Baja California Plants Screened for Antitumor Activity
Spjut and Richard Marin
World Botanical Associates
Laurel, Maryland and Temecula, California
Prepared August 2000
Presented in Spanish by Richard Marin at the Symposium IV on Botany Research of Baja California
Ensenada, Mexico (September 2000)
World Botanical Associates Web Page
Prepared by Richard W. Spjut
We reviewed plants that
have been screened from Baja California, and list those species that are known to be active.
This includes an overview of plants screened for
antitumor activity from the southwestern deserts.
Most samples from Baja California were screened in KB Cell
Culture, P-388 Leukemia, and Astrocytoma. Additional collections have been
obtained for many active species; however, we lack information on the active compounds. The
National Cancer Institute had terminated their screening program in 1981
just after most samples were collected and screened (1979-1980).
Fractionation and further screening has been undertaken for some
species by chemists affiliated with drug discovery groups at
The vegetation of Baja California is well known for its diversity of plant forms; thus, one might expect to find new chemical substances for treating cancer and other diseases. We present a historical summary on plants that we know have been collected from North American Deserts for antitumor screening, and specifically mention those that have shown antitumor activity from samples we collected in Baja California.
The samples we have obtained for drug discovery programs generally follow three steps in screening:
Preliminary Screening—Crude Extracts—from Random or
Isolation of Active Agents from Recollections: 5-100 kg,
Clinical Evaluation of Active Agents: 50-20,000 kg
Initial (general) samples of root, stems, twigs, leaves, or any combination of these, weighing 100 g to 2 kg dried, are collected for extraction in which crude extracts are tested in several or more bioassays. During 1978-1980 general samples from ~ 400 species were collected from the southwestern deserts including Baja California. These were extracted with aqueous/ethanol and chloroform by the NCI contract facility in Wisconsin (RALTECH). Based on NCI reports of Cumulative Plant and Animal Materials considered active, the extracts of Baja California plants were tested in KB Cell Culture or Astrocytoma, and P-388 Leukemia.
A second stage in the evaluation requires recollections in amounts of 5-100 kg to isolate, identify and evaluate the active agents. Isolation of active agents is guided by bioassay results in which activity is determined by significant inhibitory effects on tumor or cell growth. Not all recollections reconfirmed because activity may depend on environmental factors or stages in development of the plant. For example, samples of Asclepias albicans collected by Spjut in the Chuckawalla Mountains of California showed activity in KB in an initial sample when plants were collected in flower bud, but failed to reconfirm when later collected in flower from the same locality. No recollections of plants were made from Baja California for the NCI because the NCI had terminated the screening of natural products in October 1982; however, later collections were made of active plants that were screened in bioassays other than the ones originally employed.
A third stage in the evaluation requires massive samples—usually many tons—to obtain sufficient quantities of the active compound for clinical evaluation. About one in every thousand species screened by the National Cancer Institute between 1960 and 1982 had reached this stage. During this time the NCI screened ~35,000 species. Examples of plants from the Sonoran and Chihuahuan deserts include Castela emoryi (holacanthone), Colubrina californica (colubrinol), and Bouvardia ternifolia (bouvardin). None of these passed clinical studies, however.
Thus far, the successful compounds are from plants collected elsewhere. Taxol, currently the most successful drug from the NCI program, was discovered from stem-bark of Taxus brevifolia in Pacific Northwest America. Another is synthetic derivatives of camptothecin, which was isolated from Camptotheca acuminata (Nyssaceae), a species native to China that was collected in cultivation in southern California. The need for more Camptotheca led to large-scale cultivation at a USDA plant introduction station in Chico, California. Despite the relatively few discoveries, the collection of 35,000 species of plants during the initial 22+ years (1960–1982) provided valuable pharmacological data on secondary metabolites in plants.
The Baja Flora Screened
Other compounds of interest were isolated from species of Aristolochia, Thevetia, Stemmadenia, and Hunnemannia; however, these occur mostly outside the desert regions.
