Intracellular chemiluminescence activates targeted photodynamic destruction of leukaemic cells

Photodynamic therapy (PDT) involves a two-stage process. A light-absorbing photosensitiser (Ps) is endocytosed and then stimulated by light, inducing transfer of energy to a cytoplasmic acceptor molecule and the generation of reactive oxygen species that initiate damage to cellular membrane components and cytolysis. The expanded use of PDT in the clinic is hindered by the lack of Ps target-cell specificity and the limited tissue penetration by external light radiation. This study demonstrates that bioconjugates composed of transferrin and haematoporphyrin (Tf–Hp), significantly improve the specificity and efficiency of PDT for erythroleukemic cells by a factor of almost seven-fold. Fluorescence microscopy showed that the conjugates accumulate in intracellular vesicles whereas free Hp was mostly membrane bound. Experiments with cells deliberately exposed to Tf–Hp at <LD₁₀₀ doses showed that surviving cells did not develop resistance to subsequent treatments with the conjugate. Furthermore, we show that the compound luminol induces intracellular chemiluminescence. This strategy was then used to obviate the use of external radiation for Ps activation by incubating the cells with luminol either before or together with Tf–Hp. This novel chemical means of PDT activation induced cytotoxicity in 95% of cells. These combined approaches provide an opportunity to develop broader and more effective applications of PDT.

Differentiation-dependent photodynamic therapy regulated by porphobilinogen deaminase in B16 melanoma

Protoporphyrin IX (PpIX) synthesis by malignant cells is clinically exploited for photodiagnosis and photodynamic therapy following administration of 5-aminolevulinic acid (ALA). The expression and activity of the housekeeping porphobilinogen deaminase (PBGD) was correlated to PpIX synthesis in differentiating B16 melanoma cells. Differentiation was stimulated by two inducers, butyrate and hexamethylene bisacetamide (HMBA), both of which promote the formation of typical melanosomes and melanin, as well as morphological changeover. A marked decrease in total PBGD activity and PpIX synthesis was observed following stimulation by butyrate, while HMBA induced an opposite effect. In contrast, ferrochelatase levels remained unchanged. Photodynamic inactivation of the cells undergoing differentiation was largely dependent on the PpIX accumulation, which was modulated by the two inducers butyrate and HMBA. Fluorescence immunostaining with anti-PBGD antibodies revealed a major PBGD fraction in the nucleus and a minor fraction in the cytosol. This nuclear localisation pattern was confirmed by expression of PBGD fused to green fluorescence protein. We suggest that efficient photodynamic therapy of cancer facilitated by ALA administration can be enhanced using combined therapeutic modalities.

Specificity of photosensitizer accumulation in undifferentiated versus differentiated colon carcinoma cells

The relationship between tumor cell differentiation and photosensitizer accumulation used in PDT is poorly defined. In the present work, specific cell differentiation of colon carcinoma CT26 cells induced by sodium butyrate was manifested by morphological changes, proliferation and protein expression and was correlated with the accumulation of endogenous and exogenous photosensitizes. Reduced accumulation of the endogenous protoporphyrin IX and the exogenous hypericin and MC540 was detected in differentiated cells. In contrast, a differentiation-dependent increase was measured with TPPS4, TMPyP, the pheophorbides (C5, C6, C12), HypS4 and helianthrone. In conclusion, PpIX, Hypericin and MC540 show specific binding and accumulation in poorly differentiated tumors, giving these tumors tissue-specific advantage in photo-diagnostic PDT applications.

