- Email: [email protected]
Effect of LY293111 in combination with gemcitabine in colonic cancer
Cancer Letters 210 (2004) 41–46 www.elsevier.com/locate/canlet
Effect of LY293111 in combination with gemcitabine in colonic cancer Rene Henniga, Xian-Zhong Dinga, Wei-Gang Tonga, Richard C. Witta, Borko D. Jovanovicb, Thomas E. Adriana,* a
Department of Surgery and Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Tarry Building, 4-711, 303 East Chicago Ave, Chicago, IL 60611, USA b Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA Received 5 November 2003; accepted 19 February 2004
Abstract New adjuvant therapies are needed for the treatment of stage III colon cancer. The essential fatty acids, linoleic and arachidonic acid enhance tumorigenesis through the cyclooxygenase and lipoxygenase pathways. Leukotriene B4 (LTB4) is a product of 5-lipoxygenase (5-LOX) which has tumor-promoting effects. The LTB4 receptor antagonist, LY293111 inhibited tumor growth and induced apoptosis in vitro. The effectiveness of LY293111, alone and in combination with gemcitabine was investigated in a heterotopic xenograft model in athymic mice using HT29 and LoVo human colonic cancer cells. The combined therapy markedly inhibited tumor growth and could warrant consideration as a new therapeutic option. q 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Colon cancer; Heterotopic xenografts; LY293111; Gemcitabine
1. Introduction Colon cancer is the third leading cause of cancer death for both men and women in the United States [1]. This year, about 98,000 patients will be diagnosed with colon cancer and approximately 48,000 will die from this disease [1]. Both incidence and mortality rates have been decreasing since 1985 and, fortunately, 75– 80% of colon cancer patients are diagnosed with the disease at a localized stage [2]. However, even after apparently curative surgery, * Corresponding author. Tel.: þ 312-503-3489; fax: 312-5033491. E-mail address: [email protected] (T.E. Adrian).
about 40% of patients suffer from tumor recurrence or development of metastases [2]. In attempts to improve this situation, considerable effort has gone into developing adjuvant treatment strategies. Radiotherapy is effective in rectal cancer but is not improving the overall outcome in this disease [2]. A combination of 5-fluorouracil and leucovorin has been established as the standard therapy for stage III colon cancer patients [2]. Nevertheless, new adjuvant strategies are still needed to improve efficacy and tolerance, hopefully using drugs that combine lower toxicity with effectiveness. Substantial evidence has linked colon cancer growth with high intake of dietary fat, particularly the omega-6 polyunsaturated fatty acids (PUFAs),
0304-3835/$ - see front matter q 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.canlet.2004.02.023
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arachidonic acid and linoleic acid which enhance tumorigenesis through the production of eicosanoids [3 – 6]. In contrast, omega-3 PUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in high concentrations in fish oils, have anti-cancer effects [5]. There are two major metabolic pathways for arachidonic acid, the cyclooxygenase (COX) pathway and the lipoxygenase (LOX) pathway. Early investigations into the role of arachidonic acid metabolism in cancer have mainly focused on the COX pathway, particularly involving the inducible COX-2 enzyme, as a result of epidemiological observations that the incidence of colonic cancer was significantly reduced in regular users of aspirin and other non-steroid anti-inflammatory drugs [7,8]. Leukotriene B4 (LTB4), like prostaglandins stimulates colon cancer cell growth [9]. LTB4 has been widely implicated in the pathogenesis of several inflammatory diseases, such as asthma, psoriasis, rheumatoid arthritis and inflammatory bowel disease [10]. Although LTB4 is a final product of the 5-LOX pathway of arachidonic acid metabolism, its function in tumorigenesis has not been fully investigated. However, previous studies in our laboratory revealed overexpression of 5-LOX and LTB4 receptors in human pancreatic cancer tissues and stimulation of pancreatic cancer cell growth by LTB4 via the extracellular regulated mitogen activated kinase (ERK1/2) pathway [11,12]. In contrast, the LTB4 receptor antagonist LY293111 had growth inhibitory effects and induced apoptosis via the mitochondrial pathway both in vitro and in vivo [12]. The tumorpromoting effects of LTB4 have also been reported in breast cancer, melanoma and lymphoma as well as head and neck carcinoma [13 – 16]. Moreover, LTB4 stimulates proliferation of HT29 human colonic cancer cells and this effect is inhibited by the competitive LTB4 antagonist, SC-41930, suggesting the presence of LTB4 receptors in epithelial cells [9]. Based on the above evidence, the current study was aimed at investigating the effectiveness of the LTB4 antagonist, LY293111 on colon cancer cell proliferation in a heterotopic xenograft model in athymic mice. The study was designed to evaluate the potential of a combined therapy of gemcitabine and LY293111. Gemcitabine has already been suggested as a new adjuvant therapeutic option in colonic cancer patients because of its excellent antitumor activity against
solid tumors and contribution to radiosensitization [17 –19].
