HISTOCHEMICAL LOCALIZATION OF ACID PHOSPHATASE AND CATHEPSIN-LIKE ACTIVITIES IN REGRESSING TAILS OF XENOPUS LARVAE AT METAMORPHOSIS

Macrophages and cancer

The uncontrolled growth of metastases resistant to conventional therapeutic modalities is a major cause of death from cancer. Data from our laboratory and others indicate that metastases arise from the nonrandom spread of specialized malignant cells that preexist within a primary neoplasm. These metastases can be clonal in their origin, and different metastases can originate from different progenitor cells. In addition, metastatic cells can exhibit an increased rate of spontaneous mutation compared with benign nonmetastatic cells. These data provide an explanation for the clinical observation that multiple metastases can exhibit different sensitivities to the same therapeutic modalities. These findings suggest that the successful therapy of disseminated metastases will have to circumvent the problems of neoplastic heterogeneity and the development of resistance. Appropriately activated macrophages can fulfill these demanding criteria. Macrophages can be activated to become tumoricidal by interaction with phospholipid vesicles (liposomes) containing immunomodulators. Tumoricidal macrophages can recognize and destroy neoplastic cells in vitro and in vivo, leaving nonneoplastic cells uninjured. Although the exact mechanism(s) by which macrophages discriminate between tumorigenic and normal cells is unknown, it is independent of tumor cell characteristics such as immunogenicity, metastatic potential, and sensitivity to cytotoxic drugs. Moreover, macrophage destruction of tumor cells apparently is not associated with the development of tumor cell resistance. Macrophages are found in association with malignant tumors in a definable pattern, suggesting that the most direct way to achieve macrophage-mediated tumor regression is in situ macrophage activation. Intravenously administered liposomes are cleared from the circulation by phagocytic cells, including macrophages, so when liposomes containing immunomodulators are endocytosed, cytotoxic macrophages are generated in situ. The administration of such liposomes in certain protocols has been shown to bring about eradication of cancer metastases. Macrophage destruction of metastases in vivo is significant, provided that the total tumor burden at the start of treatment is minimal. For this reason, we have been investigating various methods to achieve maximal cytoreduction in metastases by modalities such as chemotherapy or radiotherapy prior to macrophage-directed therapy. It is important to note that even the destruction of 99.9% of cells in a metastasis measuring 1 cm2 would leave 10(6) cells to proliferate and kill the host. The ability of tumoricidal macrophages to distinguish neoplastic from bystander nonneoplastic cells presents an attractive possibility for treatment of the few tumor cells which escape destruction by conventional treatments. Macrophage-directed therapy has been studied in several human protocols, yielding important biological information about the use of liposome-encapsulated macrophage activators in cancer patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Activated macrophages distinguish undifferentiated-tumorigenic from differentiated-nontumorigenic murine erythroleukemia cells

The interaction between macrophages and differentiating cells was examined using murine erythroleukemia cells (MELC). Inflammatory macrophages activated with recombinant murine interferon-gamma (rMuIFN-gamma) and lipopolysaccharide (LPS) first specifically recognized and bound tumorigenic-undifferentiated MELC and then produced their lysis. MELC that were induced to differentiate by a 5-day treatment with 5 mM N,N'-hexamethylene-bis-acetamide (HMBA) accumulated hemoglobin (benzidine positive) and were not recognized by the macrophages. Qualitative examination by light and electron microscopy confirmed the specific nature of the macrophage-MELC interaction. Quantitative assessment showed that the binding was dependent on the temperature and divalent cations and independent of serum components. A 24-h treatment of MELC with HMBA resulted in decreased binding, prior to hemoglobin accumulation and commitment to differentiation. The lack of binding of nontumorigenic-differentiated cells by macrophages was not due to residual HMBA. It thus appears that macrophages can distinguish MELC at different stages of differentiation.