3. 1970–1981. In addition to these novel discoveries, the WA and KB assays were sensitive to sesquiterpene lactones, while activity in the LE 1210 bioassay was so infrequent that it was felt leads were being missed. In 1969, the NCI substituted P-388 (PS) Leukemia for LE, and in 1980 replaced the KB assay with Astrocytoma (ASK). They also modified the extraction procedure in 1976. Further limitations were imposed on plant procurement in 1978; excluded from screening were many pantropical and pantemperate genera and many widely distributed species that were combined into a single listing know as SLOP for Species Low On Priority; collectively, these taxa amounted to ~60,000 species being precluded from further collecting.
In 1978 Spjut identified areas in the United States, Mexico and elsewhere where random collecting might be less impacted by SLOP and where many new plant genera might be encountered for collection. From the North American deserts he obtained samples from ~ 400 species in 256 genera. Represented from Baja California were 89 root samples, 129 stem or twig samples, and 32 samples of other plant parts. Subsequently, he collected 74 samples during May 1986, and ~100 samples since then. The active plants from Baja California are as follows:
Acalypha californica (Euphorbiaceae) stems-leaves and flower KB
Acanthogilia gloriosa (Polemoniaceae) root, twig-leaf 1-5 tumors
Atamisquea emarginata (Capparaceae) root ASK
Bergerocactus emoryi (Cactaceae) root ASK
Berginia virgata (Acanthaceae) stem-leaf ASK
Bursera microphylla (Burseraceae) root, stembark, twig-leaf KB
Bursera sp. twig-leaf KB
Camissonia crassifolia (Onagraceae) root-stem-leaf-flower ASK
Castela peninsularis (Simaroubaceae) twig-leaf KB
Castela polyandra root, twig KB, PS
Crossosoma bigelovii (Crossosomataceeae) twig-leaf 1-5 tumors
Dalea (Psorothamnus) juncea root, stem-leaf-flower 1-5 tumors
Dicraurus alternifolius (Amaranthaceae) twig-leaf ASK
Dyssodia anthemidifolia (Asteraceae) root-stem-leaf-flower ASK
Eriogonum preclarum (Polygonaceae) root-stem-leaf-flower 1-5 tumors
Esenbeckia flava (Rutaceae) stem-bark KB
Forchhammeria watsonii (Koeberliniaceae) root ASK
Frankenia palmeri (Frankeniaceae) stem-leaf-flower 1-5 tumors
Gochnatia arborescens (Asteraceae) stem-bark KB
Hermannia palmeri (Sterculiaceae) root-stem-leaf-flower KB
Hoffmannseggia intricata (Fabaceae) root, stem-leaf-flower ASK
Jatropha cinerea (Euphorbiaceae) stem-bark PS
Krameria erecta (Krameriaceae) stem-leaf ASK
Mascagnia macroptera (Malpighiaceae) root, twig-leaf ASK
Merremia aurea (Convolvulaceae) stem-leaf ASK
Nama cf. hispidum (Hydrophyllaceae) root-stem-leaf-flower 1-5 tumors
Olneya tesota (Fabaceae) root 1-5 tumors
Orobanche cooperi (Orobanchaceae) stem-leaf-flower ASK
Pachycormus discolor (Anacardiaceae) root 1-5 tumors
Phaulothamnus spinescens (Achaptocarp.) root ASK
Rhus integrifolia (Anacardiaceae) root 1-5 tumors
Salvia mellifera (Lamiaceae) inflorescence (flower) 1-5 tumors
Sphaeralcea axillaris (Malvaceae) root, stem-leaf-flower ASK
Stegnosperma halimifolium (Stegnosperm.) root ASK
Stillingia linearifolia (Euphorbiaceae) root PS
Viguiera deltoidea (Asteraceae) root KB
Xylonagra arborea (Onagraceae) tuber PS
24 stem-leaf or twig-leaf
Because many of these samples were obtained just
prior to the NCI terminating their agreement with the USDA in 1982, we
have little knowledge of the active agents. Based on other screening
data, phorbol esters were isolated from many Euphorbiaceae, lignans from
Burseraceae, alkaloids from Rutaceae, and sesquiterpene lactones from
Asteraceae. We know nothing about the active compounds that might be
responsible for activity in Astrocytoma (ASK).
