Sometimes our strength is our weakness…

Targeting cancer cells with their own weapon



     From a molecular point of view, every cancer is unique. Each one is equipped with a different set of mutations and abnormalities that drive oncogenic transformation. While these abnormalities give cancer cells the necessary tools for their survival, they also distinguish them from normal cells and serve as therapeutic targets. The chemotherapeutics used today mostly suffer from the destructive side effects on healthy tissues as a result of failure to selectively target tumor cells. As the Targeted Cancer Therapies laboratory, we aim to develop strategies to selectively kill cancer cells, using their own deficits as potential targets for cancer therapy. Towards this goal, we undertake different complementary approaches against the anomalies that cancer cells exhibit.

1- In cancer cells, asymmetric divisions with more than two poles are frequently observed which leaves the cells with abnormal numbers of chromosomes. In addition to gain of chromosomes triggering tumorigenesis, multipolar spindle (MPS) can also lead to deadly consequences by losing essential genetic material. MPS is strongly associated with an increase in centrosome number. In order to provide viable progeny, cancer cells adapted to extra numbers of centrosomes by forming pseudo-bipolar shaped spindles via a process called “centrosomal clustering”. Recently, the prevention of centrosomal coalescence became an active area of research, and novel drug candidates have been tested as a potential cancer therapy, specifically targeting mitotic cells exhibiting supernumerary centrosomes. Therefore, identifying the molecules involved in centrosomal clustering is one of our major goals.

Figure. Metaphase of cancer cells during mitosis; bipolar (A) and multipolar (B) metaphases (centrosomes; green, DNA; purple).



Nek2 is a mitotic kinase that plays a role in several processes including centrosome duplication and separation, spindle assembly checkpoint, kinetochore attachment, microtubule stabilization, and organization, all of which are is essential elements for faithful chromosome segregation. We have shown that whilst disruption of Nek2A reclusters centrosomes, and its overexpression leads to unclustering, but only in cancer cells with amplified centrosomes. Nek2A is frequently overexpressed in cancer cells and is associated with increased genomic instability in cells, as well as poorer prognosis and survival in cancer patients. At Koc University, we investigate how Nek2A accomplishes these tasks and whether interfering with its targets can reverse cancer cells’ clustering ability. Additionally, we aim to identify novel Nek2A targets via proximity end labeling followed by mass spectrometry and characterize their role in centrosomal clustering.

These projects are funded by TUBITAK 3501, L’oreal UNESCO, TUBA GEBIP, Science Academy BAGEP, Eczacibasi Holding and KUSOM.



Figure. 3D reconstruction of a confocal image of a cell undergoing abnormal mitosis (centrosomes; green, DNA; blue)
Figure. 3D reconstruction of a confocal image showing centrosome rosettes induced by Plk4
2- Despite the substantial advancement in chemotherapeutic strategies for cancer management, clinical drug resistance remains a major obstacle to successful treatment. One of the mechanisms that drive gene expression changes leading to oncogenic transformation or drug resistance is through epigenetic regulations. Inhibition of epigenetic factors through small molecules have been shown to promote growth arrest and cell differentiation or apoptosis. Not surprisingly, the FDA has approved several epigenetic inhibitors for the treatment of various malignancies including prostate cancer. The objective of our second major project is to understand drug resistance mechanisms in cancer cells and identify epigenetic modifiers that revert resistance through targeted screens. In our laboratory, we use prostate cancer cell models, where we generated isogenic drug-resistant cell lines against Docetaxel and Cabazitaxel (the first line chemotherapeutics for prostate cancer). As a strategy, we used both ‘Epigenetic Screening Library’, which contain a series of selective inhibitors of known epigenetic regulators, and CRISPR drop-out screens, which are generated by our group in collaboration with others to target ~800 epigenetic factors. Our studies identified the essential genes from both screens to revert taxane resistance in prostate cancer. Currently, we focus on the molecular mechanism of action of these modifiers and aim to understand whether we can target these proteins to revert resistance in vivo. These projects are funded by TUSEB, TUBITAK 1003, TUBITAK 3501 and Koc University Seed Funds.



A recently recognized strategy by which cancer cells escape killing, is the absorption of chemotherapeutic drugs by lysosomes followed by expulsion by lysosomal exocytosis. In the context of our ICGEB funded project, we proposed that the lysosomal drug flux is a significant burden on drug discovery and clinical use; therefore suppressing it will be impactful. To identify molecules that play a role in lysosome flux of cisplatin, we focused on the above-mentioned ‘Epigenetics Screening Library’. We identified epidrugs that 1-inhibit the lysosomal flux (which will be studied to answer whether they improve the frontline drug/cisplatin efficacy) or 2-facilitate the lysosomal flux (which will be used in conjunction with the currently available drugs and/or gene knockdown to reverse activation of lysosomal flux). Whether selected drugs that can resensitize cells to cisplatin will then be explored for their mechanism of action.

Another well-described factor in cisplatin resistance is the upregulation of ATP7B, which is a Cu‐transporting ATPase, playing a critical role in the maintenance of the copper balance in the body. ATP7B can transfer other metals in addition to Cu, such as platinum-based drugs, into the lysosome and detoxifying them through exocytosis. To date, there is very little information on the transcriptional regulation of ATP7B, as to which transcriptional regulators or epigenetic factors play a role in this process. The only known factor is MTF1 (Metal regulatory transcription factor 1), yet its expression does not always correlate with ATP7B expression in cancers, indicating other regulator proteins in its expression.  Therefore, with the aim of finding upstream regulators of ATP7B, we hypothesized that the expression of ATP7B protein is primarily controlled at the transcriptional level and regulated by proteins that bind to the promoter region. In our TUBITAK 1001 project, Genomic Locus Proteomics (GLoPro) approach is taken to observe which transcriptional factors bind to the ATP7B promoter and the candidate regulatory proteins will be tested for their effect on cisplatin resistance.