[CANCER RESEARCH 44,1928-1932, May 1984]

Anticancer Activity of the Structurally Novel Antibiotic CI-920 andIts Analogues1

Wilbur R. Leopold,2 Joan L. Shillis, Amie E. Mertus, James M. Nelson, Billy J. Roberts, and Robert C. Jackson

Warner-Lambert/Parke-Davis Pharmaceutical Research Division, Ann Arbor, Michigan 48105

ABSTRACT

CI-920 is a structurally novel phosphate ester antibiotic that

contains an unsaturated lactone and a conjugated triene system.It has potent antileukemic activity in mice. At doses of 25 mg/kggiven i.p. once daily for 5 days to mice bearing approximately107 L1210 leukemia cells, CI-920 is curative in about 10% of the

mice. Life span increases in noncured mice are typically in excessof 150%. The unsaturated lactone and phosphate ester moietiesare required for activity against L1210 leukemia. Ring hydroxyl-

ation or removal of the terminal hydroxyl group have only modesteffects on activity. Schedule studies suggest that prolongedexposure to low levels of CI-920 is considerably more toxic than

is daily or intermittent administration. Daily administration produces optimal activity against L1210 leukemia. Administrationi.p. and i.v. of CI-920 produce roughly equal toxicity and equalactivity against an i.p. implant of L1210 leukemia. CI-920 isinactive when given p.o. or s.c. CI-920 failed to show confirmed

activity against the following tumors in mice: M5076 sarcoma,B16 melanoma, and Ridgway osteogenic sarcoma. The lack ofsolid tumor activity in mice may be caused by a transportdeficiency similar to that found with methotrexate.

INTRODUCTION

CI-9203 is a structurally novel phosphorus-containing antibiotic

that was discovered in a fermentation beer of a previouslyundescribed subspecies of Streptomyces pulveraceus (subspecies fostreus ATCC-31906). CI-920 was detected as a compo

nent of a complex of similar compounds that were cytotoxic toL1210 leukemia cells in vitro. The structures of CI-920 and

related compounds are shown in Chart 1. The fermentationconditions and biological characterization of the producing organism (9), as well as details of the isolation (8) and structureelucidation (4), have been presented elsewhere.

Initial work indicated that CI-920 was cytotoxic to a number

of human tumor cell lines in vitro and to L1210 and P388leukemias in vivo (5). The novel structure of CI-920 coupled with

its apparent anticancer activity in mice prompted further study(at Warner-Lambert/Parke-Davis and the NCI) of its potential

application to cancer chemotherapy.

MATERIALS AND METHODS

CI-920, PD 113,270, PD 113,271, and PD 114,027 were isolated as

the sodium salts from fermentation cultures as described by Stampwalaet al. (B). PD 114,631 was prepared by alkaline phosphatase treatment

of CI-920 (4). PD 116,250 and PD 116,251 were prepared by acetylationof CI-920 and PD 113,271, respectively (4).

In Vitro Cytotoxicity Assays. The L1210 murine leukemia and theHCT-8 human colon adenocarcinoma cell lines were obtained from EG

& G Mason Research Institute (Worcester, MA) and Dr. Joseph Berlino(Yale University), respectively. Both cell lines were grown in RPM11640supplemented with 10% fetal bovine serum and gentamicin sulfate (50Mg/ml) (Schering Corp., Union, NJ).

Dilutions of test compound (20 /il) in water were inoculated into wellsof 24-well Linbro plates (1.7 x 1.6 cm, flat bottom), followed by theaddition of L1210 cells (3 x 104/ml) in 2 ml of growth medium. Afterincubation for 3 days at 37°in a humidified atmosphere containing 5%

CÛ2in air, cell growth was determined by cell count with a Coulter ModelZM electronic cell counter (Coulter Electronics, Inc., Hialeah, FL).

HCT-8 cells were planted in 24-well Linbro plates at a concentrationof 3 x 104 cells/ml/well. After incubation at 37°for 48 hr in 5% CO2 in

air, 10 M' of each drug dilution in growth medium was added to eachwell, followed by further incubation for 4 days. Nuclei then were releasedfrom the cells with Lysing Reagent (Scientific Products Division, AmericanHospital Supply Corp., McGaw Park, IL) using a modification of thetechnique described by van der Bosch ef al. (10) and were counted witha Coulter Counter.

