A novel tetraester construct that reduces cationic lipid-associated cytotoxicity. Implications for the onset of cytotoxicity.

The preparation of cationic amphiphiles that induce minor cytotoxic response during polynucleotide delivery into mammalian cells has been limited by the conventional use of ester, amide, or carbamate linkages to tether either the polar or the hydrophobic domains. The deleterious effects of ammonium-based lipidic salts on cellular processes have been well-established. The present report is the first example of a linchpin tetraester construct that utilizes ester linkages to tether both the polar and hydrophobic domains. Dimyristoyl and dioleoyl analogues were prepared from pentaerythritol, N,N-dimethylglycine, and their corresponding fatty acyl groups via successive diesterifications followed by amine quaternization. The resultant cationic tetraesters were examined in transfection (luciferase) and cell proliferation (MTS) assays using NIH 3T3 and 16HBE14o- cells. The tetraesters exhibited transfection activity comparable to the well-studied lipids DOTAP and DC-cholesterol (DC-chol) in both cell lines. The tetraester construct afforded no cytotoxicity in NIH3T3 cells and provided a significant lowering of cytotoxicity relative to DC-chol in the 16HBE14o- cells. The expression of green fluorescent protein (GFP) in both cell lines also was examined using the lipid panel. Comparison of fluorescent and corresponding phase-contrast images confirmed the chemical cytotoxicity results and revealed that the cytotoxic response was not dependent on transgene expression. Phase-contrast micrographs of cells treated with the cationic lipid panel in the absence of GFP plasmid showed identical morphology to the GFP-transfected cells, suggesting that the onset of a lipid-mediated cytotoxic response might occur at a stage prior to endosomal encapsulation.

Cationic lipid-mediated gene delivery to murine lung: correlation of lipid hydration with in vivo transfection activity.

A panel of lipidic tetraalkylammonium chlorides has been prepared and screened in studies of both lipid hydration and in vivo mouse transfection. The effect of cationic lipid structure on liposome surface hydration was determined using differential scanning calorimetry. Increases in headgroup steric bulk and the inclusion of cis-unsaturation in the hydrophobic domain led to greater lipid hydration, indicative of a decrease in lipid polar domain associations. Cationic lipids containing hydrogen-bonding functionality in the polar domain exhibited a corresponding decrease in observed lipid hydration, indicative of an increase in lipid polar domain associations. To explore a potential correlation of the hydration data with transfection activity, we examined the in vivo transfection activity of the lipid panel by direct intratracheal instillation of cationic liposome-DNA complexes into BALB/c mice. The more active transfection agents were the lipids that featured headgroup structures promoting close polar domain association in combination with fatty acyl cis-unsaturation. The hydration data suggest that the more effective transfection lipids for mouse lung delivery are those possessing the greatest imbalance between the cross-sectional areas occupied by the polar and hydrophobic domains.

Structural and functional analysis of cationic transfection lipids: the hydrophobic domain.

Cationic lipids (cytofectins) have gained widespread acceptance as pharmaceutical polynucleotide delivery agents for both cultured cell and in vivo transfection, and the cytofectins DOTAP and DC-Cholesterol are being tested in clinical human gene therapy trials. This study reports the effects of modifications in the hydrophobic domain of a prototypic cytofectin (DORI), including modifications in lipid side-chain length, saturation, and symmetry. A panel of related compounds was prepared and analyzed using DNA transfection, electron microscopy, and differential scanning calorimetry (DSC). Lipid formulations were prepared with dioleoylphosphatidylethanolamine (DOPE) as unsonicated preparations and sonicated preparations. Transfection analyses were performed using cultured fibroblasts, human bronchial epithelial, and Chinese hamster ovarian cells as well as a mouse model for pulmonary gene delivery. In general, cytofectins containing dissymmetric hydrophobic domains were found to work as well or better than the best symmetric analogs. Optimal side-chain length and symmetry varied with cell type. Compounds with phase transitions (Tc) above and below physiological temperature (37 degrees C) were tested for DNA transfection activity. In contrast to previous reports, cytofectin Tc was not found to be predictive of transfection efficacy. Pulmonary treatment with free DNA was found to be at least as effective as treatment with commonly used cytofectin:DNA complexes. However, cytofectins that incorporate a hydroxyethylammonium moiety in the polar domain were found to enhance in vivo gene delivery relative to free DNA.

The counterion influence on cationic lipid-mediated transfection of plasmid DNA.

