- Email: [email protected]
Human cell cultures for screening anti-cancer drugs
TIPS -July
1987 [Vol. 81
8 Schwartz, J. C. (1977) Annu. Rev. Dhar9
10 11 12 13 14
maco2. Toxicol. 17,325-339 Watanabe, T., Taguchi, Y., Shiosaka, S., Tanaka, J., Kubota, J., Terano, Y., Tohyama, M. and Wada, H. (1984) Brain Res. 295, 15-25 Hdl, S. J., Daum, P. and Young, J. M. (1981) 1. Neurochem. 35,1357-1360 Nichoison, A. N., Stone, B. M. and Pascoe, P. A. (1985) Neurophnrmacoloxy-_ 24.245-250 Peck, A. W., Fowle, A. S. E. and Bye, C. (1975) Eur. j. Clin. Pharmacol. f&455-463 Nicholson, A. N. and Stone, B. M. (1986) Eur. 1. Clin. Pharmacol. 30, 27-32 Bye, C., Dewsbury, D. and Peck, A. W.
249 (1974) Br. j. Clin. Pharmacol. 1, 71-78 15 Clarke, C. H. and Nicholson, A. N. (1978) Br. 1. Clin. Phannacol. 6, 31-35 16 Nicholson, A. N. (1979) Br. j. Clin. Pharmacol. 8,321-324 i7 Friedman, A. H. and Walker, C. A. (1968) j. Physiol. (London) 197,77-85 18 Orr, E. and Quay, W. 8. (1975) Endocrinology 96,941-945 19 Schwartz, J. C., Barbin, G., Garbarg, M., Pollard. H.. Rose, C. and Verdiere. M. (1976) Adv: Biochem. Psychopharmbcoj. 15,111-126 20 Quach, T. T., Duchemin, A. M., Rose, C. and Schwartz, J. C. (1979) Eur. 1. Pharmocol. 60,391-392
Human cell cuhres for screening anti-cancer drugs Although tumours are clonal in origin’, genetic instability inevitably leads to the progressive development of intraneoplastic heterogenei@3. This heterogeneity is manifested in differences in the cellular architecture, growth kinetics and functional properties of individual tumours and in their responsiveness to chemotherapeutic agents. Prognostically, the consequences for the patient are far-reaching. In a significant number of cases, the responsiveness of specific lesions is unpredictable and the therapeutic approach adopted is of necessity empirical. Thus the need for reliable routine in-vitro cell culture assays for assessing the functional properties of proliferating tumour cells and screening anti-cancer drugs: preclinically to identify novel, potentially useful cytotoxic agents, and clinically to predict the outcome of therapy in individual patients. The ability to extrapolate pharmacokinetic data obtained in vitro to predict the response to tumourigenic-cell lines to chemotherapeutic drugs in viva in experimental animal models* shows that this is feasible. In experimental models of tumourigenicity and cell transformation, the ability of single cells to grow as anchorage-independent clones when immobilized in semisolid culture has been the property most closely associated with tumourigenic potentia15r6. The ability of tumour cells from human biopsy specimens to grow in clonal
agar culture was first documented in 1968 by McAllister and Reed7, but it was primarily the work of Courtenay et dazg, and Hamburger and Salmoni’ and their colleaguesl’ which drew attention to the potential of this assay system. The soft-agar tumour colonyforming
cc& assay
Was ;ixnd
!r:
