Promotion of tumor angiogenesis and growth induced by low-dose antineoplastic agents via bone-marrow-derived cells in tumor tissues.

Background: More research is needed to solidify the basis for reasonable metronomic chemotherapy regimens due to the inconsistent clinical outcomes from studies on metronomic chemotherapy with antineoplastic agents, along with signs of a nonlinear dose-response relationship at low doses. The present study therefore explored the dose-response relationships of representative antineoplastic agents in low dose ranges and their underlying mechanisms. Methods: Cyclophosphamide (CPA) and 5-fluorouracil (5-Fu) were employed to observe the effects of the frequent administration of low-dose antineoplastic agents on tumor growth, tumor angiogenesis, and bone-marrow-derived cell (BMDC) mobilization in mouse models. The effects of antineoplastic agents on tumor and endothelial cell functions with or without BMDCs were analyzed in vitro. Results: Tumor growth and metastasis were significantly promoted after the administration of CPA or 5-Fu at certain low dose ranges, and were accompanied by enhanced tumor angiogenesis and proangiogenic factor expression in tumor tissues, increased proangiogenic BMDC release in the circulating blood, and augmented proangiogenic BMDC retention in tumor tissues. Low concentrations of CPA or 5-Fu were found to significantly promote tumor cell migration and invasion, and enhance BMDC adhesion to endothelial cells in vitro. Conclusion: These results suggest that there are risks in empirical metronomic chemotherapy using low-dose antineoplastic agents and the optimal dosage and administration schedule of antineoplastic agents need to be determined through further research.

Dual­directional effect of vinorelbine combined with cisplatin or fluorouracil on tumor growth and metastasis in metronomic chemotherapy in breast cancer.

Metronomic chemotherapy (MCT) regimens may be associated with risks to the patient due to the ambiguity surrounding low dosages and schedules. In the present study, metronomic regimens of vinorelbine (NVB) combined with cisplatin (CDDP) or fluorouracil (5­FU) were chosen to study the dose­response associations with tumor growth and metastasis, along with the underlying mechanisms in angiogenesis, apoptosis and tumor immunity, using experimental techniques such as immunofluorescence, immunohistochemistry, western blotting and flow cytometry. The results demonstrated a dual­directional pharmacological action of promoting and suppressing tumor growth or metastasis in BALB/c mice bearing a 4T1 tumor at certain low and high doses of the drugs. Low doses of NVB combined with CDDP or 5­FU accelerated tumor growth by enhancing angiogenesis, increasing the expression of angiogenic proteins, NF­κB and osteopontin in tumor tissues, and inducing the accumulation of myeloid­derived suppressor cells and macrophages. By contrast, higher doses inhibited tumor growth by suppressing these effects. Notably, the upregulation of apoptotic proteins was observed after low­ and high­dose treatments. Furthermore, at low concentrations, NVB combined with CDDP or 5­FU stimulated certain functions of endothelial and tumor cells, including migration and invasion, whereas at higher concentrations they suppressed proliferation and induced apoptosis. Therefore, the results of the present study suggested the potential risks of metronomic combination chemotherapy by demonstrating that, at certain low doses, tumor growth or metastasis was promoted, and emphasized the existence of an effective dose interval that changes with different drug combinations. However, further studies are needed before a specific metronomic combination regimen can be administered clinically for cancer treatment.

Low-dose Cisplatin Induces Tumor Growth via Mobilization of Proangiogenic Bone Marrow-derived Cells in Mouse Models.

