Antitumor Effects of Combining Docetaxel (Taxotere) with the Antivascular Action of Ultrasound Stimulated Microbubbles

Ultrasound stimulated microbubbles (USMB) are being investigated for their potential to promote the uptake of anticancer agents into tumor tissue by exploiting their ability to enhance microvascular permeability. At sufficiently high ultrasound transmit amplitudes it has also recently been shown that USMB treatments can, on their own, induce vascular damage, shutdown blood flow, and inhibit tumor growth. The objective of this study is to examine the antitumor effects of ‘antivascular’ USMB treatments in conjunction with chemotherapy, which differs from previous work which has sought to enhance drug uptake with USMBs by increasing vascular permeability. Conceptually this is a strategy similar to combining vascular disrupting agents with a chemotherapy, and we have selected the taxane docetaxel (Taxotere) for evaluating this approach as it has previously been shown to have potent antitumor effects when combined with small molecule vascular disrupting agents. Experiments were conducted on PC3 tumors implanted in athymic mice. USMB treatments were performed at a frequency of 1 MHz employing sequences of 50 ms bursts (0.00024 duty cycle) at 1.65 MPa. USMB treatments were administered on a weekly basis for 4 weeks with docetaxel (DTX) being given intravenously at a dose level of 5 mg/kg. The USMB treatments, either alone or in combination with DTX, induced an acute reduction in tumor perfusion which was accompanied at the 24 hour point by significantly enhanced necrosis and apoptosis. Longitudinal experiments showed a modest prolongation in survival but no significant growth inhibition occurred in DTX–only and USMB-only treatment groups relative to control tumors. The combined USMB-DTX treatment group produced tumor shrinkage in weeks 4–6, and significant growth inhibition and survival prolongation relative to the control (p<0.001), USMB-only (p<0.01) and DTX-only treatment groups (p<0.01). These results suggest the potential of enhancing the antitumor activity of docetaxel by combining it with antivascular USMB effects.

Antitumor Effects of Combining Docetaxel (Taxotere) with the Antivascular Action of Ultrasound Stimulated Microbubbles

Ultrasound stimulated microbubbles (USMB) are being investigated for their potential to promote the uptake of anticancer agents into tumor tissue by exploiting their ability to enhance microvascular permeability. At sufficiently high ultrasound transmit amplitudes it has also recently been shown that USMB treatments can, on their own, induce vascular damage, shutdown blood flow, and inhibit tumor growth. The objective of this study is to examine the antitumor effects of ‘antivascular’ USMB treatments in conjunction with chemotherapy, which differs from previous work which has sought to enhance drug uptake with USMBs by increasing vascular permeability. Conceptually this is a strategy similar to combining vascular disrupting agents with a chemotherapy, and we have selected the taxane docetaxel (Taxotere) for evaluating this approach as it has previously been shown to have potent antitumor effects when combined with small molecule vascular disrupting agents. Experiments were conducted on PC3 tumors implanted in athymic mice. USMB treatments were performed at a frequency of 1 MHz employing sequences of 50 ms bursts (0.00024 duty cycle) at 1.65 MPa. USMB treatments were administered on a weekly basis for 4 weeks with docetaxel (DTX) being given intravenously at a dose level of 5 mg/kg. The USMB treatments, either alone or in combination with DTX, induced an acute reduction in tumor perfusion which was accompanied at the 24 hour point by significantly enhanced necrosis and apoptosis. Longitudinal experiments showed a modest prolongation in survival but no significant growth inhibition occurred in DTX–only and USMB-only treatment groups relative to control tumors. The combined USMB-DTX treatment group produced tumor shrinkage in weeks 4–6, and significant growth inhibition and survival prolongation relative to the control (p<0.001), USMB-only (p<0.01) and DTX-only treatment groups (p<0.01). These results suggest the potential of enhancing the antitumor activity of docetaxel by combining it with antivascular USMB effects.

Synthesis and Cytotoxic Activity of Several Novel N-Alkyl-Plinabulin Derivatives With Aryl Group Moieties

