Next Generation Cancer Treatment: Targeting the Tumour Microenvironment

Holly -

Targeting the tumour microenvironment may enable patients to receive drugs which are as if not more effective, and have fewer side effects, when compared to traditional chemotherapeutic drugs. How do some of these new targeted therapeutics work?

Cancer is a group of over 100 diseases that involve abnormal, uncontrolled cell growth and division. The disease has the potential to spread to other parts of the body (metastasis) - distinguishing the conditions from benign tumours which stay localised to their area of formation. Whilst traditional treatments include surgery (physically removing the tumour), radiotherapy (killing cells by irreversibly damaging the DNA beyond repair with radiation) and chemotherapy (cytotoxic drugs that kill dividing cells), some drugs currently in clinical trials and development form a category known as targeted therapeutics. Targeted therapeutics identify specific molecular features of the tumour such as specific mutations or base sequences which enables them to exploit the Hallmarks of Cancer. Currently, these drugs are very expensive to develop and deliver - particularly due to the drugs generally only fitting very specific patient cohorts. However, the prospect of more personalised treatment with fewer severe side effects is very appealing to both healthcare professionals and patients.

Some targeted therapeutics are being developed to target the tumour microenvironment. So, what actually is the tumour microenvironment (TME)?

The tumour microenvironment is a dynamic area surrounding a tumour which contains many components including cells and vessels. When inflammation occurs due to oncogenic changes within cancer cells, the internal environment changes. This in turn leads to changes in the surrounding environment - the TME. Tumour cells predominantly display the Warburg phenotype (increased rate of glucose uptake, preferential production of lactate even in the presence of oxygen). However, many tumour cells are still able to use normal metabolic pathways as well as their own. The TME's ability to activate cancer cells even years into the dormancy of the tumour has been noted in many studies. Hence, understanding the TME, and ways in which we can target it, could lead to the development of new targeted therapeutic drugs in the future.

The tumour microenvironment is an immunosuppressive environment, meaning that it debilitates the anti-tumour immune responses through numerous methods, including the following:

  • Cancer associated fibroblasts: transfer cysteine, which is converted to glutathione. Glutathione inhibits oxidative stress, which in turn leads to increased resistance against some chemotherapy drugs.
  • Angiogenesis: the growth of blood vessels from the existing vessel network of the tumour. This is promoted by an increased concentration of lactate in the TME, which also has an effect on the signalling of cancer-associated endothelial cells.
  • Restriction of glucose to T cells (responsible for cell-mediated immunity): an increased concentration of lactate results in the disruption of proliferation of T cells, which in turn affects their function and results in the TME becoming more immunosuppressive.
  • Depletion of arginine (as a result of overexpression of the enzyme arginase): the breakdown of arginine and hence arginine depletion within the TME leads to unresponsive T cells, thus increasing the immunosuppressive nature of the TME even further.

As a result of the aforementioned, the TME can be shown to be influenced by tumour cells, leading to development of the tumour by promoting the immunosuppressive nature of its surrounding environment - in this sense, tumours could be seen as self-supporting.

Trabectedin: a targeted therapeutic drug isolated from an anti-neoplastic marine species?

Since targeted therapeutics targeting the TME are fairly new, their impact alone is not fully understood. However, studies are already showing that these drugs may be more effective when used in combination with conventional therapy treatments. What does this mean? Potentially low doses of both drugs, whilst still hitting a threshold to prevent growth of the tumours, which could reduce the chances of any severe side effects otherwise experienced.

Trabectedin was originally isolated from Ecteinoscida turbinata, an anti-neoplastic marine species; contemporarily it is prepared by chemical synthesis. Typically it is used to treat advanced cases of soft tissue sarcomas (STS). However, it has also been used to treat ovarian cancer in conjunction with doxorubicin (a traditional chemotherapy drug).

Figure 1: The structure of trabectedin, shown on the left - simplified to a hexagon with a T on one of its vertices for the rest of the figure. On the right, it is displayed next to a DNA molecule (diagram not to scale). Trabectedin binds specific triplet sequences within the minor groove of the DNA molecule, as indicated in the diagram where both the major and minor groove regions are labelled. However, part of trabectedin (here represented by the T) sticks out of the DNA molecule which leaves it free to interact with other molecules – mainly proteins such as RNA polymerase II.

