Abstract 793: Preclinical study of efficacy and specificity of p53-reactivating drugs in multiple myeloma, identification of biomarkers.
Authors: Surget Sylvanie , Descamps Géraldine , Brosseau Carole , Moreau Philippe , Le Gouill Steven , Amiot Martine , Pellat-Deceunynck Catherine 
Published: August 2014

Abstract
In this study, the efficacy of RITA (Reactivating p53 and Inducing Tumor Apoptosis) to kill multiple myeloma (MM) cells was evaluated in comparison to that of nutlin3a (MDM2 inhibitor) and in relation to the TP53 status of 32 human myeloma cell lines (HMCLs, 9 wt, 15 mutated, 6 truncated, 2 KO) and primary samples (n=19). This panel of HMCLs is representative of the molecular diversity of patients for both the chromosomal abnormalities (14q32 translocation) and the TP53 status, and thus allows us to perform an accurate evaluation of both the specificity and efficacy of molecules. TP53 status of HMCLs was established by direct sequencing of TP53 mRNA while that of primary cells was evaluated by the presence of chromosome 17p deletion (del17p), which is strong adverse prognostic value for patients with MM. Both drugs induced the apoptosis of MM cells, as shown by the loss of CD138 expression (a marker of viability for myeloma cells), Apo2.7 staining, appearance of a subG1 peak and activation of caspases 3 and 9. RITA induced cell death in about one third of HMCLs and primary samples. The apoptosis induced by RITA was not related to the t(14q32) or TP53 status of HMCLs or primary samples (p=0.52 and p=0.96, respectively). RITA failed to increase the expression level of p53 or of p53 targets i.e., Noxa, p21, Bax or DR5 in sensitive cells. In primary samples, RITA slightly increased DR5 expression in resistant samples without del17p and decreased it in sensitive samples with or without del17p. RITA failed to modulate p53 re-localization to the mitochondria or nucleus in sensitive cells. Finally, silencing of p53 in two highly sensitive TP53mutated HMCLs failed to inhibit apoptosis induced by RITA, confirming that the RITA-induced apoptosis in myeloma cells was p53 independent. In contrast, the apoptosis induced by nutlin3a was directly linked to the TP53 status of HMCLs and primary samples (p&lt;0.001 and p=0.026, respectively) and nutlin3a increased the level of both p53 and p53 targets in a p53-dependent manner. Moreover, nutlin3a increased p53 localization to the mitochondria and nucleus only in TP53wt HMCLs in good agreement with cell death response. In primary cells, we further showed that a nutlin3a-induced DR5 increase (≥1.2 fold increase) was a specific and sensitive marker (p=0.0001) of a weak incidence of del17p within the samples, and thus a biomarker of a functional p53 pathway.
These data show that 1) RITA effectively induced apoptosis in a subset of MM cells independently of p53 and 14q32 heterogeneity, and could be of interest for patients with del17p, who are resistant to current therapies; 2) nutlin3a was effective in myeloma cells retaining a functional p53 pathway.
The efficacy and specificity of other p53-reactivating small molecules i.e., PRIMA-1met and CP-31398, are currently under evaluation.
Citation Format: Sylvanie Surget, Géraldine Descamps, Carole Brosseau, Philippe Moreau, Steven Le Gouill, Martine Amiot, Catherine Pellat-Deceunynck. Preclinical study of efficacy and specificity of p53-reactivating drugs in multiple myeloma, identification of biomarkers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 793. doi:10.1158/1538-7445.AM2013-793