VAOLUME: 09, Special Issue 06, (IMC-RMSPE-2022) Paper id-IJIERM-IX-VI, August 2022 37
STRUCTURE ACTIVITY RELATIONSHIP OF TAXOL DERIVATIVES AND THEIR ANTI- CANCER ACTIVITY ALONG WITH APPLICATIONS IN PHOTODYNAMIC THERAPY
Dr. Meena Wadhwani, Ms. Nikita Patidar, Ms. Kirti Bamniya
Lakshmi Narain College of Professional Studies, (SKC-LNCT Group) Indore (M.P.) Abstract - Taxol, an anti-neoplastic agent is a potent, natural anticancer product which is derived from the Pacific Yew tree. Many Cancer Institutions are calling it 'the best anti- cancer agent in the last twenty years'. The application of nanotechnology in medical science is a rapidly expanding field. There is a growing interest among the medical community for the medical applications of nanomaterials and nanotechnology due to its ability to bring more progress and breakthroughs in diagnostics, treatments and prevention of diseases.
The drug paclitaxel has received much attention for scientists and researchers since long time. Paclitaxel and its semi-synthetic derivative Docetaxel are two drugs frequently used in cancer therapy (particularly lung, ovary, breast, Kaposi's sarcoma and other). These drugs have been employed in several experimental systems in combination with photodynamic therapy (PDT), with gratifying results.
Keywords: Taxol, Nanomedicines, Anti-cancer, Photodynamic therapy.
1 INTRODUCTION
Nanoparticles are attractive drug-delivery vehicles because of the enhanced permeability and retention effect (EPR effect) by which nanoparticles accumulate more rapidly in tumor tissues than in normal tissues. This effect is believed to be due to the fact that the tumor neovasculature is formed quickly to provide increased blood supply to the growing tumor, and as such is ill-formed and “leaky”. These leaky blood vessels coupled with a late-forming lymphatic system result in a net flow of fluids into the tumor which ultimately establishes a pressure gradient within the tumor. This pressure gradient, known as the interstitial fluid pressure gradient, acts as a physical barrier that limits the effective penetration of systemically administered chemotherapies within the tumor.
Photodynamic therapy (PDT) is a type of cancer therapy that makes use of lasers. In PDT, a certain drug, called a photosensitizer or photosensitizing agent, is injected into a patient and absorbed by cells all over the patient’s body. After a couple of days, the agent is found mostly in cancer cells. Laser light is then used to activate the agent and destroy cancer cells. Since a photosensitizer makes the skin and eyes sensitive to light, patients are advised to evade direct exposure to sunlight and bright indoor light during that time.
Paclitaxel (Taxol) has been reported as one of the most important member of the clinically useful natural anticancer agents. Taxol promotes polymerization and stabilization of tubulin to cellular microtubules as a result; it interferes with the normal breakdown of microtubules during cell division. It was first discovered in the bark of western yew (Taxus brevifolia). Taxol was approved by United States Food and Drug Administration (FDA) for refractory ovarian cancer in December 1992 and for breast cancer in April 1994.
1.1 Paclitaxel
Taxanes are complex terpenes produced by plants of the genus Taxus. When used as drugs (Paclitaxel and Docetaxel), their principal mechanism of action consists of the disruption of microtubule function by stabilizing microtubule formation, thereby stopping cellular division.
2 REVIEW OF STATUS OF RESEARCH AND DEVELOPMENT IN THE SUBJECT
Paclitaxel in various studies is showed as effective anticancer agent against lung, breast, ovarian, leukopenia and liver canceri,ii,iii,iv. Paclitaxel has a role in treating various kinds of
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cancer by targeting tubulin or inducing cell cycle arrest or enhancing the signaling factors or mutating them.v,vi Research on the synthesis of anti-cancer medicines has started in the international arena since early 1970s. Both theoretical and experimental researches are reported in the literature. The molecule was discovered in a screening process initiated by the American Cancer Institute and in 1971, the structure was elucidated by Wani and Wallvii (1971). They discovered that Taxol promoted the assembly of tubulin into stable microtubules and they explained the basis for Taxol’s known action as an antimitotic drug.
The single crystal X-ray structure obtained by Wani and Wall revealed Taxol as a tetracyclic, highly oxygenated diterpene. It wasn't until 1979 when Taxol's unique mode of activity was discovered by Horwitz et alviii (1979). By this time Taxol had shown to exhibit anticancer activity and the race was on to develop Taxol as a chemotherapy agent. Abraham E. Mathew, Magdalena R. Mejilano, Jyoti P. Nath, Richard H. Himes and Valentino J.
