The addition of bryostatin 1 to cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy improves response in a CHOP-resistant human diffuse large cell lymphoma xenograft model.
The incidence of non-Hodgkin's lymphoma has been increasing at a rate of 4% per year since 1950; more than 62,000 cases will be diagnosed in the United States in 2000. Diffuse large cell lymphoma (DLCL) is the prototype of curable non-Hodgkin's lymphoma. Empirically designed chemotherapy regimens did not increase the cure rate of 30-40% achieved by the original four-drug regimen introduced in the 1970s [cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP)]. We studied the antitumor effects of the CHOP regimen alone or in combination with a unique protein kinase C activator, bryostatin 1, on a xenograft model for resistant DLCL in mice with severe combined immune deficiency (WSU-DLCL2-SCID). In this model, the efficacy of bryostatin 1 given at 75 microg/kg, i.p., alone for 1 or 2 days [B(1x) and B(2x)]was compared with the efficacy of CHOP alone, bryostatin 1 + CHOP (B+CHOP) given concurrently, bryostatin 1 for 1 day followed by CHOP on day 2 [B(1x)-CHOP], and bryostatin 1 for 2 days followed by CHOP on day 3 [B(2x)-CHOP]. CHOP doses were as follows: (a) cyclophosphamide, 40 mg/kg, i.v.; (b) doxorubicin, 3.3 mg/kg, i.v.; (c) vincristine, 0.5 mg/kg, i.v.; and (d) prednisone, 0.2 mg/kg, every day for 5 days, p.o. Tumor growth inhibition (T/C), tumor growth delay (T-C), and log10 kill for B(1x), B(2x), CHOP, B+CHOP, B(1x)-CHOP and B(2x)-CHOP were 49%, 39%, 25.8%, 15.1%, 14.6%, and 12%; 6, 7, 16, 25, 12, and 15 days; and 0.6, 0.5, 2.2, 3.6, 1.7, and 2.0, respectively. To begin elucidating the mechanism whereby bryostatin 1 potentiated the effects of CHOP in the mouse model; we studied the effect of bryostatin 1 on Bax, Bcl-2, and poly(ADP-ribose) polymerase proteins in vitro and in vivo. Bax protein increased in a time-dependent manner without any measurable change in Bcl-2 expression. However, significant cleavage of the preapoptotic marker poly(ADP-ribose) polymerase was not recorded, and the percentage of apoptotic cells detected by flow cytometry increased only slightly (approximately 8%) after 96 h of bryostatin 1 exposure. The in vitro and in vivo results emphasize the superiority of combining bryostatin 1 with the CHOP regimen against the WSU-DLCL2 model. One possible mechanism may be the modulatory effects of bryostatin 1 on the Bax:Bcl-2 family of apoptosis-regulatory proteins. The use of this combination should be further explored clinically in the treatment of lymphoma.
Mohammad
R M
RM
Division of Hematology and Oncology, Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA. Mohammad@karmanos.org
Wall
N R
NR
Dutcher
J A
JA
Al-Katib
A M
AM
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage* / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D054713:Bryostatins; D003520:Cyclophosphamide / Q000008:administration & dosage*; D004317:Doxorubicin / Q000008:administration & dosage*; D004789:Enzyme Activation; D005434:Flow Cytometry; D006801:Humans; D007783:Lactones / Q000008:administration & dosage*; D016403:Lymphoma, Large B-Cell, Diffuse / Q000188:drug therapy*; D018942:Macrolides; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D011065:Poly(ADP-ribose) Polymerases / Q000096:biosynthesis; D011239:Prednisolone / Q000008:administration & dosage*; D011493:Protein Kinase C / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014750:Vincristine / Q000008:administration & dosage*; D051028:bcl-2-Associated X Protein
D000970:Antineoplastic Agents; C494826:BAX protein, human; C494827:Bax protein, mouse; D054713:Bryostatins; D007783:Lactones; D018942:Macrolides; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C046785:bryostatin 1; D014750:Vincristine; D004317:Doxorubicin; D003520:Cyclophosphamide; D011239:Prednisolone; D011065:Poly(ADP-ribose) Polymerases; D011493:Protein Kinase C