Celastrol Overcomes Chemoresistance in Vitro and Potentiates the Effect of Bortezomib Against Human Multiple Myeloma in Nude Mice Mode

Multiple myeloma (MM) is a B cell malignancy characterized by clonal proliferation of B cell in the bone marrow with low proliferative index. Despite the advent of novel therapeutics in addition to conventional chemotherapeutics, MM remains incurable because of the development of chemoresistance. Persistent activation of NF-κB/STAT3 signaling pathways and deregulation of apoptosis is considered to play an important role in the development of chemoresistance. The use of anticancer drugs derived from natural sources may be able to overcome resistance without some of the debilitating side effects of conventional chemotherapy. Celastrol is one such compound that has gained substantial attention recently for its anti-inflammatory and anticancer activities and is derived from the Chinese medicinal plant ‘Tripterygium wilfordii.

We have demonstrated that celastrol overcomes the chemoresistance and induce apoptosis in MM cells by inhibiting NF-κB and STAT 3 pathways cell lines sensitive and resistant to various chemotherapeutic agents and Bortezomib. Our experimental findings have indicated that celastrol in combination with bortezomib/thalidomide can inhibit proliferation, induce apoptosis and overcome chemoresistance in MM cells in synergistic manner. We also observed that celastrol inhibited the activation of NF-κB and STAT3 and downregulated the expression of various genes involved in MM proliferation, survival and angiogenesis.

Male athymic balb/c nude mice were implanted with 2×10⁶ cells with either Human MM U266 cell lines subcutaneously. When tumors have reached more than 0. 3 cm in diameter, the mice were randomized into four groups. Group I (control) received corn oil 100 ul i. p. for five days a week, group II received 0. 25 mg/kg celastrol in 100ul corn oil for five days a week, group III received 0. 25 mg/kg bortezomib in 100 ul corn oil i. p. weekly and group IV received 0. 25mg/kg celastrol in 100 ul corn oil i. p. 5 days a week and 0. 25 mg/kg bortezomib in 100 ul corn oil i. p. weekly for 3 consecutive weeks. The tumor volume and body weight of the mice were monitored twice a week for the duration of the experiment. On completion of the treatment period, mice were euthanized by i. p. phentobarbital (40 mg/kg b. w) followed by cervical dislocation and then tumors were dissected and diameters measured. The tumor volume was calculated using the formula [L × W2]/2, where W and L are the width (short diameter) and the length (long diameter) of the tumor and the tumors were subjected to histological examination.

In the MM xenograft mice model, we observed that celastrol potentiated the antitumor effects of bortezomib and this correlated with significant suppression of NF-κB, STAT3, COX-2 and VEGF which was demonstrated by IHC. Overall, our data indicates that celastrol could be a potential therapeutic agent for the treatment of MM, especially in combination with the novel anti-myeloma agents.

No relevant conflicts of interest to declare.