Abstract 3382: Formation of transient membrane channels targets doxorubicin resistance.
Authors: van Hell Albert J. , Melo Manuel , van Blitterswijk Wim , Dijkema Tim , Pedrosa Lilia , Koning Gerben , Marrink Siewert Jan , Jonkers Jos , Verheij Marcel 
Published: August 2014

Abstract
Poor accumulation of anti-cancer drugs in tumor cells is a major limitation in clinical cancer therapy. The main barrier for a drug to traverse through the body and reach its intracellular target is the plasma membrane. A typical (candidate) drug is therefore small, amphiphilic and of limited charge. Still, membrane traversal remains a highly inefficient and impeding process. In clinical oncology in particular there is an urgent need for new ways to improve drug efficacy and reduce toxicity.
We have elucidated a mechanism that effectively accelerates membrane translocation of the stereotypical and widely used amphiphilic drug, doxorubicin. Well-defined short-chain sphingolipids, when co-inserted into the membrane, diminish the barrier for doxorubicin translocation. In vicinity of doxorubicin, the lipid analogues rapidly self-assemble at nanosecond timescale, and form a small, transient membrane channel. As a result, the doxorubicin drug readily translocates the membrane, thereby reducing the energetic barrier significantly by two-fold. Monte-Carlo based full-atom simulations revealed the structure and dynamics of channel formation at molecular detail.
By means of a high-throughput screening approach of classical and targeted anti-cancer agent libraries, we identified various anti-cancer drugs in addition to doxorubicin, which share critical molecular characteristics, like defined amphiphilicity. Short-chain sphingolipids enhance cellular accumulation of these anti-cancer compounds similar to doxorubicin.
Guided by these mechanistic insights, we applied the concept of facilitated doxorubicin traversal in genetically engineered WAPcre;EcadF/F;p53F/F mouse models for breast cancer. These tumors are multi-drug resistant to conventional and targeted anti-cancer agents. Co-administration of the sphingolipid analogue GC with liposomal doxorubicin effectively overcame drug resistance. While toxicity and normal tissue exposure reduced, GC caused elevated levels of intracellular doxorubicin in the tumor, improved tumor growth inhibition and significantly prolonged survival. Thus, a strategy of GC-mediated doxorubicin translocation was the only therapeutic approach that generated a sustained doxorubicin anti-tumor response.
Notably, enhanced doxorubicin translocation was strongest over membranes of the tumor, a spectacular observation confirmed in vitro. We demonstrate that composition and local organization of the plasma membrane determine the efficiency of membrane channel formation.
In conclusion, transient membrane channels target the tumor cell membrane to overcome multi-drug resistance. Our results illuminate a critical role of the (tumor) plasma membrane in restricting the efficacy of anti-cancer drugs and its contribution to multi-drug resistance. Moreover, our findings present a mechanism to address these limitations of (candidate) drugs in a clinically applicable way.
Citation Format: Albert J. van Hell, Manuel Melo, Wim van Blitterswijk, Tim Dijkema, Lilia Pedrosa, Gerben Koning, Siewert Jan Marrink, Jos Jonkers, Marcel Verheij. Formation of transient membrane channels targets doxorubicin resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3382. doi:10.1158/1538-7445.AM2013-3382