Cyano-morpholino-adriamycin (MRA-CN) and some of its congeners represent a new and exciting sub-class of anticancer drugs. They exhibit major differences in pharmacodynamic properties and in their apparent mechanisms of action from other anthracyclines. The antitumor activity of MRA-CN is markedly more potent (500 to 1000-fold) than doxorubicin (DOX), both in cell lines and in transplantable tumor models, with no corresponding increase in cardiac toxicity. MRA-CN produces cross-linking of DNA, unlike other anthracyclines. MRA-CN is not cross resistant with DOX or other anthracyclines in DOX-selected variants of P388 leukemia and the human sarcoma cell line, MES-SA. The purpose of this proposal is to study the cellular pharmacology of MRA-CN, with regard to its selectivity, mechanisms of action and resistance, and modulation by other agents. Preliminary data indicate that the major normal tissue toxicity of MRA-CN may be to the bone marrow. We will be able to study the drug sensitivities of bone marrow CFU-C from patients with lymphomas and leukemias in remission, as well as in cell lines derived from their tumors before and after treatments. A therapeutic index will then be estimated in vitro for MRA-CN and compared directly to DOX and melphalan as model anthracyclines and alkylating agents. It is likely that some of the paired cell lines will differ in their MRA-CN sensitivity after patients have relapsed from anthracycline and alkylator containing regimens, or that some lines will be resistant to MRA-CN (relative to marrow) a priori. These lines which are resistant de novo or after treatments in vivo will be used for further studies of possible mechanisms of resistance, cross-resistance and selective modulation. The ability to obtain and propagate both tumor cell lines and normal marrow from the same patient offers an ideal opportunity for reproducible in vitro observations on clinically derived material. In addition, resistance to MRA-CN will be developed by step-wise exposure to MRA-CN in vitro. DOX and MRA-CN cellular accumulation, DNA cross-link formation and repair, and glutathione pathways will be assessed in the paired sensitive and resistant lines. Possible sensitizing effects of modulators of pleiotropic resistance (e.g., verapamil and tamoxifen), inhibitors of glutathione synthesis (buthionine sulfoximine), and agents which interact with alkylators (misonidazole) will be assessed. The selectivity of any such modulation relative to human bone marrow will be evaluated. Finally, the extreme potency and non-basicity of the amino-nitrogen of MRA-CN make it an attractive candidate for liposomal encapsulation and monoclonal antibody-liposome targeting, offering the potential for greatly increased selectivity.
