JOURNAL OF BONE AND MINERAL RESEARCH Volume 3, Number 2, 1988 Mary Ann Liebert, Inc., Publishers Interferon-Inhibited Human Osteosarcoma Xenografts Induce Host Bone in Nude Mice SIMON FORSTER,' JAMES T. TRIFFITT,' HENRIK C.F. BAUER,2OTTE BROSJ0,2 OLLE S. NILSSON,2 ROGER SMITH,' and BRYAN SYKES4 ABSTRACT The growth of human osteosarcoma xenografts in nude mice can be inhibited by human interferon-alpha (IFN-a). Histologic examination of growth-inhibited tumors has revealed mineralization and partial replace- ment of the tumor by normal bone tissue. We have investigated whether the normal bone tissue was formed by differentiated tumor cells or by induction of host stroma to differentiate into bone tissue. Employing antibodies to both murine and human type I collagen, it was found that the normal bone produced in IFN-in- hibited osteosarcomas was host derived. These results suggest that IFN induced the osteosarcoma cells to produce a bone-inductive agent that interacts with the host cells, and leads to the formation of mature normal bone tissue in a heterotopic site. INTRODUCTION NTERFERON (IFN) can inhibit the growth of leukemic and I solid tumors in vivo and in vitro.") The mechanism of the anti-tumor effect is largely unknown, but there have been re- cently several reports of IFN-induced differentiation of leu- kemic The growth-inhibitory effect of IFN on tumor cells has been associated with reduced rate of transition from a quiescent GdG, state into S phase of the cell ~ y c l e . ( ~ - ~ ) He- matopoietic cells, when treated with IFN in vitro, accumulate in the GdG, phase and have been found to transform and dif- ferentiate.(2,3,6) Thus, the growth inhibition elicited with IFN may be the result of removing cells from a proliferative to a differentiating pathway. The differentiating action has been associated with induction of morphological and specific bio- chemical changes in the cells. IFN also inhibits the growth of solid tumors, but in these cases actual differentiation has not been In a recent study of 11 human osteosarcoma xenografts in nude mice, it was found that the growth of all tumors could be inhibited by IFN.(Io)The lowest IFN dose that induced growth inhibition ranged from 5 X 10' IU/day for the most IFN-sensi- tive tumors to more than 1 X lo6 IU/day for the most refrac- tory. Sensitivity to growth inhibition by IFN was directly re- lated to tumor characteristics, i.e., tumors with low growth rate and low proliferative activity were inhibited by the lower dose of IFN. This finding suggested that the susceptibility to growth inhibition by IFN was dependent on the degree of growth control that the tumors retained. Histologic examination of different human tumor xenografts in nude mice treated with IFN have, generally, revealed the same appearance as tumors from untreated m i ~ e . ( ~ - ~ ) There- fore, growth inhibition can be attained without altering histo- logic features, including frequency of mitoses. This has also been found for the majority of investigated osteosarcoma xeno- grafts.('O)However, four osteosarcomas, all growth-arrested by the relatively low IFN dose of 2 x 105 IUlday, were found to be partly, or completely, replaced by normal bone and the re- maining tumor tissue became heavily mineralized. This finding was suggestive of tumor differentiation, but it is unclear whether the bone trabeculae were formed by differentiated tumor cells or by induced host stromal cells. The aim of this study was to investigate whether the normal bone, formed in IFN-inhibited human osteosarcoma xeno- grafts, was tumor or host derived, by applying antibodies to human and murine type I collagen, respectively. 'MRC Bone Research Laboratory, Nuffield Department of Orthopaedic Surgery, University of Oxford, Oxford OX3 7LD UK. 2Depannent of Orthopaedic Surgery, Karolinska Hospital and Institute, S-104 01 Stockholm, Sweden. )Nuffield Departments of Medicine and Orthopaedic Surgery, Nuffield Orthopaedic Centre, Oxford OX3 7LD UK. 4Nuffield Department of Pathology, The John Radcliffe Hospital, University of Oxford, Oxford OX3 7LD UK. 199