Antibiotics & Antivirals Flashcards
Summary of Lecture Outcomes
1) Explain how the introduction of the sulfonamides helped to pave the way for
the discovery and effective use of penicillin.
2) Identify the distinct roles Fleming and Florey played in the discovery of
penicillin.
3) Explain how breakthroughs in synthetic chemistry that allowed chemical
modification of the core penicillin structure led to the development of improved
penicillin derivatives
4) Identify in basic terms the key steps in the killing of sensitive bacteria by
penicillin.
5) Identify the problems raised by the emergence of drug-resistant organisms
(MDRO), the complex factors contributing to this global problem as well as the
“discovery void” afflicting this area of pharmaceutical innovation.
Aim of Lecture
To explore major successes and
re-emerging threats in the use of
pharmaceuticals during the war
on microbial disease.
How Sulfonamides Paved the Way
Proved that fatal infectious diseases
were “manageable” with drugs (e.g.,
pneumonia)
Fostered development of hospital
microbiology infrastructure:
Well-equipped labs
Handling lots of patient samples
Sample analysis protocols
Dosing guidelines
Trained medical, nursing & scientific
staff
Limitations of Salvarsan & “Sulfa Drugs”
Narrow “spectrum of action”
i.e. didn’t kill a wide enough range of bacterial
species
Toxicity to patient with salvarsan (arsenic)
Skin stained with Prontosil (not a problem with
other sulfonamides)
Bacterial resistance a problem with sulfa drugs
The Three “A” Drug Classes that Made Modern Surgery Possible
Anaesthetics
Antibiotics
Analgesics
Alexander Fleming and the Discovery of Penicillin
Born 1881 [Scotland] (d.1955)
Watched soldiers die of infected wounds in Medical
Corps (WW-1)
Noted failure of antiseptics to cure internal bacterial
infections
1928, Director, Inoculation Lab, St Mary’s Hospital,
London
Worked on anti-bacterial properties
of human nasal secretions
(lysozyme)
“The Beginning of the Antibiotic Era”
2 Innovative Synthetic Drugs found via Animal
Testing of “Compound Libraries”
Salvarsan = (arsenic drug for treating
syphilis infections - 1911)
Prontosil = (azo drug for streptococcal
infections - 1935)
The Penicillium Mould A Goldmine for Drugs?
Antiquity: Use of mouldy bread to treat infected wounds
(Greece, China, Egypt, etc)
Anglo-Saxon recipe (1,000 yrs) recently shown to kill MRSA (methicillinresistant “Golden Staph”)
1870, Burdon-Sanderson, UK, attracted by Pasteur’s germ
theory
1871, reports ability of Penicillium mould (from fruit & jam) to
stop bacterial growth
Joseph Lister [1827-1912] (found antiseptic properties of
phenol)
Observed curative properties of Penicillium-soaked
dressings on infected wounds
“An antibacterial with a broad
spectrum and high efficiency in
killing bacteria with minimal
toxic side-effects was badly
needed.”
A Fluke Observation by Fleming
July 1928, Fleming took 2-week
vacation
Left used agar plates (Streptococcal
cultures) on lab bench
Unusual cold snap (growth advantage
to Penicillium mould contaminant)
Returned to work and noticed
inhibitory effect of mould on bacterial
growth
Fleming’s “Half-Hearted” Follow-Up
Fleming made bright yellow filtered broth from Penicillium
notatum mould
Very active against growing Staph cultures as well as against other
bacterial species
Non-irritating if applied directly to tissue
Safe if injected into healthy mice (but
not tested in Staph-infected mice!)
Couldn’t purify active chemical
(penicillin was unstable)
“Forgot” drug for 13 years!
Florey & Chain – The Penicillin
Extraction Problem Solved
Howard Florey, University of Adelaide-trained
clinical pathologist
Professor of Pathology, Oxford
1937, hired Ernst Chain (talented biochemist)
Fled Nazi Germany with the rise of anti-Semitism
Chain overcame penicillin instability & extraction
problems
Made penicillin as a stable lyophilised salt at pH 5-8
“The abrasive Australian who had more effect
upon the world than any other.”
Australian PM Robert Menzies
Feb 1941 - The First Human Tests
43 y.o. policeman with invasive Strep & Staph infections
200 mg penicillin (i.v. drip) + 100 mg every 3 hrs
24 hr, strong recovery but drug ran-out after 3 days
Administered recycled penicillin (from urine)
Good response but death after drug ran out
Heroic effort to scale-up penicillin production in the
hospital (War-time Britain – limited resources)
Grew the penicillium mould in bedpans!
