Introduction
A new type of viral pneumonia cases occurred in Wuhan, Hubei Province in China, on December 31, 2019; named ”COVID-19” on January 12, 2020 by the World Health Organization (WHO) [1]. Approximately, 292,893 people died as a result of the COVID-19 outbreak, 4,342,685 cases had been confirmed in 212 countries and territories till May 13, 2020. The fatality rate of COVID-19 remains under assessment [2]. However, infections of human coronavirus had resulted in lethal endemics, which include endemic SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) [3]. CoV infection begins with the interaction of the receptor binding domain located in the spike protein (S protein) and target receptor on the host cell surface, such as, Angiotensin Converting Enzyme 2 (ACE2) for SARS-CoV and Dipeptidyl Peptidase-4 (DPP4) for MERS-CoV [4]. Compared to SARS-CoV, the novel coronavirus (2019-nCoV) uses ACE2 as its host-entry receptor. Binding between the receptor-binding domain in S protein and the cellular receptor, mediates membrane fusion and starts the COVID-19 life cycle [5]. S protein on the viral membrane plays a critical role in virus entry and is the key antigenic factor responsible for inducing the immune response of the host [6]. For 2019-nCoV, in addition to knowing the COVID-19 Spike protein (S protein) sequences (GenBank: MN908947.3), there are no studies on how immunogenic this specific protein can go beyond surrogate comparisons to SARS and MERS, which restrict the possible capacity to generate a vaccine quickly [7]. Since it is a respiratory syndrome that has never been seen before and with the potential to spread extensively and rapidly, it gained the attention of the world but without the manual of treatment and management [8]. Several national and international research groups are working on vaccine production and drug repurposing to prevent and treat the 2019-nCoV, but successful vaccines and drugs are still not available. Active prevention and drug discoveries approaches for the 2019-nCoV outbreak are urgently needed [9, 10]. This review will offer an accumulate information to the scientific research community about numerous potential candidates of repurposable drugs that can provide a synergistic effect in potentially treating 2019-nCoV/SARS-CoV-2.