Stellaix (1992) studied the synthesis and evaluation of some water soluble pro-drugs and derivatives of taxol with anti-tumor activity. Phase I clinical trials began in 1983 with Taxol and later with a taxol analogue called Taxotere. Nicolaou et al.x (1994) and Holton et alxi (1994) published a total synthesis, virtually concurrently in early 1994, but no commercially viable synthesis of Taxol has been published. L.W. Ma, K. Berg, H.E. Daniel sen, O. Kaalhus, V. Iani, J. Moanxii (1996) studied The combination of photodynamic therapy (PDT) and the microtubule (MT) inhibitor, vincristine (VCR) or taxol in the CaD2 mammary tumour model in mice. Meso-tetra (di-adjacent-sulphonatophenyl) porphine (TPPS2a) was used as a photosensitizer. An enhanced antitumour effect was found when VCR, at an almost non-toxic dose (1 mg/kg1, was injected i.p. into the mice 6 h before PDT, while no such enhanced effect was observed when the same dose of VCR was given either 12 or 24 h before PDT or immediately before PDT. Furthermore, it was found that the number of mitotic cells increased 4-5-fold 6 h after the injection of VCR into the mice. VCR did not enhance the sensitivity of normal skin to PDT. Combination of PDT and taxol was also studied. The anti-tumour activity of PDT could be increased by taxol when the drug (35 mg/kg) was administered i.p. either 6 h prior to PDT or immediately after or before PDT. No significant enhancement in PDT efficiency was found when PDT with photofrin was combined with VCR. D. J. Newman, G. M. Cragg and K.M. Snaderxiii (2003) studied the importance of natural products as sources of new drugs. In this work the attention was drawn towards the rapidly evolving recognition that a significant number of natural product drugs are actually produced by microbes and microbial interactions with the host from where it is isolated and therefore it is considered that this area of natural product research should be expanded significantly. Park et. alxiv (2008) found that Paclitaxel enhanced the cytotoxic effect of Verteporfirin/PDT on gastrointestinal human tumor. In particular, these authors observed that cytotoxicity induced by PDT was markedly potentiated by pre- treatment of cells with Paclitaxel at low doses. They also reported that cell death occurred through an apoptotic mechanism with a significant mitochondria cytochrome c release, independent of Bax or Bid activation. O. Expósito, M. Bonfill, E. Moyano, M. Onrubia, M.H.
Mirjalili, R.M. Cusidó and J. Palazónxv (2009) reported the biotechnological production of taxol and related taxoids with reference to the current state and prospects. According to the observation of Ilaria Postiglione, Angela Chiaviello and Giuseppe Palumboxvi (2011), the association of PDT with Paclitaxel has additional positive features in that the combination seems to overcome tumor cell resistance against the drug. The problem of Paclitaxel resistance can apparently be solved by another type of association. Indeed, it has been demonstrated that the combination of the protein kinase C (PKC) inhibitor calphostin C with PDT potently kills breast tumor cells resistant to Paclitaxel. The mechanism by which this resistance is overcome requires the induction of cytoplasmic vacuolization without activation of typical apoptotic pathways. Consequently, it has been suggested that calphostin C may prove useful clinically to combat tumor growth in breast cancer patients particularly in association with PDT. A. Weaver Beth and Bement Williamxvii (2014) explained the mechanism of action of Taxol/Paclitaxel illustrating that how it kills cancer cells. This insight encouraged the collaboration between basic scientists and clinicians.
Yongjin Liu, Bin Zhang and Bing Yanxviii (2015) reported the anticancer therapeutics by nanoparticle carriers with reference to the delivery of Paclitaxel.
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A variety of research has been conducted in India on the development of anti-cancer medicines. Shreekanthxix (2009) and colleagues published their study on production, purification and characterization of taxol and 10 DAB III from a new endophytic fungus Gliocladium sp. isolated from the Indian yew tree, Taxus Baccata. The purified taxol from the fungus showed the cytotoxic activity towards cancer lines HL-60 (leukemia), A-431 (epidermal Carcinoma) and MCF-7 (Breast Cancer). Imran Ali, Waseem A. Wani and Kishwar Saleemxx(2011) described the cancer scenario in India with future perspectives.
