Drug Targeting Organ-Specific Strategies

to evaluate the large variety of results, to understand the reasons for limited success, and the great number of concepts to improve the treatment strategies. It should be emphasized that after more than 15 years of experience with monoclonal antibody therapy of cancer, we have no definite idea of essential mechanisms required for clinical activity. The findings of e.g. Clynes et al. [153,154] support the idea that the anti-tumour effects of MAbs depend on many mechanisms. For instance, myeloid cells, probably macrophages and monocytes that express both activation and inhibitory Fc receptors, are essential immune effector cells for MAb therapy. Blocking inhibitory receptors or MAbs that selectively trigger activating Fc receptors without affecting inhibitory Fc receptors could increase potency. The underlying mechanisms of the therapeutic effects of MAbs may also vary from one MAb to another. These findings should be considered in the improvement of drug-targeting strategies based on MAbs, including Mab derivatives such as those used in ADEPT. The same holds true for approaches such as modulating growth factor receptor functions or inducing immune responses using BsMAbs or the combination of tumour cell-directed strategies combined with BsMAbs delivering agents which inhibit the supply of blood to the tumour.

Liposomal drugs have been suggested to be the ‘magic bullet’ of cancer therapy due to their ability to accumulate selectively in the tumour. The problem remains that not all cancers and patients respond in the same way. The drug actually delivered to the required site of action plays an important role in the response achieved, while the potential toxicity of the surface modified liposomes in the macrophage system have to be taken into account on chronic administration.

Multi-drug resistance represents a significant obstacle in the use of standard chemotherapy regimens to cure cancer. It is unlikely that tumours resistant to free drug therapy will be eradicated by liposome-encapsulated or any other targeted form of drug. Additional studies that attempt to encapsulate drugs which exhibit non-overlapping modes of drug resistance and significant activity against a particular form of cancer, or combine free drugs with nonoverlapping modes of drug resistance with currently available liposomal drugs, will address the potential and limitations of these approaches. There is also a need to develop liposomal formulations of other drugs and therapeutic regimens designed to stimulate host immunity alone or in combination with other treatment modalities.

In conclusion, research needs to be aimed at improving the potency and reducing the immunogenicity and toxicity of drug formulations in order to increase the therapeutic index. Methods to increase the overall therapeutic index of a drug, e.g. by using tumour-specific ligands, increasing extravasation of liposomes into tumours and increasing the bioavailability of the drug selectively at the site of the tumour, should be explored further.

In addition to this, research must focus on optimizing the biophysical properties of the carriers and drug-conjugates, as these properties are of major importance to the decision of whether or not to use these molecules in vivo. A wealth of innovative strategies involving recombinant molecules with novel effector functions are in the early stages of clinical evaluation and hold great promise for the future. These developments will initiate other studies which should focus on long-term safety and cost–benefit analyses. Only adequately designed case–control studies supported by international collaboration can show the long-term safety of these new therapies. The same holds true for studies evaluating the costs of these therapeutic regimens and the resultant improvement in the quality of life, in relation to the cumulative social and health-care costs of current therapies. These multidisciplinary collaborative

228 8 Strategies for Specific Drug Targeting to Tumour Cells

efforts will be the basis for the introduction of new therapeutics with optimum efficacy and cost, into clinical practice.

References

[1]Jain RK, Sci. Am. 1994, 271, 58–65.

[2]Jain RK, Science 1996, 271, 1079–1080.

[3]Foulds L, J. Chron. Dis. 1958, 8, 2–37.

[4]Bishop JM, Annu. Rev. Biochem. 1983, 52, 301–354.

[5]Hunter T, Cooper JA, In: Enzyme Control by Protein Phosphorylation. (Eds Boyer PD, Krebs EG), p. 191. Academic Press, New York, 1986.

[6]Marshall CJ, Cell 1991, 64, 313–326.

[7]De Vita Jr VT, Hellman S, Rosenberg SA (Eds) Cancer, Principles and Practice of Oncology, 5th edn. J. B. Lippincott Company, Philadelphia, PA, 1997.

[8]Nagy JA, Brown LF, Senger DR, Lanir N, van de Water L, Dvorak AM, Dvorak HF, Biochim. Biophys. Acta 1988, 948, 305–326.

[9]Folkman J, J. Natl Cancer. Inst. 1990, 82, 4–6.

[10]Griffioen AW, Molema G, Pharmacological Rev. 2000, 52, 237–268.

[11]Bicknell R, Harris AL, Eur. J. Cancer 1991, 27, 781–785.

[12]Polverini PJ, Leibovich SJ, Lab. Invest. 1984, 51, 635–642.

[13]Konerding MA, Steinberg F, Streffer C, Acta Anat. 1989, 136, 21–26.

[14]Jain RK, J. Control. Rel. 1998, 53, 49–67.

[15]Juliano RL, Ling V, Biochim. Biophys. Acta 1976, 455, 152–162.

