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 gear since 1950; more than 62,000 cases will be diagnosed in the Unite d States in 2000, Diffuse large cell lymphoma (DLCL) is the prototype of cu rable non-Hodgkin's lymphoma. Empirically designed chemotherapy regimens di d not increase the cure rate of 30-40% achieved by the original four-drug r egimen introduced in the 1970s [cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP)], We studied the antitumor effects of the CHOP regim en alone or in combination with a unique protein kinase C activator, bryost atin 1, on a xenograft model for resistant DLCL in mice with severe combine d immune deficiency (WSU-DLCL2-SCID), In this model, the efficacy of bryost atin 1 given at 75 mug/kg, i.p., alone for I or 2 days [B(lx) and B(2x)]was compared with the efficacy of CHOP alone, bryostatin 1+CHOP (B+CHOP) given concurrently, bryostatin 1 for I day followed by CHOP on day 2 [B(lx)-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) doxorubic in, 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 log,, kill for B(lx), B(2x), CHOP, B+CHOP, B(lx)-CH OP 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 b egin elucidating the mechanism whereby bryostatin 1 potentiated the effects of CHOP in the mouse model; we studied the effect of bryostatin 1 on Pax, Bcl-2, and poly(ADP-ribose) polymerase proteins in vitro and in vivo. Pas p rotein increased in a time-dependent manner without any measurable change i n Bcl-2 expression, Rowel er, significant cleavage of the preapoptotic mark er poly (ADP-ribose) polymerase was not recorded, and the percentage of apo ptotic cells detected by flow cytometry increased only slightly (similar to 8%) after 96 h of bryostatin I exposure. The in vitro and ill vivo results emphasize the superiority of combining bryostatin 1 with the CHOP regimen a gainst the WSU-DLCL2, model. One possible mechanism may be the modulatory e ffects of bryostatin 1 on the Bax:Bcl-2 family of apoptosis-regulatory prot eins. The use of this combination should be further explored clinically in the treatment of lymphoma.