The document discusses drug resistance in cancer therapy and antibiotic therapy. It provides causes and mechanisms of drug resistance, including alterations in drug targets, drug inactivation, reduced drug accumulation, and increased efflux pumps. Strategies to overcome resistance include pharmacokinetic monitoring, pharmacogenetic monitoring, and inhibiting efflux pumps. Drug resistance is a major challenge in cancer treatment and antibiotic use.

1. DRUG
RESISTANCE
SUBMITTED BY :
RINSHANA FATHIMA ABDUL AZEEZ
FIRST YEAR M.PHARM
PHARMACEUTICAL CHEMISTRY
AL SHIFA COLLEGE OF PHARMACY

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.
 It occurs when a formerly effective drug dose is no longer
effective.

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.

5.  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.

6. CAUSES
Alterations in
drug targets
Alteratioins
in Drug
detoxification
Defective
Apoptosis
Increased
DNA Repair
Alterations in
intracellular
retention of
drug

7. 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.

8. Eg. DHFR, Methotrexate
Tumor cells has decreased levels of dihydrofolate reductase (DHFR)
after being exposed to an antifolate (Methotrexate).

9. 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.

10. 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.

11. 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.

12. 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.

13. 3. ALTERATIONS IN INTRACELLULAR RETENTION OF DRUG
By reducing the drug's ability to enter the cell or by rapid efflux of
the drug from the cell, the cancer cells effectively removes the
ability of drug to exert its effects.
This can be accomplished by either reducing the drug's influx
into the cell or by increasing the copy number of genes encoding
transporters that rapidly efflux either parent drug ot the activated
drug metabolite from the cell.

14. • Members of the ATP-binding cassette (ABC) transporter family proteins
enable this efflux and are important, well-studied regulators at the plasma
membranes of healthy cells. ABC transporters are transmembrane
proteins present not only in human cells, but in all extant phyla,
functioning to transport a variety of substances across cellular
membranes
• When a given substrate binds to the transmembrane domain, ATP
hydrolysis at the nucleotide binding s0ite drives a change in conformation
that pushes the substrate out of the cell. This efflux mechanism plays an
important role in preventing over accumulation of toxins within the cell

15. • While efflux via ABC transporters is a normal physiological process, it is
also a known mechanism of drug resistance in cancer cells. Three
transporters—multidrug resistance protein 1 (MDR1), multidrug
resistance-associated protein 1 (MRP1), and breast cancer resistance
protein (BCRP)—are implicated in many drug resistant cancers. All
three transporters have broad substrate specificity and are able to
efflux many xenobiotics, including vinca alkaloids, epipodophyllotoxins,
anthracyclines, taxanes, and kinase inhibitors, from cells. Thus, they
protect cancer cells from many first line chemotherapies.

16. • MDR1, which produces Pgp, was the first of these to be identified and
has been studied extensively. Normal expression of the MDR1 gene in
the colon, liver, and kidney is increased when these tissues become
cancerous.

17. Interestingly, in one study it was shown that treatment with doxorubicin
induced a large increase in MDR1 expression in lung cancer cells, while no
significant change in expression was observed in normal lung cells,
suggesting that there are both intrinsic and acquired mechanisms of MDR1
over-expression. Tissues that do not normally express MDR1, such as lung,
breast, and prostate cells, are often drug resistant due to the expression of
the related transporters MRP1 or BCRP.

18. BCRP protects normal cells from the effects of toxins like
xenobiotics, maintains heme and folate homeostasis, and is
expressed in stem cells.
Classic anti-folates (Methotrexate) are also transported via RFC
into the cell. Through mutations occuring in RFC, they acquire
resistance to methotrexate. These mutations in RFC resulted in
decreased Methotrexate accumulation in tumor cells.

19. 4. 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 inorder 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.

20. 5. 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.

21. 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.

22. 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.
Apotosis is required for maintaining appropriate function and the
structure of normal proliferating renewable tissues. 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.

23. 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.

24. 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.

25. STATEGIES TO COMBAT RESISTANCE
The future strategy to overcome resistance will be individual
patient's therapy prspectively, 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
pharmacokinectic strategies, pharmacogenetic based strategies , and
basic tumor biology directed strategies for dosing.

26. 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.
For 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 .

27. 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
monogentic trais 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.

28. BIOLOGIC INHIBITION OF TUMOR CELL PROPERTIES (ABC
TRANSPORTERS)
Cyclosporin A (CSA) and PC 833 are agents that block MDR1-
mediated efflux of substrates in vitro and have been used systematically
to inhibit MDR1 during chemotherapy, probably because of the fact that
it is a non-selective inhibitor and also inhibits BCRP mediated efflux.
Expression of mutated TP53 causes defects in the apoptotic
pathway, allowing cancerous cells to avoid death. Re-expression of the
wild type gene in cancer cells has been shown to inhibit cell
proliferation, induce cycle arrest and apoptosis.

29. DRUG RESISTANCE IN ANTIBIOTIC THERAPY
Antibiotic resistance has reached an
alarming stage worldwide. Many organisms
today have acquired mutiple 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.

