Terms Of Tumor Growth Inhibition Research Articles

Enhanced Activity of GA101, a Novel Type II, Glycoengineered CD20 Antibody, In Combination with Bendamustine or Fludarabine, and with the Bcl-2 Family Inhibitors ABT-737 or ABT-263

AbstractAbstract 3915GA101 is type II, glycoengineered CD20 antibody currently in PhII/III clinical trials. GA101 mediates enhanced direct cell death with a concomitant reduction of CDC; and high ADCC induction due to increased affinity for FcgRIIIa. We have shown that GA101 compared to rituximab mediates superior efficacy in NHL xenograft models including the induction of complete tumor remission.In clinical practice the combination of rituximab with chemotherapy e.g. CHOP, CVP, bendamustine, fludarabine or FC results in a substantial clinical benefit. To assess the potential of GA101 for combination with bendamustine or fludarabine, in vivo combination studies in s.c. Z138 (MCL) xenografts in Scid beige mice were devised. GA101 and rituximab at sub-optimal doses of 1 mg/kg (once weekly) were combined with 3 mg/kg bendamustine (days 19, 20, 21, 22); or with 40 mg/kg fludarabine (days 22, 23, 24) and compared to the corresponding monotherapy arms. GA101 in combination with bendamustine mediated statistically superior efficacy in terms of tumor growth inhibition (TGI) compared to the combination of rituximab and bendamustine: TGI values on day 33 were 29% for rituximab, 42% for rituximab + bendamustine, 47% for GA101 and 72% for GA101 + bendamustine. Treatment with bendamustine did not show significant antitumor activity. Statistical evaluation based on sAUC showed a more than additive and significant effect on tumor growth for the combination of GA101 with bendamustine compared to the corresponding monotherapy arms. GA101 in combination with fludarabine demonstrated statistically superior efficacy in terms of TGI and yielded a significant difference compared to the combination of rituximab and fludarabine or GA101 as monotherpy. TGI values on day 36 were 50% for fludarabine, 60% for rituximab, 85% for rituximab + fludarabine, 86% for GA101 and >100% for GA101 + fludarabine. Furthermore, the superiority of the GA101-fludarabine combination was demonstrated by the observation of 3 tumor-free animals at the end of the study.ABT-263 (navitoclax) is a Bcl-2 family inhibitor that is currently in Phase I/II clinical trials for lymphoid malignancies. To provide evidence that GA101 can be combined with ABT-263 and the experimental Bcl-2 family inhibitor ABT-737, in vivo combination studies in s.c. SU-DHL4 (DLBCL) xenografts in Scid beige mice were devised. 10 mg/kg GA101 and rituximab (once weekly) were combined with 50 mg/kg ABT-737 (i.p., days 19, 22, 24, 26, 29, 31, 33). In a second study, 3 mg/kg GA101 or 10 mg/kg rituximab (once weekly) were combined with 100 mg/kg ABT-263 (orally, once daily). GA101 at a sub-optimal dose of 10 mg/kg demonstrated statistically superior efficacy in combination with ABT-737 in terms of tumor growth inhibition compared to GA101 alone or the combination of 10 mg/kg rituximab and ABT-737. Both combination treatments were statistically significant compared to the corresponding monotherapy arms. TGI values based on means on day 36 were 20% for ABT-737, 45% for rituximab, 92% for rituximab + ABT-737, 96% for GA101 and >100% for GA101 + ABT-737. The superiority of the combination of GA101 and ABT-737 was supported by complete tumor regression in all animals whereas none was observed with the combination of rituximab and ABT-737. GA101 at a sub-optimal dose of 3 mg/kg or rituximab at a dose of 10 mg/kg mediated statistically superior efficacy in terms of tumor growth inhibition in combination with ABT-263 compared to the respective monotherapy arms. TGI values based on means on day 43 were 15% for ABT-263, 89% for rituximab, >100% for rituximab + ABT-263, 80% for GA101 (at the sub-optimal dose) and >100% for GA101 (sub-optimal dose) + ABT-263.Taken together i) GA101 as single agent was at least as efficacious as the combination of rituximab with bendamustine, fludarabine or ABT-737; ii) the combination of GA101 with bendamustine or fludarabine was superior to the respective monotherapy arms and resulted in an enhanced, at least additive effect of the combination; iii) the combination of GA101 with Bcl-2 family inhibitors ABT-737 and ABT-263 was superior to the respective monotherapy arms and resulted in an enhanced effect of the combination including the induction of tumor remission. These data strongly support the further clinical investigation of GA101 in combination with Fludarabine, Bendamustine or Bcl-2 family inhibitors. Disclosures:Herting:Roche: Employment. Bader:Roche: Employment. Umana:Roche: Employment, Equity Ownership. Klein:Roche: Employment, Equity Ownership.