As shown in Figure 1, trabectedin treats cancer by binding to the minor groove of DNA as a result of locating triplets within the DNA sequence that have a guanine (G) base in the middle of them. Trabectedin covalently binds to one of the two DNA strands and holds the other through hydrogen bonding and van der Waals forces. This:

  • blocks transcription through the stabilisation of the double stranded DNA molecule
  • inhibits the binding of transcription factors to the DNA molecule, thus preventing cells from replicating their DNA, and leading to the degradation of tumour cells via the proteasome pathway
  • interrupts RNA polymerase II during the elongation phase of transcription

Overall, the cells are most sensitive to trabectedin in the G1 phase of the cell cycle (GAP 1), but the drug arrests cells in the G2 and M phases (GAP 2, and mitosis). How was it shown that the microenvironment is the key for trabectedin's mechanism of action? Tumour cells were shown to be resistant to trabectedin in vitro (in cell cultures in petri dishes / in the lab), but sensitive in vivo in the mouse trials conducted - thus showing that only when the tumour microenvironment is present, the drug is effective.

Further developments... do analogues of trabectedin act in a similar way?

Currently, there are ongoing clinical trials involving lurbinectedin - an analogue of trabectedin! This means that the drugs are very similar, both chemically and pharmacologically. There is a very subtle difference in structure between the two which you will be able to identify if you closely observe the top left corner of each drug in Figures 1 and 2.  The mechanisms of action for the drugs are also similar with both targeting both the cancer itself, and the TME. However, lurbinectedin also interacts with mRNA and affects transcription which consequently affects protein production. There are 3 main mechanisms by which lurbinectedin acts as a targeted therapeutic that have been identified so far, as shown in Figure 2:

Figure 2: the chemical structure of lurbinectedin is shown on the left. On the right are three mechanisms used by lurbinectedin to inhibit tumour growth and hence treat cancer. 1: Lurbinectedin binds to a CG base pair rich sequence near to or in the promoter which causes the transcription factor to dissociate, thus preventing transcription. 2: Lurbinectedin binds near to RNA Polymerase II on the template strand, which also leads to transcription inhibition. 3: If both lurbinectedin and XPF (a protein) are present, nucleotide excision repair (NER) does not occur. Instead, breaks in either ssDNA or dsDNA can occur, ultimately leading to apoptosis.

As shown in Figure 2, lurbinectedin acts via 3 main mechanisms, namely:

  1. binding to a CG base pair rich sequence near to, or in, the promoter which leads to the inhibition of transcription as a result of causing the transcription factor to dissociate (transcription inhibition via this method is a common method targeted by chemotherapy drugs already)
  2. binding near to RNA polymerase II on the template strand, also leading to transcription inhibition - this form of inhibition is not so widely studied or known about yet
  3. lurbinectedin and the protein XPF are both present which prevents nucleotide excision repair, and instead leads to breaks in both single and double stranded DNA molecules, ultimately then leading to apoptosis (programmed cell death)

Other targeted therapeutics you may find interesting!

There are other targeted therapeutics that I have not touched on here which you may find interesting to look at, here are a couple of others:

  • herceptin: binds to the HER2 receptor which is overexpressed on abnormal HER2+ breast cancer cells
  • iressa (gefitinib): inhibits signalling via Her (EGF) receptors - mutations in EGFR receptor cells renders the cancer cells iressa-sensitive

I hope that through this article I've been able to outline some of the key ideas related to treating cancer using targeted therapeutics - particularly focusing on two drugs, trabectedin and lurbinectedin, the former of which is already being used to treat rare conditions such as soft tissue sarcomas. If you are interested in this area, feel free to ask questions in the "Any Questions?" page and I will reply as soon as possible! In the meantime, look out for another article related to this soon on caspase-8 - the possible link between the tumour and its microenvironment? Stay tuned for more!

References:

