Hypoxia in head and neck cancer

Targeting the delivery of glycan-based paclitaxel prodrugs to cancer cells via glucose transporters

This report describes the synthesis of four novel paclitaxel based prodrugs with glycan conjugation (1-4). Glycans were conjugated using an ester or ether bond as the linker between 2'-paclitaxel and the 2'-glucose or glucuronic acid moiety. These prodrugs showed good water solubility and selective cytotoxicity against cancer cell lines, but showed reduced toxicity toward normal cell lines and cancer cell lines with low expression levels of GLUTs. The ester conjugated prodrug 1 showed the most cytotoxicity among the prodrugs examined and could be transported into cells via GLUTs. Fluorescent and confocal microscopy demonstrated that targeted cells exhibited morphological changes in tubulin and chromosomal alterations that were similar to those observed with paclitaxel treatment. Therefore, these glycan-based prodrugs may be good drug candidates for cancer therapy, and the glycan conjugation approach is an alternative method to enhance the targeted delivery of other drugs to cancer cells that overexpress GLUTs.

Prospective trial incorporating pre-/mid-treatment [18F]-misonidazole positron emission tomography for head-and-neck cancer patients undergoing concurrent chemoradiotherapy

PURPOSE

To report the results from a prospective study of a series of locoregionally advanced head-and-neck cancer patients treated with platinum-based chemotherapy and intensity-modulated radiotherapy and to discuss the findings of their pre-/mid-treatment [(18)F]-misonidazole ((18)F-FMISO) positron emission tomography (PET) scans.

METHODS AND MATERIALS

A total of 28 patients agreed to participate in this study. Of these 28 patients, 20 (90% with an oropharyngeal primary cancer) were able to undergo the requirements of the protocol. Each patient underwent four PET scans: one pretreatment fluorodeoxyglucose PET/computed tomography scan, two pretreatment (18)F-FMISO PET/computed tomography scans, and a third (18)F-FMISO PET (mid-treatment) scan performed 4 weeks after the start of chemoradiotherapy. The (18)F-FMISO PET scans were acquired 2-3 h after tracer administration. Patients were treated with 2-3 cycles of platinum-based chemotherapy concurrent with definitive intensity-modulated radiotherapy.

RESULTS

A heterogeneous distribution of (18)F-FMISO was noted in the primary and/or nodal disease in 90% of the patients. Two patients had persistent detectable hypoxia on their third mid-treatment (18)F-FMISO PET scan. One patient experienced regional/distant failure but had no detectable residual hypoxia on the mid-treatment (18)F-FMISO PET scan.

CONCLUSION

Excellent locoregional control was observed in this series of head-and-neck cancer patients treated with concurrent platinum-based chemotherapy and intensity-modulated radiotherapy despite evidence of detectable hypoxia on the pretreatment (18)F-FMISO PET/computed tomography scans of 18 of 20 patients. In this prospective study, neither the presence nor the absence of hypoxia, as defined by positive (18)F-FMISO findings on the mid-treatment PET scan, correlated with patient outcome. The results of this study have confirmed similar results reported previously.

Hypoxia-induced energy stress inhibits the mTOR pathway by activating an AMPK/REDD1 signaling axis in head and neck squamous cell carcinoma

The mammalian target of rapamycin (mTOR) signaling network is frequently hyperactivated in patients with head and neck squamous cell carcinoma (HNSCC). Recent studies suggest that hypoxia, a common microenvironmental stress found in tumors, blocks this mitogenic pathway. Here, we demonstrate that in HNSCC cell lines, the expression of the phosphorylated forms of the mTOR downstream targets S6 kinase and S6 (pS6) decreased after hypoxia. These events were associated with a marked up-regulation of the regulated in development and DNA damage 1 (REDD1), a recently characterized hypoxia-induced protein that negatively controls mTOR activity. Conversely, pS6 levels were retained under hypoxia in REDD1 knock-down cells and in HNSCC cells lacking endogenous REDD1 expression. Furthermore, we observed that prolonged hypoxia induced an energy-depleting response as evidenced by decreased cellular ATP levels and AMP-activated protein kinase (AMPK) activation. Interestingly, AMPK inhibition before prolonged hypoxia prevented REDD1 expression, thereby sustaining mTOR activity. These results suggest a novel mechanism by which AMPK activation after hypoxia-induced energy stress may be crucial in regulating REDD1 expression to control the mTOR pathway in HNSCC. Furthermore, we found that, in some HNSCC cells, the reduced mTOR activity in response to hypoxia through AMPK/REDD1 was deregulated, which hence might contribute to the persistent activation of the mTOR pathway in this cancer type.

