IADR Abstract Archives
Fenretinide Inhibits Stat3 Activation in Oral Squamous Cell Carcinoma (OSCC)
Objectives: While fenretinide’s (4-HPR) best-recognized chemopreventive effects are apoptosis & differentiation induction, this vitamin-A derivative also binds to & affects proteins. We demonstrated that 4-HPR binds to FAK’s & its functional analogue PYK2’s kinase sites where it obstructs ATP binding & inhibits their prosurvival & proinvasive effects. Stat3, like FAK, is a dual-function signaling tyrosine kinase that serves as a downstream signaling hub. In its transcription-factor capacity, activated Stat3 enables expression of cancer-promoting proinflammatory, proproliferative & angiogenic genes. Notably, nuclear pStat3 increases occur during both oral intraepithelial neoplasia & overt OSCC-where sustained levels correlate with poor prognosis. Investigate whether 4-HPR’s kinase inhibition extends to the Stat3 pathway.
Methods: Three recently-isolated OSCC cell lines [JSCC1(tonsil), JSCC2(ventral tongue), JSCC3(floor of mouth), all HPV-negative] were evaluated to:1)determine baseline Stat3 signaling [immunoblotting, densitometry normalized to cytosolic (GAPDH) or nuclear (histone H3) genes], 2)assess 4-HPR’s effects on Stat3 phosphorylation & nuclear translocation (immunoblotting), & 3)employ molecular modeling to assess 4-HPR-Stat3/related-kinase interactions.
Results: Cells showed line-specific differences in autologous Stat3 activation: 1) JSCC1 (moderate), JSCC2 (strong), JSCC3 (negligible). JSCC1 & JSCC2 cells (sera-free medium 48h, 5µM 4-HPR treatment last 24h) demonstrated:1)detectable constitutive Stat3 phosphorylation/nuclear translocation,2)significant inhibition of Stat3 activation during 4-HPR treatment (p<0.05, Wilcoxon matched-pairs test, n=7). Molecular modeling studies revealed 4-HPR’s: 1)binding to Stat3’s dimerization-enabling alpha helix (Kd=1.36e-6, comparable to other Stat3 inhibitors),2)binding to Src’s & Abl’s ATP-binding sites (Kd=1.68e-8, Kd=1.13e-9, respectively) at affinities likely to perturb ATP binding (Kd range=e-6 to e-7).
Conclusions: 4-HPR’s interference with Stat3 activation & its associated Stat3-activating kinases (Src, Abl) provides mechanistic insights for our Western data. As OSCC pathogenesis encompasses many signaling pathways in addition to Stat3, in vivo efficacy studies with 4-HPR & complementary chemopreventives are ongoing. R01CA129609, R01CA171329, T32DE014320
Methods: Three recently-isolated OSCC cell lines [JSCC1(tonsil), JSCC2(ventral tongue), JSCC3(floor of mouth), all HPV-negative] were evaluated to:1)determine baseline Stat3 signaling [immunoblotting, densitometry normalized to cytosolic (GAPDH) or nuclear (histone H3) genes], 2)assess 4-HPR’s effects on Stat3 phosphorylation & nuclear translocation (immunoblotting), & 3)employ molecular modeling to assess 4-HPR-Stat3/related-kinase interactions.
Results: Cells showed line-specific differences in autologous Stat3 activation: 1) JSCC1 (moderate), JSCC2 (strong), JSCC3 (negligible). JSCC1 & JSCC2 cells (sera-free medium 48h, 5µM 4-HPR treatment last 24h) demonstrated:1)detectable constitutive Stat3 phosphorylation/nuclear translocation,2)significant inhibition of Stat3 activation during 4-HPR treatment (p<0.05, Wilcoxon matched-pairs test, n=7). Molecular modeling studies revealed 4-HPR’s: 1)binding to Stat3’s dimerization-enabling alpha helix (Kd=1.36e-6, comparable to other Stat3 inhibitors),2)binding to Src’s & Abl’s ATP-binding sites (Kd=1.68e-8, Kd=1.13e-9, respectively) at affinities likely to perturb ATP binding (Kd range=e-6 to e-7).
Conclusions: 4-HPR’s interference with Stat3 activation & its associated Stat3-activating kinases (Src, Abl) provides mechanistic insights for our Western data. As OSCC pathogenesis encompasses many signaling pathways in addition to Stat3, in vivo efficacy studies with 4-HPR & complementary chemopreventives are ongoing. R01CA129609, R01CA171329, T32DE014320