AN INSIGHT ON MEDICINAL ATTRIBUTES OF PHTHALAZINE SCAFFOLD, WITH A FOCUS ON THEIR ANTICANCER PROPERTIES AS VEGFR-2 INHIBITORS

: The antitumor properties of synthetic heterocyclic compounds are among the most powerful properties that can be made use in medicinal chemistry. More specifically, their significant cytotoxic effects against many types of human tumor cells, as well as their roles as various kinase inhibitors. In recent years, Phthalazine derivatives, have frequently attracted the interest of medicinal chemistry researchers due to their promising anticancer properties. The present study is a review of the latest advances in Phthalazine derivative-related research, with a focus on their anticancer activities as VEGFR-2 inhibitors.


Introduction:
Cancer is the rapid creation of abnormal cells that grow beyond their usual limits, which can then invade adjoining parts of the body and spread to other organs, this process is referred to as metastasizing (C.C. Harris, 1993).Cells reproduce by a series of well arranged events where cellular macromolecular contents are duplicated, followed by division into two daughter cells.Dividing cells pass through four distinct phases during the cell cycle (Cheeseman & Desai, 2008).The G 1 -phase where cells increase in size and prepare to copy their DNA.Then, The S-phase during which DNA is replicated (S for DNA synthesis).The G 2 -phase during which cells further grow.Mphase when chromosomes separate, and cells divide (M for mitosis).After one cycle, the daughter cells can continue to enter a new cycle, enter G 0 phase or become terminally differentiated (Sui et al., 2023).Cancer arises from the transformation of normal cells into malignant cells in a multistage process that generally progresses from a pre-cancerous lesion to a malignant tumour (Colditz, Sellers, & Trapido, 2006) .Current cancer therapies include four major types: surgery, radiotherapy immunotherapy, and chemotherapy.Chemotherapy can be used alone, but is usually used in combined therapy modalities, along with surgery and/or radiotherapy, to achieve and maintain remission.The aim of chemotherapy is to completely eradicate disease.Tumors nevertheless commonly relapse, and such relapses may occur locally or at a distance (metastasis) from the primary tumor site (Schirrmacher, 2019).

Chemotherapeutic agents
The history o f chemotherapy traces back to medical observations in World War 1 where soldiers who were exposed to chemical warfare (Sulphur Mustard), suffered from lowering of their white blood cells, especially lymphocytes.Since the discovery of the toxic action of nitrogen mustards on blood cells, many chemotherapeutic agents have been discovered by screening the cytotoxic potency of a large number compounds in vitro or in vivo models (Abotaleb et al., 2018).

They are generally classified according to their mechanism of action into:
2.1.Alkylating agents, this type of drugs are cell cycle-nonspecific agents, they cause cell death by cross-linking DNA strands ,which result in inhibition of DNA, RNA and protein synthesis.It includes, nitrogen Mustards (Cyclophosphamide), Alkyl Sulphonates (Busulfan), Nitrosureas (Carmustine), and Platinum Agents (Cisplatin) (Warwick, 1963).
2.2.Antimetabolites,they have structural similarities to natural existing substances, such as Vitamins, nucleosides or amino acids.They mainly comprise folic acid antagonists ,pyrimidine analogues and purine analogues.They act by competing with natural substrates for the active site on receptors.Some antimetabolites are incorporated directly into DNA or RNA, resulting in inhibition of DNA, RNA and protein synthesis (Kaye, 1998).It includes, Purine analogues (Azathioprine), pyrimidine analogues (5-Fluorouracil, 5-FU), and antifolate (Methotrexate, MTX) (Alam et al., 2018).
2.3.Topoisomerase Inhibitors, there are two classes in topoisomerase Inhibitors: Topoisomerase I inhibitors and Topoisomerase II inhibitors.They are involved in all DNA synthesis, such as DNA replication, transcription, recombination, and chromosome condensation.Inhibition of topoisomerase results in induction of DNA strand breaks and inhibition of cell proliferation.This class of drugs are cell cyclespecific and prevent cells from entering mitosis (Ewesuedo & Ratain, 1997).It includes, topoisomerase I inhibitor (Topotecan), Topoisomerase II inhibitors (Doxorubicin) (Gelderblom & Sparreboom, 2007).2.5.Anti-microtubule agents, Vinca alkaloids and Taxoids are the two main groups of anti-microtubule agents.Although both types of agents cause microtubule dysfunction, resulting in blocking of cell division, they have opposite mechanisms of action.The Vinca alkaloids prevent the polymerization of the microtubules, whereas Taxoids prevent microtubule depolymerization.Examples for this class includes: -Vincristine and Paclitaxel, PTX (Florian & Mitchison, 2016).

Hormone therapy, the principle hormonal treatments available are Selective
Estrogen Receptor Modulators (SERMS) and Selective Androgen Receptor Modulators (SARMS).Their basic principle is to prevent the hormone signals that contribute to cancer cell growth.Tamoxifen (Nolvadex®) was the first SERM to be widely used.SERMS mechanism of action lies in their binding to the estrogen receptor and thereby inducing a conformational change.Its major drawback is that it has an estrogenic effect in endometrial tissue.The next generation of SERMS such as Raloxifene (Evista®) do not display this estrogenic effect.SARMS such as flutamide (Eulexin®) work by binding preferentially to androgen receptors on the cancer cell thereby blocking the binding of Testosterone and Dihydroxytestosterone (DHT).Other important hormone-based therapies include Luteinising Hormone-Releasing Hormone (LHRH) agonists which are used in the treatment of prostate cancer.These include peptides such as Leuprolide, Goserelin, and Buserelin (Johnston & Cheung, 2018).

