Characterization of a R115777-Resistant Human Multiple Myeloma Cell Line with Cross-Resistance to PS-341

Abstract

The farnesyl transferase inhibitor R115777 has been found to have clinical activity in diverse hematopoietic tumors. Clinicalefficacy, however, doesnot correlate with Rasmutationstatus orinhibition of farnesyl transferase. To further elucidate the mechanisms by which R115777 induces apoptosis and to investigate drug resistance, we have identified and characterized a R115777-resistant human myeloma cell line. 8226/R5 cells were found to be at least 50 times more resistant to R115777 compared with the parent cell line 8226/S. K-Ras remained prenylated in both resistant and sensitive cells after R115777 treatment; however, HDJ-2 farnesylation was inhibited in both lines, implying that farnesyl transferase (the drug target) has not been mutated. Whereas many 8226 lines that acquire drug resistance have elevated expression of P-glycoprotein, we found that P-glycoprotein expression is not increased in the 8226/R5 line and intracellular accumulation of R115777 was not reduced. In fact, 8226/R5 cells were insensitive to a diverse group of antitumor agents including PS-341, and multidrug resistance didnot correlate with the expressionof heat shock proteins.Comparison of gene expression profiles between resistant and sensitive cells revealed expression changes in several genes involved in myeloma survival and drug resistance. Future experiments will attempt to identify genes that are directly linked to the resistant phenotype. Identification of molecules associated with R115777 and PS-341resistance is clinically relevant because both compounds are being tested in solid tumors and hematopoietic malignancies.

Novel Targeting of Phospho-cMET Overcomes Drug Resistance and Induces Antitumor Activity in Multiple Myeloma

“…Culture supernatants were centrifuged (200 Â g for 10 minutes), and stored at À80 C as conditioned media. (27); MM.1R cells are resistant to dexamethasone (28). The cell lines were cultured in RPMI-1640 medium supplemented with 10% fetal calf serum (both from Euroclone, Milan, Italy).…”

Cancerous inhibitor of protein phosphatase 2A determines bortezomib-induced apoptosis in leukemia cells

“…Buzzeo et al have also demonstrated that G2/M arrest induced by bortezomib's proteasome inhibition is not correlated with the sensitivity of cells to bortezomib-induced apoptosis. 36 We showed that bortezomib efficiently inhibits proteasome activity in all tested leukemia cells, as demonstrated by proteasome activity analysis and by efficient NF-kB inhibition even in bortezomib-resistant leukemia cells ( Figure 1C and D). However, bortezomib induces differential apoptotic effects in these leukemia cells.…”

Cooperation between Apo2L/TRAIL and bortezomib in multiple myeloma apoptosis

“…First, we generated a resistant cell Page 11 of 31 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 resistance to this drug [27] and also greater than the resistance of SUDHL-4 lymphoma cells (Fig. 6), previously used in several works as a model of bortezomib resistance [28][29][30].…”