Optimized anti-tumor effects of anthracyclines plus Vinca alkaloids using a novel, mechanism-based application schedule

Investigation of the effects of catharanthine and Q10 on Nrf2 and its association with MMP-9, MRP1, and Bcl-2 and apoptosis in a model of hepatocellular carcinoma

Since the role of Nrf2 in cancer cell survival has been highlighted, the pharmacological modulation of the Nrf2-Keap1 pathway may provide new opportunities for cancer treatment. This study purposed to use ubiquinone (Q10) as an antioxidant and catharanthine alkaloid as a cAMP inducer suppressing HepG2 cells by reducing Nrf2 level. The effects of Q10 and catharanthine on HepG2 cells in terms of viability were analyzed by MTT test. MTT results were used to determine the effective concentration of both drugs for the subsequent treatment and analysis. Subsequently, the effects of Q10 and catharanthine in a single and combined manner on oxidant/antioxidant status, apoptosis, metastasis, and drug resistance of HepG2 cells were investigated by related methods. Both Q10 and catharanthine decreased the level of oxidative stress products and increased antioxidant capacity in HepG2 cells. Nrf2 gene expression decreased by Q10, but catharanthine unexpectedly increased it. Following Nrf2 alterations, the expression levels of MMP-9 and MRP1 involved in metastasis and drug resistance were significantly and dose-dependently decreased by Q10, while catharanthine slightly increased both. However, both drugs increased caspase 3/7 activity and apoptosis rate, and the effect of Q10 on apoptosis was stronger than that of catharanthine. Most of the effects of the combination treatments were similar to those of the Q10 single treatment and indicated the dominant effect over the catharanthine component. Despite the antioxidant and apoptotic properties of both agents, Q10 was better than catharanthine in inducing apoptosis, counteracting drug resistance, and metastasis in HepG2 cells.

The International Natural Product Sciences Taskforce (INPST) and the power of Twitter networking exemplified through #INPST hashtag analysis

BACKGROUND

The development of digital technologies and the evolution of open innovation approaches have enabled the creation of diverse virtual organizations and enterprises coordinating their activities primarily online. The open innovation platform titled "International Natural Product Sciences Taskforce" (INPST) was established in 2018, to bring together in collaborative environment individuals and organizations interested in natural product scientific research, and to empower their interactions by using digital communication tools.

METHODS

In this work, we present a general overview of INPST activities and showcase the specific use of Twitter as a powerful networking tool that was used to host a one-week "2021 INPST Twitter Networking Event" (spanning from 31st May 2021 to 6th June 2021) based on the application of the Twitter hashtag #INPST.

RESULTS AND CONCLUSION

The use of this hashtag during the networking event period was analyzed with Symplur Signals (https://www.symplur.com/), revealing a total of 6,036 tweets, shared by 686 users, which generated a total of 65,004,773 impressions (views of the respective tweets). This networking event's achieved high visibility and participation rate showcases a convincing example of how this social media platform can be used as a highly effective tool to host virtual Twitter-based international biomedical research events.

Targeting TPC2 sensitizes acute lymphoblastic leukemia cells to chemotherapeutics by impairing lysosomal function

Despite novel therapy regimens and extensive research, chemoresistance remains a challenge in leukemia treatment. Of note, recent studies revealed lysosomes as regulators of cell death and chemotherapy response, suggesting this organelle is a novel target for chemosensitization. Interestingly, drug-resistant VCR-R CEM acute lymphoblastic leukemia (ALL) cells have an increased expression of the lysosomal cation channel Two-Pore-Channel 2 (TPC2) compared to drug-naïve CCRF-CEM ALL cells. Concurrently, knockout (KO) of TPC2 sensitized drug-resistant VCR-R CEM cells to treatment with cytostatics. The chemosensitizing effect could be confirmed in several cell lines as well as in heterogeneous, patient-derived xenograft ALL cells, using the pharmacological TPC2 inhibitors naringenin and tetrandrine. We reveal that a dual mechanism of action mediates chemo sensitization by loss of lysosomal TPC2 function. First, because of increased lysosomal pH, lysosomal drug sequestration is impaired, leading to an increased nuclear accumulation of doxorubicin and hence increased DNA damage. Second, lysosomes of TPC2 KO cells are more prone to lysosomal damage as a result of morphological changes and dysregulation of proteins influencing lysosomal stability. This leads to induction of lysosomal cell death (LCD), evident by increased cathepsin B levels in the cytosol, truncation of pro-apoptotic Bid, as well as the reversibility of cell death by co-treatment with the cathepsin B inhibitor CA-074Me in TPC2 KO cells. In summary, this study establishes TPC2 as a novel, promising, druggable target for combination therapy approaches in ALL to overcome chemoresistance, which could be exploited in the clinic in the future. Additionally, it unravels LCD signaling as an important death-inducing component upon loss of TPC2 function.