2. Materials and methods 2.1. Materials DMEM, F12 media, penicillin-streptomycin solution and trypsin-EDTA solution were purchased from Sigma Chemicals (St Louis, MO). Fetal bovine serum (FBS) was from Atlanta Biologicals (Norcross, GA). Gemcitabine and the selective LTB4 receptor antagonist, LY293111 were provided by the Eli Lilly and Company (Indianapolis, IN). 2.2. Cell line and cell culture The human colon carcinoma cell lines LoVo and HT29 were purchased from American Type Culture Collection (Rockville, MA) and grown in F12 and DMEM media, respectively, supplemented with 10% FBS. Cells were seeded into 75 cm2 flasks and cultured in a humidified atmosphere of 95% O2 and 5% CO2 at 37 8C, with media changes every other day. 2.3. Heterotopic xenograft tumor model Thirty-six athymic nude mice (BALB/c nu/nu, 5-weeks old females) were purchased from the Frederick Cancer Research and Development Center (Charles River, USA). The mice were acclimatized to the animal facility for one week prior to receiving xenografts. Three million LoVo or HT29 human colon cancer cells were injected into both flanks of 20 and 16 nude mice, respectively. Once visible tumors were established 4 days after injection, the mice were randomized into four groups with 4 (HT29) and 5 (LoVo) mice/group: Group I (Control) received daily p.o. dosages of DMSO (0.5 ml/g/day); Group II (LY293111) received daily p.o. dosages of LY293111 (250 mg/kg/day dissolved in DMSO and administered 0.5 ml/g body weight/day); Group III (Gemcitabine) received daily p.o. dosages of DMSO (0.5 ml/g/day) and 4 i.p. injections of gemcitabine (60 mg/kg/dose dissolved in PBS and administered 2 ml/g/day). Group IV (LY293111 þ Gemcitabine)
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
received daily p.o. dosages of LY293111 (250 mg/kg/day) and 4 i.p. injections of gemcitabine (60 mg/kg/dose). Animal weight and tumor size were recorded every third day. The formula for calculating tumor volume was: ðlengthÞ £ ðwidthÞ£ ðlength þ width=2Þ £ 0:526 ¼ volume: After 30 days of treatment the animals were euthanized and the tumors were carefully dissected and tumor weights measured. This study was approved by the Institutional Animals Care and Use Committee and all animal studies were conducted in accordance with the principles and procedures outlined in the NIH Guide for the Care and Use of Animals. 2.4. Statistical analysis Tumor weight and volume were compared using ANOVA with Tukeys post hoc test for multiple comparisons. Differences were considered statistically significant when P # 0:05: Graphs were created using the GraphPad Prism Software. Analysis was performed using S-Plus Statistics Software (Insightful Corporation 2001).
3. Results Both LY293111 and gemcitabine inhibited growth of human LoVo and HT29 colon cancer xenografts in athymic mice, measured as both tumor volume and tumor weight (Fig. 1). The weights of the LoVo tumors at the end of the experiment were significantly lower in the gemcitabine alone and gemcitabine þ LY293111-treated animals compared with controls ðP ¼ 0:01Þ: Measurement of LoVo tumor volumes over time revealed significant differences between control and treated animals for the first time on day 12 and this difference was maintained until the end of the experiment (P between 0.007 and 0.05). Moreover, the combined treatment of LY293111 and gemcitabine was more effective in inhibiting tumor growth compared to either treatment alone in the LoVo xenograft tumor model (Fig. 1). This difference was a consistent trend from day 15, becoming almost statistically significant by the final day of the experiment ðP ¼ 0:06Þ: Analysis of HT29 tumors revealed a similar pattern of results with significant differences in tumor
43
weights in the end of the experiment between control and gemcitabine or LY293111 þ gemcitabine treatments ðP ¼ 0:009Þ: Similarly, HT29 tumor volumes are significantly lower in animals treated with gemcitabine or the combination of LY293111 þ gemcitabine, starting from day 12 ðP ¼ 0:02Þ (Fig. 1). An additional benefit of adding LY293111 to gemcitabine for the treatment of HT29 tumor xenografts was not revealed, because of the effectiveness of gemcitabine alone in inhibiting growth of tumors derived from this cell line (Fig. 1). There was no significant difference in body weights between the control and treated animals throughout the entire treatment period, although the untreated control animals were less active because of large tumor burden.