[16]Cole SPC, Bhardwaj G, Gerlach JH, Machie JE, Grant CE, Almquist KC, Stewart AJ, Kurz EU, Duncan AMV, Deeley RG, Science 1992, 258, 1650–1654.

[17]Scheffer GL, Wijngaard PLJ, Flens JM, Isquierdo MA, Slovak ML, Pinedo HM, Meijer CJLM, Clevers HC, Scheper RJ, Nature Med. 1995, 1, 578–582.

[18]Izquierdo MA, Scheffer GL, Flens MJ, Giaccone G, Boxterman HJ, Meijer CJLM, van der Valk P, Scheper RJ, Am. J. Pathol. 1996, 148, 877–887.

[19]Meijer DK, Smit JW, Hooiveld GJ, Van Montfoort JE, Jansen PL, Muller M, Pharm. Biotechnol. 1999, 12, 89–157.

[20]Wang JC, Biochim. Biophys. Acta 1987, 909, 1–9.

[21]Köhler G, Milstein C, Nature 1997, 256, 495–497.

[22]Farah RA, Clinchy B, Herrera L, Vitetta ES, Crit. Rev. Euk. Gene Expr. 1998, 8, 321–356.

[23]De Leij L, Encycloped. Cancer 1997, 1, 1818–1839.

[24]Demanet C, Brissincle J, De Jonge, Thielemans K, Blood 1996, 81, 4390–4398.

[25]Mellstedt H, Frodin JE, Masucci G, Ragnhammer P, Fagerberg J, Hjelm AL, Shetye J, Wersall P, Osterborg A, Sem. Oncol. 1991, 18, 462–477.

[26]Hendler FJ, Ozanne BW, J. Clin. Invest. 1984, 74, 647–651.

[27]Berger MS, Gullick WJ, Greenfield C, J. Pathol. 1987, 52, 297–307.

[28]Tateishi M, Ishida T, Mitsudomi T, Sugimachi K, Cancer Res. 1990, 50, 7077–7080.

[29]Schneider PM, Hung MC, Chiocca SM, Cancer Res. 1989, 49, 4968–4971.

[30]Weiner DB, Nordberg J, Robinson R, Cancer Res. 1990, 50, 5184–5191.

[31]Mezzanzanica D, Canevari S, Colnaghi MI, Int. J. Clin. Lab. Res. 1991, 21, 159–164.

[32]Bolhuis RLH, Lamers CHJ, Goey SH, Int. J. Cancer 1992, S7, 78–81.

[33]Miotti S, Canevari S, Menard S, Mezzanzanica D, Porro G, Int. J. Cancer 1987, 39, 297–303.

[34]Bumol TF, Marder P, van de Herdt S, Borowitz MJ, Apelgren LD, Hybridoma 1988, 7, 407–415.

[35]Huang X, Molema G, King S, Watkins L, Edgington TS, Thorpe PE, Science 1997, 275, 547–550.

[36]Ran S, Gao B, Duffy S, Watkins L, Rote N, Thorpe PE, Cancer Res. 1998, 58, 4646–4653.

[37]Molema G, Kroesen BJ, Helfrich W, Meijer DKF, de Leij LFMH, J. Control. Rel. 2000, 64, 229–239.

[38]Clackson T, Hoogenboom M, Griffiths AD, Winter G, Nature 1991, 352, 624–28.

[39]Lobuglio AF, Saleh MN, Am. J. Med. Sci. 1992, 304, 214–224.

[40]Debatin K-M, Krammer PH, Leukaemia 1995, 9, 815–820.

[41]Trauth BC, Klas C, Peters AMJ, Matzhu S, Moller P, Falk W, Debatin K-M, Krammer PH, Science 1989, 245, 301–305.

[42]Gethie M-A, Podar EM, Ilgen A, Gordon BE, Uhr JW, Vitetta ES, Proc. Natl Acad. Sci. USA 1997, 94, 7509–7514.

References 229

[43]Chaouchi NA, Vazquez, Galanaud P, Leprince C, J. Immunol. 1995, 154, 3096–3104.

[44]Vuist W.MJ, Levy R, Maloney DG, Blood 1994, 83, 899–906.

[45]Baselga J, Mendelsohn J, Pharmacol. Ther. 1994, 64, 127–154.

[46]Shepard HM, Lewis GD, Sarup JC, Fendly BM, Maneval D, Mordenti J, Figari I, Kotts CE, Palladino MA, Ullrich A, Slamon D, J. Clin. Immunol. 1991, 11, 117–127.

[47]Wu X, Fan Z, Masui H, Rosen S, Mendelsohn J, J. Clin. Invest. 1995, 95, 1897–1905.

[48]Schneider-Gadicke E, Riethmuller G, Eur. J. Cancer 1995, 31, 1326–1330.

[49]Greiner JW, Guadagni F, Roselli M, Nieroda CA, Anti-cancer Res. 1996, 16, 2129–2133.

