4 Combinations of Topoisomerase Inhibitors and Ionizing Radiation
Michael Bastasch and Hak Choy
M. Bastasch, MD
H. Choy, MD, Professor and Chairman
Department of Radiation Oncology, The University of Texas Southwestern Medical Center at Dallas, 5801 Forest Park Rd., Dallas, TX 75390-9183, USA
4.1
Introduction
Radiation has been used in the treatment of cancer since its discovery and has recently undergone significant innovations through increased techni- cal refinements. With increased computing power, three-dimensional radiation therapy, intensity- modulated radiation therapy, tomotherapy, and ste- reotactic radiation have emerged as tools to increase the therapeutic ratio. While safe implementation of such programs has resulted in improvements in local control through pure dose escalation and/or alterations in fraction sizes, limitations still exist secondary to adjacent normal tissue toxicity. Fur- thermore, radiation has never been more than a local therapy, unable to affect disease distant to the treatment field. Chemotherapy agents, in con- trast, act systemically, although they are unlikely to
control completely gross solid tumors. Combining highly effective local therapy and systemic therapy might enhance the overall chance of cure, especially in disease entities known to harbor microscopic metastatic deposits frequently. Additional benefit in terms of local tumor control might be derived from an additive effect of chemotherapy; thus, cytotoxic agents might provide several advantages over radia- tion alone for improved local, regional, and systemic disease control.
4.2
Topoisomerases
DNA topoisomerases (Topo) function to regulate the topology of DNA to ensure correct DNA metabolism.
Currently five human topoisomerases for DNA have been identified, Topo1, Topo2D, Topo2E, Topo3D, and Topo3E (Wang 2002). They serve in a vital capacity for successful DNA synthesis (Wang 1985;
Wang 1991). As such, DNA topoisomerases I and II (Topo I and II) are important targets for cancer che- motherapeutic agents. These nuclear enzymes are essential for DNA replication, RNA transcription, chromosomal condensation, and mitotic chromatid separation (Wang and Sinha 1996). The level of Topo I is independent of cell cycle phases, although cytotoxicity is manifested only in proliferating cells (Choy and Macrae 2001). Topo II, in contrast, is cell-cycle dependent. It increases at the onset of G2 and S phases and disappears in G0/G1 phase (Heck and Earnshaw 1986). Topoisomerases also have activity in G1 cells or cells held in plateau phase (Ng et al. 1994). The difference between Topo I and Topo II is number of DNA strands involved.
The human DNA topoisomerase I is a monomeric 100 kDa protein that is able to relax supercoiled DNA.
This is achieved through the introduction of a single stranded break in DNA followed by the passing of the intact strand through the break prior to religa- tion. This activity is key in many aspects of DNA
CONTENTS
4.1 Introduction 53 4.2 Topoisomerases 53
4.3 Topoisomerase-I Inhibitors 54 4.4 Topoisomerase-II Inhibitors 54
4.5 Topoisomerase Inhibition Enhances Radiation In Vivo and In Vitro 55
4.6 Lung 56
4.6.1 Non-Small Cell Lung Cancer 56 4.6.2 Small Cell Lung Cancer 57 4.7 Gastrointestinal Tumors 58 4.7.1 Esophageal Cancer 58 4.7.2 Rectal Cancer 59 4.8 CNS Tumors 60
4.9 Head and Neck Tumors 61 4.10 Conclusion 62
References 63
metabolism including transcription, replication and the regulation of DNA supercoiling, which is impor- tant in maintaining genomic stability. It is believed that the camptothecins function by stabilizing a topoisomerase I-DNA intermediate called the cleav- able complex such that the 5’phosphoryl end of the DNA single-stranded break is bound covalently to a topoisomerase-I tyrosine residue (Chen et al. 1999).
It is believed that collision of this drug-trapped com- plex with the DNA replication machinery will lead to G2 phase cell-cycle arrest and cell death (Chen and Liu 1994; Cheng et al. 1994). Topo II acts similarly, but on two strands of DNA (Wang 1985). Topo II binds covalently to double-stranded DNA, cleaves both strands, and reseals the cleaved complex. Col- lisions of Topo II–etoposide cleavable complexes with DNA tracking enzymes, such as polymerases or helicases, generate DNA DSBs. The resulting DNA DSBs may lead to cell death by apoptosis. Through analysis of their dysfunction in otherwise normal cells, other duties involving DNA repair have been implicated. When not performing properly, muta- tion (Bae et al. 1988), sister chromatid exchange (Pommier et al. 1984, 1998; Downes et al. 1991) illegitimate recombination (Bae et al. 1988), DNA fragmentation (Kaneko and Horikoshi 1987), and tumor promotion (Downes et al. 1994; Andoh et al. 1987) may occur.
4.3
Topoisomerase-I Inhibitors
Camptothecin, the parent compound (see Fig, 4.1), was initially isolated from the tree, Camptotheca acuminata, and was found to have a broad spectrum of activity in a variety of solid tumors through inhi- bition of Topo I (Chen and Liu 1994); however, early clinical trials with the ring-open form of the drug
showed excessive toxicity and the trials were termi- nated (Muggia et al. 1972). More recently, interest has been rekindled in these drugs with the advent of derivatives that have significant antitumor activity and much less toxicity. Irinotecan, one of these deriv- atives, is actually a prodrug which is metabolized intracellularily into SN-38 (Takimoto et al. 1998).
SN-38 is approximately a 1000 times more potent inhibitor of Topo I than irinotecan (Kawato et al.