predict drug resistance in individual patients with a high degree of accuracy1’*12. The capacity of tumour cells from surgical specimens to clone in agar appeared to be of prognostic significance in determining patient survival*~15. Significant heterogeneity in the properties of clonogenic cells and in their sensitivity to cytotoxic agents at different sites within individual patients and within individual tumours151s was identified. The assay was also used to assess the effect of chemotherapeutic agents and irradiation in xenografted human turnours’“, and to evaluate novel analogs of anti-cancer drugs”. Preclinical protocols These findings raised the possibility that this assay system could play an important role in preclinical drug-screening protocolszo by facilitating the screening of potential anti-cancer drugs against a large panel of freshly excised human tumours and human tumour cell lines reflecting the heterogeneity and intraneoplastic diversity encountered * clinically. For such an assay system to fulfil these objectives it must meet a
21 Kanh S. and Richelson, 8. (19~) B~UUI Res. 304, l-7 22 Uzan, A., Le Fur, G. and Malgouris, C. (1979) j. Phnrm. Pharmncol. 31.701-702 23 Gervats. P.,Gervais, A., DeBeule, R. and Van der Pijl. W. (1975) Acta Allergol. 30, 286-297 24 Nicholson, A. N. and Stone, 8. M. (1983) Eur. 1. Clin. Phnrmacol. 25,565-566 25 Nicholson, A. N. (1982) Arzneim.-Fonch. Drug Res. 32,1191-1193 26 Nicholson, A. N. and Stone, 8. M. (1982) Br. j. Chk Phnrmacol. 13,199-202 27 Nicholson, A. N., Smith, P. A. and Spencer, M. B. (1982) Br. j. Clin. Pharmaco!. 14, 683-690
number of criteria. Firstly, it must be reliable and widely applicable. Secondly, it must identify those tumour cells which determine the course of the disease in the patient. Thirdly, the end-point of the assay in vitro - the ablation of colonyforming cells by chemotherapeutic agents - must predict the clinical outcome in the patient - the ablation of the tumour. While the initial results summarized above are encouraging, the assay has serious Xmitations, particularly in the evaluation of fresh biopsy specimens’3*151’. Only a proportion of tumours a~ amenable to successful clonal culture from fresh biopsy material at present. Technical problems associated with the preparation of single cell suspensions make it difficult to exclude cell aggregates and this affects interpretation of the assay. Not all tumours contain clonogenic cells, and only tumours biopsied in the terminal phases of disease exhibit the quality of growth which would permit routine use of the assay in individual patients”. It has generally been assumed that the tumour colony-forming cell assay detects tumour stem cells, but there is little evidence to support this conclusion. The assay is biased to the detection of those tumour cells capable of growth in the prevailing culture conditions within the relatively short timeframe of the assay (14-21 days) and may not detect cells in the dormant state (Go/G1 phase of cell cycle) which are an important factor in refractoriness to therapp. The clinical significance of the ablation of the colony-for,qiing cell is also unclear. The correlations between clonogenic capacity and proliferative potential of the colonyforming ce11’3-15, and the ability of the assay to predict drug sensitivity i1~12indicates that these cells
@ 1987, Elsevier Publications.
Cambridge
0165 - 6147/87&02.00
TIPS -July
F@. I f%). Human ovadan ~~~~rna cellsgait in adl?en?nt monolayer cuJfr.rt~and (b) as a~~~-i~~t clones in semi-sofd agar et&we photographed at x I W and x20 magnifications respectively.
