RESUMEN
Cytochalasin B (CB), at 100 or at 10 mg/kg single dose s.c. in carboxymethyl-cellulose (2%)/Tween-20 (1%) 24 h after s.c. challenge of B6D2F1 mice with trocar implants of B16F10 tumor s.c., delayed the appearance of measurable tumor nodules by 157 and 93%, respectively, and extended host survival by 65 and 26%. Tumor growth was also delayed when CB treatment was given 1 day after the appearance of palpable tumor nodules. By in vivo bioassay, in vitro cloning, and dye exclusion measurements, solid tumor nodules treated in vivo with CB at either 100 or 10 mg/kg showed the same viability and tumorigenicity as did vehicle-treated nodules 4 and 6 days after drug treatment, at which time growth inhibition was still apparent. This indicates that growth inhibition by CB is not dependent on a gross cytotoxic effect. CD2F1 mice challenged s.c. with Madison 109 lung carcinoma cells and treated with CB s.c. at 100 or 150 mg/kg 24 h later showed a 66% delay in the median day of tumor nodule appearance. When administered under these conditions or at the time of nodule appearance. CB markedly inhibited the rate of tumor growth, prevented tumor invasion at day 23, extended life span by 23%, and significantly inhibited spontaneous lung metastases measured 28 days after tumor challenge. Maximum tolerated doses of CB administered i.p., s.c., or i.v. in suspension or in solution are defined. These results delineate the conditions under which CB can be tested for in vivo biological activities and establish that this microfilament-active natural product in a single-agent protocol inhibits local tumor growth and extends survival in B16F10 melanoma and Madison 109 lung carcinoma, and, in the latter model, inhibits invasion and spontaneous lung metastases by mechanisms that do not appear to depend on cytotoxicity. This work on formulation, tolerated doses in vivo, and localized peritumoral effects of CB now permits evaluation of systemic antitumor effects of cytochalasin B as a single agent. It also permits chemotherapy studies using CB as a potential amplifier of the activity of other antitumor agents in vivo.
Asunto(s)
Citocalasina B/farmacología , Neoplasias Pulmonares/tratamiento farmacológico , Melanoma Experimental/tratamiento farmacológico , Animales , Supervivencia Celular/efectos de los fármacos , Cromatografía en Capa Delgada , Citocalasina B/administración & dosificación , Citocalasina B/análisis , Relación Dosis-Respuesta a Droga , Evaluación Preclínica de Medicamentos , Neoplasias Pulmonares/patología , Melanoma Experimental/patología , Ratones , Ratones Endogámicos BALB C , Invasividad Neoplásica , Metástasis de la Neoplasia , Células Tumorales CultivadasRESUMEN
Cytochalasin B (CB) was prepared by methanol extraction of dehydrated mold (Drechslera dematioidea) matte, reverse-phase C18 silica gel batch adsorption, selective elution with 1:1 (v/v) hexane:tetrahydrofuran (THF), crystallization, preparative TLC, and recrystallization. Unit gravity silica gel normal phase chromatography afforded additional CB. Yield per liter of medium was 300 mg of CB greater than 95% pure by NMR, HPLC (60:40 hexane:THF, Lichrosorb Si60 silica gel, 230 nm), and TLC. CB added exogenously to mouse organs at 1 and 5 micrograms/organ was recovered 70 to 100% by methanol extraction, adsorption to C18 silica gel Sep-Pak cartridges, elution with ethyl acetate, and analysis by TLC and/or HPLC. Limiting sensitivity (micrograms/extract) was 0.5 TLC; 1.0 HPLC. Quantitative extraction was confirmed with 3H-labeled CB. CB ip in mice at 50 mg/kg (LD10) distributed rapidly into liver, renal fat, kidney, intestines, mesentery, pancreas, spleen, and blood cells and was cleared from all but liver within 24 h. CB was below detectable levels in thymus, lymph nodes, heart, brain, bone marrow, and lungs. Cytochalasin A is fixed to tissues and not extractable. This work affords a source of CB in quantities permitting in vivo study, provides methods for extraction and analysis, and reveals the pharmacokinetics of ip bolus CB.