sdz-psc-833 and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

Valspodar, a non-immunosuppressive analog of cylosporine, is a potent P-glycoprotein (MDR1) inhibitor. As MDR1-mediated efflux of chemotherapeutic agents from leukemic blasts may contribute to drug resistance, a phase 1 study of valspodar combined with mitoxantrone and etoposide in pediatric patients with relapsed or refractory leukemias was performed.. Patients received a valspodar-loading dose (2 mg/kg) followed by a 5-day continuous valspodar infusion (8, 10, 12.5, or 15 mg/kg/day) combined with lower than standard doses of mitoxantrone and etoposide. The valspodar dose was escalated using a standard 3 + 3 phase I design.. Twenty-one patients were evaluable for toxicity and 20 for response. The maximum tolerated dose (MTD) of valspodar was 12.5 mg/kg/day, combined with 50% dose-reduced mitoxantrone and etoposide. The clearance of mitoxantrone and etoposide was decreased by 64% and 60%, respectively, when combined with valspodar. Dose-limiting toxicities included stomatitis, ataxia, and bone marrow aplasia. Three of 11 patients with acute lymphoblastic leukemia (ALL) had complete responses while no patient with acute myeloid leukemia (AML) had an objective response. In vitro studies demonstrated P-glycoprotein expression on the blasts of 5 of 14 patients, although only 1 had inhibition of rhodamine efflux by valspodar.. While this regimen was tolerable, responses in this heavily pretreated population were limited to a subset of patients with ALL.

Topics: Adolescent; Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B, Member 1; Child; Child, Preschool; Cyclosporins; Drug Resistance, Multiple; Drug-Related Side Effects and Adverse Reactions; Etoposide; Female; Humans; Leukemia, Myeloid, Acute; Male; Maximum Tolerated Dose; Mitoxantrone; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Recurrence; Salvage Therapy; Young Adult

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 microM PSC 833 (P = 0.025), 1.5-fold using 4 microM CsA (P = 0.003) and 1.6-fold using 6 microM Vp (P = 0.012) whereas the adverse effect of 25 microM genistein was median 1.8-fold (P < 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 P-gp, 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.

Topics: Antibiotics, Antineoplastic; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Cell Survival; Cyclosporine; Cyclosporins; Daunorubicin; Drug Resistance, Neoplasm; Genistein; Humans; In Vitro Techniques; Multidrug Resistance-Associated Proteins; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Verapamil