Perifosine accumulates preferentially in tumor tissues: Correlation between intratumoral accumulation and inhibition of cell proliferation and tumor growth (2007)

C178 Purpose of the study:  Perifosine is an alkylphospholipid compound, which demonstrates anti-tumor activity in vitro, in vivo and in human clinical trials. Recent studies indicate that perifosine inhibits the phosphatidylinositol-3’-kinase (PI3K) pathway by preventing cell membrane recruitment of the AKT pleckstrin-homology (PH) domain. In addition, it has been shown that perifosine induces apoptosis through the activation of death receptor-dependent pathways. An attempt to explain the sensitivity pattern of different cells in vitro and in vivo to perifosine based on the observed mechanism of action such as inhibition of Akt activation fails to deliver a consistent model for prediction of activity. Another potential explanation for Perifosine tumor specificity lies in the observation that the drug accumulates preferentially in certain tumor cell types. For example, in a pharmacokinetic study of perifosine in A431, HNXOE and KB human cells induced xenografts, perifosine accumulation in KB tumors was 2-fold higher compared to A431 and HNXOE. Moreover, perifosine intratumoral concentration in the KB model was approximately 10 fold higher than in plasma (Vink, Schellens et al. 2005). Significantly, a strong correlation was found between intracellular drug accumulation and inhibition of tumor growth in vitro.  The purpose of this study was to evaluate the hypothesis that the differential sensitivity of cells and xenografts models to perifosine and its effects on molecular biomarkers are related to the differential intratumoral drug level.  Methods: Perifosine tissues and plasma concentration were evaluated using a validated LC-MS assay. A functional proteomics technology, reverse phase protein array (RPPA), was used to establish and absolutely quantify effects of perifosine on activation of components of pathways such as PI3K in vivo.  Results:  The tumor growth inhibition results fit within a model that shows dependence on the intratumoral steady state perifosine concentration. Accumulation in the tumor tissue as defined by the intratumoral/plasma concentration ratio varied in the different models between 1-10. In tumors displaying both high accumulation and Akt high baseline activation there was a highly statistically significant correlation between the degree of antitumor efficacy of different perifosine doses and quantified downregulation of phosphorylation of Akt and of its downstream targets, particularly S6.  Conclusions:  Perifosine differential cell accumulation explains well the drug’s differential effects in vitro and in vivo. Miltefosine, one of perifosine parent compounds is active in Leishmaniasis and has been approved for treatment of this disease. Similarly to perifosine, miltefosine shows, both in the leishmania parasite and mammalian cells, a strong correlation between intracellular accumulation and inhibition of cell proliferation. In leishmania a miltefosine transporter (LdMT), has been cloned (Perez-Victoria, Castanys et al. 2003; Perez-Victoria, Gamarro et al. 2003) and found homologous to the mammalian P4-ATPases, which appear to function in the cell membrane as well as in other membrane compartments as phospholipid flippases. Further studies are ongoing to characterize at the molecular level the selective intratumoral accumulation of perifosine.