"Effects of Cimetidine on Cisplatin-induced Nephrotoxicity"

2 Background and introduction

2.1 Cisplatin: background

Cis-diamminedichloroplatinum (cisplatin) is a commonly used anticancer drug
with a broad spectrum of activity against malignant solid tumors, including
lung, head and neck, bladder, germ cell, ovarian, endometrial, and cervical
cancer1,2. It was first identified in 1965 and gained FDA approval in 1978.
Cisplatin*s mechanism of action is that it becomes activated intracellularly by
the aquation of its chloride groups, which subsequently leads to covalently
binding to DNA, forming DNA adducts. This activates various signal-transduction
pathways; for example, those involved in DNA-damage recognition and repair,
cell-cycle arrest, and programmed cell death/apoptosis3.
Dose-limiting side effects such as ototoxicity and dose-limiting nephrotoxicity
(renal tubular dysfunction) typically occur with conventional 3-weekly or
4-weekly regimens of cisplatin2,4. Hydration therapy has been incorporated into
cisplatin treatment, however, approximately one third of patients still show
signs of acute renal toxicity5-7. Although cisplatin-induced toxicity is
dose-dependent, the individual susceptibility to side effects varies
considerably. Previous studies have revealed significant relationships between
cisplatin pharmacokinetics and the likelihood of drug-related side effects2,8.

2.2 Metabolism of cisplatin

Cisplatin does not undergo enzymatic metabolism, with >=90% of the drug excreted
in the urine and <=10% excreted in the feces1. Previous investigations have
demonstrated that cisplatin accumulates in human renal cortex slices against a
concentration gradient9, and that cisplatin competitively inhibits the active
uptake of the cation tetraethylammonium (TEA) by mouse kidney slices10 and by
basolateral membrane vesicles from the rat renal cortex11. Furthermore,
cisplatin inhibits the renal clearance of organic ions from a basolateral site
in the isolated-perfused rat kidney.12 These findings suggest that an organic
cation transporter (OCT) likely mediates the cellular uptake of cisplatin. The
expression of the OCT2 transporter is particularly high at the basolateral
membrane of renal tubular epithelial cells, and this solute carrier is
considered a major transporter in the active secretion of organic cations in
the kidney.13,14 The use of Oct knockout animals in the lab of Dr. Sparreboom
(St Jude Children*s Research Hospital, Memphis, TN) has provided some
preliminary evidence supporting the roll of OCT2 in cisplatin excretion in the
liver, as well as the nephrotoxicity associated with this drug.15 While
cisplatin is not metabolized by conventional hepatic cytochrome P450 enzymes,
several transporter proteins have been identified as being important for influx
and efflux of cisplatin. ATP-binding cassette transporter C2 (ABCC2), multidrug
and toxin extrusion tranporter 1 (MATE1), and MATE2 have all expressed on the
apical membrane of the renal tubule cells and have been implicated in the
efflux of cisplatin.16,17 However, in contrast to the common mechanism of drug
resistance, cisplatin resistance is primarily due to decreased uptake, rather
than the increased efflux.18 This highlights the importance of uptake
transporters for platinum-based therapy, such as cisplatin. Interestingly,
there is no correlation between the expression of OCT2 and cisplatin efficacy
in tumor cells, which suggests that another uptake transporter is important in
cisplatin*s anti-tumor effects. Based on the above information we hypothesize
that inhibiting OCT2 will decrease cisplatin*s nephrotoxicity by inhibiting the
uptake of cisplatin into the renal tubule, without impacting the efficacy of
cisplatin as a chemotherapeutic.
The plasma half-life of cisplatin is approximately 20-30 minutes after a bolus
injection of 50 or 100 mg/m2 doses. Cisplatin does not undergo typical plasma
protein binding, although within 3 hours of infusion approximately 90% of the
platinum from cisplatin becomes bound to several plasma protein, including
albumin, transterrin, and gamma globulin. The protein bound platinum is slowly
eliminated with a half-life of 5 days or more. Platinum is detectable in
tissues for as long as 180 days after the final administration. Concentrations
are highest in liver, prostate, and kidney, with somewhat lower concentrations
in bladder, muscle, testicle, pancrease, and spleen.
The dose-limiting toxicity with cisplatin treatment is nephrotoxicity, which is
noted during the second week in 28-36% of patients treated with a single dose
of 50 mg/m2. Renal toxicity is determined by elevations in BUN and creatinine,
serum uric acid, and/or a decrease in creatinine clearance. Nephrotoxicity
becomes more prolonged and severe with repeated courses of the drug. An
association with renal tubular damage has been identified. Renal toxicity is
still seen when preventative methods are used (longer infusion rate,
intravenous hydration, and concomitant mannitol), although the severity is
somewhat reduced. Other forms of cisplatin-induced toxicity include ototoxicity
(up to 31% of patients), myelosuppression (25-30% of patients), and marked
nausea and vomiting (almost all patients). Relatively rare toxicities include
general vascular toxicities (due to serum electrolyte disturbances),
hyperuricemia, neurotoxicity, ocular toxicity (optic neuritis, papilledema,
cerebral blindness), hepatotoxicity, anaphylactic-like reactions, hiccups,
elevated serum amylase, and rash.

