Combination Of Difluoromethylornithine Research Articles

The growth-inhibitory effect of 4-hydroperoxycyclophosphamide against human non-small cell lung carcinoma is enhanced by low-dose difluoromethylornithine.

Surgically unresectable human non-small cell lung carcinoma (NSCC) is highly resistant to present chemotherapy and radiation therapy regimens. Cyclophosphamide, a potent alkylating agent, has shown some efficacy, especially in combination chemotherapy. Difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase (ODC) which produces minimal toxicity in animals and humans, has shown antiproliferative effect against human SCC in culture but a much smaller effect (cytostatic) against NSCC. We therefore investigated 4-hydroperoxycyclophosphamide (4HC) and DFMO alone and in combination against a human NSCC line (NCI-H157). Cells were treated with DFMO at graded concentrations of 0 to 800 microM from day 0 to day 7. On day 3, cells were exposed for 1 h to 4HC at graded concentrations of 0 to 80 microM, washed, and refed with media containing DFMO at initial concentrations. On day 7, cells were counted by hemacytometer. Cells treated with DFMO or 4HC alone exhibited dose-dependent growth inhibition. Growth inhibition by 4HC was enhanced through combination with DFMO. On day 7, 50 microM (5 x 10(-5) M) DFMO effected a 37% inhibition, 8 microM 4HC 47% inhibition, and the combination of 50 microM DFMO and 8 microM 4HC yielded an elevated 71% inhibition. The growth inhibitory effect and potentiating effect of DFMO were reversible upon addition of putrescine (PU) to the culture medium. The combination of DFMO and 4HC, two agents with different toxicity spectra, may represent an effective chemotherapeutic regimen for the treatment of lung cancer.

Inhibition of Mouse Bladder Tumor Proliferation by Alpha Difluoromethylornithine and Interferon in Vitro and in Vivo

Previous studies have reported that alpha difluoromethylornithine (DFMO), an enzyme-activated, irreversible inhibitor of ornithine decarboxylase (ODC), has anti-tumor activity in several tumor systems. Recently, investigations have revealed that combinations of DFMO and Interferon (IFN) are synergistic in inhibiting tumor cell growth. We tested the effects of DFMO and IFN α,β alone and in combination on the growth of mouse bladder tumor (MBT-2) cells both in vitro and in vivo.MBT-2 cells were incubated for 72 hours in 96 well microtiter plates with DFMO, IFN α,β and combinations of both agents and percentage inhibition was calculated. In vivo studies utilized the intravesical implantation method as well as subcutaneous implantation. DFMO was administered as a 1% solution in the drinking water. IFN α,β was given bi-weekly by intravesical administration. DFMO effectively inhibited MBT-2 growth in vitro. The ID 50 was 0.08mM and peak inhibitory activity was reached at concentrations of 0.16mM and remained constant with concentrations of up to 10mM. IFN α,β also inhibited the in vitro proliferation of MBT-2 with maximum inhibition (46%) at 2,000U/ml. Combinations of DFMO and IFN α,β showed increased anti-proliferative activity. The degree of enhancement varied with synergism, additivity, or sub-additivity at varying drug concentrations. In vivo, DFMO significantly retarded the growth of tumors implanted subcu-taneously (p <.05) and significantly delayed the outgrowth of tumors implanted intravesically (p <.01). IFN α,β alone was ineffective in vivo and produced no additive effect in vivo when used in combination with DFMO.Results of our investigation show that DFMO inhibits proliferation of MBT-2 cells in vitro and exhibits a similar effect in vivo against subcutaneous and intravesical tumor implants. IFN α,β alone demonstrated anti-proliferative activity in vitro but did not affect MBT-2 growth in vivo. Although the combination of DFMO and IFN α,β exhibited enhanced activity in vitro, no enhancement was observed with combination therapy in vivo.

Combined Effects of α-Difluoromethylornithine and Doxorubicin Against Pancreatic Cancer Cell Lines in Culture

Pancreatic adenocarcinoma presents a clinical and experimental challenge because of its relative resistance to conventional modes of therapy. The present study explores a novel, biologically based approach to enhancing its chemosensitivity and to overcoming its chemoresistance in a panel of pancreatic adenocarcinoma cell lines (two human lines: PANC-1 and COLO-357; and two hamster lines: WD PaCa and PD PaCa). Difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC) that produces antiproliferative effects by polyamine depletion, was combined with the cytotoxic agent doxorubicin (DOX) in vitro. The inhibitory effects of DFMO were cytostatic and roughly additive to those of DOX. Although the response to the combination varied as a function of the cell lines studied and the response to DFMO as a single agent, all cell lines studied showed some increased inhibition with the combination. The most striking enhancement was seen in our most DOX-resistant cell line, WD PaCa, and also in PANC-1, a relatively sensitive cell line. Thus, the combination of DFMO and DOX shows promise as an experimental approach to the problem of drug resistance and the limited chemosensitivity of pancreatic cancer.

Regulation of Epidermal Proliferation in Mouse Epidermis by Combination of Difluoromethyl Ornithine (DFMO) and Methylglyoxal Bis(guanylhydrazone) (MGBG)

Topical methylglyoxal bis(guanylhydrazone) (MGBG) and alpha-difluoromethylornithine (DFMO) individually have been shown to produce partial clinical improvement in psoriasis. In an effort to further enhance therapeutic activity, studies were designed to optimize percutaneous penetraton of DFMO in vitro and to determine the effects of the combination of DFMO and MGBG on DNA synthesis and polyamine levels in hairless mouse skin. MGBG was shown to be more effective than DFMO in inhibiting DNA synthesis in vitro and in vivo. Maximum in vitro percutaneous penetration of DFMO (5%) was obtained in Vehicle N containing 10% Azone (297 micrograms/h/cm2). Topical administration of the combination of 5% DFMO and 0.1% MGBG in this vehicle produced a greater inhibition of DNA synthesis and depletion of polyamine levels than either drug individually. The simultaneous topical administration of DFMO and MGBG, allowing the use of lower concentrations of the more toxic MGBG, may be useful for therapy of psoriasis and other cutaneous disorders associated with abnormalities in polyamine metabolism.

Role of diamine oxidase during the treatment of tumour-bearing mice with combinations of polyamine anti-metabolites.

Treatment of mice bearing L1210 leukaemia with 2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a profound depletion of putrescine and spermidine in the tumour cells. Sequential combination of methylglyoxal bis(guanylhydrazone), an inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), with difluoromethylornithine largely reversed the polyamine depletion and led to a marked accumulation of cadaverine in the tumour cells. Experiments carried out with the combination of difluoromethylornithine and aminoguanidine, a potent inhibitor of diamine oxidase (EC 1.4.3.6), indicated that the methylglyoxal bis(guanylhydrazone)-induced reversal of polyamine depletion was mediated by the known inhibition of diamine oxidase by the diguanidine. In spite of the normalization of the tumour cell polyamine pattern upon administration of methylglyoxal bis(guanylhydrazone) to difluoromethylornithine-treated animals, the combination of these two drugs produced a growth-inhibitory effect not achievable with either of the compounds alone.