An overview on anti-tubulin agents for the treatment of lymphoma patients

Anti-tubulin agents constitute a large class of compounds with broad activity both in solid tumors and hematologic malignancies, due to the interference with microtubule dynamics. Since microtubules play crucial roles in the regulation of the mitotic spindles, the interference with their function usually leads to a block in cell division with arrest at the metaphase/anaphase junction of mitosis, followed to apoptosis. This explains the reason why tubulin-binding agents (TBAs) proved to be extremely active in patients with cancer. Several anti-tubulin agents are indicated in the treatment of patients with lymphomas both alone and in combination chemotherapy regimens. The article reviews the literature on classic and more recent anti-tubulin agents, providing an insight into their mechanisms of action and their use in the treatment of lymphoma.

STK405759 as a combination therapy with bortezomib or dexamethasone, in in vitro and in vivo multiple myeloma models

Multiple myeloma (MM) remains an incurable hematological malignancy. Combination regimens of conventional and novel drugs have improved patient’s survival. However, most patients inevitably relapse and become refractory to the current therapeutic armamentarium.

We investigated the efficacy of combining the microtubule-targeting agent STK405759 with dexamethasone or bortezomib in vitro and in vivo.

STK405759 combined with dexamethasone or bortezomib had synergistic cytotoxic activity in RPMIS, CAG and MM1.S human MM cell lines through activation of caspase 2, 3, 8, 9 and PARP. These treatments remained cytotoxic in the presence of bone marrow stroma cells. In other MM cells, including cells resistant to vincristine, melphalan, mitoxantrone or dexamethasone, these combinations decreased significantly survival as compared to single agents.

In in vivo studies, STK405759 disrupted existing blood vessels in xenograft tumors, acting not only as a cytotoxic agent but also as an anti-angiogenic drug. Mice treated with STK405759 in combination with dexamethasone or bortezomib resulted in greater tumor growth inhibition, increased overall response and prolonged survival as compared to as compared to BTZ or DEXA alone. Their anticancer activity was mediated by activation of apoptosis and reduction of tumor microvessel density.

These preclinical studies provide the rationale for future clinical trials of STK405759, dexamethasone and bortezomib combinations to improve the outcome of multiple myeloma patients.

Microtubule destabilising agents: far more than just antimitotic anticancer drugs

Vinca alkaloids have been approved as anticancer drugs for more than 50 years. They have been classified as cytotoxic chemotherapy drugs that act during cellular mitosis, enabling them to target fast growing cancer cells. With the evolution of cancer drug development there has been a shift towards new "targeted" therapies to avoid the side effects and general toxicities of "cytotoxic chemotherapies" such as the vinca alkaloids. Due to their original classification, many have overlooked the fact that vinca alkaloids, taxanes and related drugs do have a specific molecular target: tubulin. They continue to be some of the most effective anticancer drugs, perhaps because their actions upon the microtubule network extend far beyond the ability to halt cells in mitosis, and include the induction of apoptosis at all phases of the cell cycle. In this review, we highlight the numerous cellular consequences of disrupting microtubule dynamics, expanding the textbook knowledge of microtubule destabilising agents and providing novel opportunities for their use in cancer therapy.