A panel of DOTAP analogs was prepared by altering the anionic counterion that accompanies the trimethylammonium polar domain. The transfection of plasmid DNA into NIH3T3 cells and mouse lung was examined using the counterion analogs. The in vitro transfection activity decreased as follows: DOTAP.bisulfate > trifluoromethanesulfonate approximately equal to iodide approximately equal to bromide > dihydrogenphosphate approximately equal to chloride approximately equal to acetate > sulfate. A similar activity trend was observed in vivo.

Stabilization of beta-ribbon structures in peptides using disulfide bonds.

The effect of a disulfide crosslink between two peptide chains on the stability of beta-ribbon secondary structures formed by these peptides has been investigated. Based on structural principles, we hypothesized that introduction of an unstrained disulfide crosslink at appropriate locations on two peptide chains should have a stabilizing effect on the beta-ribbon structure formed by these two peptide chains. To test this hypothesis, we designed and synthesized two sets of 9-residue peptides incorporating cysteine in one and (S)-alpha-amino-epsilon-mercaptohexanoic acid in the other. Comparison of the CD data clearly show that the dimer containing a disulfide bond between the longer sidechains of (S)-alpha-amino-epsilon-mercaptohexanoic acid shows dramatically higher beta-ribbon character as compared to the dimer with cystine disulfide bond, thus validating our structural hypothesis.

Pulmonary alveolar proteinosis. Occurrence with metastatic melanoma to lung.

Pulmonary alveolar proteinosis is characterized by excessive accumulation of surfactant-like material in the alveoli, resulting in part from defective alveolar clearance by macrophages. We present a case of alveolar proteinosis in a patient with malignant melanoma metastatic to lung and discuss possible alteration in macrophage function in the pathogenesis of these two concomitant processes.

CEA immunoreactivity in odontogenic tumors and keratocysts.

Forty-five oral tumors and cysts were stained immunohistochemically for the presence of carcinoembryonic antigen (CEA). CEA, or a CEA-like antigen that is not nonspecific cross-reacting antigen (NCA), was demonstrated in the majority of aggressive or malignant tumors showing squamous differentiation, including cases of ameloblastoma, odontogenic carcinoma, and squamous carcinoma. CEA immunoreactivity was also found in cases of odontogenic keratocyst and focally in squamous odontogenic tumors but was not found in any of the ameloblastic fibromas, myxofibromas, odontogenic adenomatoid tumors, malignant melanomas, or apical cysts.

Anastomotic line renal artery stenosis after transplantation.

We report on 5 patients with renal artery stenosis after renal transplantation. Renal arteriography showed the stenosis to be localized at the line of arterial anastomosis. The patients presented with refractory hypertension, with or without renal failure, 10 days to 13 months after transplantation. Percutaneous transluminal balloon angioplasty in 4 patients failed in 3 and produced temporary improvement in 1. Resection of the stenosis resulted in dramatic improvement of the clinical state in all 5 patients. Histological examination of the resected stenotic segment revealed a nodular fibrotic lesion at the anastomotic line in all cases, and was associated with extensive calcification in 3. Anastomotic line stenosis should be recognized as a specific entity causing transplant renal artery stenosis. The pathological changes observed explain the failure of transluminal angioplasty and suggest that surgical repair is the treatment of choice. Possible factors in the etiology of anastomotic line stenosis are discussed.

Squamous cell carcinoma of the lip developing in discoid lupus erythematosus.

Since the substitution of steroids and antimalarials for irradiation in the treatment of discoid lupus erythematosus, squamous cell carcinoma arising in discoid lupus erythematosus is thought by some to be an uncommon occurrence. A review of the recent literature (subsequent to 1945) revealed fifteen cases, of which seven occurred in the lips. In one of twelve of the cases a history of irradiation was documented. In three other cases, there was no evidence of its use. We report an additional case of squamous cell carcinoma occurring in the lower lip of a 24-year-old black woman in the absence of radiation therapy. A review of the literature and a discussion of possible predisposing factors are presented.

Lobular (polymorphous low-grade) carcinoma of minor salivary glands. A clinicopathologic study of twenty cases.

Twenty cases of a recently described adenocarcinoma of minor salivary gland--lobular carcinoma--are reviewed. This distinctive lesion occurs most frequently on the palate of patients in their sixth and seventh decades and displays no apparent sex or race predilection. Histomorphologically, the tumor is characterized by cytologic uniformity, bland nuclear chromatin, and low mitotic rate. Its lobular configuration and marked infiltrative tendency, often by single-filed tumor cells, are reminiscent of lobular carcinoma of the breast. Follow-up data indicate a favorable prognosis and are in accord with findings of previous investigators. The possible relationship of this lesion to adenoid cystic carcinoma is discussed.