For both assays, drug activity was expressed as the amount of drugrequired to produce 50% inhibition of cell growth when compared tocontrols.

Tumor Passage. Hosts for tumor passage and treatment were purchased from Charles River Breeding Laboratories, Inc., Wilmington, MA,or Simonsen Laboratories, Inc., Gilroy, CA, except for AKR mice, whichwere obtained from The Jackson Laboratory, Bar Harbor, ME.

Routine tumor passage was carried out in the inbred strain of originof the tumor. L1210 and P388 leukemias were passed weekly in maleDBA/2 mice as i.p. implants of 104 and 10s cells, respectively. Solid

tumors were passed as s.c. implants of trocar fragments from tumorsweighing approximately 1 g.

Chemotherapy. All testing at the Warner-Lambert/Parke-Davis labo

ratories was carried out as described below. Those tests performedunder the auspices of the NCI (indicated in "Results") followed standard

NCI protocols (3).Anticancer activity was routinely carried out in F, hybrid mice derived

from the host of tumor origin, except for tests involving the Ridgwayosteogenic sarcoma, in which AKR mice were used. On day 0, the testmice were inoculated with counted numbers of tumor cells or trocarfragments (~30 mg) as appropriate and randomized before distribution

to treatment or control groups. All mice were weighed on the first andlast days of treatment or on each treatment day for the daily andintermittent dosing regimens, respectively. Each group was treated onthe basis of group average weight. The test compounds were dissolvedin 0.9% aqueous NaCI.

Median life spans were calculated by methods appropriate for groupedobservations (7). The % T/C was calculated as

1This investigation was supported in part by USPHS Contract NCI-CM-37556.2To whom requests for reprints should be addressed.3The abbreviations used are: CI-920,5,6-dihydro-6-[3,6,13-trihydroxy-3-methyl-

4-(phosphonooxy)-1,7,9,11 -tridecatetraenyl]2-H-pyran-2-one(monosodium salt); %

T/C, percentage of treated/control.Received November 14, 1983; accepted February 9, 1984.

100 xMedian life span of treated mice

Median life span of control mice

Host body weight change data is reported as the difference of the meangroup weights between the last and first days of treatment for life spanassays or as the maximum of treatment-related weight loss for tumor

1928 CANCER RESEARCH VOL. 44

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Anticancer Activity of CI-920

HO CH3

CI-920

PD 113,270

PD 113,271PD 111,027*

PD 111,631

PD 116,250

PD 116,251

«1

H

H

OH

H

H

H

OCOCH3

R2P03-

P03=

P03-

P03-

HP03-

P03-

MH

H

H

H

H

COCH3

COCH3

OH

H

OH

OH

OH

OCOCH3

OCOCH3

OPENED LACTONE

Chart 1. Structures of CI-920 and related compounds.

growth delay assays.Results of the Ridgway osteogenic sarcoma tests are expressed as

% T/C on Day 35, where

%T/C = 100 x Median size of treated tumors

Median size of control tumors

For this test, treated/control values <42% were considered indicative of

significant anticancer activity. Measurements of tumor growth delay wereused to assess activity against mammary adenocarcinoma 16c (1,6). Tobe considered active, the test compound had to produce a gross logâ„¢tumor cell kill in excess of 0.7 log in the growth delay assay.

All mice which were tumor free at 60 days were considered "cured."

Data from these mice were excluded from calculations of % T/C, tumorgrowth delay, and logio tumor cell kill. Determinations of tumor cell killwere carried out as described by Schabel ef al. (6) and Corbett ef al. (1).

Table 1In vitro cytotoxicity of CI-920 andanaloguesTest

sampleCI-920

PD 113,270PD 113,271PD 114,027PD 114,6311CL12100.21

0.220.832.5W

kg/mi)HCT-82.3

1.54.2

563.7

8 IC»,concentration of drug that will reduce tumor cell growth to 50% of the

control value.

RESULTS

Initial evidence for the in vivo anticancer activity of CI-920 wasobtained against i.p. implanted (106 cells, Day 0) P388 leukemia.

In these NCI tests, dose levels above 25 mg/kg/injection (giveni.p. as once-daily injections on Days 1 through 5) were toxic.

