PhD Candidate The University of Adelaide ST GEORGES, South Australia, Australia
Introduction: Immunomodulatory imide drugs (IMiDs), such as lenalidomide, are vital agents in the therapeutic arsenal against multiple myeloma (MM). IMiDs directly promote MM cell death via cell cycle arrest and stimulate anti-tumour immune responses in the bone marrow (BM) niche. Lack of amino acid conservation between human and mouse orthologues of Cereblon (Crbn), the IMiD binding protein, render mice resistant to IMiDs. Given this, preclinical evaluation of IMiDs’ pleiotropic mechanisms of action is hindered by a lack of immunocompetent MM mouse models displaying drug sensitivity. Notably, substitution of an isoleucine in murine Crbn with the analogous human valine residue (CrbnI391V) confers IMiD sensitivity to mouse cells. Here we investigate lenalidomide sensitivity in two immunocompetent MM mouse models where either the recipient mice or engrafted tumour cells harbour a humanised CrbnI391V gene.
Methods: C57BL/6-CrbnI391V or C57BL/KaLwRij mice were intravenously inoculated with Vk*MYC or 5TGM1-CrbnI391V cells, respectively. MM tumour burden was monitored weekly by serum paraprotein quantification or bioluminescence (BLI) imaging. After tumour establishment, mice received daily intraperitoneal injections of 10mg/kg lenalidomide or 4% DMSO. C57BL/6-CrbnI391V mice (n=8-9/group) were treated for 28-days beginning at week 7 and C57BL/KaLwRij mice (n=8/group) received 14-days of treatment from week 2. Endpoint BM and splenic GFP+ tumour burden was assessed by flow cytometry.
Results: We aimed to separately model: (1) lenalidomide-mediated BM microenvironment anti-myeloma immune responses in C57BL/6-CrbnI391V mice transplanted with Vk*MYC cells, and (2) lenalidomide-induced direct cytotoxicity in C57BL/KaLwRij mice transplanted with 5TGM1-CrbnI391V cells. Lenalidomide produced modest, non-significant reductions in whole body, BM and splenic Vk*MYC tumour burden in C57BL/6-CrbnI391V mice (t-tests, p>0.05). In contrast, lenalidomide’s antiproliferative effects significantly delayed 5TGM1-CrbnI391V tumour growth in C57BL/KaLwRij mice. Compared to DMSO treatment, lenalidomide treated mice showed a 46.4% decrease in whole body BLI signal (two-way ANOVA, p< 0.05), as well as 50.4% and 58.2% reductions in paraprotein intensity (t-test, p< 0.001) and BM tumour burden (t-test, p< 0.05), respectively.
Conclusions: Inadequate anti-myeloma efficacy of lenalidomide in the Vk*MYC model, where only the host C57BL/6-CrbnI391V mice displayed IMiD sensitivity, highlights the need for a fully IMiD-susceptible murine system. As such, a 5TGM1-CrbnI391V transplant C57BL/KaLwRij-CrbnI391V mouse model is under development. So far, we have demonstrated that CrbnI391V expression sensitises the 5TGM1 cell line to lenalidomide’s direct, antiproliferative effects in vivo. C57BL/6-CrbnI391V mice have been backcrossed onto the C57BL/KaLwRij strain for 6 generations and future studies will investigate the synergy of lenalidomide-mediated tumoricidal and immunomodulatory anti-myeloma actions utilising this novel mouse model.
