e-content of Combating Drug Resistance for M.pharm students.

1. DRUG RESISTANCE
Presenting by:
Mr. PURSHOTHAM K N
Asst. Professor,
Dept. of Pharmaceutical Chemistry
SAC College of Pharmacy.
2021-2022

2.  DRUG RESISTANCE is the ability of microbes, such as bacteria,
viruses, parasites or fungi, to grow in the presence of a chemical
(drug) that would normally kill it or limit its growth.
 It is the reduction in the effectiveness of a drug in curing a disease
or condition.
DRUG RESISTANCE

3. DRUG RESISTANCE IN ANTI CANCER THERAPY
 Anticancer drugs resistance is a complex process that arises from
alterations in the drug targets. Advances in the DNA microarray,
proteomics technology and the development of targeted therapies
provide the new strategies to overcome the drug resistance.
 Cancer causes the uncontrolled growth of abnormal cells and
dynamic altering in the genome (which cause cancerous features in
normal cells).

4.  The cancer progression impairs the normal biological process of
healthy cells which is achieved by the invasion of nearby tissues and
metastasize to distant tissues.
 In addition to, common cancer treatments such as surgery, radiation
therapy, chemotherapy, combination therapy and laser therapy; the
selective therapies are the promising treatments.
 Today, despite these advances, the promising option for cancer
treatment is chemotherapy. Currently, 90% of failures in the
chemotherapy are during the invasion and metastasis of cancers
related to drug resistance.
 In the chemotherapy, by following the administration of a certain
drug, a large number of patient tumor cells become resistant to the
drug. So, the drug resistance appears as a serious problem in the field
of cancer. There are many other problems in the cancer therapy, such
as cytotoxic agents resistance and toxic chemotherapy.

5. CAUSES
5. Alterations in
intracellular
retention of
drug
1. Alterations
in
drug targets
4. Increased
DNA Repair
3. Defective
Apoptosis
2. Alterations
in Drug
detoxification

6. 1. ALTERNATIONS IN DRUG TARGETS
 One of the first mechanisms of acquired drug resistance to
chemotherapy by tumor cells was designed to be an alternation of
the protein targeted by the drug, either by loss or gain of function.
 Additionally, some tumor cells can amplify copies of the genes
encoding the drug's target and transcribe and translate more of the
target molecules overwhelming the drug's cytotoxicity ability.
 Finally, some pre-existing somatic mutations that are present in
the tumor cells confer resistance to therapy and must be
considered when choosing active agents for individuals

7. Eg. DHFR, Methotrexate
Tumours cells has decreased levels of Dihydro folate reductase (DHFR) after
being exposed to an antifolate (Methotrexate).

8. • Some tumors that developed resistance to methotrexate overtime
were found to have amplified the DHFR gene and subsequently
increased levels of expressed DHFR enzyme.
• These cells had increased DHFR activity and an increased
concentration of methotrexate was required to destroy these cells.

9. Cancer cells can acquire structural
changes in drug targets over time.
Eg. Topoismoerase is an enzyme often
targeted by several anti-cancer drugs.
Multiple mutations have resulted in
resistance of topoisomerase either by
reduction in enzymatic activity or by
alterations in protein structure.
ETOPOSIDE

10. 2. DRUG INACTIVATION
Drug activation in vivo involves complex mechanisms in
which substances interact with different proteins. These interactions
can modify, partially degrade, or complex the drug with other
molecules or proteins, ultimately leading to its activation. Many
anticancer drugs must undergo metabolic activation in order to
acquire clinical efficacy. However, cancer cells can also develop
resistance to such treatments through decreased drug
activation.

11. One example of this is observed in the
treatment of acute myelogenous leukemia
with cytarabine (AraC), a nucleoside drug
that is activated after multiple
phosphorylation events that convert it to
AraC-triphosphate. Down-regulation or
mutation in this pathway can produce a
decrease in the activation of AraC, and this
can lead to AraC drug resistance. CYTARABINE

12. 3. ALTERATIONS IN DRUG DETOXIFICATION
Cells use secondary metabolic pathways (Eg. Phase II
metabolism) for the primary purpose of making the drug molecules
more water soluble in order to efflux them from the cell. By
enhancing Phase II metabolism, cancer cells can rapidly excrete
drugs, thereby reducing their overall exposure time to the cytotoxic
agents.
4. INCREASED DNA REPAIR
By increasing either the rapidity of DNA repair or
decreasing the efficiency of repair, cancer cells can overcome
some of the DNA damage exerted by certain chemotherapeutic
agents.

13. Eg. 06-alkyl guanine alkyl transferase (0GAT), a constitutively
expressed DNA repair protein, which removes alkyl groups from
the 06-position of guanine in DNA. Tumor cells that exhibit high
0GAT activity are resistant to agents that forms 06-alkyl adducts ,
such as Triazene compounds.