Abstract A113: Enhancement of the lethality of platinum-based therapy by antiprogestin mifepristone in ovarian cancer

Abstract The overall goal of our research is to study the feasibility of “repositioning” antiprogestin compounds originally designed for contraceptive purposes for ovarian cancer therapeutics. Ovarian cancer is the most deadly disease of the reproductive tract in women. When the disease is diagnosed, in most cases abnormal growths have already progressed beyond the confines of the ovaries and into the nearby fallopian tubes, uterus, and various other sites within the peritoneal cavity. As a result, the majority of patients diagnosed with ovarian cancer require surgery followed by platinum-based chemotherapy. Yet the efficacy of this therapy is hindered by the elevated toxicity of platinum derivatives, the development of mechanisms to evade drug toxicity, and the repopulation of cells between treatment intervals. Thus, finding therapeutic interventions to overcome the limitations of platinum-based therapies is of critical clinical relevance. Our laboratory published that the prototypical antiprogestin mifepristone has potent anti-ovarian cancer activity in vitro and in vivo (1); is cytostatic at pharmacological doses in platinum-sensitive and platinum-resistant ovarian cancer cells, and regardless of p53 tumor suppressor expression (1-2); and when intertwined among courses of cisplatin treatment, prevents repopulation of ovarian cancer cells (3). We now provide data demonstrating that mifepristone potentiates the lethality of cisplatin. We show that the toxicity of cisplatin can be enhanced 4 fold when associated to cytostatic concentrations of antiprogestin mifepristone. We also demonstrate that mifepristone potentiates the long-term effect of short-term exposure of OV2008 cells to sub-lethal doses of cisplatin. Finally we provide evidence that mifepristone enhances cisplatin toxicity in platinum sensitive OV2008 (wt p53) and A2780 (wt p53) lines, their platinum-resistant siblings, OV2008/C13 (wt p53) and A2780/CP70 (mut p53), and semi-platinum-resistant SK-OV-3 (null p53). In summary, we demonstrate that the prototypical antiprogestin mifepristone potentiates cisplatin toxicity regardless of platinum sensitivity and p53 genetic background. Our studies provide proof-of-principle that antiprogestin-of which mifepristone is FDA approved for reproductive medicine-can be “repurposed” for another modality-of-use as part of the chemotherapeutic armamentarium for ovarian cancer patients. The strategy of adding an antiprogestin such as mifepristone to the platinum-based chemotherapeutic schedule in ovarian cancer should allow reducing the number of platinum cycles or the dose of the platinum agent without losing efficacy in terms of tumor growth inhibition yet reducing undesirable side effects.

Abstract 5461: Novel antitumor amino-pancratistatin derivatives inhibitors of protein and DNA synthesis

