HDAC Inhibitors as Epigenetic Regulators

The protein levels of MKP1 in the lysates were quantified by SDS-PAGE/Western blotting (28) using a commercial antibody for the phosphatase (sc-1109, Santa Cruz Biotech, Santa Cruz, CA). MKP1 expression in human melanoma tissue samples was investigated via immunohistochemistry (IHC) analysis of an institutional melanoma micro-tissue array. (10 mg/kg, 5d/week) and IFN2b. MKP1 expression was detected in human melanoma cell lines and tissues samples at levels up to 6 x higher than those 10058-F4 in normal or non-malignant melanocytes. TPI-3 also interacted positively with chemotherapeutics 5FU/LV against MC-26 colon cancer cellsin vitroand in mice. Our data together demonstrate pre-clinical activities of TPI-3 in overcoming cancer resistance to bio- and chemotherapeutics, implicate MKP1 as a drug-resistant molecule in melanoma and support targeting MKP1 for improving cancer therapeutic efficacy. Keywords:Melanoma, MKP1, IFN2b, 5FU and colon cancer == INTRODUCTION == Drug resistance is common in many types of cancers. It could be intrinsic but is often acquired following initial treatments. It is a major obstacle for clinical efficacy of biological, cytotoxic or targeted therapeutics (1-4). Identification of mediators of drug resistance and understanding their mechanism of action could provide insights for overcoming resistance and lead to novel approaches for improving cancer treatments. MKP1 (MAPK phosphatase-1, DUSP1, 10058-F4 and CL-100) was identified recently as a mediator of resistance to several chemotherapeutics in breast and lung cancer cells (5-7). Transient or stable over-expression of MKP1 in breast cancer cells enhanced viability in the face of treatment with alkylating agents (mechlorethamine), anthracylines (doxorubicin), and microtubule inhibitors (paclitaxel) (5). Over-expression of MKP1 rendered lung cancer cells resistant to 10058-F4 cisplatin, whereas knocking down MKP-1 expression with siRNA sensitized lung cancer cells to cisplatin (6,7). The clinical significance of these observations is indicated by the frequent over-expression of MKP1 in many cancer tissues including breast cancer, colon cancer, lung, prostate cancer, ovarian cancer and pancreatic cancer (6,8-12). Potential clinical impact is underscored by the association of MKP1 over-expression with early transformation and poor prognosis (9-11). MKP1 mediates chemo-resistance in a significant part via its anti-apoptotic activity through dephosphorylating/inactivating JNK, a pro-apoptoic signaling molecule (13). Over-expression of MKP1 in breast cancer cells reduced Caspase activation induced by chemotherapeutics (5). Knocking down MKP1 expression in cancer cells increased apoptosis (12,14). Among the MKP1 substrates (JNK, p38 and ERK1/2) (15,16), JNK was reported as a key molecule in MKP1 anti-apoptotic action. Inducible MKP1 expression blocked JNK activation and inhibited apoptosis (17) whereas suppression of MKP1 expression potentiates JNK activation coincident with apoptosis (14). Interestingly, MKP-1 is also a negative regulator of innate and adaptive immune responses (18). Being an anti-apoptotic mediator of chemo-resistance in several types of cancers (6,8-12,19), MKP1 is a potential cancer therapeutic target. Indeed, MKP1 inhibitory compounds active at low mM range induced cancer cell death in culture and sensitized cancer cells to chemotherapeuticsin vitro(20). However, the effectiveness and safety of targeting MKP1 as an anti-cancer strategyin vivoremain to be established. MKP1 inhibitors with pre-clinical anti-tumor activityin vivohave not been reported. It has not been clear whether MKP1 is significant 10058-F4 also in cancer resistance to bio-therapeutics. In this work, a novel MKP1 inhibitor was identified and named as TPI-3 (tyrosine phosphatase inhibitor-3). Being a small organic compound (274 Da) with defined structure (Fig 1) and of little prior Mouse monoclonal to S100B interest, TPI-3 has not been reported for biological activities. The compound was included in chemical collections for high throughput screening and found 10058-F4 inactive for the measles virus RNA polymerase or 14-3-3 molecule (pubchem). Herein, we provide pre-clinical evidence demonstrating that TPI-3 improved the efficacy of bio- and chemo-therapeutics for melanoma and colon cancer in mice as a tolerated oral agent. Our data suggest that targeting MKP1 could be an effective and tolerated strategy for overcoming resistance to multiple types of anti-cancer agents and implicate TPI-3 as a promising lead compound for further development. == Fig 1. == Identification of MKP1 inhibitors TPI-2 and TPI-3. A) Chemical structure of TPI-2 (L6). B) Jurkat cells treated with TPI-2 for 30 min were analyzed by Western blotting to quantify pERK1/2 and ERK1/2.