Pharmacokinetics of the thioether phospholipid analogue BM 41.440 in rats

Thioethers: An Overview

:

Spreading rapidly in recent years, cancer has become one of the causes of the highest mor-tality rates after cardiovascular diseases. The reason for cancer development is still not clearly under-stood despite enormous research activities in this area. Scientists are now working on the biology of cancer, especially on the root cause of cancer development. The aim is to treat the cancer disease and thus cure the patients. The continuing efforts for the development of novel molecules as potential anti-cancer agents are essential for this purpose. The main aim of this review was to present a survey on the medicinal chemistry of thioethers and provide practical data on their cytotoxicities against various cancer cell lines. The research articles published between 2001-2020 were consulted to pre-pare this review article; however, patent literature has not been included. The thioether-containing heterocyclic compounds may emerge as a new class of potent and effective anti-cancer agents in the future.

Synthetic Glycosylated Ether Glycerolipids as Anticancer Agents

Glycosylated antitumor ether lipids (GAELs) are a class of synthetic antitumor ether lipids (AELs) with a sugar moiety in place of the phosphocholine found in the prototypical AEL, edelfosine. This chapter reviews the development of GAELs as antitumor agents. Studies on structure–activity relationships, mechanism of induction of cell death, metabolism, selectivity against cancer cells, toxicity, hemolysis and thrombogenic effects are discussed. The requirements for significant cytotoxic activity include a glycerol moiety, a cationic sugar other than mannose and an O- or C-glycosidic bond with either α- or β-configuration. Compounds with S- and N-glycosidic linkages are not very active. The most active GAEL to date, 1-O-hexadecyl-2-O-methyl-3-O-(2′-amino-2′-deoxy-α-d-galactopyranosyl)-sn-glycerol, displays greater in vitro activity than edelfosine, the AEL “gold standard”. The unique properties of GAELs as antitumor agents include their apoptotic-independent mechanism of inducing cell death and the ability to kill cancer stem cells. These characteristics of GAELs offer the potential for their development into chemotherapeutic agents to prevent the recurrence of tumors as well as for treatment against drug-resistant cancers.

Cytotoxic properties of D-gluco-, D-galacto- and D-manno-configured 2-amino-2-deoxy-glycerolipids against epithelial cancer cell lines and BT-474 breast cancer stem cells

Glycosylated antitumor ether lipids (GAELs) 6 and 7 containing a α- or β-D-gluco-configured 2-amino-2-deoxy (2-NH2-Glc) sugar moiety linked to a glycerolipid aglycone kill cancer cell lines via a non-apoptotic mechanism that could be exploited to kill cancer stem cells. To test this hypothesis and develop novel potent GAEL analogs, we synthesized GAELS which contain D-galacto- and D-manno-configured 2-amino-2-deoxy sugar moieties (2-NH2-Gal or 2-NH2-Man) and investigated their cytotoxicity against human epithelial cancer cell lines and cancer stem cells derived from BT-474 breast cancer cells. Within the class of D-galacto-configured GAELs, we prepared both O- and S-glycosidic linkages as well as their corresponding α- and β-anomers and screened against breast (BT-474, JIMT-1 and BT-549), pancreas (MiaPaCa2) and prostate cancer (DU145, PC3) cancer cell lines. The α-anomeric 2-NH2-Gal-based lipid 1 was the most active of all the compounds tested with CC50 values of 4.4-8 μM and is the most active GAEL synthesized to date. The β-anomer 2 was 4->5-fold less active than 1. Replacement of the α-O-glycosidic by an α-S-glycosidic linkage resulted in a 2-4-fold reduction in activity, while the β-S-glycolipid 4 was inactive. In comparison, α-configured 2-NH2-Man-based glycerolipid 5 displayed very little activity with CC50 > 30 μM. The effect of the most active GAELs, 1, 6, or 7, on cancer stem cell viability revealed that all three inhibited the formation of tumorspheres from BT-474 cancer stem cell lines, caused the disintegration of preformed tumorspheres and resulted in total loss of cell viability of the cancer stem cells at concentrations of 20 μM. In contrast, the related antitumor ether lipid gold standard, edelfosine that is in clinical development was much less effective in preventing tumorsphere formation and affecting the viability of the cancer stem cells. Taken together our study demonstrates that α-GAEL anomers are more potent than their corresponding β-anomers and that the nature of the CHO moiety as well as the glycosidic bond significantly affects activity. The study also showed that GAELs are effective in killing CSCs while the apoptosis-inducing edelfosine is not.