1991). All of the camptothecins have a terminal lac- tone ring with can be hydrolyzed to a less active car- boxylate species; however, under acidic conditions, like those expected in a tumor’s microenvironment, the active lactone species is favored (Takimoto et al. 1998). After an intravenous infusion, SN-38 can have a plasma half-life of 5.9–13.8 h and this cer- tainly can have implications in terms of both direct cytoxicity and radiosensitization abilities. The major method of SN-38 elimination is through hepatic glucuronidation, and it is felt that a decreased ability to glucuronidate the drug correlates with increased gastrointestinal side effects (Takimoto et al. 1998).
One of the major side effects of irinotecan is late onset diarrhea. This is felt to be related to the high S-phase fraction of the intestinal mucosa as well as action of intestinal flora glucoronidase in cleaving the camptothecin-glucuronidase conjugate leading to the drug’s release into the intestinal lumen (Araki et al. 1993). Other common toxicities include neutro- penia, nausea, vomiting, anorexia, fatigue, asthenia, and elevation of hepatic transaminases.
Currently available camptothecin drugs include irinotecan (CPT-11), topotecan (9-aminocamptoth- ecin; Lamond et al. 1996), 7-ethyl-10-hydroxycamp- tothecin (Kohara et al. 2002), and 9-nitro-20(S)- camptothecin (RFS-2000; Amorino et al. 2000; see Table 4.1).
4.4
Topoisomerase-II Inhibitors
Etoposide (VP-16) is one of the most frequently used Topo-II inhibitors with specific action in late S or early G
2phase of the cell cycle. Etoposide forms a ternary complex with Topo II and DNA (Sakamoto et al. 2001). An early change in etoposide treated cells is an interruption in the transition from S phase prior to G
2arrest. Coinciding with this S-phase delay is a selective inhibition of thymidine incorporation into DNA and a severing of DNA strands. Very low doses of etoposide can initiate DNA strand inter-
Fig. 4.1. Chemical structure of camptothecin
ruption. The suggestion is that DNA strand scission is the initial event in the sequence of kinetic and biosynthetic changes leading to growth inhibition and death of etoposide treated cells (Kalwinsky et al. 1983). In vitro data indicate that cytotoxic effi- cacy can be increased with chronic exposure. The more frequent the exposure, the higher the cytoxic effect ( Dombernowsky and Nissen 1973). Given its availability as an oral agent, etoposide may be sequenced daily. In a phase-I trial, daily administra- tion was tolerated in refractory lymphoma patients treated days 1–21 with tolerable hematological tox- icity (Hainsworth et al. 1990). Similar trials have been conducted with refractory (Einhorn et al. 1992) and untreated (Clark and Cottier 1992) small cell lung cancer (SCLC).
4.5
Topoisomerase Inhibition Enhances Radiation In Vivo and In Vitro
The principle mechanism of radiation’s lethality is the creation of irreparable DNA damage. Chemotherapy that disrupts normal DNA repair may act definitively to cause cell death or serve to complete partial damage caused by ionizing radiation thereby causing cell death (Ng et al. 1994; Amorino et al. 2000; Kim et al. 2002).
The DNA strand breaks are a critical pathway by which ionizing radiation exerts a lethal effect on a cell. Che- motherapeutic agents that induce or prevent repair of DNA strand breaks may act synergistically with ion- izing radiation to kill cells. The DNA topoisomerases are one such class of enzymes involved in DNA strand break repair. If the DNA topoisomerase enzymes are blocked, then transient DNA breaks cannot be repaired.
Cells thus affected die. The effect of combining these
agents may be supra-additive. Preclinical data show that both Topo-I and Topo-II inhibitory agents can act as radiosensitizers (Kim et al. 1992; Kirichenko et al.
1997; Takahashi et al. 2003). Topo-I inhibition has enhanced radiosensitity through in vitro experiments with camptothecin derivatives in V-79 Chinese ham- ster cells (Marples et al. 1996), MCF-7 breast cancer cells (Chen et al. 1997), and human U1-Mel melanoma cells ( Boothman et al. 1992). This effect has been seen in further in vivo experiments in murine MCa-4 mam- mary tumors (Kirichenko et al. 1997) and fibrosar- coma (Kim et al. 1992). Topo-II inhibition has been seen to enhance radiosensitivity in vitro in V-79 fibroblasts ( Giocanti et al. 1993; Haddock et al. 1995; Marples et al. 1996) and human breast cancer cells (Iwata and Kanematsu 1999). Human clinical studies followed these encouraging preclinical results.
The exact mechanism by which topoisomerase inhibitors act to sensitize cells to ionizing radiation is unknown. Stabilization of the cleavable complex of the topoisomerase and DNA occurs with inhibition (see Fig. 4.2). The cellular apparatus geared for DNA replication encounters this complex and apparently at this junction the cell becomes more sensitive to ionizing radiation. The replication forks in the DNA and the cleavable complex lead to several interac- tions: (a) a double-stranded DNA break; (b) arrest of the replication fork, and (c) an aborted DNA-topoi- somerase complex. This is shown in Figure 4.3. This damage can be repaired over the course of time lead- ing to the comparison to sublethal damage repair, SLDR, a known phenomenon in radiation; therefore, combining both agents can lead to a supra-additive effect whereby SLDR from either agent is rendered impotent leading to cell death that otherwise would not occur. The DNA Topo II helps the introduction of double-stranded DNA breaks and subsequent rejoining necessary for DNA replication. Etopo-
Table 4.1. List of Topo-I and Topo-II agents used with radiation in patients. CNS central nervous system
Name Type of inhibitor Combined use with radiation
Topotecan Topo I Glioma
CNS metastasis Cervix Lung
Irinotecan Topo I Lung
Esophagus Rectum 9-nitro-20(S)-camptothecin
(RFS-2000)
Topo I Pancreas
Etoposide (VP-16) Topo II Lung
side, a member of the epipodophyllotoxin family of chemotherapeutic agents and commonly used concurrently with radiation, forms a complex with the DNA and DNA Topo II. This complex decreases DNA rejoining and causes chromosomal breakage.