Tumor hypoxia detected by positron emission tomography with 60Cu-ATSM as a predictor of response and survival in patients undergoing Neoadjuvant chemoradiotherapy for rectal carcinoma: a pilot study

PURPOSE

The response of rectal cancers to neoadjuvant chemoradiotherapy is variable. Tumor hypoxia reduces the effectiveness of both radiation therapy and chemotherapy and is a well-known risk factor for tumor radioresistence. We hypothesized that imaging with the novel hypoxia-detecting agent, (60)Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) ((60)Cu-ATSM), previously validated in cervical and lung cancers, would predict the response of rectal cancers to neoadjuvant chemoradiotherapy and prognosis.

METHODS

Patients with locally invasive (T2-4) primary or node-positive rectal cancer located <12 cm from the anal verge were recruited for this pilot study. Pretreatment tumor size and stage were determined by endorectal ultrasonography, CT, and magnetic resonance imaging. Eleven patients also underwent clinical positron emission tomography with (18)F-fluorodeoxyglucose at the discretion of the treating clinician. The primary tumor was imaged by positron emission tomography with (60)Cu-ATSM, and accumulation of the tracer was measured semiquantitatively by determining the tumor-to-muscle activity ratio. Neoadjuvant chemoradiotherapy was then administered (within 2 weeks of (60)Cu-ATSM-positron emission tomography) and consisted of 45 Gy given in 25 fractions to the pelvis with continuous intravenous infusion of 5-fluorouracil (225 mg/m(2)/day). Proctectomy was performed six to eight weeks after neoadjuvant chemoradiotherapy and the tumor submitted to pathology for size measurement and staging. Tumor-to-muscle activity ratios were compared with tumor (18)F-fluorodeoxyglucose uptake, tumor response to neoadjuvant chemoradiotherapy, and with patient survival.

RESULTS

Nineteen patients were enrolled in the study, two of whom were excluded from final analysis (1 death during neoadjuvant chemoradiotherapy and 1 tumor perforation during neoadjuvant chemoradiotherapy requiring emergent surgery). Of the 17 remaining patients, 14 had a reduction in tumor size and 13 were downstaged. The median tumor-to-muscle activity ratio of 2.6 discriminated those with worse prognosis from those with better prognosis. Both overall and progression-free survivals were worse with hypoxic tumors (tumor-to-muscle activity ratio >2.6) than with nonhypoxic tumors (tumor-to-muscle activity ratio <or=2.6; both P < 0.05). In addition, 2 of the 3 tumors with no change in size had tumor-to-muscle activity ratios >2.6 (positive predictive value 66 percent), whereas 6 of 14 with decreased size had tumor-to-muscle activity ratios >2.6 (negative predictive value 57 percent). Three of the 4 tumors not downstaged had tumor-to-muscle activity ratios >2.6 (positive predictive value 75 percent), whereas 5 of 13 downstaged tumors had tumor-to-muscle activity ratios >2.6 (negative predictive value 62 percent). The mean tumor-to-muscle activity ratio for downstaged tumors (2.2) was significantly lower than that of nondownstaged tumors (3.3) (P = 0.03). The difference in mean tumor-to-muscle activity ratio between downsized (2.3) and nondownsized (2.9) tumors did not reach statistical significance (P = 0.36). Tumor (18)F-fluorodeoxyglucose uptake (n = 11) did not correlate with (60)Cu-ATSM uptake (r = 0.4; P = 0.9) and there was no significant difference in mean tumor (18)F-fluorodeoxyglucose uptake between patients with hypoxic tumors and those with normoxic tumors (P = 0.3).

CONCLUSIONS

The results of this small pilot study suggest that (60)Cu-ATSM-PET may be predictive of survival and, possibly, tumor response to neoadjuvant chemoradiotherapy in patients with rectal cancer. A larger Phase II study is warranted to validate these results.

In vitro and in vivo evaluations of a hydrophilic 64Cu-bis(thiosemicarbazonato)-glucose conjugate for hypoxia imaging

A water-soluble glucose conjugate of the hypoxia tracer 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) was synthesized and radiolabeled (64Cu-ATSE/A-G). Here we report our initial biological experiments with 64Cu-ATSE/A-G and compare the results with those obtained for 64Cu-ATSM and 18F-FDG.

