Potentials of Beta-lactam and its Effective use as Anti-cancer and Anti-diabetic Drugs

Introduction

The class of organic compounds in which three or more atoms are joined to form a cyclic structure containing one or more heteroatoms is classified as heterocyclic compound.¹ The cyclic part in the heterocyclic compound indicates at least one ring is present in the structure. β-lactam antibiotics are a class of drugs of much discussion and investigation for both scientific as well as for the public sector.² β-Lactam, a four-membered heterocyclic compound, holds a prominent position among medicinally important compounds due to the interesting biological activities of both natural and synthetic β-lactam derivatives.^1,2 Since the discovery of penicillin, β-lactam has been recognised as a potential antibiotic. Cancer is a heterogeneous disease and can be identified as the growth of a malignant cell population that ultimately leads to the interference of normal physiological functions and lifestyle.³ Anti-cancer drugs are synthesised by harnessing natural products to decrease the side effects of certain chemotherapeutic drugs.⁴ They focus on the inhibition of tumour cell growth and induction of apoptosis (a phenomenon in which a cell undergoes self–suicide without affecting the adjoining cell) in the malignant cell population.^4,5

Atherosclerotic coronary heart disease (CHD) has been the leading cause of death due to lifestyle changes and increasing serum cholesterol levels in the population.⁵ Beta-lactams are also used as potential and highly efficacious cholesterol absorption inhibitors.⁶ Recent research focuses on the potential of antibiotic drugs to treat cancer (e.g. bleomycin).

Diabetes mellitus (DM) is a metabolic disorder resulting from a defect in insulin secretion and action. Insulin deficiency in turn leads to chronic hyperglycaemia with disturbances of carbohydrate, fat, and protein metabolism which ultimately affect the normal cycle of a large population.⁷ Beta lactams are derived from various cyclization processes and are used as potential anti-diabetic drugs. The presence of heteroatoms such as nitrogen, oxygen, and sulfur, shows many biological activities like antibacterial, anti-tubercular, anti-inflammatory, anti HIV (human immunodeficiency virus), analgesic, anti-diabetic, anti-cancer, and anticonvulsant. Figure 1 shows the applications of heterocyclic compounds. Moreover, they are the major constituents of our genetic material- DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).⁸

Figure 1: Application of heterocyclic compounds⁸

History and development

In 1928, Alexander Fleming, the Director of Inoculation at St. Mary Hospital in Paddington, London, noticed that some of the Staphylococcus-inoculated Petri-dish forgotten on the lab table had been accidentally infected by a fungus called Penicillium notatum. He also observed a transparent halo (ring-like) around the contaminating mold which indicated rupturing of the walls and there is a reduction in the growth rate of the Staphylococcus colonies. This indicated that the fungus could produce some bactericidal biologically active compounds.⁹

In 1932, Fleming published the complete results of his work on identifying a new antimicrobial agent from Penicillium notatum metabolites. In 1943 Robert Robinson interpreted and elucidated the chemical structure of penicillin, which provided the path for future synthesis of new drugs. These discoveries awarded Fleming, Chain, and Florey the first Nobel Prize in Physiology or Medicine in 1945.^9,10

Research up until the early 1990s primarily centered on the antibacterial properties of beta-lactams. However, recent years have seen a renewed interest in synthesising novel β-lactam derivatives with a wide range of pharmacological activities. These include anticancer effects, cholesterol absorption inhibition, thrombin and chymase inhibition, antagonist activity, as well as anti-diabetic, anti-inflammatory, anti-parkinsonian, and anti-HIV properties.¹⁰

Structure and nomenclature

Lactam is a cyclic amide in which a nitrogen atom is attached to beta-carbon. 2-Azetidinone is the simplest beta-lactam possible. Classification of beta-lactam antibiotics depends on the chemical nature of the ring that is fused to the β-lactam pharmacophore unit, generating a non-coplanar bicyclic scaffold (Figure 2).^10,11

Figure 1: Classification of β-lactam antibiotics11

β-lactam is a carbonyl derivative of azetidines which contains the carbonyl group at the second position. It is a four-membered cyclic amide, with an oxo group in the second position of the ring. β-lactams are also called 2-azetidines because β-lactams are not fused with any other ring system and are grouped as monobactams. β-lactam is a highly strained and reactive cyclic amide. There are five relevant ring systems, including the penam, carbapenem, cefem and monobactam ring structure. The chemistry of β-lactams fosters scientific interest because of their important role in antibacterial agents and other bioactive compounds.⁸ For half a century, monocyclic beta-lactams have been considered safe and non-toxic drugs.¹² PerkinElmer ChemDraw Professional version 19.0.0.22 was employed to create two-dimensional molecular structures for the beta lactams.

Monocyclic beta-lactams are known for their antibacterial activity, but in recent years they have also been recognized in other therapeutic areas. The first monocyclic beta-lactam, Nocardin A, was discovered in 1976 in the bacterium Nocardia uniformis.13 The structure of 2-Azetidinone ring and penicillin is illustrated in Figure 3 and 4 respectively.

Figure 3: Structure of the 2-Azetidinone ring.

Figure 4: Structure of the 2-Azetidinone ring.