Optimal dose levels produced % T/C values of 157 and 174(total dosages, 62.5 and 125 mg/kg, respectively). CI-920 was

subsequently shown in our laboratory to have significant activityagainst L1210 leukemia.

Structure/Activity Relationship. CI-920 was isolated as one

component of a group of structurally related compounds (4, 8,9). CI-920, an enzymatically modified analogue, and several other

related fermentation and semisynthetic products were examinedboth in vitro and in vivo to determine the effect of variousstructural changes on cytotoxicity and antitumor activity (Tables1 and 2).

Table 1 compares the ability of CI-920 and its analogues toinhibit growth of L1210 and HCT-8 cells in vitro. For this series

of compounds, the mouse leukemia cells were more sensitivethan were the human colon adenocarcinoma cells. CI-920 was

highly effective, giving 50% inhibition at a concentration of 0.21ng/ml against L1210 cells and 2.3 ng/m\ against HCT-8 cells. CI-

920 was also cytotoxic to Lewis lung carcinoma cells (concentration of the drug that reduced tumor cell growth to 50% of the

Table 2Influenceof structural changes on the anti-L1210 activity of CI-920

Representativeoptimal responses from individualexperiments. All mice were given i.p. inocula of L1210 cells on Day0. Treatment was ¡.p.as indicated.All NCI-sponsoredtests were carried out as described by Geranet al. (3).

DrugCI-920PD

113,270PD

113,271PD

114,027PD114,631PD116,250PD116,251Dose

(mg/kg/injection)402512.512.56.25C8.126.256.00C1.5e251017.56.0e6.0e3.12e25"50"50"50"ScheduleDays

3-7Days3-7Days3-7Days3-11Days1-9Days3-7Days3-7Days1-9Days1-9Days3-7Days3-7Days3-11Days1-9Days1-9Days1-9Days3-7Days3-7Days3-7Days

3-7Inoculum

(Day0)5x10*5X1045X1041

X1041x10s5X1045X1041

X1051x1065x10*1

x1041X1011

x10*1x1051

X1055X1045X1041

X1041X104Wt

change<gf-2.5-0.90.0-1.2-1.4-1.10.0-0.3+0.4-3.2-0.5-1.1-1.0-1.4-0.6+2.6+3.6+2.2+3.0%T/C"267250289307Curative25027122618018014019012812312810010910110260-daysurvivors0/61/61/60/66/60/60/60/60/60/60/60/60/60/60/60/60/60/60/6

a Differencebetween the mean weights on the fifth and first days of treatment.Excludes 60-day survivors.

e Data from the screening program, Drug EvaluationBranch, Divisionof CancerTreatment, NCI." Highest dose tested.

MAY 1984 1929

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W. R. Leopold et al.

control value, 1.4 ¿ig/ml)in a similar in vitro assay. Removal ofthe primary alcohol moiety (PD 113,270) had little or no effecton cytotoxicity. Hydroxylation of the ring y to the lactone function(PD 113,271) caused a moderate reduction in activity, whileremoval of the phosphate group (PD 114,631) or opening of thelactone (PD 114,027) resulted in a marked loss of activity againstL1210 cells.

In general, the results of in vivo testing paralleled those foundin vitro (Tables 1 and 2). CI-920 showed strong activity andproduced "cures" in the i.p. L1210 leukemia system when administered i.p. on a daily dosing regimen of 5 or 9 days' duration.

Removal of the primary alcohol moiety (PD 113,270) appearedto increase potency approximately 3-fold, while efficacy at the

optimal dose was unchanged. PD 113,270 was also activeagainst P388 leukemia (% T/C = 183) using the NCI protocol(4). Hydroxylation of the lactone ring (PD 113,271) reducedactivity against L1210 leukemia, while potency was essentiallyunchanged.

