The Development of Non-Teratogenic Thalidomide Analogues as a Potential New Treatment for Multiple Myeloma and Cancer

Abstract

Thalidomide, with its ability to inhibit angiogenesis and to inhibit the production of survival factors in the bone marrow, has proven to be very effective for the treatment of multiple myeloma. Previous studies from our laboratory identified 3 metabolites in the blood and urine of myeloma patients who were responding to thalidomide therapy (Lu et al, 2003). One hydrolysis product, N-(O-carboxybenzoyl)glutamic acid imide (CGI) was as potent as lenalidomide in inhibiting angiogenesis and in inhibiting cytokine production in vitro. Structurally related molecules of CGI have been synthesized in an effort to produce analogues with improved potency, stability and activity. The analogues were each tested for activity for inhibition of tube formation by endothelial cells on Matrigel, as well as for inhibition of IL-6 production by RPMI-8226 myeloma cells stimulated by lipopolysacharide (LPS) and for their ability to inhibit TNF production by human peripheral blood leukocytes stimulated with LPS. Analogues with significantly improved potency compared to CGI in inhibiting tube formation and with less cytotoxicity have been synthesized. The N-methylated analogue (SN 31615) was 25-fold and a morpholide-analogue (SN 31721) was 7-fold more potent than CGI. The hybrid (SN 31924) compound of analogues SN 31615 and SN 31721 was one of the better analogues in inhibiting LPS-induced IL-6 production by RPMI-8226 cells. At the concentration of 10 μg/ml SN 31924 inhibited IL-6 production by 50 % compared to SN 31721 which inhibited IL-6 production by 15 %. SN 31721 and SN 31924 were both more stable than CGI at low pH levels. These analogues were well-tolerated in mice, with no signs of toxicity seen after an intra-peritoneal dose of 1000 mg/kg. Nor were toxicities observed following daily gavage at 200 mg/kg for 30 days. Plasma pharmacokinetics of SN 31924 and SN 31721 after an intra-peritoneal injection of 200 mg/kg was measured and the results indicated that the analogues were rapidly absorbed and eliminated in comparison to Lenalidomide at the same dose. The plasma AUC0-∞ and t1/2 for SN 31721 and SN 31924 in mice was 1659.3 μM.h, 0.6 h and 820.7 μM.h, 0.5 h respectively compared to 954.2 μM.h, 0.7 h for lenalidomide at the same dose. Lenalidomide potentiates the activity of DMXAA and cyclophosphamide against subcutaneous murine tumours, compared to the analogues SN 31721 and SN 31924, which were counter-effective and did not work as expected.