Heme regulation in mouse mammary carcinoma and liver of tumor bearing mice--I. Effect of allyl-isopropylacetamide and veronal on delta-aminolevulinate synthetase, cytochrome P-450 and cytochrome oxidase

Topical and intratumoral photodynamic therapy with 5-aminolevulinic acid in a subcutaneous murine mammary adenocarcinoma

One of the most promising substances used in photodynamic therapy (PDT) is 5-aminolevulinic acid (ALA), which induces endogenous synthesis and accumulation of porphyrins in malignant cells. In this paper we have shown that both topical and intratumoral administration of ALA in a subcutaneously implanted mammary carcinoma produced a significant synthesis of porphyrins and subsequent sensitization to laser light. Porphyrin accumulation was greater when ALA was administered intratumorally and tumour/normal skin porphyrin concentration ratios were higher compared with topical application. Irradiation was optimal between 2 and 3 h after topical application of 50 mg of a 20% ALA cream and 2-4 h after intratumoral administration of 30 mg ALA/cm3. The pattern of tumour response evaluated as the delay of tumour growth was similar following either route of drug administration. Applications of PDT were performed once, twice or three times in the study. The response to successive applications was constant for the same tumour, indicating that no resistance was acquired. Microscopic analysis showed both induction of foci of necrosis and haemorrhage, morphological features of apoptotic cells and total absence of cellular immune response. This paper reports on PDT with topical ALA in a subcutaneous carcinoma leading to tumour growth delay. These findings may have great relevance in the treatment of cutaneous metastasis of mammary carcinomas.

Metabolism of a chylomicron-like emulsion in rats with Walker 256 tumor: influence of a polyunsaturated (n-6) compared with a saturated fatty acid-rich diet

OBJECTIVE

Defects in lipid metabolism secondary to development of cancer are frequently observed and, in experimental animals, manipulation of the lipid content of the diet can significantly influence tumor growth. The effects of a high polyunsaturated fat vs a high saturated fat diet upon the chylomicron metabolism of rats bearing Walker 256 tumor were examined.

METHODS

Chylomicron-like emulsions labeled with radioactive lipids were injected into rats bearing the tumor and control rats. The two groups were previously given a high polyunsaturated (n-6) (15% fat) or a high saturated fat diet (15% fat) for 6 weeks. Following injection, plasma samples were collected at 8 time intervals in 60 minutes and tissue fragments were excised after the animals were killed, for determination of the plasma fractional clearance rate (FCR, min-1) and organ uptake of radioactive lipids.

RESULTS

FCR of the emulsion triacylglycerols (TG) and cholesteryl oleate ether (CE) decreased in the tumor-bearing rats fed the polyunsaturated fat-rich diet (FCR-TG control = 0.26 +/- 0.09, tumor = 0.11 +/- 0.04; FCR-CE controls = 0.18 +/- 0.05, tumor = 0.10 +/- 0.02), as did activity of the lipoprotein and hepatic lipases (p < 0.05). This indicates that in this group, the presence of the tumor elicited defective lipolysis and delayed removal of the emulsion from the plasma. In the group fed the saturated fatty acid-rich diet, however, these alterations were not observed (FCR-TG control = 0.21 +/- 0.11, tumor = 0.20 +/- 0.08; FCR-CE control = 0.13 +/- 0.06, tumor = 0.10 +/- 0.05). The uptake by several tissues of the emulsion CE was similar in all rat groups.

CONCLUSION

The saturated fat-rich diet avoids the deficiency in chylomicron lipolysis elicited by the implanted Walker 256 tumor.

Porphyrins, porphyrias, cancer and photodynamic therapy--a model for carcinogenesis

Porphyrins are the only and most powerful photosensitizers synthesized internally. To understand better the involvement of porphyrins in photosensitization reactions, the heme biosynthetic pathway is first described, as well as the main features of its regulation in both erythroid and hepatic cells. Most disorders of porphyrin metabolism, known as porphyrias, are characterized by porphyrin accumulation. A full discussion of these diseases, their classification and relevant biochemical and clinical signs are presented. Abnormalities in heme biosynthesis in disorders other than porphyrias, such as iron-deficient and sideroblastic anemias, lead poisoning, hereditary tyrosinemia, chronic renal disease and alcoholism, are briefly considered. A complete survey of the experimental research on the biosynthesis of porphyrins in tumors and of the important association between cancer and porphyrias is dealt with. The link to photodynamic therapy (PDT) emerges naturally and this is treated from the point of view of using porphyrins endogenously formed by the tumors for their localization and PDT. Finally, considering the nature of the alterations occurring in heme metabolism in tumors, and porphyrias and their ubiquity, a model is discussed where the abnormality of heme synthesis is involved in the initiating lesion of carcinogenesis. The model strongly predicts that the incidence of cancer will be high in cells with abnormal heme metabolism, suggesting that porphyric patients may be at greater risk of the development of cancer.

