Sylvia S. W. Ng

Taxane-Mediated Antiangiogenesis in Vitro Influence of Formulation Vehicles and Binding Proteins

Paclitaxel (Taxol) and docetaxel (Taxotere) have been shown to inhibit angiogenesis at low concentrations that do not affect cancer cell proliferation. Here, we used rat aortic rings and human umbilical vein endothelial cells to evaluate the influence of their formulation vehicles Cremophor EL and polysorbate 80, as well as serum binding proteins on taxane-mediated antiangiogenesis. The data show that clinically relevant concentrations of the vehicles and binding proteins nullify the antiangiogenic activity of both taxanes. It is suggested that these agents may need to be used at much higher doses than anticipated for effective antiangiogenic chemotherapy.

Influence of formulation vehicle on metronomic taxane chemotherapy: albumin-bound versus cremophor EL-based paclitaxel.

Purpose: Low-dose metronomic chemotherapy treatments, especially when combined with ‘dedicated’ antiangiogenic agents, can induce significant antitumor activity without serious toxicity in various preclinical models. It remains unclear, however, whether some cytotoxic drugs are better suited for metronomic regimens than others. Paclitaxel appears to be a strong candidate for metronomic chemotherapy given its ability to inhibit endothelial cell functions relevant to angiogenesis in vitro at extraordinarily low concentrations and broad-spectrum antitumor activity. Clinically relevant concentrations of the formulation vehicle cremophor EL in Taxol, however, were previously reported to nullify the antiangiogenic effect of paclitaxel, the result of which would hamper its usefulness in metronomic regimens. We hypothesized that ABI-007, a cremophor EL–free, albumin-bound, 130-nm form of paclitaxel, could potentially alleviate this problem. Experimental Design: The antiangiogenic activity of ABI-007 was assessed by multiple in vitro assays. The in vivo optimal dose of ABI-007 for metronomic chemotherapy was determined by measuring circulating endothelial progenitors in peripheral blood. The antitumor effects of metronomic and maximum tolerated dose ABI-007 and Taxol were then evaluated and compared in severe combined immunodeficient mice bearing human MDA-MD-231 breast cancer and PC3 prostate cancer xenografts. Results: ABI-007 significantly inhibited rat aortic microvessel outgrowth, human endothelial cell proliferation, and tube formation. The optimal metronomic dose of ABI-007 was determined to be between 3 and 10 mg/kg. Metronomic ABI-007 but not Taxol, significantly suppressed tumor growth in both xenograft models. Furthermore, the antitumor effect of minimally toxic metronomic ABI-007 approximated that of the maximum tolerated dose of Taxol. Conclusions: Our results underscore the influence of formulation vehicles on the selection of cytotoxic drugs for metronomic chemotherapy.

Antitumor Effects of Thalidomide Analogs in Human Prostate Cancer Xenografts Implanted in Immunodeficient Mice

Purpose: Thalidomide has demonstrated clinical activity in various malignancies including androgen-independent prostate cancer. The development of novel thalidomide analogs with better activity/toxicity profiles is an ongoing research effort. Our laboratory previously reported the in vitro antiangiogenic activity of the N-substituted thalidomide analog CPS11 and the tetrafluorinated analogs CPS45 and CPS49. The current study evaluated the therapeutic potential of these analogs in the treatment of prostate cancer in vivo. Experimental Design: Severely combined immunodeficient mice bearing s.c. human prostate cancer (PC3 or 22Rv1) xenografts were treated with the analogs at their maximum tolerated doses. Tumors were then excised and processed for ELISA and CD31 immunostaining to determine the levels of various angiogenic factors and microvessel density (MVD), respectively. Results: CPS11, CPS45, and CPS49 induced prominent and modest growth inhibition in PC3 and 22Rv1 tumors, respectively. Thalidomide had no effect on tumor growth in either xenograft. Vascular endothelial growth factor and basic fibroblast growth factor levels were not significantly altered by any of the thalidomide analogs or thalidomide in both PC3 and 22Rv1 tumors. CPS45, CPS49, and thalidomide significantly reduced PC3 tumor platelet-derived growth factor (PDGF)-AA levels by 58–82% (P < 0.05). Interestingly, treatment with the analogs and thalidomide resulted in differential down-regulation (≥1.5-fold) of genes encoding PDGF and PDGF receptor isoforms as determined by DNA microarray analysis. Intratumoral MVD of 22Rv1 xenografts was significantly decreased by CPS45 and CPS49. CPS49 also reduced MVD in PC3 xenografts. Conclusions: Thalidomide analogs CPS11 and 49 are promising anti-cancer agents. PDGF signaling pathway may be a potential target for these thalidomide analogs. Detailed microarray and functional analyses are under way with the aim of elucidating the molecular mechanism(s) of action of these thalidomide analogs.

