Treatment Overview > What is a Drug?

Last update: 10/17/2016

For newer arrivals:

The newly diagnosed can be initially fearful of chemotherapy, which are also called a cytotoxic agents.

... It’s important to appreciate that blood cell cancers are especially sensitive to this class of drug (and for similar reasons also to radiotherapy). These agents work by damaging the DNA of rapidly dividing cells – inducing the cells to self destruct -- similar to how a too much sun exposure causes our skin cells to self-destruct and peel.

Blood cells are inherently born to die (compared to say heart or lung cells). Thus, the doses of chemotherapy agents needed to have this effect is lower for lymphoma than for other types of cancers.

… Lymphoma arises from defective lymphocytes – a type of immune cell. Lymphocytes will expand in number in response to an infection and then die off when the cells receive signals from other cells that the task has been accomplished.

So lymphoma cells can be induced to die in different ways: by damaging them, by altering the signals they receive, or by targeting the defects that cause them to multiply too fast or persist too long.

The first types of cancer to be cured were the blood cell cancers treated with chemotherapy agents. Investigators looking for ways to treat childhood leukemias developed the concept by observing that the blood cell counts of soldiers drop when exposed to mustard gas, and that the counts would rebound later. They reasoned that at the right dose this kind of drug could treat blood cell cancers.

Rituxan, a biologic agent, is a very different class of drug. It’s an antibody (protein molecule) similar to the antibodies our bodies make to respond to an infection. It’s given by vein and circulates in the body where it sticks to cells that have a specific molecule on the cell surface called cd20. CD20 only exists on mature b-cells. The effect of this drug is to kill (or deplete) all mature b-cells. Stem cells, however, from which the b-cells arise do not have CD20. This allows the normal b-cells to come back after some time (roughly 6 to 9 months later). Rituxan works directly by changing the balance of signals inside the cell to favor cell-death (self killing), and by flagging the cells it sticks to for eradication by other types of immune cells (called effector cells).

Radioimmunotherapy (such as Zevalin) is also an antibody (or biologic agent) that has been tagged with radiation. Rituxan is given first to help clear the normal b-cells. The Zevalin antibody is given on a subsequent day so that the radiation attached to it is more focused on the abnormal b-cells (the lymphoma).

All treatments that are effective will have side effects, such as lowered normal blood cell counts. Antibodies can sometimes cause immune-mediated infusion reactions.

To be approved by the FDA as a therapy, the potential benefits of the drug must outweigh the known risks. This risk/benefit profile must be demonstrated in well controlled or large clinical trials that prospectively define the number of patients in the study and how the effects are measured. This provides a denominator, which is needed to estimate the rate of good and bad effects … such as for every 100 patients treated, 80 (80%) had a response that lasted … X months / years.

 

 

ON NATURAL MEDICINES 

Andrew Dodds writes:

"It isn't very surprising that plants contain anti-cancer chemicals; they have being fighting a biochemical war against the world's animals for approximately 300 million years (land plants, anyway..) and have hence evolved chemicals that probably interfere with virtually every biochemical pathway that exists. Hence it is very likely that there are chemicals out there that interfere with those chemical pathways crucial to the survival and proliferation of cancer cells.

However, this does NOT mean that 'natural is best'. First, the compound in question will only fight cancer as a secondary effect to it's primary purpose (killing an insect that feeds on the plant, for instance). Hence a synthetic derivative may be far more effective.

Second, the [natural] compound may be too unstable in vivo, so again a synthetic derivatives will be more successful.

Thirdly, useful dose ranges (between ' no effect' and 'killing the patient') may be quite narrow, making direct consumption of leaves/bark/etc either ineffective or highly dangerous or both.

In short, the 'big pharma' versions of these 'natural' drugs are going to be more effective.

That does not mean that all information from these companies should be taken uncritically at face value - you should always look closely and critically at the real data supporting the claims made. However, at least this is possible. With alternative 'cures', all you get is the marketing."

posted by Andrew Dodds to

scienceblogs.com 

 

See also

Agents that target disease pathways

We are entering an exciting and promising era in cancer therapeutics.  Our goal is to foster a general understanding of how agents (standard and targeted) for lymphoma are thought to work as an aid to informed consent.  

A little History

Our ancestors experimented with plants, minerals and animal parts as possible medicines to relieve pain and suffering from disease.  Today the endeavor continues, aided by insights into how drugs act against disease, and, of course, a much better understanding of disease processes, but also the ability to modify drug compounds in order to better target disease processes or to limit the toxicities. 

Still the answers cannot come quickly enough, and people continue to die and suffer from cancers and other diseases.  The process of drug discovery and testing is not fast enough, or efficient enough.  "The patients are waiting."

The objective here is to answer some basic questions about drugs:

	What is a drug?
	What makes a drug active?
	What makes it effective?
	How do drugs work?
	What are the key terms about drugs:     affinity, specificity, pathway, PK, mechanism of action, synergy ...
	Why does it take so long to develop and test new drugs for cancers?