[50]Krebber A, Bornhauser S, Burmester J, Honegger A, Willuda J, Bosshard HR, Plückthun A, J.

Immonol. Methods 1997, 201, 35–55.

[51]Reiter Y, Brinkmann U, Lee B, Pastan I, Nature Biotechnol. 1996, 14, 1239–1245.

[52]Orlandi R, Gussow DH, Jones PT, Winter G, Proc. Natl Acad. Sci. USA 1989, 86, 3833–3837.

[53]Hoogenboom M, Griffiths AD, Johnson KS, Chiswell DJ, Hudson P, Winter G, Nucleic Acids Res. 1991, 19, 4133–4137.

[54]Winter G, Griffiths AD, Hawkins RE, Hoogenboom HR, Annu. Rev. Immunol. 1994, 12, 433–455.

[55]Huls GA, Heijnen IA, Cuomo ME, Koningsberger JC, Wiegman L, Boel E, Van der Vuurst de Vries AR, Loyson SA, Helfrich W, Van Berge Henegouwen GP, Van Meijer M, de Kruif J, Logtenberg T, Nature Biotechnol. 1999, 17, 276–281.

[56]Davis CG, Gallo ML, Corvalon, Cancer Metast. Rev. 1999, 18, 421–425.

[57]Yokota T, Milenic DE, Whitlow M, Schlom J, Cancer Res. 1992, 52, 3402–3408.

[58]Jurcic JG, Scheinberg DA, Houghton AN, In: Cancer Chemotherapy and Biological Response Modifiers Annual 16 (Eds Pinedo HM, Longo DL, Chabner BA), pp. 168–188. Elsevier Science, Amsterdam, 1996.

[59]Caron PC, Scheinberg DA, Curr. Opin. Oncol. 1994, 6, 14–22.

[60]Dall’Acqua W, Carter P, Curr. Opin. Struct. Biol. 1998, 8, 443–450.

[61]Jung S, Plückthun A, Protein Eng. 1997, 10, 959–966.

[62]Willuda J, Honegger A, Waibel R, Schubiger PA, Stahel R, ZangemeisterWittke U, Plückthun A, Cancer Res. 1999, 59, 5758–5767.

[63]Helfrich W, Haisma HJ, Magdolen V, Luther T, Blom VJJ, Westra J, van der Hoeven R, Kroesen BJ, Molema G, de Leij L, J. Immunol. Methods 2000, 237, 131–145.

[64]Thrush GR, Lark LR, Clinchy BC, Vitetta ES, Annu. Rev. Immunol. 1996, 14, 49–71.

[65]Dillman RO, Johnson DE, Ogden J, Beidler D, Mol. Biotherapy. 1989, 1, 250–255.

[66]Ghose T, Norvell ST, Guclu A, Cameron D, Bodurtha A, MacDonald AS, Br. Med. J. 1972, 3, 495–499.

[67]Goldenberg DM, Am. J. Med. 1993, 94, 297–312.

[68]Trail PA, Willner D, Hellstrom KE, Drug Deliv. Res. 1995, 34, 196–209.

[69]King HD, Yurgaitis D, Willner D, Firestone RA, Yang MB, Lasch SJ, Hellstrom KE, Trail PA,

Bioconjug. Chem. 1999, 10, 279–288.

[70]Smith AL, Nicolaou KC, J. Med. Chem. 1996, 39, 2103–2117.

[71]Hinman LM, Hamann PR, Wallace R, Menendez AT, Durr FE, Upeslacis J, Cancer Res. 1993, 53, 3336–3342.

[72]Lode HN, Reisfeld RA, Handgretinger R, Nicolaou KC, Gaedicke Gand Wrasidlo W, Cancer Res. 1998, 58, 2925–2928.

[73]Wilder RB, DeNardo GL, DeNardo SJ, J. Clin. Oncol. 1996, 14, 1383–1400.

[74]Stigbrand T, Ullen A, Sandstrom P, Mirzaie-Joniani H, Sundstrom B, Nilsson B, Arlesting L, Norrlund RR, Ahlstrom KR, Hietala S, Acta Oncol. 1996, 35, 259–265.

[75]Kroesen BJ, Helfrich W, Molema G and de Leij L, Adv. Drug. Del. Rev. 1998, 31, 105–129.

[76]Staerz UD, Kanagawa O, Bevan MJ, Nature 1985, 314, 628–631.

[77]Pluckthun A, Pack P, Immunotechnology 1997, 3, 83–105.

[78]Schmidt M, Wels W, Br. J. Cancer 1996, 74, 853–862.

[79]Van Spriel AB, Ojik HH, van de Winkel JGJ, Immunol. Today 2000, 21, 391–397.

[80]Kroesen BJ, Helfrich W, Bakker A, Wubbema AS, Bakker H, Kal HB, The TH, de Leij L, Int. J. Cancer 1995, 61, 812–818.

