dolastatin-10 and Leukemia--Lymphocytic--Chronic--B-Cell

We tested the activity of dolastatin 10 (a natural product derived from the shell-less marine mollusk, Dolabella auricularia, a sea hare) and its structural modification, auristatin PE, alone and in combination with bryostatin 1 (a protein kinase C activator derived from the marine bryozoan Bugula neritina) on a human B-cell chronic lymphocytic leukemia cell line (WSU-CLL) and in a severe combined immune deficient (SCID) mouse xenograft model bearing this cell line. WSU-CLL cells were cultured in RPMI 1640 at a concentration of 2 x 10(5)/ml using a 24-well plate. Agents were added to triplicate wells, and cell count, viability, mitosis, and apoptosis were assessed after 24 h of incubation at 37 degrees C. Results showed that dolastatin 10 had no apparent inhibition of cell growth at concentrations less than 500 pg/ml. Auristatin PE, on the other hand, showed significant growth inhibition at concentrations as low as 50 pg/ml. Auristatin PE-treated cultures, at this concentration, exhibited 27 and 4.5% mitosis and apoptosis, respectively. Dolastatin 10, at the same concentration, did not exert any effect and was comparable with that of control cultures. In the WSU-CLL-SCID mouse xenograft model, the efficacy of these agents alone and in combination with bryostatin 1 was evaluated. Tumor growth inhibition (T/C), tumor growth delay (T-C), and log10 kill for dolastatin 10, auristatin PE, and bryostatin 1 were 14%, 25 days, and 1.98; 2%, 25 days, and 1.98; 19%, 13 days, and 1.03, respectively. Auristatin-PE produced cure in three of five mice, whereas dolastatin 10 showed activity but no cures. When given in combination, auristatin PE + bryostatin 1-treated animals were all free of tumors (five of five) for 150 days and were considered cured. Dolastatin 10 + bryostatin 1-treated animals produced cure in only two of five mice. We conclude that: (a) auristatin-PE is more effective in this model than dolastatin 10; (b) auristatin PE can be administered at a concentration 10 times greater than dolastatin 10; (c) there is a synergetic effect between these agents and bryostatin 1, which is more apparent in the bryostatin 1 + auristatin PE combination. The use of these agents should be explored clinically in the treatment of CLL.

Topics: Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Bryostatins; Cell Count; Depsipeptides; Drug Screening Assays, Antitumor; Female; Humans; Lactones; Leukemia, Lymphocytic, Chronic, B-Cell; Macrolides; Mice; Mice, SCID; Mitosis; Oligopeptides; Subrenal Capsule Assay; Survival Analysis; Treatment Outcome; Tumor Cells, Cultured

Dolastatins are naturally occurring peptides isolated from marine animals and are known to be potent anti-neoplastic agents. Here, the three compounds dolastatin 10 (Dola 10), dolastatin 15 (Dola 15) and deo-dolastatin 10 (Deo-Dola 10) were added to cultures of two human chronic B-leukemia cell lines, JVM-2 and EHEB. The three dolastatins (Dola 10 > Dola 15 > Deo-Dola 10) inhibited cell proliferation and immunoglobulin production. Decreased cell growth and lack of accumulation of immunoglobulin was not caused by cytotoxicity as cell viability in the cultures remained high. The unchanged surface marker immunoprofiles during treatment and a predominance of treated cells in S and G2/M phase suggested cytostatic rather than directly cytotoxic effects. Exposure to these reagents increased quickly, albeit only short c-myc and bcl-2 mRNA expression. These results indicate that the three dolastatins are potent inhibitors of leukemic B-cell proliferation.

Topics: Antigens, Neoplasm; Antigens, Surface; Antineoplastic Agents; Cell Cycle; Cell Division; Cell Survival; Depsipeptides; Humans; Immunoglobulins; Leukemia, Lymphocytic, Chronic, B-Cell; Leukemia, Prolymphocytic; Oligopeptides; Proto-Oncogenes; Transcription, Genetic; Tumor Cells, Cultured