Creatine and Creatinine Metabolism - Physiological Reviews
Creatine and Creatinine Metabolism - Physiological Reviews
Creatine and Creatinine Metabolism - Physiological Reviews
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July 2000 CREATINE AND CREATININE METABOLISM 1155<br />
expressing high levels of CK may be a result of the accumulation<br />
of cCr or of the synthetic phosphagen PcCr.<br />
Four tumor cell lines expressing high levels of CK,<br />
namely, ME-180 (human metastatic cervical carcinoma),<br />
DU145 (human prostate carcinoma), MCF-7 (breast adenocarcinoma),<br />
<strong>and</strong> OVCAR-3 (human ovarian adenocarcinoma),<br />
were sensitive to cCr <strong>and</strong> accumulated substantial<br />
amounts of PcCr [0.33–0.63 �mol � (mg cellular protein)<br />
�1 ] (559). In contrast, two cell lines expressing low<br />
levels of CK, U-87 MG (human glioblastoma/astrocytoma)<br />
<strong>and</strong> A2058 (human melanoma), were resistant to cCr <strong>and</strong><br />
had undetectable levels of PcCr. All six cell lines, however,<br />
accumulated between 5 <strong>and</strong> 27 �mol cCr � (mg cellular<br />
protein) �1 .<br />
To further test the correlation between accumulation<br />
of the synthetic phosphagen PcCr <strong>and</strong> growth inhibition,<br />
the unresponsive, low CK expressing melanoma cell line<br />
A2058 (see above) was transformed into a high CK expressing<br />
line, A2058–055. This was accomplished by<br />
transfecting the cells with a plasmid containing the human<br />
B-CK gene linked to the cytomegalovirus IE promoter<br />
<strong>and</strong> enhancer (559). The engineered line expressed<br />
�2,000 times the CK activity of the parent line A2058 <strong>and</strong><br />
accumulated a large pool of the phosphagen PcCr. Remarkably,<br />
A2058–055, but not the parent line, was growth<br />
inhibited by cCr. These findings suggest that accumulation<br />
of the synthetic phosphagen PcCr is essential for<br />
inhibition of tumor growth.<br />
Metastasis, the primary feature in fatal tumor pro-<br />
FIG. 13. Correlation between the CK<br />
activity of tumor cell lines <strong>and</strong> their responsiveness<br />
to cyclocreatine (cCr) (IC 50<br />
of cCr for inhibition of colony formation<br />
of the cell lines in soft agar). For a description<br />
of the cell lines, see Lillie et al.<br />
(559).<br />
gression, involves cell motility as a major determinant<br />
step (562, 953). Tumor cell motility is an energy-requiring<br />
process <strong>and</strong> depends on glycolysis. In in vitro studies in<br />
the high CK expressing cell lines A2058–055 <strong>and</strong> DU145,<br />
cCr was found to inhibit motility in response to different<br />
stimuli (676). In low CK expressing cell lines (A2058 <strong>and</strong><br />
A2058–032), on the other h<strong>and</strong>, motility was not or only<br />
partially inhibited. Cr had no effect on the motility of the<br />
four cell lines when given alone but reversed the inhibition<br />
of motility by cCr. These results suggest that 1) the<br />
CK system may not only be important in solid tumor<br />
growth, but could also play an important role in the<br />
spread <strong>and</strong> invasion of these tumors, <strong>and</strong> that 2) cCr<br />
affects a key step utilized by several motility-stimulating<br />
systems.<br />
The in vitro findings were complemented by evaluating<br />
the antiproliferative activity of cCr in vivo in a human<br />
tumor xenograft nude mouse model (559, 641). The<br />
growth of tumors derived from freshly injected ME-180<br />
cells was significantly inhibited in athymic mice by feeding<br />
a diet supplemented with 1% cCr compared with animals<br />
fed a control diet (149 vs. 506 mm 3 by day 36). cCr<br />
also inhibited the growth of established (�50 mm 3 )ME-<br />
180 cell-derived tumors, as evidenced by tumor volumes<br />
on day 44 of 465 <strong>and</strong> 1,033 mm 3 for cCr-fed <strong>and</strong> control<br />
mice, respectively. Similarly, dietary cCr inhibited the<br />
growth of human neuroblastoma cell line-derived tumors<br />
in nude mice by up to 46%.<br />
A variety of rat tumors were evaluated for respon-