Distribution and photosensitizing efficiency of porphyrins induced by application of exogenous 5-aminolevulinic acid in mice bearing mammary carcinoma

By means of a chemical extraction procedure and confocal laser scanning microscopy, we investigated the kinetic patterns of uptake and biolocalization of 5-aminolevulinic acid (ALA)-induced porphyrins in s.c. transplanted tumors, adjacent normal skin and muscle, and liver of mice bearing mammary carcinoma, after i.p. injection of 250 mg/kg ALA or topical application of ALA (20% in an oil-in-water emulsion). Furthermore, we evaluated the tumor responses after either i.p. injection or topical application of 5-ALA followed by laser irradiation (632 nm, 150 mW/cm2, 25 min) by measuring the treated tumor regression/regrowth time and by light and electron microscopy. Strong fluorescence of ALA-induced porphyrins was detected in the tumor, skin and liver tissues, while little fluorescence was seen in the adjacent muscle tissue. Moreover, the highest amounts of ALA-induced porphyrins in the tumor and skin tissues were found 1 hr after i.p. injection, whereas the amounts of the porphyrins in both tissues increased with increasing time after topical application of ALA. The fluorescence of the porphyrins was localized in several components of the skin tissue (epidermis, hair follicles and their associated sebaceous glands). Furthermore, the fluorescence was diffusely distributed in the s.c. transplanted tumor tissue. Little could be observed under a confocal laser scan microscope (CLSM) in the muscle tissue. The uptake and biolocalization data correlate well with the results of PCT efficiency of the same tumor model with ALA-induced porphyrins. Light and electron microscopy showed that the mitochondria of the tumor cells and of the endothelial cells and the basal lamina of vascular walls beneath the endothelium in the tumor tissue were initially extensively destroyed after PCT with ALA-induced porphyrins. Thereafter, diffuse degeneration followed by local and/or diffuse severe necrosis of the tumor cells was found. This may be due mainly to the initial damage to mitochondria in the cancerous and endothelial cells and also to the destruction of the vascular wall in the tumor tissue.

Heme biosynthesis pathway regulation in a model of hepatocarcinogenesis pre-initiation

1. Heme regulation before the appearance of hyperplastic nodules was investigated in mice models of hepatocarcinogenesis. 2. With this aim 5-aminolaevulinate synthetase (ALA-S), microsomal heme-oxygenase (MHO), mitochondrial and cytoplasmic rhodanese activities were examined throughout a period of 35 days in animals exposed to dietary p-dimethylaminoazobenzene (DAB). 3. ALA-S activity was significantly diminished (50%) on day 14, then showing a sharply rising profile from day 28 onwards, and reaching 350% on day 35. 4. A similar profile was observed for mitochondrial rhodanese activity. 5. Changes in MHO and cytoplasmic rhodanese activities were almost the opposite to those observed for ALA-S. 6. The distinctive alteration in mitochondrial and cytoplasmic rhodanese would suggest that it plays a subtle role in ALA-S regulation during carcinogenesis initiation through a mechanism that appears to involve subcellular localization controls perhaps by means of the breakage of cystine trisulphide postulated to act as an ALA-S activator. 7. Taking into account the present results, we suggest a probable mechanism for the onset of hepatocarcinogenesis that includes a primary activating liver status, provoking biochemical aberration leading to the stage of initiation of hepatocarcinogenesis involving the whole organ.

Rhodanese and ALA-S in mammary tumor and liver from normal and tumor-bearing mice

1. Basal levels and allyl-isopropylacetamide (AIA) or veronal induced levels of delta-amino-levulinate synthetase (ALA-S), cytoplasmic and mitochondrial rhodanese were determined in tumor (T) and liver of both normal mice (NM) and T-bearing mice (TBM). 2. Rhodanese tumoral mitochondrial levels were higher than the hepatic normal mitochondrial fraction, while the cytoplasmic activity was nearly equal in all sources. 3. In neither case was the activity of tumoral ALA-S and rhodanese altered by any of the porphyrinogenic drugs. 4. Mitochondrial and cytoplasmic rhodanese activity was also measured in tumor and liver of TBM at different intervals after transplantation. We concluded that the behaviour of rhodanese is a property inherent to the tissue and not one attained with time.

Heme biosynthesis in human breast cancer--mimetic "in vitro" studies and some heme enzymic activity levels

1. Porphyrin biosynthesis from delta-aminolevulinic acid (ALA) was investigated using the technique of tissue explant cultures, in both human breast cancer and its original normal tissue. 2. The activity of ALA-dehydratase, porphobilinogenase and uroporphyrinogen decarboxylase was directly determined in both tumor and normal mammary tissues. 3. Porphyrin synthesis capacity of human breast carcinoma was 20-fold enhanced, as compared with normal tissue, at least between the stages of porphobilinogen and coproporphyrinogen formation. 4. The activity of the three enzymes examined was always lower in normal tissue than in tumoral tissue. 5. Present findings show that porphyrin biosynthesis is increased in breast cancer tissue.