Classification of lymphoproliferative disorders by spectral imaging of the nucleus

Spectral nuclear morphometry was used for the classification of lymphocytes in lymphoproliferative disorders. May-Grunwald-Giemsa-stained blood specimens were taken from thirty patients with infectious mononucleosis, non-Hodgkin lymphoma or chronic lymphocytic leukemia, and from ten healthy individuals. Blood specimens were analyzed by spectral imaging. Seventeen distinct spectra were collected into a spectral library and a distinct pseudo color was assigned to each one of them. The library was used to scan all the cells in the database and to create a spectrally classified image of each cell. The spectral map, per cell, reveals distinct spectral-response regions in each cellular compartment, via the distinct region colors. Computational analysis of the spectral maps allows for the objective quantification of a set of parameters, or features, representing the cell. The features used in this work include the area and perimeter of the nucleus, circularity, edginess and the spectral pattern. The analysis pursued showed that each class of cells is associated with a set of unique parameters. We conclude that spectral analysis combined with feature analysis provides significant information in the analysis of lymphoproliferative disorders and may serve as an additional tool for the histopathological evaluation of disease.

Nuclear distribution of porphobilinogen deaminase (PBGD) in glioma cells: a regulatory role in cancer transformation?

Recently, considerable interest has been directed to red-fluorescence photodiagnosis of brain and other tumours during surgery using the protoporphyrin IX natural precursor, 5-aminolaevulinic acid. In the present study we focused on the role of the rate-limiting enzyme porphobilinogen deaminase in glioma C6 cell activity, differentiation and sub-cellular distribution. Over-expression of the human housekeeping porphobilinogen deaminase in the glioma cells, using the housekeeping-porphobilinogen deaminase plasmid, induced a G1 cell cycle attenuation accompanied by increases in enzyme activity and c6 differentiation toward astrocytes. Visualisation of subcellular localisation of the porphobilinogen deaminase using the independent techniques of fluorescence immuno-staining with specific anti-human porphobilinogen deaminase antibodies and cellular expression of porphobilinogen deaminase fused to green fluorescent protein, revealed (unexpectedly) a major fraction of porphobilinogen deaminase in the nucleus and only a minor fraction in the cytoplasm. Both C and N terminals of porphobilinogen deaminase fused to green fluorescent protein revealed a major fraction of the newly synthesized fused porphobilinogen deaminase in the nucleus. Furthermore, newborn rat brain cells grown in a primary culture showed the same localisation pattern of porphobilinogen deaminase in the nuclei. Stimulation of C6 glioma cell differentiation by butyrate induced a marked decrease in porphobilinogen deaminase both in the nucleus and in the cytoplasm as determined by Western blotting and fluorescence immuno-localisation. These findings suggest a possible dual role for housekeeping porphobilinogen deaminase in fast dividing glioma cells, one related to the porphyrin synthesis pathway and another coupled to nuclear function, which might be linked to tumorigenesis.

Nuclear transport of photosensitizers during photosensitization and oxidative stress

The nuclear transport pathways of the photosensitizers meso-tetra(4-sulfonatophenyl)porphyrin (TPPS4) and meso-tetra(4-N-methylpyridyl)porphyrin (TMPyP) during photosensitization and oxidative stress were characterized in CT-26 murine colon carcinoma cells using fluorescence microscopy and multi-pixel spectral imaging. Prior to irradiation, TPPS4 and TMPyP localized mainly in the lysosomes, while irradiation or H2O2 treatment induced a relocalization into the nucleus and nucleoli. Flow cytometry analysis of isolated nuclei from the treated cells showed an increase in nuclear fluorescence accompanying the relocalization. Isolation and separation of the nuclear proteins according to molecular weight was performed using a sephadex G-100 column. The protein fractions exhibiting high fluorescence were separated by high performance liquid chromatography. Five major classes of proteins with a retention time of 1, 7, 11, 12 and 15 min were obtained. Each photosensitizer was associated with a distinct class of proteins. While TPPS4 fluorescence was detected in the protein fraction with a retention time of 11 min, TMPyP fluorescence was associated with a protein fraction having a retention time of 7 min. We conclude that although oxidative stress triggers entry into the nucleus of both TPPS4 and TMPyP, each sensitizer uses a distinct transport mechanism based on its chemical properties.