14. 6. DEFECTIVE APOPTOSIS
Apoptosis or Programmed cell death , is an energy
dependent process by which cells undergo an orderly series of
intracellular events leading to cell death.
Apoptosis is required for maintaining appropriate function
and the structure of normal proliferating renewable tissues and
disruption of normal programmed cell death response prevents cells
from self destructing when irreversible damage takes place , and
they survive with this damage. Because they don't apoptose, these
cells can continue to replicate unchecked.

15. Apoptosis has two established pathways: an intrinsic pathway
mediated by the mitochondria that involves B-cell lymphoma 2
(BCL-2) family proteins, caspase-9 and Akt, and an extrinsic
pathway that involves death receptors on the cell surface.
BCL-2 is an oncogene , the expression of which inhibits apoptosis and
thus making cancer cells resistant to chemotherapy BCL-2 family
protein inhibitors ( Eg .Venetoclax) are effective in inducing apoptosis
in cancer cells, but prolonged use can produce resistance.

16. STATEGIES TO COMBAT RESISTANCE
The future strategy to overcome resistance will be
individual patient's therapy prospectively, employing both
knowledge of the patient's somatic mutation in drug
metabolizing enzymes, drug receptors, and drug targets with the
knowledge of tumor – specific changes that effect cytotoxicity
of agents normally given systematically to patients. Some
strategies used clinically are pharmacokinetic strategies,
pharmacogenetic based strategies, and basic tumor biology
directed strategies for dosing.

17. PHARMACOKINETIC MONITORING
One strategy to overcome tumor cell resistance to
chemotherapy is to employ pharmacokinetic strategies to
further intensify doses of drugs by giving the maximally
tolerated dose of drugs as close together as possible.
Eg. By using 24-hr methotrexate infusions clinically, one can
overcome the resistance phenotype seen in tumors over
expressing certain ABC transporters , whereby long exposure
to methotrexate was able to overcome the high levels of
resistance observed after short (4G) exposure .

18. Additionally high serum concentration of methotrexate can
overcome the resistance achieved by increased quantities of
DHFR intracellularly or decreased expression of the reduced
folate carrier.
PHARMACOGENETIC MONITORING
Pharmacogenetic based strategies are currently used to identify
monogenetic trails in patients that would alter either a
predisposition to toxicity or the efficiency of response. Currently,
these strategies are not used prospectively in patients to alter
dosing in prior, but rather once a patient experiences toxicity or
doesnot respond to therapy, genotyping is performed.

19. DRUG RESISTANCE IN ANTIBIOTIC THERAPY
Antibiotic resistance has reached an
alarming stage worldwide. Many
organisms today have acquired
multiple systems to reduce or avoid
the action of antibiotics. The most
threatening mechanisms of resistance
involve changes in the target site for
antibiotic interaction, because that
confers resistance to all compounds
with the same mechanism of action.

20. Exogenous Resistance occurs when new proteins are
developed by the organism to protect it from drugs.
Endogenous Resistance occurs by mutation, even single
point mutations

21. Types of Drug
Resistance
PRIMARY / NATURAL/
NON GENETIC ORIGIN
OF DRUG RESISTANCE
AQUIRED / GENETIC
ORIGIN OF DRUG
REISTANCE
1. CHROMOSOME
MEDIATED
RESISTANCE
2. TRANSFERABLE
RESISTANCE
(i) PLASMID
MEDIATED
RESISTANCE
(ii) TRANSPOSON
MEDIATED
RESISTANCE

22. RESISTANCE
A. NATURAL RESISTANCE:
Some microbes have always been resistant to certain AMAs. They lack
the metabolic protein or the target site which is affected by the particular
drug. This is generally a group or species characteristics.
Eg, Gram negative bacilli are normally unaffected by penicillin G is
insensitive to tetracycline. This type of resistance does not pose a
significant clinical problem.

23. B. ACQUIRED RESISTANCE:
It is the development of resistance by an organism due to the use of an
AMA over a period of time. Development of resistance is dependent
on the microorganism as well as on the drug.
Eg. Gonococci quickly developed resistance to sulfonamides, but only
slowly and low grade resistance to penicillin.
Penicillin

24. MECHANISMS OF DRUG RESISTANCE
The four main mechanisms by which microorganisms exhibit
resistance to antibiotics are :
a) Drug inactivation or modification:
Eg. Enzymatic deactivation of penicillin G in some penicillin
resistant bacteria through the production of β-lactamases.
b) Reduced drug accumulationz:
By decreasing the drug permeability or increasing active efflux of
the drugs across the cell surface.