The breakage leads to cell death. Additional actions of the epipodophyllotoxins include intrinsic produc-
tion of metabolic byproducts consisting of reactive oxygen species and hydroxyl radicals. These species could create abasic sites, potent position-specific enhancers of DNA Topo-II cleavage (Larsen et al.
2003). Radiation is a known cause of reactive oxygen species and hydroxl radicals through which some of its cytoxic effects are exerted. Some of the synergy between these two agents can be understood through this shared biochemical pathway. Topo-II, in addi- tion to catalyzing the unwinding of DNA for replica- tion, also serves as a recruiter for other proteins to arrive at their specific sites in chromatin domains, e.g., MAR/SAR regions, which are located in the base of the chromatin loops. Essential, well-known proteins, including the tumor suppressor proteins Rb and p53 and the protein kinases ERK2, CK2, and Cdc2 kinase, are recruited with the assistance of Topo II (Escargueil et al. 2001). Their inhibition by etoposide could inhibit repair of DNA damage caused by radiation and, therefore, prevent sublethal damage repair to “fix” sublethal to lethal damage.
4.6 Lung
4.6.1
Non-Small Cell Lung Cancer
Topo-1 inhibitors have demonstrated activity in NSCLC (Chastagner et al. 2001). Concurrent administration of chemotherapy and radiation therapy in the definitive management of locally advanced NSCLC has been shown to improve out- comes (Clamon et al. 1999). While acute toxici- ties are increased compared with radiation therapy alone, they are tolerable. Irinotecan has been com- bined with radiation in phase-I and phase-II trials with demonstrated efficacy. Takeda et al. (2001) performed a phase-I/II trial of escalated doses of irinotecan with standard radiation of 60 Gy in 30 fractions over 6 weeks. Inclusion criteria were East- ern Cooperative Oncology Group (ECOG) perfor- mance status of 0, 1, or 2, unresectable disease, non-small cell histology. Irinotecan doses started at 30 mg/m
2IV weekly concurrent with radiation to a maximally tolerated dose of 60 mg/m
2. Yamada et al. (2002) investigated the maximally tolerated dose of irinotecan when combined with carboplatin in the same group of patients (unresectable Stage IIIA/B) treated with the same radiation parameters.
That phase-II trial showed the maximally toler-
Fig. 4.2. Formation and proposed mechanism of Topo-I cleav- able complex leading to cell death
TOP1 Non-cleavable complex
TOP1 Cleavable complex
TOP1-targeted drug
DNA replication fork in S-phase
Cell death
Fig. 4.3. Possible mechanism of radiosensitization (RS) by Topo-I inhibitors. The drug-trapped TOP1 cleavable complex may initiate TOP1-mediated RS by „interacting“ with replica- tion fork during active DNA synthesis. Three major biochemi- cal events, including double-strand DNA breaks, arrest of rep- lication fork, and an aborted „cleaved“ TOP1–DNA complex, can be generated. It is plausible that one or a combination of these three events may be responsible for the induction of TOP1-mediated RS. The current data indicate the involvement of a currently undefi ned repair process in the induction of TOP1-mediated RS and suggest that dissociation between the pathways leads to RS and cytotoxicity
Drug-trapped TOP1 Cleavable complex
DNA replication fork in S-phase
Radiosensitization Aported TOP1 Cleavable complex
double-stranded DNA breaks
Replication fork arrest
Cytotoxicity
ated dose to be 60 mg/m
2weekly with carboplatin dosed daily at 20 mg/m
2. Toxicities were esophagitis, pneumonitis, neutropenia, and thrombocytopenia.
Serious toxicities at the maximally tolerated dose level were two grade-4 cases and one grade-5 case of pneumonitis. The authors recommended a dose of irinotecan of 50 mg/m
2when combined with daily carboplatin. An objective response was noted in 60%
of the patients’ tumors. The median survival time was 14.6 months with 1- and 2-year survival rates of 52 and 32%, respectively. Similar dosing con- clusions had been drawn previously by Takeda et al. (2001) with a small study of 17 patients using a minimum of two 28-day cycles of carboplatin and irinotecan. Irinotecan was delivered intravenously days 1, 8, and 15 with carboplatin at an area under the concentration–time curve dose of 5 mg/ml u min (Calvert's formula) on day 1. An overall response rate of 35% was noted with median overall survival of 10.5 months and 1-year survival rate of 35%. Dose limiting toxicities were hematologic. The MTD was 60 mg/m
2. They recommended a dose of 50 mg/m
2for future trials (Takeda et al. 2001). The radiation field size was relatively large with the primary and elective nodal basin receiving a dose of 40 Gy and the primary disease sites receiving additional dose to 60 Gy. The lateral mediastinal margin was 1.5 cm and the ipsilateral supraclavicular fossa was treated from the cricoid cartilage to the middle of the clavi- cle. The impact of the additional normal lung volume by elective nodal irradiation may have contributed to the grade-4 and grade-5 pneumonitis experienced at the 60 mg/m
2dose level (Takeda et al. 2001).
Typical doublet chemotherapy for NSCLC consists of a platinum compound coupled with another agent.