[81]Huennekens FM, Trend. Biotechnol. 1994, 12, 234–239.

[82]Bagshawe KD, Clin. Pharmacokinet. 1994, 27, 368–376.

[83]Kerr DE, Schreiber GJ, Vrudhula VM, Svensson HP, Hellström I, Hellström KE, Senter PD, Cancer Res. 1995, 55, 3558–3563.

[84]Haisma HJ, Boven E, van Muijen M, de Jong J, van der Vijgh WJ, Pinedo HM, Br. J. Cancer 1992, 66, 474–478.

2308 Strategies for Specific Drug Targeting to Tumour Cells

[85]Leenders RGG, Damen EWP, Bijsterveld EJA, Scheeren HW, Houba PHJ, van der MeulenMuileman IH, Boven E, Haisma HJ, Bioorg. Med. Chem. Lett. 1999, 718, 1597–1610.

[86]Bosslet K, Straub R, Blumrich M, Czech J, Gerken M, Sperker B, Kroemer HH, Gesson JP, Koch M, Monneret C, Cancer Res. 1998, 58, 1195–1219.

[87]Bosslet K, Czech J, Hoffman D, Tumour Target. 1995, 1, 45–50.

[88]de Groot FMH, de Bart ACW, Verheijen JH, Scharen HW, J. Med. Chem. 1999, 42, 5277–5283.

[89]Takakura Y, Hashida M, Crit. Rev. Oncol. Hematol. 1995, 18, 207–231.

[90]Duncan R, Spreafico F, Clin. Pharmacokinet. 1994, 27, 290–306,.

[91]Duncan R, Anti-Cancer Drugs 1992, 3, 175–210.

[92]Sezaki H, Takakura Y, Hashida M, Adv. Drug Delivery Rev. 1989, 3, 247–266.

[93]Seymour LW, CRC Crit. Rev. Ther. Drug Carrier. Syst. 1992, 9, 135–187.

[94]Vasey PA, Kaye SB, Morrison R, Twelves C, Wilson P, Duncan R, Thomson AH, Murray LS, Hilditech TE, Murray T, Burtles S, Fraier D, Frigerio E, Cassidy J, Clin. Cancer Res. 1999, 5, 83–94.

[95]Lasic DD, Papahadjopoulos D, Science 1995, 267, 1275–1276.

[96]Gregoriadis G, Trends Biotechnol. 1995, 13, 527–537.

[97]Lasic DD, From Physics to Applications. Elsevier, Amsterdam, 1993.

[98]Lasic DD, Martin FJ, (Eds) Stealth Liposomes. CRC, Boca Raton, FL, 1995.

[99]Daemen T, Regts J, Meesters M, Ten Kate MT, Bakker-Woudenberg IAJM, Scherphof GL, J.

Control. Rel. 1997, 44, 1–9.

[100]Doroshaw JH, Cancer Chemotherapy and Biotherapy: Principles and Practice. (eds Chabner BA and Longo DL) pp. 409–433. Lippincott-Raven, Philadelphia, PA. 1996.

[101]Harrigan PR, Wong KF, Redelmeier TE, Wheeler JJ, Cullis PR, Biochim. Biophys. Acta 1993, 1149, 329–338.

[102]Cullis PR, Hope MJ, Bally MB, Madden TD, Mayer LD, Fenske DB, Biochem. Biophys. Acta 1997, 1331, 187–211.

[103]Park JW, Hong K, Kirpotin DB, Meyer O, Papahadjopoulos D, Benz CC, Cancer Lett. 1997, 118, 153–160.

[104]Crosasso P, Brusa P, Dosio F, Arpicco S, Pacchioni D, Schuber F, Cattel L, J Pharm. Sci. 1997, 86, 832–839.

[105]Tseng YL, Hong RL, Tao MH, Chang FH, Int. J. Cancer 1999, 80, 723–730.

[106]Kirpotin D, Park JW, Hong K, Zalipsky S, Li WL, Carter P, Benz CC, Papahadjopoulos D, Biochemistry 1997, 36, 66–75.

[107]Lopes de Menezes DE, Pilarski LM, Allen TM, Cancer Res. 1998, 58, 3320–3330.

[108]Killion JJ, Fidler IJ, Pharmacol. Ther. 1998, 78, 141–154.

[109]Dass CR, Walker TL, DeCruz EE, Burton MA, Drug Deliv. 1997, 4, 151–165.

[110]Li S, Huang L, Gene Therapy 1997, 4, 891–900.

[111]Kaneda Y, Saeki Y, Morischita R, Mol. Med. Today 1999, 5, 298–303.

[112]Mayer LD, Cancer Metast. Rev. 1998, 17, 211–218.

[113]Drummond DC, Meijer O, Hong K, Kirpotin DB, Papahadjopoulos D, Pharmacol. Rev. 1999, 51, 691–743.