Subsequent patient also died (girl) before success
with 2 patients
The Semi-Synthetic Penicillins
Nov 1942 – An Unplanned Human Trial (USA)
Over 500 deaths in tragic night club fire (Boston)
220 survivors secretly treated with penicillin
US Military amazed by drug’s effectiveness
By 1944, monthly US production > 130 billion units
Sufficient for Allied troops at Normandy invasion
(i.e., D-Day, June 6, 1944)
Allayed fears regarding gangrene from gunshot wounds
March 1940 – Florey has Stunning Success in First Animal Tests
1941 – Uncle Sam to the Rescue
1940 &1941 – two papers published in The Lancet
British drug companies unable to help (war pressures)
US$5000 grant from Rockefeller Foundation allowed travel to US
Links with US Dept Agriculture researchers
Isolated high yield Penicillium strain (i.e., produced more penicillin than Oxford
strains)
Collected from the skin of a rock melon or “cantaloupe”
Consortium with US companies (e.g. Pfizer, Squibb, Eli Lilly, Abbott, Merck, etc)
Perfected large scale deep vat growth of Penicillium mould
A Remaining Mystery: How Does Pencillin Work?
Jack Strominger, Professor of Pharmacology, Uni of Wisconsin
(USA)
Studied bacterial cell wall + around 30 enzymes needed to
make it
Identified peptidoglycan– chains of aminosugars cross-linked
by small peptides
1965 – famous paper on inhibitory effect of penicillin on cell
wall synthesis in bacteria
Penicillin = CWSI – cell wall synthesis inhibitor
Cell wall = semi-rigid but dynamic structure which helps
bacteria maintain their shape
Identified transpeptidase as key target for many CWSIs
The Race to Make Penicillin
1943, both US and UK teams made drug
crystals but found they were working with
different “penicillins” (wrong structures)
Many penicillin variants soon isolated from
Penicillium broths
WW2: >1000 scientists, 39 unis & companies
tried to make drug synthetically (most gave
up!)
1945, Dorothy Hodgkin (UK) solved unusual
β–lactam structure (X-ray crystallography)
1957, John Sheehan (USA) – first “total
synthesis” of penicillin
The “Golden Age” of Antibiotic Discovery
After WW-2, need for secrecy concerning
penicillin ended
Allowed commercial development of many
new drug classes
Widespread, global screening of microbes for
new drugs (e.g., derived from soil samples)
Of all antibiotics discovered from 1945 to 1978,
55% came from the genus Streptomyces (soil)
Many lethal diseases receded (pneumonia,
syphilis, gonorrhoea, diphtheria, scarlet fever,
childbirth infections, etc
)
Penicillin Blocks A Key “Crosslinking” Step in Bacterial Peptidoglycan
Production for Cell Wall
Microbial Origins of Some Classic Antibiotics
Antibiotics: The Big Picture
“It has been suggested that during
the 20th century, antibiotics have
been responsible for a ten-year
increase in lifespan because of their
ability to diminish the threat of
premature death through bacterial
infection; this is compared to a twoyear increase in lifespan if all
cancers were curable.”
Consequences of MDRO Emergence for Humanity
The Golden Age is over
More antibiotics are losing effectiveness
ADR: Antibiotic
Drug
Resistance
O’Neill Report (UK, 2016) – predicted 10 million deaths p.a. due to
ADR by 2050
↑↑ Cost of treaTng paTents with resistant strains
Resorting to nastier drugs
MDRO are a growing problem in hospitals
Especially in low- and middle-income countries (LMICs)
Need to be smarter with existing drugs
“antibiotic stewardship
Drug Resistance: The Bugs Fight Back!
- Loss of effectiveness common for
most if not all antibiotics
*Bacteria can develop resistance
spontaneously
*Or acquire via plasmids
*Often share multiple resistance
mechanisms via plasmids –“superbugs” [i.e., bacteria that are
resistant to many antibiotics from
different classes] –Much harder to treat (increase cost
and duration of treatment)
The Visible Impact of Multiple Drug Resistance Organisms (MDRO)
The Economic Dimension of the Problem
Drug companies need to receive adequate
returns on their antibiotic investments
Recover huge discovery and development costs
Can’t do this if drugs quickly lose effectiveness
due to emergence of drug resistance
i.e., the “lifespan” of clinical use of many
antibiotics is shorter than for many other
medicines
We need cheaper ways of discovering and
testing antibiotics in humans
Complexities of Antibiotic Drug Resistance in LMICs
Lecture Conclusions
- Penicillin effected one of the most dramatic revolutions
in human health standards ever - Fleming, Florey, Chain - primary discoverers
- Hodgkin, Sheehan, Strominger - crucial follow-up discoveries
- Confidence from the Penicillin Revolution inspired
discovery of many other valuable antibiotics in
subsequent 30 years - But today, we are struggling with the impact of overuse - multidrug resistance & drug discovery void
- “The more you use them, the more you lose them.”
- Thankfully, the news is not all bleak
- Good antibiotic stewardship can reverse MRDO prevalence
- Genetic engineering of organisms is leading to promising new
anTbioTcs (switch on dormant genes in bugs → make novel
antibiotic drugs)
Further Reading
Amyes, SGB (2013) Bacteria: A Very Short Introduction, Chapter 7, OUP.
