Summer Research Fellowship Programme of India's Science Academies 2017
Investigating the role of PARP-1 and GCS inhibitors
in cisplatin sensitive ovarian cancer cells
Harshdeep Kaur
Sri Venkateswara College, University of Delhi
Guided by
Dr. Lalit Kumar
Department of Medical Oncology, Dr. B.R. Ambedkar Institute of Rotary Cancer Hospital
(IRCH), All India Institute of Medical Sciences (AIIMS), New Delhi
1. Introduction
Gynaecological cancers are among the most common cancers in women and hence an
important public health issue. Ovarian cancer is the second leading cause of death from
gynaecological malignancies in women in India [1]. On the basis of cell of origin, OC is
classified into three types epithelial, germline, and stromal. Approximately 90% of primary
malignant ovarian tumours arise from ovarian surface epithelium and categorised as serous,
mucinous, endometrioid, clear cell, transitional, and undifferentiated type [2,3].
OC is a ‘silent killer’ as majority of the patients are diagnosed at late stage due to lack of
evident symptoms and effective screening facilities in developing countries such as India,
adversely affecting the prognosis and clinical outcomes. Ultrasonography and CA 125 testing
are two major ovarian cancer screening modalities. Surgery is the primary treatment for OC. It
is used for staging and cytoreduction (debulking), but it is potentially curative in disease
confined to the ovaries.
The current treatment for epithelial ovarian cancer (EOC) includes- primary surgery followed
by adjuvant paclitaxel plus platinum based chemotherapy. Chemotherapy plays a major role in
ovarian cancer therapeutics and disease management. Among the presently used anticancer
drugs, the most effective and widely used is Cisplatin. Its effectiveness is due to its unique
property of entering the cells and damaging the DNA by forming multiple DNA-platinum
adducts, which form intrastrand cross links that activate the apoptotic pathway, resulting in cell
death. It is observed that patients usually have good initial response to cisplatin but later
relapse, because of development of cisplatin resistance [4]. Resistance, a major drawback in
cisplatin based chemotherapy, can arise due to various causes which include poor uptake, rapid
efflux of drug or active role of the DNA repair enzymes. To overcome this obstacle, targeted
therapies are being developed.
Poly (ADP-ribose) polymerase (PARP) is a family of proteins implicated in DNA damage
response by activating Base excision repair (BER) pathway. PARP-1 is the most important
member which is involved in DNA repair, genomic stability, inflammation and cell death. It is
a highly conserved zinc binding protein and uses NAD+ as a substrate during DNA repair. The
inhibition of PARP-1 using pharmacological agents can lead to accumulation of single strand
breaks which will progress to double-strand breaks during cellular replication. The cells are
then unable to efficiently repair the DNA, leading to cell death. Therefore, PARP inhibitors
(PARPi) like PJ34 are a promising class of chemotherapeutic agents in cancers associated with
resistance and recurrence, especially in ovarian cancer [5].
Another targeted molecule to overcome platinum resistance is Glutathione because it is
observed that resistance is essentially linear with cellular levels of GSH [6]. GSH is a tripeptide
which participates in antioxidant defense mechanism. Its major function is detoxification of
xenobiotics, some endogenous compounds and regulating oxidative stress. Proxidant therapies
including chemotherapeutic agents adds oxidative stimulus to constitutive oxidative stress in
tumor cells, causing collapse of antioxidant systems, leading to cell death. But high levels of
GSH- related enzymes, such as ɣ-glutamylcysteine ligase (GCL) and ɣ-glutamyl-
transpeptidase (GGT) makes neoplastic tissues resistant to chemotherapy. Therefore, GSH-
depleting agents like buthionine sulfoximine (BSO) can be used to sensitize cancer cells to
chemotherapy [7].
OV-SAHO cell line were used in the study and treated with different concentrations of CDDP
and PJ34. OV-SAHO cells are immortal human ovarian cancer cells derived from a Japanese
women with stage IIIc adenocarcinoma. Cell lines are used to study nature of the disease, the
effect of drugs, developing vaccines etc. The development of cell lines has made a tremendous
impact in the medical and biological research.
The aim of this project is to determine the inhibitory concentration of cytotoxic drugs CDDP
and PJ34 in vitro.
2. Review of literature
2.1. Epidemiology of ovarian cancer
Ovarian carcinomas are heterogenous group of neoplasms responsible for 6% death in women.
According to Globocan, it is the seventh most commonly diagnosed cancer among women in
the world and the fourth most common in India. Although India has a relatively low incidence
rate (4.9 per 100,000), the large population translates to an estimated 26,834 new incidences
and 19,549 related deaths in 2012 [1]. Despite the high mortality rates, the etiology of this
disease is poorly understood. A woman’s lifetime risk of developing OC is 1 in 75. One of the
most significant risk factors for OC is family history of the disease [8,9]. Women with inherited
mutations in BRCA1 and BRCA2 are at significantly higher risk of developing breast and
ovarian cancer. Data from the Breast Cancer Linkage Consortium suggest that the risk of OC
through 70 years of age is up to 44% inBRCA1 families and approaches 27% in
BRCA2 families. Other hormonal, lifestyle and environmental factors contributing to this
disease include early menarche, infertility, PCOS and pre- menopausal obesity, exposure to
asbestos [8].
2.2. Classification and prognosis
Nearly all benign and malignant ovarian tumors originate from one of three cell types:
epithelial cells, stromal cells, and germ cell. More than 90% of malignant ovarian tumors are
epithelial in origin, 56% constitute stromal tumors and 2–3% are germ cell tumours [10].
Carcinomas comprise of five main histotypes: high-grade serous (70%), endometrioid (10%),
clear cell (10%), mucinous (3%) and low grade serious (<5%) [11,12]. Fatality due to OC is
high due to difficulty in early diagnosis and limited effective treatment options. The disease is
typically diagnosed at late stage (FIGO IV) when the 5-year relative survival rate is only 29%.
Few cases (15%) are diagnosed with localized tumor (FIGO stage 1) when the 5-year survival
rate is 92% [13].