing a terminal acetylene, is the most potent inhibitor with IC(50) (microM) 0.4+/-0.3 for MCF-7 and 4.4+/-0.4 for MDA-MB-231.

A cytotoxic sesquiterpene alkaloid from the South China Sea gorgonian Subergorgia suberosa

A new sesquiterpene alkaloid, 6-(9'-purine-6',8'-diolyl)-2beta-suberosanone (1), together with three known sesquiterpenes, suberosenol A (2), subergorgic acid (3), and subergorgiol (4), was isolated from the EtOH/CH2Cl2 extracts of the South China Sea gorgonian Subergorgia suberosa. The structure of 1 was determined through spectroscopic methods. Compound 1 showed moderate cytotoxicity against the human breast carcinoma MDA-MB-231 cell line with an IC50 of 8.87 microg/mL.

Synthesis, X-ray crystal structures, stabilities, and in vitro cytotoxic activities of new heteroarylacrylonitriles

Twenty-three acrylonitriles, substituted at position 2 with either triazoles or benzimidazoles and at position 3 with various substituted furan, thiophene, or phenyl rings, were prepared by Knoevenagel condensation and tested for in vitro cytotoxic potency on 11 human cancer cell lines. X-ray crystal analysis of two representative compounds showed that the olfenic bond is E-configured. Structure-activity-relationships (SAR) indicated that position 2 is flexible for substituents with various nitrogen heterocyclics while position 3 is very sensitive to change; the most potent compounds contained a 5-nitrothiophen-2-yl ring at position 3 and either benzimidazol-2-yl (11) or a 5-benzyl-1H-[1,2,4]-triazol-3-yl (7) group at position 2 of acrylonitrile. SARs for the thiophen-2-yl-benzimidazoles show the following trend for position 5: NO2 >> H > Cl = CH3. Compound 11 was on average 10- and 3-fold more potent than cisplatin and etoposide, respectively. However, the acrylonitrile functionality is not an absolute requirement for cytotoxic activity because replacement of the nitrile group for either a hydrogen or a methyl group also gave active compounds. The acrylonitriles caused delayed cell death characterized by giant cells with multilobed nuclei. Compound 11 was found to bring about the increase in the activities of caspases 3 and 9 in the HL-60 cell line in a manner similar to etoposide, strongly indicating that apoptosis is the mechanism of cell death. The selectivity of various compounds toward cancer cells was estimated by comparing the IC50 values obtained from a noncancerous epithelial cell line, h-TERT-RPE1, with the average IC50 value from the cancer cell lines; 11 showed an average 1.7-fold greater activity toward cancer cells. The stabilities of the new compounds under cell culture conditions, estimated by HPLC, indicated that a major fraction of the compounds were lost from the medium over the first 24 h.

Quantification of elastase-like activity in 13 human cancer cell lines and in an immortalized human epithelial cell line by RP-HPLC

A sensitive and specific RP-HPLC assay was developed to measure the levels of polymorphonuclear elastase (PMN-E) activity in growing cell cultures. By combining a pre-incubation of the cells with a relatively non-toxic, PMN-E-specific inhibitor, MeOSuc-Ala-Ala-Pro-Val-chloromethylketone (MAAPVCK), the p-nitroaniline formed by the hydrolysis of the substrate MeOSuc-Ala-Ala-Pro-Val-p-NA by PMN-E is quantified. Elastase-like activity was measured in 14 human cells lines: 13 cancer cell lines (HL-60, U-937, A-427, LCLC-103H, YAPC, DAN-G, PA-TU-8902, KYSE-70, -510, -520, 5637, SISO and MCF-7) and one immortalized epithelial cell line (hTert-RPE1). Activity was detected in all lines; the lowest was found in hTert-RPE1 cells while the highest was detected in a pancreas adenocarcinoma line (PA-TU-8902). When the results were normalized according to cell volume instead of cell number, the leukemia line HL-60 had the highest activity and PA-TU-8902 ranked second. A 1 h pre-incubation with 9.0 microM of the irreversible PMN-E inhibitor MAAPVCK led to varying degrees of enzyme inhibition depending on the cell line; the strongest inhibition was observed with the PA-TU-8902 pancreatic cancer cell line (90% inhibition) while the weakest was seen with the A-427 lung cancer cell line (52%). These results indicate that PA-TU-8902 is a suitable in vitro model for testing the efficacy of PMN-E-activated prodrugs of antitumor agents.