Uptake of the phospholipase A2 inhibitor 1-dodecyl 2-[1-14C] octanamido-sn-2-deoxy glycero-3-phosphocholine by peritoneal macrophages

The [14C] phospholipid analogue 1-dodecyl-2-[1-14C] octanamido-sn-2-deoxy glycero-3-phosphocholine was synthetized. With 2 short fatty chains linked by alkyl and amido bonds to positions 1 and 2 of the glycerophosphate backbone, it was an inhibitor of phospholipase A2 in ionophore A23187-stimulated macrophages. Its uptake by rat peritoneal macrophages and its resistance towards phospholipases A2 were determined at nanomolar or micromolar concentrations in the culture medium. A control substrate for phospholipases A2 activity was established with the lecithin 1-octadecanoyl 2-[3H] eicosatetraenoyl-sn-glycero-3-phosphocholine ([3H] 20:4-GPC), a source of [3H] arachidonic acid after cleavage at position 2. Non-stimulated- or ionophore A23187-stimulated macrophages incorporated extensively the [14C] phospholipid analogue added at 30-4000 nM. At 4000 nM which induced 50% inhibition of the phospholipase, 40% of the dose was found associated with the [14C] phospholipids of 2 x 10(6) stimulated macrophages after 120 min incubation, while only low amounts of [14C] non-phosphorous lipids were detected. It is concluded that the [14C] phospholipid analogue was readily taken up by the macrophages with limited hydrolysis.

Distribution of hexadecylphosphocholine and octadecyl-methyl-glycero-3-phosphocholine in rat tissues during steady-state treatment

The distribution of the alkylphosphocholine hexadecylphosphocholine (He-PC) and the (alkyl)lysophospholipid 1-0-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine (ET18-OCH3) was analyzed in rats. The compounds were given orally at a daily dose of 75 mumol/kg body weight. After 6, 11, and 18 days, three rats in each treatment group were killed and the drug concentration in various tissues and fluids was determined. With the exception of the kidney (He-PC) and brain (He-PC and ET18-OCH3), steady-state levels of the drugs could be achieved in all organs investigated and in serum. Maximal concentrations of He-PC were found in the kidney, adrenal glands, and spleen, whereas the highest concentrations of ET18-OCH3 were detected in the adrenal glands, spleen, and small intestine. The concentrations of He-PC exceeded those of ET18-OCH3 in most tissues by a factor of about 2-25. Since samples of urine and feces did not contain detectable amounts of the compounds, the absorption of both lipid analogues was assumed to be complete. The total amount of He-PC recovered after 6, 11, and 18 days was 15%, 12%, and 6%, respectively, and that of ET18-OCH3 was 1.3%, 0.8%, and 0.3%, respectively. This indicates that the bioavailability of He-PC and ET18-OCH3 is not controlled by differences in the uptake of the two drugs, but by differences in their metabolism. The results could explain the differing efficacy of these two compounds in their antitumor action in animal models.

Antitumor activity of Ilmofosine (BM 41.440) in the 3Lewis-lung carcinoma model

Ilmofosine (1-hexadecylthio-2-methoxymethyl-1,3-propanediol-phosphocholine, BM 41.440) is a thioether phospholipid with cytostatic/cytotoxic properties. The antineoplastic activity of this compound was investigated in vivo in the 3Lewis-lung carcinoma system. 3Lewis lung tumor-bearing C57Bl/6 mice were treated with 0.625 to 40 mg Ilmofosine/kg per day p.o. either from days 1 to 9 or from days 11 to 28 after intrafoot-pad tumor cell inoculation. Ilmofosine caused a significant dose-related response on tumor growth and metastases, expressed in terms of tumor diameter, tumor weight, survival time and number of metastases-free animals as compared to sham-treated and positive (cyclophosphamide) controls. The results suggest that direct cytostatic/cytotoxic effects, rather than immune-modulatory mechanisms, preferentially contribute to the antitumor activity of Ilmofosine in vivo.