[114]Brown SL, Miller RA, Levy R, Semin. Oncol. 1989, 16, 199–210.

[115]Dillman RO, J. Clin. Oncol. 1994, 12, 1497–1515.

[116]Renner C, Trümper L, Pfreundschuh M, Leukaemia 1997, 11, S55–S59.

[117]Irie RF, Morton DL, Proc. Natl Acad. Sci. USA 1986, 83, 8694–8698.

[118]Cheung N-KV, Lazarus H, Miraldi FD, Abramowsky CR, Kallick S, Saarinen UM, Spitzer T, Strandjord SE, Coccia PF, Berger NA, J. Clin. Oncol. 1987, 51, 430–1440.

[119]Vadhan-Raj S, Cordon-Cardo C, Carswell E, Mintzer D, Dantis L, Duteau C, Templeton MA, Oettgen HF, Old LJ, Houghton AN, J. Clin. Oncol. 1988, 6, 1636–1648.

[120]Handgretinger R, Baader P, Dopfer R, Klingebiel T, Reuland P, Treuner J, Reisfeld RA, Niethammer D, Cancer Immunol. Immunother. 1992, 35, 199–204.

[121]Saleh MN, Khazaeli MB, Wheeler RH, Dropcho E, Liu T, Urist M, Miller DM, Lawson S, Dixon P, Russell CH, LoBuglio A, Cancer Res. 1992, 52, 4342–4347.

[122]Riethmuller G, Holz e, Schlimok G, Schmiegel W, Raab R, Hoffken K, Gruber R, Funke I, Pichlmaier H, Hirche H, J. Clin. Oncol. 1998, 16, 1788–1794.

[123]Oosterwijk E, Debruyne FMJ, Schalken JA, Semin. Oncol. 1995, 22, 34–41.

[124]Weiner LM, Semin. Oncol. 1999, 26, 41–50.

[125]McLaughlin P, Grillo-Lopez AJ, Link BK, Levy R, Czuczman MS, Williams ME, Heyman MR, Bence-Bruchler I, White CA, Canabillas F, Jain V, Ho AD, Frister J, Wey K, Shen D, Dallaize BK, J. Clin. Oncol. 1998, 16, 2824–2833.

References 231

[126]Czuczman MS, Grillo-Lopez AJ, White CA, Saleh M, Gordon L, LoBuglio AF, Jonas C, Klippenstein D, Dallaize B, Warms C, J. Clin. Oncol. 1999, 26, 268–276.

[127]Dyer MJS, Semin. Oncol. 1999, 26, 52–57.

[128]Baselga J, Tripathy D, Mendelsohn J, Baughman S, Benz CC, Dantis L, Shlarin NT, Seidman AD, Hudis CA, Moore J, Rosen PP, Twaddell T, Henderson IC, Norton L, J. Clin. Oncol. 1996, 14, 737–744.

[129]Pegram MD, Lipton A, Hayes DF, Weber BL, Baselga MM, Tripathy D, Baly D, Baighman SA, Twaddell T, Glaspy JA, Slalom DJ, J. Clin. Oncol. 1998, 16, 2659–2663.

[130]Baselga J, Tripathy D, Mendelsohn J, et al., Semin. Oncol. 1999, 26, 78–83.

[131]Sievers EL, Appelbaum FR, Spielberger RT, Forman SJ, Flowers D, Smith FO, Shannon-Dorcy K, Berger MS, Berstein ID, Blood, 1999, 93, 3678–3684.

[132]Saleh MN, LoBuglio AF, Trail PA, In: Monoclonal Antibody-Based Therapy of Cancer (Ed. Grossband M), pp. 397–416. Marcel Dekker, New York, 1998.

[133]Tolcher AW, Sugarman S, Gelmon KA, Cohen R, Saleh M, Isaacs C, Young L, Healey D, Onetto N Slichenmyer W, J. Clin. Oncol. 1999, 17, 478–484.

[134]Kaminski MS, Zasadny KR, Francis IR, Fenner MC, Ross CW, Milik AW, Estes J, Tude M, Regan D, Fisher S, Glenn SD, Wahl RL, J. Clin. Oncol. 1996, 14, 1974–1981.

[135]Press OW, Eary JF, Appelbaum FR, Martin PJ, Badger CC, Nelp WB, Glenn S, Butchko G, Fisher D, Porter B, N. Engl. J. Med. 1993, 329, 1219–1224.

[136]Press OW, Eary JF, Appelbaum FR, Martin PJ, Nelp WB, Glenn S, Fisher DR, Porter B, Matthews DC, Gooley T and Bernstein ID, Lancet 1995, 346, 336–340.

[137]Liu SY, Eary JF, Petersdorf SH, Martin PJ, Maloney DG, Appelbaum FR, Matthews DC, Bush SA Duracke LD, J. Clin. Oncol. 1998, 16, 3270–3278.

