PKH-95: Does anyone know if this compound is still commercially available?

Question

I've found a few papers that came out between 1991 and 1996 which describe a compound called PKH-95. This is an aliphatic compound linked to I-125, and proposed for use in research on immune cell trafficking. According to the literature, this compound seems superior to indium-111 (which is still used today), but it seems like all studies using this compound came to a halt by 1996. Does anyone know if this stuff is still made? I know that Sigma makes fluorescent PKH compounds, but I am specifically looking for a radiolabeled compound. Also, if anyone has any additional info on this compound (maybe something that might suggest why it's not used anymore... or how to make it myself), I'd appreciate it.

Thanks!

Answer 1

PKH95, a 125 I-radioactive cell label, are both potentially valuable endothelial cell labels because they bind irreversibly within cell membranes. These labels would be particularly well suited to tract transplanted endothelial cells in vivo. However, no previous studies documenting lack of transfer of the label to unlabeled endothelial cells, as well as the effect of the label on endothelial cell function, have been undertaken. The purpose of this study was to determine the optimal method of endothelial cell (EC) labeling with PKH26 and PKH95, whether significant to EC-to-EC transfer of the label occurs, the effects of these labels on EC proliferation and membrane function, and the feasibility of using these labels for long-term quantitative EC tracking in vivo. Canine ECs in confluent monolayers or in cell suspension were labeled by exposure to 1.0 or 5.0 microM PKH26 for 1, 3, or 5 min. Cell viability was determined by trypan blue exclusion. The percentage of cells labeled and their fluorescence intensity were determined in a fluorescent-activated cell sorter (FACS). Effect of the label on cell function was assessed by measuring EC proliferation rates as well as intercellular adhesion molecule (ICAM) expression before and after induction with tumor necrosis factor (TNF). To determine if transfer of the label occurs, both labeled and nonlabeled ECs were grown in coculture and subjected to FACS analysis. For in vivo cell tracking, doubly labeled ECs were injected into the femoral artery of rat hind-limbs, and whole-body tissue analysis was undertaken to determine labeled-EC distribution at 60 days. Endothelial cells were labeled with equal efficacy as monolayers or in suspension. Labeling had no effect on EC proliferation rates nor on TNF-induced upregulation of ICAM expression. Coculture experiments revealed no significant label transfer to nonlabeled ECs. In vivo cell tracking studies documented that 8% of label remained within the skeletal muscle capillaries at 60 days after injection. PKH26 and PKH95 labels incorporate stably into EC membranes, do not alter endothelial cell function, and provide a precise means for quantitative EC tracking and histologic localization both in vitro and in vivo. These labels should prove to be very useful for studies of endothelial cell biology and transplantation.

Mouse macrophages purified by elutriation from thioglycollate-induced peritoneal exudate cells were labelled with indium-111-oxine and injected intravenously into mice. A substantial amount of unbound radioactivity remained in the circulation, suggesting that the radionuclide was not stably bound to the cells. Culture experiments with radiolabelled cells showed that indium-111 was released in the medium. Another cell marker, PKH-95, an iodine-125-labelled aliphatic compound insertable into the cell membrane, bound more stably than indium-111. Five minutes after injection of 125I-PKH-95-labelled macrophages, about 98% of the cells were in a non-circulating pool. It was checked that PKH-95 labelling did not compromise the viability and functions of the macrophages and that autologous erythrocytes and blood mononuclear cells labelled with PKH-95 remained in the circulation after i.v. injection. One hour after injection, 125I-PKH-95-labelled macrophages were distributed mainly in lung (36%), liver (19%) and spleen (5%). Subsequently, radioactivity decreased in the lung while increasing in liver, spleen and in an artificially induced footpad inflammation. The radioactivity accumulation in the inflammation persisted at least for 7 days. It represented a small proportion of radioactivity injected (0.2%) but was trapped very specifically in the inflammation. This raised the hypothesis that macrophages of the non-circulating pool could be released in the circulation and recruited into the inflammation with slow kinetics.