The phosphate ester and unsaturated lactone moieties werenecessary for antitumor activity, as shown by the absence ofactivity of PD 114,631 and PD 114,027 against L1210 leukemiaat the doses tested. In addition, these compounds were considerably less toxic than was CI-920. Acetylation of the primary andsecondary hydroxyl groups of CI-920 or PD 113,271 (PD

116,250 and PD 116,251, respectively) significantly reducedpotency and abolished anti-L1210 leukemia activity at total doses

up to 250 mg/kg (Table 2).Schedule Dependence. CII-920 appeared to be a moderately

schedule-dependent agent. Because of its sensitivity to CI-920,

the L1210 leukemia system was used to explore the scheduledependency of CI-920, PD 113,270, and PD 113,271. The datafor CI-920 are presented in Table 3. CI-920 was the least potent

(on the basis of total dose to give an optimal response) and themost active against L1210 leukemia when administered on aregimen of daily injections for 5 treatments or daily injections for9 treatments. Single dose treatments appeared to be somewhatless active, while the intermittent dose schedules (every 4 daysfor 2 or 3 treatments) were considerably less effective (net logâ„¢tumor cell kill, ~1 log). The divided dose regimen (multiple doses

per day for 5 days) was significantly more toxic than the dailydose schedules. In addition, antileukemic activity was considerably lower with the divided dose regimen than with the daily doseregimen. The data suggest that host toxicity would be greatestunder conditions of continuous exposure to CI-920. The relative

orders of the toxic and therapeutic effects of different doseregimens with CI-920 were: toxicity, daily ~ intermittent < single

dose < multiple daily doses; and efficacy, daily > single dose >intermittent ~ multiple daily doses.

Limited data suggested that PD 113,270 and PD 113,271have route and schedule dependencies similar to that of CI-920.

Non-tumor-bearing mice given injections of lethal (doses lethalto 10% to 30% of mice) total doses of CI-920 on a daily schedule

typically died with severe diarrhea within 3 to 7 days of the lasttreatment, suggesting that gastrointestinal toxicity may be doselimiting in the mouse. Daily treatment regimens were used forsubsequent work with CI-920.

Route of Administration. The schedule dependence experiments suggested that administration of CI-920 by routes ex

pected to give prolonged absorption at a lower rate mightenhance toxicity. The data in Table 4 were in agreement withthis hypothesis. Injection s.c. of CI-920 on a schedule of daily

injections for 5 treatments was approximately twice as toxic aswas treatment i.p., but it caused no gross signs of necrosis orulcérationat the injection site. Total p.o. doses of 500 mg/kg

TablesEffect of treatment schedule on the anti-L1210 leukemia activity of CI-920

All mice were Inoculated i.p. (except as noted) with the counted L1210 cells on Day 0. All treatments were given i.p.using the schedules indicated. Results at the optimal dose level from individualexperiments are listed.

ScheduleDay

1onlyEvery4 days for 2 treatments (DaySfEvery4 days for 3 treatments (Day1)Daily

for 5 treatments (Day3)Daily

for 9 treatments (Day 3)Daily for 9 treatments (Day1)Every

6 hr for 3 treatments, daily for 4Inoculum"1

X10"1x 10*(i.v.)1

X1061X1041

xIf/fl.v.)5x10*5x10*5x

10*5xirr5X1051

X1041 x1051

x1051X1055X105Total

dose(mg/kg)40140751252002001257562.5125112.5

112.556.556.517%

T/C6141180197250213267250

(1/6)6198289(1/6)253307

203(3/6)207(6/6)139Net

togiocellkill0(2.8)1.6

(1.6)(-0.5)~7

(~7)3.7(3.8)(-7.4)(-7.4)4.2

(4.5)(-7.4)5.8

(6.8)-7(-7)

-61.6-5.60.2

(-1.0)days (Day 3)

Every 4 hr for 3 treatments, daily for 5days (Day 3)

1 x 10* (i.v.) 45 168 0.8 (0.8)

* Estimated tumor burden at first treatment is -107 cells on Day 3 from a 10* cell inoculumor -107 cells on Day 1 froma 10acell inoculum, based on a doubling time of 0.33 days.

" % T/C was calculated for dying mice only (cures excluded).c Since «traitonsthat enable the calculation of log™cell kill were not done for all experiments, those cell kill values

reported in parentheseswere made using the meantumor doubling time (mean,0.33 days; range, 0.29 to 0.36 days)fromthose Warner-Lambert experiments with titrations. These estimates were not applied to NCI data. Those values not inparenthesesare the actual values based upon the titratton data for that experiment.

'' Numbers in parentheses, beginningday of treatment.8 Numbers in parentheses,number of mice surviving/numberof mice on test.

Test performed under the screening program, Drug EvaluationBranch, Divisionof Cancer Treatment, NCI.