Protein kinases inhibitors, Protein kinases (PKs) catalyze phosphorylation of different cellular substrates. Phosphorylation in turn regulates various cellular functions.
Normally, their activity is stringently regulated.However, under pathological conditions, PKs can be deregulated, leading to alterations in the phosphorylation, resulting in uncontrolled cell division, apoptosis inhibition and consequently tumor.Various cancers and other diseases are known to be caused or accompanied by deregulation of the phosphorylation.Inhibition of PKs has been shown to be a promising therapeutic strategy for treatment of cancer (Shchemelinin, Sefc, & Necas, 2006).Tyrosine kinases are primarily classified as: i) receptor tyrosine kinase (RTK) (e.g., EGFR, VEGFR, FGFR and ILGFR).They are not only cell surface transmembrane receptors but are also enzymes having kinase activity.So that, they are activated by ligand binding to the extracellular domain (Hunter, 1995;Schlessinger, 2000).ii) Non-receptor tyrosine kinase (NRTK) (e.g., SRC, ABL, FAK and Janus kinase).They are cytoplasmic proteins, exhibiting considerable structural variability (Schenk & Snaar-Jagalska, 1999).VEGFR-2 is the major regulator of VEGF-driven responses in endothelial cells, including permeability, proliferation, invasion, and migration.Moreover, it is considered to be a crucial signal transducer in both physiologic and pathologic angiogenesis.VEGFR-2 is over-expressed in several malignancies, including hepatocellular carcinoma, breast, colorectal, ovarian and thyroid cancer, melanoma and medulloblastoma (Gershtein, Dubova, Shchegolev, & Kushkinskii, 2010;Otrock, Makarem, & Shamseddine, 2007;Smith et al., 2010).Thence, the discovery of small molecule inhibitors that block the autophosphorylation of VEGFR-2 arises as a prime target for discovering therapies for many human malignancies.

Phthalazine derivatives,
Vatalanib 9 is being developed by Bayer Schering and Novartis.It inhibits all known VEGF receptors, as well as platelet-derived growth factor receptor-beta and c-kit but is most selective for VEGFR-2.Vatalanib was one of the earliest VEGFR2 inhibitors used for wet AMD.Vatalanib was reported that oral vatalanib was being evaluated for safety and efficacy in patients with subfoveal CNV at doses of 500 and 100 mg/day (Zaib & Khan, 2020).Also, telatinib 10, the furopyridazine derivative, emerged as a potent and orally available inhibitor of VEGFR-2, VEGFR-3 with IC50s 6 and 4 nM, respectively.It is currently in clinical trials for gastric and colorectal cancer (SalwaElmeligie, Aboul-Magd, Lasheen, & Abouzid, 2018).
In 2016 et al, synthesized phthalazine-based derivatives linked to abiarylamide or biarylurea tail to position 1 of the phthalazine core via an amino or ether linkage have been designed and synthesized as VEGFR-2 kinase inhibitors 16 and 17 (Elmeligie, 2016).In 2017 El-Hashash et al, synthesized new series of Phthalazine derivatives with anti-tumor activity 18 and 19 (El-Hashash et al., 2017).
In 2021, Khedr et al, designed compounds with a new linker was inserted in the form of fragments with verified VEGFR-2 inhibitory potential, including an α,β-unsaturated ketonic fragment, pyrazole, and pyrimidine.Also, new distal hydrophobic moieties were attached to these linkers that are expected to increase the hydrophobic interaction with VEGFR-2, 27-30 (Khedr, Ibrahim, Eissa, Abulkhair, & El-Adl, 2021).In 2022, Akl et al, synthesized novel series of 1-piperazinyl-4-benzylphthalazine derivatives as promising anticancer agents with CDK1 inhibitory activity.The anti-proliferative activity of these agents was first screened on a panel of 11 cell lines representing 5 cancers (pancreas, melanoma, leukemia, colon and breast), and then confirmed on two CDK1-overexpressing PDAC cell lines (MDA-PATC53 and PL45 cells) 31 and 32 (Akl et al., 2022).

Conclusion:
Phthalazine scaffold was considered as an important class of bicyclic Nheterocycles, have received considerable attention due to their beneficial biological and pharmacological activities.phthalazines play a significant role in medicinal chemistry and have emerged as a pharmacophore.The phthalazine ring is a crucial pharmacophoric scaffold present in the core structures of numerous anticancer molecules with potent activity against hepatocellular carcinoma, colon cancer, and breast cancer.Many studies were reported in the synthesis of several phthalazine derivatives as promising anticancer agents as powerful VEGFR-2 inhibitors.The first anilinophthalazine derivative to be identified as a strong inhibitor of VEGFR-2 was vatalanib.According to this review, phthalazine is a major biological active pharmacophore in medicinal chemistry, as well as a new lead scaffold for safe and effective drugs.
, most of them are derived from bacteria and fungi.They have various mechanisms of action.They affect the function and synthesis of nucleic acids in various ways.It includes Mitomycin C, Actinomycin D, Bleomycin and Anthracyclines ("Cytotoxic Antibiotics," 2012).