4. Discussion Previous studies from our group and those of others have demonstrated the importance of the LOX metabolic pathways of arachidonic acid in the proliferation of cancer cells [20 –23]. LTB4 receptors and 5-LOX are expressed in pancreatic cancer cells, but not in normal pancreatic ductal cells [11,23]. The 5-lipoxygenase metabolites, 5-HETE and LTB4 stimulate human pancreatic cancer cell proliferation and blockade of the pathway using specific enzyme inhibitors or receptor antagonists blocks proliferation and induces apoptosis [12,23]. Prostaglandins, 12-RHETE and LTB4 all stimulate colonic cancer cell proliferation; effects that can be abolished by COXand LOX-inhibitors or leukotriene B4 receptor antagonists, respectively [9,24]. In the present study, the effectiveness of LY293111 was examined in athymic mice bearing subcutaneously transplanted human colon cancer cells. The heterotopic xenograft tumor model is widely used and accepted as an effective method for studying the in vivo effects of anti-cancer treatments. Oral administration of LY293111 at a dose of 250 mg/kg/day markedly inhibited tumor growth compared with that in vehicle-treated control animals during the 30-day treatment period. There did not appear to be any toxic effects of LY293111 at the dose used in these animals. All animals tolerated the treatment very well and there was no significant
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Fig. 1. Xenograft tumor volumes over a 30-day period and tumor weights at the end of the experiments (mean ^ SEM) 30 days after s.c. injection of HT29 and LoVo human colonic cancer cells. Groups included control; LY293111 (LY; 250 mg/kg/day); gemcitabine (Gem, 60 mg/kg/dose) and combined LY293111 þ gemcitabine (LY þ Gem) therapy. Tumor burden, measured by both tumor weight and volume was significantly lower in animals treated with gemcitabine or LY293111 in combination with gemcitabine. A beneficial effect of LY293111 on gemcitabine treatment was revealed in LoVo tumors but not in HT29 tumors, because of marked tumor suppression by gemcitabine alone in the latter. LY293111 alone inhibited growth of both LoVo and HT29 tumors, however, this did not reach statistical significance at 5% a-level:
change in body weight between control and treated animals. However, the most effective treatment in mice with LoVo tumors was the combination of LY293111 and gemcitabine. For treatment of HT29 tumors gemcitabine alone was so effective that a beneficial effect of adding LY293111 could not be seen. Gemcitabine has been suggested as a possible new adjuvant treatment option for colon cancer because of its marked effects on solid tumors and properties as a radiosensitizer [17 – 19,25]. However, a multitargeted strategy is often superior to a single
therapy, as shown by Tonkinson et al. when they observed a potentiation of gemcitabine toxicity on HT29 cells after pretreatment with the antiproliferative antifolate LY231514 [26]. Moreover, the PI3 kinase (PI3K) inhibitor, LY294002 caused tumor suppression and induction of apoptosis in LoVo tumors by inactivating the Akt/PKB pathway, which is important for cell survival [27]. Since LY293111 is a LTB4 antagonist that inhibits activation of the extracellular activated mitogen activated kinase (ERK1/2) and the PI3K/Akt pathway and induces
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
apoptosis via the mitochondrial pathway, we were expecting marked tumor growth inhibition with this compound [12]. The results confirmed these expectations and revealed that LY293111 can potentiate the cytotoxic effects of gemcitabine. However, this effect was cell line-dependent, because of a different degree of response to gemcitabine alone. LY293111 can be orally administered and is well tolerated and, therefore, compliance of patients can be expected. We conclude that a combined adjuvant treatment with LY293111 and gemcitabine might be a valuable new approach for the therapy of colonic cancer.
[10] [11]
[12]
[13]
Acknowledgements [14]
Supported by grants from the National Cancer Institute SPORE program (CA72712), The American Institute for Cancer Research (00B065) and the Lilly Research Laboratories. RH received a fellowship award from the Deutsche Forschungsgemeinschaft (RH).
