I believe that studies are showing that it simply ISN'T true that glutamine potentially could promote tumor growth...
Here's what I found: (from March 2007)
http://theoncologist.alphamedpress.o.../full/12/3/312
Excerpts:
"...Glutamine is a gluconeogenic nonessential amino acid that is<sup> </sup>stored primarily in skeletal muscle and liver [
14], and is often<sup> </sup>depleted in stress states, such as malignancy [
16]. It serves<sup> </sup>as the primary carrier of nitrogen and is the main energy source<sup> </sup>for rapidly proliferating cells. Rapid proliferation of a tumor<sup> </sup>may deplete glutamine stores and subsequently lead to cancer-related<sup> </sup>cachexia [
17]. Studies have indicated that glutamine supplementation<sup> </sup>is well tolerated and potentially effective in preventing side<sup> </sup>effects for patients receiving high-dose chemotherapy and bone<sup> </sup>marrow transplantation [
25]. Supplementation with glutamine<sup> </sup>can also protect against doxorubicin-induced cardiac toxicity<sup> </sup>[
26] and prevents atrophy of the intestinal mucosa in patients<sup> </sup>receiving total parenteral nutrition [
27]. Preliminary animal<sup> </sup>studies suggest that glutamine may prevent neurotoxicity caused<sup> </sup>by vincristine, cisplatin, as well as paclitaxel [
28,
29]. Clinically,<sup> </sup>paclitaxel-induced myalgias and arthralgias have been successfully<sup> </sup>reduced by glutamine in breast cancer patients [
30]. Glutamine<sup> </sup>supplements may also reduce the severity of peripheral neuropathy<sup> </sup>in metastatic breast cancer patients receiving high-dose paclitaxel<sup> </sup>and hematopoietic stem cell transplantation [
18]. Interestingly,<sup> </sup>a byproduct of glutamine metabolism has been identified that<sup> </sup>protects advanced CRC patients from oxaliplatin-induced neuropathy<sup> </sup>[
13].<sup> </sup>
In the current study, supplementation with glutamine significantly<sup> </sup>reduced the incidence and severity of peripheral neuropathy<sup> </sup>as well as the need for dose reduction of oxaliplatin in these<sup> </sup>patients (
Tables 1 and
3). These properties may increase the<sup> </sup>therapeutic index of oxaliplatin. The potential role of glutamine<sup> </sup>as a neuroprotectant may be better understood in the context<sup> </sup>of the current hypothesis explaining chemotherapy-induced neuropathy.<sup> </sup>A study of circulating nerve growth factor (NGF) levels in cancer<sup> </sup>patients treated with neurotoxic chemotherapeutic agents found<sup> </sup>that peripheral neuropathy worsened as serum levels of NGF declined<sup> </sup>[
31]. Moreover, the administration of NGF prevents paclitaxel-induced<sup> </sup>neuropathy in mice [
32]. Because glutamine is known to upregulate<sup> </sup>NGF mRNA in an animal model [
33], glutamine supplements may<sup> </sup>prevent chemotherapy-induced neuropathy via upregulating the<sup> </sup>NGF level. On the other hand, it has also been hypothesized<sup> </sup>that high systemic levels of glutamine may downregulate the<sup> </sup>conversion of glutamine to an excitatory neuropeptide, glutamate,<sup> </sup>which may also account for the reduced symptoms observed in<sup> </sup>patients receiving glutamine [
34]...."<sup> </sup>
<sup>
</sup>"...A major concern is that glutamine supplements might protect<sup> </sup>tumor cells from the cytotoxic effects of chemotherapy. However,<sup> </sup>in the current study, no between-group difference was found<sup> </sup>in the response to chemotherapy (52.4% versus 47.8%;
p = .90)<sup> </sup>or survival (
p = .79; log-rank test). Although in vitro evidence<sup> </sup>of the dependence of tumor growth on glutamine has deterred<sup> </sup>its application in cancer patients [
36], several studies have<sup> </sup>failed to show that supplemental glutamine stimulates tumor<sup> </sup>growth [
37,
38]. In fact, accumulating in vivo evidence suggests<sup> </sup>that glutamine may actually decrease tumor growth, possibly<sup> </sup>by upregulating the immune system [
37,
39]. The net outcome<sup> </sup>may improve the therapeutic index of oxaliplatin. The overall<sup> </sup>lymphocyte response (i.e., entry into the cell cycle and proliferation)<sup> </sup>has been directly correlated with glutamine concentration of<sup> </sup>the culture medium [
40]. In a breast cancer xenograft model,<sup> </sup>the supplemental glutamine group had higher natural killer cell<sup> </sup>activity and nearly one half the tumor volume, compared with<sup> </sup>the placebo group [
41]..."