Abstract The Amaryllidaceous alkaloids pancratistatin and narciclasine are known to exert marginal antitumor properties but associated with toxicities. Despite extensive investigations, pancratistatin or analogues did not succeed to provide sufficient therapeutic benefit although a new pro-drug strategy was applied recently to narciclasine. We decided to undertake a chemistry program aimed at modifying the skeleton of this attractive pharmacophore in order to improve its therapeutic application. At first sight, literature survey suggests that any change in the structure would lead to a loss of activity but a careful examination of published data indicated that position −1 of the molecule may be of potential interest although poorly investigated. We report here the synthesis of a series of 39 novel derivatives of 1-aminopancratistatin by chemical modification of the naturally available narciclasine extracted from Narcissus bulbs. These new compounds present improved pharmaceutical properties such as higher aqueous solubility (from 300 µg/ml for narciclasine up to 2000 µg/ml) without loss of stability tested on human and murine microsomal assays (70-90% stability after 1h incubation). A sub-set of these novel derivatives demonstrated a drastic increase of the cytotoxic activity reaching nM range tested on a panel of 8 different cell lines. The higher antiproliferative activity translates towards the induction of stronger pro-apoptotic signals evidenced with Annexin V, caspase 3/7 and JC-1 assay. Besides the previously described inhibition of protein synthesis, our studies originally demonstrated that part of the mechanism of action involves inhibition of DNA synthesis as well. The contribution of these two pharmacological properties elaborates a SAR (structure - activity relationship) and segregates our new pancrastistatin derivatives into different categories depending on their ability to inhibit protein synthesis, DNA synthesis or both. Based on their differential in vitro activity profile, the compounds were selected for evaluation of their in vivo antitumor properties on murine and xenografted models. As a major result F 98604 (dimethylaminomethyl benzamide derivative of pancratistatin) exhibited significant and reproducible activity on the murine B16 sc and human A375 melanoma models in terms of tumor growth inhibition as well as increased therapeutic index. The present SAR suggests that modification of the natural pancratistatin or narciclasine pharmacophore at the position −1 open new perspectives as potential anticancer agents with novel pharmacological profiles. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5461.

Novel Bis-platinum Complexes Endowed with an Improved Pharmacological Profile

Multinuclear platinum complexes are characterized by a peculiar DNA binding mode and higher cytotoxic potency than the mononuclear complexes, and efficacy against a wide range of preclinical tumor models. To reduce the high irreversible plasma protein binding and improve the chemical and metabolic drug stability, novel bis-platinum complexes were designed starting from the parent compound CT-3610. The novel second-generation bis-platinum complexes utilize alkylcarboxylate as leaving groups to improve their pharmacokinetic and pharmacodynamic profiles, thus overcoming the limitations of the previously developed multinuclear compounds. The selected compounds [CT-47518 and CT-47463, respectively (bis-capronate) platinum and (bis-butyrate) platinum], have similar in vitro degradation kinetics in human and murine plasma and, above all, an increased stability when compared to CT-3610, particularly in human plasma. In addition, both compounds exhibited a marked cytotoxic potency as compared with cisplatin and oxaliplatin. Interestingly, they were capable of overcoming resistance mediated by DNA mismatch repair defects in different cellular models. The complexes showed marked antitumor efficacy in Pt-refractory tumor xenografts, with remarkable activity in terms of tumor growth inhibition and tumor growth delay. The improved stability profile in human plasma compared to early bis- and triplatinum complexes together with the marked activity in cellular systems as well as in in vivo models, make CT-47518 and CT-47463 attractive candidates for further development.

Compared Antitumor Activity of GA101 and Rituximab against the Human RL Follicular Lymphoma Xenografts in SCID Beige Mice.

