T cell molecular targets for psoralens

Activity of psoralen-functionalized nanoscintillators against cancer cells upon X-ray excitation

We report development of a nanoparticle-based, X-ray-activated anticancer "nanodrug" composed of yttrium oxide (Y(2)O(3)) nanoscintillators, a fragment of the HIV-1 TAT peptide, and psoralen. In this formulation, X-ray radiation is absorbed by the Y(2)O(3) nanoscintillators, which then emit UVA light. Absorption of UVA photons by nanoparticle-tethered psoralen has the potential to cross-link adenine and thymine residues in DNA. UVA-induced cross-linking by free psoralen upon activation with UVA light has previously been shown to cause apoptosis in vitro and an immunogenic response in vivo. Studies using the PC-3 human prostate cancer cell line demonstrate that X-ray excitation of these psoralen-functionalized Y(2)O(3) nanoscintillators yields concentration-dependent reductions in cell number when compared to control cultures containing psoralen-free Y(2)O(3) nanoscintillators.

Photopheresis affects the course of experimental allergic encephalomyelitis in Lewis rat

BACKGROUND/PURPOSE

The mechanism responsible for the beneficial effects of extracorporeal photochemotherapy (ECP) remains unknown. In the rat model of experimental allergic encephalomyelitis (EAE), the transfer of encephalitogenic cells (EAE cells) induces transient passive EAE, followed by resistance to subsequent disease induction through immunization with central nervous system antigens (active EAE).

METHODS

We tested whether ECP exerts its therapeutic effect by inducing an immune response targeted on circulating pathogenic T-lymphocytes, which results from their increased immunogenicity. We compared the potential of untreated versus ECP-treated encephalitogenic cells to transfer passive EAE and protect against active induction of the disease. The UVA irradiation conditions were derived from intensive ECP protocols used in human clinical studies.

RESULTS

Animals receiving untreated cells showed clinical symptoms following cell transfer but not after subsequent immunisation, whereas those receiving ECP-treated cells remained healthy following cell transfer but experienced clinical symptoms after subsequent immunisation. However, these symptoms were less marked than in control naive rats.

CONCLUSION

Under these ECP protocol conditions, ECP-treated cells have no greater active stimulatory potential for the recipient immune system than untreated cells, since they are less effective at triggering the response that causes the resistant state to active EAE. We suggest that intensive ECP protocol may have deleterious effects with a risk of relapses after treatment discontinuation. The search for the irradiation threshold that would inhibit the T-cell pathogenic properties, but retain their ability to educate the immune system, remains a major research challenge.

Pharmacokinetics of 8-methoxypsoralen during extracorporeal photopheresis

BACKGROUND/PURPOSE

Extracorporeal photopheresis (ECP) is a widely used therapy for the treatment of diverse diseases such as cutaneous lymphomas and graft-vs-host disease. Knowledge of the effective concentration of 8-methoxypsoralen (8-MOP) in the photopheresis apparatus and the photodegradation time-course of 8-MOP during ECP is a prerequisite for a successful therapy.

METHODS

The time course of 8-MOP concentration was measured in patients' serum and in the photoactivation chamber (so-called buffy coat fraction) during ECP. Samples were analyzed by high-performance liquid chromatography. Half-lives of 8-MOP in both fractions were calculated assuming first-order kinetics (exponential decay). Losses due to adsorption and photodegradation were investigated and the recovery of bioavailable 8-MOP calculated.

RESULTS

In female patients (average age 61+/-9 years) given 0.4-0.6 mg 8-MOP/kg body weight in the form of Oxsoralen capsules, peak serum concentrations averaged 420+/-80 ng/ml (n=8). In contrast, peak concentrations in the photoactivation chamber averaged only 134 ng/ml, or 32% of serum values. In serum, peak 8-MOP concentrations were reached < or =40 min following ingestion; the half-life of 8-MOP in the serum was 50+/-14 min (n=7). The effective half-life of 8-MOP in the photoactivation chamber was considerably longer (about 4 h). The recovery of free, bioavailable 8-MOP in the photoactivation chamber at the end of ECP averaged 42% of the applied dose; losses stemmed mainly from photodegradation of 8-MOP and from adsorption of 8-MOP to the surfaces of the apparatus.

CONCLUSION

We conclude that interpretation of investigations on clinical success and dose-response aspects of ECP must take into account the complex pharmacokinetic behaviour of 8-MOP during the ECP procedure.

Photoactivated 8-methoxypsoralen treatment causes a peptide-dependent increase in antigen display by transformed lymphocytes

Ex vivo exposure of malignant human T cells to photoactivated 8-methoxypsoralen (8-MOPa), followed by their i.v. return, appears to vaccinate patients against tumor-associated antigens of cutaneous T cell lymphoma in a procedure termed photopheresis. The molecular basis of this Food and Drug Administration-approved therapy, administered in 100 centers worldwide, is unclear. Most of the attention to the mechanism of action of the drug has focused on its capacity to form covalent cross-links with pyrimidine bases of DNA, thereby inhibiting cellular proliferation. Because immunologic factors appear to be important in the clinical response and could potentially serve as a model for immunotherapy of other malignancies, we explored the possibility that 8-MOP-treated cells display increased quantities of antigenic peptides at their cell surface. In this work, human B-lymphoblastoid tissue culture lines were exposed to 8-MOPa and expression of cell surface class I major histocompatibility complex proteins assessed, since CD8 T cells recognize antigenic moieties in the context of class I molecules. A peak 200-300% increase in MHC class I expression in 8-MOPa-treated cells occurred at 20 hr. 8-MOPa was far more effective in inducing this increase in class I MHC than other modalities, including mitomycin C, gamma-irradiation, ultraviolet B or heat or cold shock. This increase in surface class I MHC molecules appears to be driven by the degradation of cytoplasmic proteins into small peptides, followed by the transport of these peptides to MHC class I molecules in the endoplasmic reticulum. The data suggest that 8-MOPa treatment may augment the immunogenicity of tumor and/or antigen-presenting cells by enhancing processing and transport of class I MHC antigenic peptides.

The immunological effect of 8-methoxypsoralen and UVA treatment on murine T-cell leukemia

8-Methoxypsoralen (8-MOP) plus long-wavelength UV radiation (UVA, 320-400 nm) have been used to treat various diseases such as cutaneous T-cell lymphoma, systemic scleroderma, rheumatoid arthritis and rejection of heart transplants. However, the immunological mechanism of this treatment remains unknown. In this report, we investigated the effect of 8-MOP/UVA on the modulation of the immunogenicity of a T-cell leukemia cell line (RL male 1 cells). The results demonstrated that the stimulator function of the in vitro 8-MOP/UVA-treated RL male 1 cells was enhanced in both RL male 1-specific allogeneic and syngeneic immune responses. Furthermore, the enhancement of the immunogenicity of the 8-MOP/UVA-treated RL male 1 cells was found to be strongly associated with the increase of intercellular adhesion molecule-1 expression on these 8-MOP/UVA-treated tumor cells. Therefore, our findings suggested that the alteration of the expression of the immune-related cell surface molecules might be an important effect of 8-MOP/UVA treatment on the elevation of the immunogenicity of the 8-MOP/UVA-treated tumor cells.