Effects of water-soluble antioxidant from spinach, NAO, on doxorubicin-induced heart injury

Doxorubicin (DOX) produces clinically restorative responses in numerous human cancers, but its cardiotoxicity has limited its usefulness. Because reactive oxygen species may affect DOX-induced antitumor activity and cardiotoxicity, we evaluated the prophylactic effect of spinach natural antioxidant (NAO) on DOX-induced cardiotoxicity and oxidative stress in female Balb/c mice using histological, electron microscopical and biochemical parameters. Mice were treated with NAO for 7 days prior to and/or for 6 days after DOX administration. Pretreatment with NAO (cumulative dose: 130 mg/kg) did not hinder the effectiveness of DOX. Light and electron microscopy of DOX-treated heart revealed myocardial degeneration. When administered combined before and after DOX, NAO conferred the most significant cardiac protection. The effects of NAO on the lipid peroxidation product, malondialdehyde, and on H2O2/ hydroperoxides were examined on day 6 following DOX administration; levels of both were elevated in DOX-treated mice, compared to control. Pretreatment with NAO prevented these changes. Pretreatment with NAO before DOX administration decreased catalase and increased superoxide dismutase activities compared to the DOX group. Our results suggest usage of NAO in combination with DOX as a prophylactic strategy to protect heart muscle from DOX-induced cellular damage.

Structural characterization of erythroid and megakaryocytic differentiation in Friend erythroleukemia cells

OBJECTIVE

The aim of this study was to examine the structural characterization of erythroid and megakaryocytic cell differentiation in Friend erythroleukemic cells using spectral imaging and electron microscopy.

MATERIALS AND METHODS

Two variants of Friend erythroleukemia cells were treated with hexamethylene bisacetamide (HMBA) to induce differentiation: 1) MEL, which exhibit the normal phenotype and are susceptible to differentiation; and 2) the resistant R1 cells. The cells were analyzed by spectral imaging along with transmission and scanning electron microscopy. The expression of cell cycle regulatory proteins was analyzed by Western blotting.

RESULTS

Spectral imaging of HMBA-treated MEL and R1 cells stained by May-Grünwald-Giemsa and subjected to spectral similarity mapping revealed five morphologic cell types: proerythroblast-like cells, normoblast-like cells, reticulocyte-like cells, megakaryocytes, and apoptotic cells. In MEL cells, both megakaryocytic differentiation characterized by nuclear lobes and erythroid differentiation characterized by accumulation of hemoglobin were detected; R1 cells were not committed to terminal differentiation. HMBA-induced cell cycle arrest at G(1) affected the expression of regulatory proteins in a similar manner in both types of cells. Expression of cyclin-dependent kinase 4 decreased and expression of p21(WAF1) increased. The level of the underphosphorylated form of phosphorylated retinoblastoma protein increased, inducing a decrease in the level of c-myc. In addition, we detected a decrease in the expression of the anti-apoptotic regulator, Bcl-2, and an increased expression of the pro-apoptotic regulator, Bax.

CONCLUSIONS

Spectral imaging provides new insight for the morphologic characterization of erythroid and megakaryocytic cell differentiation as well as apoptosis. Image analysis was well correlated to cell cycle arrest and the expression of regulatory proteins.

Spectral imaging of MC540 during murine and human colon carcinoma cell differentiation