GA101 is a third generation, glycoengineered type II IgG1 anti-CD20 monoclonal antibody (Mab) with enhanced ADCC and superior caspase-independent apoptosis induction in comparison to other anti-CD20 antibodies, including rituximab which is a type I antibody. We compared the antitumor efficacy of GA101 and rituximab in established RL human lymphoma xenografts in SCID beige mice. One million exponentially growing RL cells were injected SC, yielding fast growing xenografts. GA101 was given twice weekly at 3 dosages (10, 30 and 100 mg/kg), whereas Rituximab was given at fixed dose of 30 mg/kg twice weekly. Both Mabs were administered as intravenous injections, for a total of 5 injections. GA101 was dose-related active against RL xenografts in terms of tumor growth inhibition (TGI). TGI was calculated using NCI formula and showed values of 25, 75 and 85% for the 10, 30 and 100 mg/kg dosages of GA101 respectively while the 30 mg/kg dose of rituximab induced a TGI of 43% only. Both higher doses of 30 and 100 mg/kg significantly inhibited the growth of RL tumors and resulted in some complete tumor remissions (10–30 %). The antitumor activity of Rituximab against RL xenografts was inferior to equivalent dosing of GA101. Toxicity of GA101 with these regimens was excellent with no toxic deaths and no significant modification of body weight. In a separate series of experiments rituximab 30 mg/kg and GA101 30 mg/kg administered once weekly i.v. for 4 weeks were combined or not to cyclophosphamide 50 mg/kg administered once weekly intraperitoneally for 4 weeks. This study confirmed the previous observation that the new anti CD20 GA101 was more active than rituximab administered at similar doses on established RL tumors. TGI values were 79, 35% and 93% for GA101, rituximab and cyclophosphamide administered as single agents when compared to untreated controls. When groups receiving combined therapy were compared to the groups receiving the corresponding single agent Mab, cyclophosphamide increased antitumor efficacy with TGI values of 83 and 94% for rituximab and GA101, respectively. Thus using a suboptimal dose of the classical antilymphoma alkylating agent cyclophosphamide, the combination of either antibody with cyclophosphamide was more active than either agent alone, and the most active combination was GA101 with cyclophosphamide. These results show that GA101 is more active than rituximab on RL xenografts at similar doses, both administered as a single agent or in combination with cyclophosphamide. In the SCID mice model it is not expected that a major contribution to antitumor efficacy comes from the interaction of glycoengineered Mab with murine FcgRIV receptors. Complementary experiments with cobra venom factor, which is used for in vivo complement inhibition, suggest that rituximab antitumor effect was strongly dependent on complement dependent cytotoxicity while GA101 remained active when complement was depleted.

Anti-angiogenic inhibition of tumor growth by systemic delivery of PEI- g-PEG-RGD/pCMV-sFlt-1 complexes in tumor-bearing mice

Vascular endothelial growth factor (VEGF) is an endogenous mediator of tumor angiogenesis. Blocking associations of the VEGF with its corresponding receptors (Flt-1, KDR/flk-1) have become critical for anti-tumor angiogenesis therapy. Previously, we synthesized PEI- g-PEG-RGD conjugate and evaluated as an angiogenic endothelial polymeric gene carrier. In this study, PEI- g-PEG-RGD/pCMV-sFlt-1 complexes are evaluated in terms of tumor growth inhibition in vivo. Complexes were repeatedly injected systemically via tail vein into subcutaneous tumor-bearing mice. As a result, tumor growth was inhibited in the PEI- g-PEG-RGD/pCMV-sFlt-1 injected group. However, this effect was not identified in PEI- g-PEG/pCMV-sFlt-1 or PEI- g-PEG-RGD/pCMV-GFP control groups. Moreover, the survival rate increased in the PEI- g-PEG-RGD/pCMV-sFlt-1 group compared with the controls group. These results suggest that delivery of pCMV-sFlt-1 using PEG- g-PEG-RGD may be effective for anti-angiogenic gene therapy.

Enhanced Intracellular Uptake of Sterically Stabilized Liposomal Doxorubicin in Vitro Resulting in Improved Antitumor Activity in Vivo

To investigate the correlation between the in vitro intracellular uptake and the in vivo antitumor activity of anticancer drugs delivered by sterically stabilized liposomes (SSL). Arginine-glycine-aspartic acid (RGD) peptide or RGD mimetic (RGDm) was coupled onto the surface of SSL to obtain the cell-binding carrier to facilitate the intracellular delivery of the encapsulated drugs. DOX-loaded SSL (SSL-DOX), DOX-loaded RGD-modified SSL (RGD-SSL-DOX) and DOX-loaded RGDm-modified SSL (RGDm-SSL-DOX) were prepared by lipid film dispersion followed by remote loading of DOX. The intracellular uptake of DOX from the various liposomal formulations was evaluated in vitro with melanoma B16 cells, and the pharmacokinetics, biodistribution, and antitumor activity were compared in C57BL/6 mice carrying melanoma B16 tumors. In vitro intracellular uptake of DOX by B16 cells and in vivo antitumor activity in terms of tumor growth inhibition and mice survival time prolongation for various liposomal DOX were in the following order: RGD-SSL-DOX > RGDm-SSL-DOX > SSL-DOX. The mean survival time of the mice treated with RGD-SSL-DOX, RGDm-SSL-DOX, and SSL-DOX was 55, 49, and 44 days, respectively. The three liposomal DOX formulations produced very close DOX accumulation in tumor, which is significantly higher than that of free DOX. RGD- or RGDm-SSL-DOX demonstrated prolonged circulation time similar to that of SSL-DOX, whereas they showed significantly lower DOX level in blood and remarkably higher uptake by spleen than SSL-DOX. Enhanced intracellular uptake of DOX encapsulated in SSL could produce an improved therapeutic effect for the melanoma B16 tumors. Enhancing intracellular delivery of the anticancer drugs encapsulated in SSL may be a promising strategy to improve their therapeutic efficacy for solid tumors.