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Anticancer Activity of CI-920

Table4Influenceof route of administrationon the anti-L1210 activity of CI-920

Counted L1210 leukemia cells were implanted i.p. or i.v. on Day 0. All mice were treated on the basis ofcage average weight (Day 1) once daily for 5 consecutive days. Optimal results from single experiments arepresented.

Drugroutei.p.i.V.s.c.P.O.Tumorsitei.p.i.v.¡.p.i.p.i.p.Tumorinoculum

(Day0)1x10*5x10*5x1045X1045X1045X1045X1051

X1041X1045x10*1

X105"5X1045X1055X104Total

dose(mg/kg)1252001251257562.51252002501501255050500%T/Ca250267243250(1/6)c198289(1/6)25321321919425999120101Net

log,ocellkill"~7

(-7)(-7.4)(-7.4)(-7.4)4.2

(4.5)(-7.4)5.8

(6.8)3.7(3.8)~7

(6.3)4.0(4.2)5.4(-3.7)-0.5

(-2.2)(-3.6)

" % T/C was calculatedfor dying mice only (cures excluded).'' Since titrations that enable the calculationof log,0cell kill were not done for all experiments, those cell kill

values reported in parentheseswere made using the mean tumor doubling time (mean,0.33 days; range, 0.29to 0.36 days) from those Warner-Lambert experiments with titrations. These estimates were not applied toNCI data. Those values not in parentheses are the actual values based upon the titration data for thatexperiment.

c Numbers in parentheses,number of mice surviving for 60 days/number of mice on test.

Data produced under the auspicesof the screening program, Drug EvaluationBranch, Divisionof CancerTreatment, NCI.

were not toxic, while administration i.v. was similar to dosing i.p.with respect to toxicity. CI-920 was approximately equally effective against i.p. L1210 when given either ¡.p.or i.v. CI-920 also

had similar activity against i.v. implanted L1210 when given i.p.Treatment of i.p. L1210 s.c. and p.o. were not effective. Therelative orders of potency and efficacy for different routes ofadministration of L1210 (i.p.)-bearing mice were: toxicity, p.o. <i.v. ~ i.p. < s.c.; efficacy, p.o. ~ s.c. < i.v. ~ i.p.

Solid Tumor Activity. CI-920 had little or no activity againstsolid mouse tumors or against the human tumor xenografts. CI-

920 had no significant activity against Ridgway osteogenic sarcoma, B16 melanoma,4 Lewis lung carcinoma,4 the CX-1 colon

carcinoma, MX-1 mammary carcinoma, and LX-1 lung carcinomaxenografts in nude mice,4 CD8F, mammary adenocarcinoma,4colon 38 adenocarcinoma,4 M5076 sarcoma,4 and 16/C mammary adenocarcinoma.4 PD 113,270 and PD 113,271 were also

inactive in the Ridgway osteogenic sarcoma system. PD 113,270had confirmed activity against B16 melanoma (% T/C = 184 at6 mg/kg/injection ¡.p.,daily for 9 treatments), while PD 113,271was inactive.

DISCUSSION

The relative activities of the various analogues of CI-920 in the

L1210 leukemia system indicate that the lactone ring and phosphate ester groups are required for activity. The nature of theinfluence of these groups and of the conjugated triene systemwith respect to anticancer activity is unknown. These data alsosuggest that primary and ring hydroxyl groups do not markedlyinfluence either anticancer activity or potency. However, acety-

lation of the primary and secndary hydroxyl groups (PD 116,250and PD 116,251) results in the complete loss of anticanceractivity and a marked reduction in potency. Since the results

with CI-920 and PD 113,270 indicate that the ring and primary

hydroxyl moieties are not required for activity, these data arecompatible with the hypothesis that the secondary hydroxylgroups ßto the phosphate ester is necessary for activity in theL1210 system. It is not clear whether the hydroxyl group isrequired for transport or for intracellular cytotoxic activity.