We studied the staining pattern of merocyanine 540 (MC540) by spectral imaging of murine CT26 and human HT29 colon carcinoma cells incubated with the dye MC540. This dye, usually considered a potential membrane probe, localized mainly in the cytoplasmic vesicles of the colon carcinoma cells. However, in cells incubated in an environment similar to that of a tumor (pH 6.7), high fluorescence was detected in the nuclear membrane and nucleoli. Under these acidic conditions, resembling the Krebs effect, a population of CT26 cells displayed fluorescent plasma membranes. In differentiating cells, exhibiting cell cycle arrest at G(1)-phase and an elevated level of alkaline phosphatase, MC540 fluorescence was confined to cytoplasmic vesicles and was not detected in the plasma membrane or in the nucleoli. Cell sorting analysis of both cell types at pH 5.0 revealed higher fluorescence intensity in proliferating cells compared to differentiating cells. The fluorescence intensity of MC540-stained cells reached a maximum at pH 5.0, although the fluorescence of MC540 dye was maximal at pH 7.2. This phenomenon may result from increased binding of MC540 monomers to the cells because disaggregation of the dye with Triton X-100 produced similar results. We conclude that nucleolar localization of MC540 and an elevated fluorescence intensity can be used as indicators for proliferating cells in the characteristically acidic tumor environment. (J Histochem Cytochem 49:147-153, 2001)

Mitochondrial localization and photodamage during photodynamic therapy with tetraphenylporphines

The subcellular localization sites of TPPS4 and TPPS1 and the subsequent cellular site damage during photodynamic therapy were investigated in CT-26 colon carcinoma cells using spectroscopic and electron microscopy techniques. The association of both porphyrins with the mitochondria was investigated and the implications of this association on cellular functions were determined. Spectrofluorescence measurements showed that TPPS4 favors an aqueous environment, while TPPS1 interacts with lipophilic complexes. The subcellular localization sites of each sensitizer were determined using spectral imaging. Mitochondrial-CFP transfected cells treated with porphyrins revealed localization of TPPS1 in the peri-nuclear region, while TPPS4 localized in the mitochondria, inducing structural damage and swelling upon irradiation, as shown by transmission electron microscopy. TPPS4 fluorescence was detected in isolated mitochondria following irradiation. The photodamage induced a 38% reduction in mitochondrial activity, a 30% decrease in cellular ATP and a reduction in Na(+)/K(+)-ATPase activity. As a result, cytosolic concentrations of Na(+) and Ca(2+) increased, and the level of K(+) decreased. In contrast, the lipophilic TPPS1 did not affect mitochondrial structure or function and ATP content remained unchanged. We conclude that TPPS4 induces mitochondrial structural and functional photodamage resulting in an altered cytoplasmic ion concentration, while TPPS1 has no effect on the mitochondria.

Green fluorescent protein photobleaching: a model for protein damage by endogenous and exogenous singlet oxygen

Characterization of protein damage during photosensitization of chlorin e6-treated cells was performed using the green fluorescent protein (GFP). The GFP-chromophore damage caused by singlet oxygen was studied in COS 7 kidney cells and E. coli bacteria following light irradiation. Electron spin resonance (ESR) revealed the generation of endogenous singlet oxygen (1O2) by photoactivated GFP, an effect similar to that produced by the exogenous photosensitizer chlorin e6. A light dose-dependent photobleaching effect of GFP was pronounced at low pH or upon photosensitization with chlorin e6. However, the 1O2 quenchers beta-carotene and sodium azide minimized GFP photo-bleaching. Gel electrophoresis of photosensitized GFP followed by fluorescence multi-pixel spectral imaging revealed the binding of chlorin e6 to GFP, affecting the photobleaching efficacy. Fluorescence multi-pixel spectral imaging of GFP-transfected COS 7 cells demonstrated the presence of GFP in the cytoplasm and nucleus, while chlorin e6 was found to be concentrated in the perinuclear vesicles. Exposure of the cells to light induced GFP photobleaching in the close vicinity of chlorin e6 vesicles. We conclude that photoactivated GFP generates endogenous 1O2, inducing chromophore damage, which can be enhanced by the cooperation of exogenous chlorin e6.