Yokoyama et al. (1998) reported the results of a phase- I/II trial of irinotecan and cisplatin for patients with unresectable stage-IIIA/B NSCLC. Thirteen patients were enrolled with 12 being available for analysis for maximum tolerated dose on a schedule of one course of chemotherapy every 4 weeks for three cycles. Stan- dard thoracic radiation was initiated on day 2 of cycle one consisting of 60 Gy in 30 fractions over 6 weeks.
Of the 6 patients in the initial cohort, only four were able to complete the scheduled courses of chemo- therapy because of associated hematologic toxicities.
Only 3 of 6 patients at dose level two completed all planned chemotherapy. Irinotecan doses and radia- tion doses were low in the two initial cohorts leading to early termination of the trial.
Emerging trends in radiation therapy include the refinement of radiation fields for lung cancer. The need for extensive fields in combined treatment
with chemotherapy has been questioned as toxic- ity increases with field size and subclinical disease may be addressed adequately by chemotheraphy alone. To pursue combined modality therapy with acceptable toxicity, efforts have been undertaken to limit the radiation field to the known sites of dis- ease with modest margins. Socinski et al. (2004) took this path while escalating the radiation dose with concurrent carboplatin and paclitaxel after induction chemotherapy of carboplatin, paclitaxel, and irinotecan. Sequential treatment with irinote- can failed to show promising results in a study by Scagliotti et al. (1996), consistent with findings of Radiation Therapy Oncology Group (RTOG) study 94-10 (Curran et al. 2000).
Graham et al. (1996) investigated the use of another Topo-1 inhibitor, topotecan, with concur- rent thoracic radiation for inoperable NSCLC in a phase-I trial. Using standard dose radiation of 60 Gy in 30 fractions over 6 weeks with large fields, pri- mary tumor and mediastinum, the maximum toler- ated dose was 0.5mg/m
2. Toxicities were primarily hematologic and gastrointestinal (esophagitis and diarrhea with the former related to the inclusion of the mediastinum into the field). No patient had a report of pneumonitis. Although it is tempting to attribute that fact to a drug difference between topo- tecan and irinotecan, it is important to remember that the study by Takeda et al. (2001) with irinote- can, which showed several severe cases of pneumo- nitis at 60 mg/m
2, had an even larger field including the ipsilateral supraclavicular fossa.
4.6.2
Small Cell Lung Cancer
Etoposide, a Topo-II inhibitor, has been in routine
use with radiation for SCLC for many years (Sierocki
et al. 1979; Turrisi et al. 1988). The current standard
consists of cisplatin and etoposide concurrent and
adjuvant to thoracic radiotherapy of 45 Gy deliv-
ered 1.5 Gy b.i.d. (Turrisi et al. 1999; Takada et
al. 2002). Recent trial paradigms for limited stage
SCLC have begun integrating irinotecan. The RTOG
initiated a phase-I trial, RTOG 0241, using a fixed
dose of cisplatin 60 mg/m
2combined with sequen-
tial increases of irinotecan 40, 50, and 60 mg/m
2.
Dose escalations occur until the dose limiting tox-
icity is met. The chemotherapy is given every three
weeks. The trial has begun to accrue with radiation
either being 45 Gy b.i.d. or 70 Gy in just one fraction
per day. The radiation ports are limited to areas
of known involvement at time of diagnosis without elective nodal irradiation. Sequencing of cisplatin and etoposide was the subject of a large Canadian trial. Maksymiuk et al. (1994) found the optimal sequence to be cisplatin 30 mg/m
2i.v. bolus followed by etoposide 130 mg/m
2bolus. Phase-I data for once- daily radiotherapy concurrent with chemotherapy (cisplatin, etoposide, and cyclophosphamide) has shown the maximally tolerated radiation dose to be 70 Gy in 35 fractions of 2 Gy/day. For b.i.d. radia- tion, the maximally tolerated radiation dose with identical chemotherapy proved to be 45 Gy at 1.5 Gy b.i.d. (Choi et al. 1998). The phase-I study RTOG 97-12 showed that a total dose of 61.2 Gy with b.i.d.
radiation given for the last 9 days of treatment was the maximally tolerated dose (Komaki et al. 2005).
Patients received four cycles of cisplatin 60 mg/m
2day 1 and etoposide either orally 240 mg/m
2or i.v.
120 mg
2days 2 and 3. Reduction in tumor volume by induction chemotherapy has been shown to be acceptable if required in rare cases. It may be neces- sary in situations where the volume of normal lung treated exceeds tolerance. No increase in marginal failures developed with use of two to three induction cycles in case series (Arriagada et al. 1991). Tho- racic radiation should be started as soon as possible for maximal benefit (Murray et al. 1993).
With the advent of Topo-I inhibitors, their use is expanding. Topo-I inhibitors have shown effi- cacy combined with radiation and combined with a Topo-II inhibitor in patients with extensive stage disease (Sekine et al. 2003). Phase-III data indi- cate a difference in efficacy favoring combination cisplatin and Topo-1 inhibition with irinotecan in the treatment of extensive stage disease compared with cisplatin and Topo-2 inhibition with etoposide (Noda et al. 2002). Kubota et al. (2005) reported on alternating chemotherapy using both Topo-1 and Topo-2 inhibitors with accelerated hyperfraction- ation for limited stage SCLC. Using standard radia- tion doses for limited SCLC, 45 Gy at 1.5 Gy b.i.d., chemotherapy was one cycle of etoposide 100 mg/m
2on days 1–3, and cisplatin 80 mg/m
2on day 1. Radi- ation started on day 2 and was completed over 15 treatment days after which irinotecan and cisplatin started on day 29. Irinotecan was given at 60 mg/m
2on days 1, 8, and 15, and cisplatin 60 mg/m
2on day 1, with three 28-day cycles. The response rate was 97%
(complete response, 37%; partial response, 60%).