Their study revealed that all types of cancers have been reported in Indian population including the cancers of skin, lungs, breast, rectum, stomach, prostate, liver, cervix, esophagus, bladder, blood, mouth etc. K. Priyadarshini and A. Keerthixxi (2012) published a review article to explain a few advancements in cancer treatment using Paclitaxel since its discovery. S. Bhatia, S. Singh, R. Kumar, A.Kumar, C.E.Olsen and A.K. Prasadxxii (2013) developed an efficient, economical and industry-friendly methodology for the synthesis of C- 13 side chain of taxol, (2R,3S)-3-benzamido-2-hydroxy-3-phenylpropanoic acid by oxidative cleavage of alkene precursor N-[(1S,2S)-2-(1′-ethoxyethoxy)-1-phenylbut-3-en-1-yl]
benzamide using KMnO4-NaIO4-K2CO3 as oxidant in acetone-water in much higher yields of 80% than the conventional RuCl3-NaIO4 method. Further, the developed methodology has been successfully used for the synthesis of O-acetylated taxotere side chain (2R,3S)-2- acetoxy-3-[N-(tert-butoxycarbonyl)amino]-3-phenylpropanoic acid and taxol side chain analogues (2R, 3S) -2- acetoxy- 3- (4′′-chloro-4′′-fluoro-4′′-trifluoromethyl-benzamido) -3- phenylpropanoic acid from their corresponding alkene precursor, which demonstrate the generality of the developed oxidative cleavage methodology. A. A. Rnanade, D.A. Joshi, G.K.Phadke, P.P. Patil, R.B. Kasbekar, T. G. Apte, R.R. Dasare, S.D. Mengde, P.M. Parikh, G.S. Bhattacharya and G.L. Lopesxxiii (2013) reported the clinical and economic implications of the use of nanoparticle paclitaxel (nanoxel) in India. Neeraj K. Sharma, Vimal Kumarxxiv(2015) published their work on the recent advancements in the delivery of paclitaxel by using liposomes. Far-Red Light-Activatable Prodrug of Paclitaxel for the Combined Effects of Photodynamic Therapy and Site-Specific Paclitaxel Chemotherapy was prepared by Pritam Thapa, Mengjie Li, Moses Bio, Pallavi Rajaputra, Gregory Nkepang, Yajing Sun, Sukyung Woo, and Youngjae Youxxv (2016). The synthesis was done by conjugating photosensitizer via singlet oxygen-cleavable aminoacrylate linker. Tubulin polymerization enhancement and cytotoxicity of prodrugs were dramatically reduced.
3 STRUCTURE-ACTIVITY RELATIONSHIP
Paclitaxel has been thoroughly investigated ever since its discovery in the early 1960s.
Extensive structure-activity relationship (SAR) studies have been performed in order to better understand its unique mechanism of action and to reveal the minimal structural requirements to maintain tubulin binding. As a result of the SAR studies, a pharmacophore model of paclitaxel has been developedxxvi.
In general, paclitaxel can be divided into three areas, the northern part, the southern part, and the side chain. As far as the structure is concerned the study revealed that the northern part of molecule is of less importance for the activity. This area, including the C-7, C-9, and the C-10 positions allows for rather large structural modifications, indicating that this part is not directly involved in the interaction with tubulin.
In fact, modifications at C-7 and/or C-10 have resulted in taxoids with improved activity in resistant cancer cell lines.24 The southern part of paclitaxel includes C-14, C-1, C-2, C-4, and the oxetane ring. In this region, the acceptance for modifications is small, although minor changes at the C-14 and C-1 positions still result in retained activity. On the contrary, the acyl groups at C-2 and C-4 play significant roles in the interaction with tubulin. When replaced by various hydrophobic groups, an enhanced activity is achieved for several analogues. However, complete loss of activity is observed upon deacylation.
The function of the oxetane ring has been debated over the years. It has been suggested to contribute to stabilization through hydrogen bonding with tubulin. Also, it is believed to provide rigidity to the C-ring, thus fixing the orientation of the crucial C-4 acetyl group. Recently, Snyder et al.xxvii reported the first active taxoid analogue lacking the oxetane ring. Finally, the 2’R, 3’N-phenylisoserine side chain at the C-13position is vital for activity. A free C-2’ hydroxyl group along with N-3’ acylation are other structural demands
VAOLUME: 09, Special Issue 06, (IMC-RMSPE-2022) Paper id-IJIERM-IX-VI, August 2022 40 necessary for retained activity.
In addition to the SAR studies, intense research has focused on the determination of the bioactive conformation of paclitaxel. If revealed, this knowledge would enable the design of paclitaxel analogues with improved activities as well as simplified nontaxanes with comparable binding affinity and bioactivity.
