Preclinical pharmacologic evaluations of R406/R788, a multi-kinase inhibitor which exhibits unique, differential in vitro anticancer activity as well as in vivo antitumor efficacy following oral adminstration.
Authors: Michael Alley, Melinda Hollingshead, Christine Pacula-Cox, John Carter, William Jacob, Polly Pine
Journal: Cancer Research (2008)

4889   R406 (NSC 742317) and prodrug R788 (NSC 745942) have been reported to be a potent multi-kinase inhibitor in several cell-based assay systems and to impact a number of signaling pathways (e.g.,  J. Pharm. Exp. Ther. 319 : 998-1008, 2006 and  Clinical Immunology 124:  244-257, 2007). In the current study, R406 has been found to exhibit multi-log differential  in vitro  activity in the NCI DTP 60 cell line cancer screen. In two separate experiments, GI-50 levels ranged from 0.051 to >100 uM and 0.0069 to >100 uM. Greatest sensitivity was exhibited by specific renal and non-small cell lung cancer cell lines for which GI-50 levels ranged from 0.0069 - 0.54 uM. In subsequent experiments, we performed a series of  in vitro  and  in vivo  pharmacologic evaluations of R406 and R788 to determine whether these agents confer anticancer activity in selected cell lines exposed to drug  concentration x time  parameters associated with effective, well-tolerated  in vivo  dosages of R788.  In vitro  concentration x time  assays of R406 were performed on a group of three renal cancer cell lines (A498, CaKi-1 and RXF-393) and four lung cancer cell lines (HOP-62, HOP-92, NCI-H226, and NCI-H522). While GI-50 activity can be achieved with   in these cell lines, anticancer activity was more effective with longer exposures (> 48 hrs) to lower R406 concentrations: GI-50 activity was achieved with   In fact, total growth inhibition was achieved in the most sensitive cell lines (RXF-393 and NCI-H226) with  0.10 - 0.23 uM x 48 hr .  In vivo  efficacy testing of R788 (R406 prodrug) was performed using an intrarenal RXF-393 human tumor xenograft model. Five days after tumor cell injections, host mice were randomized into four groups and then received daily oral dosages of R788 via animal feed for a total of 16 days. The two highest dosages produced significant reductions in tumor burden in the absence of apparent toxicity. Plasma samples were collected on day 12 of treatment from 3 mice in each group and analyzed for the presence of the active agent, R406. Analysis revealed that oral R788 is readily absorbed and efficiently converted to R406.  In vivo  R788 treatments of 0, 75, 300 and 450 mg/kg/day resulted in dose-dependent plasma concentrations of R406: 0, 0.14 - 0.47; 0.46 - 1.33; and 1.57 - 2.56 uM, respectively. R406 concentrations associated with the highest two  in vivo  treatment regimens not only exceed the  in vitro concentration x time  indices required for total growth inhibition in sensitive renal and lung cancer cell lines (RXF-393, HOP-92 and NCI-H226), but also are similar to - or exceed - levels associated with GI-50 activity measured following 48-hour R406 exposures for several other cell lines tested in the NCI DTP 60 cell line screen.  In vivo  efficacy testing of R788 in A498 and other human tumor xenograft models is currently in progress.