Seven novel N-alkyl-plinabulin derivatives with aryl groups moieties (nitroquinoline, 1,4-dihydroquinoline, 4-methoxybenzene, and 4-chlorobenzene) have been synthesized via aldol condensation and alkylation in one-pot, and tested for their cytotoxicity against 4 cancer cell lines (KB, HepG2, Lu, and MCF7). Compounds ( Z)−3-((6,8-dimethyl-4-oxo-1,4-dihydroquinolin-2-yl)methylene)−6-(( Z)−4-methoxybenzylidene)−1-(prop-2-yn-1-yl)piperazine-2,5-dione (5a), ( Z)−6-(( Z)−4-methoxybenzylidene)−1-(prop-2-yn-1-yl)−3-((1,6,8-trimethyl-4-oxo-1,4-dihydroquinolin-2-yl)methylene)piperazine-2,5-dione (5b), and ( Z)−3-(( Z)−4-chlorobenzylidene)−1,4-dimethyl-6-((8-methyl-4-nitroquinolin-2-yl)methylene)piperazine-2,5-dione (8) showed strong cytotoxicity against 3 of the cancer cells lines (KB, HepG2 and Lu) with IC50 values ranging from 3.04 to 10.62 µM. The quinoline-derived compounds had higher cytotoxic activity than the benzaldehyde derivatives. The successful synthesis of these derivatives offers useful information for the development of more potent vascular disrupting agents based on plinabulin.

Tumors Resistant to Checkpoint Inhibitors Can Become Sensitive after Treatment with Vascular Disrupting Agents

Immune therapy improves cancer outcomes, yet many patients do not respond. This pre-clinical study investigated whether vascular disrupting agents (VDAs) could convert an immune unresponsive tumor into a responder. CDF1 mice, with 200 mm3 C3H mammary carcinomas in the right rear foot, were intraperitoneally injected with combretastatin A-4 phosphate (CA4P), its A-1 analogue OXi4503, and/or checkpoint inhibitors (anti-PD-1, PD-L1, or CTLA-4 antibodies), administered twice weekly for two weeks. Using the endpoint of tumor growth time (TGT5; time to reach five times the starting volume), we found that none of the checkpoint inhibitors (10 mg/kg) had any effect on TGT5 compared to untreated controls. However, CA4P (100 mg/kg) or OXi4503 (5–50 mg/kg) did significantly increase TGT5. This further significantly increased by combining the VDAs with checkpoint inhibitors, but was dependent on the VDA, drug dose, and inhibitor. For CA4P, a significant increase was found when CA4P (100 mg/kg) was combined with anti-PD-L1, but not with the other two checkpoint inhibitors. With OXi4503 (50 mg/kg), a significant enhancement occurred when combined with anti-PD-L1 or anti-CTLA-4, but not anti-PD-1. We observed no significant improvement with lower OXi4503 doses (5–25 mg/kg) and anti-CTLA-4, although 30% of tumors were controlled at the 25 mg/kg dose. Histological assessment of CD4/CD8 expression actually showed decreased levels up to 10 days after treatment with OXi4503 (50 mg/kg). Thus, the non-immunogenic C3H mammary carcinoma was unresponsive to checkpoint inhibitors, but became responsive in mice treated with VDAs, although the mechanism remains unclear.

Predicting Clinical Efficacy of Vascular Disrupting Agents in Rodent Models of Primary and Secondary Liver Cancers: An Overview with Imaging-Histopathology Correlation

Vascular disrupting agents (VDAs) have entered clinical trials for over 15 years. As the leading VDA, combretastatin A4 phosphate (CA4P) has been evaluated in combination with chemotherapy and molecular targeting agents among patients with ovarian cancer, lung cancer and thyroid cancer, but still remains rarely explored in human liver cancers. To overcome tumor residues and regrowth after CA4P monotherapy, a novel dual targeting pan-anticancer theragnostic strategy, i.e., OncoCiDia, has been developed and shown promise previously in secondary liver tumor models. Animal model of primary liver cancer is time consuming to induce, but of value for more closely mimicking human liver cancers in terms of tumor angiogenesis, histopathological heterogeneity, cellular differentiation, tumor components, cancer progression and therapeutic response. Being increasingly adopted in VDA researches, multiparametric magnetic resonance imaging (MRI) provides imaging biomarkers to reflect in vivo tumor responses to drugs. In this article as a chapter of a doctoral thesis, we overview the construction and clinical relevance of primary and secondary liver cancer models in rodents. Target selection for CA4P therapy assisted by enhanced MRI using hepatobiliary contrast agents (CAs), and therapeutic efficacy evaluated by using MRI with a non-specific contrast agent, dynamic contrast enhanced (DCE) imaging, diffusion weighted imaging (DWI) are also described. We then summarize diverse responses among primary hepatocellular carcinomas (HCCs), secondary liver and pancreatic tumors to CA4P, which appeared to be related to tumor size, vascularity, and cellular differentiation. In general, imaging-histopathology correlation studies allow to conclude that CA4P tends to be more effective in secondary liver tumors and in more differentiated HCCs, but less effective in less differentiated HCCs and implanted pancreatic tumor. Notably, cirrhotic liver may be responsive to CA4P as well. All these could be instructive for future clinical trials of VDAs.