Dual PI3K/mTOR inhibition shows antileukemic activity in MLL-rearranged acute myeloid leukemia

In acute myeloid leukemia (AML), several signaling pathways such as the phosphatidylinositol-3-kinase/AKT and the mammalian target of rapamycin (PI3K/AKT/mTOR) pathway are deregulated and constitutively activated as a consequence of genetic and cytogenetic abnormalities. We tested the effectiveness of PI3K/AKT/mTOR-targeting therapies and tried to identify alterations that associate with treatment sensitivity. By analyzing primary samples and cell lines, we observed a wide range of cytotoxic activity for inhibition of AKT (MK-2206), mTORC1 (rapamycin) and PI3K/mTORC1/2 (BEZ-235) with a high sensitivity of cells carrying an MLL rearrangement. In vivo PI3K/mTOR inhibition delayed tumor progression, reduced tumor load and prolonged survival in an MLL-AF9(+)/FLT3-ITD(+) xenograft mouse model. By performing targeted amplicon sequencing in 38 MLL-AF9(+) and 125 cytogenetically normal AML patient samples, we found a high additional mutation rate for genes involved in growth factor signaling in 79% of all MLL-AF9(+) samples, which could lead to a possible benefit of this cohort. PI3K/mTOR inhibition for 24 h led to the cross-activation of the ERK pathway. Further in vitro studies combining PI3K/mTOR and ERK pathway inhibition revealed highly synergistic effects in apoptosis assays. Our data implicate a possible therapeutic benefit of PI3K/mTOR inhibition in the MLL-mutated subgroup. Inhibiting rescue pathways could improve the therapeutic efficacy of PI3K-targeted therapies in AML.

Production of IL-1β by bone marrow-derived macrophages in response to chemotherapeutic drugs: synergistic effects of doxorubicin and vincristine

Cytotoxic chemotherapeutic drugs, especially when used in combination, are widely employed to treat a variety of cancers in patients but often lead to serious symptoms that negatively affect physical functioning and quality of life. There is compelling evidence that implicates cytotoxic chemotherapy-induced inflammation in the etiology of these symptoms. Because IL-1β plays a central role as an initiator cytokine in immune responses, we compared doxorubicin, a drug known to induce IL-1β production, with ten other commonly prescribed chemotherapeutic drugs in their ability to lead to processing and secretion of IL-1β by primary mouse macrophages. Seven of them (melphalan, cisplatin, vincristine, etoposide, paclitaxel, methotrexate, and cytarabine) caused the production of IL-1β in cells pretreated with lipopolysaccharide. When delivered in combination with doxorubicin, one of the drugs, vincristine, was also capable of synergistically activating the NLRP3-dependent inflammasome and increasing expression of IL-1β, IL-6, and CXCL1. The absence of TNF-α and IL-1 signaling caused a partial reduction in the production of mature IL-1β. Three small-molecule inhibitors known to suppress activity of kinases situated upstream of mitogen-activated kinases (MAPKs) inhibited the expression of IL-1β, IL-6, and CXCL1 when doxorubicin and vincristine were used singly or together, so specific kinase inhibitors may be useful in reducing inflammation in patients receiving chemotherapy.

Enhanced anti-tumour effects of Vinca alkaloids given separately from cytostatic therapies

BACKGROUND AND PURPOSE

In polychemotherapy protocols, that is for treatment of neuroblastoma and Ewing sarcoma, Vinca alkaloids and cell cycle-arresting drugs are usually administered on the same day. Here we studied whether this combination enables the optimal antitumour effects of Vinca alkaloids to be manifested.

EXPERIMENTAL APPROACH

Vinca alkaloids were tested in a preclinical mouse model in vivo and in vitro in combination with cell cycle-arresting drugs. Signalling pathways were characterized using RNA interference.

KEY RESULTS

In vitro, knockdown of cyclins significantly inhibited vincristine-induced cell death indicating, in accordance with previous findings, Vinca alkaloids require active cell cycling and M-phase transition for induction of cell death. In contrast, anthracyclines, irradiation and dexamethasone arrested the cell cycle and acted like cytostatic drugs. The combination of Vinca alkaloids with cytostatic therapeutics resulted in diminished cell death in 31 of 36 (86%) tumour cell lines. In a preclinical tumour model, anthracyclines significantly inhibited the antitumour effect of Vinca alkaloids in vivo. Antitumour effects of Vinca alkaloids in the presence of cytostatic drugs were restored by caffeine, which maintained active cell cycling, or by knockdown of p53, which prevented drug-induced cell cycle arrest. Therapeutically most important, optimal antitumour effects were obtained in vivo upon separating the application of Vinca alkaloids from cytostatic therapeutics.

