Investigating the role of PARP-1 and GCS inhibitors in cisplatin sensitive ovarian cancer cells

Back

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, 5–6% 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].