Potential use of spectral image analysis for the quantitative evaluation of estrogen receptors in breast cancer

Evaluation of estrogen receptor (ER) content is an important factor in the choice of therapy and prognosis of breast cancer patients. In this study, we demonstrate a new spectral image analysis technique for objective and quantitative evaluations of stained specimens. The SpectraCube system was used to analyze nuclear antigens in thirteen cases of breast cancer stained by the immunoperoxidase method with hematoxylin counterstain. Spectral imaging segregated the spectrum of diaminobenzidine (DAB) from the background color of hematoxylin and a spectral index was calculated. The spectral index essentially agreed with the pathologist's index (on a scale of 0 to 3) in seven out of the thirteen cases. A substantial number of ER positive pixels was detected in the two cases scored as 0 by the pathologist's index. In a test case scored as 1 by the pathologist's index we detected a significant number of pixels, representing 47% of the nuclei, with DAB-intensity values higher than the cut-off value of 1.2. These data suggest that spectral image analysis is a sensitive method providing intensive information with high reproducibility. Our spectral imaging method is highly flexible, enabling the user to define the spatial resolution of the analyzed specimen by choosing the number of pixels per one nucleus.

Photothermic treatment of pigmented B16 melanoma using a broadband pulsed light delivery system

Pulsed photothermic treatment (PTT) of pigmented B16 mice melanoma tumors was carried out using a Photodyne incoherent light delivery system. Tumor heating with average temperature of 41-44 degrees C was observed during broadband photoirradiation (600-800 nm) at light doses of 60-120 J/cm(2) delivered using 0.6 J/cm(2) pulses (2 ms) at 1 Hz repetition rate. Electron microscopy of tumor samples revealed pronounced structural changes in microvasculature and melanosomes. Pulsed PTT caused damage to endothelial cells and vascular walls, swelling of mitochondria and melanosomal disruption without nuclear alteration. Significant tumor response with necrosis formation followed by tumor regression was observed by a tumor growth study after PTT at 120 J/cm(2).

Photodynamic therapy of cutaneous lymphoma using 5-aminolevulinic acid topical application

BACKGROUND

Photodynamic therapy (PDT) with topical application of 5-aminolevulinic acid (ALA) is a new and effective modality for treatment of superficial basal and squamous cell carcinomas.

OBJECTIVE

We present the kinetics of ALA-induced protoporphyrin IX (PP) accumulation and the results of ALA PDT treatment on two patients with different stages (stage I and stage III) of mycosis fungoides (MF)-type cutaneous T-cell lymphoma (CTCL).

METHODS

ALA-Decoderm cream was applied to the lesions for 16 hours. Spectrofluorescence measurements of PP accumulation were carried out before, during, and 1 hour after photoirradiation (580-720 nm) using the VersaLight system.

RESULTS

Different patterns of PP fluorescence kinetics were observed in patients with early and advanced stages of the disease. During photoirradiation the intensity of fluorescence decreased depending on the lesion thickness. One hour after the photoirradiation procedure no PP fluorescence was observed in the stage I MF lesion, while in the thick stage III MF lesions, PP fluorescence reappeared; after an additional 10-15 minutes of irradiation PP fluorescence disappeared. Complete response with excellent cosmetic results was observed in the stage I lesion after a single irradiation with a light dose of 170 J/cm2; in five stage III lesions, complete response was achieved after fractionated irradiation with a total light dose of 380 J/cm2 (follow-up at 27 and 24 months, respectively).

CONCLUSION

The results showed a high response of both stage I and stage III MF lesions to ALA PDT. This modality appears to be very effective and can be used successfully for MF treatment.

Treatment of viral infections with 5-aminolevulinic acid and light

BACKGROUND AND OBJECTIVE

When 5-aminolevulinic acid (ALA) is exogenously supplied, protoporphyrin IX (PpIX) is accumulated in various cells and makes them light sensitive. The possibility of using such an approach for the treatment of viral infections was studied in this work.