Median overall survival was 20 months; 1-, 2-, and 3-year survival rates were 76, 41, and 38%, respec- tively. Of the 30 patients evaluable, 22 received mul- tiple courses of adjuvant chemotherapy. Similarly,
Johnson et al. (2003) reported on the use of combi- nation Topo-1 and Topo-2 inhibitors combined with b.i.d. fractionated thoracic radiotherapy to 45 Gy.
This phase-I trial used alternating fixed dosing of cisplatin 20 mg/m
2day 1 and etoposide 60 mg/m
2days 1–3 or irinotecan. Three irinotecan doses, 60, 80, or 100 mg/m
2, substituted for the etoposide. Radi- ation was given weeks 4–6 for patients with limited SCLC while on a course of cisplatin and etoposide.
Granulocyte stimulating factor was administered on days 2–5 and days 4–7 after irinotecan/cisplatin and etoposide/cisplatin, respectively. Therapy lasted a total of 12 weeks. Irinotecan toxicity was accept- able up to the third dose level of 100 mg/m
2and is the subject of further investigation.
Despite prior phase-III data and a meta-analy- sis, irinotecan and cisplatin have been used neoad- juvantly in a recent trial of 35 patients (Han et al.
2005). Two cycles of induction irinotectan and cispl- atin were given with excellent results, 97% objective response rate. Three patients had a complete and 31 had a partial response. Following induction chemo- therapy, twice-daily radiation with a cisplatin/eto- poside combination similar to that of Turrisi et al.
(1999) was given yielding a 100% CR rate. Toxicities were not insubstantial, however. Hematologic tox- icities predominated with 68% of patients suffering grade-3 to grade-4 neutropenia during induction and 100% during radiochemotherapy. With rela- tively short median follow up of 26.5 months, the median progression-free survival was 13 months and median overall survival was 25 months. The 1- and 2-year overall survival rates were 86 and 54%, respectively. The rates reported previously were a median overall survival of 23 months with a 2-year overall survival rate of 47% for the b.i.d group at a median follow-up of 8 years (Turrisi et al. 1999).
It is unclear what improvement from neoadjuvant chemotherapy with alternating agents for overall survival might be.
4.7
Gastrointestinal Tumors
4.7.1
Esophageal Cancer
Standard treatment in the United States for inoper-
able cancer of the esophagus is chemoradiation with
cisplatin, 5-fluorouracil, and radiation to 50.4 Gy at
1.8 Gy/day (Cooper et al. 1999; Herskovic et al.
1992). Long-term results show that at 5 years 26%
of patients with non-metastatic disease at diagnosis are alive with chemoradiation but with locoregional failure remaining a significant problem. Investiga- tors looked for additional agents that might add further radiosensitization to address persistence of local disease. Ilson et al. (1999, 2003) reported on phase-I and phase-II trials looking at cisplatin and irinotecan combined with radiation for esophageal cancer. Nineteen patients with clinical stage-II to stage-III esophageal squamous cell or adenocarci- noma were enrolled. Induction chemotherapy with weekly cisplatin 30 mg/m
2and irinotecan 65 mg/
m
2was administered for four treatments during weeks 1–5. Radiotherapy was delivered weeks 8–13 in 1.8-Gy daily fractions to a dose of 50.4 Gy. Cispla- tin 30 mg/m
2and escalating-dose irinotecan (40, 50, 65, and 80 mg/m
2) were administered on days 1, 8, 22, and 29 of radiotherapy. The dose-limiting toxic- ity was defined as a 2-week delay in radiotherapy for grade-3 to grade-4 toxicity. Minimal toxicity was observed during chemoradiotherapy, with no grade- 3 or grade-4 esophagitis, diarrhea, or stomatitis.
Myelosuppression caused the dose-limiting toxic- ity in 2 of 6 patients treated at the 80 mg/m
2dose level; thus, irinotecan 65 mg/m
2was defined as the recommended phase-II dose. Dysphagia improved or resolved after induction chemotherapy in 13 (81%) of 16 patients who reported dysphagia before therapy. Only 1 patient (5%) required a feeding tube. Six complete responses (32%) were observed, including four pathologic complete responses in 15 patients selected to undergo surgery (27%). These data were further supported by another phase-I trial that found the maximum tolerated dose of iri- notecan as a single agent concurrent with 50.4 Gy at 1.8 Gy/day to be 60 mg/m
2infused over 90 min weekly starting on day 1 of radiation. In this trial patients suffered principally from hematologic grade-3 or grade-4 toxicity with non-hematologic toxicities consisting typically of gastrointestinal, nausea, vomiting, dehydration, anorexia, hypother- mia, and hypotension (Komaki et al. 2000). Another approach has been investigated using preoperative induction irinotecan and cisplatin chemotherapy followed by concurrent paclitaxel and radiation (Ajani et al. 2004). Forty-three patients with endo- scopically proven locally advanced esophageal or gastroesophageal junction tumors were given iri- notecan 70 mg/m
2and low-dose cisplatin 20 mg/
m
2once weekly for 4 weeks (one cycle) and then repeated 2 weeks later provided all toxicities were less than or equal to grade 1. Routine i.v. hydration
and anti-emetic prophylaxis were given before che- motherapy. At the completion of the induction che- motherapy, patients started on a course of radiation to 45 Gy at 1.8 Gy/day to standard volumes (5 cm proximal and distal to the lesion and 2 cm lateral to the lesion). Concurrent chemotherapy was adminis- tered. Patients received 5-fluoruracil at 300 mg/m
2for 5 days per week by continuous infusion typi- cally on a Monday-to-Friday schedule. Paclitaxel was given once weekly, typically on Mondays, at 45 mg/m
2on a 3-h infusion schedule. Surgery fol- lowed in 39 patients (91%), but the exact type was not prescribed by protocol. Objective disease responses were seen in 16 of the 43 patients (37%); no changes were noted in 24 (56%); and disease progressed in 3 (7%). Responses were gauged based on barium swallows, endoscopies, or both, 4–6 weeks at the end of therapy, as positron emission tomography was not used. The overall pathologic response rate was 63% (27 of 43). A quarter of patients had a patho- logic complete response and an additional 37% had pathologic partial response. Overall survival with a minimum follow up of 28 months was 37%. Patients typically died from disease progression, whereas two deaths were from myocardial infarctions in the perioperative period. Patterns of disease recurrence changed from predominately local to distant with or without local disease. Future trials will be using irinotecan concurrently with radiation.
