Alkylphospho-L-serine analogues: Synthesis of cytostatically active alkylphosphono derivatives

Effect of Polar Head Group Modifications on the Tumor Retention of Phospholipid Ether Analogs: Role of the Quaternary Nitrogen

We have previously described the remarkable capacity of radioiodinated alkyl phospholipids to be sequestered and retained by a variety of tumors in vivo. We have already established the influence of certain structural parameters of iodinated alkyl phospholipids on tumor avidity, such as stereochemistry at the sn-2 carbon of alkylglycerol phosphocholines, meta-or para-position of iodine in the aromatic ring of phenylalkyl phosphocholines, and the length of the alkyl chain in alkyl phospholipids. In order to determine the additional structural requirements for tumor uptake and retention, three new radioiodinated alkylphospholipid analogs, 2-4, were synthesized as potential tumor imaging agents. Polar head groups were modified to determine structure-tumor avidity relationships. The trimethylammonio group in 1 was substituted with a hydrogen atom in 2, an ammonio group in 3 and a tertiary butyl group in 4. All analogs were separately labeled with iodine-125 or iodine-124 and administered to Walker 256 tumor-bearing rats or human PC-3 tumor-bearing SCID mice, respectively. Tumor uptake was assessed by gamma-camera scintigraphy (for [I-125]-labeled compounds) and high-resolution micro-PET scanning (for [I-124]-labeled compounds). It was found that structural modifications in the polar head group of alkyl phospholipids strongly influenced the tumor uptake and tissue distribution of these compounds in tumor-bearing animals. Phosphoethanolamine analog 3 (NM401) displayed a very slight accumulation in tumor as compared with phosphocholine analog 1 (NM346). Analogs 2 (NM400) and 4 (NM402) lacking the positively charged nitrogen atom failed to display any tumor uptake and localized primarily in the liver. This study provided important insights regarding structural requirements for tumor uptake and retention. Replacement of the quaternary nitrogen in the alkyl phospholipid head group with non-polar substituents resulted in loss of tumor avidity.

Photophosphatidylserine Guides Natural Killer Cell Photoimmunotherapy via Tim-3

Natural killer (NK) cells, in addition to their cytotoxicity function, harbor prominent cytokine production capabilities and contribute to regulating autoimmune responses. T-cell immunoglobulin and mucin domain containing protein-3 (Tim-3) is one of the inhibitory receptors on NK cells and a promising immune checkpoint target. We recently found that phosphatidylserine (PS) binding to Tim-3 can suppress NK cell activation. Therefore, based on the therapeutic potential of Tim-3 in NK-cell-mediated diseases, we developed a photoswitchable ligand of Tim-3, termed photophosphatidylserine (phoPS), that mimics the effects of PS. Upon 365 or 455 nm light irradiation, the isomer of phoPS cyclically conversed the cis/trans configuration, resulting in an active/inactive Tim-3 ligand, thus modulating the function of NK cells in vitro and in vivo. We also demonstrated that reversible phoPS enabled optical control of acute hepatitis. Together, phoPS may be an appealing tool for autoimmune diseases and cytokine storms in the future.

Phosphorus-containing amino acids with a P–C bond in the side chain or a P–O, P–S or P–N bond: from synthesis to applications

Strategies for the preparation of phosphorus-containing amino acids and their utility in the organic chemistry, physico-chemistry, agrochemistry, and pharmacology fields are reported.

Bio-orthogonal phosphatidylserine conjugates for delivery and imaging applications

The syntheses of phosphatidylserine (PS) conjugates are described, including fluorescent derivatives for potential cellular delivery and bioimaging applications. Installation of terminal functional groups (amine, thiol, or alkyne) onto the sn-2 chain provides reactive sites for bio-orthogonal conjugation of cargo with suitably protected PS derivatives. An amine-containing PS forms amide bonds with peptidic cargo, a thiol derivative is designed for conjugation to cargo that contain alpha-halo carbonyls or Michael acceptors, and the terminal alkyne PS analogue permits "click" conjugation with any azide-tagged molecule. This latter conjugation method is quite versatile as it can be performed without PS headgroup protection, in aqueous media, and with acid-labile cargo.

Synthesis and antiproliferative activity of alkylphosphocholines

Alkylphosphocholines (APC) with one or more methylene groups in the alkyl chain replaced by oxygen atoms or carbonyl groups, or both have been assembled modularly using omega-diols as central building blocks. Out of 25 new compounds of this kind, 11 were evaluated for their antiproliferative activity on four cell lines and compared with miltefosine to evaluate their hemolytic activity (HA) and cytotoxicity on non-tumoral cells (MT2), used as markers of adverse effects. Compound 13 was more active on cancer cell lines than on non-tumoral cells and the data were similar for MTT and thymidine incorporation assays. It had less HA than miltefosine. Compound 13 could therefore be a candidate for the preparation of compounds with higher cytotoxicity on cancer cells and lower general toxicity.

Opposite effects on cytosolic Ca2+ of antitumor phospholipids by induction of calcium influx and activation of endoplasmic reticulum Ca(2+)-ATPase

The ability of four different antitumor phospholipids, 1-O-hexadecyl-2-chloro-2-deoxyglycero-3-phosphocholine (ET16CIPC), hexadecylphosphocholine (C16OPC), hexadecylphospho-L-serine analogs (C16OPS, C16OPS-N-Ac) and cytidine-5'-hexadecylphosphonophosphate (C16PCMP) to modulate the cytosolic Ca2+ concentration [Ca2+]i was studied in an immortalized human mammary epithelial cell line H184 A1N4. The compounds induced different modes of activity depending on their structure and concentration. ET16CIPC induced between 0.31 and 5 microM a concentration dependent transient increase which was followed by a sustained increase at 10 microM. Studies using LaCl3 and Mn2+ quench of the Fura-2 fluorescence indicated that both effects are the result of an extracellular Ca2+ influx. Low concentrations of C16OPC, C16OPS and C16OPS-N-Ac induced no, or only a small, transient increase, whereas C16PCMP caused a decrease in [Ca2+]i. Thapsigargin and cyclopiazonic acid, specific inhibitors of the endoplasmic reticulum Ca(2+)-ATPase, prolonged the transient [Ca2+]i increase following ET16CIPC concentration dependently, increased markedly the small transient increase following C16OPC and the C16-phosphoserine analogs and converted the decrease in the basal [Ca2+]i level induced by C16PCMP to an increase. The identical effects with thapsigargin and cyclopiazonic acid provide evidence that the [Ca2+]i response observed is an expression of the balance between the ability of an analog to raise [Ca2+]i and to remove Ca2+ by activation of the endoplasmic reticulum Ca(2+)-ATPase. This behaviour might contribute to the antiproliferative effectiveness of antitumor phospholipids.