Deoxyribonuclease treatment prevents blood-borne liver metastasis of cutaneously transplanted tumour cells in mice

Abstract

Summary Murine L5178Y-ML cells, when transplanted subcutaneously into the flank of (BALB/c x DBA/ 2)F, mice, grew locally and always formed spontaneous metastases in the liver. Even after surgical removal of the primary tumour mass 5 or 7 days after tumour cell inoculation, all mice died due to liver metastases within 18 days. Using this model of tumour metastasis, we examined whether serine protease or deoxyribonuclease I (DNase I) would affect metastasis. Spontaneous liver metastasis of L5 1 78Y-ML cells was (Sugihara et al., 1990). We also observed that these alterations in frequency of metastasis were direct reflections of changes of sequestration intensity in the lungs of the tumour cells, probably due to aggregation and disaggregation in vivo (Sugihara et al., submitted for publication). Our electron microscopic study showed that this aggregation seemed to be caused by formation of a sleeve-like structure which surrounded the cells and connected them with each other. This structure probably originated from the cell surface glycocalyx in some sort of association with DNA molecules (Sugihara et al., 1991 Recently we examined a spontaneous metastasis model in mice using the L5178Y-ML cell line established by Watanabe and his co-workers (Watanabe et al., 1988). The L5178Y-ML cell line was derived from L5178Y, a murine T-lymphoma cell line isolated from a methylcholanthrene-induced lymphoma in DBA/2 mice. In order to establish a liver-oriented metastatic tumour cell line, cells were propagated further sequential cycles of subcutaneous inoculation of L5178Y cells which were isolated from the metastatic liver masses. L5178Y-ML cells, therefore, metastasised predominantly to the liver after intravenous or subcutaneous injection (Watanabe et al., 1988). In our preliminary study. L5178Y-ML cells were also sensitive to serine proteases and to DNase I in tumour cell aggregation and disaggregation, respectively. The present study was, therefore, undertaken to confirm the effects of protease and nuclease in altering the blood-borne metastatic rate in this model which more closely resembles clinical blood-borne metastasis.

Extracellular DNA: A Bridge to Cancer

“…A synthesis of over 50 years of independent studies measuring exDNA-exDNase dynamics strongly supports the suggestion by several authors (14,30,31,37) that DNase I application in cancer treatment alone or in combination with other methods is a logical clinical approach. This is especially true now that there is a context for understanding how exDNA arises in response to inflammation and how it may facilitate metastasis unless controlled by adequate DNase I activity.…”

“…Sugihara and colleagues (37) documented that injection of DNase I for 3 days after implantation of tumor cells in a mouse model resulted in increased survival of up to 24 days compared with controls treated with saline injection only (P < 0.01). In situ electron microscopy revealed that aggregates that developed on the liver after tumor cell transplantation (Fig.…”

“…Based on the observation that cancer cells were found to be associated with mesh-like extracellular structures, which were not observed after DNase I treatment, Sugihara and colleagues (37) speculated that DNA might be part of an extracellular matrix that facilitates implantation. This hypothesis is supported by studies documenting that treatment of diverse cancer cells or their supernatants with DNase I results in loss of the ability to transmit cancer (30,34,36,41).…”

“…This concept provides a new basis for interpreting long-standing observations that increased exDNA (also called circulating free DNA or cfDNA), and reduced DNase levels in human blood occur in correlation with cancer development and progression (25)(26)(27)(28)(29)(30)(31)(32)(33). Studies by independent laboratories around the world, moreover, repeatedly have documented that DNase 1 added to diverse cancer cells inhibits their metastatic potential (30,(34)(35)(36)(37)(38)(39)(40)(41).…”

A recombinant cytotoxic chimera based on mammalian deoxyribonuclease-I

“…The bovine enzyme has been used in combination with fibrinolysis as a necrolytic agent in the treatment of wounds and ulcers, bronchitis, inflammatory conditions and herpes infection (for review: Lloyd, 1968) with favourable results and no adverse side effects. There is also evidence relating the activity of DNase-I to the metastatic potential of tumours, with viscous DNA possibly being involved in the formation of new tumour foci (Sugihara et al, 1993). The most successful use of DNase-I has been as a drug for the relief of cystic fibrosis symptoms (Pulmozyme; Shak et al, 1990) and other diseases where thick purulent secretions containing DNA can cause illness.…”