Isolation of lysosomes from the tail of metamorphosing bullfrog tadpole

A mitochondrial-lysosomal fraction obtained by differential centrifugation of the tail homogenate of metamorphosing Rana catesbeiana tadpoles was fractionated on iso-osmotic self generating gradients composed of modified colloidal silica (Percoll). More than half the activities of most lysosomal hydrolases were recovered to a heavy fraction, which contained little activities of cytochrome oxidase and of catalase. The activities of lysosomal enzymes in the heavy fraction showed latency, and the median density of those was 1.09. These results indicate that intact lysosomes, which are considerably purified, could be obtained by this method.

Tail muscle hydrolases during metamorphosis of the anuran tadpole. I. Histochemical studies

Naphthylamidase, beta-glucuronidase and trimetaphosphatase have been studied histochemically in the tail muscles of Rana catesbeiana, Rana japonica and Xenopus laevis tadpoles. During the early stages of growth, tadpole tail muscles showed very low activity of these hydrolases, whereas during the prometamorphic and metamorphic stages, they exhibited a marked increase in enzyme activity. This was localized in the subepidermal and subnotochordal mesenchymous tissue and in the myoseptum, i.e. between the muscle bundles.

[Characterization and behaviour of lysosomal enzymes in tail tissue of xenopus larvae during involution]

1. The distribution of lysosomal enzymes obtained by density gradient centrifugation of cell-free extracts of Xenopus tail tissue was compared during growth and involution. The particles containing lysosomal enzymes were also characterized by means of electron microscopy. 2. Cytochromeoxidase is recovered to more than 90% in bound form (mitochondria), whereas lysosomal enzymes are characterized by a high proportion of soluble activity (up to 67%). The particle-bound activity ofβ-glucuronidase, cathepsin, and acid RNase show two peaks after centrifugation, in contrast to the activity of acid phosphatase, which is distributed over the whole gradient. During tail involution an increasing proportion of soluble activity is observed, especially for cathepsin and acid RNase. 3. Electronmicroscopical examination reveals a rather heterogeneous composition of the particle populations obtained by density gradient centrifugation. In fractions with highest activity of lysosomal enzymes various types of electron dense granules are found, thus precluding characterization of a specific lysosomal structure. 4. The distribution of enzymes after induction of tail involution with thyroxine was almost similar to the results obtained from spontaneously metamorphosing animals. Since actinomycin D inhibits the increase in lysosomal enzymes and tissue involution it is concluded that the synthesis of soluble acid hydrolases is a prerequisite of hormonal induced tissue involution.

Lysosomal enzyme changes in growing and regressing mammary tumours

Rat mammary tumours induced by 7,12-dimethylbenz[a]anthracene can undergo repeated growth and regression during successive pregnancies. In a 10-day period after birth about half of the tumours regressed 50% or more. The concentrations of the lysosomal enzymes increased in regressing mammary tumours to the following multiples of the initial values: beta-glucuronidase, 7.7; beta-galactosidase, 3.9; cathepsin, 2.9; acid ribonuclease, 2.1; arylsulphatase A, 1.5; acid phosphatase, 1.4. In contrast, several non-lysosomal enzymes failed to increase. Activities in the post-partum uterus increased to the following multiples of the initial values: beta-glucuronidase, 5.8; cathepsin, 5.5; acid ribonuclease, 4.3; beta-galactosidase, 2.2; acid phosphatase, 1.8. Arylsulphatase A in the post-partum uterus decreased significantly, suggesting a non-lysosomal distribution or a special function related to pregnancy. No other significant changes were observed in the lysosomal or non-lysosomal enzymes in the hormone-independent liver or hormone-dependent normal mammary gland. The ratio of free to bound arylsulphatase A and acid ribonuclease decreased slightly 1-3 days after birth because of problems in homogenizing the tumours. At days 4-8, however, there was a dramatic increase in the ratio of the free to bound activities. The results can be explained in terms of the lysosomal theory of intracellular digestion.