are clinically relevant. However, there is no reliable information on the longer term survival of patients treated on the basis of drug sensitivity testing in vitro. The proliferative potential of tumour colonyforming cells within a single culture is variable, and Buick and MacKillop I6 have suggested that the ability of cells from primary clones to reclone in secondary culture would be of more prognostic significance than the primary cloning data. Where there is heterogeneity in the drug-sensitivity of tumour colony-forming cells from different lesions in the same patient a decision about the most appropriate drug to use is impaired because not enough is known about the relationship of
clonogenic cells to the tumour cells ultimately determining the fate of the tumour in viva. Recognizing the potential of the tumour colony-forming cell assay system the National Cancer Institute in the United States entered into feasibility studies to assess the assay for screening new compounds for anti-tumour aCtivity2”.= and their initial findings have now been publishedz4. This comprehensive study confirmed the limitations of the assay which were identified above. In addition, it was shown that compounds requiring systemic metabolic activation were inactive in the assay, medium constituents could block the activity of certain antimetabolites, and therapeutic-
1987 [Vol. 81
ally inactive compounds could give a false positive result in vitroz4. Several interesting compounds were identified but it was concluded that because of the complexities of working with fresh Mological material, the assay should be confined to selected tumour types and that screening could only be conducted on a moderate scalez3*” On the other hand, the potential of the assay for the preclinical screening of anti-cancer drugs against a large panel of human tumour cell lines and xenografts which reflect the heterogeneity intraneoplastic diversity and encountered clinically appears to be more promisings3. Recently we have shown that, with appropriate selection of fresh tumour biopsies, the tumour colony-foxing cell assay can be used to facilitate the selection of sub-populations of clonogenic tumour cells from a single tumour. Cells derived from these clones can be propagated and established as continuous cell lines or xenografts at early passage level’s. In this way the assay could be used to establish a more comprehensive human tumour cell library for the screening of anticancer drugs, and for furthering the study of tumour cell biology and clonal heterogeneity within tumours. In the future, clarification of the factors regulating the proliferation of tumour cells may also lead to the refinement of the tumour colonyforming cell assay so that it will encompass cells with long cycle times which remain undetected in the present assay, improving its effectiveness and efficiency. I. BERTONCELLO AND T. R. BRADLEY
CeJt Biology Group, Peter ~ffcCai1~~ Research Laboratories, Peter MacCalJutn Cancer Institute, 481 Little Lonsdale Street, Melbourne, Victoria 3000, Australia.
References 1 Nowell. P. C. (1974) Science 194.23-28 2 Dexter,’ D. L. and Calabresi, ti. (1982) Riochem. ~~o~bys. Acta. 695,97-112 3 Schnipper, i. I? (1986) N. Engi. f. Med. 314,1423-1431 4 Wheeler, K. T., Levin, V. A. and Dean, D. F. (1978) Radiat. Res. 76,441-458 5 Smete, L. A. (1980) Biochim. Biophys. Acta. 605, 91-111 6 Shin, S., Freedman, V. H., Risser, R. and Pollack, R. (1975) Proc. NatJ Acad. Sci. l&A 72,4435-4439 7 McAllister, R. M. and Reed, C. (1968)
TIPS -July 1987 [Vol. 81 Pediatr. Res. 2, 356-360 8 Courtenay, V. D. and Mills,!. (1978) Br. ,l, Cancer 27 261-2ti8 9 Courterray, V. D., Selby, P. J., Smith, I. E., Mills, J. and Peckham, M. J. (1978) Br. 1. Cancer 38.77-81 10 Hamburger, A: W. and Salmon, S.E. (1977) Science 197,461-463 11 Salmon, S. E., Hamburger, A. W., Soehnlen, B., Durie, B. G. M., Alberts, D. S. and Moon, T. E. (1978) N. Engl. J. Med. 298,1321-1327 12 Salmon, S. E., Alberts, D. S., Durie, B. G. M., Meyskens, F. L., Jones, S. E., Soehnlen, B., Chen, H.-S. G. and Moon, T. (1980) Recent Results in Cancer Res. 74, 300-305 13 Bertoncello, I., Bradley, T. R., Campbell, J. J., Day, A. J., McDonald, I. A.,
251
14 15 16 17 18 19 20
McLeish. G. R...-Ouinn. M. A... Rome. R. ~,~ and Hodgson, G. S. (1982) Br. 1. Cancer 45,8G3-811 Aapro, M. S. (1985) Eur. J. Cancer Clin. Oncol. 21, 397-400 Von Hoff, D. D. (1985) Seminarsin Oncol. 12,327-331 Buick, R. N. and MacKillop, W. J. (1981) Br. 1. Cancer 44.34%%5 S&lag, P. and Schreml, W. (1982) Cancer Res. 42,4086-4089 Von Hoff, D. D., Clark, G. M., Forseth, B. J. and Cowan, J. D. (1985) Cancer 58, lOB7-1013 Salmon, S. E., Liu, R. M. and Casazza, A. M. (1981) Cancer Chemother. Pharmacd. 6, 103-109 Shoemaker, R. H., Wolpert-DeFiippes, M. K., Makuch, R. W. andvenditti, J. M.