STUDY DESIGN/MATERIALS AND METHODS

ALA was added to cultured cells infected with human immunodeficiency virus (HIV). Accumulation of PpIX in the cells as well as virus infectivity after photodynamic treatment (PDT) were assessed. For in vivo studies, guinea pigs were infected with herpes simplex virus (HSV) and then administered ALA at intervals after infection. The animals were exposed to PDT at the site of infection 3 hours after ALA administration. Clinical observations and virus titration were made daily. For clinical studies, two patients with Molluscum contagiosum and Verrucae vulgares were treated with ALA fortified with an iron chelating agent and dimethylsulfoxide, followed 4 hours later by PDT.

RESULTS

Cells that are infected with HIV accumulated PpIX upon addition of ALA in vitro. This accumulation was enhanced approximately two-fold in the presence of an iron chelator. Subsequent exposure to red light PDT drastically reduced the virus titer (> 99% for U1 cells latently infected with HIV). In guinea pigs infected with HSV, subsequent administration of ALA and exposure of the lesions to red light shortened the duration of vesicles' appearance from more than a week to a few days and reduced HSV titer in the lesions by > or = 5 log10. ALA-PDT treated AIDS patient suffering from Molluscum contagiosum or a kidney transplant patient with Verrucae vulgares showed greatly improved clinical symptoms one month after treatment.

CONCLUSION

It is concluded that ALA-PDT could be effective in treating certain viral infections, particularly those resulting in warts.

Spectral imaging of red blood cells in experimental anemia of Cyprinus carpio

In the present work we have studied the effect of experimental anemia induced at both low and optimal temperatures on erythropoiesis in Cyprinus carpio. The results showed that hemoglobin concentration per cell was similar in both temperature conditions, however, red blood cell (RBC) concentration was higher at the optimal temperature. Induced anemia caused an abrupt decrease in RBC concentration, while the hemoglobin concentration per cell remained unchanged. Recovery, as shown by electron microscopy, was characterized by the release of differentiating young and intermediate cells to the peripheral blood. It was revealed that with the progression of differentiation the nucleus/cytoplasm ratio decreases, the chromatin condenses and the shape of the nucleus changes from round to elliptical. Spectral imaging revealed an increase in the optical density of chromatin with the maturation of the cells. The chromatin that was dispersed over the nuclear volume in the young cells becomes highly ordered in the mature cells. Spectral similarity mapping revealed the formation of a novel structure of high symmetry, representing chromatin rearrangement during the process of cellular differentiation.

Proteinase inhibitors from desert locust, Schistocerca gregaria: engineering of both P(1) and P(1)' residues converts a potent chymotrypsin inhibitor to a potent trypsin inhibitor

Two peptides, SGCI and SGTI, that inhibited chymotrypsin and trypsin, respectively, were isolated from the haemolymph of Schistocerca gregaria. Their primary structures were found to be identical with SGP-2 and SGP-1, two of a series of peptides isolated from ovaries of the same species (A. Hamdaoui et al., FEBS Lett. 422 (1998) 74-78). All these peptides are composed of 35-36 amino acid residues and contain three homologous disulfide bridges. The residues imparting specificity to SGCI and SGTI were identified as Leu-30 and Arg-29, respectively. The peptides were synthesised by solid-phase peptide synthesis, and the synthetic ones displayed the same inhibition as the natural forms: SGCI is a strong inhibitor of chymotrypsin (K(i) = 6.2 x 10(-12) M), and SGTI is a rather weak inhibitor of trypsin (K(i) = 2.1 x 10(-7) M). The replacement of P(1) then P(1)' residues of SGCI with trypsin-specific residues increased affinity towards trypsin 3600- and 1100-fold, respectively, thus SGCI was converted to a strong trypsin inhibitor (K(i) = 5.0 x 10(-12) M) that retained some inhibitory affinity towards chymotrypsin (K(i) = 3.5 x 10(-8) M). The documented role of both P(1) and P(1)' highlights the importance of S(1)'P(1)' interactions in enzyme-inhibitor complexes.