[138]Matthews DC, Appelbaum FR, Eary JF, Fischer DR, Durack LD, Hui TE, Martin PJ, Mitchell D, Press OW, Storb R, Bernstein ID, Blood 1999, 94, 1237–1247.

[139]De Gast GC, Haagen IA, van Houten AA, Klein SC, Duits AJ, de Weyer RA, Vroom TM, Clark MR, Phillips J, Van Dijk AJ, Cancer Immunol. Immunother. 1995, 40, 390–396.

[140]Janssen RAJ, Kroesen BJ, Buter J, Mesander G, Sleijfer DT, The TH, Mulder NH, de Leij L, Br. J. Cancer 1995, 72, 795–799.

[141]Kroesen BJ, Nieken J, Sleijfer DT, Molema G, de Vries EGE, Groen HJM, Helfrich W, The TH, Mulder NH, de Leij L, Cancer Immunol. Immunother. 1997, 45, 203–206.

[142]Valone FH, Kaufman PA, Guyre PM, Lewis LD, Memoli V, Deo Y, Graziano R, Fisher JL, Meyer L, Mrozek–Orlowski M, Wardwell K, Guyre V, Morley TL, Arvinu C, Fanger MW, J. Clin. Oncol. 1995, 13, 2281–2292.

[143]Weiner LM, Clark JI, Davey M, Li WS, Garcia de Palazzo I, Ring DB, Alpaugh RK, Cancer Res. 1995, 55, 4586–4593.

[144]Martin J, Stribbling SM, Poon GK, Begent RH, Napier M, Sharma SK, Springer CJ, Cancer Chemother. Pharmacol. 1997, 40, 189–201.

[145]Fuertges F, Abuchowski A, J. Control. Rel. 1990, 11, 139–148.

[146]Ho DH, Brown NS, Yen A, Holmes R, Keating M, Abuchowski A, Newman RA, Kozahoff IH, Drug Metab. Dispos. 1986, 14, 349–352.

[147]Meyers FJ, Paradise C, Scudder SA, Goodman G, Konrad M, Clin. Pharmacol. Ther. 1991, 49, 307–313.

[148]Martin FJ, Medical Applications of Liposomes (Eds frasic DD and Papahadjopoulos D) pp. 635–688, Elsevier, Amsterdam, 1998.

[149]Eckhardt JR, Campbell E, Burris HA, Wiess GR, Rodriguez GI, Fields SM, Thurman AM, Peacock NW, Cobb P, Rothenberg ML, Ross ME, Von Hoff DD, Am. J. Clin. Oncol. 1994, 17, 498–501.

[150]Gill PS, Espina BM, Muggia F, Cabriales S, Tulpule A, Esplin JA, J. Clin. Oncol. 1995, 13, 996–1003.

[151]Valero V, Buzdar AU, Theriault RL, Azarnia N, Fonseca GA, Willey J, Ewer M, Walter RS, Mackay B, Podoloff D, Booser D, Lee LW, Hortobagyi GN, J. Clin. Oncol. 1999, 17, 1425–1434.

[152]McLaughlin PMJ, Kroesen BJ, Dokter HA, van der Molen H, de Groot M, Brinker MGL, Kok K, Ruiters MHJ, Buys CHCM, de Leij LFMH, Cancer Immunol. Immunother. 1999, 48, 303–311.

[153]Clynes RA, Takechi Y, MoroiY, Houghton A, Ravetch JV, Proc. Natl Acad. Sci. USA 1998, 95, 652–656.

[154]Clynes RA, Towers TL, Persta LG, Ravetch JV, Nature Med. 2000, 6, 443–446.

[155]Houghton AN, Scheinberg DA, Nature Med. 2000, 6, 373–375.

Drug Targeting Organ-Specific Strategies. Edited by G. Molema, D. K. F. Meijer Copyright © 2001 Wiley-VCH Verlag GmbH ISBNs: 3-527-29989-0 (Hardcover); 3-527-60006-X (Electronic)

9 Tumour Vasculature Targeting

Daisy W. J. van der Schaft, S. Ramakrishnan, Grietje Molema, Arjan W. Griffioen

9.1 Introduction

Various stages in solid tumour growth can be discriminated. After multiple genetic changes, cellular growth progresses via hyperplasia and dysplasia towards an in situ tumour. Only after the so-called ‘angiogenic switch’, an as yet, ill-defined set of molecular changes leading to the formation of new blood vessels, does a tumour progress towards a mass extending more than several millimetres in diameter [1]. By recruitment of new blood vessels, the tumour provides itself with a continuous supply of nutrients and paves the way for metastasis formation.

The architecture of a solid tumour is such, that numerous layers of tumour cells are fed by one blood vessel. This poses a significant barrier for macromolecular drug targeting preparations aimed at the tumour cells that need to extravasate from the blood into the tumour tissue to reach the target cells: the larger the chosen carrier, the less accessible the tumour tissue will be. In contrast, endothelial cells lining the tumour vasculature are easily accessible for these macromolecular preparations. Tumour endothelial cell specific delivery of generally toxic anti-neoplastic or blood coagulation-inducing agents presents an attractive option for increasing therapeutic efficacy and reducing toxic side-effects elsewhere in the body. Furthermore, the pivotal role of endothelial cells in the maintenance of tumour cell survival and growth also makes them an interesting target for therapeutic intervention.