METHODS

The uptake of 64Cu-ATSE/A-G and 64Cu-ATSM into HeLa cells in vitro was investigated at a range of dissolved oxygen concentrations representing normoxia, hypoxia, and anoxia. Small-animal PET with 64Cu-ATSE/A-G was performed in male BDIX rats implanted with P22 syngeneic carcinosarcomas. Images of 64Cu-ATSM and 18F-FDG were obtained in the same model for comparison.

RESULTS

64CuATSE/A-G showed oxygen concentration-dependent uptake in vitro and, under anoxic conditions, showed slightly lower levels of cellular uptake than 64Cu-ATSM; uptake levels under hypoxic conditions were also lower. Whereas the normoxic uptake of 64Cu-ATSM increased linearly over time, 64Cu-ATSE/A-G uptake remained at low levels over the entire time course. In the PET study, 64CuATSE/A-G showed good tumor uptake and a biodistribution pattern substantially different from that of each of the controls. In marked contrast to the findings for 64Cu-ATSM, renal clearance and accumulation in the bladder were observed. 64Cu-ATSE/A-G did not display the characteristic brain and heart uptake of 18F-FDG.

CONCLUSION

The in vitro cell uptake studies demonstrated that 64Cu-ATSE/A-G retained hypoxia selectivity and had improved characteristics when compared with 64Cu-ATSM. The in vivo PET results indicated a difference in the excretion pathways, with a shift from primarily hepatointestinal for 64Cu-ATSM to partially renal with 64Cu-ATSE/A-G. This finding is consistent with the hydrophilic nature of the glucose conjugate. A comparison with 18F-FDG PET results revealed that 64Cu-ATSE/A-G was not a surrogate for glucose metabolism. We have demonstrated that our method for the modification of Cu-bis(thiosemicarbazonato) complexes allows their biodistribution to be modified without negating their hypoxia selectivity or tumor uptake properties.

Engineering human tumor-specific cytotoxic T cells to function in a hypoxic environment

Hypoxia occurs in many tumors and reduces the effectiveness of radio- and chemotherapy. Hypoxia also impedes immune responses to tumors, reducing T lymphocyte production of cytokines such as interleukin-2 (IL-2) and interferon gamma, as well as the survival and proliferation of these cells. We constructed a lentiviral vector encoding a bidirectional hypoxia-inducible responsive element (HRE) derived from human vascular endothelial growth factor, which drives the hIL-2 gene and a marker gene. We used a model of human B cell lymphoma to show that tumor-specific T cells modified with this vector upregulate hIL-2 expression when oxygen tension is low in vitro and in vivo. The consequence of this effect is to increase T-cell survival and proliferation whilst sustaining effector function, even in O(2) concentrations as low as 1%. The phenotype of the transduced cells is unchanged, as is their ability to migrate to tumor. HRE-IL-2-modified cytotoxic T lymphocytes (CTLs) produce faster and more complete tumor regression than parental CTLs and increase overall survival. Hypoxia-resistant T cells may thus be of value in the treatment of human tumors in which areas of hypoxia may otherwise account for resistance to this therapeutic strategy.

Assessing tumor hypoxia in cervical cancer by PET with 60Cu-labeled diacetyl-bis(N4-methylthiosemicarbazone)

Tumor hypoxia indicates a poor prognosis. This study was undertaken to confirm our prior pilot results showing that pretreatment tumor hypoxia demonstrated by PET with (60)Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) ((60)Cu-ATSM) is a biomarker of poor prognosis in patients with cervical cancer. Thirty-eight women with biopsy-proved cervical cancer underwent (60)Cu-ATSM PET before the initiation of radiotherapy and chemotherapy. (60)Cu-ATSM uptake was evaluated semiquantitatively as the tumor-to-muscle activity ratio (T/M). A log-rank test was used to determine the cutoff uptake value that was strongly predictive of prognosis. All patients also underwent clinical PET with (18)F-FDG before the institution of therapy. The PET results were correlated with clinical follow-up. Tumor (60)Cu-ATSM uptake was inversely related to progression-free survival and cause-specific survival (P = 0.006 and P = 0.04, respectively, as determined by the log-rank test). We found that a T/M threshold of 3.5 best discriminated patients likely to develop a recurrence from those unlikely to develop a recurrence; the 3-y progression-free survival of patients with normoxic tumors (as defined by T/M of < or = 3.5) was 71%, and that of patients with hypoxic tumors (T/M of > 3.5) was 28% (P = 0.01). Tumor (18)F-FDG uptake did not correlate with (60)Cu-ATSM uptake, and there was no significant difference in tumor (18)F-FDG uptake between patients with hypoxic tumors and those with normoxic tumors (P = 0.9). Pretherapy (60)Cu-ATSM PET provides clinically relevant information about tumor oxygenation that is predictive of outcome in patients with cervical cancer.

