Abstract 5107: Fisetin treatment reduces tumor growth and metastasis by modulating PI3K/AKT and MEK/ERK pathways in a BRAFV600E/PTENNULLmouse model of melanoma

Melanoma is the deadliest form of skin cancer due to its propensity to metastasize. It accounts for about 80% of skin cancer-related deaths. A substitution of valine for glutamic acid at position 600 results in the BRAFV600E mutation found in approximately 50% of melanomas. The BRAFV600E mutation drives activation of MEK/ERK signaling and also cooperates with the PI3K/AKT pathway, thus enhancing tumor initiation, progression, metastasis, and drug resistance. Fisetin (3,39,49,7-tetrahydroxyflavone), a naturally occurring flavonoid found in fruits, vegetables, nuts, and wine, exhibits anti-proliferative, anti-invasive, and anti-tumorigenic properties. Earlier, we showed that fisetin treatment downregulates the PI3K/AKT pathway and reduces phosphorylation of MEK/ERK in melanoma. In this study we determined the effects of fisetin on tumor growth and metastasis in a genetically engineered transgenic mouse model of metastatic melanoma. Melanocyte specific Cre activity was induced in six-week-old BRAFV600E/PTENNull/CreTg mice by topical application of 4-hydroxytamoxifen on shaved backs once per day for 3 consecutive days. Mice were observed daily until a highly pigmented measurable tumor appeared. Size of the tumors was measured twice weekly and treatment with fisetin (45mg/kg b.wt. & 90mg/kg b.wt.; orally 5 times/week) was started when tumor size reached 100 mm3. Measurement and quantification of tumor volume showed that fisetin administration inhibited melanoma growth in these mice as compared to the control group. Hematoxylin and eosin staining revealed that fisetin treatment reduced pigmented cells in the ear and skin. In addition, fisetin treatment reduced the metastasis of melanoma cells into the spleen and draining lymph nodes. Furthermore, evaluation of tumor tissues revealed that fisetin treatment reduced the (i) expression of PI3Kp110α and p85, (ii) phosphorylation of AKT at Ser473 and Thr308, (iii) phosphorylation of mTOR at Ser2481, and (iv) expression of raptor and rictor. In addition, fisetin treatment reduced the phosphorylation of MEK and ERK when compared to control tumor samples. Fisetin treatment also resulted in (i) cleavage of caspase-3, (ii) inhibition of Bcl2 and Bcl-xL, (iii) induction of Bax, and (iv) inhibition of PCNA and Ki67 expression. Further, fisetin treatment reduced the expression of mesenchymal marker proteins (N-cadherin and vimentin) with concomitant increase in epithelial marker proteins (E-cadherin and desmoglein). These data suggest the ability of fisetin to exhibit anti-proliferative, pro-apoptotic, anti-tumorigenic, and anti-metastatic potentials in a mouse model of melanoma. We suggest that fisetin could be used as an adjuvant chemotherapy to prevent drug resistance and improve the therapeutic efficacy of anti-melanoma drugs for the management of melanoma. Citation Format: Harish C. Pal, Mary Katherine Montes de Oca, Pooja Sharma, Ross L. Pearlman, Farrukh Afaq. Fisetin treatment reduces tumor growth and metastasis by modulating PI3K/AKT and MEK/ERK pathways in a BRAFV600E/PTENNULL mouse model of melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5107. doi:10.1158/1538-7445.AM2017-5107