Manumycin inhibits farnesyltransferase and induces apoptosis of drug‐resistant interleukin 6‐producing myeloma cells

Abstract

Summary. Interleukin 6 (IL-6) is an important survival and growth factor for myeloma cells and exerts its effects by activating several transduction pathways, including the Ras cascade. As farnesylation of the activated Ras oncogene product by protein farnesyltransferase (FTase) is a critical step for Ras functional activity, FTase has emerged as a potential target for the development of new anti-cancer agents. Based on our previous demonstration that IL-6-producing myeloma cells are refractory to drug-induced apoptosis, we have analysed the effect of manumycin, a natural FTase inhibitor, on IL-6-producing myeloma cells resistant to Fas-, dexamethasone-and doxorubicin-induced apoptosis. Treatment of myeloma cells with manumycin prevented cell proliferation and induced apoptosis. Western blotting experiments demonstrated that this effect was related to inhibition of the post-translational Ras processing. Further analysis showed that manumycin-induced apoptosis involved caspase-3. Activation of caspase-3, in fact, was observed in 6 h-treated myeloma cells expressing Apo 2AE7 antigen, the marker of early apoptosis, whereas their treatment with cell-permeable DEVD-fmk, that irreversibly inhibits caspase-3 activity, prevented their apoptosis. Overexpression of caspase-3 was also demonstrated by reverse transcription-polymerase chain reaction. Finally, overexpression of Bcl-2 and its homologue Bcl-xL was observed in manumycin-treated cells as well as in control myeloma cells, implying that the Bcl-2 family is not involved. FTase inhibitors may thus be proposed as a potential pharmacological weapon, as they block the Ras pathway and induce the apoptosis of drug-resistant IL-6-producing myeloma cells.

Reactive oxygen species‐dependent destruction of MEK and Akt in Manumycin stimulated death of lymphoid tumor and myeloma cell lines

“…Together, the data from this panel of experiments agree with those of Frassanito et al who showed that Man-A still induced apoptosis in IL-6-dependent multiple myeloma cells expressing both Bcl-2 and BclXL. 15 However, since ROS responses in the more resistant cells were only 25-30% of those noted in sensitive cells (Fig. 3a and data not shown), and because NAC prevented MEK and Akt processing and apoptosis in otherwise sensitive cells (Figs.…”

“…10 Dysfunctional Ras is found in 30% of all known human cancers, including lymphomas and prostate cancers, 3 and moreover, constitutively active Ras is found in >90% of pancreatic cancers and in 20-30% of multiple myeloma isolates. 3,15 Therefore, compounds such as Man-A were especially prospected for their potential use as first lines of defense against tumors harboring constitutively active Ras. Because Ras controls pathways that regulate cell growth, catabolic processes, survival, proliferation and motility, 43 it is considered to be one of the most valued targets in anticancer therapy.…”

“…11,12 It synergizes with the chemotherapeutic paclitaxel to kill anaplastic thyroid carcinoma cells more effectively, 13 and in culture, it is especially potent in the killing of pancreatic tumors and human myeloma cells harboring dysfunctional Ras signaling networks. 14,15 Although the tumoricidal effects of Man-A and other related compounds that interfere with prenylation have been widely described, the underlying mechanism(s) of their actions are incompletely understood. In fact, it is becoming clear that cell death mediated through the farnesyltransferase inhibitor (FTI) class of compounds appears to involve both FTase-dependent and -independent pathways.…”

Manumycin A induces apoptosis in malignant pleural mesothelioma through regulation of Sp1 and activation of the mitochondria-related apoptotic pathway

“…Recently, the anti-neoplastic activity of Manu A has been demonstrated in various experimental systems (18). It exerts antitumor activity against a variety of cancer cells such as human pancreatic cancer cells (19), anaplastic thyroid cancer cells (20,21), human colon tumor cells (22) and human hepatocellular carcinoma HepG2 cells (23), medulloblastoma cells (24,25), leukemic cells (26), lymphoid tumor and myeloma cell lines (27,28). However, little is known concerning the anticancer mechanisms of Manu A by which it can induce apoptosis in MPM cells.…”

Enhancing Therapeutic Radiation Responses in Multiple Myeloma

“…(Karp and Lancet, 2005;Santucci et al, 2003). Manumycin (Man)-A induces apoptosis in B-c e l l t u m o r s b y i n h i biting prenylation (Frassanito et al, 2002) and also by generating ROS that inhibits Ras/MEK/ERK and Ras/PI3K/Akt pathways by cleaving MEK and Akt (Sears et al, 2008). R115777 (zarnestra/tipifarnib) is a FTI that has shown promising clinical results in acute myeloid leukemia, myelodysplastic syndromes, chronic myelogenous leukemia, and MM and with anti-tumor effects noted independent of Ras mutations (Martinelli et al, 2008).…”