[15]
[16]
[17]
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of gemcitabine in HT29 colon carcinoma, Cancer Res. 59 (1999) 3671–3676. [27] S. Semba, N. Itoh, M. Ito, M. Harada, M. Yamakawa, The in vitro and in vivo effects of 2-(4-morpholinyl)-8-phenylchromone (LY294002), a specific inhibitor of phosphatidylinositol 30 -kinase, in human colon cancer cells, Clin. Cancer Res. 8 (2002) 1957– 1963.
Effect of LY293111 in combination with gemcitabine in colonic cancer Rene Henniga, Xian-Zhong Dinga, Wei-Gang Tonga, Richard C. Witta, Borko D. Jovanovicb, Thomas E. Adriana,* a
Department of Surgery and Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Tarry Building, 4-711, 303 East Chicago Ave, Chicago, IL 60611, USA b Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA Received 5 November 2003; accepted 19 February 2004
Abstract New adjuvant therapies are needed for the treatment of stage III colon cancer. The essential fatty acids, linoleic and arachidonic acid enhance tumorigenesis through the cyclooxygenase and lipoxygenase pathways. Leukotriene B4 (LTB4) is a product of 5-lipoxygenase (5-LOX) which has tumor-promoting effects. The LTB4 receptor antagonist, LY293111 inhibited tumor growth and induced apoptosis in vitro. The effectiveness of LY293111, alone and in combination with gemcitabine was investigated in a heterotopic xenograft model in athymic mice using HT29 and LoVo human colonic cancer cells. The combined therapy markedly inhibited tumor growth and could warrant consideration as a new therapeutic option. q 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Colon cancer; Heterotopic xenografts; LY293111; Gemcitabine
1. Introduction Colon cancer is the third leading cause of cancer death for both men and women in the United States [1]. This year, about 98,000 patients will be diagnosed with colon cancer and approximately 48,000 will die from this disease [1]. Both incidence and mortality rates have been decreasing since 1985 and, fortunately, 75– 80% of colon cancer patients are diagnosed with the disease at a localized stage [2]. However, even after apparently curative surgery, * Corresponding author. Tel.: þ 312-503-3489; fax: 312-5033491. E-mail address: [email protected] (T.E. Adrian).
about 40% of patients suffer from tumor recurrence or development of metastases [2]. In attempts to improve this situation, considerable effort has gone into developing adjuvant treatment strategies. Radiotherapy is effective in rectal cancer but is not improving the overall outcome in this disease [2]. A combination of 5-fluorouracil and leucovorin has been established as the standard therapy for stage III colon cancer patients [2]. Nevertheless, new adjuvant strategies are still needed to improve efficacy and tolerance, hopefully using drugs that combine lower toxicity with effectiveness. Substantial evidence has linked colon cancer growth with high intake of dietary fat, particularly the omega-6 polyunsaturated fatty acids (PUFAs),
0304-3835/$ - see front matter q 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.canlet.2004.02.023
42
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
arachidonic acid and linoleic acid which enhance tumorigenesis through the production of eicosanoids [3 – 6]. In contrast, omega-3 PUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in high concentrations in fish oils, have anti-cancer effects [5]. There are two major metabolic pathways for arachidonic acid, the cyclooxygenase (COX) pathway and the lipoxygenase (LOX) pathway. Early investigations into the role of arachidonic acid metabolism in cancer have mainly focused on the COX pathway, particularly involving the inducible COX-2 enzyme, as a result of epidemiological observations that the incidence of colonic cancer was significantly reduced in regular users of aspirin and other non-steroid anti-inflammatory drugs [7,8]. Leukotriene B4 (LTB4), like prostaglandins stimulates colon cancer cell growth [9]. LTB4 has been widely implicated in the pathogenesis of several inflammatory diseases, such as asthma, psoriasis, rheumatoid arthritis and inflammatory bowel disease [10]. Although LTB4 is a final product of the 5-LOX pathway of arachidonic acid metabolism, its function in tumorigenesis has not been fully investigated. However, previous studies in our laboratory revealed overexpression of 5-LOX and LTB4 receptors in human pancreatic cancer tissues and stimulation of pancreatic cancer cell growth by LTB4 via the extracellular regulated mitogen activated kinase (ERK1/2) pathway [11,12]. In contrast, the LTB4 receptor antagonist LY293111 had growth inhibitory effects and induced apoptosis via the mitochondrial pathway both in vitro and in vivo [12]. The tumorpromoting effects of LTB4 have also been reported in breast cancer, melanoma and lymphoma as well as head and neck carcinoma [13 – 16]. Moreover, LTB4 stimulates proliferation of HT29 human colonic cancer cells and this effect is inhibited by the competitive LTB4 antagonist, SC-41930, suggesting the presence of LTB4 receptors in epithelial cells [9]. Based on the above evidence, the current study was aimed at investigating the effectiveness of the LTB4 antagonist, LY293111 on colon cancer cell proliferation in a heterotopic xenograft model in athymic mice. The study was designed to evaluate the potential of a combined therapy of gemcitabine and LY293111. Gemcitabine has already been suggested as a new adjuvant therapeutic option in colonic cancer patients because of its excellent antitumor activity against
solid tumors and contribution to radiosensitization [17 –19].