What is a Drug?

The first question is the easier to answer.  A drug is a compound used (ingested, infused, or applied)  to correct, slow down, or relieve a medical condition.  A definition that could apply to chicken soup for the common cold, or to Cytoxan for a cancer.   For the first example, the mechanism is lacking and the evidence is thin.

A distinction should be made between a food and a drug.  Foods provide energy and nutrients to support health and functions. Most drugsmust be absorbed into the blood at sufficient levels to affect the disease process.   

Notably, FDA oversight begins when medical claims are made for the intervention. 

Chicken soup is a food, of course, but if promoted as a cancer cure, it could then be regulated as a drug, and the sponsor would have to prove it first before being able to market it as such.  

Is the drug active?  Is it effective? 
What's the difference?

An active drug stops or interrupt a disease process, such as cell division in cancer. However, an active drug is not necessarily an effective drug, because the side effects might offset the positive effects.

For example, you might shrink a tumor with a new compound, but also do greater harm to bone marrow function. That is, an active drug may not help the patient to live better or longer, even if it's active against the disease.

An effective drug is one that has been proven to provide a net benefit: the positive effects exceed the negative and the patients are better off to use the intervention than to let the condition run untreated, or treated with another drug.

In other words, an effective drug is one that provides clinical benefit. The most convincing measure of clinical benefit is when the drug improves survival compared to another effective drug.  This assessment is made possible by randomized clinical trials that test the new drug against the standard of care.  

Note: Sometimes surrogate measures of benefit (surrogate endpoints) are used when it's not practical to measure survival because survival is very long - or because the effects of subsequent treatments confounds the assessment of survival - second and third line treatments are also effective.   A commonly used surrogate for survival is progression or event-free survival.     

So an effective drug provides clinical benefit, which is best measured by an improvement in survival, but also if it can stop or reverse a disease process when no other therapy can.  An effective drug might also provide relief from symptoms, without impairing survival, or quality of life.

The search for effective drugs starts with agents that seem active in pre-clinical experiments.  

Active drugs interfere with a disease processes. The mechanisms of action (how they work) are many.  It may be useful to think about drugs that are very familiar to us. 

	Aspirin, for example, can help to reduce the sensation of pain by inhibiting inflammatory enzymes in our body.
	Other painkillers put locks on neural receptors to reduce the sensation of pain.
	Antibiotics, such as the well-known penicillins,  work by killing bacteria.  They do this by interfering with the formation of the cell walls or cell  contents of the bacteria. Other antibiotics work by stopping bacteria from multiplying.
	Chemotherapy agents damage rapidly dividing cells, causing the cells  to self-destruct ... not unlike skin cells do when exposed to too much sun.

Before aspirin there was willow bark. Opium and cocaine relieved pain. Early scientists extracted and purified the active ingredients from such early natural compounds. Clever organic chemists delighted in fragmenting these molecules in order to find their structures. 

Aspirin and penicillin have been around for a long time, but the drugs that stop and kill cancer cells are among the newest drugs being discovered and fine-tuned. 

	How do scientists develop them?
	How do we know what happens when a drug is received in the body, introduced by mouth, IV drip, or by patch?

Drug Discovery or Design

Briefly, the investigation is done in phases: preclinical, clinical (human testing), and regulatory assessment. 

The first task in in the preclinical phase is to find by screening or design a promising compound and then to determine how much of the drug is needed to do the job. The necessary concentration is determined in preclinical experiments involving cell cultures as in the well-known Petrie dish, or with animals.  

(NOTE: This phase is essential to credible drug research. Sometimes herbal products are inappropriately hyped as cancer treatments based on cell culture experiments, without accounting for the concentration needed in the blood to achieve the cell-culture effect, or if that concentration would be toxic.)

Increasingly for cancer and other diseases new compounds are designed to bind to parts of cell that are driving cell survival or proliferation. These abnormal working parts of the cell are called disease pathways. 

See also Agents that target disease pathways

In the body the drug interacts with, binds to, or disrupts, some process underlying the disease. Targets of the compound can be cell membranes; enzymes, structures or carriers - all proteins - or any one of the cellular chemicals or processes that have been hijacked to keep the disease going. 

The fit between a drug and a body molecule or diseased cell structure is known as affinity. 

One important goal of therapy related to affinity is specificity ... that the compound binds as exclusively as possible to the target of treatment and minimally impairs normal processes. 

The interaction between drug and disease is known as mechanism of action - how the drug works. 

However, even well-targeted drugs, such as the cancer drug Gleevec, can have off-target effects:  significant side effects, emphasizing the need for caution in the testing of new drugs in human subjects, particularly classes of drugs that work by new mechanisms of action or even when approved agents are combined for the first time.  

