Prima-1met Induces Cytotoxicity in Multiple Myeloma Cells Irrespective of p53 Status and Displays a Synergistic Cytotoxic Response with Conventional Chemotherapeutic Drugs.
Hua Jiang, Manujendra N Saha, Mei-Hsi Chen, Hong Chang. University Health Network, Toronto, Canada
Background: Multiple myeloma (MM) cells carrying mutant p53 are resistant to chemotherapy. Although p53 mutation is relatively rare in MM, reactivation of mutant p53 by restoring wild type conformation may render MM cells more susceptible to chemotherapy. Prima-1met, a methylated derivative and more active analog of Prima-1, was shown to induce cytotoxic effects and apoptosis in certain types of human tumor cells harboring mutant p53. However, it is unkown whether Prima-1 exerts anti-myeloma activity.
Design: Human MM cell lines harbouring wild type, mutant or null p53 and primary MM samples were treated with Prima-1met alone or in combination with currently used chemotherapeutic drugs such as doxorubicin and dexamethasone. Cells treated with these agents were assessed for cell viability and apoptosis.
Results: Treatment of MM cells or primary MM samples with Prima-1met resulted in significant inhibition of survival of the cells irrespective of p53 status. However, the similar cytotoxic response was not observed in bone marrow or peripheral blood mononuclear cells from healthy volunteers suggesting a preferential killing of MM cells by Prima-1met. The IC50 of MM cells varies from cell to cell, i.e, IC50 values for MM.1S and H929 cells harbouring wild type p53 was <10 µM; whereas, the IC50 values for 8226 and LP1 cells harbouring mutant p53 and 8226R5 cells harbouring null p53 was >10 µM. Importantly, the combination of 2 µM Prima-1met and 0.5 µM doxorubicin or 0.5 µM dexamthasone produced a synergistic cytotoxic response (CI=0.6-0.8) in both p53 mutant and wild type cells, whereby each drug alone had a relatively weak effect. The apoptosis induced in MM cells harbouring mutant p53 is a relatively late event than demonstrated in cells carrying wild type p53. After 48 hrs treatment with 20 µM Prima-1met, 40% of MM.1S or H929 cells were Annexin V-positive, whereas a similar level of apoptosis was achieved in 8226 or 8226R5 cells at 100 µM Prima-1met after 72 hrs treatment. This was confirmed by the time-dependent activation of caspase-3 and cleavage of PARP by Western blot analysis. Activation of caspase-3 and PARP was observed between 8-12 hrs in MM.1S and H929 cells, whereas it was shown between 12-24 hrs in 8226 or 8226R5 cells.
Conclusions: Our results indicate that the combination of chemotherapeutic drugs with Prima-1met can synergistically trigger MM cell apoptosis, thus, may represent a novel and more efficient therapeutic strategy for treatment of high-risk MM patients, particularly carrying mutant p53.
Tuesday, March 1, 2011 9:30 AM
Poster Session III # 246, Tuesday Morning