Fluorine-18-labeled fluoromisonidazole positron emission and computed tomography-guided intensity-modulated radiotherapy for head and neck cancer: a feasibility study

PURPOSE

Hypoxia renders tumor cells radioresistant, limiting locoregional control from radiotherapy (RT). Intensity-modulated RT (IMRT) allows for targeting of the gross tumor volume (GTV) and can potentially deliver a greater dose to hypoxic subvolumes (GTV(h)) while sparing normal tissues. A Monte Carlo model has shown that boosting the GTV(h) increases the tumor control probability. This study examined the feasibility of fluorine-18-labeled fluoromisonidazole positron emission tomography/computed tomography ((18)F-FMISO PET/CT)-guided IMRT with the goal of maximally escalating the dose to radioresistant hypoxic zones in a cohort of head and neck cancer (HNC) patients.

METHODS AND MATERIALS

(18)F-FMISO was administered intravenously for PET imaging. The CT simulation, fluorodeoxyglucose PET/CT, and (18)F-FMISO PET/CT scans were co-registered using the same immobilization methods. The tumor boundaries were defined by clinical examination and available imaging studies, including fluorodeoxyglucose PET/CT. Regions of elevated (18)F-FMISO uptake within the fluorodeoxyglucose PET/CT GTV were targeted for an IMRT boost. Additional targets and/or normal structures were contoured or transferred to treatment planning to generate (18)F-FMISO PET/CT-guided IMRT plans.

RESULTS

The heterogeneous distribution of (18)F-FMISO within the GTV demonstrated variable levels of hypoxia within the tumor. Plans directed at performing (18)F-FMISO PET/CT-guided IMRT for 10 HNC patients achieved 84 Gy to the GTV(h) and 70 Gy to the GTV, without exceeding the normal tissue tolerance. We also attempted to deliver 105 Gy to the GTV(h) for 2 patients and were successful in 1, with normal tissue sparing.

CONCLUSION

It was feasible to dose escalate the GTV(h) to 84 Gy in all 10 patients and in 1 patient to 105 Gy without exceeding the normal tissue tolerance. This information has provided important data for subsequent hypoxia-guided IMRT trials with the goal of further improving locoregional control in HNC patients.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

The hypoxic tumour microenvironment, patient selection and hypoxia-modifying treatments

Tumour hypoxia has been found to be a characteristic feature in many solid tumours. It has been shown to decrease the therapeutic efficacy of radiation treatment, surgery and some forms of chemotherapy. Successful approaches have been developed to counteract this resistance mechanism, although usually at the cost of increased short- and long-term side-effects. New methods for qualitative and quantitative assessment of tumour oxygenation have made it possible to establish the prognostic significance of tumour hypoxia. The ability to determine the degree and extent of hypoxia in solid tumours is not only important prognostically, but also in the selection of patients for hypoxia-modifying treatments. To provide the best attainable quality of life for individual patients it is of increasing importance that tools be developed that allow a better selection of patients for these intensified treatment strategies. Several genes and proteins involved in the response to hypoxia have been identified as potential candidates for future use in predictive assays. Although some markers and combinations have shown potential benefit and are associated with treatment outcome, their clinical usefulness needs to be validated in prospective trials. A review of published studies was carried out, focusing on the assessment of tumour hypoxia, patient selection and the possibilities to overcome hypoxia during treatment.

Synthesis of 2'-paclitaxel methyl 2-glucopyranosyl succinate for specific targeted delivery to cancer cells

A novel glucose-conjugated paclitaxel 5 was synthesized using succinic acid as linker between 2'-paclitaxel and methyl 2'-glucopyranose. 5 has not only improved the pharmaceutical properties of paclitaxel, such as solubility and stability, but also enhanced the specific target delivery to MCF-7 cells without the cytotoxicity against normal cells. Therefore, the glucose conjugation may be potentially used in the targeted delivery of other drugs into cells via glucose transporters (GLUTs) for cancer therapy.