A relatively new drug target is found on the surface of cancer cells. These are molecular binding sites. One binding site, known as CD20, is targeted by the drug Rituxan.  Here a mouse/man-made antibody binds to the CD20 receptor which can cause the cell to self destruct, or leads to killing of the tumor cell by immune cells. 

     
          Click antibody engaging b-cell tumor images to enlarge

The field of identifying new potential drug targets is accelerating.  Drug targets may be within the cell, such proteins or genes that prevent cell death, on the cell surface as described above, or the target may be other "normal" cells that contribute to the survival and expansion of the malignant cells in the tumor microenvironment.

Many chemotherapy drugs exploit the overt behavior of cancerous cells - rapid cell division.  The dividing cell more readily takes up the drug, which leads to damage of its DNA (the vital information that determine cell behavior and functions) which is more vulnerable during cell division.  ...

Source: http://www.nih.gov/sigs/aig/ 

... The cell, detecting the damage to its DNA , self destructs in a process called apoptosis, similar to when diminishing light triggers leaves to fall from trees.  

Abnormal cells, being living parts of the body, can adapt to drugs leading to drug resistance.  Here getting the dose right and the rationale combination of drugs can minimize the ability of the cells to adapt and survive.    Combining drugs can have an ad

There can be an additive or synergistic effects when combing drugs agents.  Also it's possible that one active agent can work against the mechanism of another active agent (as an agonist) - such as when the second agent causes cell cycle arrest, which is needed for first agent to work.

Additive:      1+1 equals 2
Synergistic:  1+1 equals 3
Agonistic:     1+1 is less than 2 

Researches will also study the mechanisms of resistance. To do this they will need tumor sample from the participants of studies - samples before and after resistance to identify what pathways are turned on in the cells that survive the targeted agent - that may also be targeted. ... As was done with Gleevec.

Identifying the Right Dose: the therapeutic window

The dose differentiates a remedy and a poison. ~ Paracelsus

That a compound is active is just the starting point in the drug development process. 

The agent might be highly toxic at the concentration needed be active in a test tube (In vitro).  Or it may not be absorbed well if taken orally, or it may be cleared too quickly to have a meaningful treatment effect in the body (in vivo).

Thus, pharmacokinetics (PK) is an essential part of new drug development and assessment in the clinical phase.  It's the study of what your body does to a drug. The initial PK research is carried out on animals and then ever-so-slowly and carefully in humans.  See also Wikipedia.org

How long the drug remains in the bloodstream, and at what concentration, are vital to the safety and effectiveness of drug, which are determined by

	Absorption,
	Distribution,
	Metabolism and
	Excretion  (ADME for short).

The organs that have a major impact on ADME are the liver and the kidneys and therefore liver and kidney function are monitored very closely when new drugs are first administered in humans.

Individual differences in ADME can result in faster or slower clearance of the drug from the body.. Differences in clearance rates can affect the course of treatment and severity of side effects. 

(See also the side bar on HETEROGENEITY.)

If the drug remains in the blood too long it can increase side effects. Conversely, a drug that's excreted or cleared too rapidly will not be around long enough, or at the proper concentration, to do its job well. 

Moreover, interaction with other drugs or herbs can affect how drugs are absorbed or cleared from the body. 

Yet another vital aspect of the drug development and testing is the called pharmacodynamics, or PD, which is the study of the effects of drugs on the body or on disease processes within the body and the mechanisms of drug action and the relationship between drug concentration and effect.  See also Wikipedia.org

The objective of PD studies is to identify the therapeutic window:  the dose needed to achieve sufficient levels of the agent in the blood at acceptable toxicity. 

The larger the therapeutic window the more likely the drug can be administered in a safe and effective protocol. 

If the new drugs shows reasonable safety and activity in early phases of clinical trials, it is then tested against approved therapies in large randomized controlled clinical trials.  The goal of phase III studies is to objectively determine the safety and efficacy in a way that minimizes bias.  

Notably, failures outnumber successes in the drug development process.  Only 1 in 5,000 new compounds evaluated in the preclinical stage makes it to the clinic ... and about 1 in 5 new therapies that reach phase III clinical testing. 

The regulatory evaluation of the data submitted by the sponsor for marketing approval does not take very long ... about 6 to 9 months; while the preclinical and clinical testing phase can take ten years or longer.  The cost to the sponsor can exceed 1 billion dollars.  

Because the financial risks of cancer drug development are high and most new drugs fail to win approval, incentives (primarily in the form of marketing exclusivity) are granted to new drugs that win approval.  

Related resources:

	Notes on the dose Having a basic understanding of the importance of getting the dose right in clinical research, you will know what to expect in a phase I clinical trial … and also what questions to ask when advised to take an herb to treat a cancer.
	Introduction to Pharmacokinetics and Pharmacodynamics ashp.org
	Patents  wikipedia.org
	Treatment mechanisms | Treatment types