In contrast to our results with PD 113,271, NCI testing indicates that PD 113,271 does not have high activity against L1210leukemia (Table 2) but does have activity (% T/C = 156) against

P388 leukemia (data not shown). This discrepancy between theNCI and Warner-Lambert/Parke-Davis L1210 results may be due

to factors such as drug instability and tumor line variability.A possible explanation of the lack of solid tumor activity of CI-

920 in mice is suggested from studies of its biochemical mechanism of action (2).5 6The data of Fry ef a/.6 indicate that CI-920

is transported into cells by the reduced folate carrier protein,which is also responsible for methotrexate transport. Their studies further indicate that CI-920 does not, however, exert its

cytotoxic effect on L1210 leukemia cells by acting as a folateantagonist (2).5 The lack of effect of CI-920 against solid tumors

in mice may be analogous to the well-known inactivity of meth

otrexate (which has demonstrated activity against human solidtumors) in these mouse tumor systems. In a single test (NCI)against the MX-1 mammary tumor xenograft implanted in thesubrenal capsule in nude mice, CI-920 nearly met the criterionfor activity (% T/C < 20), producing a % T/C value of 29 when

administered i.p. on a schedule of injections every 4 days for 3treatments. This tumor, believed to contain the reduced folatecarrier, is sensitive to 10-deazaaminopterin, a close analogue ofmethotrexate. Further study of CI-920 against the MX-1 xeno

graft on a more appropriate (daily) schedule may demonstrate

4Data from the screening program. Drug EvaluationBranch, Divisionof CancerTreatment, NCI.

5D. W. Fry, T. J. Boritzki, and R. C. Jackson. Studies on the biochemicalmechanismof actionof the novelanticanceragentCI-920,submittedfor publication.

" D. W. Fry, J. A. Besserer, and T. J. Boritzki. Evidence that the antitumorantibiotic CI-920 is transported into L1210 leukemia cells by the reduced folatecarrier system, submitted for publication.

MAY 1984 1931

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lY.RLeopo/cfefa/.

its solid tumor activity.The observed interaction of CI-920 with the reduced folate

carrier may also help to explain the observed schedule dependence against L1210 leukemia. Fry ef a/.6 have found that, in

addition to using the reduced folate carrier for entry into the cell,CI-920 inactivates the carrier. CI-920 is least active against

L1210 leukemia when administered as multiple doses per dayon consecutive days. This dosage regimen may result in low butrelatively continuous blood levels of CI-920, which could resultin shutdown of CI-920 transport before lethal intracellular levelsare achieved. Once-daily dosing might allow replacement ofinactivated carrier protein in time to allow accumulation of cyto-toxic levels of CI-920.

Further development of CI-920 is underway on the basis of itsunusual structure and its strong activity against murine leuke-mias. Although CI-920 is without murine solid tumor activity

(presumably because of its transport properties), the possibilityof activity against solid tumors in the clinic remains. In supportof the possible solid tumor activity of CI-920 in the clinic are

preliminary results from the human clonogenic assay system,indicating that CI-920 had significant activity against approximately 34% of the human tumors against which it was tested.7

7D. D. Von Hoff, personal communication.

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2. Fry, D. W., Boritzki, T. J., and Jackson, R. C. Biochemical studies on the novelanticancer agent PD 110,161. Proc. Am. Assoc. Cancer Res., 24: 320, 1983.

3. Geran, R. I., Greenberg, N. H., MacDonald, M. M., Schumaker, A. M., andAbbott, B. J. Protocols for screening chemical agents and natural productsagainst animal tumors and other biological systems. Cancer Chemother. Rep.,3: 1-103,1972.

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8. Stampwala, S. S., Bunge, R. H., Hurley, T. R.. Willmer, N. E., Brankiewicz, A.J., Steinman, C. E., Smitka, T. A., and French, J. C. Novel antitumor agentsCI-920, PD 113,270, and PD 113,271. II. Isolation and characterization. J.Antibiot. (Tokyo), 36: 1601-1605,1983.

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920, PD 113,270, and PD 113,271.1. Taxonomy, fermentation, and biologicalproperties. J. Antibtot (Tokyo), 36: 1595-1600,1983.

10. Van der Bosch, J., Masul, H., and Sato, G. Growth characteristics of primarytissue cultures from heterotransplanted human colorectal carcinomas in serum-free medium. Cancer Res., 41:611-618,1981.

1932 CANCER RESEARCH VOL. 44

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1984;44:1928-1932. Cancer Res   Wilbur R. Leopold, Joan L. Shillis, Amie E. Mertus, et al.   and Its AnaloguesAnticancer Activity of the Structurally Novel Antibiotic CI-920

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