Irinophore C, a Novel Nanoformulation of Irinotecan, Alters Tumor Vascular Function and Enhances the Distribution of 5-Fluorouracil and Doxorubicin

Purpose: To examine the antitumor effects of Irinophore C, a nanopharmaceutical formulation of irinotecan, on the tissue morphology and function of tumor vasculature in HT-29 human colorectal tumors. Experimental Design: Fluorescence microscopy was used to map and quantify changes in tissue density, tumor vasculature, hypoxia, and the distribution of Hoechst 33342, a perfusion marker, and the anticancer drug, doxorubicin. Noninvasive magnetic resonance imaging was used to quantify Ktrans, the volume transfer constant of a solute between the blood vessels and extracellular tissue compartment of the tumor, as a measure of vascular function. Following treatment with Irinophore C, 19F magnetic resonance spectroscopy was used to monitor the delivery of 5-fluorouracil (5-FU) to the tumor tissue, whereas scintigraphy was used to quantify the presence of bound [14C]5-FU. Results: Irinophore C decreased cell density (P = 8.42 × 10−5), the overall number of endothelial cells in the entire section (P = 0.014), tumor hypoxia (P = 5.32 × 10−9), and Ktrans (P = 0.050). However, treatment increased the ratio of endothelial cells to cell density (P = 0.00024) and the accumulation of Hoechst 33342 (P = 0.022), doxorubicin (P = 0.243 × 10−5), and 5-FU (P = 0.0002) in the tumor. Vascular endothelial growth factor and interleukin-8, two proangiogenic factors, were down-regulated, whereas the antiangiogenic factor TIMP-1 was up-regulated in Irinophore C-treated tumors. Conclusions: Irinophore C treatment improves the vascular function of the tumor, thereby reducing tumor hypoxia and increasing the delivery and accumulation of a second drug. Reducing hypoxia would enhance radiotherapy, whereas improving delivery of a second drug to the tumor should result in higher cell kill.

Report from the Society for Biological Therapy and Vascular Biology Faculty of the NCI Workshop on Angiogenesis Monitoring

The field of tumor angiogenesis has seen explosive growth over the last 5 years. Preclinical as well as early clinical evaluation of novel compounds is progressing at a rapid pace. To gain a perspective on the field and to take stock of advances in the understanding of molecular mechanisms underlying the process of tumor angiogenesis as well as ways of monitoring the activity of agents, the Society for Biologic Therapy and the National Cancer Institutes Vascular Biology Faculty convened a Workshop on Angiogenesis Monitoring in November 2002. The Workshop was composed of invited speakers and participants from academia, industry, and government. It was divided into 3 sessions, each chaired by leaders in the field. The first focused on advances in the understanding of the cellular and molecular mechanisms of angiogenesis in tumors. The second examined preclinical assay systems that are useful in vascular biology. The third addressed the translation to the clinic and monitoring of antiangiogenic activity of agents in patients and novel trial designs. What follows is a summary of the discussions and findings of each session.

