Beta-adrenergic influences on doxorubicin-sensitive or -resistant P388 leukemia cells

Taking into account the possible regulatory influences of the beta-adrenergic system on lymphocyte proliferation as well as the proposed role of cyclic 3'-5'-adenosine monophosphate (cAMP) in the modulation of multidrug resistance (MDR) in tumour cells, we have tried to assess the status of the interactions between the beta-adrenergic system and a mouse lymphocytic leukemia, the P388, both as a doxorubicin-sensitive (P388) and -resistant (MDR) variant (P388/DXR). P388 showed a low total number of high affinity 125I-pindolol binding sites (340 +/- 33/cell, Kd 108 pM) when compared with normal splenocytes (1221 +/- 67 sites/cell, Kd 97 pM). The number of beta-adrenergic receptors was even lower in P388/DXR cells (230 +/- 41 sites/cell, Kd 101 pM). In addition, these receptors were subnormally expressed on the cell surface: only 26% and 52% of the total receptors were surface receptors in P388 and P388/DXR, respectively, whereas it was 87% in normal splenocytes. Isoproterenol slightly (less than 1-fold) stimulated cAMP accumulation in P388 and P388/DXR; the stimulation observed in splenocytes was 2.5-fold. In addition, the basal levels of cAMP appeared to be low (0.48 +/- 0.05 pmoles/10(6) cells in P388 and 0.71 +/- 0.08 pmoles/10(6) cells in P388/DXR; 3.47 +/- 0.28 pmoles/10(6) cells in splenocytes) in the two leukemias and they were only slightly (less than 2-fold) increased by forskolin, which otherwise stimulated about 15-fold cAMP accumulation in splenocytes; thus, P388 and P388/DXR were probably also defective in their adenylate cyclase activity. It can be concluded that, owing to multifactorial mechanisms, the lymphocytic leukemia P388, also as an MDR variant, is minimally sensitive to the direct influences of the beta-adrenergic system, probably including any effect of this system on drug-sensitivity.