According to Dr. McCloud at the Drug Development and
Therapeutic Branch in Frederick, Maryland, this assay may have become
(4) 1986–2000. Extracts from 74 samples
representing 56 species were collected in Baja California plants during
1986 by Spjut, Marin, John Cassady (Dean, School of Pharmacy at the Ohio
State University; http://ntpd.pharmacy.ohio-state.edu/Dean/) and Tom McCloud (former student of Cassady at Purdue
University, now at the NCI extraction lab in Frederick, Maryland; http://spheroid.ncifcrf.gov/stb/staff/mccloud/mccloud.cfm).
These were later screened against 60 tumor cell lines.
(4) 1986–2000. Extracts from 74 samples representing 56 species were collected in Baja California plants during 1986 by Spjut, Marin, John Cassady (Dean, School of Pharmacy at the Ohio State University; http://ntpd.pharmacy.ohio-state.edu/Dean/) and Tom McCloud (former student of Cassady at Purdue University, now at the NCI extraction lab in Frederick, Maryland; http://spheroid.ncifcrf.gov/stb/staff/mccloud/mccloud.cfm). These were later screened against 60 tumor cell lines.
Examples of Human Cancer Cell Lines
Currently Employed by the National Cancer Institute for
Screening Plant Extracts
DC-145 T 43D
The cell lines are divided into panels. Each panel includes one or more assays pertaining to a particular organ such as lung, colon, ovarian, etc. None of the Baja plant extracts showed specific cytotoxicity—that is activity that is selective to one panel, as opposed to general cytotoxicity in many tumor panels that is seen more often. Additionally, extracts of these samples were screened for anti-AIDS activity, and the Baja plants were being considered for screening of drug resistant antibiotics. The lack of discoveries thus far should not be interpreted as negative as screening criteria by which plants are being selected for drug development have become more stringent.
Approximately 100 samples collected during
1986-1990 from Baja California were also screened by university chemists, Dr.
Ching-jer Chang at Purdue University, and Dr. John Cassady at Ohio State
University. They also employed the NCI human cancer cell lines, but on a
more limited scale. Included were five cancer lines in four panels
involving lung (1), breast (1), colon (1) and two of the skin (2).
Species that were of interest in these screens are indicated as active
in 1 to 5 cell tumor lines. However, most recollections did not meet
activity criteria to justify further pharmacological study.
Those that did are Dalea (Psorothamnus) junceus and Pachycormus
discolor. A paper was reportedly
in press by Dr. Chang and his associates on the active chemical
compounds they isolated from samples of Dalea juncea. Dr.
Cassady reported only marginal activity in Pachycormus, presented
by one of his students in a poster paper at the 1988 annual meeting of the
American Institute of Biological Sciences.
Approximately 100 samples collected during 1986-1990 from Baja California were also screened by university chemists, Dr. Ching-jer Chang at Purdue University, and Dr. John Cassady at Ohio State University. They also employed the NCI human cancer cell lines, but on a more limited scale. Included were five cancer lines in four panels involving lung (1), breast (1), colon (1) and two of the skin (2). Species that were of interest in these screens are indicated as active in 1 to 5 cell tumor lines. However, most recollections did not meet activity criteria to justify further pharmacological study. Those that did are Dalea (Psorothamnus) junceus and Pachycormus discolor. A paper was reportedly in press by Dr. Chang and his associates on the active chemical compounds they isolated from samples of Dalea juncea. Dr. Cassady reported only marginal activity in Pachycormus, presented by one of his students in a poster paper at the 1988 annual meeting of the American Institute of Biological Sciences.
Additionally, there are other active plants that were collected outside Baja California that occur in Baja California. These include KB active Colubrina californica as mentioned earlier and Crossosoma bigelovii. Colubrinol is an ansamacrolid related to maytansine that underwent clinical trials but trials were discontinued due to cytotoxicity with a low therapeutic index. Recollections of Crossosoma, on the other hand, were reportedly inconsistent in activity; nevertheless, one active compound, 5,7-Dihydroxy-8-methoxy-2-methylochromona, was isolated from samples collected in Arizona.
