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Resistance of in vitro grown IgM immunocytoma cells to cis-diamminedichloroplatinum (II) (cis-DDP) and cross-resistance to other DNA interacting drugs.

Previously, we reported on the resistance to cis-diamminedichloroplatinum(II) (cis-DDP) of tumor cells in IgM immunocytoma tumors. In vitro cell lines were established, from tumors both sensitive and resistant to cis-DDP. The cultured cells obtained from the parent tumor were designated IgM-I, and those from a cis-DDP resistant tumor IgM/cDDP. In vitro dose response studies showed a difference in cis-DDP sensitivity with a resistance factor of approximately 20 at a relative survival of the tumor cells of 50 percent. The resistance factor was determined both in an assay with continuous cis-DDP exposure for 72 h, and in a clonogenic assay after an exposure for 1 h to various dosages of cis-DDP. The IgM/cDDP cells showed cross-resistance, in vitro and in vivo, to the currently used cis-DDP analogs carboplatin (CBDCA or JM8) and iproplatin (CHIP or JM9). Cross-resistance was also observed against the recently developed platinum(IV) compound tetraplatin. In addition, the cell line IgM/cDDP was resistant to other drugs interacting with DNA, such as doxorubicin (DXR), mitomycin C (MMC) and melphalan (L-PAM). For two non DNA-interacting drugs, vincristine (VCR), a mitosis inhibitor, and VP-16, a topoisomerase inhibitor, both cell lines were equally sensitive.