Tumour growth does not expand more than several millimetres in diameter in the absence of new blood vessel formation. Many tumours diagnosed in the clinic have a size beyond 0.5 cm in diameter and are considered pro-angiogenic. Endothelial cells are important executioner cells in the angiogenic cascade. Disruption of these pro-angiogenic characteristics by inhibiting pro-angiogenic signal transduction in endothelial cells therefore provides a powerful tool with which to intervene in tumour growth. The majority of research on inhibiting the function of tumour vasculature focuses at the development of drugs that may have an explicit action on the endothelial cells in the tumour. Based on their mechanism(s) of action and the fact that angiogenesis is a normal physiological process, these drugs in theory can also interrupt the functioning of healthy endothelial cells in the body. Recently, several angiogenesis inhibitors were withdrawn from clinical studies, most likely as a result of lack of selectivity for tumour endothelium.This emphasizes the need for systems that can deliver potent angiogenesis inhibitors at/in the tumour endothelial cells only.

At present, most target epitopes capable of discriminating tumour endothelium from normal endothelium are molecules that are expressed during angiogenesis. In this chapter a summary of current knowledge regarding tumour growth-related angiogenic endothelial processes in angiogenesis will be given. Furthermore, target epitopes and drug-targeting approaches exploited to date, with potential for future therapeutic application will be discussed.

234 9 Tumour Vasculature Targeting

9.1.1 Functions of Vascular Endothelial Cells in the Body

The vasculature can be considered to be one of the crucial organs in the body, extending more than 900 m2 and playing a major role in maintaining the body’s integrity in various ways. Blood vessels consist of endothelial cells that are directly in contact with the blood, pericytes located beneath the endothelium, smooth muscle cells, fibroblasts, basement membrane, and extracellular matrix (ECM). Depending on the location in the body and the organ microenvironment, the cellular constituents, basement membrane and ECM differ in phenotype, composition, and function [2]. The endothelial cells form a monolayer in every blood vessel in the circulation. They are actively involved in several regulatory processes in the body. Besides being metabolically active and selectively permeable for small solutes and peptides/proteins, endothelial cells are actively involved in regulating haemostasis [3]. Furthermore, they are able to recruit cells of the immune system to specific sites of e.g. infection or inflammation by virtue of the regulated expression of cell adhesion molecules and production of cytokines and chemokines [4] (see also Chapter 7). In addition, endothelial cells are actively involved in vascular remodelling in for example ovulation, wound healing, tumour growth and diabetic retinopathy [5,6].

9.1.2 Molecular Control of Tumour Growth-related Angiogenesis

Physiological stimuli during wound healing and during the reproductive cycle in women lead to controlled angiogenesis. However, pathologic conditions such as tumour growth, rheumatoid arthritis, and diabetic retinopathy are also characterized by abundant angiogenesis.

Angiogenesis is rapidly initiated in response to hypoxic or ischaemic conditions. In tumour growth, this active vascular remodelling is reflected by enhanced tumour endothelial cell

EC

angiogenic stimulus

ECM

Figure 9.1. In tumours that have undergone the angiogenic switch, the expression of a variety of growth factors and other soluble molecules, and the changes in the extracellular matrix (ECM), among others, lead to angiogenesis, the formation of new blood vessels from pre-existing ones. In this process, endothelial cells (EC) covering the blood vessel wall become activated, migrate into the tissue, proliferate and eventually differentiate into mature blood vessels. These vessels serve as a supply of nutrients for the ongoing demands of the growing tumour cells.

proliferation to up to 20–2000 times faster than in healthy adult endothelium [7]. In all types of angiogenesis, either under physiological or pathologicaal conditions, endothelial cell activation is followed by matrix degradation, cellular migration, proliferation, and ultimately neovasculature maturation (Figure 9.1).