  • Acikgoz, E., Guven, U., Duzagac, F., Uslu, R., Kara, M., Soner, B. C. and Oktem, G. (2015) Enhanced G2/M Arrest, Caspase Related Apoptosis and Reduced E-Cadherin Dependent Intercellular Adhesion by Trabectedin in Prostate Cancer Stem Cells PLoSOne doi: 10.1371/journal.pone.014109
  • Ahmed, N., Escalona, R., Leung, D., Chan., E and Kannourakis., G. (2018) Tumour microenvironment and metabolic plasticity in cancer and cancer stem cells: Perspectives on metabolic and immune regulatory signatures in chemoresistantovarian cancer stem cells Seminars in Cancer Biology doi: 10.1016/j.semcancer.2018.10.002
  • Anderson, K.G., Stromnes, I.M. and Greenberg, P.D. (2017) Obstacles posed by the tumormicroenvironment to T cell activity: a case for synergistic therapies Cancer Cell doi: 10.1016/j.ccell.2017.02.008
  • Aune, G. J., Takagi, K., Sordet, O., Guirouilh-Barbat, J., Antony, S., Bohr, V. A. and Pommier, Y. (2008) Von Hippel-Lindau-coupled and transcription-coupled nucleotide excision repair-dependent degradation of RNA polymerase II in response to trabectedin Clinical Cancer Research doi: 10.1158/1078-0432.CCR-08-0730
  • Balkwill, F.R., Capasso, M. and Hagemann, T. (2012) The tumormicroenvironment at a glance Journal of Cell Science doi: 10.1242/jcs.116392
  • Belgiovine, C., Bello, E., Liguori, M., Craparotta, I., Mannarino, L., Paracchini, L., Beltrame, L., Marchini, S., Galmarini, C. M., Mantovani, A., Frapolli, R., Allavena, P. and D’Incalci, M. (2017) Lurbinectedin reduces tumour-associated macrophages and the inflammatory tumour microenvironment in preclinical models British Journal of Cancer doi: 10.1038/bjc.2017.205
  • Bensaude, O. (2011) Inhibiting eukaryotic transcription. Which compound to choose? How to evaluate its activity? Transcription doi: 10.4161/trns.2.3.16172
  • Bielenberg, D.R. and Zetter, B.R. (2015) The Contribution of Angiogenesis to the Process of Metastasis The Cancer Journal doi: 10.1097/PPO.0000000000000138
  • Bueren-Calabuig, J. A., Giraudon, C., Galmarini, C. M., Egly, J. M. and Gago, F. (2011) Temperature-induced melting of double-stranded DNA in the absence and presence of covalently bonded antitumour drugs: insight from molecular dynamics simulations Nucleic Acids Research doi: 10.1093/nar/gkr512
  • Choi, B-S., Martinez-Falero, I. C., Corset, C., Munder, M., Modolell, M., Müller, M. and Kropf, P. (2009) Differential impact of L-arginine deprivation on the activation and effector functions of T cells and macrophages Journal of Leukocyte Biology doi: 10.1189/jlb.0508310
  • Cuevas, C. and Francesch, A. (2009) Development of Yondelis(trabectedin, ET-743). A semisynthetic process solves the supply problem Natural Product Reports doi: 10.1039/b808331m
  • D’Incalci, M. and Galmarini, C. M. (2010) A Review of Trabectedin (ET-743): A Unique Mechanism of Action Molecular Cancer Therapeutics doi: 10.1158/1535-7163.MCT-10-0263
  • D’Incalci, M., Badri, N., Galmarini, C. M. and Allavena, P. (2014) Trabectedin, a drug acting on both cancer cells and the tumour microenvironment British Journal of Cancer doi: 10.1038/bjc.2014.149
  • Elez, M.E., Tabernero, J., Geary, D., Macarulla, T., Kang, S.P., Kahatt, C., Pita, A, S-M., Teruel, C.F., Siguero, M., Cullell-Young, M., Szyldergemajn, S. and Ratain, M.J. (2014) First-in-human phase I study of Lurbinectedin (PM01183) in patients with advanced solid tumorsClinical cancer research doi: 10.1158/1078-0432.CCR-13-1880
  • Farago, A.F., Drapkin, B.J., Lopez-Vilarinode Ramos, J.A., Galmarini, C.M., Núñez, R., Kahatt, C. and Paz-Are, L. (2019) ATLANTIS: a Phase III study of lurbinectedin/doxorubicin versus topotecan or cyclophosphamide/doxorubicin/vincristine in patients with small-cell lung cancer who have failed one prior platinum-containing line Future Oncology doi: 10.2217/fon-2018-0597
