Immune system stimulation by thermochemotherapy
Description coming soon!
Hyperthermia as an enhancer of systemic gene therapy
Gene therapy involves inserting genetic material (plasmid DNA) into critical cells that results in the manufacture of protein(s) which are either directly therapeutic or interact with other substances to exert a therapeutic effect. In order to treat cancer effectively, the genetic material must (i) exert its effect only on tumor or tumor-associated cells, not on normal cells, (ii) be able to be administered systemically in order to treat unknown or distant foci of disease (metastases), and (iii) not eliminate the body's immune response that is so critical in fighting cancer. In order to achieve these goals we are developing an experimental approach to gene therapy which combines fever-range whole body hyperthermia (FR-WBH) with a gene that only affects tumor cells (HSVtk suicide gene + prodrug gancyclovir) spliced with additional genetic material designed to cause the suicide gene to be expressed predominantly in tumor cells (cationic liposomes). The hyperthermia is expected to help in several ways: (i) to open up the pores of tumor blood vessels so that more liposomes reach the tumors and deliver their DNA content to tumor cells, (ii) to increase the amount of protein created by the incorporated DNA, (iii) to boost the bystander effect whereby cells that are not transfected are nonetheless killed by the prodrug, and (iv) to boost the immune system so that it sends specialized cells into the tumors to help kill them. This work is being carried out in collaboration with Dr. Amy S. Lee at the University of California, Los Angeles; Dr. Nancy S. Templeton at Baylor College of Medicine, Houston; Dr. David Loose, University of Texas Medical School, Houston, and Dr. Joseph Alcorn, University of Texas Medical School, Houston.
The interaction of hyperthermia with chemotherapy drugs
We have studied the anti-tumor effect of hyperthermia administered with chemotherapy drugs including platinum analogs (cisplatin, carboplatin, oxaliplatin), anthracylines (doxorubicin, doxil, epirubicin), antimetabolites (5-FU, gemcitabine), and topoisomerase inhibitors (irinotecan). Hyperthermia generally enhances the tumor-killing effect of the drugs, sometimes in a synergistic fashion. We also found that after primary tumor excision, FR-WBH combined with low-dose irinotecan (a topoisomerase-I inhibitor) significantly inhibited lymph node metastasis development and prolonged survival significantly without toxicity.
It is also clear that the timing of the hyperthermia treatment relative to drug administration is critical in determining the anti-tumor effect. For example, we found that when gemcitabine was given to tumor-bearing rats simultaneously with, or 48 hours after fever-range whole body hyperthermia (FR-WBH) there was a 50 - 60% tumor cure rate, yet when FR-WBH was given 24 hours after gemcitabine, the enhancing effect of the thermal therapy was lost and no tumor cures were achieved. There is also a sequence dependency of the anti-tumor effect of FR-WBH combined with oxaliplatin. When oxaliplatin was given 12 or 24 hours before FR-WBH to mammary tumor-bearing rats, survival was significantly increased and cure of the primary tumor and all metastases was seen in at least half of the animals. Toxicity was also least when oxaliplatin was given 24 hours before FR-WBH (as shown in the right-hand graph at the top of the page). When oxaliplatin was administered simultaneously with, 3 hours before, or 24 hours after thermal therapy there were no cures and survival was not significantly different from treatment with oxliplatin alone. Furthermore, lower doses of oxaliplatin given 12 or 14 hours before FR-WBH were more effective than the maximally tolerated dose. These results are summarized in the graphs below.
Results from our pre-clinical studies are constantly being applied to develop clinical protocols for treatment combining FR-WBH with chemotherapy drugs.
The effect of hyperthermia on tumor vasculature and drug delivery
As a prelude to determining vascular effects of fever-range whole body hyperthermia, we have studied the development of tumor vasculature during tumor growth using a metastatic tumor model in rats that mimics advanced human breast cancer. The relationship between micro-vessel density (MVD), vascular endothelial growth factor (VEGF) expression, and histopathology was compared in primary and metastatic axillary and inguinal lymph nodes over 5 - 6 tumor doublings. MVD and VEGF scores rose asymptotically with increasing tumor weight in both primary and metastatic tumors but the number of microvessels was significantly higher in primary tumors than for metastases. VEGF levels were not significantly different between primary and metastatic tumors, but VEGF expression rose to maximal levels at much smaller tumor sizes in primary tumors than lymph node metastases. Maximal VEGF expression preceded significant microvessel development in primary and metastatic tumors. Both MVD and VEGF expression in lymph node metastases were proportional to increasing metastatic invasion. Lymph node metastases limited to the subcapsular sinus had the lowest MVD, indicating an ability to survive without significant vasculature. These findings underscore the differences between primary and metastatic tumors and have implications for the therapy of metastatic cancer. FR-WBH (6 hours at 40oC) resulted in an initial decrease in VEGF expression over 12 hours, followed by a steady increase to almost double baseline levels by 96 hours. Microvessel density, especially the number of small vessels, decreased over the first 48 hours after FR-WBH. At 96 hours, there was a significant reduction in tumor volume. These observations are consistent with VEGF induction ocurring in response to microvessel destruction by FR-WBH, which in turn leads to death of tumor cells. We have also shown that hyperthermia causes tumor cell death by apoptosis rather than necrosis.
Delivering adequate concentrations of therapeutic drugs to solid tumors is a continuing challenge, and an active area of research. Hyperthermia can help with drug delivery because (i) it increases systemic blood flow thereby bringing more drug to tumors, (ii) it opens the pores in tumor microvessels allowing drugs to enter the tumor, and (iii) by killing tumor cells, it reduces the high interstitial pressure of tumors thus allowing better penetration of drugs into the tumor. We have used radioactively labeled liposomes to study the effect of hyperthermia on liposome uptake in experimental tumors. We found that FR-WBH could increase the tumor uptake of liposomes by 40% 24 hours after injection, and that liposomes appear to be retained longer in tumors after FR-WBH than without the thermal therapy.
Cell death induced by hyperthermia and chemotherapy
Whole body hyperthermia (WBH) has been shown to increase the anti-tumor effect of several anti-cancer
drugs, but the mechanisms of heat-drug interaction remain to be elucidated. We studied one aspect of the heat-drug
interaction by examining the relationship between tumor growth delay (TGD) and the kinetics of tumor cell death by
apoptosis and necrosis in rat mammary tumors following treatment with WBH alone, cisplatin (CDDP) and doxorubicin (DOX)
chemotherapy, and combinations of WBH with either drug. WBH was administered for either 1 or 2 hours at 41.5oC
or 6 hours at 40.0oC while the drugs were given at several doses up to the maximally tolerated dose (MTD).
At sub-MTD of drug alone, or drug with WBH, the area under the curve of apoptosis rose in proportion to TGD,
as did cumulative necrosis only much more slowly. At the MTD of drug alone or drug + WBH, apoptosis fell to near control levels
and cumulative necrosis increased significantly with a consequent down- and right-shift of the apoptosis vs. necrosis rgression line.
It appears therefore, that in the MTLn3 rat tumor model, the anti-tumor effect of WBH and sub-MTD drug doses is mediated more via apoptosis
than necrosis while at MTDs of CDDP or DOX, with or without WBH, cell death shifts from apoptosis to necrosis. The supra-additive
enhancement of tumor growth delay by addition of WBH to CDDP is associated with correspondingly increased apoptosis, not necrosis.
We are currently studying whether another form of cell death known as autophagy, the process by which cells recycle cytoplasm and dispose of excess or
defective organelles, is involved in tumor responses to thermal therapy.