BACKGROUND/AIM: It is generally accepted that low-dose metronomic (LDM) chemotherapy mostly exerts its antitumor effects by inhibiting tumor angiogenesis. However, there is some evidence that LDM chemotherapy subsequently promotes tumor angiogenesis under certain regimens in animal models. The mechanisms responsible for these contradictory results are unclear. MATERIALS AND METHODS: Cisplatin (CDDP) was intraperitoneally administered to tumor-bearing mice at doses of 0.05-3 mg/kg every other day. The effects of LDM chemotherapy with CDDP on tumor growth and angiogenesis were observed. To determine the involved mechanisms, we analyzed the expression of vascular basement membrane proteins, transcription of angiogenesis-related genes in tumor tissues, and mobilization of proangiogenic bone marrow-derived cells (BMDCs) in circulating blood. RESULTS: The mean tumor weight with the 3 mg/kg q.o.d. regimen CDDP was significantly lower (by 57.3%) in the CDDP than in the control group. However, the tumor weight was 52.1% higher for the 0.19 mg/kg q.o.d. regimen in the CDDP group, which could be antagonized using 30 mg/kg all-trans retinoic acid. For the 0.19 mg/kg q.o.d., more tumor vascular structures were observed in the CDDP than in the control group (47.9±5.0 vs. 22.3±0.8, p<0.001). The mobilization of VEGFR2+ BMDCs and the mRNA expression of the proangiogenic genes MMP9, VEGFR1, VEGFR2 and VE-cadherin were increased in the 0.19 mg/kg regimen. CONCLUSION: These results indicate that metronomic CDDP promoted tumor angiogenesis and tumor growth via increased mobilization of proangiogenic BMDCs at certain low doses. This implies a potential therapeutic risk from an inappropriate LDM chemotherapy dosage and suggests that optimizing the LDM chemotherapy regimen is urgently needed.

Quantitative evaluation and pharmacokinetic characteristics of the irreversible BTK inhibitor zanubrutinib in mouse plasma using LC-MS/MS.

Zanubrutinib (BGB-3111) belongs to the class of irreversible inhibitors of Bruton's tyrosine kinase (BTK) for treating B-cell malignancies. A validated assay with excellent sensitivity, selectivity, and simplicity is required to measure plasma concentration and investigate its pharmacokinetics. The plasma of mice containing zanubrutinib and roxithromycin (internal standard) was processed with acetonitrile for protein precipitation. Then the supernatant was analyzed by high-performance liquid chromatography coupled with a triple quadrupole mass spectrometer using electrospray ionization in the positive mode. Zanubrutinib was given to mice intragastrically at 30 mg/kg to determine its pharmacokinetic parameters. The method was verified and showed good linearity in the range of 0.1-100 ng/mL. The method's sensitivity, accuracy, and precision were all within acceptable bounds. By this method, the pharmacokinetic profile of zanubrutinib in mouse plasma was measured.

Promotion of tumor progression induced by continuous low-dose administration of antineoplastic agent gemcitabine or gemcitabine combined with cisplatin.

MAJOR FINDING: This study observes a previously neglected pharmacological phenomenon and investigates its mechanism of that the continuous low-dose administration of some antineoplastic agents in certain dose ranges can promote tumorigenesis and tumor progression in vitro and in vivo, through stimulation of tumor cell functions directly as well as enhancement of tumor angiogenesis by BMDCs recruitment indirectly. The results alert to a potential risk in current empirically based continuous low-dose chemotherapy regimens such as metronomic chemotherapy. BACKGROUND AND OBJECTIVES: There are indications that certain antineoplastic agents at low dosages may exhibit abnormal pharmacological actions, such as promoting tumor growth. However, the phenomenon still needs to be further confirmed, and its underlying mechanisms have not yet been fully elucidated. METHODS: Gemcitabine (GEM) and cisplatin (CDDP) were employed as representative antineoplastic agents to observe effects of continuous low-dose chemotherapy with GEM or GEM combined with CDDP (GEM+CDDP) on tumor formation and growthin xenograft tumor models in vivo. Tumor and endothelial cell functions, apoptosis, cell cycle analysis, as well as bone marrow derived cells (BMDCs) mobilization, were evaluated with transwell, MTT or flow cytometry analysis in vitro, respectively. Histological methods were employed to assess angiogenesis in tumor tissues. RESULTS: The results showed that tumor formation and growth were both significantly promoted by GEM or GEM+CDDP at as low as half of the metronomic dosages, which were accompanied by enhancements of angiogenesis in tumor tissues and the release of proangiogenic BMDCs in the circulating blood. Additionally, GEM or GEM+CDDP at low concentrations dramatically facilitated the proliferation, migration, and invasion of tumor cells in vitro. Cell-cycle arrest, activation of associated apoptotic proteins, and inhibition of apoptosis were also observed in tumor cells. CONCLUSIONS: These findings indicate that, the continuous low-dose administration of GEM and GEM+CDDP can promote tumorigenesis and tumor progression in vivo by inhibiting apoptosis, mobilizing BMDCs, and promoting angiogenesis in certain dose ranges. These findings urge further investigations to avoid the potential risks in current empiric continuous low-dose chemotherapy regimens with antineoplastic agents.