‘The naming of receptors is a ditkult matter’
Receptor nomenclature: how, who and when? To paraphrase T. S. Eliot,l ‘The naming of receptors is a difficult matter, it isn’t just one of your holiday games’. In his timely, erudite and comprehensive consideration of the classification of both receptors and ‘acceptors’, jack Peter Green highlights many of the issues which, as he points out, have ‘impaired . . . simple discourse’ on many of the recent findings related to receptor characterization*. Using the example of the S-I-IT receptor which increases in complexity on a monthly basis, Professor Green proposes a rational taxonomy based on the cognitive i.e. receptor recognition characteristics and transduction characteri,;tics related to receptor function. There are however, factors that might be considered before this proposal moves further from concept to implementation. Unlike enzymes for which a highly visible and comprehensive system exists3, receptors lack a simple identifying feature, namely that of the conversion of substrate to a defined product that can easily be quantified using the isolated, purified enzyme. In contrast, the product of receptor activation is rarely, if ever, a function of the activation of a single, defined receptor. For instance, the activation of many types of receptor can lead to incredses in CAMP (Ref. 4). Irrespective therefore, of the
infancy of the system of taxonomy for receptors (which is compared with that existing for enzymes in the 195Os), there are many different, and probably equally valid ways by which to define receptors, none of which is unambiguous. One of these would be the pharmacology of ligand binding, again the ‘cognitive’ portion of receptor characterization. However, to take Table 1 of the Green article, the proposed competitive antagonist of the 5-I-Hi* receptor, spiperone, is best known as a dopamine receptor antagonist5. Its use in viva to define 5-I-IT** receptor function would therefore be clearly inappropriate. A similar comment can be made for the use of (-)cyanopindolol as a 5-HTrs receptor antagonist in the light of its better known activity as a P-adrenoceptor antagonist6. Conversely, while ketanserin is a selective 5HT2 antagonist in vitro, the in-viva effects of the compound appear to ar-adrenoceptor also involve modulation’. Clearly, receptor classification based on the pharmacological actions of ‘polypharmic’ agonists and antagonists emphasizes the need for caution in identifying receptors based on the actions of a single compound or class of compounds and for the need to develop more selective receptor entities. The further characterization of a receptor based on the observed
(1982) Stern Cells 1, 308 21 Selby, P., Buick, R. N. and Tannock, I. (1983) N. En@. j. Med. 308,12%134 22 Clarkson, 8. D. (1974) in Control of Proliferationin AnimalCells(Clarkson. B. D. and Baserga, R., eds), pp. 945-972; Cold Spring Harbor Laboratories 23 Venditti, J. M. (1983) Cancer Treat. Rep. 67,767-772 24 Shoemaker, R. H., Wolpert-DeFiBppes, M.K., Kern, D.H., Lieber, M.M., Makuch, R. W., Melnick, N. R., Miller, W. T., Salmon, S. E., Simon, R. M., Venditti, J. M. and Von Hoff, D. D. (1985) Cancer Res. 45,2145-2153 25 Bertoncello, I., Bradley, T. R., Webber, L. M., Hodgson, G. S. and Campbell, J. J. (1985) Aust. J. Exp. Biol. Med. Sci. 63,241248
effects of the endogenous ligand and its ‘useful’ agonists together with the anatomical locale of the proposed receptor and the potential coupling to transduction mechanisms, be these adenylate cyclase, phosphatidylinositol turnover or ion flux modulation, add additional caveats to such a h:
@ 1987, Elmvier Publications,
Cambridge
0165 - 6147187602.00
1987 [Vol. 81
8 Schwartz, J. C. (1977) Annu. Rev. Dhar9
10 11 12 13 14
maco2. Toxicol. 17,325-339 Watanabe, T., Taguchi, Y., Shiosaka, S., Tanaka, J., Kubota, J., Terano, Y., Tohyama, M. and Wada, H. (1984) Brain Res. 295, 15-25 Hdl, S. J., Daum, P. and Young, J. M. (1981) 1. Neurochem. 35,1357-1360 Nichoison, A. N., Stone, B. M. and Pascoe, P. A. (1985) Neurophnrmacoloxy-_ 24.245-250 Peck, A. W., Fowle, A. S. E. and Bye, C. (1975) Eur. j. Clin. Pharmacol. f&455-463 Nicholson, A. N. and Stone, B. M. (1986) Eur. 1. Clin. Pharmacol. 30, 27-32 Bye, C., Dewsbury, D. and Peck, A. W.