Bud, R (2007) Penicillin: Triumph and Tragedy, OUP.
Goldsworthy, PD (2002) Howard Florey, Alexander Fleming and the Fairy Tale of Penicillin, Med J Aust, 176,
178-180.
Henderson, JW (1997) The Yellow Brick Road to Penicillin, Mayo Clinic Proc. 72, 683-687
Hutchings, M et al (2019) Antibiotics: past, present & future. Current Opinion in Microbiology, 51, 72-80
Joklik, WK (1996) The Story of Penicillin, FASEB Journal, 10, 525-528.
Li, JJ (2006) Laughing Gas, Viagra & Lipitor, Chapter 2, OUP.
Siulis, et al (2021) Antimicrobial resistance in low- & middle-income countries: current status and future
directions. Expert Rev Anti Infect Ther, 19;1-14.
Van den Brink, R (2021) The End of an Antibiotic Era: Bacteria’s Triumph Over a Universal Remedy, Springer
(available as e-book from UWA library).
Zaffiri, L et al (2012) History of Antibiotics, J Invest Surg, 25, 67-77
Learning outcomes
After completing this lecture, you should be able to
* describe the current trends in HIV prevalence and incidence in Australia and the key
contributing factors
* list the two clinical markers for AIDS
* describe the origin and structure of HIV and list key HIV proteins as drug targets
* list key steps of the HIV life cycle and the relevant anti-HIV drug class(es)
* describe the scientific events surrounding the development and action of zidovudine as the
first approved anti-HIV drug
* describe anti-HIV drug development and HIV treatment
* relate HIV prevention strategies to the mode of HIV transmission
* distinguish between pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP)
First official reporting of AIDS
1981
a cluster of cases of pneumocystis carinii
pneumonia in five young, previously healthy
gay men in LA
* fungal infection
a cluster of cases of Kaposi’s Sarcoma among
gay men in New York and California
* cancer affecting the skin and mucous
membranes; caused by viral infection
AIDS - clinical markers
epidemiological investigations → low CD4+ T cell counts and acquired immune deficiency
* CD4+ T cell count
* HIV RNA copies
The structure of a HIV virion
The origin of HIV
originated from simian immunodeficiency virus (SIV)
* from primates to humans - preparation and consumption of bushmeat?
earliest known case of HIV-1 infection
* a 1959 plasma sample (Democratic Republic of Congo)
The HIV life cycle and anti-HIV drug classes
BFRIM
HIV1 and HIV2
HIV-1: first isolated in 1983 (Barré-Sinoussi et al., 1983)
* Françoise Barré-Sinoussi (shared the 2008 Nobel Prize in Physiology or Medicine)
HIV-2: first isolated in 1986 (Clavel et al., 1986) and is mostly limited to West Africa
Anti-HIV drug development - challenges
- few antiviral drugs available when AIDS epidemic broke in 1981
- existing antiviral drugs ineffective against HIV
- HIV has a small number of genes → few drug targets
- HIV hijacks human cells
- integration of HIV DNA into genome of host cells
treat complications from opportunistic infections
Important anti-HIV drug classes
Reverse transcriptase inhibitors (RTIs)
* nucleoside reverse transcriptase inhibitors (NRTIs)
* non-nucleoside reverse transcriptase inhibitors (NNRTIs)
Protease inhibitors (PIs)
Integrase strand transfer inhibitors (INSTIs)
HIV-host cell interaction
Antimetabolites to block DNA synthesis
Zidovudine - the first anti-HIV drug
Anti-HIV drug development
HIV treatment
HIV/AIDS is now a manageable chronic disease - life-long ART
* viral suppression (< 200 copies/ml)
* undetectable viral load (< 20 copies/ml) = untransmissible (U=U)
Treatment initiation
* CD4
+ cell count (< 350) in decision-making has changed
* immediately following HIV diagnosis
Antiretroviral regimens
* INSTI-based (e.g., Stribild®)
* NNRTI-based (e.g., Atripla®)
* PI-based
Mutations and (multi)drug resistance
From treatment to prevention
unprotected sexual contact
- Use condoms: highly effective in preventing HIV transmission and certain STIs
- Treatment as prevention (TasP): initiate ART in seropositive individuals
- PrEP (pre-exposure prophylaxis)
- PEP (post-exposure prophylaxis)
blood-borne exposure
- needle and syringe programs
perinatal transmission
- PrEP / HIV screening and initiation of ART
- CDC: avoid breastfeeding completely
HIV prevention - PrEP and PEP
Summary - what you have learned
- HIV: global and local perspective
- HIV: clinical markers, origin, structure
- HIV: life cycle and relevant drug classes
- HIV: drug development and treatment
- HIV: prevention, with a focus on comparing PrEP and PEP
