Altered LKB1/AMPK Signaling and Chemosensitivity in NSCLC

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LKB1 is a serine/threonine kinase located on chromosome 19p13.3. Inherited mutations in LKB1 give rise to Peutz-Jeghers syndrome, a disorder characterized by benign hemartomas of Gl tract and a predisposition to certain cancers, including lung. While acquired mutations in LKB1 are relatively rare in most sporadic tumor types, more than 30% of NSCLC harbor inactivating mutations in LKB1. Recent progress on the function of LKB1 places this gene at the apex of a novel signaling pathway that ultimately serves to inhibit the mammalian Target of Rapamycin (mTOR). Current evidence supports a model in which LKB1 mediates the suppression of mTOR through the sequential activation of AMP regulated kinase (AMPK) and the tumor suppressor TSC2, overriding PIS kinase/AKT survival signaling under conditions of low energy or nutrient deprivation. Data from the literature and preliminary work from our laboratories indicate that cells with compromised LKB1 function are more resistant to effects of microtubule-targeted chemotherapeutic agents. These data have led us to hypothesize that LKB1 may act as a sensor of microtubule integrity, and that LKB1 mediated suppression of mTOR activity may promote apoptosis in response to microtubule-directed agents. LKB1 is also farnesylated at a CAAX motif in the C-terminus and may be a target of farnesyltransferase inhibitors. Thus, LKB1 and its downstream effectors may represent a convergence point between existing agents like the taxanes that interfere with microtubule dynamics and contemporary signal transduction inhibitors such as the mTOR inhibitors and the farnesyltransferase inhibitors. It is our hypothesis that LKB1/AMPK/TSC2 pathway is a frequent target of inactivation in NSCLC and that the integrity of this pathway is a critical determinant of the sensitivity of NSCLC to selected chemotherapeutic agents. The goals of this proposal are to (i) determine the frequency of LKB1/AMPK signaling pathway alterations in NSCLC, (ii) determine the impact of LKB1/AMPK pathway alterations on the response of NSCLC to selected chemotherapeutic agents, and (iii) determine whether LKB1/AMPK/TSC pathway alterations are predictive of clinical response to therapeutic agents in NSCLC patients. A better understanding of the consequences of altered LKB1/AMPK/TSC2 signaling in NSCLC and its role in chemosensitivity will provide novel insight into the mechanism(s) underlying intrinsic drug resistance and may provide a molecular basis for future implementation of "individualized" therapies.