249 (1974) Br. j. Clin. Pharmacol. 1, 71-78 15 Clarke, C. H. and Nicholson, A. N. (1978) Br. 1. Clin. Phannacol. 6, 31-35 16 Nicholson, A. N. (1979) Br. j. Clin. Pharmacol. 8,321-324 i7 Friedman, A. H. and Walker, C. A. (1968) j. Physiol. (London) 197,77-85 18 Orr, E. and Quay, W. 8. (1975) Endocrinology 96,941-945 19 Schwartz, J. C., Barbin, G., Garbarg, M., Pollard. H.. Rose, C. and Verdiere. M. (1976) Adv: Biochem. Psychopharmbcoj. 15,111-126 20 Quach, T. T., Duchemin, A. M., Rose, C. and Schwartz, J. C. (1979) Eur. 1. Pharmocol. 60,391-392
Human cell cuhres for screening anti-cancer drugs Although tumours are clonal in origin’, genetic instability inevitably leads to the progressive development of intraneoplastic heterogenei@3. This heterogeneity is manifested in differences in the cellular architecture, growth kinetics and functional properties of individual tumours and in their responsiveness to chemotherapeutic agents. Prognostically, the consequences for the patient are far-reaching. In a significant number of cases, the responsiveness of specific lesions is unpredictable and the therapeutic approach adopted is of necessity empirical. Thus the need for reliable routine in-vitro cell culture assays for assessing the functional properties of proliferating tumour cells and screening anti-cancer drugs: preclinically to identify novel, potentially useful cytotoxic agents, and clinically to predict the outcome of therapy in individual patients. The ability to extrapolate pharmacokinetic data obtained in vitro to predict the response to tumourigenic-cell lines to chemotherapeutic drugs in viva in experimental animal models* shows that this is feasible. In experimental models of tumourigenicity and cell transformation, the ability of single cells to grow as anchorage-independent clones when immobilized in semisolid culture has been the property most closely associated with tumourigenic potentia15r6. The ability of tumour cells from human biopsy specimens to grow in clonal
agar culture was first documented in 1968 by McAllister and Reed7, but it was primarily the work of Courtenay et dazg, and Hamburger and Salmoni’ and their colleaguesl’ which drew attention to the potential of this assay system. The soft-agar tumour colonyforming
cc& assay
Was ;ixnd
!r:
predict drug resistance in individual patients with a high degree of accuracy1’*12. The capacity of tumour cells from surgical specimens to clone in agar appeared to be of prognostic significance in determining patient survival*~15. Significant heterogeneity in the properties of clonogenic cells and in their sensitivity to cytotoxic agents at different sites within individual patients and within individual tumours151s was identified. The assay was also used to assess the effect of chemotherapeutic agents and irradiation in xenografted human turnours’“, and to evaluate novel analogs of anti-cancer drugs”. Preclinical protocols These findings raised the possibility that this assay system could play an important role in preclinical drug-screening protocolszo by facilitating the screening of potential anti-cancer drugs against a large panel of freshly excised human tumours and human tumour cell lines reflecting the heterogeneity and intraneoplastic diversity encountered * clinically. For such an assay system to fulfil these objectives it must meet a