However, once illuminated with far-red light, the prodrug effectively killed SKOV-3 ovarian cancer cells through the combined effects of PDT and locally released PTX. It was highlighted as the first PTX prodrug that can be activated by singlet oxygen using tissue penetrable and clinically useful far-red light, which kills the cancer cells through the combined effects of PDT and site-specific PTX chemotherapy.
Paclitaxel-induced mitotic arrest occurs due to activation of the mitotic checkpoint (also known as the spindle assembly checkpoint), the major cell cycle control mechanism acting during mitosis to prevent chromosome missegregation. The mitotic checkpoint delays separation of the chromosomes, which enter mitosis as replicated pairs of sister chromatids, until each pair has made stable attachments to both poles of the mitotic spindle. This arrangement ensures that each daughter cell will receive one copy of every chromatid. Chromatids connect to spindle microtubules through their kinetochores, protein complexes that assemble on centromeric regions of DNA. Unattached kinetochores, which have not made stable attachments to microtubules, activate a signal transduction cascade that delays mitotic progression by inhibiting the anaphase-promoting complex/cyclosome.
Paclitaxel treatment arrests cells in mitosis due to the presence of a small number of unattached kinetochores.
Cancerous tumors are characterized by cell division, which is no longer controlled as it is in normal tissue. "Normal" cells stop dividing when they come into contact with like cells, a mechanism known as contact inhibition. Cancerous cells lose this ability. Cancer cells no longer have the normal checks and balances in place that control and limit cell division. The process of cell division, whether normal or cancerous cells, is through the cell cycle. The cell cycle goes from the resting phase, through active growing phases, and then to mitosis (division).
The ability of chemotherapy to kill cancer cells depends on its ability to arrest cell division. Usually, the drugs work by damaging the RNA or DNA that tells the cell how to copy itself in division. If the cells are unable to divide, they die. The faster the cells are dividing, the more likely it is that chemotherapy will kill the cells, causing the tumor to shrink. They also induce cell suicide (self-death or apoptosis).
Chemotherapy drugs that affect cells only when they are dividing are called cell- cycle specific. Chemotherapy drugs that affect cells when they are at rest are called cell- cycle non-specific. The scheduling of chemotherapy is set based on the type of cells, rate at which they divide, and the time at which a given drug is likely to be effective. This is why chemotherapy is typically given in cycles.
Chemotherapy is most effective at killing cells that are rapidly dividing.
Unfortunately, chemotherapy does not know the difference between the cancerous cells and the normal cells. The "normal" cells will grow back and be healthy but in the meantime, side effects occur. The "normal" cells most commonly affected by chemotherapy are the blood cells, the cells in the mouth, stomach and bowel, and the hair follicles; resulting in low blood counts, mouth sores, nausea, diarrhea, and/or hair loss. Different drugs may affect different parts of the body.
Taxol belongs to a class of chemotherapy drugs called plant alkaloids. Plant alkaloids are made from plants. The vinca alkaloids are made from the periwinkle plant (catharanthus rosea). The taxanes are made from the bark of the Pacific Yew tree (taxus).
The vinca alkaloids and taxanes are also known as antimicrotubule agents. Camptothecan analogs are derived from the Asian "Happy Tree" (Camptotheca acuminata).
Podophyllotoxins and camptothecan analogs are also known as topoisomerase inhibitors.
The plant alkaloids are cell-cycle specific. This means they attack the cells during various phases of division.
Antimicrotubule agents (such as Taxol), inhibit the microtubule structures within the cell. Microtubules are part of the cell's apparatus for dividing and replicating itself.
Inhibition of these structures ultimately results in cell death.
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Taxol/Paclitaxel, an antitumor drug that is demonstrating encouraging activity in human malignancies, is likely to play a major role in cancer chemotherapy. Paclitaxel has an unusual chemical structure--it is a complex diterpene having a taxane ring with a four- membered oxetane ring and an ester side chain at position C-13--and a unique mechanism of action. In vitro, paclitaxel enhances the polymerization of tubulin to stable microtubules and also interacts directly with microtubules, stabilizing them against depolymerization by cold and calcium, which readily depolymerize normal microtubules. The fact that the drug has a specific binding site on the microtubule polymer makes it unique among chemotherapeutic agents, and the ability of paclitaxel to polymerize tubulin in the absence of cofactors like guanosine triphosphate and microtubule-associated proteins is unusual.