Lipid conjugates of antiretroviral agents. I. Azidothymidine-monophosphate-diglyceride: anti-HIV activity, physical properties, and interaction with plasma proteins

3'-Azido-3'-deoxythymidine-5'-phosphate diglyceride (16:0/18:1 omega 9), a phosphatic acid conjugate of AZT, is active against HIV replication in H9 cells and syncytia formation in MOLT-3 cells. The activities rank as AZT greater than pure conjugate greater than conjugate in mixed liposomes, with the pure conjugate having about one-third the activity of free AZT. The compound binds very rapidly to serum lipoproteins, but not to serum albumin, alpha and beta globulins, or red cells. Pancreatic phospholipase A2 hydrolyzes it to the lysophosphatidic acid conjugate.

Lipid conjugates of antiretroviral agents. II. Disodium palmityl phosphonoformate: anti-HIV activity, physical properties, and interaction with plasma proteins

Disodium palmityl phosphonoformate, a novel lipid phosphoester of the anti HIV agent phosphonoformate (foscarnet), inhibits HIV replication in H9 cells and syncytia formation in MOLT-3 cells as effectively as foscarnet itself, as shown by dose-response data from assays for expression of p17 and p24 viral antigens and syncytia formation. Protein binding studies indicate that in serum, the derivative exists bound to albumin and the lipoproteins, and would therefore be likely to exhibit improved serum lifetime in vivo.

Synergistic enhancement of the antiproliferative activity of cis-diamminedichloroplatinum(II) by the ether lipid analogue BM41440, an inhibitor of protein kinase C

The new phospholipid analogue 3-hexadecylmercapto-2-methoxy-methyl-propyl-1-phosphocholine inhibits the phospholipid-calcium-dependent protein kinase, partially purified from Walker carcinoma cells with a Ki value of 0.56 microM. The compound inhibits the phorbol ester stimulated phosphorylation of the ribosomal protein S6 indicating that the depression of Ca2+-phospholipid-dependent protein kinase by the alkyl phospholipid also occurs in intact cells. The dose effect curve for the inhibition of cell proliferation by 3-hexadecylmercapto-2-methoxy-methyl-propyl-1-phosphocholine in Walker cells exhibits a close correlation to the dose effect curve for the depression of Ca2+-phospholipid-dependent protein kinase activity. Although alternative mechanisms cannot be excluded, the data suggest that the growth inhibitory activity of 3-hexadecylmercapto-2-methoxy-methyl-propyl-1-phosphocholine correlates with the inhibition of Ca2+-phospholipid-dependent protein kinase. The antiproliferative activity of 3-hexadecylmercapto-2-methoxy-methyl-propyl-1-phosphocholine is synergistically enhanced by cis-diamminedichloroplatinum(II).

Hexadecylphosphocholine, a new ether lipid analogue. Studies on the antineoplastic activity in vitro and in vivo

Hexadecylphosphocholine (He-PC) is a new compound synthesized according to the minimal structural requirements deducted from studies with other ether lipids. In vitro studies on He-PC revealed remarkable antineoplastic activity on HL60, U937, Raji and K562 leukemia cell lines. In addition, He-PC, applied orally, showed a superior effect in the treatment of dimethylbenzanthracene-induced rat mammary carcinomas when compared to intravenously administered cyclophosphamide. After oral application He-PC was well absorbed from the intestine and metabolized in the liver by phospholipases C and D. During a 5-week treatment no hematotoxic effects were detected. In a clinical pilot study on breast cancer patients with widespread skin involvement, topically applied He-PC showed skin tumor regressions without local or systemic side effects.