30. 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 .

31. 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

32. 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 tetracyclines.
This type of resistance does not pose a significant clinical problem.

33. 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.

34. CAUSES FOR RESISTANCE
1. MICROBIAL BEHAVIOUR :
Resistance may be developed by MUTATION or GENE TRANSFER
MICROBIAL
FACTORS
MUTATION
GENE
TRANSFER

35. MUTATION :- It is the stable and heritable genetic change that occurs
spontaneously and randomly among microorganisms. [3
Any sensitive population of a microbe contains a few mutant cells
which require higher concentration of AMA for inhibition. These
are selectively preserved and get a chance to proliferate when the
sensitive cells are eliminated by the AMA. Thus in time, it would
appear that a sensitive strain has been replaced by a resistant one.
Eg. When a single anti tubercular drug is used.
This is called vertical transfer of resistance and is relatively slow and
usually of lower grade.

36. Mutation and resistance may be single step or
multi step.
a) Single Step : A Single step mutation may confer
high degree of resistance, emerges rapidly.
Eg. Enterococci to streptomycin, and E.coli to
Rifampin.
b) Multi Step : A no. of gene modifications are
induced. Resistance to erythromycin,
tetracyclin, and chloramphenicol is developed
by many organisms in this manner.

37.  GENE TRANSFER :- The resistance causing gene is paired from
one organism to the other, a process called as 'Horizontal
Transfer of Resistance'.[3]
Rapid spread of resistance can occur by this mechanism and
high level reistance to several antibiotics (multi drug resistance)
can be acquired concurrently.

38. 2. OVERUSE : As early as 1945, Sir Alexander Fleming raised the alarm
regarding antibiotic overuse when he warned that the “public will
demand [the drug and] … then will begin an era … of abuses.”The
overuse of antibiotics clearly drives the evolution of resistance.
Epidemiological studies have demonstrated a direct relationship
between antibiotic consumption and the emergence and dissemination
of resistant bacteria strains.

39. In bacteria, genes can be inherited from relatives or can be acquired
from nonrelatives on mobile genetic elements such as plasmids.This
horizontal gene transfer (HGT) can allow antibiotic resistance to be
transferred among different species of bacteria. Resistance can also
occur spontaneously through mutation. Antibiotics remove drug-
sensitive competitors, leaving resistant bacteria behind to reproduce
as a result of natural selection. Despite warnings regarding overuse,
antibiotics are overprescribed worldwide.[4]

40. 3. Inappropriate Prescribing : Incorrectly prescribed antibiotics also
contribute to the promotion of resistant bacteria.[5]
Incorrectly prescribed antibiotics have questionable therapeutic benefit
and expose patients to potential complications of antibiotic therapy.[6]
Subinhibitory and subtherapeutic antibiotic concentrations can promote
the development of antibiotic resistance by supporting genetic alterations,
such as changes in gene expression, HGT, and mutagenesis.[7]

41. 4. Extensive Agricultural Use : In both the developed and developing
world, antibiotics are widely used as growth supplements in
livestock.Treating livestock with antimicrobials is said to improve the
overall health of the animals, producing larger yields and a higher-
quality product.[8]The antibiotics used in livestock are ingested by
humans when they consume food.[9]

42. More recently, molecular detection methods have demonstrated that
resistant bacteria in farm animals reach consumers through meat
products.[10] This occurs through the following sequence of events:
1) antibiotic use in food-producing animals kills or suppresses
susceptible bacteria, allowing antibiotic-resistant bacteria to thrive;
2) resistant bacteria are transmitted to humans through the food
supply;
3) these bacteria can cause infections in humans that may lead to
adverse health consequences.[5]

43. 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 accumulation.
By decreasing the drug permeability or increasing active efflux of
the drugs across the cell surface.

44. 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.

45. d) Alteration of metabolic pathway.
If the effect of a drug is to block the production of a metabolite by
enzyme inhibtion, 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.

46. STATEGIES TO COMBAT RESISTANCE
No indiscriminate and inadequate or unduly prolonged use of AMAs
should 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.

47. 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,ec.
Destruction of resistant bacteria can also be achieved by Phage
Therapy, in which a specific bacteriophage is used.

48. 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 .

49. 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).

50. 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.

51. 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), 1769-1792;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
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3. Read AF, Woods RJ. Antibiotic resistance management. Evol Med Public
Health. 2014;2014(1):147.

52. 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
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7. Viswanathan VK;Off-label abuse of antibiotics by bacteria; Gut
Microbes. 2014 Jan-Feb; 5(1):3-4.

53. 8. Michael CA, Dominey-Howes D, Labbate M; The antimicrobial
resistance crisis: causes, consequences, and management.;Front
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9. Golkar Z, Bagasra O, Pace DG; Bacteriophage therapy: a potential
solution for the antibiotic resistance crisis.;J Infect Dev Ctries. 2014
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10. Bartlett JG, Gilbert DN, Spellberg B; Seven ways to preserve the
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