CONCLUSION AND IMPLICATIONS

Clinical trials are required to prove whether Vinca alkaloids act more efficiently in cancer patients if they are applied uncoupled from cytostatic therapies. On a conceptual level, our data suggest the implementation of polychemotherapy protocols based on molecular mechanisms of drug-drug interactions.

LINKED ARTICLE

This article is commented on by Solary, pp 1555-1557 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12101.

Tubulin-targeting agent combination therapies: dosing schedule could matter

Tubulin-binding agents are potent cytotoxic drugs that are largely used to treat haematological malignancies and solid tumours. In this issue of British Journal of Pharmacology, doxorubicin was shown to decrease the activity of vincristine when administered simultaneously, unless cell cycle arrest mechanisms were disrupted. This observation emphasizes the need to better explore schedule-dependent antagonist effects in anticancer drug combination therapies.

LINKED ARTICLE

This article is a commentary on the research paper by Ehrhardt et al., pp. 1558-1569 of this issue. To view this paper visit http://dx.doi.org/10.1111/bph.12068.

Cell cycle-arrested tumor cells exhibit increased sensitivity towards TRAIL-induced apoptosis

Resting tumor cells represent a huge challenge during anticancer therapy due to their increased treatment resistance. TNF-related apoptosis-inducing ligand (TRAIL) is a putative future anticancer drug, currently in phases I and II clinical studies. We recently showed that TRAIL is able to target leukemia stem cell surrogates. Here, we tested the ability of TRAIL to target cell cycle-arrested tumor cells. Cell cycle arrest was induced in tumor cell lines and xenografted tumor cells in G0, G1 or G2 using cytotoxic drugs, phase-specific inhibitors or RNA interference against cyclinB and E. Biochemical or molecular arrest at any point of the cell cycle increased TRAIL-induced apoptosis. Accordingly, when cell cycle arrest was disabled by addition of caffeine, the antitumor activity of TRAIL was reduced. Most important for clinical translation, tumor cells from three children with B precursor or T cell acute lymphoblastic leukemia showed increased TRAIL-induced apoptosis upon knockdown of either cyclinB or cyclinE, arresting the cell cycle in G2 or G1, respectively. Taken together and in contrast to most conventional cytotoxic drugs, TRAIL exerts enhanced antitumor activity against cell cycle-arrested tumor cells. Therefore, TRAIL might represent an interesting drug to treat static-tumor disease, for example, during minimal residual disease.

Expression of cyclin A, B1 and D1 after induction of cell cycle arrest in the Jurkat cell line exposed to doxorubicin

Jurkat human lymphoblastoid cells were incubated in increasing concentrations of doxorubicin (0.05, 0.1 and 0.15 μM) to induce cell death, and their expression of cyclin A, B1 and D1 was evaluated by flow cytometry (cell cycle progression, Annexin V assay, percentages and levels of each of the cyclins), transmission electron microscopy (ultrastructure) and confocal fluorescence microscopy (expression and intracellular localization of cyclins). After low-dose doxorubicin treatment, Jurkat cells responded mainly by G2/M arrest, which was related to increased cyclin B1, A and D1 levels, a low level of apoptosis and/or mitotic catastrophe. The influence of doxorubicin on levels and/or localization of selected cyclins was confirmed, which may in turn contribute to the G2/M arrest induced by the drug.

Impact of the p53 status of tumor cells on extrinsic and intrinsic apoptosis signaling

Background

The p53 protein is the best studied target in human cancer. For decades, p53 has been believed to act mainly as a tumor suppressor and by transcriptional regulation. Only recently, the complex and diverse function of p53 has attracted more attention. Using several molecular approaches, we studied the impact of different p53 variants on extrinsic and intrinsic apoptosis signaling.

