The Biphasic Effects of TIMP-2 on the Growth and Infiltration of SHI-1 Cells on Nude Mice.

TIMP-2 is considered to block tumor metastasis by inhibiting the proteolytic activity of MMP-2. Recent studies indicated that overexpression of TIMP-2 may predict distant metastasis and/or poor prognosis. Besides, little is know about the functions of TIMP-2 in leukemic growth and infiltration. We have investigated the effects of TIMP-2 overexpression on the growth and infiltration of retroviral transfected monocytic leukemic SHI-1 cells (SHI-1/TIMP-2 and SHI-1/MSCV as control ) in nude mice. Total of 32 6-week-old nude mice pretreated by splenectomy, cytclophosphamide intraperitoneal injection, and sublethal irradiation (named SCI-nu/nu mice), were intravenously (IV) injected with 1×10⁷ SHI-1/TIMP-2 or SHI-1/MSCV cells. Infiltration and proliferation of SHI-1 cells were pathologically examined in 16 mice on day 30. 5×10⁶ SHI-1/TIMP-2 or SHI-1/MSCV cells inoculated subcutaneously in 20 nude mice without any pretreatment. Volume of neoplasm, the expression of TIMP-2 and micro vessel density (MVD)were measured on day 23 and 30. We have found :[circ1]4 weeks after IV injection of SHI-1 cells, SHI-1/TIMP-2 cells demonstrated higher capacity of infiltration and proliferation in SCI-nu/nu mice. All the mice with SHI-1/TIMP-2 cells developed paralysis of hind legs in the 5^th week, while only 2 of 8 mice with SHI-1/MSCV cells paralyzed. The median survival time of mice with SHI-1/TIMP-2 cells was 6.3 days shorter than that of mice with SHI-1/MSCV cells. On day 30 autopsy of 8 mice revealed more neoplastic nodules in organs of the mice injected with SHI-1/TIMP-2 cells, including stomach, thoracic and lumber vertebra, kidneys and head et al. More organ infiltration and more severe CNS leukemia was found in mice with SHI-1/TIMP-2 cells. [circ2] 11 days after inoculation, neoplastic nodules formed in 8/10 nude mice with SHI-1/TIMP-2 cells versus 4/10 mice with SHI-1/MSCV cells, without statistic difference (P>0.05). On day 23 and 30, the average volume of neoplasms from SHI-1/TIMP-2 cells were 102.4±32.9, 408.5±197mm³, versus 471±327.3, 1388±498.7mm³ from SHI-1/MSCV cells(P<0.05). Furthermore, MVD in tumor tissue in SHI-/TIMP-2 group (9.8±1.9 per 200×field) was markedly less than that in SHI-1/MSCV group (20.6±3.3 per 200× field). Our results suggested that TIMP-2 has biphasic effects on the growth and infiltration of SHI-1 cells in nude mice depending on different inoculating avenues. Upon subcutaneous inoculation, TIMP-2 overexpression in SHI-1/TIMP-2 cells led to an earlier appearance while a smaller size of xenograted tumor in nude mice probably due to an inhibition of tumor angiogenesis. These results were consistent with the notion that TIMP-2 may promote the growth and infiltration of leukemia cells.