Two active compounds isolated early in the NCI program include synthetic derivatives that are either currently used in treating cancer, or are undergoing further clinical evaluation. These are derivatives of camptothecin from Camptotheca acuminata (Nyssaceae) and quassinoids in Simaroubaceae. Synthetic derivatives of holacanthone and other naturally occurring quassinoids are actively being studied by Paul Grieco at Montana State University who has found other novel compounds in Castela such as polyandrol in C. polyandra and peninsularinone in C. peninsularis ((http://www.chemistry.montana.edu/grieco.html) .
It is interesting that 23 of the 39 species
listed from Baja California are represented by root and stem-bark
samples. Twelve species showed
activity only in their root part (or tuber), compared to eight species for
aerial parts only. These results are consistent
with KB and P-388 data on plants screened from Kenya, Tanzania, Ghana,
Peru, and Turkey as presented elsewhere (Spjut unpublished, see home
page and click on World Botanical Associates). Generally,
active chemical agents in tropical species are most often found in
stem-bark, whereas activity in plants from drier regions is more often
found in extracts of root.
The importance of root samples is also evident from
ethnobotanical studies. A case in point is root of octotillo (Fouquieria
splendens) that has been used by the Apache Indians to treat painful
swellings (Krochmal et al., Economic Botany, 1954). This species usually
grows on rocky soils where it is not easy to dig, and the spreading
thorny stems also makes access to the root even more difficult; thus, if
the Apache Indians had to expend considerable effort to get to the root,
we should make the same effort to collect root for screening.
In view of the preceding data on active plants in Baja California, the flora of Baja California probably contains many novel active chemicals yet to be discovered. Such discoveries are likely if plants are sampled systematically. Our efforts in previous years have focused on perennial and woody plants, but we have not had the resources to compile a record as to what plants might best be collected in the future. Currently, we draw mainly from our knowledge and experience as we travel in the field for collections. Further information about our program can be found on our website, www.worldbotanical.com.
Attaché, American Embassy, Mexico, D.F.
Consejo Nacional de Ciencia y Tecnologia
Direccion General de Investigación y Capacitación Forestales
General de Eonomía Agrícola
Universidad Autonoma de Baja California, Facultad de Ciencias
Herbario (BCMEX) y Farmaclogía Marina
Memoranda, Permits, and Reports
Memoranda, Permits, and Reports
American Embassy letter, 3 Jan. 1979, indicating permit status and where voucher specimens and accomplishment report are to be deposited.
[USDA ARS]Accomplishment Report. Procurement of Plant Samples from Mexico & U. S. for Antitumor Screening. August 1981. 17 pp.
1982 Correspondence: Travel Plans to recollect antitumor active plants in Mexico
Wall M. E., M. C. Wani, G. Manikumar, H. Taylor and R. McGivney. 1989. Plant antimutagens, 6. Intricatin and intricatinol, new antimutagenic homoisoflavonoids from Hoffmanosseggia intricata. J Nat Prod. 52(4): 774–778.
Zhang H, X.
Li, C. L. Ashendel and C. J. Chang. 2000. Bioactive compounds from
Psorothamnus junceus. J. Nat. Prod. 2000 63(9): 1244–1228.
“During a search for bioactive
compounds from Psorothamnus junceus, four heterocyclic compounds,
psorothamnone A (1), psorothamnone B (2), dalrubone (3), and emorydone
(4) were isolated from the ethanol extract of the stem bark.
Psorothamnones A (1) and B (2) demonstrated inhibitory activity against
protein kinase C (PKC), a key enzyme involved in the signal transduction
of cell proliferation and differentiation. Dalrubone (3) and emorydone
(4) showed cytotoxicity against several human tumor cell lines.”
Zhang H, X. Li, C. L. Ashendel and C. J. Chang. 2000. Bioactive compounds from Psorothamnus junceus. J. Nat. Prod. 2000 63(9): 1244–1228. “During a search for bioactive compounds from Psorothamnus junceus, four heterocyclic compounds, psorothamnone A (1), psorothamnone B (2), dalrubone (3), and emorydone (4) were isolated from the ethanol extract of the stem bark. Psorothamnones A (1) and B (2) demonstrated inhibitory activity against protein kinase C (PKC), a key enzyme involved in the signal transduction of cell proliferation and differentiation. Dalrubone (3) and emorydone (4) showed cytotoxicity against several human tumor cell lines.”