ALBERT

Description: SDX-105 (Treanda™) is an alkylating agent with a distinct mechanism of action that has been shown to be active in clinical trials in NHL and CLL patients refractory to traditional DNA-damaging agents. SDX-105 induces unique changes in gene expression in NHL cells and displays a lack of cross resistance with other 2-chloroethylamine alkylating agents. Quantitative PCR analysis confirmed that the G2/M checkpoint regulators Polo-like kinase 1 (PLK-1) and Aurora A kinase (AurkA) are down-regulated in the NHL cell line SU-DHL-1 after 8 hours of exposure to clinically relevant concentrations of SDX-105. No changes in these same genes were observed when cells were exposed to equi-toxic doses of chlorambucil or an active metabolite of cyclophosphamide. Because our previous studies demonstrated that SDX-105 treatment can activate apoptotic cell death pathways, we examined the ability of SDX-105 to induce cytotoxicity in cells unable to undergo ‘classical’ caspase-mediated apoptosis. Multi-drug resistant MCF-7/ADR cells and p53 deficient RKO-E6 colon adenocarcinoma cells were exposed for two or three days to either 50 μM SDX-105 alone or 50 μM SDX-105 and 20 μM pan-caspase inhibitor zVAD-fmk. Although zVAD-fmk was able to inhibit SDX-105 induced increases in Annexin-V-positive cells, microscopic analysis of nuclear morphology using the DNA stain DAPI in cells treated with either SDX-105 alone or in combination with zVAD-fmk showed increased incidence of micronucleation. Multi/micro-nucleation and abnormal chromatin condensation are both hallmarks of mitotic catastrophe and have been observed in tumor cells exposed to microtubule-binding drugs such as the vinca alkaloids and taxanes. Activation of mitotic catastrophe may amplify the cytotoxicity of SDX-105 and its activity in tumor cells where classical apoptotic pathways are inhibited. This may explain, at least in part, the potent anti-tumor activity of SDX-105 in tumor cells refractory to conventional 2-chloroethylamine DNA-damaging agents. Additional studies are ongoing to further elaborate the role of mitotic catastrophe in SDX-105’s mechanism of action. The capacity to induce mitotic catastrophe may explain the anti-tumor activity of SDX-105 in chemotherapy relapsed and resistant patients.

Description: SDX-101 (R-etodolac), which is currently being evaluated in clinical trials for treatment of chronic lymphocytic leukemia, down regulates the activity of the β-catenin pathway and inhibits the growth of non-Hodgkin’s Lymphoma Daudi tumor xenografts in vivo when dosed orally (AACR PROC 2004 Abs# 2061 and #4574). Initial co-immunoprecipitation experiments conducted on cell nuclear fractions identified a heteromeric nuclear protein complex containing β-catenin and PPAR-γ. Furthermore, we have demonstrated that SDX-101 treatment reduces nuclear β-catenin in the immunoprecipitated complex, indicating that this complex may represent a target of SDX-101 (AACR PROC 2004 Abs# 3672). We recently reported evaluation of novel structural analogs of SDX-101 and have shown that these analogs, whose structures were not disclosed, are 5–10 fold more potent in in vitro cytotoxicity assays than SDX-101 and that they are orally efficacious in vivo (NCI/EORTC 2004 Abs #383). Our current studies further characterize the mechanism of action and safety of these analogs and identify the structures of selected analogs. Novel functional assays were developed to test and compare SDX-101 and the analogs at 4 hours post-treatment, a time before appreciable loss of viability was detected. Best results were obtained using a functional assay co-transfecting a β-catenin-dependent reporter construct (TOPFLASH) and β-catenin and RXR expression vectors. The average IC50 of analogs in this β-catenin reporter system ranged from 50 to 160 μM. These values were approximately five- to ten- fold lower than the IC50 for SDX-101 (~700 μM). Similar results were obtained assessing the inhibition of PPAR-γ-mediated transcription, using a PPAR-dependent reporter and co-transfection with PPAR-γ and RXR expression vectors. The average IC50s of the analogs ranged from 50–150 μM in this functional assay, demonstrating an approximately 10-fold increase in potency of the analogs when compared to SDX-101 (~1000 μM). No effect was observed at the 4 hour time point using a constitutive SV40-based control reporter vector. These results suggest that the primary target for these compounds may be a nuclear complex containing β-catenin, PPAR-γ and RXR, supporting a hypothesis developed upon evaluation of earlier results generated with SDX-101. To evaluate the safety of two SDX-101 analogs in vivo, normal mice were administered each analog at 240, 120 and 60 mg/kg/d (M-F) for four weeks. Mortality, morbidity, clinical signs, hematology/chemistry were monitored. There were no mortalities, overt toxicities or abnormal observations at necropsy with either of the analogs at any of the tested dose levels. There was a transient body weight loss (