  • Forni, C., Minuzzo, M., Virdis, E., Tamboriini, E., Simone, M., Tavecchio, M., Erba, E., Grosso, F., Gronchi, A., Aman, P., Casali, P., D’Incali, M., Pilotti, S. and Mantovani, R. (2009) Trabectedin (ET-743) promotes differentiation in myxoid liposarcoma tumorsMolecular Cancer Therapeutics doi: 10.1158/1535-7163.MCT-08-0848
  • Germano, G., Frapolli, R., Belgiovine, C., Anselmo, A., Pesce, S., Liguori, M., Erba, E., Uboldi, S., Zucchetti, M., Paqualini, F., Nebuloni, M., van Rooijen, N., Mortarini, R., Beltrame, L., Marchini, S., Nerini, I. F., Sanfilippo, R., Casali, P. G., Pilotti, S., Galmarini, C. M., Anichini, A., Mantovani, A., D’Incalci, M. and Allavena, P. (2013) Role of macrophage targeting in the antitumor activity of trabectedin Cancer Cell doi: 10.1016/j.ccr.2013.01.008
  • Hurley, L. H. and Zewail-Foote, M. (2001) The antitumor agent ecteinascidin 743: Characterization of its covalent DNA adducts and chemical stability Advances in Experimental Medicine and Biology doi: 10.1007/978-1-4615-0667-6_46
  • Knowles, H. J. and Harris, A. L. (2007) Macrophages and the hypoxic tumour microenvironment Frontiers in Bioscience doi: 10.2741/2389
  • Kouidhi, S., Ayed, F. B. and Elgaaied, A. B. (2018) Targeting Tumor Metabolism: A New Challenge to Improve Immunotherapy Frontiers in Immunology doi: 10.3389/fimmu.2018.00353
  • Landskron, G., De la Fuente, M., Thuwajit, P., Thuwajit, C. and Hermoso, M.A. (2014) Chronic Inflammation and Cytokines in the TumorMicroenvironment Journal of Immunology Research doi: 10.1155/2014/149185
  • Moneo, V., Martinez, P., de Castro, B., Cascajares, S., Avila, S., Garcia-Fernandez, L.F. and Galmarini, C.M. (2014) Abstract A174: Comparison of the antitumor activity of Trabectedin, Lurbinectedin, Zalypsisand PM00128 in a panel of human cells deficient in transcription/NER repair factors Molecular Cancer Therapeutics doi: 10.1158/1535-7163.TARG-13-A174
  • Páez, D., Labonte, M.J., Bohanes, P., Zhang, W., Benhanim, L., Ning, Y., Wakatsuki, T., Loupakis, F. and Lenz, H-J. (2012) Cancer Dormancy: A Model of Early Dissemination and Late Cancer Recurrence Clinical Cancer Research doi: 10.1158/1078-0432.CCR-11-2186
  • Patra, J.K., Das, G., Fraceto, L.F., Campos, E.V.R., Rodriguez-Torres, M.dP., Acosta-Torres, L.S., Diaz-Torres, L.A., Grillo, R., Swamy, M.K., Sharma, S., Habtemariam, S. and Shin, H-S. (2018) Nano based drug delivery systems: recent developments and future prospects Journal of Nanobiotechnology doi: 10.1186/s12951-018-0392-8
  • Polet, F. and Feron, O. (2013) Endothelial cell metabolism and tumour angiogenesis: glucose and glutamine as essential fuels and lactate as the driving force Journal of Internal Medicine doi: 10.1111/joim.12016
  • Santamaría Nuñez, G., Robles, C.M.G., Giraudon, C., Martínez-Leal, J.F., Compe, E., Coin, F., Aviles, P., Galmarini, C.M. and Egly, J-M. (2016) Lurbinectedin Specifically Triggers the Degradation of Phosphorylated RNA Polymerase II and the Formation of DNA Breaks in Cancer Cells Molecular Cancer Therapeutics doi: 10.1158/1535-7613.MCT-16-0172
  • Tumini, E., Herrera-Moyano, E., Martín-Alonso, M.S., Barroso, S., Galmarini, C.M. and Aguilera, A. (2019) The Antitumor Drugs Trabectedin and Lurbinectedin Induce Transcription-Dependent Replication Stress and Genome Instability Molecular Cancer Research doi: 10.1158/1541-7786.MCR-18-0575
  • Végran, F., Boidot, R., Michiels, C., Sonveaux, P. and Feron, O. (2011) Lactate Influx through the Endothelial Cell Monocarboxylate Transporter MCT1 Supports an NF-KB/IL-8 Pathway that Drives TumorAngiogenesis Cancer Research doi: 10.1158/0008-5472.CAN-10-2828
  • Wermuth, C.G. (2006) Similarity in drugs: reflections on analogue design Drug Discovery Today doi: 10.1016/j.drudis.2006.02.006
  • Zhang, W., Trachootham, D., Liu, J., Chen, G., Pelicano, H., Garcia-Prieto, C., Lu, W., Burger, J. A., Croce, C. M., Plunkett, W., Keating, M.J. and Huang, P. (2012) Stromal control of cystine metabolism promotes cancer cell survival in chronic lymphocytic leukaemia Nature Cell Biology doi: 10.1038/ncb2432