Resistance and gain-of-resistance phenotypes in cancers harboring wild-type p53

Novel trisubstituted harmine derivatives with original in vitro anticancer activity

To overcome the intrinsic resistance of cancer cells to apoptotic stimuli, we designed and synthesized approximately 50 novel β-carbolines structurally related to harmine. Harmine is known for its anticancer properties and is a DYRK1A inhibitor. Of the synthesized compounds, the most active in terms of growth inhibition of five cancer cell lines are cytostatic and approximately 100 times more potent than harmine but demonstrated no DYRK1A inhibitory activity. These novel β-carbolines display similar growth inhibitory activity in cancer cells that are sensitive and resistant to apoptotic stimuli. Using ChemGPS-NP, we found that the more active β-carbolines are all more lipophilic and larger than the less active compounds. Lastly, on the basis of the NCI human tumor cell line anticancer drug screen and the NCI COMPARE algorithm, it appears that some of these compounds, including 5a and 5k, seem to act as protein synthesis inhibitors.

Wip1 sensitizes p53-negative tumors to apoptosis by regulating the Bax/Bcl-xL ratio

Wip1 is a stress-response phosphatase that negatively regulates several tumor suppressors, including p53. In a sizeable fraction of tumors, overexpression or amplification of Wip1 compromises p53 functions; inhibition of Wip1 activity is an attractive strategy for improving treatment of these tumors. However, over half of human tumors contain mutations in the p53 gene or have lost both alleles. Recently, we observed that in cancer cells lacking wild type p53, reduction of Wip1 expression was ineffective, whereas, surprisingly, overexpression of Wip1 increased anticancer drug sensitivity. The increased sensitivity resulted from activation of the intrinsic pathway of apoptosis through increased levels of the pro-apoptotic protein Bax and decreased levels of the anti-apoptotic protein Bcl-xL. We showed that interaction of Wip1 and the transcription factor RUNX2, specifically through dephosphorylation of RUNX2 phospho-S432, resulted in increased expression of Bax. Interestingly, overexpression of Wip1 increased drug sensitivity only in the p53-negative tumor cells while protecting the wild type p53-containing normal cells from drug-induced collateral injury. Here, we provide evidence that Wip1 overexpression decreases expression of Bcl-xL through negative regulation of NFκB activity. Thus, Wip1 overexpression increases the sensitivity of p53-negative cancer cells to anticancer drugs by separately affecting Bax and Bcl-xL protein levels.

A texaphyrin-oxaliplatin conjugate that overcomes both pharmacologic and molecular mechanisms of cisplatin resistance in cancer cells

A texaphyrin-oxaliplatin conjugate, oxaliTEX, was designed to test the concept that a platinum analog can overcome defects in drug accumulation and p53-dependent DNA damage response in a tumor model expressing multifactorial mechanisms of cisplatin resistance. Cytotoxic studies resulted in a resistance factor of only 1.2, which essentially indicated complete reversal of resistance in 2780CP cells expressing a factor of 22 with cisplatin. Unlike cisplatin, oxaliTEX accumulated and formed DNA adducts, stabilized and activated p53 at similar levels in both sensitive and resistant cells, and induced apoptosis in both models. The ability and importance of a designer drug, such as oxaliTEX, to overcome cisplatin resistance by targeting two dominant resistance mechanisms is discussed.