Inhibition of Balb/c 3T3 cell transformation by synthetic acyclic retinoid NIK-333; possible involvement of enhanced gap junctional intercellular communication.
BACKGROUND
In an attempt to develop effective and non-cytotoxic cancer chemopreventive derivatives of retinoids, a novel acyclic retinoid has previously been synthesized. This acyclic retinoid, NIK-333, had been reported to suppress recurrence of primary hepatocellular carcinomas. We explored the molecular mechanisms by which NIK-333 exerts anti-proliferative effects.


METHODS
We employed Balb/c 3T3 cells, since they can be used as a quantitative transformation assay and since we can study a possible involvement of gap-junctional intercellular communication (GJIC) in their growth control. We included all-trans-retinoic acid (ATRA) for comparison.


RESULTS
We first confirmed that these cells express the retinoid receptors, RARalpha, gamma and RXRalpha, suggesting that they respond to NIK-333 and ATRA. When NIK-333 or ATRA was added to Balb/c 3T3 cells during the induction of cell transformation by a standard (3-methylcholanthrene (MCA) alone) or two-stage (low dose of MCA plus 12-O-tetradecanoylphorbol-13-acetate (TPA)) protocol, there was a significant decrease in the number of transformed foci. The extent of inhibition of transformation by NIK-333 was similar to that exerted by ATRA. Employing the microinjection dye-transfer assay, we found that both retinoids increase GJIC level when measured 24h after treatment. The extent of GJIC increase by NIK-333 was similar to that of ATRA. These retinoids also increased the amount of connexin 43 (Cx43) on the plasma membrane as revealed by immunostaining.


CONCLUSIONS
These data indicate that NIK-333 suppresses chemical carcinogenesis in vitro and support the hypothesis that enhancement of GJIC is involved in this process.
Tsujino
Takashi
T
Department of Bioscience, School of Science & Technology, Kwansei Gakuin University, 1-2, Gakuen, Sanda 669-1337, Japan.
Nagata
Tomoya
T
Katoh
Fumitaka
F
Yamasaki
Hiroshi
H
D000818:Animals; D041702:BALB 3T3 Cells; D002450:Cell Communication / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D018031:Connexin 43 / Q000378:metabolism; D017629:Gap Junctions / Q000235:genetics; D051379:Mice; D012176:Retinoids / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology
D018031:Connexin 43; D012176:Retinoids; C487689:(2E,4E,6E,10E)-3,7,11,15-tetramethyl-2,4,6,10,14-hexadecapentaenoic acid; D014212:Tretinoin