Antitumor activity of combinations of anti-HER-2 antibody trastuzumab and oral fluoropyrimidines capecitabine/5'-dFUrd in human breast cancer models.

The anti-HER-2 antibody, trastuzumab (Herceptin), and the oral fluoropyrimidine, capecitabine (Xeloda), are both effective in breast cancer with different modes of action and toxicity profiles. Therefore, the efficacy in combination therapy of these agents for the treatment of HER-2-overexpressing breast cancer was of interest. An antagonistic interaction in vitro between trastuzumab and 5-fluorouracil (5-FUra) in combination has previously been reported. In the same study, the in vivo antitumor activity of this combination was investigated. However, the results were inconclusive since 5-FUra at the dose used had sufficient antitumor efficacy as a single agent and therefore it was not possible to clarify the potential difference between 5-FUra alone and the combination. In the present study, we investigated the efficacy of trastuzumab in combination with capecitabine or its intermediate metabolite 5'-dFUrd in HER-2-overexpressing human breast cancer cell lines and xenograft models. In vivo antitumor activity of the combination was at least additive, in terms of tumor growth inhibition and tumor growth delay, in human breast cancer models KPL-4 and BT-474. The combination treatment in vivo was superior to the treatment with either single agent alone, even though in vitro treatment with trastuzumab and 5'-dFUrd/5-FUra showed antagonistic antiproliferative activity in these cell lines. The reason for the discrepancy between the in vivo and in vitro results was not clarified. However, observed additive in vivo antitumor activity clearly indicates that the clinical efficacy of the combination of trastuzumab and capecitabine/5'-dFUrd against HER-2-overexpressing breast cancer is worth investigating.

Pharmacologic interactions between the resistance-modifying cyclosporine SDZ PSC 833 and etoposide (VP 16-213) enhance in vivo cytostatic activity and toxicity.

Cyclosporin A reverses multidrug resistance (MDR) and increases the in vivo cytostatic activity and toxicity of the anticancer agent etoposide (VP 16-213). SDZ PSC 833 (PSC 833), a non-immunosuppressive, non-toxic cyclosporin and very active modifier of P-gp 170-mediated MDR, elicits similar effects when administered with adriamycin. The underlying mechanisms, however, are not yet understood. The present pharmacological interaction study with PSC 833 and VP 16-213 was carried out to reveal the nature of this enhancement of cytostatic activity and toxicity. Rats pre-treated with either PSC-833 or solvent received a single dose of VP 16-213. Plasma levels of VP 16-213 were measured by high-performance liquid chromatography (HPLC). The resulting increase in cytostatic activity and toxicity of VP 16-213 mediated by PSC 833 was paralleled by marked changes in the pharmacokinetic parameters of VP 16-213 in vivo. Bioavailability and blood levels of VP 16-213 were significantly increased 30 min after administration if PSC 833 had been given before. The disappearance rate of VP 16-213 from the intravascular compartment was considerably slowed down by PSC 833. In drug-sensitive xenografts of human colon carcinoma, the PSC-833-induced pharmacologic changes in vivo could be counteracted by dose reduction of VP 16-213 while a full therapeutic potential was maintained. Doses of VP 16-213, 1.5 to 2 times smaller, combined with PSC 833, were as effective in terms of tumor-growth inhibition as the maximum tolerated dose of VP 16-213 alone. Thus, pharmacologic interactions between PSC 833 or other resistance modifiers and VP 16-213 and other cytostatic agents require careful attention if they are to be used in humans to overcome MDR.