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Anti-Cancer Drugs

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Chemistry

Cells are remarkable things. Scientists estimate that nearly two trillion of your cells divide every day, producing identical daughter cells with exactly the same DNA sequence as the original cell. At least, that is what is supposed to happen. However, sometimes DNA isn't copied exactly. The genetic sequence changes and this can cause the new daughter cell to behave differently. It may start dividing rapidly and uncontrollably. This is known as cancer.

Cancer is a disease caused by uncontrolled cell division in a part of the body.

However, there are many drugs that we have at our disposal to help fight against rogue cancerous cells. We will focus on one of them in particular: cisplatin.

  • This article is about the anti-cancer drug cisplatin.
  • We'll start by providing an overview of anti-cancer drugs on general before focusing on cisplatin.
  • We'll look at its structure and mechanism of action before exploring some of its side effects.

For your exams, you only have to know about the drug cisplatin and its mechanism of action - knowledge about cancer and other anticancer drugs isn't required. However, we've included this information to provide you with some background knowledge of the subject.

What is cancer?

As we defined at the start, cancer is a disease characterised by rapid, uncontrolled cell division. Healthy cells divide regularly as part of a process called the cell cycle. They have many security measures that help regulate this, telling them when to divide and when to go about other cellular activities. Cells are limited to how many times they can divide before they die. However, in cancerous cells these security measures are either missing or faulty. Instead, the cell divides rapidly and uncontrollably.

The uncontrolled cell division is caused by mutations in the cell's DNA. Mutations come from many different sources. In fact, DNA naturally mutates all the time - it is just that most of these mutations have no effect whatsoever on the cell. Only occasionally does a mutation cause a harmful effect such as cancer. You can also get mutations from carcinogenic substances such as x-rays and other radiation.

Because cancerous cells divide so rapidly, they grow faster than normal cells. They can then invade and destroy surrounding healthy tissue, including organs. This is why cancer is life-threatening.

For more on this topic, head over to Cancer.

What are anti-cancer drugs?

Anti-cancer drugs, as the name suggests, are drugs used to treat cancers in the body.

Using anti-cancer drugs to treat cancers is known as chemotherapy. 28 percent of all cancer patients undergo chemotherapy as part of their treatment regime. It can have up to a 90 percent success rate against some forms of cancer.

Different anti-cancer drugs have different mechanisms and methods of treatment. depending on their classification. They also all have different side effects and dosages, and attack separate types of cancer. Doctors need to take all these factors into consideration when prescribing anti-cancer drugs.

Classification of anti-cancer drugs

Let's explore some of the different types of anti-cancer drugs:

  • Alkylating agents work by interfering with the cancerous cell's DNA replication. They do this by cross-linking DNA strands or matching up DNA base pairs abnormally.
  • Antimetabolites interfere with the enzymes involved in DNA synthesis.
  • Hormonal agents alter the amounts of hormones in and around the cancerous cell, which affects its cellular division.
  • Plant alkaloids bind to certain proteins during specific stages of the cell cycle, causing the cancerous cell to enter mitotic arrest and die.

Cisplatin

Cisplatin is a particular anti-cancer drug. To be exact, it is a type of alkylating agent. For the rest of this article, we're going to look specifically at how it works in treating cancers.

Cisplatin as an anti-cancer drug

As we mentioned above, cisplatin is an example of an anti-cancer drug, or more specifically, an alkylating agent. It treats cancer by stopping DNA replication, which prevents the cell from dividing.

It is easy to get confused between DNA replication and cell division. DNA replication is when a new set of DNA is copied from the parent DNA within a cell, whereas cell division is when the entire cell divides to form two daughter cells. However, before cells divide, they need to replicate their DNA, which is an essential part of (almost) all human cells.

Interested in learning more? Cell Division and DNA Replication are good introductions to these topics.

Structure

Cisplatin has the molecular formula . It is an example of a complex ion with two chloride ligands and two ammonia ligands bonded to a central platinum atom.

By looking at the term ‘cisplatin’, we can visualise its structure. Cisplatin is actually one of a pair of two optical isomers, molecules with the same structural formulae but different arrangements of groups around a central atom. In the cis- isomer, the chloride ligands are next to each other. In the trans- isomer, they are opposite one another.

Anti-cancer Drugs cisplatin transplatin StudySmarterCisplatin and transplatin. The chloride ligands are circled to help you identify their position. Created using images from commons.wikimedia.org

The shape of cisplatin is a square planar. The cis- structure and the square planar shape of cisplatin give it the correct geometry that is fundamental to its function.

We cover these types of isomers in more detail in the article Optical Isomerism. If you want to learn about molecular shapes, check out Shapes of Molecules.

Mechanism of action

The structure of cisplatin plays an important role in how it acts as an anti-cancer agent.

When cisplatin is in the body, water displaces one of the chloride ligands in a ligand substitution reaction called aquation. This happens because the concentration of water around the complex cisplatin ion is much higher than the concentration of chloride ions.

Aquation makes it easier for cisplatin to then bind to DNA bases - in particular, guanine. A nitrogen atom in guanine donates its lone pair of electrons to the platinum ion in cisplatin, forming a dative covalent bond. This gets rid of the newly-acquired water ligand in another ligand substitution reaction.

Nitrogen can replace water in a ligand substitution reaction because out of the pair, nitrogen is a stronger ligand. It holds its lone pair of electrons less tightly than oxygen, which is more electronegative than nitrogen. It is therefore easier for nitrogen to donate its lone pair of electrons to platinum, forming a dative covalent bond.