Photoproduct formation from a zinc benzochlorin iminium salt detected by fluorescence microscopy

When examined by fluorescence microscopy, tumor cells loaded with a zinc benzochlorin iminium salt showed a very faint deep-red fluorescence that was rapidly transformed to a substantially brighter red-orange fluorescence. Fourier transfer spectroscopy analysis with a red-sensitive detection system revealed that an initial fluorescence at 770 nm was gradually converted to 640 nm fluorescence during excitation. Image analysis showed that photoproduct formation was accompanied by a change in the site of drug localization from the cytoplasm to the nucleus. These studies illustrate the power of interferometry for the characterization of photoproducts and changes in sensitizer localization during photoproduct formation.

Enhancement of ALA-PDT damage by IR-induced hyperthermia on a colon carcinoma model

The interaction of photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) and hyperthermia is not well understood. In the present study, significant enhancement of tumor damage was observed after simultaneous application of ALA-PDT and IR-induced hyperthermia using a broad-band incoherent light source. One hour after systemic administration of ALA at a dose of 200 mg/kg, subcutaneously transplanted C26 colon carcinoma tumors were irradiated with two bands of the VersaLight system, red (R, 580-720 nm) and red plus IR (R + IR, 580-720 nm and 1250-1600 nm). Photoirradiation using the R + IR band at different fluence rates and exposures caused mild heating of the tumor to 39-43 degrees C at a 3 mm depth. Electron microscopy after ALA + R, ALA + R + IR and R + IR treatments showed early mitochondrial swelling that was more pronounced in the ALA + R + IR group. Tumor necrosis assessment, using histology and vital staining, revealed an enhancement of tumor necrosis depth in the ALA + R + IR group compared to ALA + R and R + IR. The results showed that subhyperthermic heating to 39-39.5 degrees C in the ALA + R + IR group decreased the threshold light dose required for 100% tumor necrosis from 210 J/cm2 (observed in the ALA + R group) to 140 J/cm2. A tumor growth delay test, based on tumor volume measurement, also revealed significant enhancement of antitumor effect after application of ALA + R + IR compared to ALA + R.

Spectral morphometric characterization of breast carcinoma cells

The spectral morphometric characteristics of standard haematoxylin and eosin breast carcinoma specimens were evaluated by light microscopy combined with a spectral imaging system. Light intensity at each wavelength in the range of 450-800 nm was recorded for 10(4) pixels from each field and represented as transmitted light spectra. A library of six characteristic spectra served to scan the cells and reconstruct new images depicting the nuclear area occupied by each spectrum. Fifteen cases of infiltrating ductal carcinoma and six cases of lobular carcinoma were examined; nine of the infiltrating ductal carcinoma and three of the lobular carcinoma showed an in situ component. The spectral morphometric analysis revealed a correlation between specific patterns of spectra and different groups of breast carcinoma cells. The most consistent result was that lobular carcinoma cells of in situ and infiltrating components from all patients showed a similar spectral pattern, whereas ductal carcinoma cells displayed spectral variety. Comparison of the in situ and the infiltrating ductal solid, cribriform and comedo carcinoma cells from the same patient revealed a strong similarity of the spectral elements and their relative distribution in the nucleus. The spectrum designated as number 5 in the library incorporated more than 40% of the nuclear area in 74.08% of the infiltrating lobular cells and in 13.64% of the infiltrating ductal carcinoma cells (P < 0.001). Spectrum number 2 appeared in all infiltrating ductal cells examined and in none of the lobular cells. These results indicate that spectrum number 5 is related to infiltrating lobular carcinoma, whereas spectrum number 2 is characteristic for infiltrating ductal carcinoma cells. Spectral similarity mapping of central necrotic regions of comedo type in situ carcinoma revealed nuclear fragmentation into defined segments composed of highly condensed chromatin. We conclude that the spectral morphometric features found for lobular and ductal cell populations may serve future automated histological diagnostics.