21 Kanh S. and Richelson, 8. (19~) B~UUI Res. 304, l-7 22 Uzan, A., Le Fur, G. and Malgouris, C. (1979) j. Phnrm. Pharmncol. 31.701-702 23 Gervats. P.,Gervais, A., DeBeule, R. and Van der Pijl. W. (1975) Acta Allergol. 30, 286-297 24 Nicholson, A. N. and Stone, 8. M. (1983) Eur. 1. Clin. Phnrmacol. 25,565-566 25 Nicholson, A. N. (1982) Arzneim.-Fonch. Drug Res. 32,1191-1193 26 Nicholson, A. N. and Stone, 8. M. (1982) Br. j. Chk Phnrmacol. 13,199-202 27 Nicholson, A. N., Smith, P. A. and Spencer, M. B. (1982) Br. j. Clin. Pharmaco!. 14, 683-690
number of criteria. Firstly, it must be reliable and widely applicable. Secondly, it must identify those tumour cells which determine the course of the disease in the patient. Thirdly, the end-point of the assay in vitro - the ablation of colonyforming cells by chemotherapeutic agents - must predict the clinical outcome in the patient - the ablation of the tumour. While the initial results summarized above are encouraging, the assay has serious Xmitations, particularly in the evaluation of fresh biopsy specimens’3*151’. Only a proportion of tumours a~ amenable to successful clonal culture from fresh biopsy material at present. Technical problems associated with the preparation of single cell suspensions make it difficult to exclude cell aggregates and this affects interpretation of the assay. Not all tumours contain clonogenic cells, and only tumours biopsied in the terminal phases of disease exhibit the quality of growth which would permit routine use of the assay in individual patients”. It has generally been assumed that the tumour colony-forming cell assay detects tumour stem cells, but there is little evidence to support this conclusion. The assay is biased to the detection of those tumour cells capable of growth in the prevailing culture conditions within the relatively short timeframe of the assay (14-21 days) and may not detect cells in the dormant state (Go/G1 phase of cell cycle) which are an important factor in refractoriness to therapp. The clinical significance of the ablation of the colony-for,qiing cell is also unclear. The correlations between clonogenic capacity and proliferative potential of the colonyforming ce11’3-15, and the ability of the assay to predict drug sensitivity i1~12indicates that these cells
@ 1987, Elsevier Publications.
Cambridge
0165 - 6147/87&02.00
TIPS -July
F@. I f%). Human ovadan ~~~~rna cellsgait in adl?en?nt monolayer cuJfr.rt~and (b) as a~~~-i~~t clones in semi-sofd agar et&we photographed at x I W and x20 magnifications respectively.