Unusual reactivity of cisplatin analogs that bear o-phenylenediamine ligands: insights for the design of more effective cytotoxic agents

The stabilities of dichloro(o-phenylenediamine)platinum(II) (1) and several 4,5-disubstituted analogs [i.e., with: Cl (2), Br (3), Me (4), or MeO (5)] were investigated under various aqueous conditions. The Pt complexes 1-5- decomposed by reactions which were independent of the amount of chloride in the medium. The poor aqueous stabilities of 1-5 were attributed to two factors: 1) The compounds underwent facile oxidation reactions in aqueous solution at pH 7.4 and 37 degrees C, resulting in the formation of intensely colored Pt-species as well as H2O2. Compounds 2 and 3 oxidized considerably faster than 1, 4, and 5. Based on the redox behavior and UV-Vis spectra of the decomposition products, it is proposed that they are o-benzoquinonediimine Pt complexes. 2) Compound 4 underwent an unusually rapid substitution reaction with L-methionine, a component of the culture medium, whereby both of the chloro ligands of platinum were replaced by an N,S-chelated methionine. At an L-methionine concentration of 0.5 mM, the reaction ran to completion within 1 min. Thus, the weak growth inhibitory activities of 1-5 on human cancer cells in vitro was likely a result of their poor chemical stability in the culture medium. Based on a knowledge of the decomposition pathways, analogs were designed to be resistant to these types of reactions. Dichloro(o-aminomethylaniline)platinum(II) (6) and [bis-1,2(aminomethyl)benzene]-di-chloroplatinum(II) (7) were synthesized and their aqueous stabilities investigated. Both 6 and 7 were considerably more stable than 1-5 under aqueous conditions, as well as being more effective in inhibiting the growth of human cancer cells in vitro.

Third generation antitumor platinum(II) complexes of the [1-(fluoro/difluorophenyl)-2-phenylethylenediamine]platinum(II) type

The diastereomeric 1-(fluoro/difluorophenyl)-2-phenylethylene-diamines (4-fluoro: erythro-1/threo-1; 2,4-difluoro: erythro-2/-threo-2; 2,6-difluoro: erythro-3/threo-3) and the diastereomeric 1-(4-fluorophenyl)-2-(3-hydroxyphenyl)ethylenediamines (erythro-4/-threo-4) were synthesized from appropriately substituted stilbenes by reaction with IN3 and subsequent LiAlH4 reduction. Coordination of the 1,2-diphenylethylenediamines to platinum was carried out by use of K2PtI4. The water-soluble aquasulfato-platinum(II) complexes (erythro/threo-1-PtSO4-erythro/threo-4-PtSO4) were obtained from the diiodoplatinum(II) complexes by reaction with Ag2SO4. Additionally erythro/threo-1-PtSO4 and erythro/threo-4-PtSO4 were transformed into the dichloroplatinum(II) complexes (erythro/threo-1-PtCl2, erythro/threo-4-PtCl2) by treatment with KCl. In contrast to the less effective erythro-configurated sulfatoplatinum(II) complexes the threo-analogues showed comparable or even superior activities to cisplatin on the human MDA-MB-231 breast cancer cell line. On the MXT-M-3.2 breast cancer of the mouse only erythro- and threo-4-PtSO4 caused similar effects like cisplatin. The strong inhibitory effect of the diastereomeric sulfatoplatinum(II) complexes on the P-388 leukemia of the mouse was equal to that of cisplatin. On the latter tumor threo-4-PtCl2 was the most active among the less toxic dichloroplatinum(II) derivatives.