4.7.2
Rectal Cancer
Rectal cancer has been the subject of investigations combining Topo-I inhibitors with 5-fluorouracil for metastatic patients. Improvements in disease con- trol resulted in a change in the standard of care for metastatic patients (see chapter on rectal cancer).
These results began to influence chemoradiation for
locally advanced patients through a series of early
phase trials. Investigators from Stanford University
led a phase-II trial of protracted venous infusion
5-fluorouracil, weekly CPT-11 with radiation fol-
lowed by surgery in patients with endoscopic ultra-
sound based staging (Mehta et al. 2003). Thirty-
two patients, most of whom had uT3N0 or uT3N1,
entered the trial and received 45 Gy to the draining
lymphatics followed by a boost to 50.4 Gy to the
primary tumor that excluded small bowel. Standard
fractionation of 1.8 Gy/day with three-dimensional
conformal planning was used. Starting simultane-
ously with radiation, irinotecan 50 mg/m
2on days 1,
8, 15, and 22, and 5-fluorouracil 200 mg/m
2daily 7 days a week on days 1–33, were given. The type of surgery was not prescribed in the protocol. Resec- tion occurred 6–10 weeks after the completion of therapy. Toxicity from the neoadjuvant therapy was frequent with 18 patients (56%) requiring chemo- therapy dose reductions or interruptions >3 days of radiotherapy. No grade-IV toxicity was seen, but grade-III toxicity was frequently observed; diar- rhea in 9 (28%), mucositis in 7 (21%), rectal sores in 7 (21%), and abdominal cramping in 3 (3%).
One patient withdrew from the trial after 10 days because of grade-III toxicity consisting of diarrhea and cramping. All patients underwent surgery with 12 (37.5%) showing a pathologic complete response.
Downstaging occurred in 23 (71%). These results compare favorably with conventional regimens that have noted a 27% rate of pathologic complete response. The impressive downstaging results can be attributed partially to the delay until surgery in some patients, but these results are superior to those noted in the Lyon R90-01 multicenter, randomized controlled trial (26%; Francois et al. 1999).
Hofheinz et al. (2005) conducted a phase-I trial combining capecitabine with irinotecan and radia- tion for 19 patients with locally advanced, T3/T4 NX, rectal cancer. Irinotecan was administered weekly at 50 mg/m
2days 1, 8, 15, 22, and 29. Capecitabine was prescribed at two different dose levels daily days 1 through 38. Dose level 1 was 500 mg/m
2b.i.d., and dose level 2 was 625 mg/m
2b.i.d. Patients received 45 Gy to the lymphatics with a boost to 50.4 Gy to the primary with three-dimensional conformal radiation at 1.8 Gy/day. Dose level 1 was tolerated without any dose limiting toxicities. Dose level 2 caused grade-3 diarrhea in three of seven patients.
None of the 12 patients on dose level 1 required chemotherapy dose reductions in either drug. Only one patient suffered a grade-3 or grade-4 toxic- ity, a grade-3 asthenia. All patients underwent an R0 resection with four (21%) showing a pathologic complete response and an additional five (26%) with microscopic disease remaining.
4.8
CNS Tumors
Investigators have examined the use of the Topo- I inhibitor, topotecan, in both adult and pediatric populations combined with cranial radiation in the treatment of high-grade, primary CNS malignancies.
The interest in topotecan was driven by intriguing in vivo data in grade-IV glioma xenograft models ( Chastagner et al. 2001; Ciusani et al. 2005).
Children’s Cancer Group 0952 phase-I trial data on tolerance of pediatric patients with intrinsic, diffuse pontine glioma to daily i.v. topotecan showed the mean tolerated dose to be 0.40 mg/m
2(Sanghavi et al. 2003). Topotecan was infused 30–60 min prior to radiation. Of the 17 patients enrolled, 16 were able to complete therapy to 59.4 Gy at 1.8 Gy/day. The dose limiting toxicity was grade-IV neutropenia. Phase-II data have been reported in children with various brain tumors: grade-IV glioma; anaplastic astrocytoma;
ependymoma; medulloblastoma/primitive neuro- ectodermal tumors; and diffuse intrinsic pontine gliomas (Turner et al. 2002). No concurrent radia- tion was administered. The patients received three cycles of topotecan i.v.125 mg/m
2weekly for 4 weeks followed by a 2-week break. Reassessment occurred at the end of each course with contrast-enhanced magnetic resonance imaging. Remarkable response in several patients occurred. Of the total 22 patients, 2 of 4 patients with recurrent grade-IV gliomas had a complete response lasting 9 and 48+ months. One of 4 patients with newly diagnosed grade-IV glioma of the midbrain had a partial response, leading to a delay in initiation of radiation by 18 months. None of the 5 patients with diffuse, intrinsic brain-stem gliomas responded. Only one of the 5 patients with recurrent ependymoma had a partial response for 11 months. Half of the patients suffered grade-II or grade-IV myelotoxicity, typically neutropenia, lead- ing to dose reductions in seven. Subsequent phase-II data from the National Cancer Institute failed to find any complete or partial responders with high-grade CNS malignancies though stabilization of low-grade neoplasms was noted for prolonged periods (Blaney et al. 1996). These data are also supported by a phase-II trial in recurrent, pretreated high-grade glioma patients by the National Cancer Institute of Canada that assessed response to 1.5 mg/m
2/d for 5 days every 3 weeks (Macdonald et al. 1996). The trial found only a modest benefit with two patients (6%) of 31 with a response.
