Preclinical antitumor activity of F14512, a novel targeted cytotoxic agent

A276 A novel approach for the selective targeting of a potent cytotoxic agent to cancer cells is proposed. The strategy consists in exploiting the Polyamine Transport System (PTS), an active and energy-dependent machinery frequently over-expressed by many tumor cell types because of their high demand for polyamines. The PTS allows the selective accumulation of certain polyamine-drug conjugates in tumor cells. Here we demonstrate that the podospermine conjugate F14512 functions as a PTS-vectored cytotoxic agent in vivo . This study was aimed to define F14512 anticancer efficacy against a panel of murine and human tumor models. F14512 has provided evidence of marked or moderate antitumour activity in vivo in 9 over 13 experimental tumor models, yielding a response rate of 69%, with complete tumor regressions noted in LXFL529 (NSCLC) and MX-1 (breast) xenografts. F14512 also showed antitumour activity when administered by the oral route, inducing an increase in survival of 86% of P388 leukemia-bearing mice treated with multiple oral doses. Overall F14512 level of activity was superior to that of etoposide, a structurally-related molecule in many of the experimental models used. F14512 also exhibited a high level of activity against the etoposide-resistant NSCLC xenografts (LXFL529/VP), as reflected by a tumor growth inhibition of 91%. Since in vitro studies have provided evidence that F14512 utilizes the PTS to accumulate in tumors, we further investigated whether the in vivo antitumour activity of F14512 was correlated to the level of PTS expression in tumors. This was indirectly demonstrated using a fluorescent probe bearing the same polyamine moiety as F14512, namely the spermine. The uptake of the fluorescent probe F16746 in F14512-sensitive (MX-1) or -resistant (LS174T) cells, extracted from tumors by fine needle aspiration, was measured ex vivo by flow cytometry. The results showed a high level of uptake of the fluorescent probe in the F14512-sensitive tumor cells, which was inhibited by F14512, when added as a competitor. In contrast, F14512-resistant tumor cells showed a very low accumulation of this probe, which was not inhibited by increasing concentrations of F14512. Therefore these data demonstrated that F14512 targets tumor cells in vivo using its spermine chain and overall provided a favorable preclinical profile, which justifies a further clinical development.