are clinically relevant. However, there is no reliable information on the longer term survival of patients treated on the basis of drug sensitivity testing in vitro. The proliferative potential of tumour colonyforming cells within a single culture is variable, and Buick and MacKillop I6 have suggested that the ability of cells from primary clones to reclone in secondary culture would be of more prognostic significance than the primary cloning data. Where there is heterogeneity in the drug-sensitivity of tumour colony-forming cells from different lesions in the same patient a decision about the most appropriate drug to use is impaired because not enough is known about the relationship of
clonogenic cells to the tumour cells ultimately determining the fate of the tumour in viva. Recognizing the potential of the tumour colony-forming cell assay system the National Cancer Institute in the United States entered into feasibility studies to assess the assay for screening new compounds for anti-tumour aCtivity2”.= and their initial findings have now been publishedz4. This comprehensive study confirmed the limitations of the assay which were identified above. In addition, it was shown that compounds requiring systemic metabolic activation were inactive in the assay, medium constituents could block the activity of certain antimetabolites, and therapeutic-
1987 [Vol. 81
ally inactive compounds could give a false positive result in vitroz4. Several interesting compounds were identified but it was concluded that because of the complexities of working with fresh Mological material, the assay should be confined to selected tumour types and that screening could only be conducted on a moderate scalez3*” On the other hand, the potential of the assay for the preclinical screening of anti-cancer drugs against a large panel of human tumour cell lines and xenografts which reflect the heterogeneity intraneoplastic diversity and encountered clinically appears to be more promisings3. Recently we have shown that, with appropriate selection of fresh tumour biopsies, the tumour colony-foxing cell assay can be used to facilitate the selection of sub-populations of clonogenic tumour cells from a single tumour. Cells derived from these clones can be propagated and established as continuous cell lines or xenografts at early passage level’s. In this way the assay could be used to establish a more comprehensive human tumour cell library for the screening of anticancer drugs, and for furthering the study of tumour cell biology and clonal heterogeneity within tumours. In the future, clarification of the factors regulating the proliferation of tumour cells may also lead to the refinement of the tumour colonyforming cell assay so that it will encompass cells with long cycle times which remain undetected in the present assay, improving its effectiveness and efficiency. I. BERTONCELLO AND T. R. BRADLEY
CeJt Biology Group, Peter ~ffcCai1~~ Research Laboratories, Peter MacCalJutn Cancer Institute, 481 Little Lonsdale Street, Melbourne, Victoria 3000, Australia.
References 1 Nowell. P. C. (1974) Science 194.23-28 2 Dexter,’ D. L. and Calabresi, ti. (1982) Riochem. ~~o~bys. Acta. 695,97-112 3 Schnipper, i. I? (1986) N. Engi. f. Med. 314,1423-1431 4 Wheeler, K. T., Levin, V. A. and Dean, D. F. (1978) Radiat. Res. 76,441-458 5 Smete, L. A. (1980) Biochim. Biophys. Acta. 605, 91-111 6 Shin, S., Freedman, V. H., Risser, R. and Pollack, R. (1975) Proc. NatJ Acad. Sci. l&A 72,4435-4439 7 McAllister, R. M. and Reed, C. (1968)
TIPS -July 1987 [Vol. 81 Pediatr. Res. 2, 356-360 8 Courtenay, V. D. and Mills,!. (1978) Br. ,l, Cancer 27 261-2ti8 9 Courterray, V. D., Selby, P. J., Smith, I. E., Mills, J. and Peckham, M. J. (1978) Br. 1. Cancer 38.77-81 10 Hamburger, A: W. and Salmon, S.E. (1977) Science 197,461-463 11 Salmon, S. E., Hamburger, A. W., Soehnlen, B., Durie, B. G. M., Alberts, D. S. and Moon, T. E. (1978) N. Engl. J. Med. 298,1321-1327 12 Salmon, S. E., Alberts, D. S., Durie, B. G. M., Meyskens, F. L., Jones, S. E., Soehnlen, B., Chen, H.-S. G. and Moon, T. (1980) Recent Results in Cancer Res. 74, 300-305 13 Bertoncello, I., Bradley, T. R., Campbell, J. J., Day, A. J., McDonald, I. A.,
251
14 15 16 17 18 19 20
McLeish. G. R...-Ouinn. M. A... Rome. R. ~,~ and Hodgson, G. S. (1982) Br. 1. Cancer 45,8G3-811 Aapro, M. S. (1985) Eur. J. Cancer Clin. Oncol. 21, 397-400 Von Hoff, D. D. (1985) Seminarsin Oncol. 12,327-331 Buick, R. N. and MacKillop, W. J. (1981) Br. 1. Cancer 44.34%%5 S&lag, P. and Schreml, W. (1982) Cancer Res. 42,4086-4089 Von Hoff, D. D., Clark, G. M., Forseth, B. J. and Cowan, J. D. (1985) Cancer 58, lOB7-1013 Salmon, S. E., Liu, R. M. and Casazza, A. M. (1981) Cancer Chemother. Pharmacd. 6, 103-109 Shoemaker, R. H., Wolpert-DeFiippes, M. K., Makuch, R. W. andvenditti, J. M.
