Assessment ofall-trans retinoic acid (ATRA) efficacy as a single agent in primary lymphoid neoplasia

All-trans retinoic acid (ATRA) is currently widely used in the therapy of acute promyelocytic leukemia and is being tested in vitro and in vivo on several other malignancies. Previously ATRA has been shown to inhibit the growth in vitro, of established human myeloma cell lines as well as cultured primary myeloma cells from patients. ATRA acts by down-regulating IL-6-receptor-alpha or gp130 on the surface of the myeloma cells. However, despite its in vitro effects on myeloma cells, ATRA therapy on advanced stage multiple myeloma (MM) patients has so far largely been ineffective. In current studies, we have assessed the efficacy of ATRA therapy against primary murine plasma cell tumors, which are an animal model for human MM. These tumors are induced at about 50% incidence in pristane-primed BALB/c mice by injection of v-raf/v-myc- containing retroviruses and are IL-6 dependent. Using this animal model, we assessed the effect of ATRA as a therapeutic agent against primary tumors at two early time points in disease development. ATRA was administered in liposomal vesicles (ATRAGEN), since liposomal-ATRA has been shown to circumvent clearance mechanisms by hepatic microsomes, which normally occur with free ATRA. In addition, ATRAGEN was previously shown to be less toxic in mice than free ATRA. ATRAGEN was administered beginning on day 25 or day 45 after virus injection and continued twice weekly for 8-11 weeks. ATRAGEN administration begun at either time point did not alter the incidence or the latency of plasma cell tumors compared with control animals. These results suggest that ATRA may not be an effective sole therapy against early MM.