KPV

KPV is a tripeptide (lysine-proline-valine) matching positions 11–13 of α-MSH, a hormone with strong anti-inflammatory effects in animals. Full-length α-MSH also darkens skin, which limits its use. KPV keeps the anti-inflammatory action without the pigmentary one, so it has been proposed for inflammatory skin, bowel, lung, eye and joint disease [1][5].

Colitis. In human intestinal cells, nanomolar KPV damped inflammatory signaling. Given in the drinking water, it reduced colitis caused by two different chemicals in mice [2]. A separate group in Germany found that KPV sped recovery in both chemical and T-cell transfer colitis, and it saved every KPV-treated mouse lacking a functional MC1R from death during colitis [3]. Packaging KPV in hyaluronic-acid nanoparticles inside a hydrogel improved its effect in mouse colitis [6].

Tumors. In a mouse model of colitis-associated cancer, KPV reduced inflammation and tumor numbers. It did not work in mice without PepT1. It also did not reduce tumors in APCMin/+ mice, which develop intestinal tumors without colitis [4].

Bacteria. In the lab, acetylated and amidated forms of KPV had antibacterial activity against Staphylococcus aureus and E. coli, about as potently as α-MSH [7].

No clinical trial of KPV was found. The oral colitis studies from Atlanta all come from one research group [2][4][6].

KPV enters intestinal epithelial cells and T cells through PepT1, a transporter for small peptides. PepT1 is normally found in the small intestine and appears in the colon during inflammatory bowel disease. Once inside, KPV blocks NF-κB and MAP kinase activation and lowers pro-inflammatory cytokine output [2]. In the same intestinal cells, α-MSH itself had no such effect and melanocortin receptors did not appear to be working, which points to a receptor-independent route [2]. In mice lacking a functional melanocortin-1 receptor, KPV still worked [3].

The transporter step is unusually favorable for a peptide drug. Human PepT1 takes up KPV with a Km of about 160 µmol/L in Caco-2/BBE cells — among the lowest affinities reported for the transporter, against 1 mmol/L or more for glycyl-sarcosine, its standard substrate — which is why nanomolar concentrations suffice in cells and why low doses can be moved across the epithelium efficiently [2][4].

The clearest demonstration that this route is the mechanism, rather than a plausible story about one, comes from knockout mice. In the azoxymethane/dextran-sulfate model of colitis-associated cancer, 100 µmol/L KPV in the drinking water through both colitis cycles cut tumor number, tumor size and overall tumor burden in wild-type mice, along with inflammatory infiltrate and Ki67-positive crypt cells. In PepT1-knockout mice the same treatment did none of those things to a significant degree [4]. Without the transporter, the peptide does not work.

What it does not do is act on tumor biology directly. In APC^Min/+ mice — a genetic adenoma model with little baseline inflammation — 13 weeks of KPV in the drinking water left adenoma counts in the small intestine and colon unchanged, while still lowering fecal lipocalin-2. The anti-inflammatory effect was intact; it simply was not sufficient where inflammation was not driving the tumors [4].

Plain KPV was given in drinking water in the mouse colitis studies [2][4]. To deliver more of it to the colon, one group loaded KPV into hyaluronic-acid-coated nanoparticles inside a chitosan and alginate hydrogel. This worked better in mouse colitis than uncoated nanoparticles [6]. On human skin in the lab, KPV did not pass through by passive diffusion. Microneedles let 4.4 µg/cm² per hour through, and adding an electric current (iontophoresis) raised that about 35-fold [8].

KPV has no human safety data, because it has not been given to a person in a published study. In the mouse work it was given in drinking water for up to 13 weeks, and the treated animals had less colitis and fewer tumors than controls rather than added harm [4]. The KPV-loaded nanoparticles were not toxic to intestinal epithelial cells in culture [6], and the anti-inflammatory effects in cells appear at nanomolar concentrations, far below the levels used in toxicity screens [2].