Introduction
Research on polycyclic aromatic hydrocarbons and
their derivatives has received significant attention from chemists,
biologists and medical investigators (1). However the use of these molecules as
anticancer agents has yet to be investigated systematically. Bair
et al reported the effectiveness of polyaromatic compounds
against tumor cell lines (2). The
compounds were believed to interact with DNA by intercalation and
to inhibit topoisomerase II. Intercalation was also confirmed for
napthalimide, amonafide and mitonafide derivatives, and their
antitumor activity was suggested to result from this interaction
(3–6).
To extend a previously published investigation
involving biologically active aromatic compounds, this study
describes the synthesis of several novel 6,12-disubstituted
chrysene derivatives. Notably, one of these compounds demonstrated
marked activity in vivo against a colon cancer cell
line.
Materials and methods
Materials
Chrysene, nitric acid, hydrazine hydrate,
isobutylcholoformate, lithium aluminum hydride, tetrahydrofuran,
hydrochloric acid, and the colon cancer HT-29 cell line were used
in the study.
Synthesis
Chrysene 1 on nitration with nitric acid
produced 6,12-dinitrochrysene 2 and this compound was then
reduced by hydrazine hydrate/Pd-C to yield 6,12-diaminochrysene
3. 6,12-Diaminochrysene 3 was then condensed with
acid 5 in the presence of isobutylchloroformate to yield
amide 6. Amide 6 on reduction yielded amine 7.
Amine 7b was converted to its salt 8 (7–12).
Experiment
N,
N-(6,12-chrysenyl)-bis-(4-(4N-methylpipera-zinyl)-butane-1,4-diamine
(8): mp 166–168°C; IR (film): 3383,
2932, 2849, 2798, 1594, 1524, 1452, 1357, 1277, 1225, 1162, 1113,
1048, 1012; cm−1H NMR (CDCl3): δ1.6 (m, 8H),
2.3 (s, 6H), 2.5 (m, 20H), 3.5 (t, 4H), 7.6 (m, 6H), 8.0 (d, 2H,
J = 8 Hz), 8.6 (d, 2H, J = 8 Hz); UV: 370, 286, 234
with a mass of 567, 531, 313, 304, 284, 263, 230, 216, 206, 154 and
130 was used. The analysis was calculated for
C36H50N6: C, 76.3, H, 8.9, N,
14.8. The result obtained was: C, 76.61, H, 8.88, N, 14.67.
Preparation of salt 8
The hydrochloride salt 8 of the amine
7 was prepared by mixing it with an excess hydrochloric acid
solution in ether for 1 h and filtering the residue (100% yield).
The salt was characterized after regenerating the parent amine by
the basification-extraction procedure.
In vivo results
Compound 8 activity against the
human colon cancer HT-29 cell line
Table I shows a
typical in vivo experiment.
 | Table ICompound 8 activity against the
colon cancer HT-29 cell line in vivo. |
Table I
Compound 8 activity against the
colon cancer HT-29 cell line in vivo.
| Tumor
volume/mouse
Day |
|---|
|
|
|---|
| 11 | 13 | 17 | 20 | 25 | 27 |
|---|
| Controls (17) | 85.9
mm3 | 240.8
mm3 | 285.8
mm3 | 404.1
mm3 | 450.0
mm3 | 8/17 |
13 (10) 35 mg/kg
a.m.
25 mg/kg p.m i.p. x 5 | 50.1
mm3 | 91.4
mm3 | 129.3
mm3 | 204.0
mm3 | 276.0
mm3 | 1/10 |
13 (5) 35 mg/kg a.m.
i.p. x 5
10 mg/kg 6 h later i.p. x 5
15 mg/kg 12 h later i.p. x 5 | 43.2
mm3 | 92.0
mm3 | 97.7
mm3 | 201.3
mm3 | 216.6
mm3 | 1/5 |
Following the injection of 1.25×106
cells, tumor growth was evident in the majority of mice at day 11,
with a rapid increase in the average tumor volume at day 25. Growth
of this tumor in the control mice was consistently between 85 and
100%. When tumors achieved a volume of 1 cm3 the animals
were sacrificed. As shown in Table
I, 47% of the control mice were sacrificed by day 27, and this
result was quite typical of many runs. When treated with 8
either BID (twice daily) or TID (three times a day), inhibition of
the growth of tumors in terms of tumor growth was consistently
evident. Subsequently, on day 27 only 10% of the 8 BID and 20% of
the 8 TID mice were sacrificed. Another indication of the
inhibition of growth of this tumor was best evidenced at day 20
when each regimen inhibited the average tumor volume by 50%.
In a number of in vivo tests compound
8 in various regimens demonstrated consistent inhibition of
the growth of HT-29 cells. Although we did not achieve 100%
inhibition of the tumor growth it should be noted that there are no
agents in clinical use against this tumor that are curative.
Discussion
The in vivo results demonstrated that
compound 8 was active against the colon cancer HT-29 cell
line. Notably, this compound is a hydrochloride salt and is soluble
in water. We are also encouraged by the finding that in repeated
in vitro testing by the NCI Program, additional human colon
cancers demonstrated even greater sensitivity to this agent.
Acknowledgements
We gratefully acknowledge the financial support for
this project from NIH/NCI (B.K.B.) and the Golden Family Fund
(F.F.B.); as well as the shared resources of the pharmacology core
facility of the University of Texas M.D. Anderson Cancer
Center.
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