BNP1350, 7‐[(2‐trimethylsilyl)ethyl]‐20(S)‐camptothecin, is a novel semi‐synthetic, highly lipophilic, silicon‐containing camptothecin and an inhibitor of topoisomerase I. It has been supercomputer engineered for superior oral bioavailability, superior lactone stability, broad anti‐tumor activity, increased potency and insensitivity to Pgp/MRP/LRP drug resistance. We determined the efficacy of BNP1350 in experimental human colon cancer and compared its anti‐tumor effects with those of CPT‐11/SN‐38. We also determined a possible influence of Pgp, MRP and LRP on the efficacy of BNP1350. The in vitro anti‐proliferative capacity of the compounds using various exposure times was assessed in five colon cancer cell lines and indicated that BNP1350 was similarly effective or slightly more potent than SN‐38. Four cell lines of other origin with sublines expressing Pgp, MRP and/or LRP showed that BNP1350 was significantly more effective than SN‐38 (p < 0.05) and that the activity of BNP1350 was not reduced in multidrug‐resistant cells. For in vivo experiments, BNP1350 was given 1.0 mg/kg i.p. or 1.5 mg/kg p.o. daily × 5 and CPT‐11 20 mg/kg i.p. daily × 5 being equitoxic schedules in nude mice bearing s.c. human tumor xenografts. The schedules were studied in colon cancer xenografts COLO320, COLO205 or WiDr as well as in two Pgp‐positive xenografts 2780AD and BRO/mdr1.1 and the parental Pgp‐negative A2780 ovarian cancer xenografts and BRO melanoma xenografts. Growth inhibition of >50% was obtained for BNP1350 given i.p. in six out of the seven xenografts studied. BNP1350 was similarly effective when given i.p. or p.o. CPT‐11 was as effective as BNP1350, except in BRO and BRO/mdr1.1 xenografts. Pgp expression in xenografts in vivo confirmed that there was no negative influence on the efficacy of BNP1350. In conclusion, BNP1350 shows a broad spectrum of activity in experimental human tumors and is a suitable candidate for oral treatment of cancer. Int. J. Cancer 88:260–266, 2000. © 2000 Wiley‐Liss, Inc.

Vascular endothelial growth factor (VEGF) is suggested to be an important regulator of angiogenesis in ovarian cancer. We have evaluated the effects of VEGF overexpression on the histology and growth rate of human ovarian cancer xenografts. OVCAR-3 human ovarian cancer cells were stably transfected with an expression vector encoding the 165-amino acid isoform of VEGF. As subcutaneous xenografts, moderately and highly VEGF(165)-overexpressing OVCAR-3 cells formed tumors with large cysts. Immunohistochemistry demonstrated an increase in the number of CD31-positive microvessels, some of which were larger in diameter than those in the parental tumors, as well as extensive vascular rimming around the cysts. Weakly VEGF(165)-overexpressing tumors also contained an increased number of CD31-positive microvessels and occasional vascular rimming, but cysts were not present. Immunohistochemistry further revealed the presence of monocytes and macrophages in both parental and VEGF(165)-overexpressing xenografts. Interestingly, the number of monocytes/macrophages was greatly increased in moderately and highly VEGF(165)-overexpressing xenografts and large areas populated with monocytes/macrophages were detected within the tumor stroma. Although the higher number of CD31-positive cells would suggest a better vascularization pattern in VEGF(165)-overexpressing xenografts, tumor growth rates were not increased when compared with that of parental xenografts. These data provide functional evidence for a role of VEGF(165) in cyst formation and monocyte/macrophage infiltration.

The novel camptothecin derivative BNP1350 (7-[2-trimethylsilyl)ethyl]-20(S)-camptothecin), also known as Karenitecin, has been developed for superior oral bioavailability and increased lactone stability. In our study, we describe the antiproliferative effects of BNP1350, SN-38 and topotecan in 4 human ovarian cancer cell lines. BNP1350 was found to be slightly more potent than SN-38 (p<0.01) and was considerably more potent than topotecan (p<0.01). We extended these studies to well-established human ovarian cancer xenografts in which we compared the growth inhibition induced by BNP1350 with that of topotecan given in equitoxic schedules. The growth inhibition in all 3 xenografts induced by BNP1350 was >75%, which was significantly better than that resulting from topotecan (p<0.05). We then selected BNP1350-resistant variants of the A2780 human ovarian cancer cell line, 2780K4 (resistance factor: 41) and 2780K32 (resistance factor: 90), to analyze possible resistance mechanisms. These variants exhibited cross-resistance against all camptothecins tested. In comparison with 2780K4 cells, 2780K32 cells were relatively more resistant against SN-38, topotecan, DX-8951f and BNP1350. In addition, 2780K32 cells were highly cross-resistant against mitoxantrone. In both 2780K4 and 2780K32, the amount of topoisomerase I was not changed but the catalytic activity was reduced. Furthermore, 2780K32 cells clearly overexpressed the breast cancer resistance protein (BCRP), as demonstrated for both the gene and the protein. In contrast to topotecan, BNP1350 proved not to be a good substrate for BCRP. Overall, we conclude that BNP1350 offers advantages over topotecan expressed by high efficacy in experimental human ovarian cancer and poor affinity for BCRP.

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Summary The low-affinity monoclonal antibody (MAb) chimeric 17-lA(c-17-lA) and the high-affinity MAb mouse 323/A3 (m-323/A3) were used to study the effect of the MAb affinity on the tumour uptake and efficacy of radioimmunotherapy in nude mice bearing subcutaneously the human ovarian cancer xenografts FMa, OVCAR-3 and Ov.Pe. Both MAbs are directed against the same pancarcinoma glycoprotein. In vitro, the number of binding sites on tumour cells at 40C was similar for both MAbs, but m-323/A3 had an approximately 5-fold higher affinity (1.3 -3.0 x 109M-') than c-17-lA (3.0 -.4 x IO' M-). This difference in affinity was more extreme at 37°C, when no binding of c-17-IA could be observed. MAb m-323/A3 completely blocked the binding of c-17-lA to tumour cells, whereas the reverse was not observed. Immunohistochemistry showed a similar but more intense staining pattern of m-323/A3 in human ovarian cancer xenografts than of c-17-1A. In vivo, the blood clearance in non-tumour-bearing nude mice was similar for both MAbs with terminal half-lives of 71.4 h for m-323/A3 and 62.7 h for c-17-lA. MAb m-323/A3 targeted better to tumour tissue, but was more heterogeneously distributed than c-17-lA. The cumulative absorbed radiation dose delivered by m-323/A3 to tumour tissue was 2.5-to 4.7-fold higher than that delivered by c-17-lA. When mice were treated with equivalent radiation doses of ['311]m-323/A3 and ['31I]c-17-lA, based on a correction for the immunoreactivity of the radiolabelled MAbs, m-323/A3 induced a better growth inhibition in two of the three xenografts. When the radiation doses were adjusted to obtain a similar amount of radiation in the tumour c-17-lA was more effective in tumour growth inhibition in all three xenografts.