For more about ligands, check out Substitution Reactions.

The same substitution then happens to the other chloride ligand, but this time the chloride ligand is replaced by a nitrogen atom from guanine on the opposite DNA strand. The binding to guanine cross-links the two DNA strands and distorts the shape of the DNA. This prevents the cell from replicating its DNA. The cell tries to fix the DNA damage using repair mechanisms but ultimately is unsuccessful. This triggers apoptosis, cell death.

Anti-cancer Drugs cisplatin binding guanine StudySmarterCisplatin binds to guanine bases on opposite DNA strands. commons.wikimedia.org

Cisplatin can only bind to both strands of DNA because its chloride ligands are positioned on the same side of the platinum ion. In contrast, transplatin can't bind to DNA because its chloride ligands are on opposite sides of the platinum ion. This means it can't stop DNA replication and is completely ineffective as an anti-cancer drug.

Side effects

Cisplatin isn't selective. It binds to DNA in all cells, not just cancer cells. However, because cancer cells replicate much more rapidly than healthy human cells, cisplatin's effect on them is much greater. But other frequently replicating cells like hair follicle cells are also affected and killed off. This is why chemotherapy patients sometimes experience hair loss. Other side effects include nausea, vomiting, and fatigue.

However, it is important to remember that chemotherapy can be extremely beneficial, and for some people, it is their best shot at treating cancer. Cisplatin in particular has a 90 percent success rate against testicular cancer. Although the side effects are unpleasant, they can be managed through drugs such as antiemetics. However, it should always be up to the patient as to whether they want to undergo any sort of cancer treatment or not.

Anti-Cancer Drugs - Key takeaways

  • Cancer is a disease caused by uncontrolled cell division in a part of the body.
  • Anti-cancer drugs are drugs used to treat cancers in the body. Types of anti-cancer drugs include alkylating agents and antimetabolites.
  • Cisplatin is an alkylating agent that prevents DNA replication in cells. It consists of two ammonia ligands and two chloride ligands bonded to a central platinum ion.
  • Cisplatin works by bonding to nitrogen atoms in the base guanine using a ligand substitution reaction. This damages the cell's DNA, prevents DNA replication and triggers cellular death.
  • Cisplatin has a success rate of up to 90 percent. However, it can also cause unpleasant side effects like nausea and hair loss.

Anti-Cancer Drugs

In addition to cisplatin, the most common cancer drugs include vincristine, paclitaxel, and methotrexate. 

There are many classes of cancer drugs. These include alkylating agents, antimetabolites, and hormonal agents.

Cancer drugs work in different ways. They mainly work by stopping the cancer cells from further dividing, though different cancer drugs stop the cell division process differently. For example, cisplatin kills cancer cells by stopping them replicating their DNA and triggering cellular death.

An anti-cancer drug is a drug used to treat cancers.

Unfortunately anticancer drugs can bring about the risk of further cancers developing, as they can also act on non-cancerous cells. Therefore, anti-cancer therapy is very stringently monitored to help prevent such risk from occurring.

Final Anti-Cancer Drugs Quiz

Question

Define the term cancer.

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Answer

Cancer is a disease where mutations in cells lead to uncontrolled cell division.

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Question

Normal cells are able to divide without limits. True or false?


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Answer

False - normal cells have a limit to how many times they can divide.

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Question

Explain why cancer cells grow faster than normal cells.


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Answer

Cancer cells experience a mutation in their genes, causing them to grow and divide beyond the limits of cell division as seen in normal cells.

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Question

Briefly explain why cancer can be life-threatening.


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Answer

Cancer cells not only grow faster than normal cells, but they can also invade and destroy surrounding healthy tissue, including organs.

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Question

Briefly outline how anti-cancer drugs work.


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Answer

Anti-cancer drugs work by stopping cancer cells from dividing further.

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Question

In cisplatin, the functional groups attached to the central platinum (ammonia and chlorine) are on opposite sides of the molecule. True or false?

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Answer

False - The functional groups are on the same sides of the molecule

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Question

What is the shape of cisplatin?


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Answer

Square-planar

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Question

Briefly explain the importance of the cis structure and square planar shape of cisplatin.

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Answer

The cis structure and the square planar shape of cisplatin give the correct geometry fundamental to ensure the drug’s function.

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Question

Name the atoms in cisplatin that are crucial for its anti-cancer properties.


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Answer

Platinum and chlorine.

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Question

Describe how cisplatin stops cellular division.

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Answer

Water in the body displaces the chlorine atoms of cisplatin. Cisplatin then forms dative bonds with guanine base in DNA, effectively forming crosslinks, distorting the shape of the DNA required for DNA replication in cell division.

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Question

Apoptosis is defined as controlled cell death. True or false?


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Answer

True

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Question

Name the process where water in the body displaces the chlorine atoms of cisplatin.


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Answer

Aquation

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Question

Explain why cisplatin can cause hair loss as a side effect.

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Answer

Cisplatin binds to guanine found in the DNA of both healthy and cancerous cells. Even though it is more selective of cancer cells due to their higher replication rates, cisplatin cannot distinguish between cancer cells and healthy cells that replicate quickly, such as hair follicles. Hence it causes hair loss as a side effect.

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Question

Suggest a type of research into improving the selectivity of anti-cancer agents.


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Answer

Research into new anti-cancer agents/methods of delivering anti-cancer agents.

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