The modulating effect of PSC 833, cyclosporin A, verapamil and genistein on in vitro cytotoxicity and intracellular content of daunorubicin in childhood acute lymphoblastic leukemia

Abstract

Resistance to anthracyclines is related to a poor prognosis in childhood acute lymphoblastic leukemia (ALL). Resistance to this class of drugs may (partly) be reversed by modulating agents, as has been demonstrated in a variety of cell lines. However, it is unknown which modulators may be of clinical benefit in childhood ALL. Therefore, we studied the modulating effect of PSC 833, cyclosporin A (CsA), verapamil (Vp) and genistein on daunorubicin (DNR) cytotoxicity, accumulation and retention in childhood ALL cells. DNR cytotoxicity was determined using the MTT assay; DNR accumulation, DNR retention and the expression of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and major vault protein/lung resistance protein (LRP) were determined by flow cytometry. In the majority of samples PSC 833 (19/26), CsA (22/26) and Vp (15/18) sensitized the cells to DNR whereas genistein made 25 out of 26 samples more resistant to DNR. The sensitizing effect on the cytotoxicity of DNR was median 1.2-fold using 2 M PSC 833 (P = 0.025), 1.5-fold using 4 M CsA (P = 0.003) and 1.6-fold using 6 M Vp (P = 0.012) whereas the adverse effect of 25 M genistein was median 1.8-fold (P Ͻ 0.0001). No relationship was found between the sensitizing effect of PSC 833, CsA or Vp and the degree of DNR resistance. In contrast, the adverse effect of genistein was largest in DNR sensitive samples (P = 0.003). The effect of each modulator on the cytotoxicity of DNR did not differ between initial and relapse ALL samples although the latter were median 1.4-fold more resistant to DNR (P = 0.005). Modulation of DNR cytotoxicity was not correlated with changes in the accumulated and retained intracellular DNR content or with the expression of Pgp, MRP and LRP. Besides genistein, PSC 833, CsA and Vp incidentally made ALL cells more resistant to DNR. CsA stimulated the leukemic cell survival in seven out of 26 samples, a phenomenon that was not related to the degree of DNR resistance. In conclusion, PSC 833, CsA and Vp but not genistein may be used to sensitize cells to DNR in childhood ALL. The data also indicate that not all patients may have a therapeutic benefit from these modulators. Therefore, an in vitro culture assay may be necessary to screen for patients who may benefit by a modulator in their therapy.

Effects of Naturally Occurring Polymethyoxyflavonoids on Cell Growth, P-Glycoprotein Function, Cell Cycle, and Apoptosis of Daunorubicin-Resistant T Lymphoblastoid Leukemia Cells

“…Inhibiting P-gp function with diverse pharmacological agents circumvents the MDR phenotype. Compounds such as verapamil, cyclosporine, and certain kinds of flavonoids were reported to sensitize MDR cells to cytotoxic agents (3)(4)(5). Rhodamine 123 (Rh123) has been observed to accumulate in the mitochondria of cells and is used as a standard functional indicator of MDR (6)(7)(8)(9).…”

Different expression of glutathione S‐transferase α, μ and π in childhood acute lymphoblastic and myeloid leukaemia

“…We recently demonstrated that the expression of MRP did not correlate with resistance to DNR and the intracellular accumulated DNR concentration in a large series of childhood ALL (Den Boer et al , 1997a, b; 1998b). Moreover, accumulation deficits could not be reversed by P‐gp and/or MRP modulators such as PSC 833, cyclosporin A, verapamil and genistein (Den Boer et al , 1998a). Therefore our data do not directly support the hypothesis that drug resistance in childhood ALL is due to MRP‐mediated transport of (glutathione‐conjugated) drugs out of the cell.…”

Emerging nanotechnology-based therapeutics to combat multidrug-resistant cancer

“…To prevail over the adverse side effects of first-generation inhibitors, researchers modified their structures and these inhibitors, known as second-generation P-gp inhibitors, were developed including dexverapamil, S9788, and PSC-833 also called valspodar (cyclosporine A analog), etc. The second-generation P-gp inhibitors often caused interference with anticancer drugs and affected their pharmacokinetics, resulting in adverse side effects [ 37 , 38 ]. The third generation of inhibitors such as elacridar, zosuquidar and tariquidar were subsequently tested in clinical studies but also failed to achieve clinical approval due to severe cytotoxic side effects [ 39 , 40 ].…”