In adults, phase-I data also assessed topotecan and radiation for biopsy-proven grade-IV gliomas (Grabenbauer et al. 2002). Three-dimensional con- formal radiation therapy was used to deliver 1.75 Gy b.i.d. to 57.75 Gy. Concurrently, topotecan was given as a continuous infusion starting at a dose of 0.30 mg/
m
2. The maximum tolerated dose was 0.7 mg/m
2per
day with half the cohort suffering dose limiting tox-
icities. Three patients suffered febrile sinusitis, bac-
terial sepsis, and grade-IV thrombocytopenia. The recommended dosing of topotecan was 0.6 mg/m
2per day on a 21-day infusion cycle. No significant toxicity from radiation was noted. Another phase-I trial used more conventional fractionation patterns, 60 Gy at 2 Gy/day, in patients with grade-IV gliomas (Fisher et al. 2001). The maximum tolerated dose of topotecan was 1.5 mg/m
2per day intravenously for 5 days every 3 weeks. The median survival of the 47 patients was 9.7 months. This trial’s successor was the phase-II trial RTOG 9513 and enrolled 87 patients.
The addition of topotecan 1.5 mg/m
2per day intra- venously for 5 days every 3 weeks for three cycles concurrent with radiation failed to improve overall survival (Fisher et al. 2002). Additional phase-II trial data, however, arrived at a different conclusion about the efficacy of the addition of topotecan 1 h prior to standard radiation, 60 Gy at 2 Gy/day, for patients with grade-IV gliomas (Gross et al. 2001).
The topotecan dose was 0.5 mg (absolute dose). The median cumulative dose of topotecan was 15 mg, range 7.5–18.5 mg. All but 3 of the 60 patients com- pleted radiotherapy. Toxicity was acceptable with six cases of grade III and three cases of grade IV. Neuro- toxicity appeared in 4 patients split evenly between grades III and IV. Two patients died of sepsis believed related to corticosteriod immune suppres- sion. The median overall survival was 15 months.
Different approaches with dose and administration of topotecan might improve the therapeutic ratio compared with radiation alone for high-grade glio- mas in adults. Additional investigation into possible genetic differences between responders and non- responders, especially in children, might elucidate the different results. This selection might improve outcomes in future trials. Further accumulation of data in children is warranted.
4.9
Head and Neck Tumors
Local failure remains a problem in the control of head and neck cancers despite the integration of chemotherapy with radiation or alterations in frac- tionation. Cisplatin-based regimens have emerged as the standard (Fu et al. 1996). This drug is often combined with 5-fluorouracil, which independently can cause severe mucositis. Its use was tested in a phase-III randomized, controlled trial and found to improve local control but without additional ben- efit to overall survival (Jacobs et al. 1992). Altered
fractionation also improves local control (Fu et al. 2000). Use of altered fractionation and cispla- tin alone is being explored in an effort to improve local control (Ang et al. 2005). Improvements have been noted in the postoperative setting for locally advanced patients treated with radiation and cis- platin alone (Al-Sarraf et al. 1997; Cooper et al.
2004; Bernier et al. 2005). The addition of agents which do not cause mucositis but also exhibit activ- ity against squamous cell cancers of the head and neck may result in further therapeutic gain with acceptable toxicity.
Irinotecan has known activity as a single agent for recurrent squamous cell cancers of the head and neck, unlike topotecan or 9-nitro-20(S)-camptoth- ecin (RFS-2000; Murphy et al. 2001). Its activity was modest exhibiting an overall response rate of 21%. Patients treated with it as a single agent had a median survival of 7 months and a 1-year survival rate of 30%. With results as modest as this, irino- tecan would be considered as a single agent with radiation, but might become part of a doublet che- motherapy (Salama et al. 2005). Two early trials have assessed the impact of irinotecan combined with a second chemotherapy agent with radiation in the primary treatment of locally advanced head and neck cancer.
Humerickhouse et al. (2000). elected to com- bine irinotecan with 5-fluorouracil and hydroxy- urea with radiation in a phase-I trial in 16 patients.
Patients either had recurrent or inoperable disease.
The radiation schedule was hyperfractionated split course at 1.5 Gy b.i.d. for 2 weeks for four or five courses. The radiation fractionation schedule would not be considered standard today off proto- col. Irinitotecan was given intravenously days 1–5 with radiation. The 5-fluorouracil was given as a continuous infusion days 1–5 along with hydroxy- urea orally days 0–5 with each cycle of radiation.
The maximum tolerated dose of irinotecan given daily with radiation and these other agents was 15 mg/m
2. Only 14 patients were assessable for tox- icity and eight for response out of the 16 enrolled.
The grade-III to grade-IV mucositis rate was 10 of 14 (71%) patients. The grade-III to grade-IV dermatitis rate was 8 of 14 (57%) patients by third to fifth cycle.