9.1.2.1 Role of Growth Factors VEGF and FGF-2

More than 20 cytokines from various sources have now been reported to be involved in the processes taking place during angiogenesis [8]. Vascular endothelial growth factor (VEGF) and basic Fibroblast Growth Factor (bFGF or FGF-2) are the two growth factors whose roles in angiogenesis have been most extensively studied to date.VEGF (also known as VEGF-A) isoforms VEGF-121, 145, 165, 183, 189 and 205 are produced through alternative splicing from a single VEGF gene located on chromosome 6 [9]. The isoforms differ in their molecular composition and weight, and biological properties. The larger forms of VEGF differ from VEGF-121 by the presence of a heparin-binding domain, which is encoded by the exon-7. VEGF is abundantly produced by hypoxic tumour cells, macrophages and other cells of the immune system [10]. It induces vasodilatation via endothelial nitric oxide production and increases endothelial cell permeability [11]. This allows plasma proteins to enter the tissue to form a fibrin-rich provisional network [12]. VEGF also induces the expression of various proteases and receptors important in cellular invasion and tissue remodelling, it activates cellular proliferation and prevents endothelial cell apoptosis [13,14].The two VEGF-specific tyrosine kinase receptors,VEGFR-1 (Flt-1) and VEGFR-2 (KDR/flk-1), are expressed on vascular endothelium, and to a lesser extent on monocytes/macrophages and certain tumour cell types. Interaction of VEGF with VEGFR-2 is a critical requirement to induce the full spectrum of VEGF biological responses. In addition to the two VEGF receptors, VEGF-165 has been found to bind neuropilin-1, which is also expressed on endothelial cells [15]. A recent study using genetic deletion methods has determined that neuropilin-1 is important for embryonic vessel formation [16].

Endothelial cells exploit various proteases such as matrix metalloproteinases to penetrate into new areas of the body by degrading the basement membrane. Furthermore, urokinaseplasminogen activator and tissue type-plasminogen activator convert the ubiquitous plasma protein plasminogen to plasmin. Plasmin is believed to be the most important protease for the mobilization of FGF-2 from the ECM pool. FGF-2 induces endothelial cell motility, proliferation and proteinase activity, and modulates integrin levels [17,18].The cellular effects of FGFs are mediated via specific binding to high-affinity tyrosine kinase receptors [17]. In addition, low affinity FGF receptors consist of polysaccharide components of heparan sulfate proteoglycans on cell surfaces and ECM. Binding to these components present in the ECM has been proposed as a mechanism to stabilize and protect FGF from inactivation. Heparan sulfate on cell surfaces, on the other hand, plays a more active role in displacing ECM-bound FGF-2 and its subsequent presentation to the high affinity signal transducing receptors [19]. Angiogenesis seems exquisitely sensitive to small changes in factors such as VEGF and FGF- 2, which may have important therapeutic implications in treatment of angiogenesis-driven disorders [20,21].

(pericytes in small vessels and smooth muscle cells in large vessels) need to be recruited. Endothelial cells accomplish this via the synthesis and secretion of platelet-derived growth factor (PDGF), a mitogen and chemoattractant for a variety of mesenchymal cells. Subsequent differentiation of the mural precursor cells into pericytes and smooth muscle cells is believed to be a cell–cell contact-dependent process. Upon endothelial cell–mural cell contact, a latent form of TGF-β, produced by both endothelium and mural cells, is activated in a plasmin-me- diated process. Activated TGF-β can induce changes in myofibroblasts and pericytes which contributes to the formation of a mature vessel, ECM production and maintenance of growth control [34]. The coincident investment of growing capillaries by pericytes with the deposition of basement membrane and cessation of vessel growth during wound healing, also indicates vessel growth regulation by pericytes [35]. The FGF-1 receptor is also implicated in endothelial cell differentiation leading to vascular tube formation. In addition to inducing plasminogen activator, and endothelial cell proliferation and migration, FGF-1 receptor signalling resulted in endothelial tube formation in collagen [36].

9.2 Angiogenesis Assays and Models

The specificity of blood vessel-targeting to eradicate solid tumours depends on altered physiological processes in the tumour vasculature relative to normal vasculature in healthy tissues. It is therefore necessary to investigate the fundamental properties of the vascular biology and cell biological events in vessel formation. A number of different assay systems and angiogenesis models can be used for the research underlying development of vascular targeting techniques for the treatment of cancer.

9.2.1 Endothelial Cell Sources

The availability of viable endothelial cells is crucial for research on vessel formation, angiogenesis and angiogenic endothelial cell targeting. Endothelial cells can be obtained from various tissues, purified and cultured in vitro. The best available source of human endothelial cells is the large vein in the umbilical cord. Because this vein is not branched, it can be filled with collagenase which will enzymatically detach the endothelial cells from the vessel wall. Endothelial cells in culture begin cell cycling and form a confluent monolayer on the tissueculture plastic. It should always be borne in mind that cultured endothelial cells are never in a quiescent state and can therefore not serve as a model for resting vasculature. For reasons of simple isolation most laboratories make use of the human umbilical vein endothelial cells (HUVEC). The major drawback of these cells is their macrovascular origin, which makes them less suitable for studies on the microvascular processes occurring during angiogenesis. Although more laborious, human microvascular endothelial cells can be isolated from other organs such as the foreskin or adipose tissue.

Endothelial cells in culture need a constant supply of growth factors such as FGFs and VEGF in order to continue cell cycling. In most cultures the addition of serum to the culture medium is sufficient to maintain a low level of endothelial cell proliferation. Cells cultured this way can be subcultured at a split ratio of 1 : 3 for four to five passages without significant