Results

We reproduced the previously published results within intrinsic apoptosis induction: while wild-type p53 promoted cell death, different p53 mutations reduced apoptosis sensitivity. The prediction of the impact of the p53 status on the extrinsic cell death induction was much more complex. The presence of p53 in tumor cell lines and primary xenograft tumor cells resulted in either augmented, unchanged or reduced cell death. The substitution of wild-type p53 by mutant p53 did not affect the extrinsic apoptosis inducing capacity.

Conclusions

In summary, we have identified a non-expected impact of p53 on extrinsic cell death induction. We suggest that the impact of the p53 status of tumor cells on extrinsic apoptosis signaling should be studied in detail especially in the context of therapeutic approaches that aim to restore p53 function to facilitate cell death via the extrinsic apoptosis pathway.

The RUNX1 transcription factor is expressed in serous epithelial ovarian carcinoma and contributes to cell proliferation, migration and invasion

Previously, we have identified the RUNX1 gene as hypomethylated and overexpressed in post-chemotherapy (CT) primary cultures derived from epithelial ovarian cancer (EOC) patients, when compared with primary cultures derived from matched primary (prior to CT) tumors. Here we show that RUNX1 displays a trend of hypomethylation, although not significant, in omental metastases compared with primary EOC tumors. Surprisingly, RUNX1 displayed significantly higher expression not only in metastatic tissue, but also in high-grade primary tumors and even in low malignant potential tumors. The RUNX1 expression levels were almost identical in primary tumors and omental metastases, suggesting that RUNX1 hypomethylation might have a limited impact on its overexpression in advanced (metastatic) stage of the disease. Knockdown of the RUNX1 expression in EOC cells led to sharp decrease of cell proliferation and induced G 1 cell cycle arrest. Moreover, RUNX1 suppression significantly inhibited EOC cell migration and invasion. Gene expression profiling and consecutive network and pathway analyses confirmed these findings, as numerous genes and pathways known previously to be implicated in ovarian tumorigenesis, including EOC tumor invasion and metastasis, were found to be downregulated upon RUNX1 suppression, while a number of pro-apoptotic genes and some EOC tumor suppressor genes were induced. Taken together, our data are indicative for a strong oncogenic potential of the RUNX1 gene in EOC progression and suggest that RUNX1 might be a novel EOC therapeutic target. Further studies are needed to more completely elucidate the functional implications of RUNX1 and other members of the RUNX gene family in ovarian tumorigenesis.

Shedding light on apoptosis at subcellular membranes

Regulation of apoptosis by Bcl-2 family proteins is a paradigm for complex protein-protein and protein-membrane systems. Elucidating the molecular mechanisms of these interactions in vitro in live cells and in animal studies has been significantly enhanced by using fluorescence techniques.

In vivo imaging enables high resolution preclinical trials on patients' leukemia cells growing in mice

Background

Xenograft mouse models represent helpful tools for preclinical studies on human tumors. For modeling the complexity of the human disease, primary tumor cells are by far superior to established cell lines. As qualified exemplary model, patients’ acute lymphoblastic leukemia cells reliably engraft in mice inducing orthotopic disseminated leukemia closely resembling the disease in men. Unfortunately, disease monitoring of acute lymphoblastic leukemia in mice is hampered by lack of a suitable readout parameter.

Design and Methods

Patients’ acute lymphoblastic leukemia cells were lentivirally transduced to express the membrane-bound form of Gaussia luciferase. In vivo imaging was established in individual patients’ leukemias and extensively validated.

Results

Bioluminescence in vivo imaging enabled reliable and continuous follow-up of individual mice. Light emission strictly correlated to post mortem quantification of leukemic burden and revealed a logarithmic, time and cell number dependent growth pattern. Imaging conveniently quantified frequencies of leukemia initiating cells in limiting dilution transplantation assays. Upon detecting a single leukemia cell within more than 10,000 bone marrow cells, imaging enabled monitoring minimal residual disease, time to tumor re-growth and relapse. Imaging quantified therapy effects precisely and with low variances, discriminating treatment failure from partial and complete responses.