Of the patients available for assessment of response, only two had a complete response (25%); four had a partial response (50%); one had stable disease (12.5%); and one progressed (12.5%).
Another preliminary trial of 12 patients investi-
gated the use of irinotecan combined with docetaxel
(Koukourakis et al. 1999). These patients had not
been previously treated and had locally advanced primary tumors. All patients were stage IVA, T3N2/3, or T4N0. In contrast to the prior trial, standard radiation schedule and fractionation were used. The total dose ranged from 66 to 70 Gy in 33–35 frac- tions treated once daily without planned breaks.
Both agents had planned escalations until dose lim- iting toxicities were reached. The maximum toler- ated doses of docetaxel and irinotecan were 20 and 40 mg/m
2, respectively, after two dose escalations of irinotecan. Eight patients successfully completed treatment with docetaxel 20 mg/m
2and either 25 or 40 mg/m
2, the initial two dose levels. Docetaxel dosing was not increased. Seven of the eight patients had a complete response and the other patient had a partial response. The results for the third dose escalation in which all four patients had such severe mucositis that a prolonged treatment break in radi- ation occurred were inferior. Two patients had a complete response, and two had a partial response.
These results underscore the critical importance of duration of radiation in the successful management of rapidly dividing tumors.
Some combination of altered fractionation and chemotherapy may become the standard of care for unresectable or locally advanced squamous cell cancers of the head and neck (Budach et al.
2005). Successful regimens likely need to contain a platinum agent and a second agent, perhaps initi- ated late in the course of therapy concurrent with radiation. As tumors are exposed to radiation, resistant clones begin to proliferate at the end of therapy. This fact makes overall treatment time an important variable in head and neck squamous cell cancer control. Optimized sequencing might help minimize treatment breaks from toxicity and aid in controlling accelerated repopulation of resistant clonogens.
4.10 Conclusion
Evidence in multiple tumor types exists for enhanced radiosensitivity and supra-additive cell killing with the combination of topoisomerase inhibitors and ionizing radiation. Combinations of topoisomerase inhibitors have been shown to be additive for cell killing in a sequence dependent manner. An effec- tive combination sequence was Topo-I inhibition followed by Topo-II inhibition in V79 Chinese ham- ster lung fibroblast lines (Bonner and Kozelsky
1996). Further work has shown this combination to be more efficacious when given simultaneously with radiation. Comparing the Topo-I inhibitor 9-nitro- 20(S)-camptothecin (RFS-2000) or etoposide alone with radiation or combined with radiation, Kim et al. (2002) noted increased radiosensitivity with the combination in human lung cancer lines.
Given the synergism noted through the simultane- ous suppression of both Topo I and II with radiation (Kim et al. 2002), intriguing combinations of oral agents, such as etoposide, 9-nitro-20(S)-camptothe- cin or oral irinotecan, capecitabine, and satraplatin, are possible. The ease of administration, decreased expense associated with oral agents, favorable toxic- ity profiles, and possibility for daily use with radia- tion as radiosensitizers argue for further studies of oral chemotherapy. A permutation in the use of conventional agents, such as intravenous irinotecan, might yield improvements. The Children’s Oncology Group recently opened ADVL0414, a phase-I study of temozolomide, oral irinotecan, and vincristine for children with refractory solid tumors (see Fig. 4.4).
Should encouraging results be noted, continuation of this paradigm combined with radiation might be feasible and logical.
Sequence might prove to be important with com- bination inhibition. Administration of Topo I fol- lowed by Topo II does not always provide synergism.
Antagonism has been reported when topotecan was followed by etoposide in glial and medulloblastoma cell lines in vitro (Janss et al. 1998). These data were obtained with chemotherapy alone. Similar findings were noted in IL-60 human progranulocytic leuke- mia cells incubated in etoposide and then treated with a Topo-I inhibitor (Kaufmann 1991). In fact, simultaneous exposure resulted in 30-fold survival compared with treatment with etoposide alone. This inhibition extended to structurally unrelated Topo- II inhibitors. By contrast, simultaneous adminis- tration of Topo-I and Topo-II inhibitors in human glial lines acted synergistically, even in cells that individually were resistant to both agents in vitro ( Ciesielski and Fenstermaker 1999). With pro- longed exposure to topotecan the timing of the administration of a Topo-II inhibitor failed to influ- ence significantly the synergism. No radiation was given in this experiment with V79 cells (Cheng et al. 1994). Other data seem to indicate that such a sequence is logical. After administration of a Topo- I inhibitor, levels of Topo IID rise (Whitacre et al.
1997). Based in part on this finding, lung cancer
cells were treated sequentially with irinotecan or 9-
nitro-20(S)-camptothecin (RFS-2000) followed by
radiation followed by etoposide (Kim et al. 2002).
Antagonism was not demonstrated; instead, syn- ergism was found. Dose enhancement ratios of 1.63 and 1.65 resulted with this sequence with irinote- can and 9-nitro-20(S)-camptothecin (RFS-2000), respectively. A small series of adult patients with a variety of refractory solid tumors received combi- nation Topo-I and Topo-II inhibitory therapy. Rela- tively low efficacy was noted. Interestingly, biopsies of accessible tumors did not substantiate the pur- ported upregulation of Topo II after Topo-I admin- istration, nor did Topo-I levels fall as expected after Topo-I administration (Hammond et al. 1998).
Variations based on the cell lines investigated and the effect of radiation might help to explain these contradictory findings. Future investigations look- ing at these variables will be needed prior to imple- mentation into clinical trials to determine for each type of tumor the optimal integration of multiple topoisomerase inhibitors and radiation.
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