‘The naming of receptors is a ditkult matter’
Receptor nomenclature: how, who and when? To paraphrase T. S. Eliot,l ‘The naming of receptors is a difficult matter, it isn’t just one of your holiday games’. In his timely, erudite and comprehensive consideration of the classification of both receptors and ‘acceptors’, jack Peter Green highlights many of the issues which, as he points out, have ‘impaired . . . simple discourse’ on many of the recent findings related to receptor characterization*. Using the example of the S-I-IT receptor which increases in complexity on a monthly basis, Professor Green proposes a rational taxonomy based on the cognitive i.e. receptor recognition characteristics and transduction characteri,;tics related to receptor function. There are however, factors that might be considered before this proposal moves further from concept to implementation. Unlike enzymes for which a highly visible and comprehensive system exists3, receptors lack a simple identifying feature, namely that of the conversion of substrate to a defined product that can easily be quantified using the isolated, purified enzyme. In contrast, the product of receptor activation is rarely, if ever, a function of the activation of a single, defined receptor. For instance, the activation of many types of receptor can lead to incredses in CAMP (Ref. 4). Irrespective therefore, of the
infancy of the system of taxonomy for receptors (which is compared with that existing for enzymes in the 195Os), there are many different, and probably equally valid ways by which to define receptors, none of which is unambiguous. One of these would be the pharmacology of ligand binding, again the ‘cognitive’ portion of receptor characterization. However, to take Table 1 of the Green article, the proposed competitive antagonist of the 5-I-Hi* receptor, spiperone, is best known as a dopamine receptor antagonist5. Its use in viva to define 5-I-IT** receptor function would therefore be clearly inappropriate. A similar comment can be made for the use of (-)cyanopindolol as a 5-HTrs receptor antagonist in the light of its better known activity as a P-adrenoceptor antagonist6. Conversely, while ketanserin is a selective 5HT2 antagonist in vitro, the in-viva effects of the compound appear to ar-adrenoceptor also involve modulation’. Clearly, receptor classification based on the pharmacological actions of ‘polypharmic’ agonists and antagonists emphasizes the need for caution in identifying receptors based on the actions of a single compound or class of compounds and for the need to develop more selective receptor entities. The further characterization of a receptor based on the observed
(1982) Stern Cells 1, 308 21 Selby, P., Buick, R. N. and Tannock, I. (1983) N. En@. j. Med. 308,12%134 22 Clarkson, 8. D. (1974) in Control of Proliferationin AnimalCells(Clarkson. B. D. and Baserga, R., eds), pp. 945-972; Cold Spring Harbor Laboratories 23 Venditti, J. M. (1983) Cancer Treat. Rep. 67,767-772 24 Shoemaker, R. H., Wolpert-DeFiBppes, M.K., Kern, D.H., Lieber, M.M., Makuch, R. W., Melnick, N. R., Miller, W. T., Salmon, S. E., Simon, R. M., Venditti, J. M. and Von Hoff, D. D. (1985) Cancer Res. 45,2145-2153 25 Bertoncello, I., Bradley, T. R., Webber, L. M., Hodgson, G. S. and Campbell, J. J. (1985) Aust. J. Exp. Biol. Med. Sci. 63,241248
effects of the endogenous ligand and its ‘useful’ agonists together with the anatomical locale of the proposed receptor and the potential coupling to transduction mechanisms, be these adenylate cyclase, phosphatidylinositol turnover or ion flux modulation, add additional caveats to such a h:
@ 1987, Elmvier Publications,
Cambridge
0165 - 6147187602.00