Conclusions

For the first time, we characterized in detail how in vivo imaging reforms preclinical studies on patient-derived tumors upon increasing monitoring resolution. In the future, in vivo imaging will enable performing precise preclinical studies on a broad range of highly demanding clinical challenges, such as treatment failure, resistance in leukemia initiating cells, minimal residual disease and relapse.

RAD001 (everolimus) induces dose-dependent changes to cell cycle regulation and modifies the cell cycle response to vincristine

More than 50% of adults and ~20% of children with pre-B acute lymphoblastic leukemia (ALL) relapse following treatment. Dismal outcomes for patients with relapsed or refractory disease mandate novel approaches to therapy. We have previously shown that the combination of the mTOR inhibitor RAD001 (everolimus) and the chemotherapeutic agent vincristine increases the survival of non-obese diabetic/severe combined immuno-deficient (NOD/SCID) mice bearing human ALL xenografts. We have also shown that 16 μM RAD001 synergized with agents that cause DNA damage or microtubule disruption in pre-B ALL cells in vitro. Here, we demonstrate that RAD001 has dose-dependent effects on the cell cycle in ALL cells, with 1.5 μM RAD001 inhibiting pRb, Ki67 and PCNA expression and increasing G0/1 cell cycle arrest, whereas 16 μM RAD001 increases pRb, cyclin D1, Ki67 and PCNA, with no evidence of an accumulation of cells in G0/1. Transition from G2 into mitosis was promoted by 16 μM RAD001 with reduced phosphorylation of cdc2 in cells with 4 N DNA content. However, 16 μM RAD001 preferentially induced cell death in cells undergoing mitosis. When combined with vincristine, 16 μM RAD001 reduced the vincristine-induced accumulation of cells in mitosis, probably as a result of increased death in this population. Although 16 μM RAD001 weakly activated Chk1 and Chk2, it suppressed strong vincristine-induced activation of these cell cycle checkpoint regulators. We conclude that RAD001 enhances chemosensitivity at least in part through suppression of cell cycle checkpoint regulation in response to vincristine and increased progression from G2 into mitosis.

NOXA as critical mediator for drug combinations in polychemotherapy

During polychemotherapy, cytotoxic drugs are given in combinations to enhance their anti-tumor effectiveness. For most drug combinations, underlying signaling mechanisms responsible for positive drug-drug interactions remain elusive. Here, we prove a decisive role for the Bcl-2 family member NOXA to mediate cell death by certain drug combinations, even if drugs were combined which acted independently from NOXA, when given alone. In proof-of-principle studies, betulinic acid, doxorubicin and vincristine induced cell death in a p53- and NOXA-independent pathway involving mitochondrial pore formation, release of cytochrome c and caspase activation. In contrast, when betulinic acid was combined with either doxorubicine or vincristine, cell death signaling changed considerably; the drug combinations clearly depended on both p53 and NOXA. Similarly and of high clinical relevance, in patient-derived childhood acute leukemia samples the drug combinations, but not the single drugs depended on p53 and NOXA, as shown by RNA interference studies in patient-derived cells. Our data emphasize that NOXA represents an important target molecule for combinations of drugs that alone do not target NOXA. NOXA might have a special role in regulating apoptosis sensitivity in the complex interplay of polychemotherapy. Deciphering the differences in signaling of single drugs and drug combinations might enable designing highly effective novel polychemotherapy regimens.

Efficient RNA interference in patients' acute lymphoblastic leukemia cells amplified as xenografts in mice

Background

Signaling studies in cell lines are hampered by non-physiological alterations obtained in vitro. Physiologic primary tumor cells from patients with leukemia require passaging through immune-compromised mice for amplification. The aim was to enable molecular work in patients' ALL cells by establishing siRNA transfection into cells amplified in mice.

Results

We established delivering siRNA into these cells without affecting cell viability. Knockdown of single or multiple genes reduced constitutive or induced protein expression accompanied by marked signaling alterations.

Conclusion

Our novel technique allows using patient-derived tumor cells instead of cell lines for signaling studies in leukemia.