25. c) Alteration of target site :
Eg.
*Alteration of PBP- the binding site of penicillin.
*Resistance to trimethoprim arises from an altered DHFR, an enzyme
inhibited by it.
*Erythromycin resistance results from drug induced formation of
N6,N6 dimethyl adenines in the 23S ribosomal RNA, the site of
action of that antibiotic. This reduces the affinity of erythromycin
for the target site.
TRIMETHOPRIM

26. d) Alteration of metabolic pathway:
If the effect of a drug is to block the production of a metabolite by
enzyme inhibition, the organism could bypass the effect of the drug
by inducing a new metabolic pathway that produces the same
metabolite.
Eg. Some sulfonamide resistant bacteria do not require p-amino
benzoic acid (PABA), an important precursor for the synthesis of
folic acid and nucleic acids in bacteria inhibited by sulfonamides.

27. STATEGIES TO COMBAT RESISTANCE
No indiscriminate and inadequate or unduly prolonged use of
AMAsshould be made. This would minimize the selection pressure
and the resistant strains will get less chance to preferentially
propogate. For acute localized infections or in healthy patients,
symptom determined shorter courses of AMAs are advocated.
One way to minimize the effect of target enzyme mutation in drug
resistance would be to design a drug that is very close in structure to
tht of the substrate for the target enzyme.

28. Prefer rapidly acting and selective (narrow spectrum) AMAs
whenever possible. Broad spectrum drugs should be used only when a
specific drug cannot be determined or is suitable.
Use combination of AMAs whenever prolonged therapy is
undertaken. Eg. TB, AIDS, etc.
Destruction of resistant bacteria can also be achieved by Phage
Therapy, in which a specific bacteriophage is used.

29. GENETIC PRINCIPLES OF DRUG RESISTANCE
Generally Drug resistance arises because of one or more of the
following reasons.
Selection of cells that have increased expression of membrane
glycoproteins, increase in levels of cytoplasmic thiols, increasing in
deactivating enzymes or decrease in activating enzymes by changes in
specific gene sequences and increase in DNA repair.
 All of these mechanisms of resistance involve gene alterations .

30. Membrane glycoproteins (P-glycoproteins) are responsible for the
efflux of drugs from cells and represent a type of Multi Drug
Resistance (MDR). These P glycoproteins bind and extrude drugs from
tumor cells.
By increasing pools of cytoplasmic thiols, such as glutathione, the
cell increases its ability to destroy reactive electrophilic anticancer
drugs. More specifically gene encoding the family of glutathione S-
transferases, which catalyze the reaction of glutathione with
electrophilic compounds, may be altered so that enzymes are
overproduced (gene amplification).

31. Many drugs bind to DNA require enzymatic activation (prodrugs).
The genes encoding these enzymes may be altered so that certain
tumor cells no longer produce sufficient quantities of the activating
enzymes to allow drugs to be effective. Finally, once the DNA has
been modified, a resistant cell could produce DNA repair enzymes, to
excise the mutation in the DNA and repair polynucleotide strands.

32. REFERENCE
1. Genevieve Housman,Shannon Byler, Sarah Heerboth,Karolina
Lapinska, Mckenna Longacre, Nicole Snyder,and Sibaji
Sarkar.Drug Resistance in Cancer: An Overview,Cancers 2014,
6(3), 1769-792;5 September 2014.
2. Sampath D, Cortes J, Estrov Z, Du M, Shi Z, Andreeff M, Gandhi V,
Plunkett W; Pharmacodynamics of cytarabine alone and in
combination with 7-hydroxystaurosporine (UCN-01) in AML blasts
in vitro and during a clinical trial; Blood. 2006 Mar 15;
107(6):2517-24.
3. Read AF, Woods RJ. Antibiotic resistance management. Evol Med
Public Health. 2014;2014(1):147.

33. 4. The antibiotic alarm. Nature. 2013;495(7440):141.
5. Centers for Disease Control and Prevention, Office of Infectious
Disease Antibiotic resistance threats in the United States, 2013. Apr,
2013. Available at: http://www.cdc.gov/drugresistance/threat-report-
2013. Accessed January 28, 2015.
6. Lushniak BD; Antibiotic resistance: a public health crisis. Public
Health Rep. 2014 Jul-Aug; 129(4):314-6.
7. Viswanathan VK;Off-label abuse of antibiotics by bacteria; Gut
Microbes. 2014 Jan-Feb; 5(1):3-4.
8. Michael CA, Dominey-Howes D, Labbate M; The antimicrobial
resistance crisis: causes, consequences, and management.;Front
Public Health. 2014.

34. 9. Golkar Z, Bagasra O, Pace DG; Bacteriophage therapy: a potential
solution for the antibiotic resistance crisis.;J Infect Dev Ctries. 2014
Feb 13; 8(2):129-36.
10. Bartlett JG, Gilbert DN, Spellberg B; Seven ways to preserve the
miracle of antibiotics. Clin Infect Dis. 2013 May; 56(10):1445-50.