2.3 Cimetidine: background

Cimetidine is a histamine H2-receptor antagonist that inhibits the
production of stomach acid. It is predominantly used for the treatment of
heartburn and peptic ulcers. Cimetidine was approved for prescriptions in 1979
and was the prototypical histamine H2-receptor antagonist from which the later
members of this class were developed. Mild diarrhea occurs in approximately 1%
of patients. CNS toxicities are generally infrequent (0.3-3% of patients) and
have been reported as headaches, dizziness and mild somnolence. Patients
treated long term with cimetidine have reported gynecomastia, although no
induction of endocrine dysfunction was found. Other extremely rare toxicities
have been reported (decreased white blood cell counts (<= 1 in 100,000
patients), agranulocytosis (3/million patients), thrombocytopenia (3/million
patients), fever, rash, and allergic reaction. Of relevance to the current
study, cimetidine has been identified with a dose-related increase in plasma
creatinine. However, this is presumed to be due to competition for renal
tubular secretion and does not signify deterioting renal function.

2.4 Metabolism of cimetidine

Cimetidine is rapidly absorbed after oral administration, with Cmax
within 45-90 minutes. The half-life of cimetidine is 2 hours, although plasma
concentrations remain above what is required to provide 80% inhibiton of
gastric acid secretion for 4-5 hours. Cimetidine is predominantly excreted by
the kidneys, with 48% of the drug recovered in the urine by 24 hours after oral
administration and 75% after intravenous or intramuscular administration.
Cimetidine is a known inhibitor of several isozymes of the cytochrome P450
(CYP) metabolic enzyme system, such as CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1,
and CYP3A4. This can lead to drug-drug interactions with compounds
predominantly metabolized in the liver (warfarin-type anticoagulants,
phenytoin, propranolol, nifedipine, chlordiazepoxide, diazepam, tricyclic
antidepressants, lidocaine, theophylline, and metronidazole). However, no
CYP450-mediated drug-drug interactions are expected with cisplatin.
Cimetidine is a known substrate for a variety of transporters. In
vitro data has demonstrated uptake of cimetidine by renal organic anion
transporter 1 (OAT1),19 OAT3,20 OCT1,21 OCT2,22,23 and OCT3.24 Despite that
cimetidine is a substrate for a variety of uptake transporters, it should be
noted that as an inhibitor, cimetidine has an IC50 that is greater than 2-fold
lower for OCT2, as compared to other SLC transporters. This suggests that
cimetidine is a very potent inhibitor for OCT2, even at clinically relevant
concentrations. Cimetidine is effluxed out of the cells by the ABCB1 and ABCG2
transporters.25,26