A novel approach to preparing water soluble prodrug forms of cisplatin analogues bearing chelating diamines

A novel method for creating water soluble prodrugs of cisplatin analogues bearing chelating diamines is introduced. When 2-(amino-methyl)aniline is reacted with K2PtCl4 between a pH of 6 and 7, the neutral chelated complex [2-(aminomethyl)aniline)dichloroplatinum(II) (1) is isolated. On the other hand, when the complexation occurs under acidic conditions (i.e. pH 3), the zwitterionic, "open-ring" form [2-(ammonio-methyl)aniline-N1]trichloroplatinate(II) (2) is obtained, whereby only the aniline nitrogen is coordinated to platinum. Compound 2 has a solubility of 10 mM in acidic aqueous medium; that is ca. 20 times greater than that of 1. However, 2 rapidly converts to compound 1 at physiologic pH; thus 2 functions as a water soluble prodrug of 1. Both 1 and 2 are equally effective at halting the growth of three different human cancer cell lines in vitro, indicating that the prodrug is quantitatively converted to the parent drug in a complex, biologically relevant medium. In animal experiments, the prodrug form, when given at a dose of 25 mumol/kg three times a week for 6 weeks, significantly inhibits the growth of the MXT (M3.2) mammary tumor in BDF mice while the same dose of the parent drug has no antitumor activity.

The effects of terbium on the accumulation of cisplatin in human ovarian cancer cells

In this investigation, we report a relationship between the terbium (Tb3+) binding protein and the accumulation of cisplatin in human ovarian cancer cells. The number of Tb3+ binding sites in cisplatin-resistant C13+ cells is significantly greater by 79% than those in cisplatin-sensitive 2008 cells. Exposure to Tb3+ also increased the cellular accumulation of cisplatin. The accumulation of cisplatin as a function of the Tb3+ concentration in the C13+ cells (0.85%/microM Tb3+) was significantly greater than the accumulation of cisplatin in 2008 cells with respect to Tb3+ (0.46%/microM Tb3+). The number of Tb3+ binding sites in revertant RH4 cells was similar to that in 2008 cells. The RH4 cells were less sensitive to the stimulatory effects of Tb3+ than the C13+ cells. Our results show that the Tb3+ binding protein correlates with cisplatin resistance, and the receptor binding of Tb3+ increases the accumulation of cisplatin in cisplatin-resistant cells.

Chemical stability, biological activity and cellular uptake of a cisplatin analogue having a 1,2-diarylethyleneamine ligand in cultures of human breast cancer cells

The platinum(II) complex PtCl2(meso-6), which has the estrogenic ligand meso-1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine (meso-6), has been reported to be an effective antitumor drug for estrogen-receptor(ER)-positive tumors in animal experiments. The goal of this study was to investigate whether the observed biological effects could be ascribed to the intact PtCl2(meso-6). Cultures of the ER-positive human breast cancer cell line MCF-7 were used as the in vitro test system. In culture medium containing 10% fetal calf serum, PtCl2(meso-6) had a half-life of about 2 h, as determined by HPLC analysis, and no PtCl2(meso-6) was detectable after 10 h. The Pt complex bound irreversibly to serum protein. After 30 min, the diamine ligand was found released, with a maximum conversion of about 35% at 24 h. At this time the culture medium still had estrogenic activity, i.e. it induced ER processing in the MCF-7 cells. This indicates that the estrogenic effect was elicited by the released diamine ligand. In contrast, the growth-inhibitory activity of the medium preincubated with PtCl2(meso-6) was lost at a rate similar to the rate of loss of PtCl2(meso-6) from the medium. This accords with the platinum complex being the main cytotoxic entity. When MCF-7 cells were incubated with PtCl2([3H]meso-6), no free Pt complex could be identified in cellular extracts, and most of the cell-associated radioactivity coeluted with meso-6 in HPLC analysis. After 12 h, only 1.4% of the total cellular platinum was bound to DNA, but no tritium label could be detected. In conclusion, diamine ligand is released from the Pt(II) complex and can account for the estrogenic effects so far ascribed to PtCl2(meso-6).