2. Materials and methods 2.1. Materials DMEM, F12 media, penicillin-streptomycin solution and trypsin-EDTA solution were purchased from Sigma Chemicals (St Louis, MO). Fetal bovine serum (FBS) was from Atlanta Biologicals (Norcross, GA). Gemcitabine and the selective LTB4 receptor antagonist, LY293111 were provided by the Eli Lilly and Company (Indianapolis, IN). 2.2. Cell line and cell culture The human colon carcinoma cell lines LoVo and HT29 were purchased from American Type Culture Collection (Rockville, MA) and grown in F12 and DMEM media, respectively, supplemented with 10% FBS. Cells were seeded into 75 cm2 flasks and cultured in a humidified atmosphere of 95% O2 and 5% CO2 at 37 8C, with media changes every other day. 2.3. Heterotopic xenograft tumor model Thirty-six athymic nude mice (BALB/c nu/nu, 5-weeks old females) were purchased from the Frederick Cancer Research and Development Center (Charles River, USA). The mice were acclimatized to the animal facility for one week prior to receiving xenografts. Three million LoVo or HT29 human colon cancer cells were injected into both flanks of 20 and 16 nude mice, respectively. Once visible tumors were established 4 days after injection, the mice were randomized into four groups with 4 (HT29) and 5 (LoVo) mice/group: Group I (Control) received daily p.o. dosages of DMSO (0.5 ml/g/day); Group II (LY293111) received daily p.o. dosages of LY293111 (250 mg/kg/day dissolved in DMSO and administered 0.5 ml/g body weight/day); Group III (Gemcitabine) received daily p.o. dosages of DMSO (0.5 ml/g/day) and 4 i.p. injections of gemcitabine (60 mg/kg/dose dissolved in PBS and administered 2 ml/g/day). Group IV (LY293111 þ Gemcitabine)
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
received daily p.o. dosages of LY293111 (250 mg/kg/day) and 4 i.p. injections of gemcitabine (60 mg/kg/dose). Animal weight and tumor size were recorded every third day. The formula for calculating tumor volume was: ðlengthÞ £ ðwidthÞ£ ðlength þ width=2Þ £ 0:526 ¼ volume: After 30 days of treatment the animals were euthanized and the tumors were carefully dissected and tumor weights measured. This study was approved by the Institutional Animals Care and Use Committee and all animal studies were conducted in accordance with the principles and procedures outlined in the NIH Guide for the Care and Use of Animals. 2.4. Statistical analysis Tumor weight and volume were compared using ANOVA with Tukeys post hoc test for multiple comparisons. Differences were considered statistically significant when P # 0:05: Graphs were created using the GraphPad Prism Software. Analysis was performed using S-Plus Statistics Software (Insightful Corporation 2001).
3. Results Both LY293111 and gemcitabine inhibited growth of human LoVo and HT29 colon cancer xenografts in athymic mice, measured as both tumor volume and tumor weight (Fig. 1). The weights of the LoVo tumors at the end of the experiment were significantly lower in the gemcitabine alone and gemcitabine þ LY293111-treated animals compared with controls ðP ¼ 0:01Þ: Measurement of LoVo tumor volumes over time revealed significant differences between control and treated animals for the first time on day 12 and this difference was maintained until the end of the experiment (P between 0.007 and 0.05). Moreover, the combined treatment of LY293111 and gemcitabine was more effective in inhibiting tumor growth compared to either treatment alone in the LoVo xenograft tumor model (Fig. 1). This difference was a consistent trend from day 15, becoming almost statistically significant by the final day of the experiment ðP ¼ 0:06Þ: Analysis of HT29 tumors revealed a similar pattern of results with significant differences in tumor
43
weights in the end of the experiment between control and gemcitabine or LY293111 þ gemcitabine treatments ðP ¼ 0:009Þ: Similarly, HT29 tumor volumes are significantly lower in animals treated with gemcitabine or the combination of LY293111 þ gemcitabine, starting from day 12 ðP ¼ 0:02Þ (Fig. 1). An additional benefit of adding LY293111 to gemcitabine for the treatment of HT29 tumor xenografts was not revealed, because of the effectiveness of gemcitabine alone in inhibiting growth of tumors derived from this cell line (Fig. 1). There was no significant difference in body weights between the control and treated animals throughout the entire treatment period, although the untreated control animals were less active because of large tumor burden.