2.5 Study rationale

The nephrotoxicity caused by cisplatin is of great concern both in that it is
dose-limiting and can be detrimental to the patient. Much work has been done to
reduce or prevent this damage to renal cells, however to date the best approach
has reduced the occurance but not completely prevented it. Most approaches to
date have involved diluting the concentration of cisplatin (via longer infusion
rate, intravenous hydration, and concomitant mannitol), which has reduced the
toxicity somewhat but has failed to prevent it. There is a growing body of
evidence that the renal cell damage is localized on the basolateral side of the
proximal tubular cells. The presence of a cisplatin transporting solute carrier
(OCT2 in humans and Oct1/2 in rodents) on the basolateral side of the proximal
tubular cells is a likely candidate for how cisplatin enters the renal cells.
Instead of attempting to dilute the circulating concentration of cisplatin, we
propose that by blocking the OCT2-mediated uptake of cisplatin we may be able
to prevent the nephrotoxicity from occurring.
Our hypothesis is supported by both in vitro and in vivo data we have generated
(manuscript submitted for publication). Using OCT2 over-expressing HEK293 cells
we have demonstrated that cimetidine is a potent inhibitor of cisplatin uptake.
Furthermore, we have used an Oct1/2 knockout mouse model, which best represents
the renal OCT2 in humans, to evaluate cisplatin-induced nephrotoxicity. The
knockout mice show little to no cellular damage in the proximal tubules of the
kidney, while 20-40% of control mice die from when administered the same dose
of cisplatin. There is also a reduction in urinary excretion of cisplatin,
confirming that the secretion of cisplatin is impaired. There was no change in
plasma pharmacokinetics of cistplatin and no other tissue damage was found in
the knockout animals. Interestingly, in vitro studies using NCI60 cancer cell
lines found no correlation between the expression of OCT2 and
cisplatin-sensitivity.
Based on these pre-clinical findings, we hypothesize that blocking
OCT2-mediated uptake of cisplatin my prevent nephrotoxicity without impacting
the efficacy of cisplatin for treating tumors. We propose to elucidate the
potential therapeutic benefit of cimetidine concomitant administration with
cisplatin using several approaches. We will evaluate kidney function and damage
both before cisplatin administration and after cisplatin administration with
and without cimetidine. Kidney function will be evaluated using creatinine
clearance to test a more complex interaction of filtration, secretion, and
absorption. Kidney damage will be evaluated by measuring
N-Aceytl-b-D-glucosaminidase activity in the urine samples. We will also
observe the pharmacokinetics of cisplatin, to confirm that inhibiting OCT2
transport does not alter the pharmacokinetics of cisplatin. If possible, a
counterbalanced *within patient*-design will be utilized to reduce the number
of patients necessary, to increase the statistical power, and to provide an
intra-patient control. This study is clinically relevant because the
dose-limiting nephrotoxicity is a major danger with the usage of cisplatin
treatment. The ability to prevent this tissue damage could greatly improve
patient outcome and quality of life.

Study objectives

3.1 Primary objective

•To investigate the ability of cimetidine to prevent cisplatin-induced
nephrotoxicity, while not impairing the efficacy of cisplatin in Head and Neck
cancer patients.

3.2Secundary objective
•To relate single-nucleotide polymorphisms in the drug transporting proteins to
the pharmacokinetics and -dynamics of cisplatin treatment.

This is a single center pharmacokinetic study intended to investigate the
possible pharmacokinetic interaction of cimetidine and cisplatin. The study
will be performed at the Erasmus MC, location Daniel den Hoed Cancer Center.

None.

- Side effects of cimetidine in clinical trials were mild and reversible. Less
than 1% of patients treated in controlled clinical trials dropped out due to
toxicity. Most common side effects were headache.
- bleeding, infection or discomfort with venous catheter.