Protoporphyrin-IX accumulation and cutaneous tumor regression in mice using a ferrochelatase inhibitor

Small-molecule inhibitors of ferrochelatase are antiangiogenic agents

Activity of the heme synthesis enzyme ferrochelatase (FECH) is implicated in multiple diseases. In particular, it is a mediator of neovascularization in the eye and thus an appealing therapeutic target for preventing blindness. However, no drug-like direct FECH inhibitors are known. Here, we set out to identify small-molecule inhibitors of FECH as potential therapeutic leads using a high-throughput screening approach to identify potent inhibitors of FECH activity. A structure-activity relationship study of a class of triazolopyrimidinone hits yielded drug-like FECH inhibitors. These compounds inhibit FECH in cells, bind the active site in cocrystal structures, and are antiangiogenic in multiple in vitro assays. One of these promising compounds was antiangiogenic in vivo in a mouse model of choroidal neovascularization. This foundational work may be the basis for new therapeutic agents to combat not only ocular neovascularization but also other diseases characterized by FECH activity.

Enhancement of Cancer-Specific Protoporphyrin IX Fluorescence by Targeting Oncogenic Ras/MEK Pathway

Protoporphyrin IX (PpIX) is an endogenous fluorescent molecule that selectively accumulates in cancer cells treated with the heme precursor 5-aminolevulinic acid (5-ALA). This cancer-specific accumulation of PpIX is used to distinguish tumor from normal tissues in fluorescence-guided surgery (FGS) and to destroy cancer cells by photodynamic therapy (PDT). In this study, we demonstrate that oncogenic Ras/mitogen-activated protein kinase kinase (MEK) pathway can modulate PpIX accumulation in cancer cells.

Methods: To identify Ras downstream elements involved in PpIX accumulation, chemical inhibitors were used. To demonstrate the increase of PpIX accumulation by MEK inhibition, different human normal and cancer cell lines, BALB/c mice bearing mammary 4T1 tumors and athymic nude mice bearing human tumors were used. To identify the mechanisms of PpIX regulation by MEK, biochemical and molecular biological experiments were conducted.

Results: Inhibition of one of the Ras downstream elements, MEK, promoted PpIX accumulation in cancer cells treated with 5-ALA, while inhibitors against other Ras downstream elements did not. Increased PpIX accumulation with MEK inhibition was observed in different types of human cancer cell lines, but not in normal cell lines. We identified two independent cellular mechanisms that underlie this effect in cancer cells. MEK inhibition reduced PpIX efflux from cancer cells by decreasing the expression level of ATP binding cassette subfamily B member 1 (ABCB1) transporter. In addition, the activity of ferrochelatase (FECH), the enzyme responsible for converting PpIX to heme, was reduced by MEK inhibition. Finally, we found that in vivo treatment with MEK inhibitors increased PpIX accumulation (2.2- to 2.4-fold) within mammary 4T1 tumors in BALB/c mice injected with 5-ALA without any change in normal organs. Similar results were also observed in a human tumor xenograft model.

Conclusion: Our study demonstrates that inhibition of oncogenic Ras/MEK significantly enhances PpIX accumulation in vitro and in vivo in a cancer-specific manner. Thus, suppressing the Ras/MEK pathway may be a viable strategy to selectively intensify PpIX fluorescence in cancer cells and improve its clinical applications in FGS.

Griseofulvin enhances the effect of aminolevulinic acid-based photodynamic therapy in vitro

OBJECTIVE

In this study, we investigated whether or not griseofulvin (GF), which is an antimycotic widely used for the oral treatment of skin fungal infections, enhanced the effect of aminolevulinic acid-based photodynamic therapy (ALA-PDT) in vitro, using several tumor cell lines.

METHODS

A human squamous cell carcinoma line (KB), two human osteosarcoma cell lines from mandible (HOSM-1, HOSM-2), and the human gingiva-derived fibroblast line (HF), representing normal cells, were used. GF enhancement of ALA-PDT was evaluated by comparing the effect of ALAin combination with GF to the effect of ALAalone (GF enhancement rate of ALA-PDT). Also, the effect of GF on intracellular accumulation of protoporphyrin IX (PpIX) was evaluated by comparing the intracellular accumulation of PpIX in the ALA and GF combined treatment with that of ALA treatment alone (pGF enhancement rate of intracellular PpIX).

RESULTS

GFenhancement rate of ALA-PDT was 2.51 in KB cells, and 1.65 and 1.27 in HOSM-1 and HOSM-2 cells, respectively. GF enhancement rates of intracellular PpIX were 1.94 in KB cells, 1.53 in HOSM-1 cells, and 1.19 in HOSM-2 cells. GF enhancement rate of intracellular PpIX followed the same trends as the levels of GF enhancement rate of ALA-PDT in the different cell types. For HF, a large effect was not revealed in this study.

CONCLUSION

The present study, although preliminary, strongly suggests that concomitant treatment with ALAand GF may be very useful to enhance the effect of ALA-PDT.

Oxidative burst of neutrophils against melanoma B16-F10

Intensive oxidative burst was determined by chemiluminescence of peripheral blood neutrophils of mice that were intramuscularly injected with melanoma B16-F10 and/or subcutaneously with Sephadex G-200. The neutrophils from papula developed at the site of Sephadex injection were cytotoxic for the B16-F10 cells in vitro. However, survival of Sephadex injected tumour-bearing mice was lower than of control animals bearing B16-F10, while their tumours grew faster and were less necrotic. Thus, it is likely that injection of Sephadex distracted the neutrophils from the tumour allowing faster progression of the tumour, indicating that neutrophils may have an important role in the host defence against malignant cells in the early stage of tumour development.