4. Discussion Previous studies from our group and those of others have demonstrated the importance of the LOX metabolic pathways of arachidonic acid in the proliferation of cancer cells [20 –23]. LTB4 receptors and 5-LOX are expressed in pancreatic cancer cells, but not in normal pancreatic ductal cells [11,23]. The 5-lipoxygenase metabolites, 5-HETE and LTB4 stimulate human pancreatic cancer cell proliferation and blockade of the pathway using specific enzyme inhibitors or receptor antagonists blocks proliferation and induces apoptosis [12,23]. Prostaglandins, 12-RHETE and LTB4 all stimulate colonic cancer cell proliferation; effects that can be abolished by COXand LOX-inhibitors or leukotriene B4 receptor antagonists, respectively [9,24]. In the present study, the effectiveness of LY293111 was examined in athymic mice bearing subcutaneously transplanted human colon cancer cells. The heterotopic xenograft tumor model is widely used and accepted as an effective method for studying the in vivo effects of anti-cancer treatments. Oral administration of LY293111 at a dose of 250 mg/kg/day markedly inhibited tumor growth compared with that in vehicle-treated control animals during the 30-day treatment period. There did not appear to be any toxic effects of LY293111 at the dose used in these animals. All animals tolerated the treatment very well and there was no significant
44
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
Fig. 1. Xenograft tumor volumes over a 30-day period and tumor weights at the end of the experiments (mean ^ SEM) 30 days after s.c. injection of HT29 and LoVo human colonic cancer cells. Groups included control; LY293111 (LY; 250 mg/kg/day); gemcitabine (Gem, 60 mg/kg/dose) and combined LY293111 þ gemcitabine (LY þ Gem) therapy. Tumor burden, measured by both tumor weight and volume was significantly lower in animals treated with gemcitabine or LY293111 in combination with gemcitabine. A beneficial effect of LY293111 on gemcitabine treatment was revealed in LoVo tumors but not in HT29 tumors, because of marked tumor suppression by gemcitabine alone in the latter. LY293111 alone inhibited growth of both LoVo and HT29 tumors, however, this did not reach statistical significance at 5% a-level:
change in body weight between control and treated animals. However, the most effective treatment in mice with LoVo tumors was the combination of LY293111 and gemcitabine. For treatment of HT29 tumors gemcitabine alone was so effective that a beneficial effect of adding LY293111 could not be seen. Gemcitabine has been suggested as a possible new adjuvant treatment option for colon cancer because of its marked effects on solid tumors and properties as a radiosensitizer [17 – 19,25]. However, a multitargeted strategy is often superior to a single
therapy, as shown by Tonkinson et al. when they observed a potentiation of gemcitabine toxicity on HT29 cells after pretreatment with the antiproliferative antifolate LY231514 [26]. Moreover, the PI3 kinase (PI3K) inhibitor, LY294002 caused tumor suppression and induction of apoptosis in LoVo tumors by inactivating the Akt/PKB pathway, which is important for cell survival [27]. Since LY293111 is a LTB4 antagonist that inhibits activation of the extracellular activated mitogen activated kinase (ERK1/2) and the PI3K/Akt pathway and induces
R. Hennig et al. / Cancer Letters 210 (2004) 41–46
apoptosis via the mitochondrial pathway, we were expecting marked tumor growth inhibition with this compound [12]. The results confirmed these expectations and revealed that LY293111 can potentiate the cytotoxic effects of gemcitabine. However, this effect was cell line-dependent, because of a different degree of response to gemcitabine alone. LY293111 can be orally administered and is well tolerated and, therefore, compliance of patients can be expected. We conclude that a combined adjuvant treatment with LY293111 and gemcitabine might be a valuable new approach for the therapy of colonic cancer.
[10] [11]
[12]
[13]
Acknowledgements [14]
Supported by grants from the National Cancer Institute SPORE program (CA72712), The American Institute for Cancer Research (00B065) and the Lilly Research Laboratories. RH received a fellowship award from the Deutsche Forschungsgemeinschaft (RH).
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