When paclitaxel and microtubule protein are irradiated with ultraviolet light, the drug preferentially binds covalently to the beta-subunit of tubulin. Paclitaxel binds to cells in a specific and saturable manner with a single set of high-affinity binding sites. The microtubule cytoskeleton is reorganized in the presence of paclitaxel and extensive parallel arrays or stable bundles of microtubules are formed in cells growing in tissue culture.
The clinical utility of Taxol has prompted a tremendous effort to obtain this complex molecule synthetically. The proposed research work is an effort to discover a new and cost- effective method for the synthesis of Taxol derivatives. Along with the various structural parameters, the present work will also focus on the dosage as well as duration that show the enhanced effect of drug. The purpose of the study is to provide an effective, non-toxic drug delivery system to fight against the various types of dreadful disease cancer.
Plant cell cultures and fungi fermentation provide extremely potential way to industrialize Taxol production if the bottlenecks of unstable and low yield could be broken in the years to come. Chemical synthesis may be the ultimate method to satisfy the urgent need of Taxol. It opens a pathway for the production of both the natural product itself and a variety of designed taxoids, which can be modified and may have strong effective activities.
3.1 Taxol (Paclitaxel)
Taxol or Paclitaxel is one of the most effective chemotherapeutic drugs ever developed and is active against a broad range of cancers, such as lung, ovarian and breasts cancers. The encapsulation of paclitaxel in biodegradable and non toxic nano-delivery systems can protect the drug from degradation during circulation and hence protect the body from toxic side effects of the drug. Further the nano-particles based drug-delivery system can take advantage of the enhanced permeability and retention (EPR) effect for passive tumor targeting, therefore, they are promising carriers to improve the therapeutic index and decrease the side effects of paclitaxel. The outcome of the study will help to physicians with a standard medicine for cancer with maximum therapeutic efficiency.
Photodynamic therapy (PDT) has recently emerged as a viable therapeutic option in the treatment of cancer. PDT uses a light-activatable chemical known as a photosensitizer, which absorbs light of a certain wavelength to generate cytotoxic oxygen-based molecular species. Nanoparticles can deliver these light-activatable chemicals, known as photosensitizer molecules, to tumor cells for use in photodynamic therapy. After the absorption of light, photosensitizer molecules can generate cytotoxic oxygen-based reactive species, which can subsequently cause cellular damage and cell death via oxidative stressxxviii.
VAOLUME: 09, Special Issue 06, (IMC-RMSPE-2022) Paper id-IJIERM-IX-VI, August 2022 42 4 CONCLUSION
Taxol used in clinic and scientific research is mainly isolated from Taxus tree with skilled extraction procedures. This synthetically challenging molecule with its 11 stereocenters, four skeletal rings, and unusual steric congestion, particularly around its 8-membered ring, provides several serious obstacles and opportunities to create new strategies and to expand the scope and generality of known synthetic methods. The research of this kind will transform the lives of those suffering from cancer.
Among various diseases, cancer has become a big threat to human beings globally.
As per Indian population census data, the rate of mortality due to cancer in India was high and alarming with about 806000 existing cases by the end of the last century. Cancer is the second most common disease in India responsible for maximum mortality with about 0.3 million deaths per year. This is owing to the poor availability of prevention, diagnosis and treatment of the disease.
Taxol is at present the most promising anti-cancer agent, and its synthesis is extremely demanding. The research project will definitely result in a significant discovery especially in the present context when cancer has become worlds dreaded killer disease accounting for 8.2 million deaths (around 13 per cent of all deaths) in 2012 as per the World Cancer Report and scientists embattling cancer are on the lookout for newer effective and safer drugs for cancer therapy. Unfortunately the high demand for Taxol from the bark of Pacific yew is a challenging aspect for this new therapeutic weapon. Therefore focus should be on developing this product by chemical/synthetic methods in order to meet the growing need of this anticancer drug.
Clinical trials have shown remarkable activity against resistant cases of advanced ovarian and breast cancer. Hopefully in the near future a Taxol/Taxol analogue will be commercially available as a potent anticancer agent in the never ending battle against nature's unpredictable and undesired actions. The discovery of anti-cancer molecules will bring a revolution in fighting the dreaded disease in an effective manner. The products can be utilized by different pharmaceutical industries for preparation of drugs viz. anti- microbial, anti-cancer etc. The results obtained will also provide a new vision to the new researches for further studies in the concerned field. This will also move nation a step towards 'ATMANIRBHAR BHARAT"
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