Cytotoxic activity of the thioether phospholipid analogue BM 41.440 in primary human tumor cultures

The inhibitory effect of the new thioether alkyl lysophospholipid analogue 1-hexadecylmercapto-2-methoxy-methyl-rac-glycero-3-phosphocholine (BM 41.440, Ilmofosine) on colony formation of different spontaneous human tumors was studied in vitro using a methyl cellulose monolayer assay. The most sensitive tumors were lung (small cell, squamous cell and adenocarcinomas), gastrointestinal and ovarian cancers and hyernephromas. On the basis of the current definition of sensitivity by the National Cancer Institute, Bethesda, MD, i.e. more than 70% inhibition of colony formation at an arbitrary concentration of 10 micrograms/ml, 34 out of 64 malignancies tested were susceptible to BM 41.440.

Phase I trial of the thioether phospholipid analogue BM 41.440 in cancer patients

BM 41.440 (1-hexadecylmercapto-2-methoxymethyl-rac-glycero-3-phosphocholine) is a new thioether phospholipid, which has been shown to possess antineoplastic, antimetastatic, anti-invasive and immunomodulating properties in several tumor models. The mechanism whereby this compound exerts its direct antineoplastic effect is thought to be related to specific interference with the normal phospholipid metabolism, preferentially of neoplastic cells. BM 41.440 was evaluated in a multicenter phase I study in patients (pts) with refractory cancers. In phase I A, 34 pts were orally treated with doses ranging from 0.5 to 7.0 mg/kg body weight (bw). Three different formulations were tested. The maximum-tolerated dose (MTD) was ca. 5 mg/kg bw. The limiting side effects were nausea and vomiting. There was no evidence for systemic toxicities like myelosuppression, nephro-, neuro-, hepatotoxicity or hematological side effects. The current phase I B is designed to determine the MTD of BM 41.440 administered orally on a daily schedule for at least eight weeks. So far, 19 pts have entered this trial at dose levels ranging from 1.0 to 5.0 mg/kg bw/day. Some pts receiving 1.0 and 2.5 mg/kg bw/day, respectively, have been treated, up to now, for more than nine months. Clinical progress was followed with at-least-weekly blood counts, chemistry profiles, urine analysis, liver function tests and recordings of side effects. Tumor parameters were evaluated at eight-week intervals. In parallel, pharmacokinetic investigations were performed in some pts in phase I A and IB. First results on tolerability and therapeutic efficacy of the long-term BM 41.440 treatment are reported in this intermediate evaluation.

Synthesis of thioether phosphocholine analogues

The synthesis of thioether phospholipids, which represent a new class of antitumor agents, is reported here. In particular, the route of synthesis of 3-hexadecylmercapto-2-methoxymethylpropyl-2'-trimethylammoni o-ethyl phosphate (BM 41.440, Ilmofosine), one of the most potent cytostatic/cytotoxic derivatives, is described in detail. Starting with diethyl bis-hydroxymethylmalonate, ethyl 2-phenyl-1,3-dioxane-5-carboxylate is formed via diethyl 2-phenyl-1,3-dioxane-5,5-dicarboxylate and 5-ethoxycar-bonyl-2-phenyl-1,3-dioxane-5-carboxylic acid. Reduction of ethyl 2-phenyl-1,3-dioxane-5-carboxylate with LiAlH4 affords 5-hydroxymethyl-2-phenyl-1,3-dioxane. Alkylation with dimethyl sulfate gives 5-methoxymethyl-2-phenyl-1,3-dioxane. The ring structure then is opened by N-bromosuccinimide, resulting in the formation of 3-bromo-2-methoxymethylproply benzoate. Reaction of 3-bromo-2-methoxymethylpropyl benzoate with the sodium salt of hexadecanethiol leads to 3-hexadecylmercapto-2-methoxy-methylpropanol, which is reacted with a cyclic chlorophosphate to give the corresponding phosphorylated 3-hexadecylmercapto-2-methoxymethylpropanol. Treatment with trimethylamine yields BM 41.440. This compound already has been tested in clinical phase I/II trials in West Germany.