Multiparameter flow cytometry for the diagnosis and monitoring of small GPI-deficient cellular populations.

BACKGROUND: Glycosyl-phosphatidylinositol (GPI)-negative blood cells are diagnostic for Paroxysmal Nocturnal Hemoglobinuria (PNH). Marrow failure states are often associated with GPI-negative cell populations. Quantification of small clonal populations of GPI-negative cells influences clinical decisions to administer immunosuppressive therapy in marrow failure states (aplastic anemia or myelodysplastic syndrome) and to monitor minimal residual disease after allogeneic blood or marrow transplantation (BMT). We studied the reliability of high-resolution flow cytometry markers operating at the limits of detection. METHODS: We performed serial quantification of the PNH clone size in 38 samples using multiparameter flow cytometry. Granulocytes, monocytes, and RBCs were gated using forward and side scatter as well as lineage-specific markers. The GPI-linked markers fluorescent aerolysin (FLAER), CD55, and CD59 were comparatively evaluated. We also evaluated CD16 on granulocytes and CD14 on monocytes. The sensitivity of detection by each marker was further defined by serial dilution experiments on a flow-sorted sample. Two patients had quantification of their GPI-negative clones before and after allogeneic BMT. RESULTS: FLAER was the most discriminant marker and allowed identification of 0.1% of GPI-negative cells despite other markers having superior signal-to-noise characteristics. CD14 and CD16 were inferior to CD55 at lower concentrations and in clinical application. CONCLUSIONS: Multiparameter flow cytometry permits quantification of small GPI-negative clones with a sensitivity limit of about 0.1%. The single most reliable marker to monitor small granulocyte or monocyte PNH clones is FLAER, especially in conditions such as myelodysplastic syndromes or BMT, when traditional GPI-linked surface marker expression can be significantly altered. © 2010 International Clinical Cytometry Society.

Tumor vascular response to photodynamic therapy and the antivascular agent 5,6-dimethylxanthenone-4-acetic acid: implications for combination therapy.

PURPOSE: Photodynamic therapy (PDT) is a clinically approved treatment for a variety of solid malignancies. 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is a potent vascular targeting agent that has been shown to be effective against a variety of experimental rodent tumors and xenografts and is currently undergoing clinical evaluation. We have previously reported that the activity of PDT against transplanted mouse tumors is selectively enhanced by DMXAA. In the present study, we investigated the in vivo tumor vascular responses to the two treatments given alone and in combination. EXPERIMENTAL DESIGN: Vascular responses to (i) four different PDT regimens using the photosensitizer 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH) at two different fluences (128 and 48 J/cm(2)) and fluence rates (112 and 14 mW/cm(2)), (ii) 5-aminolevulinic acid (ALA)-sensitized PDT (135 J/cm(2) at 75 mW/cm(2)), (iii) DMXAA at a high (30 mg/kg) and low dose (25 mg/kg), and (iv) the combination of HPPH-PDT (48 J/cm(2) at 112 mW/cm(2)) and low-dose DMXAA were studied in BALB/c mice bearing Colon-26 tumors. RESULTS: PDT-induced changes in vascular permeability, determined using noninvasive magnetic resonance imaging with a macromolecular contrast agent, were regimen dependent and did not predict tumor curability. However, a pattern of increasing (4 hours after treatment) and then decreasing (24 hours after) contrast agent concentrations in tumors, seen after high-dose DMXAA or the combination of PDT and low-dose DMXAA, was associated with long-term cure rates of >70%. This pattern was attributed to an initial increase in vessel permeability followed by substantial endothelial cell damage (CD31 immunohistochemistry) and loss of blood flow (fluorescein exclusion assay). Low dose-rate PDT, regardless of the delivered dose, increased the level of magnetic resonance contrast agent in peritumoral tissue, whereas treatment with either DMXAA alone, or PDT and DMXAA in combination resulted in a more selective tumor vascular response. CONCLUSIONS: The observed temporal and spatial differences in the response of tumor vessels to PDT and DMXAA treatments could provide valuable assistance in the optimization of scheduling when combining these therapies. The combination of PDT and DMXAA provides therapeutically synergistic and selective antitumor activity. Clinical evaluation of this combination is warranted.

Treatment with the tumor necrosis factor-alpha-inducing drug 5,6-dimethylxanthenone-4-acetic acid enhances the antitumor activity of the photodynamic therapy of RIF-1 mouse tumors.

DMXAA (5,6-dimethylxanthenone-4-acetic acid) is an antivascular agent that exerts its antitumor effect at least partly through the induction of tumor necrosis factor (TNF)-alpha. Photodynamic therapy (PDT), the activation of a photoreactive drug in tumor tissue with visible light, is used clinically to control solid malignancies. PDT has been shown previously to be potentiated, in mice, by the i.p. administration of recombinant human TNF-alpha. Here, we investigated the activity of DMXAA as a modifier of Photofrin-based PDT of implanted murine RIF-1 tumors. The DMXAA dose (20 mg.kg(-1)) used throughout this study had little effect on tumor growth. The combination of DMXAA and PDT led to a reduction in tumor volume and significant delays in regrowth, giving a PDT-dose modification factor of 2.81. This enhancement was found to be strongly schedule dependent. The most pronounced responses were achieved when DMXAA was administered 1-3 h before the local illumination of the tumors; less activity was observed at other intervals within +/-24 h of PDT-light delivery. Using a 2-h DMXAA-light interval, histological examination showed significantly reduced blood vessel counts (CD31 immunostaining) and marked necrosis (H&E) in the tumors given combination therapy compared with the tumors given either agent alone. Conversely, peritumoral tissue was still intact 24 h after the combined therapy. DMXAA did not augment the damage to normal mouse feet after low-dose PDT (1.5 mg.kg(-1) Photofrin); however, there was some enhancement of normal tissue phototoxicity when DMXAA was combined with high-dose PDT. The antitumor effect after DMXAA plus low-dose PDT (1.5 mg.kg(-1) Photofrin) appeared to be dependent on TNF-alpha because neutralizing antibodies to this cytokine reduced the tumor response to control levels. DMXAA by itself induced TNF-alpha in RIF-1 tumors whereas PDT did not. However, the addition of PDT after DMXAA resulted in decreases in TNF-alpha, suggesting that the enhanced antitumor activity of the combination therapy was not attributable simply to an increased induction of the cytokine by PDT over that from DMXAA alone. These observations suggest a promising new combination therapy with considerable therapeutic advantage.