Radiation therapy and Corynebacterium parvum in the treatment of murine tumors

The changing paradigm of tumour response to irradiation

Tumours contain multiple different cell populations, including cells derived from the bone marrow as well as cancer-associated fibroblasts and various stromal populations including the vasculature. The microenvironment of the tumour cells plays a significant role in the response of the tumour to radiation treatment. Low levels of oxygen (hypoxia) caused by the poorly organized vasculature in tumours have long been known to affect radiation response; however, other aspects of the microenvironment may also play important roles. This article reviews some of the old literature concerning tumour response to irradiation and relates this to current concepts about the role of the tumour microenvironment in tumour response to radiation treatment. Included in the discussion are the role of cancer stem cells, radiation damage to the vasculature and the potential for radiation to enhance immune activity against tumour cells. Radiation treatment can cause a significant influx of bone marrow-derived cell populations into both normal tissues and tumours. Potential roles of such cells may include enhancing vascular recovery as well as modulating immune reactivity.

CpG plus radiotherapy: a review of preclinical works leading to clinical trial

Studies performed three decades ago in our laboratory supported the hypothesis that radiation efficacy may be augmented by bacterial extracts that stimulate non-specific systemic antitumor immune responses. Application to the clinic was halted by unacceptable side effects and toxicities resulting from exposure to whole bacterial pathogens. Later scientific advances demonstrated that DNA isolated from bacteria was immunostimulatory and could be reproduced with synthetic oligodeoxynucleotides (ODNs), thus fueling the transition from bugs to drugs. Unmethylated CpG motifs within bacterial DNA induce activation of Toll-like receptor 9 and subsequently activate antigen-specific cellular immune responses. CpG ODNs have demonstrated favorable toxicity profiles in phase I clinical trials. We showed that this potent immunoadjuvant can be used in combination with radiation therapy to enhance local and systemic responses of several murine tumors. Studies demonstrated that enhanced tumor response is mediated in part by the host immune system. Antitumor efficacy was diminished in immunocompromised mice. Animals cured by combination of radiation and CpG ODN were resistant to subsequent tumor rechallenge. This body of work contributes to our understanding of the dynamic interplay between tumor irradiation and the host immune system and may facilitate translation to clinical trials.

Tumor necrosis factor as an adjunct to fractionated radiotherapy in the treatment of murine tumors

Recombinant murine tumor necrosis factor (TNF) was investigated for its ability to increase the response of a murine mammary carcinoma to fractionated local tumor irradiation. When tumors in the leg of syngeneic mice grew to 8 mm in diameter (268 mm3), they were exposed to 3, 4 or 5 Gy gamma-rays daily for 10 days. Tumor necrosis factor was given 3 hr after each irradiation at a dose of 2 micrograms per mouse. Tumor growth delay was used as the endpoint. The effect of treatment with both agents combined was greater than the additive effect of the individual treatments. Tumor necrosis factor increased local tumor radiotherapy response by a factor of about 1.2, and by itself was effective in retarding the growth of both immunogenic and nonimmunogenic tumors. These experiments suggest that tumor necrosis factor in combination with radiotherapy may be beneficial for the treatment of cancer patients.

Combination of 60Co gamma-radiation, misonidazole, and maltose tetrapalmitate in the treatment of Dunning prostatic tumor in the rat

Maltose tetrapalmitate (MTP), a synthetic nontoxic immunoadjuvant, the radiosensitizer misonidazole (MISO), and 60Co gamma-radiation, alone or in combination, were used in the management of Dunning prostatic tumor in the rat. Nine groups of 10 rats each were used to assess the efficacy of various therapeutic modalities. Tumor growth rates and animal survival times were determined for each group. Radiation was more effective when combined with MTP, but the adjuvant must be present when radiation is given for synergism to occur. MISO was as effective as MTP when used with radiation, but combining them cancels out their individual effects. In a clinical situation it would be advantageous to use separately the synergisms existing between MISO and radiation on the one hand and MTP and radiation on the other hand.

Clinical trial of Corynebacterium parvum (intra-lymph-node and intravenous) and radiation therapy in the treatment of head and neck carcinoma

Fifty-seven patients with previously untreated squamous cell carcinoma of the head and neck region of all clinical stages were entered a trial to evaluate the effectiveness of Corynebacterium parvum combined with radiation therapy in improving local and survival results. Twenty-nine patients were randomized to receive radiation therapy alone, and 28 patients were randomized to receive radiation therapy combined with C. parvum. The C. parvum was administered into the tumor-bearing lymph nodes of the neck or into the cervical node region in non-node-positive patients (4 mg/m2) and by intravenous routes (at 2, 2, 4, 4 and 4 mg/M2) at days -10, -7, and -3 before, and at +7 and +14 days after the start of radiation therapy. The study began in July 1975 and was terminated after 2 1/2 years of patient accession. The statistical analysis showed that those receiving C. parvum were not doing better than controls and, in fact, in some subgroups there was concern that they might be doing less well. Pertinently, analysis showed that those receiving C. parvum would not experience the 25% point improvement in disease-free survival frequency which had been stipulated in the design of the protocol.

The effect of chemotherapy on occult metastases after surgical removal of a non-immunogenic mouse carcinoma

A transplantable non-immunogenic murine carcinoma of spontaneous origin, WHT Carcinoma N-C (Hewitt), was used to assess the effectiveness of melphalan (Ml) and/or methotrexate (Mx) for treatment of occult metastatic disease following surgical excision of primary tumors. Early surgical excision alone cured 66% of mice; later excision gave no cures. Maximum sublethal doses of chemotherapy rarely cured mice of metastases but did extend their survival time by up to 66% as compared with mice subjected to excision only. The influence of excision and chemotherapy on the frequency of local recurrence or pulmonary metastasis is discussed. Extrapulmonary metastases were 2.5 times more frequent in long-term than in short-term survivors, independently of treatment.

A preliminary study of intralesional, intralymph node, intravenous and intraperitoneal Corynebacterium parvum treatments in patients with advanced cancer

Twenty-one patients with squamous cell carcinoma of oral cavity and/or cervical lymph node and four patients with soft tissue sarcomas were given intralesional (2-4 mg/m2) and intralymph node (2-4 mg/m2) C. parvum injections followed by 5 intravenous (2-4 mg/m2) C. parvum treatments and conventional therapies. Seven patients with Stage III ovarian carcinomas were given intraperitoneal (2-4 mg/m2) C. parvum injections followed by conventional therapies. The local and systemic effects of the C. parvum treatments were described and the anti-tumor effects were evaluated in this series of patients.

Back to the drawing board--the need for more realistic model systems for immunotherapy

In experimental animals the growth of tumors which display strong immunogenicity can be slowed by immunological maneuvers that increase the magnitude of the host response to the specific tumor antigens. Such immunogeneic tumors do not, in general, cause distant metastases and may, therefore, not be relevant to the treatment of disseminated disease in man. This may explain why the current experience with immunotherapy based on such animal models has, with very few exceptions, been disappointing. Animal tumors which are not immunogenic by standard transplantation tests frequently disseminate and it seems likely that clinically useful immunotherapy has to be based on procedures which are effective against such tumors. The lack of immunogenicity detectable by transplantation may be due to the absence of tumor-specific transplantation antigens (TSTAs), in which case if there is to be any immunotherapy it will have to be direct at boosting some innate type of host resistance. Alternatively, the lack of immunogenicity may be attributable to the intervention of "escape mechanisms" which pervert the immunologically specific host response to TSTAs. In this case, the immunological maneuvre should be directed at overcoming the escape problem and not at boosting the magnitude of the specific host reaction to the TSTAs.