Figure 5: The pharmacological activities of β-lactams^5,10,13

Anti-cancerous β-lactam hybrids designed by the molecular hybridisation approach might serve as anticancer fragments and help in synthesising more potent cytotoxic agents. “The molecular hybridisation (MH) is a strategy of rational design of various prototypes based on the recognition of pharmacophoric sub-units in the molecular structure of two or more known bioactive derivatives that lead to the design of new hybrid scaffolds that maintain potent characteristics of the original templates of the parent molecule.”^2,10

This strategy is very effective for the formation of new compounds having improved antiproliferative activity when compared to parent molecules. Moreover, hybrids are designed to counterbalance the known side effects of existing drugs through their action on other targets as one single molecule. This lowers the risk of drug-drug interactions and thus minimises their resistance.¹⁰ Hence, new anticancer scaffolds are synthesised by linking β-lactams by various anticancer biologically active entities through molecular hybridisation strategy.

Examples of anticancer β-lactam hybrids developed by MH strategy:

• Thym 1,2,3-Triazole-β-lactam hybrids.
• Chalcone-β-lactam hybrids.
• Retinoid-β-lactam hybrids.
• Isatin-β-lactam hybrids
• Benzimidazole-β-lactam hybrids

Consider the scaffolds containing the thymine heterocycle which exhibit excellent anticancer activity as thymine is an integral DNA and RNA building block that plays an important role in various processes of life. The synthesis of these compounds can be achieved through a molecular hybridisation strategy.¹⁰

The designed molecule shown in Figure 6 was evaluated for cytotoxic studies against three human cancer cell lines (L1210, CEM, HeLa). Its anti-proliferative activity against the HeLa (oldest and most used human cell line) cells was less pronounced) as compared to the activity against L1210 and CEM cells (CEM cell, a cell line derived from human T cells)

Figure 6: Thym1,2,3-Triazole-β-lactam hybrids^13,15

Structure Activity Relationship

1. R - Bn, displayed the best antiproliferative result againstCEM cells (IC50 = 3.4 µM).
2. Good selectivity between CEM cells and Hela cells.
3. Substituents on phenyl ring play an important role.

β-lactams as hypoglycaemic agents

The β-lactam (or azetidin-2-one) scaffold is an excellent highly strained heterocyclic compound due its small ring size (Figure 7). The multi-functional spectrum of beta-lactam plays an important role in the field of chemistry, biology as well as in pharmaceutical products.

Figure 7: Monocyclic beta lactams showing anti- hyperglycaemic activity^14,15

Future of beta-lactam as sensors

The β-lactam ring of penicillin interprets the antibiotics’ effectiveness by inhibiting cell wall synthesis during bacterial replication. When β-lactamase catalyses the cleavage of the β-lactam ring, it releases a proton, thus, decreasing the pH. A sensor is a device that responds to physical stimuli and transmits the observed impulse for measurement.

Biosensors were first used in 1962 for the enzymatic observation of blood glucose levels using oxygen electrodes to observe the products of glucose oxidase. Sensors accomplish their work by using a recognition element and a transducer. The recognition element responds to changes that happen in the environment, and the transducer converts that change into an electronic signal so that the change can be observed.¹⁶ A biosensor is an analytical device that monitors and transmits information about processes necessary for life. The biosensor is a device consisting of a biological component – enzyme or bacteria that reacts with a target entity and a signal is observed. Nowadays, a sensing system (pseudo-sensor) is developed for measuring the action of enzymes such as the activity of beta-lactamase. There are various bio-sensing systems such as molecular, cellular, and tissue-based. Whole cell-based biosensing systems are effective because they are stable in environments with varying temperatures and pH, making them physiologically relevant and allowing the conduction of bioavailability studies. In the sensing system, instead of a transducer, fluorescent protein is used such as GFP (green fluorescent protein), aequorin, firefly luciferase, bacterial luciferase, and red fluorescent protein.^16,17

We can extend the research for different enzymes to check their functioning in the human body having a β-lactam ring in presenting their structure because of the ring sensitivity. We can also use the different compounds as sensing agents to treat the patient or give them certain drugs for early recovery.^17,18 The mechanism of β-lactam antibiotics involves the β-lactam ring covalently binding to and inhibiting transpeptidases, carboxypeptidases, and endopeptidases, all of which are essential enzymes in the final phases of peptidoglycan cell wall biosynthesis.

All these sensing devices were developed to find ways to deactivate β-lactamase for the continued use of antibiotics instead of developing resistance in living cells.19,20 Hence, we can increase awareness and create exposure for sensing devices for cancer and diabetes regarding their–detection, measurements, and treatment.

Conclusion

In the last decades, antimicrobial resistance has evolved from being an interesting scientific observation to a significant medical concern. Monocyclic beta-lactams can be considered safe and non-toxic drugs, as they have been used in the field for more than half a decade. No new β-lactam subclass has been discovered in the last thirty years, research on the β-lactams has declined but the study of β-lactams and their derivative as potent drugs is still ongoing. A better understanding of the chemical structure of the new drug developed from β-lactam and the study of its mechanisms for different potentials such as anti-cancer activity, cholesterol absorption inhibitory activity, chymase inhibition, antagonist activity, anti-diabetic, anti-inflammatory, anti-parkinsonian and anti-HIV activity is essential. This knowledge is crucial for developing therapeutic, screening and control strategies needed to reduce the spread and evolution of resistant bacteria using sensing technologies.