Upregulation of endogenous angiogenesis inhibitors: A mechanism of action of metronomic chemotherapy

Antiangiogenic or metronomic chemotherapy, the frequent administration of conventional cytotoxic agents at low doses, is believed to target activated tumor endothelial cells. The mechanisms of action of such regimen remain poorly understood. In the March 2004 issue of Cancer Research, Hamano et al. demonstrated that low-dose cyclophosphamide inhibits tumor growth by upregulating the endogenous angiogenesis inhibitor thrombospondin-1 in tumor and perivascular cells. Thrombospondin-1, in turn, promotes endothelial cell apoptosis. It was also proposed that thrombospondin-1 levels might be used as a surrogate marker to monitor response to low-dose cyclophosphamide therapy in the clinic.

Assessment of vessel size by MRI in an orthotopic model of human pancreatic cancer

Pancreatic cancer is a devastating disease with no cure. Therapies that target the tumor vasculature are promising new treatment strategies. Magnetic resonance imaging (MRI) can non-invasively determine a vessel size index and a blood volume fraction to characterize the vascular compartment in a tumor. The changes in the T2 and T2* relaxation rate constants after the administration of superparamagnetic iron oxide (SPIO) particles are dependent on the size and morphology of tissue blood vessels. In this study, MRI was used to investigate changes in the tumor vesculature in an orthotopic primary human pancreatic cancer xenograft model during tumor progression. The SPIO contrast agent Feridex I.V. was first validated as an intravascular contrast agent over the course of the imaging session, and shown to remain in the blood for at least 1.5 h. The average vessel size index was not correlated to the tumor area within an image slice, but the average blood volume fraction was significantly and negatively correlated to the tumor area (p<0.05). Blood volume fraction may serve as a non-invasive biomerker for changes in the tumor vasculature due to tumor growth Further investigation is needed to evaluate this promising technique as a tool to monitor tumor vascular changes in response to sntiengiogenic therapies in pancreatic cancer.

Antiangiogenesis therapeutic strategies in prostate cancer

It is now well documented that tumor progression from its early stages to an advanced metastatic state requires the recruitment of new vasculature. The reliance on angiogenesis by tumors renders them susceptible to agents that can interfere with the angiogenic process. Recent interest in the therapeutic potential of using angiogenesis as a target mechanism for anticancer therapy has led to the identification of various antiangiogenic agents that interfere at various stages of the process. This review is a summary of recent progress in the identification and characterization of antiangiogenesis agents with a focus on their utility with respect to prostate cancer. Though we focus on prostate cancer, this knowledge is relevant to any cancer that involves angiogenesis.

Abstract 3661: Vascular changes and potentiating secondary drug delivery in colorectal cancer with Irinophore C

Introduction: Colorectal cancer is the third most common cancer in the world. The predominant chemotherapeutic treatment in CRC is a combination of 5-fluorouracil (5-FU) and irinotecan (CPT-11). However, the combination is limited by toxicity and resistance. We now report on the effects of 5-FU in combination with a liposomal formulation of CPT-11, Irinophore C, that is more efficacious and less toxic than free CPT-11. Materials and Methods: 5-FU was used singly and in combination with Irinophore C in a subcutaneous model of colorectal cancer, HT-29, to assess therapeutic efficacy and toxic effects. 5-FU and Irinophore C (40mg/kg) were injected intravenously on a Q7Dx3 schedule, and tumor growth delay was measured. In a subsequent study, a single bolus injection of 14 C-spiked 5-FU was delivered at different timepoints during Irinophore C (tritium-labeled) or saline treatment (Q7Dx3), and the accumulation of 5-FU in tumor tissue measured with scintigraphy. Tumors were also harvested and snap-frozen at early (days 1 - 7) and late (days 14 and 21) time points following Irinophore C treatment. Cryosections were subsequently examined for perfusion using the fluorescent dye Hoechst 33342, stained for apoptosis (TUNEL), CD31, CD105, Collagen IV and with HE 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3661.