Percoll Density Gradient Centrifugation of Rat Pituitary Tumor Cells: a Study of Functional Heterogeneity Within and Between Tumors With Respect to Growth Rates, Prolactin Production and Responsiveness to the Somatostatin Analog SMS

Tumor cells prepared from PRL-secreting rat pituitacy 73 156 tumors qf increa.ting weight were separated on continuous Percoll density gradients, according to d$jerences in their density. Whether the cell subpopulations obtained E$ dens& gradient separation .\hou,ed differences in protein content per cell, PRL production per cell, groutth rates and respon.kenej.c to the somatostatin analog SMS 20 l-995 in vitro relas investigated. In addition, we .studied PRL release ly individual 7315b tumor cells, using the reverse hemolrtirplayue a.rsq (RIfP:l). The tumor cells,from tumors “j-increasing akeight were recoupred within a narrow den@ range ( 1 .CNX-1.070 g/ml) and shozed a normal distribution projile. There alere no di&rences betnleen the subpopulations with respect to the parameters mentioned above. .Moreover, no &fjPrenres were found with respect to these parameters between tumor cells derked from tumors qf inrrea.\ing useight. In agreement with the above data wefound no eGdencefor sublvpes of adenoma cells beingpreferential!p responsive to SMS 20 l-995, using the RHPA. Conclusions: ( 1) the tramplantable PRL-secreting rat pituitary tumor 73 I56 comists of a functiona& homogeneous cell populatron; (2) growth of this tumor in viva does not lead to the induction of j‘unctional!s heterogeneous cell .subpopulations within this tumor; (3) the escape of this tumor from the tumor growth-inhibitoyy effect of SdlS 201-995. which has prerlious~,~ been demonstrated in viva, mg not harme been the result of rlonal selection of somatostatin-unresponsizle cells. INTRODUCTION MOST murine and human solid tumors show intratumor heterogeneity. Tumor cell populations can he heterogeneous for many phenotypic characteristics such as karyotypc, biochemical profile (e.g. levrls of various enzymes), hormone receptor content and drug or radiosensitivity [ 11. Little is known, however, with respect to functional heterogeneity within pituitary tumors. Although it has been demonstrated that both human and rat pituitary tumors may consist of subpopulations of cells secreting more than one hormone simultaneously 12-71, a possible differential responsiveness of these tumor Acceptrd 14 Scptemhrr 1989. Correspondcncc and rrqucsts kor reprints to: 1.co.J. Hofialld. hpartmrnt of Mrdirinr III. University Hospital Dijkzigt. 1(J Dr. Mol~watrrplein. 3015 Cl) Rottrrdam. the Nrthcrlands. cell subpopulations to hypothalamic regulatory hormones or to drugs has not been investigated extensively. In addition, it is not known whether, when cell proliferation occurs in z&o, all cells within a pituitary tumor cell suspension show similar growth rates. A knowledge of the intratumor heterogeneity ofpituitary tumors can be helpful in the understanding of the effects of certain drugs on the growth of the tumor cells or on the regulation of hormone release by these tumor cells in viuo and in vitro. The somatostatin analog SMS 201-995 has previously shown to inhibit the growth of the transplantable prolactin (PRL)-secreting rat pituitary tumor 7315, in viva [8]. However, this tumor rapidly ‘escaped’ from the tumor growth-inhibitory effect of SMS 201-995. In this study [8], one could not unequivocally exclude the possibility that this ‘escape’